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                                                                iSCSI                   March 1, 2002



           IPS                                                                             Julian Satran
           Internet Draft                                                                  Daniel Smith
           draft-ietf-ips-iscsi-11.txt                                                      Kalman Meth
           Category: standards-track                                                         Ofer Biran
                                                                                             Jim Hafner
                                                                                                     IBM

                                                                                       Costa Sapuntzakis
                                                                                             Mark Bakke
                                                                                          Cisco Systems

                                                                                          Randy Haagens
                                                                                 Mallikarjun Chadalapaka
                                                                                     Hewlett-Packard Co.

                                                                                           Matt Wakeley
                                                                                    Agilent Technologies

                                                                                       Luciano Dalle Ore
                                                                                                Quantum

                                                                                       Paul Von Stamwitz
                                                                                                Adaptec

                                                                                           Efri Zeidner
                                                                                                SANGate



                                                                iSCSI





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                                                                iSCSI            1-March-02

   Status of this Memo

           This document is an Internet-Draft and fully conforms to all provi-
           sions of Section 10 of [RFC2026].

           Internet-Drafts are working documents of the Internet Engineering
           Task Force (IETF), its areas, and its working groups. Note that other
           groups may also distribute working documents as Internet-Drafts.
           Internet-Drafts are draft documents valid for a maximum of six months
           and may be updated, replaced, or made obsolete by other documents at
           any time. It is inappropriate to use Internet- Drafts as reference
           material or to cite them other than as "work in progress."
           The list of current Internet-Drafts can be accessed at http://
           www.ietf.org/ietf/1id-abstracts.txt
           The list of Internet-Draft Shadow Directories can be accessed at
           http://www.ietf.org/shadow.html.


   Abstract

           The Small Computer Systems Interface (SCSI) is a popular family of
           protocols for communicating with I/O devices, especially storage
           devices. This memo describes a transport protocol for SCSI that oper-
           ates on top of TCP. The iSCSI protocol aims to be fully compliant with
           the requirements laid out in the SCSI Architecture Model - 2 [SAM2]
           document.

   Acknowledgements

           In addition to the authors, a large group of people contributed to
           this work through their review, comments and valuable insights. We are
           grateful to all of them. We are especially grateful to those who found
           the time and patience to participate in our weekly phone conferences
           and intermediate meetings in Almaden and Haifa, thus helping to shape
           this document: John Hufferd, Prasenjit Sarkar, Meir Toledano, John
           Dowdy, Steve Legg, Alain Azagury (IBM), Dave Nagle (CMU), David Black
           (EMC), John Matze (Veritas - now with Stonefly Networks), Steve
           DeGroote, Mark Schrandt (NuSpeed), Gabi Hecht (Gadzoox), Robert Sniv-
           ely (Brocade), Nelson Nachum (StorAge), Uri Elzur (Broadcom).  Many
           more helped clean up and improve this document within the IPS working
           group. We are especially grateful to David Robinson and Raghavendra
           Rao (Sun), Charles Monia, Joshua Tseng (Nishan), Somesh Gupta (Sil-
           verback Systems), Michael Krause, Pierre Labat, Santosh Rao, Matthew
           Burbridge (HP), Stephen Bailey (Sandburst), Robert Elliott, Martin

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                                                                      iSCSI                                                 1-March-02

           Nick (Compaq), Steve Senum, Ayman Ghanem (CISCO), Barry Reinhold
           (Trebia Networks), Bob Russell (UNH), Bill Lynn (Adaptec), Doug Otis
           (Sanlight), Robert Griswold and Bill Moody (Crossroads). The recovery
           chapter was enhanced with help from Stephen Bailey (Sandburst),
           Somesh Gupta (HP), Venkat Rangan (Rhapsody Networks), Vince Cavanna,
           Pat Thaler (Agilent), Jonathan Stone (Stanford), Eddy Quicksall
           (iVivity, Inc.) - Eddy also contributed with some examples. Last, but
           not least, thanks to Ralph Weber for keeping us in line with T10
           (SCSI) standardization.
           We would like to thank Steve Hetzler for his unwavering support and
           for coming up with such a good name for the protocol, Micky Rodeh, Jai
           Menon, Clod Barrera and Andy Bechtolsheim for helping this work hap-
           pen.

           At the time of the writing, this document has to be considered in con-
           junction with the "Naming & Discovery"[NDT], "Boot"[BOOT] and "Secur-
           ing iSCSI, iFCP and FCIP"[SEC-IPS] documents.

           The "Naming & Discovery" document is authored by:

                 Mark Bakke (Cisco), Joe Czap, Jim Hafner, John Hufferd, Kaladhar
                      Voruganti (IBM), Howard Hall (Pirus), Jack Harwood (EMC),
                      Yaron Klein (SANRAD), Lawrence Lamers (San Valley Systems),
                      Todd Sperry (Adaptec) and Joshua Tseng (Nishan).

           The "Boot" document is authored by:

                 Prasenjit Sarkar (IBM), Duncan Missimer (HP) and Costa Sapuntz-
                      akis (CISCO).

           The "Securing iSCSI, iFCP and FCIP" document is authored by:

                 Bernard Aboba, William Dixon (Microsoft), David Black (EMC),
                 Joseph Tardo, Uri Elzur (Broadcom), Mark Bakke, Steve Senum
                      (Cisco Systems), Howard Herbert, Jesse Walker (Intel), Julian
                      Satran, Ofer Biran and Charles Kunzinger (IBM).


           We are grateful to all of them for their good work and for helping us
           correlate this document with the ones they produced.

   Conventions used in this document

           In examples, "I->" and "T->" indicate iSCSI PDUs sent by the initiator
           and target respectively.

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                                                                iSCSI            1-March-02


           The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
           "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
           document are to be interpreted as described in RFC2119.

   Change Log

           The following changes were made from draft-ietf-ips-iSCSI-10 to
           draft-ietf-ips-iSCSI-11:

                 - ACA is SHOULD
                 - New format for ISID that allows factory presets
                 - New wording in section 9.5.4 that makes it clear that initia-
                      tor must discard discontiguous data PDUs during reassignment.
                 - Removed Parameter1 field definition for "drop the session"
                      Async Message.
                 - In state transitions chapter, added Logout timeout to the
                      event set causing T17, and removed the "session close" event
                      from the event set for T6. Changed "status class" to Status-
                      Class.
                 - Clarified that for ErrorRecoveryLevel < 2, the X-bit in Login
                      PDU terminates all the tasks.
                 - Clarified the various subcases of interpretation for
                      Time2Retain and Time2Wait in the Logout Response section.
                 - Added a new section in the recovery chapter on connection tim-
                      eout management.
                 - The LogoutLoginMinTime and LogoutLoginMaxTime keys are
                      respectively renamed to DefaultTime2Wait and
                      DefaultTime2Retain, since they are used only on non-Logout
                      events and also to better align with the notion of Time2Wait
                      and Time2Retain that the draft already defines.
                 - Added the new Appendix on clearing effects.
                 - Retired the X-bit in Login PDU to make the bit position
                      reserved.  Moved the content under X-bit description to a new
                      section 4.3.4 that describes "connection reinstatement".
                 - Added text to section 6.1.2 that clarifies the expectations on
                      targets during allegiance reassignment.
                 - Minor changes in error recovery algorithms to change NextCmdSN
                      to CmdSN in the Session data structure.
                 - Added a new section 4.3.5 defining the term "session rein-
                      statement".
                 - Added a new transition N11 to target session state diagram, to
                      address the session reinstatement event. Enhancing the event
                      set for N3(T) and N6(I & T) for the same event.  Adding the
                      same event to the event sets for target transitions T8, T13,
                      T15, T16, T17, T18, and M2 (I & T).
                 - Addressed the case of active TTTs when ABORT TASK SET/CLEAR
                      TASK SET is in progress in section 9.5 and section 9.6.


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                                                                iSCSI            1-March-02

                 - Added a new Section 9.6.3 Task Management actions on task sets
                      that describes the exact timeline of events on a task set task
                      management function.
                 - Clarified the usage of ITT for DataACK type of SNACK.
                 - Added error code for inexistent session to login response
                 - Changed the FIM SHOULD to should(!)
                 - Added a TTT field for Data-In when A bit is 1 and to the cor-
                      responding SNACK. To make it consistent changed slightly the
                      layout of Data-IN, SCSI Response and SNACK.
                 - Clarified the use of LUN with all PDUs holding TTT
                 - Removed the ? value from negotiations
                 - Unified text negotiations (login, ffp and formats) in one
                      chapter
                 - Clarified AHSLength and DataLength for all PDUs
                 - Clarified use of Reject
                 - Replaced Protocol Error with Negotiation Failure in negotia-
                      tions
                 - Removed FFP command before login from Reject Causes
                 - Added Invalid Request During Login to Login Errors
                 - Added tape text
                 - Clarified Security Text
                 - Aligned marker negotiations with the overall negotiations and
                      added numeric range to the negotiation forms
                 - Changed target network architecture example in Overview
                 - Clarified T bit use in Login Reject
                 - Version bumped to 04


           The following changes were made from draft-ietf-ips-iSCSI-09 to
           draft-ietf-ips-iSCSI-10:

                 - Clarifying MaxOutstandingR2T
                 - Widening the scope of Reject reason code 0x09 to mean "Invalid
                      PDU field".
                 - Changes in the "iSCSI connection termination" section to make
                      the terminology usage consistent with the rest of the draft.
                 - Adding transition T18 in standard connection state diagram,
                      and its description.
                 - Other minor wording changes in the state transitions chapter
                      to address "session close" case and others.
                 - Adding a new state Q5(IN_CONTINUE) to the target session state
                      diagram to resolve transitions N8 and N9 off Q2.
                 - Removed the AHS drop bit feature.
                 - Removed the qualifier field in Task Management Response PDU,
                      and added a new response "Function authorization failed".
                 - Clarified the fate of regular SCSI reservations on a session
                      timeout, compared to a transient session failure.
                 - Added wording in R2T section to address the case of receiving
                      a smaller write data sequence than was asked for in an R2T.


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                                                                iSCSI            1-March-02

                 - Changes and fixes in recovery algorithms to be consistent with
                      the rest of the draft.
                 - Changed the "Invalid SNACK" Reject reason code to "Invalid
                      data ACK" since the invalid SNACK is already covered under
                      "Protocol error".  Also treating DataSN and R2TSN equivalently
                      in this case.
                 - Change in the SNACK section to require a Reject "Protocol
                      error" on an invalid SNACK.
                 - Time2Retain 0 in Logout Response indicates connection/session
                      can‚ÇÖt recover
                 - Coordinate DataSequenceInOrder with Error recovery level and
                      MaxOutstandingR2T, also stating that only the last read/write
                      sequence is recoverable under digest error recovery if DataSe-
                      quenceInOrder=Yes
                 - Alias designation format appendix is again out(!) - T10 has
                      decided it will go in SPC3
                 - Task Management synchronization moved to the target (task man-
                      agement response given after task management action and con-
                      firmed delivery of all previous responses)
                 - Removed the don‚ÇÖt care value in numerical negotiations
                 - Changed Marker negotiation to allow it to be closed in one
                      round
                 - Marker position is not dependent of the length of the login
                      phase
                 - Statement made that reserved bits do not have to be checked at
                      the beginning of Chapter 9
                 - InitialR2T, BidiInitialR2T and ImmediateData changed to LO
                 - I bit (equivalent) in responses made 0
                 - Added a "double response" version for the ? key value to
                 - ? value can be used only outside Login
                 - added :, [ and ] as allowed in key values
                 - allow 0 in LogoutLoginMax and Min
                 - after task reassign no SNACK mandated, the function must be
                      performed by target with information made available by reas-
                      sign
                 - removed the third party command section - SCSI now handles
                      everything needed (including iSCSI aliasing)

           The following changes were made from draft-ietf-ips-iSCSI-08 to
           draft-ietf-ips-iSCSI-09:

                 - Added Task management response "task management function not
                      supported"
                 - Negotiation (numeric) responder driven
                 - Added vendor specific data to reject
                 - Allow logout in discovery sessions
                 - Variable DataPDULength - renamed MaxRecvPDULength
                 - Key=value pairs can span PDU boundaries
                 - Uniform treatment of text exchange resets


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                                                                iSCSI            1-March-02

                 - Reintroduced DataACK as a special form of SNACK
                 - Extended ISID in the Login Request
                 - Removed 0 as a "no limit value" (residue from mode pages)
                 - Reintroduced LogoutLoginMinTime
                 - Digests moved to Operational Keys
                 - Removed X bit in all commands and replaced it in Login and
                      added a cleaning rule to CmdSN numbering
                 - Several simplifications in state transition section - standard
                      connection and session state diagrams are separately described
                      for initiators and targets
                 - Several minor technical and language changes in the error
                      recovery section
                 - Added Irrelevant to negotiations
                 - Clarification to logout behavior
                 - Clarification to command ordering
                 - On SCSI timeout task abort instead of session failure
                 - Changed version to 0x03 - ALL VERSION NUMBERS are temporary up
                      to "Rafting" (take them with a grain of salt)


           The following changes were made from draft-ietf-ips-iSCSI-07 to
           draft-ietf-ips-iSCSI-08:

                 - Clarified the use of initiator task tag with regard to the
                      SCSI tag in Section 9.2.1.7 Initiator Task Tag
                 - Added a clarification to Section 2.2.2.1 Command Numbering and
                      Acknowledging - response to a command should not precede
                      acknowledgment.
                 - Added clarification to Section 9.7 SCSI Data-out & SCSI Data-
                      in - good status in Data-In must be supported by initiators
                 - Clarified InitiatorName is required at login in Section 4.3.1
                      Login Phase Start
                 - Another clarification for SecurityContextComplete in Section
                      4.3.2 iSCSI Security Negotiation
                 - Added "command not supported in this session type" to reject
                      reasons
                 - Discovery session implies MaxConnections = 1
                 - Second appearance of TargetAddress  deleted
                 - Padding forbidden for non-end-of-sequence data PDUs
                 - Removed Boot and Copenhagener Session types
                 - Changed explanation of ExpDataSN
                 - Removed/corrected response 05 in Section 9.4.3 Response
                 - Brought Section 2.2.7 Naming and Addressing in line with NDT
                      draft
                 - Fixed the syntax in accordance with [RFC2372] and [RFC2373]
                 - Removed forgotten references to the default iSCSI target
                 - Counters back to Reject Response
                 - Clarification - SendTargets admissible only in full feature
                      phase


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                                                                iSCSI            1-March-02

                 - Changed name of DataOrder and DataDeliveryOrder to DataSequen-
                      ceOrder and DataPDUInOrder and clarified appendix text
                 - Padding bytes SHOULD be sent as 0 (instead of MUST be 0)
                 - UA attention behavior for various resets deleted - replaced
                      with reference to SAM2
                 - Removed AccessID
                 - OpParmReset generalized
                 - Clarified the definition of full-feature phase in Section
                      2.2.5 iSCSI Full Feature Phase
                 - Added new Reject reason codes, tabular listing and a pointer
                      to Section 9.14.3 Reason Code
                 - Added additional Reject usage semantics on CmdSN and DataSN to
                      Section 9.14.3 Reason Code
                 - Added a new Logout Response code for failure
                 - Renamed BUSY as RECOVERY_START, removed RECOVERY_DONE, and
                      merged T11 and T14 transitions into T11-(1,2) in Section 5
                      State Transitions.
                 - Corrected initiator handling of format errors
                 - Clarified usage of command replay
                 - Removed the delivery in same order as presented from Text
                      Response
                 - Clarified RefCmdSN function fro abort task
                 - Corrected length field for AHS of type Extended CDB
                 - Removed LUN from text management response
                 - Clarified F bit for Bidirectional commands
                 - Removed the Async iSCSI event "target reset"
                 - Removed wording in Section 9.6 Task Management Function
                      Response linking SCSI mode pages to Async Messages
                 - Changed the ASC/ASCQ values to better mean "not enough unso-
                      licited data"
                 - Names examples include date
                 - Removed references to S bit in Section 9.4 SCSI Response
                 - Fixed NOP to simplify and avoid it consuming CmdSN
                 - Fixed CRC and examples
                 - Added the T, CSG & NSG fields to Login Command & Response,
                      rewrote Chapter 3, changed all examples in Appendix C. - Login
                      Phase Examples - to fit the above changes
                 - Key=value confined to one response
                 - Add command restart/replay to task management
                 - Removed cryptographic digests
                 - Removed "proxy required" status code
                 - Re-named and fixed descriptions of status codes
                 - Re-formatted login examples for clarity
                 - SCSI/iSCSI parameters - fixed Section 3 SCSI Mode Parameters
                      for iSCSI, out DataPDULength, DataSequenceOrder
                 - Changed all sense keys to aborted command in the table in Sec-
                      tion 9.4.2 Status
                 - Rearranged requests to have all SCSI related grouped etc.
                 - Fixed Task Management Function Request ABORT TASK and removed
                      the part about it in Chapter 8.

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                                                                iSCSI            1-March-02

                 - Reintroduced aliases (the data format) in an appendix. The
                      aliasing mechanism once part of iSCSI is part of [SPC3]
                 - Login negotiations - using only login request response
                      (instead of former login and text)
                 - F bit in login changed name to T bit
                 - Stated defaults for mode parameters in chapter 3
                 - Updated Chapter 7 to reflect the current consensus on security
                 - Changed all sense keys to aborted command in the table in
                      2.4.2
                 - Minor language clarifications in sections 1.2.3, 1.2.5, 1.2.6,
                      1.2.8.
                 - Added a new Reject reason code "Task in progress" and clari-
                      fied language in the same section.
                 - Added more description to the session state transitions in
                      Chapter 5.
                 - Several changes in Chapter 6 corresponding to the new task
                      management function "reassign".  Other language changes in
                      Chapter 6 for better description. Format errors are mandated
                      to cause session failures.
                 - Renamed the erstwhile error recovery levels as error recovery
                      classes, and renamed "within-session" recovery to "connection
                      recovery" to better reflect the mechanics.
                 - Added Section 6.13 Error Recovery Hierarchy to define the
                      error recovery hierarchy.
                 - Modifications to error recovery algorithms in Appendix F.
                 - Added a new Reject reason code "Invalid SNACK", added DataSN
                      to Reject PDU.
                 - Changed Section 9.17 Reject to use the "Invalid SNACK" reason
                      code.
                 - Removed a Logout reason code in Section 9.14 Logout Request to
                      be consistent with Section 9.9 Asynchronous Message.
                 - Collapsed the two event fields in Async Event and added vendor
                      specific event
                 - Immediate data can be negotiated anytime (consistency)
                 - Removed replay as a protocol notion and all references to it
                 - SNACK RunLength 0 means all
                 - Cleaning the bookmark mechanism for text
                 - New T10 approved ASC/ASQ codes
                 - Added a incipient definitions section - thanks to Eddy Quick-
                      sall
                 - Change OpParmReset from Yes/No to default/current
                 - Added Base64 to encode large strings
                 - The 255 limit for key values is now "unless specified other-
                      wise"
                 - Cleaned SNACK format
                 - Removed ExpR2TSN from SCSI command response it is too late
                 - MaxBurstSize/FirstBurstSize back as key=value
                 - Removed LogoutLoginMinTime (value provided in exchange)
                 - Clear language on component function in generating ISID/TSID
                 - Negotiation breaking is done through abort/reject

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                                                                 iSCSI            1-March-02

                 - Removed all iSCSI mode pages


           The following changes were made from draft-ietf-ips-iSCSI-06 to
           draft-ietf-ips-iSCSI-07:

                 - Clarified the "fate" of immediate commands and resources man-
                      dated (1.2.2.1) and introduced a reject-code for rejected
                      immediate commands
                 - Clarify CmdSN handling and checking order for ITT and CmdSN
                      1.2.2.1
                 - Added a statement to the effect that a receiver must be able
                      to accept 0 length Data Segments to 2.7.6. Added also a state-
                      ment to 2.2.1 that a zero-length data segment implies a zero-
                      length digest
                 - SCSI MODE SELECT will not really set the parameters (will not
                      cause an error either). The parameters will be set exclusively
                      with text mode and can be retrieved with either text or Mode-
                      SENSE. This enables us to disable their change after the Login
                      negotiation. Also added to the negotiation (1.2.4) the value
                      "?" with special meaning of enquiry
                 - Changed "task" to "command" wherever relevant
                 - EMDP usage in line with other SCSI protocols. EMDP governs how
                      a target may request data and deliver. Similar to FCP a sepa-
                      rate (protocol) parameter governs data PDU ordering within
                      Sequence (DataPDUInOrder). Cleaned wording of DataOrder.
                      Fixed final bit to define sequences in input stream.
                 - Added a "persistent state" part (1.2.8)
                 - Some Task Management commands may require authorization or may
                      not be implemented. If not authorized they will return as if
                      executed with a qualifier indicating "not authorized" or "not
                      implemented" (clear LU and the resets)
                 - Task management commands and responses are "generalized" to
                      all iSCSI tagged commands (they are named now Task Management
                      command and response). Their behavior with respect to their
                      CmdSN is clarified and mandated
                 - The logic to update ExpCmdSN etc. moved to 1.2.2.1
                 - Explicitly specified that a target can "initiate" negotiating
                      a parameter (offering)(1.2.4)
                 - Returned the "direction" bit and a set of codes similar to
                      version 05
                 - Introduced a "special" session type (CopyManagerSession) to be
                      used between a Copy Manager and all of its target; it may help
                      define authentication and limit the type f commands to be exe-
                      cuted in such a session
                 - Added 8.4 - How to Abort Safely a Command that Was Not
                      Received
                 - Fixed the Logout Text
                 - AHSLength is now the first field in the AHS


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                                                                 iSCSI            1-March-02

                 - Fixed wording in 2.35 indicating AHS is mandatory for Bi-
                      directional commands
                 - All key=value responses have to be explicit (none, not-under-
                      stood etc.); no more selection by hiatus
                 - Targets can also offer key=value pairs (i.e., initiate negoti-
                      ation) stated explicitly in 2.9.3
                 - Logout has a CmdSN field
                 - The Status SNACK can be discarded if the target has no such
                      recovery
                 - Some parameters have been removed and replaced by "reasonable"
                      defaults (read arbitrary defaults!); many others can't be
                      changed anymore while the session is in full-feature phase
                 - NOP-Out specifies how LUN is generated when used (copied from
                      NOP-In)
                 - Initial Marker-Less Interval is not a parameter anymore
                 - A response with F=1 during negotiation may not contain
                      key=value pairs that may require additional answers from the
                      initiator
                 - Clarified the meaning of the F bit on Write commands with
                      regard to immediate and unsolicited data; F bit 0 means that
                      unsolicited data will follow while F bit 1 means that this is
                      the last of them (if any)
                 - You can have both immediate and unsolicited Data-Out PDUs
                 - DataPDULength and FirstBurstSize of 0 are allowed and mean
                      unlimited length
                 - Task management command behavior relative to their own CmdSN
                      is now stated in no uncertain terms (they are mandated to exe-
                      cute as if issued at CmdSN and, in case of aborts and clear/
                      reset no additional response/status is expected for those com-
                      mands after the task management command response
                 - DataSN field in R2T renamed as R2TSN (better reflects seman-
                      tics) and SNACK explicitly says that it requests Data or R2T.
                 - A session can have only one outstanding text request (not
                      sequence)
                 - Text for Login Response 0301 changed (removed the maintenance
                      mention)
                 - Clarified when ExpDataSN is reserved in SCSI Response
                 - Clarified the text and parameter (timers) for iSCSI event
                 - Padding bytes should be 0 (2.1)
                 - TotalAHSLength in 2.1.1.1 includes padding
                 - DataSegmentLength in 2.1.1.2 excludes padding
                 - Clarified bits in AHS type
                 - Limit for key/value string lengths (63, 255) in 2.8.3
                 - Added an example of SCSI event to Asynchronous Message
                 - Changed "Who" to "Who can send" in appendix
                 - Clarified meaning of parameters on 2.18.1 - Asynchronous Mes-
                      sage - iSCSI Event
                 - Clarified the required initiator behavior at logout (not send-
                      ing other commands) and how one expects the TCP close to be
                      performed in 2.14

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                                                                 iSCSI            1-March-02

                 - Added a Login Response code indicating that a session can't
                      include a given connection (0208)
                 - Clarified transition to full feature phase (per session and
                      per connection and the role of the leading connection) in
                      1.2.5
                 - Corrected "one outstanding text request per connection"
                      instead of "per session"
                 - For the Login Response TSID must be valid only if Login is
                      accepted and the F bit is 1
                 - Added examples illustrating DataSN and R2TSN (from Eddy Quick-
                      sall)
                 - Added more text to the task management command 2.5
                 - Removed EnableACA and its dependents (in task management) and
                      stated the requirement for a Unit Attention conform to SAM2
                 - iSCSI Target Name if used on a connection other than the first
                      must be the same as on the first (4.1)
                 - Fixed the examples in the Login appendix to correspond to the
                      new keys
                 - Fixed SCSI Response Flags and made them consistent with the
                      Data-In PDU
                 - All specified keys except X-* MUST be accepted (2.8.3)
                 - Hexadecimal notation is 0xab123cd (not 0x'ab123cd')
                 - Clarified CmdSN usage in immediate commands and the meaning of
                      "execution engine" in 1.2.2.1
                 - Reject response that prevent the creation of a SCSI task or
                      result in a SCSI task being terminated must be followed by a
                      SCSI Response with a Check Condition status 2.19.1
                 - Additional Runs (AddRuns) dropped from the SNACK request (too
                      complex). With it disappeared also the implicit acknowledge-
                      ment of sequences "between runs"
                 - PDUs delivered because of SNACK will be exact replicas of the
                      original PDUs (including all flags) 2.16
                 - Added CommandReplaySupport key to negotiate support for full
                      command replay (a command can be replayed after the status has
                      been issued but has not been acknowledged) and a reject cause
                      of unsupported command reply
                 - Added CommandFailoverSupport key to negotiate support for com-
                      mand allegiance change (command retry on another connection)
                 - Status SNACK for an acknowledged status is a protocol error
                      (cause for reject)
                 - Reject cause "Command In Progress" when requesting replay
                      before status is issued and while command is running
                 - Premature SNACKs are silently discarded (2.16)
                 - Status SNACK has to supported only if within command or within
                      connection recovery is supported. If within session recovery
                      is supported SNACK can be discarded and followed by an Async.
                      Message requesting logout
                 - StatSN added to Logout Response
                 - Added "CID not found" to Logout Response reason codes


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                 - Async Message - iSCSI event 2 (request logout) has to be sent
                      on the connection to be dropped. Wording fixed.
                 - Naming changes - iqn (stands for iSCSI qualified name) intro-
                      duced as a replacement to fqn. Iqn prefixes also reversed
                      names
                 - text in 8.3 revised (task management implementation mechanism)
                 - Fixed bit 7 byte 1 in Task Management response to 1 (consis-
                      tency)
                 - Clarified in 1.2.2 behavior when "command window" is 0 (MaxC-
                      mdSN = ExpCmdSN -1)
                 - Added state transitions part (new part 6)
                 - Refreshed recovery chapter (new part 7)
                 - Added an appendix with detailed recovery mechanisms (Appendix
                      E)
                 - Added session types a brief explanation in part 1
                 - Added DiscoverySession key and SendTargets appendix
                 - SCSI response made to fit having both a Status and a Response
                      field. Needed for target errors that result in a check condi-
                      tion and ACA. In line with SAM2 that requires both fields
                      (former versions where modeled on FCP).
                 - The security appendix list SRP as mandatory to implement
                 - Clarified initial CmdSN and the role of TSID as a serializer
                 - Long Text Responses - additional fields added to the text
                      request and text response
                 - Added a SCSI to iSCSI concept mapping section 1.5
                 - Clarified SNACK wording to indicate that in general command.
                      Request, iSCSI command and iSCSI command have the same mean-
                      ing. Also status, response or numbered response.
                 - Changed InitStatSN and clarified how it increases
                 - Added requirement for a 0x00 delimiter after each key=value
                 - Added binary negotiations (Yes|No) explicitly to 1.2.4
                 - All keys and values in the spec are case sensitive (stated in
                      the text request)
                 - Changed the "operational parameters sent before the security.
                      MAY be discarded" into MUST be discarded
                 - Changed the login reject 0201 to read - Security Negotiation
                      Failed
                 - Added to 2.3.1 a paragraph about mandatory consistencies
                 - Stated clearly that F bit pairing is "local" (per/pair) and
                      not per negotiation
                 - Clarified dependent parameter status
                 - Added CRC Example
                 - Added OpParmReset=Yes
                 - SecurityContextComplete is mandatory if any option offered
                 - Added a warning about the implications of not sending all
                      unsolicited data to part 8
                 - Added a recommendation to send unsolicited data at FirstBurst-
                      Size and a response (error) for targets not supporting less
                 - Many more minor editorial changes, clarifications, typos etc.
                 - Responses in same position in SCSI response, logout, task etc.

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                                                            Table of Contents





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    Status of this Memo . . . . . . . . . . . . . . . . . . . . . . . . . 2
    Abstract  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
    Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . . . . 2
    Conventions used in this document . . . . . . . . . . . . . . . . . . 3
    Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   1. Definitions   . . . . . . . . . . . . . . . . . . . . . . . . . . .22
   2. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
          2.1 SCSI Concepts  . . . . . . . . . . . . . . . . . . . . . . . . .26
          2.2 iSCSI Concepts and Functional Overview   . . . . . . . . . . . .27
                2.2.1 Layers and Sessions   . . . . . . . . . . . . . . . . . . .27
                2.2.2 Ordering and iSCSI Numbering  . . . . . . . . . . . . . . .28
                       2.2.2.1 Command Numbering and Acknowledging  . . . . . . . . .29
                       2.2.2.2 Response/Status Numbering and Acknowledging  . . . . .32
                       2.2.2.3 Data Sequencing  . . . . . . . . . . . . . . . . . . .32
                2.2.3 iSCSI Login   . . . . . . . . . . . . . . . . . . . . . . .33
                2.2.4 iSCSI Full Feature Phase  . . . . . . . . . . . . . . . . .34
                2.2.5 iSCSI Connection Termination  . . . . . . . . . . . . . . .36
                2.2.6 Naming and Addressing   . . . . . . . . . . . . . . . . . .37
                2.2.7 Persistent State  . . . . . . . . . . . . . . . . . . . . .39
                2.2.8 Message Synchronization and Steering  . . . . . . . . . . .39
                       2.2.8.1 Rationale  . . . . . . . . . . . . . . . . . . . . . .39
                       2.2.8.2 Synchronization (sync) and Steering Functional Model  40
                       2.2.8.3 Sync and Steering and Other Encapsulation Layers   . .42
                       2.2.8.4 Sync/Steering and iSCSI PDU Size   . . . . . . . . . .43
          2.3 iSCSI Session Types  . . . . . . . . . . . . . . . . . . . . . .44
          2.4 SCSI to iSCSI Concepts Mapping Model   . . . . . . . . . . . . .44
                2.4.1 iSCSI Architecture Model  . . . . . . . . . . . . . . . . .45
                2.4.2 SCSI Architecture Model   . . . . . . . . . . . . . . . . .47
                2.4.3 Consequences of the Model   . . . . . . . . . . . . . . . .49
                       2.4.3.1 I_T Nexus State  . . . . . . . . . . . . . . . . . . .50
                       2.4.3.2 SCSI Mode Pages  . . . . . . . . . . . . . . . . . . .50
          2.5 Request/Response Summary   . . . . . . . . . . . . . . . . . . .51
                2.5.1 Request/Response types carrying SCSI payload  . . . . . . .51
                       2.5.1.1 SCSI-Command   . . . . . . . . . . . . . . . . . . . .51
                       2.5.1.2 SCSI-Response  . . . . . . . . . . . . . . . . . . . .51
                       2.5.1.3 Task Management Function Request   . . . . . . . . . .52
                       2.5.1.4 Task Management Function Response  . . . . . . . . . .53
                       2.5.1.5 SCSI Data-out and SCSI Data-in   . . . . . . . . . . .53
                       2.5.1.6 Ready To Transfer (R2T)  . . . . . . . . . . . . . . .54
                2.5.2 Requests/Responses carrying SCSI and iSCSI Payload  . . . .54
                       2.5.2.1 Asynchronous Message   . . . . . . . . . . . . . . . .54
                2.5.3 Requests/Responses carrying iSCSI Only Payload  . . . . . .54
                       2.5.3.1 Text Request and Text Response   . . . . . . . . . . .54

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                       2.5.3.2 Login Request and Login Response   . . . . . . . . . .55
                       2.5.3.3 Logout Request and Response  . . . . . . . . . . . . .56
                       2.5.3.4  SNACK Request   . . . . . . . . . . . . . . . . . . .56
                       2.5.3.5 Reject   . . . . . . . . . . . . . . . . . . . . . . .57
                       2.5.3.6 NOP-Out Request and NOP-In Response  . . . . . . . . .57
   3. SCSI Mode Parameters for iSCSI  . . . . . . . . . . . . . . . . . .58
   4. Login and Full Feature Phase Negotiation  . . . . . . . . . . . . .59
          4.1 Text Format  . . . . . . . . . . . . . . . . . . . . . . . . . .59
          4.2 Text Mode Negotiation  . . . . . . . . . . . . . . . . . . . . .59
          4.3 Login Phase  . . . . . . . . . . . . . . . . . . . . . . . . . .62
                4.3.1 Login Phase Start   . . . . . . . . . . . . . . . . . . . .64
                4.3.2 iSCSI Security Negotiation  . . . . . . . . . . . . . . . .65
                4.3.3 Operational Parameter Negotiation During the Login Phase  .66
                4.3.4 Connection reinstatement  . . . . . . . . . . . . . . . . .67
                4.3.5 Session reinstatement   . . . . . . . . . . . . . . . . . .68
                4.3.6 Session Continuation, closure and failure   . . . . . . . .68
          4.4 Operational Parameter Negotiation Outside the Login Phase  . . .68
   5. State Transitions   . . . . . . . . . . . . . . . . . . . . . . . .70
          5.1 Standard Connection State Diagrams   . . . . . . . . . . . . . .70
                5.1.1 Standard Connection State Diagram for an Initiator  . . . .70
                5.1.2 Standard Connection State Diagram for a Target  . . . . . .72
                5.1.3 State Descriptions for Initiators and Targets   . . . . . .74
                5.1.4 State Transition Descriptions for Initiators and Targets  .75
          5.2 Connection Cleanup State Diagram for Initiators and Targets  . .78
                5.2.1 State Descriptions for Initiators and Targets   . . . . . .80
                5.2.2 State Transition Descriptions for Initiators and Targets  .81
          5.3 Session State Diagrams   . . . . . . . . . . . . . . . . . . . .82
                5.3.1 Session State Diagram for a Target  . . . . . . . . . . . .83
                5.3.2 State Descriptions for Initiators and Targets   . . . . . .84
                5.3.3 State Transition Descriptions for Initiators and Targets  .85
   6. iSCSI Error Handling and Recovery   . . . . . . . . . . . . . . . .87
          6.1 Retry and Reassign in Recovery   . . . . . . . . . . . . . . . .87
                6.1.1 Usage of Retry  . . . . . . . . . . . . . . . . . . . . . .87
                6.1.2 Allegiance Reassignment   . . . . . . . . . . . . . . . . .88
          6.2 Usage Of Reject PDU in Recovery  . . . . . . . . . . . . . . . .89
          6.3 Connection timeout management  . . . . . . . . . . . . . . . . .89
                6.3.1 Timeouts on transport exception events  . . . . . . . . . .89
                6.3.2 Timeouts on planned decommissioning   . . . . . . . . . . .90
          6.4 Format Errors  . . . . . . . . . . . . . . . . . . . . . . . . .90
          6.5 Digest Errors  . . . . . . . . . . . . . . . . . . . . . . . . .90
          6.6 Sequence Errors  . . . . . . . . . . . . . . . . . . . . . . . .92
          6.7 SCSI Timeouts  . . . . . . . . . . . . . . . . . . . . . . . . .92
          6.8 Negotiation Failures   . . . . . . . . . . . . . . . . . . . . .93

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          6.9 Protocol Errors  . . . . . . . . . . . . . . . . . . . . . . . .94
          6.10 Connection Failures   . . . . . . . . . . . . . . . . . . . . .94
          6.11 Session Errors  . . . . . . . . . . . . . . . . . . . . . . . .95
          6.12 Recovery Classes  . . . . . . . . . . . . . . . . . . . . . . .95
                6.12.1 Recovery Within-command  . . . . . . . . . . . . . . . . .96
                6.12.2 Recovery Within-connection   . . . . . . . . . . . . . . .97
                6.12.3 Connection Recovery  . . . . . . . . . . . . . . . . . . .97
                6.12.4 Session Recovery   . . . . . . . . . . . . . . . . . . . .98
          6.13 Error Recovery Hierarchy  . . . . . . . . . . . . . . . . . . .99
   7. Security Considerations   . . . . . . . . . . . . . . . . . . . . 101
          7.1 iSCSI Security Mechanisms  . . . . . . . . . . . . . . . . . . 101
          7.2 In-band Initiator-Target Authentication  . . . . . . . . . . . 102
          7.3 IPsec  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
                7.3.1 Data Integrity and Authentication   . . . . . . . . . . . 103
                7.3.2 Confidentiality   . . . . . . . . . . . . . . . . . . . . 103
                7.3.3 Policy, Security Associations and Key Management  . . . . 104
   8. Notes to Implementers   . . . . . . . . . . . . . . . . . . . . . 106
          8.1 Multiple Network Adapters  . . . . . . . . . . . . . . . . . . 106
                8.1.1 Conservative Reuse of ISIDs   . . . . . . . . . . . . . . 106
                8.1.2 iSCSI Name and ISID/TSID Use  . . . . . . . . . . . . . . 107
          8.2 Autosense and Auto Contingent Allegiance (ACA)   . . . . . . . 108
          8.3 Command Retry and Cleaning Old Command Instances   . . . . . . 109
          8.4 Synch and Steering Layer and Performance   . . . . . . . . . . 109
          8.5 Unsolicited Data and Performance   . . . . . . . . . . . . . . 109
          8.6 Considerations for State-dependent devices   . . . . . . . . . 110
                8.6.1 Determining the proper ErrorRecoveryLevel   . . . . . . . 110
   9. iSCSI PDU Formats   . . . . . . . . . . . . . . . . . . . . . . . 112
          9.1 iSCSI PDU Length and Padding   . . . . . . . . . . . . . . . . 112
          9.2 PDU Template, Header, and Opcodes  . . . . . . . . . . . . . . 112
                9.2.1 Basic Header Segment (BHS)  . . . . . . . . . . . . . . . 113
                       9.2.1.1 I  . . . . . . . . . . . . . . . . . . . . . . . . . 114
                       9.2.1.2 Opcode   . . . . . . . . . . . . . . . . . . . . . . 114
                       9.2.1.3 Opcode-specific Fields   . . . . . . . . . . . . . . 115
                       9.2.1.4 TotalAHSLength   . . . . . . . . . . . . . . . . . . 115
                       9.2.1.5 DataSegmentLength  . . . . . . . . . . . . . . . . . 115
                       9.2.1.6 LUN  . . . . . . . . . . . . . . . . . . . . . . . . 115
                       9.2.1.7 Initiator Task Tag   . . . . . . . . . . . . . . . . 116
                9.2.2 Additional Header Segment (AHS)   . . . . . . . . . . . . 116
                       9.2.2.1 AHSType  . . . . . . . . . . . . . . . . . . . . . . 116
                       9.2.2.2 AHSLength  . . . . . . . . . . . . . . . . . . . . . 117
                       9.2.2.3 Extended CDB AHS   . . . . . . . . . . . . . . . . . 117
                       9.2.2.4 Bidirectional Expected Read-Data Length AHS  . . . . 117
                9.2.3 Header Digest and Data Digest   . . . . . . . . . . . . . 117

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                9.2.4 Data Segment  . . . . . . . . . . . . . . . . . . . . . . 118
          9.3 SCSI Command . . . . . . . . . . . . . . . . . . . . . . . . . 119
                9.3.1 Flags and Task Attributes (byte 1)  . . . . . . . . . . . 119
                9.3.2 CRN   . . . . . . . . . . . . . . . . . . . . . . . . . . 120
                9.3.3 CmdSN - Command Sequence Number   . . . . . . . . . . . . 120
                9.3.4 ExpStatSN   . . . . . . . . . . . . . . . . . . . . . . . 120
                9.3.5 Expected Data Transfer Length   . . . . . . . . . . . . . 120
                9.3.6 CDB - SCSI Command Descriptor Block   . . . . . . . . . . 121
                9.3.7 Data Segment - Command Data   . . . . . . . . . . . . . . 121
          9.4 SCSI Response  . . . . . . . . . . . . . . . . . . . . . . . . 122
                9.4.1 Flags (byte 1)  . . . . . . . . . . . . . . . . . . . . . 122
                9.4.2 Status  . . . . . . . . . . . . . . . . . . . . . . . . . 123
                9.4.3 Response  . . . . . . . . . . . . . . . . . . . . . . . . 124
                9.4.4 Residual Count  . . . . . . . . . . . . . . . . . . . . . 125
                9.4.5 Bidirectional Read Residual Count   . . . . . . . . . . . 125
                9.4.6 Data Segment - Sense and Response Data Segment  . . . . . 125
                       9.4.6.1 SenseLength  . . . . . . . . . . . . . . . . . . . . 126
                9.4.7 ExpDataSN   . . . . . . . . . . . . . . . . . . . . . . . 126
                9.4.8 StatSN - Status Sequence Number   . . . . . . . . . . . . 126
                9.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator  . . . 126
                9.4.10 MaxCmdSN - Maximum CmdSN from this Initiator   . . . . . 127
          9.5 Task Management Function Request . . . . . . . . . . . . . . . 128
                9.5.1 Function  . . . . . . . . . . . . . . . . . . . . . . . . 128
                9.5.2 LUN   . . . . . . . . . . . . . . . . . . . . . . . . . . 131
                9.5.3 Referenced Task Tag   . . . . . . . . . . . . . . . . . . 131
                9.5.4 RefCmdSN or ExpDataSN   . . . . . . . . . . . . . . . . . 131
          9.6 Task Management Function Response  . . . . . . . . . . . . . . 132
                9.6.1 Response  . . . . . . . . . . . . . . . . . . . . . . . . 132
                9.6.2 Referenced Task Tag   . . . . . . . . . . . . . . . . . . 133
                9.6.3 Task Management actions on task sets  . . . . . . . . . . 133
          9.7 SCSI Data-out & SCSI Data-in . . . . . . . . . . . . . . . . . 135
                9.7.1 F (Final) Bit   . . . . . . . . . . . . . . . . . . . . . 137
                9.7.2 A (Acknowledge) bit   . . . . . . . . . . . . . . . . . . 137
                9.7.3 Target Transfer Tag   . . . . . . . . . . . . . . . . . . 137
                9.7.4 StatSN  . . . . . . . . . . . . . . . . . . . . . . . . . 138
                9.7.5 DataSN  . . . . . . . . . . . . . . . . . . . . . . . . . 138
                9.7.6 Buffer Offset   . . . . . . . . . . . . . . . . . . . . . 138
                9.7.7 DataSegmentLength   . . . . . . . . . . . . . . . . . . . 138
                9.7.8 Flags (byte 1)  . . . . . . . . . . . . . . . . . . . . . 139
          9.8 Ready To Transfer (R2T)  . . . . . . . . . . . . . . . . . . . 140
                9.8.1 R2TSN   . . . . . . . . . . . . . . . . . . . . . . . . . 141
                9.8.2 StatSN  . . . . . . . . . . . . . . . . . . . . . . . . . 141
                9.8.3 Desired Data Transfer Length and Buffer Offset  . . . . . 141

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                9.8.4 Target Transfer Tag   . . . . . . . . . . . . . . . . . . 142
          9.9 Asynchronous Message . . . . . . . . . . . . . . . . . . . . . 143
                9.9.1 AsyncEvent  . . . . . . . . . . . . . . . . . . . . . . . 144
                9.9.2 AsyncVCode  . . . . . . . . . . . . . . . . . . . . . . . 145
                9.9.3 Sense Data or iSCSI Event Data  . . . . . . . . . . . . . 145
          9.10 Text Request  . . . . . . . . . . . . . . . . . . . . . . . . 146
                9.10.1 F (Final) Bit  . . . . . . . . . . . . . . . . . . . . . 146
                9.10.2 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 147
                9.10.3 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 147
                9.10.4 Text   . . . . . . . . . . . . . . . . . . . . . . . . . 148
          9.11 Text Response . . . . . . . . . . . . . . . . . . . . . . . . 149
                9.11.1 F (Final) Bit  . . . . . . . . . . . . . . . . . . . . . 149
                9.11.2 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 150
                9.11.3 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 150
                9.11.4 Text Response Data   . . . . . . . . . . . . . . . . . . 151
          9.12 Login Request . . . . . . . . . . . . . . . . . . . . . . . . 152
                9.12.1 T (Transit) Bit  . . . . . . . . . . . . . . . . . . . . 152
                9.12.2 CSG and NSG  . . . . . . . . . . . . . . . . . . . . . . 153
                9.12.3 Version-max  . . . . . . . . . . . . . . . . . . . . . . 153
                9.12.4 Version-min  . . . . . . . . . . . . . . . . . . . . . . 153
                9.12.5 ISID   . . . . . . . . . . . . . . . . . . . . . . . . . 153
                9.12.6 TSID   . . . . . . . . . . . . . . . . . . . . . . . . . 155
                9.12.7 Connection ID - CID  . . . . . . . . . . . . . . . . . . 155
                9.12.8 CmdSN  . . . . . . . . . . . . . . . . . . . . . . . . . 155
                9.12.9 ExpStatSN  . . . . . . . . . . . . . . . . . . . . . . . 156
                9.12.10 Login Parameters  . . . . . . . . . . . . . . . . . . . 156
          9.13 Login Response  . . . . . . . . . . . . . . . . . . . . . . . 157
                9.13.1 Version-max  . . . . . . . . . . . . . . . . . . . . . . 157
                9.13.2 Version-active   . . . . . . . . . . . . . . . . . . . . 158
                9.13.3 TSID   . . . . . . . . . . . . . . . . . . . . . . . . . 158
                9.13.4 StatSN   . . . . . . . . . . . . . . . . . . . . . . . . 158
                9.13.5 Status-Class and Status-Detail   . . . . . . . . . . . . 158
                9.13.6 T (Transit) bit  . . . . . . . . . . . . . . . . . . . . 161
          9.14 Logout Request  . . . . . . . . . . . . . . . . . . . . . . . 162
                9.14.1 CID  . . . . . . . . . . . . . . . . . . . . . . . . . . 163
                9.14.2 ExpStatSN  . . . . . . . . . . . . . . . . . . . . . . . 163
                9.14.3 Reason Code  . . . . . . . . . . . . . . . . . . . . . . 164
          9.15 Logout Response . . . . . . . . . . . . . . . . . . . . . . . 165
                9.15.1 Response   . . . . . . . . . . . . . . . . . . . . . . . 165
                9.15.2 Time2Wait  . . . . . . . . . . . . . . . . . . . . . . . 166
                9.15.3 Time2Retain  . . . . . . . . . . . . . . . . . . . . . . 166
          9.16  SNACK Request  . . . . . . . . . . . . . . . . . . . . . . . 168
                9.16.1 Type   . . . . . . . . . . . . . . . . . . . . . . . . . 169

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                9.16.2 BegRun   . . . . . . . . . . . . . . . . . . . . . . . . 170
                9.16.3 RunLength  . . . . . . . . . . . . . . . . . . . . . . . 170
          9.17 Reject  . . . . . . . . . . . . . . . . . . . . . . . . . . . 171
                9.17.1 Reason   . . . . . . . . . . . . . . . . . . . . . . . . 172
                9.17.2 DataSN   . . . . . . . . . . . . . . . . . . . . . . . . 173
                9.17.3 StatSN, ExpCmdSN and MaxCmdSN  . . . . . . . . . . . . . 173
                9.17.4 Complete Header of Bad PDU   . . . . . . . . . . . . . . 173
          9.18 NOP-Out . . . . . . . . . . . . . . . . . . . . . . . . . . . 174
                9.18.1 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 175
                9.18.2 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 175
                9.18.3 Ping Data  . . . . . . . . . . . . . . . . . . . . . . . 175
          9.19 NOP-In  . . . . . . . . . . . . . . . . . . . . . . . . . . . 176
                9.19.1 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 177
                9.19.2 LUN  . . . . . . . . . . . . . . . . . . . . . . . . . . 177
   10. iSCSI Security Keys and Values   . . . . . . . . . . . . . . . . 178
          10.1 AuthMethod  . . . . . . . . . . . . . . . . . . . . . . . . . 178
          10.2 Kerberos  . . . . . . . . . . . . . . . . . . . . . . . . . . 179
          10.3 Simple Public-Key Mechanism (SPKM)  . . . . . . . . . . . . . 180
          10.4 Secure Remote Password (SRP)  . . . . . . . . . . . . . . . . 181
          10.5 Challenge Handshake Authentication Protocol (CHAP)  . . . . . 182
   11. Login/Text Operational Keys  . . . . . . . . . . . . . . . . . . 184
          11.1 HeaderDigest and DataDigest   . . . . . . . . . . . . . . . . 184
          11.2 MaxConnections  . . . . . . . . . . . . . . . . . . . . . . . 186
          11.3 SendTargets   . . . . . . . . . . . . . . . . . . . . . . . . 186
          11.4 TargetName  . . . . . . . . . . . . . . . . . . . . . . . . . 186
          11.5 InitiatorName   . . . . . . . . . . . . . . . . . . . . . . . 187
          11.6 TargetAlias   . . . . . . . . . . . . . . . . . . . . . . . . 187
          11.7 InitiatorAlias  . . . . . . . . . . . . . . . . . . . . . . . 188
          11.8 TargetAddress   . . . . . . . . . . . . . . . . . . . . . . . 188
          11.9 InitialR2T  . . . . . . . . . . . . . . . . . . . . . . . . . 189
          11.10 BidiInitialR2T   . . . . . . . . . . . . . . . . . . . . . . 189
          11.11 ImmediateData  . . . . . . . . . . . . . . . . . . . . . . . 190
          11.12 MaxRecvPDULength   . . . . . . . . . . . . . . . . . . . . . 191
          11.13 MaxBurstSize   . . . . . . . . . . . . . . . . . . . . . . . 191
          11.14 FirstBurstSize   . . . . . . . . . . . . . . . . . . . . . . 192
          11.15 DefaultTime2Wait   . . . . . . . . . . . . . . . . . . . . . 192
          11.16 DefaultTime2Retain   . . . . . . . . . . . . . . . . . . . . 193
          11.17 MaxOutstandingR2T  . . . . . . . . . . . . . . . . . . . . . 193
          11.18 DataPDUInOrder   . . . . . . . . . . . . . . . . . . . . . . 194
          11.19 DataSequenceInOrder  . . . . . . . . . . . . . . . . . . . . 194
          11.20 ErrorRecoveryLevel   . . . . . . . . . . . . . . . . . . . . 195
          11.21 SessionType  . . . . . . . . . . . . . . . . . . . . . . . . 195
          11.22 The Vendor Specific Key Format   . . . . . . . . . . . . . . 196

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   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 197
    References and Bibliography . . . . . . . . . . . . . . . . . . . . 198
    Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 199
   Appendix A. Sync and Steering with Fixed Interval Markers  . . . . . 202
          A.1 Markers At Fixed Intervals   . . . . . . . . . . . . . . . . . 202
          A.2 Initial Marker-less Interval   . . . . . . . . . . . . . . . . 203
          A.3 Negotiation  . . . . . . . . . . . . . . . . . . . . . . . . . 203
             A.3.1 OFMarker, IFMarker  . . . . . . . . . . . . . . . . . . . 203
             A.3.2 OFMarkInt, IFMarkInt  . . . . . . . . . . . . . . . . . . 204
   Appendix B. Examples   . . . . . . . . . . . . . . . . . . . . . . . 206
          B.4 Read Operation Example   . . . . . . . . . . . . . . . . . . . 206
          B.5 Write Operation Example  . . . . . . . . . . . . . . . . . . . 207
          B.6 R2TSN/DataSN use Examples  . . . . . . . . . . . . . . . . . . 207
          B.7 CRC Examples   . . . . . . . . . . . . . . . . . . . . . . . . 211
   Appendix C. Login Phase Examples   . . . . . . . . . . . . . . . . . 213
   Appendix D. SendTargets Operation  . . . . . . . . . . . . . . . . . 222
   Appendix E. Algorithmic Presentation of Error Recovery Classes   . . 226
          E.8 General Data Structure and Procedure Description   . . . . . . 226
          E.9 Within-command Error Recovery Algorithms   . . . . . . . . . . 227
             E.9.1 Procedure Descriptions  . . . . . . . . . . . . . . . . . 227
             E.9.2 Initiator Algorithms  . . . . . . . . . . . . . . . . . . 228
             E.9.3 Target Algorithms   . . . . . . . . . . . . . . . . . . . 230
          E.10 Within-connection Recovery Algorithms   . . . . . . . . . . . 232
             E.10.1 Procedure Descriptions   . . . . . . . . . . . . . . . . 232
                  E.10.1.1 Initiator Algorithms  . . . . . . . . . . . . . . . 233
                  E.10.1.2 Target Algorithms   . . . . . . . . . . . . . . . . 235
             E.10.2 Connection Recovery Algorithms   . . . . . . . . . . . . 236
                  E.10.2.1 Procedure Descriptions  . . . . . . . . . . . . . . 236
                  E.10.2.2 Initiator Algorithms  . . . . . . . . . . . . . . . 237
                  E.10.2.3 Target Algorithms   . . . . . . . . . . . . . . . . 239
   Appendix F. Clearing effects on various events on targets  . . . . . 241
    Full Copyright Statement  . . . . . . . . . . . . . . . . . . . . . 247





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   1. Definitions

           - Alias: An alias string could also be associated with an iSCSI Node.
           The alias allows an organization to associate a user-friendly string
           with the iSCSI Name. However, the alias string is not a substitute for
           the iSCSI Name.

           - CID (Connection ID): Connections within a session are identified by
           a connection ID. It is a unique ID for this connection within the ses-
           sion for the initiator. It is generated by the initiator and presented
           to the target during login requests and during logouts that close con-
           nections.

           - Connection: Communication between the initiator and target occurs
           over one or more TCP connections. The TCP connections carry control
           messages, SCSI commands, parameters, and data within iSCSI Protocol
           Data Units (iSCSI PDUs).

           - iSCSI Initiator Name: The iSCSI Initiator Name specifies the world-
           wide unique name of the initiator.

           - iSCSI Initiator Node: The "initiator".

           - iSCSI Layer: This layer builds/receives iSCSI PDUs and relays/
           receives them to/from one or more TCP connections that form an initi-
           ator-target "session".

           - iSCSI Name: The name of an iSCSI initiator or iSCSI target.

           - iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
           iSCSI target. There are one or more iSCSI Nodes within a Network
           Entity. The iSCSI Node is accessible via one or more Network Portals.
           An iSCSI Node is identified by its iSCSI Name. The separation of the
           iSCSI Name from the addresses used by and for the iSCSI node allows
           multiple iSCSI nodes to use the same addresses, and the same iSCSI
           node to use multiple addresses. iSCSI nodes also have addresses. An
           iSCSI address specifies a single path to an iSCSI node.

           - iSCSI Target Name: The iSCSI Target Name specifies the worldwide
           unique name of the target.

           - iSCSI Target Node: The "target".


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           - iSCSI Task: An iSCSI task is an iSCSI request for which a response
           is expected.

           - iSCSI Transfer Direction: The iSCSI transfer direction is defined
           with regard to the initiator. Outbound or outgoing transfers are
           transfers from the initiator to the target, while inbound or incoming
           transfers are from the target to the initiator.

           - I_T nexus: According to [SAM2], the I_T nexus is a relationship
           between a SCSI Initiator Port and a SCSI Target Port. For iSCSI, this
           relationship is a session, defined as a relationship between an iSCSI
           Initiator's end of session (SCSI Initiator Port) and the iSCSI Tar-
           get's Portal Group. The I_T nexus can be identified by the conjunction
           of the SCSI port names; that is, the I_T nexus identifier is the tuple
           (iSCSI Initiator Name + 'i'+ ISID, iSCSI Target Name + 't'+ Portal
           Group Tag). NOTE: The I_T nexus identifier is not equal to the session
           identifier (SSID).

           - Network Entity: The Network Entity represents a device or gateway
           that is accessible from the IP network. A Network Entity must have one
           or more Network Portals, each of which can be used to gain access to
           the IP network by some iSCSI Nodes contained in that Network Entity.

           - Network Portal: The Network Portal is a component of a Network
           Entity that has a TCP/IP network address and that may be used by an
           iSCSI Node within that Network Entity for the connection(s) within one
           of its iSCSI sessions. A Network Portal in an initiator is identified
           by its IP address. A Network Portal in a target is identified by its
           IP address and its listening TCP port.

           - Originator - in a negotiation or exchange the party that initiates
           the negotiation or exchange.

           - PDU (Protocol Data Unit): The initiator and target divide their com-
           munications into messages. The term "iSCSI protocol data unit" (iSCSI
           PDU) is used for these messages.

           - Portal Groups: iSCSI supports multiple connections within the same
           session; some implementations will have the ability to combine con-
           nections in a session across multiple Network Portals. A Portal Group
           defines a set of Network Portals within an iSCSI Node that collec-
           tively supports the capability of coordinating a session with connec-

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           tions spanning these portals. Not all Network Portals within a Portal
           Group need participate in every session connected through that Portal
           Group. One or more Portal Groups may provide access to an iSCSI Node.
           Each Network Portal as utilized by a given iSCSI Node belongs to
           exactly one portal group within that node.

           - Portal Group Tag: This simple integer value between 1 and 65535
           identifies the Portal Group within an iSCSI Node. All Network Portals
           with the same portal group tag in the context of a given iSCSI Node
           are in the same Portal Group.

           - Responder: In a negotiation or exchange, the party that responds to
           the originator of the negotiation or exchange.

           - SCSI Device: This is the SAM2 term for an entity that contains other
           SCSI entities. For example, a SCSI Initiator Device contains one or
           more SCSI Initiator Ports and zero or more application clients; a SCSI
           Target Device contains one or more SCSI Target Ports and one or more
           logical units. For iSCSI, the SCSI Device is the component within an
           iSCSI Node that provides the SCSI functionality. As such, there can be
           at most one SCSI Device within a given iSCSI Node. Access to the SCSI
           Device can only be achieved in an iSCSI normal operational session.
           The SCSI Device Name is defined to be the iSCSI Name of the node and
           its use is mandatory in the iSCSI protocol.

           - SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
           Blocks) and relays/receives them with the remaining command execute
           parameters to/from the iSCSI Layer.

           - Session: The group of TCP connections that link an initiator with a
           target, form a session (loosely equivalent to a SCSI I-T nexus). TCP
           connections can be added and removed from a session. Across all con-
           nections within a session, an initiator sees one "target image".
           - SSID (Session ID): A session is defined by a session ID that is com-
           posed of an initiator part (ISID) and a target part (TSID).

           - SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
           operational session. An iSCSI normal operational session is negoti-
           ated through the login process between an iSCSI initiator node and an
           iSCSI target node. At successful completion of this process, a SCSI
           Initiator Port is created within the SCSI Initiator Device. The SCSI
           Initiator Port Name and SCSI Initiator Port Identifier are both
           defined to be the iSCSI Initiator Name together with (a) a label that

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           identifies it as an initiator port name/identifier and (b) the ISID
           portion of the session identifier.

           - SCSI Port: This is the SAM2 term for an entity in a SCSI Device that
           provides the SCSI functionality to interface with a service delivery
           subsystem or transport. For iSCSI, the definition of the SCSI Initia-
           tor Port and the SCSI Target Port are different.

           - SCSI Port Name: A name made up as UTF-8 characters and is basically
           the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.

           - SCSI Target Port: This maps to an iSCSI Target Portal Group.

           - SCSI Target Port Name and SCSI Target Port Identifier: These are
           both defined to be the iSCSI Target Name together with (a) a label
           that identifies it as a target port name/identifier and (b) the portal
           group tag.

           - TSID (Target Session ID): The TSID is the target assigned tag for a
           session with a specific named initiator that and ISID. The target is
           generating it during session establishment and its internal format
           and content are not defined by this protocol except for the value 0
           that is reserved and used by the initiator to indicate a new session.
           It is given to the target, during additional connection establishment
           for the same session.





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   2. Overview

   2.1  SCSI Concepts

           The SCSI Architecture Model-2 [SAM2] describes, in detail, the archi-
           tecture of the SCSI family of I/O protocols. This section provides a
           brief background of the SCSI architecture and is intended to familiar-
           ize readers with its terminology.

           At the highest level, SCSI is a family of interfaces for requesting
           services from I/O devices, including hard drives, tape drives, CD and
           DVD drives, printers, and scanners. In SCSI terminology, an individ-
           ual I/O device is called a "logical unit" (LU).

           SCSI is a client-server architecture. Clients of a SCSI interface are
           called "initiators". Initiators issue SCSI "commands" to request ser-
           vice from a logical unit. The "device server" on the logical unit
           accepts SCSI commands and processes them.

           A "SCSI transport" maps the client-server SCSI protocol to a specific
           interconnect. Initiators are one endpoint of a SCSI transport. The
           "target" is the other endpoint. A target can contain multiple Logical
           Units (LUs). Each Logical Unit has an address within a target called a
           Logical Unit Number (LUN).

           A SCSI task is a SCSI command or possibly a linked set of SCSI com-
           mands. Some LUs support multiple pending (queued) tasks, but the queue
           of tasks is managed by the target. The target uses an initiator pro-
           vided "task tag" to distinguish between tasks. Only one command in a
           task can be outstanding at any given time.

           Each SCSI command results in an optional data phase and a required
           response phase. In the data phase, information can travel from the
           initiator to target (e.g., WRITE), target to initiator (e.g., READ),
           or in both directions. In the response phase, the target returns the
           final status of the operation, including any errors. A response termi-
           nates a SCSI command.

           Command Descriptor Blocks (CDB) are the data structures used to con-
           tain the command parameters that an initiator hands to a target. The
           CDB content and structure is defined by [SAM] and device-type specific
           SCSI standards.



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   2.2  iSCSI Concepts and Functional Overview

           The iSCSI protocol is a mapping of the SCSI remote procedure invoca-
           tion model (see [SAM]) over the TCP protocol. SCSI commands are car-
           ried by iSCSI requests and SCSI responses and status are carried by
           iSCSI responses. iSCSI also uses the request response mechanism for
           iSCSI protocol mechanisms.

           For the remainder of this document, the terms "initiator" and "target"
           refer to "iSCSI initiator node" and "iSCSI target node", respectively
           (see Section 2.4.1 iSCSI Architecture Model) unless otherwise quali-
           fied.

           In keeping with similar protocols, the initiator and target divide
           their communications into messages. This document uses the term
           "iSCSI protocol data unit" (iSCSI PDU) for these messages.

           For performance reasons, iSCSI allows a "phase-collapse". A command
           and its associated data may be shipped together from initiator to tar-
           get, and data and responses may be shipped together from targets.

           The iSCSI transfer direction is defined with regard to the initiator.
           Outbound or outgoing transfers are transfers from initiator to tar-
           get, while inbound or incoming transfers are from target to initiator.

           An iSCSI task is an iSCSI request for which a response is expected.

           In this document "iSCSI request", "iSCSI command", request, or
           (unqualified) command have the same meaning. Also, unless otherwise
           specified, status, response, or numbered response have the same mean-
           ing.

   2.2.1  Layers and Sessions

           The following conceptual layering model is used to specify initiator
           and target actions and how they relate to transmitted and received
           Protocol Data Units:

                 -The SCSI layer builds/receives SCSI CDBs (Command Descriptor
                      Blocks) and relays/receives them with the remaining command
                      execute parameters (cf. SAM2) to/from ->.



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                 -The iSCSI layer that builds/receives iSCSI PDUs and relays/
                      receives them to/from one or more TCP connections that form an
                      initiator-target "session".

           Communication between the initiator and target occurs over one or more
           TCP connections. The TCP connections carry control messages, SCSI
           commands, parameters, and data within iSCSI Protocol Data Units
           (iSCSI PDUs). The group of TCP connections that link an initiator with
           a target, form a session (loosely equivalent to a SCSI I-T nexus - see
           Section 2.4.2 SCSI Architecture Model). A session is defined by a ses-
           sion ID that is composed of an initiator part and a target part. TCP
           connections can be added and removed from a session. Connections
           within a session are identified by a connection ID (CID).

           Across all connections within a session, an initiator sees one "target
           image". All target identifying elements, such as LUN, are the same. In
           addition, a target sees one "initiator image" across all connections
           within a session. Initiator that identifying elements, such as the
           Initiator Task Tag, can be used to identify Tag are global across the
           same entity session regardless of the connection on which they are
           sent or received.

           iSCSI targets and initiators MUST support at least one TCP connection
           and MAY support several connections in a session. For error recovery
           purposes, targets and initiators that support a single active connec-
           tion in a session may have to support two connections during recovery.

   2.2.2  Ordering and iSCSI Numbering

           iSCSI uses Command and Status numbering schemes and a Data sequencing
           scheme.

           Command numbering is session-wide and is used for ordered command
           delivery over multiple connections. It can also be used as a mechanism
           for command flow control over a session.

           Status numbering is per connection and is used to enable missing sta-
           tus detection and recovery in the presence of transient or permanent
           communication errors.

           Data sequencing is per command or part of a command (R2T triggered
           sequence) and is used to detect missing data and/or R2T PDUs due to
           header digest errors.


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                                                                 iSCSI            1-March-02

           Typically, fields in the iSCSI PDUs communicate the Sequence Numbers
           between the initiator and target. During periods when traffic on a
           connection is unidirectional, iSCSI NOPOut/In PDUs may be utilized to
           synchronize the command and status ordering counters of the target and
           initiator.

   2.2.2.1  Command Numbering and Acknowledging

           iSCSI supports ordered command delivery within a session. All com-
           mands (initiator-to-target PDUs) are numbered.

           Many SCSI activities are related to a task (SAM2). The task is identi-
           fied by the Initiator Task Tag for the life of the task.

           Commands in transit from the initiator to the target are numbered by
           iSCSI; the number is carried by the iSCSI PDU as CmdSN (Command-
           Sequence-Number). The numbering is session-wide. Outgoing iSCSI
           request PDUs carry this number. The iSCSI initiator allocates CmdSNs
           with a 32-bit unsigned counter (modulo 2**32). Comparisons and arith-
           metic on CmdSN SHOULD use Serial Number Arithmetic as defined in
           [RFC1982] where SERIAL_BITS = 32.

           Commands meant for immediate delivery are marked with an immediate
           delivery flag; they also carry CmdSN. CmdSN does not advance for com-
           mands marked for immediate delivery.

           Command numbering starts with the first login request on the first
           connection of a session (the leading login on the leading connection)
           and command numbers are incremented by 1 for every non-immediate com-
           mand issued afterwards.

           If immediate delivery is used with task management commands, these
           commands may reach the target task management before the tasks on
           which they are supposed to act. However, their CmdSN is a marker of
           their position in the stream of commands. The task management command
           MUST carry the CmdSN that is given to the next non-immediate command.
           The initiator and target must ensure that the task management commands
           act as specified by SAM2. For example, both commands and responses
           appear as if delivered in order.

           Beyond the scope of this document is the means by which one may
           request immediate delivery for a command or by which iSCSI decides by
           itself to mark a PDU for immediate delivery.


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                                                                 iSCSI            1-March-02


           The number of commands used for immediate delivery is not limited and
           their delivery to execution is not acknowledged through the numbering
           scheme. Immediate commands can be rejected by the iSCSI target due to
           a lack of resources. An iSCSI target MUST be able to handle at least
           one immediate task management command and one immediate non-task-man-
           agement iSCSI request per connection at any time.

           With the exception of the commands marked for immediate delivery, the
           iSCSI target layer MUST deliver the commands for execution in the
           order specified by CmdSN. Commands marked for immediate delivery may
           be handed over by the iSCSI target layer for execution as soon as
           detected. iSCSI may avoid delivering some commands for execution if
           required by a prior SCSI or iSCSI action (e.g., clear task set Task
           Management request received before all the commands on which it was
           supposed to act). Delivery for execution means delivery to the SCSI
           execution engine or an iSCSI-SCSI protocol specific execution engine
           (e.g., for text requests).

           On any given connection, the iSCSI initiator MUST send the commands in
           increasing order of CmdSN, except for commands that are retransmitted
           due to digest error recovery and connection recovery.

           The initiator and target are assumed to have the following three reg-
           isters that are unique session wide and that define the numbering
           mechanism:

                  - CmdSN - the current command Sequence Number, advanced by 1 on
                      each command shipped except for commands marked for immediate
                      delivery. CmdsN always contains the number to be assigned
                      next.
                  - ExpCmdSN - the next expected command by the target. The tar-
                      get acknowledges all commands up to, but not including, this
                      number. The initiator has to mark the acknowledged commands as
                      such as soon as a PDU with the corresponding ExpCmdSN is
                      received. The target iSCSI layer sets the ExpCmdSN to the
                      largest non-immediate CmdSN that it can deliver for execution
                      plus 1 (no holes in the CmdSN sequence).
                  - MaxCmdSN - the maximum number to be shipped. The queuing
                      capacity of the receiving iSCSI layer is MaxCmdSN - ExpCmdSN +
                      1.

           ExpCmdSN and MaxCmdSN are derived from target-to-initiator PDU
           fields. Comparisons and arithmetic on ExpCmdSN and MaxCmdSN SHOULD


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           MUST use Serial Number Arithmetic as defined in [RFC1982] where
           SERIAL_BITS = 32.

           The target MUST NOT transmit a MaxCmdSN that is less than the last
           ExpCmdSN. For non-immediate commands, the CmdSN field can take any
           value from ExpCmdSN to MaxCmdSN. The target MUST silently ignore any
           non-immediate command outside of this range or non-immediate dupli-
           cates within the range.

           MaxCmdSN and ExpCmdSN fields are processed by the initiator as fol-
           lows:

                 -If the PDU MaxCmdSN is less than the PDU ExpCmdSN-1 (in Serial
                      Arithmetic Sense), they are both ignored.
                 -If the PDU MaxCmdSN is less than the local MaxCmdSN (in Serial
                      Arithmetic Sense), it is ignored; otherwise, it updates the
                      local MaxCmdSN.
                 -If the PDU ExpCmdSN is less than the local ExpCmdSN (in Serial
                      Arithmetic Sense), it is ignored; otherwise, it updates the
                      local ExpCmdSN.

           This sequence is required since updates may arrive out of order being
           that they travel on different TCP connections.

           The target MUST NOT transmit a MaxCmdSN that is less than the last
           ExpCmdSN. For non-immediate commands, the CmdSN field can take any
           value from ExpCmdSN to MaxCmdSN. The target MUST silently ignore any
           non-immediate command outside of this range or non-immediate dupli-
           cates within the range.

           iSCSI initiators and targets MUST support the command numbering
           scheme.

           A numbered iSCSI request will not change its allocated CmdSN, regard-
           less of the number of times and circumstances in which it is reissue-
           dreissued (see Section 6.1.1 Usage of Retry). At the target, it is
           assumed that CmdSN is relevant only while the command has not created
           any state related to its execution (execution state); afterwards,
           CmdSN becomes irrelevant. Testing for the execution state (repre-
           sented by identifying the Initiator Task Tag) is assumed to precede
           any other action at the target, and is followed by ordering and deliv-
           ery if no execution state is found or delivery if an execution state
           is found.


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           When the current value of the CmdSN register is Q, an initiator MUST
           not advance CmdSN past R + 2**31 - 1 after reissuing a command with
           CmdSN R on a connection while this connection is operational, unless a
           new non-immediate command with CmdSN equal or greater than Q was
           issued on the given connection and its reception acknowledged by the
           target (see Section 9.3 Command Retry and Cleaning Old Command Instan-
           cesSection 8.3 Command Retry and Cleaning Old Command Instances). The
           non-immediate command MUST be sent in order after the retried command.
           A target MUST NOT issue a command response or DATA-In PDU with status
           before acknowledging the command. However, the acknowledgement can be
           included in the response or Data-in PDU itself.

   2.2.2.2  Response/Status Numbering and Acknowledging

           Responses in transit from the target to the initiator are numbered.
           The StatSN (Status Sequence Number) is used for this purpose. StatSN
           is a counter maintained per connection. ExpStatSN is used by the ini-
           tiator to acknowledge status. The status sequence number space is
           32bit integers and the arithmetic operations are the regular
           mod(2**32) arithmetic.

           Status numbering starts with the Login response to the first Login
           request of the connection. The Login response includes an initial
           value for status numbering (any initial value is valid).

           To enable command recovery, the target MAY maintain enough state
           information to enable data and status recovery after a connection
           failure. A target can discard all the state information maintained for
           recovery after the status delivery is acknowledged through ExpStatSN.

           A large absolute difference between StatSN and ExpStatSN may indicate
           a failed connection. Initiators undertake recovery actions if the
           difference is greater than an implementation defined constant that
           SHOULD NOT exceed 2**31-1.

           Initiators and Targets MUST support the response-numbering scheme.

   2.2.2.3  Data Sequencing

           Data and R2T PDUs, transferred as part of some command execution, MUST
           be sequenced. The DataSN field is used for data sequencing. For input
           (read) data PDUs, DataSN starts with 0 for the first data PDU of an
           input command and advances by 1 for each subsequent data PDU. For out-
           put data PDUs, DataSN starts with 0 for the first data PDU of a

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           sequence (the initial unsolicited sequence or any data PDU sequence
           issued to satisfy an R2T) and advances by 1 for each subsequent data
           PDU. R2Ts are also sequenced per command. For example, the first R2T
           has an R2TSN of 0 and advances by 1 for each subsequent R2T. For bidi-
           rectional commands, the target uses the DataSN/R2TSN to sequence
           Data-In and R2T PDUs in one continuous sequence (undifferentiated).
           Unlike command and status, data PDUs and R2Ts are not acknowledged by
           a field in regular outgoing PDUs.  Data-In PDUs can be acknowledged on
           demand by a special form of the SNACK PDU.  Data and R2T PDUs are
           implicitly acknowledged by status. The DataSN/R2TSN field enables the
           initiator to detect missing data or R2T PDUs.

           For any given write command, a target must have issued less than 2**32
           R2Ts. Any input or output data sequence MUST contain less than 2**32
           numbered PDUs.


   2.2.3  iSCSI Login

           The purpose of the iSCSI login is to enable a TCP connection for iSCSI
           use, authenticate the parties, negotiate the session's parameters and
           mark the connection as belonging to an iSCSI session.

           A session is used to identify all the connections with a given initi-
           ator that belong to the same I_T nexus to a target. (See Section 2.4.2
           SCSI Architecture Model for more details on how a session relates to
           an I_T nexus).

           The targets listen on a well-known TCP port or other TCP port for
           incoming connections. The initiator begins the login process by con-
           necting to one of these TCP ports.

           As part of the login process, the initiator and target MAY wish to
           authenticate each other and set a security association protocol for
           the session. This can occur in many different ways and is subject to
           negotiation.

           In order to protect the TCP connection, an IPsec security association
           MAY be established before the Login request. Using IPsec security for
           iSCSI is specified in Chapter 8Chapter 7 and in [SEC-IPS].

           The iSCSI Login Phase is carried through Login requests and responses.
           Once suitable authentication has occurred and operational parameters


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           have been set, the initiator may start to send SCSI commands. How the
           target chooses to authorize an initiator is beyond the scope of this
           document. A more detailed description of the Login Phase can be found
           in Chapter 4.


           The login PDU includes a session ID that is composed of an initiator
           part ISID and a target part TSID. For a new session, the TSID is null.
           As part of the response, the target generates a TSID.

           During session establishment, the target identifies the SCSI initia-
           tor port (the "I" in the "I_T nexus") through the value pair (Initia-
           torName, ISID) (InitiatorName is described later in this part). Any
           persistent state (e.g., persistent reservations) on the target that
           is associated with a SCSI initiator port is identified based on this
           value pair. Any state associated with the SCSI target port (the "T" in
           the "I_T nexus") is identified externally by the TargetName and portal
           group tag (see Section 2.4.1 iSCSI Architecture Model) and internally
           in an implementation dependent way. As ISID is used to identify a per-
           sistent state, it is subject to reuse restrictions (see Section 2.4.3
           Consequences of the Model).

           Before the Full Feature Phase is established, only Login Request and
           Login Response PDUs are allowed. Any other PDU, when received at ini-
           tiator or target, is a protocol error and MUST result in the connec-
           tion being terminated.

   2.2.4  Text Mode Negotiation

           During login, and thereafter, some session or connection parameters
           are negotiated through an exchange of textual information.

           The initiator starts the negotiation through a Text/Login request and
           indicates when it is ready for completion (by setting to 1 and keeping
           to 1 the F bit in a Text Request or the T bit in the Login Request).

           The general format of text negotiation is:

                 Originator-> <key>=<valuex>
                 Responder-> <key>=<valuey>|NotUnderstood|Irrelevant

           The originator can either be the initiator or the target and the
           responder can either be the target or initiator, respectively. Target


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           requests are not limited to respond to key=value pairs as offered by
           the initiator. The target may offer key=value pairs of its own.

           All negotiations are stateless (i.e., the result MUST be based only on
           newly exchanged values). Not offering a key for negotiation is not
           equivalent to offering the current (or default) value.

           The value can be a number, a single literal constant a Boolean value
           (yes or no), or a list of comma separated, literal constant values.

           In literal list negotiation, the originator sends a list of options
           (literal constants which may include "None") for each key in its order
           of preference.

           The responding party answers with the first value that it supports and
           is allowed to use for the specific originator selected from the orig-
           inator list.

           The constant "none" MUST always be used to indicate a missing func-
           tion. However, none is a valid selection only if it is explicitly
           offered.

           If a responder does not support or is not allowed to use all of the
           offered options with a specific originator, it may use the constant
           "Reject".

           For numerical and single literal negotiations, the responding party
           MUST respond with the required key. The value it selects, based on the
           selection rule specific to the key, becomes the negotiation result.
           The selection of a value not admissible under the selection rules is
           considered a protocol error and is handled accordingly.

           For Boolean negotiations (keys taking the values yes or no), the
           responding party MUST respond with the required key and the result of
           the negotiation when the received value does not determine that result
           by itself. The last value transmitted becomes the negotiation result.
           The rules for selecting the value with which to respond are expressed
           as Boolean functions of the value received and the value that the
           responding party would select in the absence of knowledge of the
           received value.

           Specifically, the two cases in which responses are OPTIONAL are:


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                 - The Boolean function is "AND" and the value "no" is received.
                      The outcome of the negotiation is "no".
                 - The Boolean function is "OR" and the value "yes" is received.
                      The outcome of the negotiation is "yes".

           Responses are REQUIRED in all other cases, and the value chosen and
           sent by the responder becomes the outcome of the negotiation.

           If a specific key is not relevant for the current negotiation, the
           responder may answer with the constant "Irrelevant" for all types of
           negotiation.

           Any other key not understood by the responder may be ignored by the
           responder without affecting the basic function. However, the Text
           Response for a key not understood MUST be key=NotUnderstood.

           The value "?" with any key has the meaning of enquiry and should be
           answered with the current value or "NotUnderstood". The value "?" MUST
           be used ONLY in Full Feature Phase.  Whenever the responder has 2 two
           values for a key - one for the offering-to-responding-party direction
           and a second one for the responding-to-offering-party direction it
           will answer with the two values separated by a comma starting with the
           requesting-to-offering-party direction.

           The constants "None", "Reject", "Irrelevant", and "NotUnderstood" are
           reserved and must only be used as described here.

           Some basic key=value pairs are described in Chapter 12. All keys in
           Chapter 12, except for the X- extension format, MUST be supported by
           iSCSI initiators and targets.

           Manufacturers may introduce new keys by prefixing them with X- fol-
           lowed by their (reversed) domain name. For example the company owning
           the domain acme.com can issue:

                 X-com.acme.bar.foo.do_something=3


   2.2.5  iSCSI Full Feature Phase

           Once the initiator is authorized to do so, the iSCSI session is in the
           iSCSI Full Feature Phase. A session is in Full Feature Phase after
           successfully finishing the login phase on the first (leading) connec-
           tion of a session. A connection is in Full Feature Phase if the ses-

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           sion is in Full Feature Phase and the connection login has completed
           successfully. An iSCSI connection is not in Full Feature Phase a) when
           it does not have an established transport connection, or b) when it
           has a valid transport connection, but a successful login was not per-
           formed or the connection is currently logged out. In a normal Full
           Feature Phase, the initiator may send SCSI commands and data to the
           various LUs on the target by wrapping them in iSCSI PDUs that go over
           the established iSCSI session.

           For an iSCSI request issued over a TCP connection, the corresponding
           response and/or requested PDU(s) MUST be sent over the same connection
           by default. We call this "connection allegiance". If the original con-
           nection fails before the command is completed, the connection alle-
           giance of the command may be explicitly reassigned to a different
           transport connection as described in detail in Section 6.1 Retry and
           Reassign in Recovery.

           For SCSI commands that require data and/or a parameter transfer, the
           (optional) data and the status for a command MUST be sent over the
           same TCP connection to which the SCSI command is currently allegiant,
           illustrating the above rule.

           Thus, if an initiator issues a READ command, the target MUST send the
           requested data, if any, followed by the status to the initiator over
           the same TCP connection that was used to deliver the SCSI command. If
           an initiator issues a WRITE command, the initiator MUST send the data,
           if any, for that command. The target MUST return Ready To Transfer
           (R2T), if any, and the status over the same TCP connection that was
           used to deliver the SCSI command. Retransmission requests (SNACK
           PDUs) and the data and status that they generate MUST also use the
           same connection.

           However, consecutive commands that are part of a SCSI linked command-
           chain task MAY use different connections. Connection allegiance is
           strictly per-command and not per-task. During the iSCSI Full Feature
           Phase, the initiator and target MAY interleave unrelated SCSI com-
           mands, their SCSI Data, and responses over the session.

           Outgoing SCSI data (initiator to target user data or command parame-
           ters) is sent as either solicited data or unsolicited data. Solicited
           data is sent in response to R2T PDUs. Unsolicited data can be sent as
           part of an iSCSI command PDU ("immediate data") or in separate iSCSI
           data PDUs. An initiator may send unsolicited data as immediate up to

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           the negotiated maximum PDU size or in a separate PDU sequence (up to
           the mode page limitFirstBurstSize). All subsequent data MUST be
           solicited. The maximum size of an individual data PDU or the immedi-
           ate-part of the first unsolicited burst MAY be negotiated at login.

           Targets operate in either solicited (R2T) data mode or unsolicited
           (non R2T) data mode. In unsolicited mode, an initial R2T that allows a
           transfer up to the FirstBurstSize is implied. A target MAY separately
           enable immediate data without enabling the more general (separate
           data PDUs) form of unsolicited data.

           An initiator SHOULD honor an R2T data request for a valid outstanding
           command (i.e., carrying a valid Initiator Task Tag) provided the com-
           mand is supposed to deliver outgoing data and the R2T specifies data
           within the command bounds.

           It is considered an error for an initiator to send unsolicited data
           PDUs to a target that operates in R2T mode (only solicited data is
           allowed). It is also an error for an initiator to send more data,
           whether immediate or as separate PDUs, than the SCSI iSCSI limit for
           first burst. At login, an initiator MAY request to send data blocks
           and a first burst of any size; in this case, the target MUST indicate
           the size of the first burst and of the immediate and data blocks that
           it is ready to accept.

           A target SHOULD NOT silently discard data and request retransmission
           through R2T. Initiators SHOULD NOT keep track of the data transferred
           to or from the target (scoreboarding); targets perform residual count
           calculation. Incoming data for initiators is always implicitly solic-
           ited. SCSI data packets are matched to their corresponding SCSI com-
           mands by using Tags specified in the protocol.

           Initiator tags for pending commands are unique initiator-wide for a
           session. Target tags are not strictly specified by the protocol. It is
           assumed that these tags are used by the target to tag (alone or in
           combination with the LUN) the solicited data. Target tags are gener-
           ated by the target and "echoed" by the initiator. The above mechanisms
           are designed to accomplish efficient data delivery and a large degree
           of control over the data flow.

           iSCSI initiators and targets MUST also enforce some ordering rules.
           Unsolicited data MUST be sent on every connection in the same order in


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           which commands were sent. A target that receives data out of order MAY
           terminate the session.

   2.2.6  iSCSI Connection Termination

           An iSCSI connection may be terminated by use of a transport connection
           shutdown, or a transport reset.  Transport reset is assumed to be an
           exceptional event.

           Graceful TCP connection shutdowns are done by sending TCP FINs. A
           graceful transport connection shutdown SHOULD be initiated by either
           party only when the connection is not in iSCSI full-feature phase.  A
           target MAY terminate a full-feature phase connection on internal
           exception events, but it SHOULD announce the fact through an Asynchro-
           nous Message PDU.  Connection termination with outstanding commands
           may require recovery actions.

           If a connection is terminated while in full-feature phase, connection
           cleanup (section 5) is required as a prelude to recovery. By doing
           connection cleanup before starting recovery, the initiator and target
           can avoid receiving stale PDUs after recovery. In this case, the ini-
           tiator sends a Logout request on one of the operational connections of
           a session that indicates which iSCSI connection should be logged out.

   2.2.7  Naming and Addressing

           All iSCSI initiators and targets are named. Each target or initiator
           is known by an iSCSI Name. The iSCSI Name is independent of the loca-
           tion of the initiator and target; two formats are provided that allow
           the use of existing naming authorities to generate names.

           One of these formats allows the use of a registered domain name as a
           naming authority; it is important not to confuse this with an address.
           The iSCSI Name is a UTF-8 text string and is defined in [NDT].

           iSCSI Names are used to provide:

                 - An initiator identifier for configurations that provide multi-
                      ple initiators behind a single IP address.
                 - A target identifier for configurations that present multiple
                      targets behind a single IP address and port.
                 - A method to recognize multiple paths to the same device on
                      different IP addresses and ports.
                 - An identifier for source and destination targets for use in
                      third party commands.

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                 - An identifier for initiators and targets to enable them to
                      recognize each other regardless of IP address and port mapping
                      on intermediary firewalls.

           The initiator MUST present both its iSCSI Initiator Name and the iSCSI
           Target Name to which it wishes to connect in the first login request
           of a new session. The only exception is if a discovery session (see
           Section 2.3 iSCSI Session Types) is to be established; the iSCSI Ini-
           tiator Name is still required, but the iSCSI Target Name may be
           ignored. The key "SessionType=Discovery" is sent by the initiator at
           login to indicate a discovery session.

           The default name "iSCSI" is reserved and is not used as an individual
           initiator or target name.

           iSCSI Names do not require special handling within the iSCSI layer;
           they are opaque and case-sensitive for purposes of comparison.

           Examples of iSCSI Names:

                 iqn.1998-03.com.disk-vendor.diskarrays.sn.45678
                 iqn.2000-01.com.gateways.yourtargets.24
                 iqn.1987-06.com.os-vendor.plan9.cdrom.12345
                 iqn.2001-03.com.service-provider.users.customer235.host90
                 eui.02004567A425678D

           iSCSI nodes also have addresses. An iSCSI address specifies a single
           path to an iSCSI node and has the following format:

                 <domain-name>[:<port>]

           Where <domain-name> is one of:

                 - IPv4 address, in dotted decimal notation. Assumed if the name
                      contains exactly four numbers, separated by dots (.), where
                      each number is in the range 0..255.
                 - IPv6 address, in colon-separated hexadecimal notation, as
                      specified in [RFC2373] and enclosed in "[" and "]" characters,
                      as specified in [RFC2732].
                 - Fully Qualified Domain Name (host name). Assumed if the
                      <domain-name> is neither an IPv4 nor an IPv6 address.

           For iSCSI targets, the <port> in the address is optional; if speci-
           fied, it is the TCP port on which the target is listening for connec-



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           tions. If the <port> is not specified, the default port 3260, assigned
           by IANA, will be assumed. For iSCSI initiators, the <port> is omitted.

           Examples of addresses:

                 10.40.1.2
                 [FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
                 [1080:0:0:0:8:800:200C:417A]
                 [3ffe:2a00:100:7031::1]
                 [1080::8:800:200C:417A]
                 [::192.9.5.5]
                 mydisks.example.com

           To assist in providing a more human-readable user interface for
           devices that contain iSCSI targets and initiators, a target or initi-
           ator may also provide an alias. This alias is a simple UTF-8 string,
           is not globally unique, and is never interpreted or used to identify
           an initiator or device within the iSCSI protocol. Its use is described
           in [NDT].

           Third party commands require that protocol-specific addresses be com-
           municated within SCSI CDBs. The iSCSI protocol-specific address con-
           sists of an iSCSI name, or an iSCSI name + TCP address.

           An initiator may discover the iSCSI Target Names to which it has
           access, along with their addresses, using the SendTargets text
           request, or by other techniques discussed in [NDT].

   2.2.8  Persistent State

           iSCSI does not require any persistent state maintenance across ses-
           sions. However in some cases, SCSI requires persistent identification
           of the SCSI initiator port name (for iSCSI, the InitiatorName plus the
           ISID portion of the session identifier). (See Section 2.4.2 SCSI
           Architecture Model and Section 2.4.3 Consequences of the Model.)

           iSCSI sessions do not persist through power cycles and boot opera-
           tions.

           All iSCSI session and connection parameters are re-initialized on
           session and connection creation.

           Commands persist beyond connection termination if the session per-
           sists and command recovery within the session is supported. However,


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           when a connection is dropped, command execution, as perceived by iSCSI
           (i.e., involving iSCSI protocol exchanges for the affected task), is
           suspended until a new allegiance is established by the 'task reassign'
           task management function. (See Section 10.5 Task Management Function
           RequestSection 9.5 Task Management Function Request.)

   2.2.9  Message Synchronization and Steering

   2.2.9.1  Rationale

           iSCSI presents a mapping of the SCSI protocol onto TCP. This encapsu-
           lation is accomplished by sending iSCSI PDUs of varying lengths.
           Unfortunately, TCP does not have a built-in mechanism for signaling
           message boundaries at the TCP layer. iSCSI overcomes this obstacle by
           placing the message length in the iSCSI message header. This serves to
           delineate the end of the current message as well as the beginning of
           the next message.

           In situations where IP packets are delivered in order from the net-
           work, iSCSI message framing is not an issue and messages are processed
           one after the other. In the presence of IP packet reordering, (i.e.,
           frames being dropped) legacy TCP implementations store the "out of
           order" TCP segments in temporary buffers until the missing TCP seg-
           ments arrive, upon which the data must be copied to the application
           buffers. In iSCSI, it is desirable to steer the SCSI data within these
           out of order TCP segments into the pre-allocated SCSI buffers rather
           than store them in temporary buffers. This decreases the need for ded-
           icated reassembly buffers as well as the latency and bandwidth related
           to extra copies.

           Relying solely on the "message length" information from the iSCSI mes-
           sage header may make it impossible to find iSCSI message boundaries in
           subsequent TCP segments due to the loss of a TCP segment that contains
           the iSCSI message length. The missing TCP segment(s) must be received
           before any of the following segments can be steered to the correct
           SCSI buffers (due to the inability to determine the iSCSI message
           boundaries). Since these segments cannot be steered to the correct
           location, they must be saved in temporary buffers that must then be
           copied to the SCSI buffers.

           Different schemes can be used to recover synchronization. One of these
           schemes is detailed in Appendix A. - Sync and Steering with Fixed
           Interval Markers -Appendix A. - Sync and Steering with Fixed Interval
           Markers -. To make these schemes work, iSCSI implementations have to

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           make sure that the appropriate protocol layers are provided with
           enough information to implement a synchronization and/or data steer-
           ing mechanism.

   2.2.9.2  Synchronization (sync) and Steering Functional Model

           We assume that iSCSI is implemented according to the following layer-
           ing scheme:

                +------------------------+
                |        SCSI            |
                +------------------------+
                |       iSCSI            |
                +------------------------+
                |  Sync and Steering     |
                |  +-------------------+ |
                |  |      TCP          | |
                |  +-------------------+ |
                +------------------------+
                | Lower Functional Layers|
                |        (LFL)           |
                +------------------------+
                |         IP             |
                +------------------------+
                |        Link            |
                +------------------------+


           In this model, LFL can be IPsec (a mechanism changing the IP stream
           and invisible to TCP). We assume that Sync and Steering operates just
           underneath iSCSI. An implementation may choose to place Sync and
           Steering somewhere else in the stack if it can translate the informa-
           tion kept by iSCSI in terms valid for the chosen layer.

           According to our layering model, iSCSI considers the information it
           delivers to the Sync and Steering layer (headers and payloads) as a
           contiguous stream of bytes mapped to the positive integers from 0 to
           infinity. In practice, though, iSCSI is not expected to handle infi-
           nitely long streams; stream addressing will wrap around at 2**32-1.

           This model assumes that the iSCSI layer will deliver complete PDUs to
           underlying layers in single (atomic) operations. The underlying layer
           does not need to examine the stream content to discover the PDU bound-


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           aries. If a specific implementation performs PDU delivery to the Sync
           and Steering layer through multiple operations, it MUST bracket an
           operation set used to deliver a single PDU in a manner that the Sync
           and Steering Layer can understand.

           The Sync and Steering Layer (which is OPTIONAL) MUST retain the PDU
           end address within the stream for every delivered iSCSI PDU.
           To enable the Sync and Steering operation to perform Steering, addi-
           tional information, including identifying tags and buffer offsets,
           MUST also be retained for every sent PDU. The Sync and Steering Layer
           is required to add enough information to every sent data item (IP
           packet, TCP packet or some other superstructure) to enable the
           receiver to steer it to a memory location independent of any other
           piece.

           If the transmission stream is built dynamically, this information is
           used to insert Sync and Steering information in the transmission
           stream (at first transmission or at re-transmission) either through a
           globally accessible table or a call-back mechanism. If the transmis-
           sion stream is built statically, the Sync and Steering information is
           inserted in the transmission stream when data are first presented to
           sync and steering.

           The retained information can be released whenever the transmitted
           data is acknowledged by the receiver. (in the case of dynamically
           built streams, by deletion from the global table or by an additional
           callback).

           On the outgoing path, the Sync and Steering layer MUST map the outgo-
           ing stream addresses from iSCSI stream addresses to TCP stream
           sequence numbers.

           On the incoming path, the Sync and Steering layer extracts the Sync
           and Steering information from the TCP stream. It then helps steer
           (place) the data stream to its final location and/or recover iSCSI PDU
           boundaries when some TCP packets are lost or received out of order.
           The data stream seen by the receiving iSCSI layer is identical to the
           data stream that left the sending iSCSI layer. The Sync and Steering
           information is kept until the PDUs to which it refers are completely
           processed by the iSCSI layer.

           On the incoming path, the Sync and Steering layer does not change the
           way TCP notifies iSCSI about in-order data arrival. All data place-

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           ments, in-order or out-of-order, performed by the Sync and Steering
           layer are hidden from iSCSI while conventional, in order, data arrival
           notifications generated by TCP are passed through to iSCSI

   2.2.9.3  Sync and Steering and Other Encapsulation Layers

           We recognize that in many environments the following is a more appro-
           priate layering model:

                +----------------------------------+
                |             SCSI                 |
                +----------------------------------+
                |            iSCSI                 |
                +----------------------------------+
                |   Upper Functional Layers (UFL)  |
                +----------------------------------+
                |     Sync and Steering            |
                |  +-----------------------------+ |
                |  |            TCP              | |
                |  +-----------------------------+ |
                +----------------------------------+
                |   Lower Functional Layers (LFL)  |
                +----------------------------------+
                |              IP                  |
                +----------------------------------+
                |             Link                 |
                +----------------------------------+

           In this model, UFL can be TLS (see[RFC2246]) or some other transport
           conversion mechanism (a mechanism that changes the TCP stream, but
           that is transparent to iSCSI).

           To be effective and act on reception of TCP packets out of order, Sync
           and Steering has to be underneath UFL, and Sync and Steering data must
           be left out of any UFL transformation (encryption, compression, pad-
           ding etc.). However, Sync and Steering MUST take into account the
           additional data inserted in the stream by UFL. Sync and Steering MAY
           also restrict the type of transformations UFL may perform on the
           stream.

           This makes implementation of Sync and Steering in the presence of oth-
           erwise opaque UFLs less attractive.



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   2.2.9.4  Sync/Steering and iSCSI PDU Size

           When a large iSCSI message is sent, the TCP segment(s) that contain
           the iSCSI header may be lost. The remaining TCP segment(s) up to the
           next iSCSI message must be buffered (in temporary buffers) since the
           iSCSI header that indicates to which SCSI buffers the data is to be
           steered was lost. To minimize the amount of buffering, it is recom-
           mended that the iSCSI PDU size be restricted to a small value (perhaps
           a few TCP segments in length). During login, each end of the iSCSI
           session specifies the maximum iSCSI PDU size it will accept.

   2.3  iSCSI Session Types

           iSCSI defines two types of sessions:

                  a)  Normal operational session - an unrestricted session.
                  b)  Discovery-session - a session opened only for target discovery;
                  the target MAY accept only text requests with the SendTargets key
                  and a logout request with reason "close the session".

           The session type is defined during login with key=value parameter in
           the login command.

   2.4  SCSI to iSCSI Concepts Mapping Model

           The following diagram shows an example of how multiple iSCSI Nodes
           (targets in this case) can coexist within the same Network Entity
           and can share Network Portals (IP addresses and TCP ports). Other more
           complex configurations are also possible. See  Section 2.4.1 iSCSI
           Architecture Model for detailed descriptions of the components of
           these diagrams.





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                         +-----------------------------------+
                         |  Network Entity (iSCSI Client)    |
                         |                                   |
                         |         +-------------+           |
                         |         | iSCSI Node  |           |
                         |         | (Initiator) |           |
                         |         +-------------+           |
                         |            |       |              |
                         | +--------------+ +--------------+ |
                         | |Network Portal| |Network Portal| |
                         | |   10.1.30.4  | |   10.1.40.6  | |
                         +-+--------------+-+--------------+-+
                                  |               |
                                  |  IP Networks  |
                                  |               |
                         +-+--------------+-+--------------+-+
                         | |Network Portal| |Network Portal| |
                         | |  10.1.30.21  | |   10.1.40.3  | |
                         | |  TCP Port 4  | |  TCP Port 4  | |
                         | +--------------+ +--------------+ |
                         |        |               |          |
                         |        -----------------          |
                         |           |         |             |
                         |  +-------------+ +--------------+ |
                         |  | iSCSI Node  | | iSCSI Node   | |
                         |  |  (Target)   | |  (Target)    | |
                         |  +-------------+ +--------------+ |
                         |                                   |
                         |   Network Entity (iSCSI Server)   |
                         +-----------------------------------+

   2.4.1  iSCSI Architecture Model

           This section describes the part of the iSCSI architecture model that
           has the most bearing on the relationship between iSCSI and the SCSI
           Architecture Model.

                  a)  Network Entity - represents a device or gateway that is acces-
                  sible from the IP network. A Network Entity must have one or more
                  Network Portals (see item d), each of which can be used by some
                  iSCSI Nodes (see item (b)) contained in that Network Entity to gain
                  access to the IP network.



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                  b)  iSCSI Node - represents a single iSCSI initiator or iSCSI tar-
                  get. There are one or more iSCSI Nodes within a Network Entity. The
                  iSCSI Node is accessible via one or more Network Portals (see item
                  d). An iSCSI Node is identified by its iSCSI Name (see Section
                  2.2.6 Naming and Addressing and Chapter 12Chapter 11). The separa-
                  tion of the iSCSI Name from the addresses used by and for the iSCSI
                  node allows multiple iSCSI nodes to use the same addresses, and the
                  same iSCSI node to use multiple addresses.

                  c)  An alias string could also be associated with an iSCSI Node.
                  The alias allows an organization to associate a user friendly
                  string with the iSCSI Name. However, the alias string is not a sub-
                  stitute for the iSCSI Name.

                  d)  Network Portal - a component of a Network Entity that has a
                  TCP/IP network address and that may be used by an iSCSI Node within
                  that Network Entity for the connection(s) within one of its iSCSI
                  sessions. In an initiator, it is identified by its IP address. In a
                  target, it is identified by its IP address and its listening TCP
                  port.

                  e)  Portal Groups - iSCSI supports multiple connections within the
                  same session; some implementations will have the ability to com-
                  bine connections in a session across multiple Network Portals. A
                  Portal Group defines a set of Network Portals within an iSCSI Node
                  that collectively supports the capability of coordinating a ses-
                  sion with connections that span these portals. Not all Network Por-
                  tals within a Portal Group need to participate in every session
                  connected through that Portal Group. One or more Portal Groups may
                  provide access to an iSCSI Node. Each Network Portal, as utilized
                  by a given iSCSI Node, belongs to exactly one portal group within
                  that node. Portal Groups are identified within an iSCSI Node by a
                  portal group tag, a simple integer value between 1 and 65535 (see
                  Section 12.3 SendTargetsSection 11.3 SendTargets). All Network
                  Portals with the same portal group tag in the context of a given
                  iSCSI Node are in the same Portal Group.

                  Both iSCSI Initiators and iSCSI Targets have portal groups, though
                  only the iSCSI Target Portal Groups are used directly in the iSCSI
                  protocol (e.g., in SendTargets). See Section Section 9.1.1 Conser-
                  vative Reuse of ISIDsSection 8.1.1 Conservative Reuse of ISIDs  for
                  references to the Initiator Portal Groups.


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                  f)  Portals within a Portal Group are expected to have similar
                  hardware characteristics, as SCSI port specific mode pages
                  may affect all portals within a portal group. (See Section 2.4.3.2
                  SCSI Mode Pages).

           The following diagram shows an example of one such configuration on a
           target and how a session that shares Network Portals within a Portal
           Group may be established.

               ----------------------------IP Network---------------------
                    |               |                    |
           |     +----|---------------|-----+         +----|---------+
           |+
           |     | +---------+  +---------+ |         | +---------+  |           |
           |     | | Network |  | Network | |         | | Network |  |           |
           |     | | Portal  |  | Portal  | |         | | Portal  |  |           |
           |     | +--|------+  +---------+ |         | +---------+  |           |
           |     |    |               |     |         |    |         |           |
           |     |    |    Portal     |     |         |    | Portal  |           |
           |     |    |    Group 1    |     |         |    | Group 2 |           |
           |     +--------------------------+         +--------------+
           |+
           |           |               |                    |                     |
           |   +--------|---------------|------------+  +--------|--------------
           -------+ |+
           |        |               |                    |                     |
           |   +----------------------------+  +-----------------------------+ |
           |   | iSCSI Session (Target side)|  | iSCSI Session (Target side) | |
           |   |                            |  |                             | |
           |   |        (iSCSI Name + TSID=2TSID = 56)          |  |       (iSCSI
           Name + TSID=1TSID = 48)           | |
           |   +----------------------------+  +-----------------------------+ |
           |                                                                   |
           |                      iSCSI Target Node                            |
           |              (within Network Entity, not shown)                   |
           +-------------------------------------------------------------------+

   2.4.2  SCSI Architecture Model

           This section describes the relationship between the SCSI Architecture
           Model [SAM2] and constructs of the SCSI device, SCSI port and I_T
           nexus, and the iSCSI constructs, described above.



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           This relationship implies implementation requirements in order to
           conform to the SAM2 model and other SCSI operational functions. These
           requirements are detailed in Section 2.4.3 Consequences of the Model.

                 a) SCSI Device - the SAM2 term for an entity that contains other
                      SCSI entities. For example, a SCSI Initiator Device contains
                      one or more SCSI Initiator Ports and zero or more application
                      clients. A SCSI Target Device contains one or more SCSI Target
                      Ports and one or more logical units. For iSCSI, the SCSI
                      Device is the component within an iSCSI Node that provides the
                      SCSI functionality. As such, there can be one SCSI Device, at
                      most, within a given iSCSI Node. Access to the SCSI Device can
                      only be achieved in an iSCSI normal operational session (see
                      Section 2.3 iSCSI Session Types). The SCSI Device Name is
                      defined to be the iSCSI Name of the node and its use is manda-
                      tory in the iSCSI protocol.

                 b) SCSI Port - the SAM2 term for an entity in a SCSI Device that
                      provides the SCSI functionality to interface with a service
                      delivery subsystem or transport. For iSCSI, the definition of
                      SCSI Initiator Port and SCSI Target Port are different.

                  SCSI Initiator Port: This maps to the endpoint of an iSCSI nor-
                      mal operational session (see Section 2.3 iSCSI Session Types).
                      An iSCSI normal operational session is negotiated through the
                      login process between an iSCSI initiator node and an iSCSI
                      target node. At successful completion of this process, a SCSI
                      Initiator Port is created within the SCSI Initiator Device.
                      The SCSI Initiator Port Name and SCSI Initiator Port Identi-
                      fier are both defined to be the iSCSI Initiator Name together
                      with (a) a label that identifies it as an initiator port name/
                      identifier and (b) the ISID portion of the session identifier.

                  SCSI Target Port: This maps to an iSCSI target Portal Group.
                      The SCSI Target Port Name and the SCSI Target Port Identifier
                      are both defined to be the iSCSI Target Name together with (a)
                      a label that identifies it as a target port name/identifier
                      and (b) the portal group tag.

                  The SCSI Port Name is mandatory in iSCSI. When used in SCSI
                  parameter data, the SCSI port name should be formatted as:
                  - The iSCSI Name in UTF-8 format, followed by
                  - a null terminator (1byte), followed by
                  - the ASCII character 'i' (for SCSI Initiator Port) or the
                      ASCII character 't' (for SCSI Target Port), followed by
                  - a null terminator (1byte), followed by
                  - zero to 3 null pad bytes so that the complete format is a
                      multiple of four bytes long, followed by


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                  - the 6byte value of the ISID (for SCSI initiator port) or the
                      2byte value of the portal group tag (for SCSI target port) in
                      network byte order (BigEndian).
                      SCSI port names have a maximum length of 264 bytes for initi-
                      ator ports, 260 bytes for target ports, and must be a multiple
                      of four bytes long. The ASCII character 'i' or 't' is the
                      label that identifies this port as either a SCSI Initiator
                      Port or a SCSI Target Port. This ASCII character also provides
                      the interpretation and size of the remaining six bytes (initi-
                      ator) or two bytes (target).

                 c) I_T nexus - a relationship between a SCSI Initiator Port and
                      a SCSI Target Port, according to [SAM2]. For iSCSI, this rela-
                      tionship is a session, defined as a relationship between an
                      iSCSI Initiator's end of the session (SCSI Initiator Port) and
                      the iSCSI Target's Portal Group. The I_T nexus can be identi-
                      fied by the conjunction of the SCSI port names. That is, the
                      I_T nexus identifier is the tuple (iSCSI Initiator Name + 'i'
                      + ISID, iSCSI Target Name + 't' + Portal Group Tag).

                 NOTE: The I_T nexus identifier is not equal to the session iden-
                      tifier (SSID).


   2.4.3  Consequences of the Model

           This section describes implementation and behavioral requirements
           that result from the mapping of SCSI constructs to the iSCSI con-
           structs defined above. The following are the two assumptions that are
           the basis of these requirements:

                  a)  Between a given iSCSI Initiator and iSCSI Target, at any given
                  time, only one session can exist with a given session identifier
                  (SSID).

                  b)  Between a given SCSI initiator port and SCSI target port,
                  only one I_T nexus (session) can exist. That is, no more than one
                  nexus relationship (parallel nexus) is allowed.

           These assumptions lead to the following conclusions and requirements.

           ISID RULE: Between a given iSCSI Initiator and iSCSI Target Portal
           Group (SCSI target port), there can be only one session with a given
           value for ISID that identifies the SCSI initiator port. See Section
           10.12.6 ISIDSection 9.12.5 ISID.



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           The structure of the ISID that contains a naming authority component
           (see Section 10.12.6 ISIDSection 9.12.5 ISID and [NDT]) provides a
           mechanism to facilitate compliance with the ISID rule (See also Sec-
           tion 9.1.1 Conservative Reuse of ISIDsSection 8.1.1 Conservative
           Reuse of ISIDs).

           The iSCSI Initiator Node is expected to manage the assignment of ISIDs
           prior to session initiation. The "ISID RULE" does not preclude the use
           of the same ISID from the same iSCSI Initiator with different Target
           Portal Groups on the same iSCSI target or on other iSCSI targets (see
           Section 9.1.1 Conservative Reuse of ISIDsSection 8.1.1 Conservative
           Reuse of ISIDs). Allowing this would be analogous to a single SCSI
           Initiator Port having relationships (nexus) with multiple SCSI target
           ports on the same SCSI target device or SCSI target ports on other
           SCSI target devices. It is also possible to have multiple sessions
           with different ISIDs to the same Target Portal Group. Each such ses-
           sion would be considered to be with a different initiator even when
           the sessions originate from the same initiator device. The same ISID
           may be used by a different iSCSI initiator because it is the iSCSI
           Name together with the ISID that identifies the SCSI Initiator Port.

           NOTE: A consequence of the ISID RULE and the specification for the I_T
           nexus identifier is that two nexus with the same identifier should
           never exist at the same time.

           TSID RULE: The iSCSI Target SHOULD NOT select a TSID for a given login
           request if the resulting SSID is already in use by an existing session
           between the target and the requesting iSCSI Initiator. See Section
           9.1.1 Conservative Reuse of ISIDsSection 8.1.1 Conservative Reuse of
           ISIDs.

   2.4.3.1  I_T Nexus State

           Certain nexus relationships contain an explicit state (e.g., initia-
           tor-specific mode pages or reservation state) that may need to be pre-
           served by the target (or more correctly stated, the device server in a
           logical unit) through changes or failures in the iSCSI layer (e.g.,
           session failures). In order for that state to be restored, the iSCSI
           initiator should re-establish its session (re-login) to the same Tar-
           get Portal Group using the previous ISID. That is, it should perform
           session recovery as described in Chapter 6. This is because the SCSI
           initiator port identifier and the SCSI target port identifier (or rel-



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           ative target port) form the datum that the SCSI logical unit device
           server uses to identify the I_T nexus.

   2.4.3.2  SCSI Mode Pages

           If the SCSI logical unit device server does not maintain initiator-
           specific mode pages, and an initiator makes changes to port-specific
           mode pages, the changes may affect all other initiators logged in to
           that iSCSI Target through the same Target Portal Group.

           Changes via mode pages to the behavior of a portal group via one iSCSI
           node should not affect the behavior of this portal group with respect
           to other iSCSI Target Nodes, even if the underlying implementation of
           a portal group serves multiple iSCSI Target Nodes in the same Network
           Entity.

   2.5  Request/Response Summary

           This section lists and briefly describes all the iSCSI PDU types
           (request and responses).

           All iSCSI PDUs are built as a set of one or more header segments
           (basic and auxiliary) and zero or one data segments. The header group
           and the data segment may be followed by a CRC (digest).

           The basic header segment has a fixed length of 48 bytes.

   2.5.1  Request/Response types carrying SCSI payload

   2.5.1.1  SCSI-Command

           This request carries the SCSI CDB and all the other SCSI execute com-
           mand procedure call output parameters such as task attributes, Com-
           mand Reference Number, Expected Data Transfer Length for one or both
           transfer directions (the later for bidirectional commands), and Task
           Tag. The I_T_L nexus is derived by the initiator and target from the
           LUN field in the request and the I_T nexus implicit in the session
           identification.

           In addition, the SCSI-command PDU carries information required for
           the proper operation of the iSCSI protocol - the command sequence num-
           ber (CmdSN) and the expected status number on the connection it is
           issued (ExpStatSN).



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           Part or all of the SCSI output (write) data associated with the SCSI
           command may be sent as part of the SCSI-Command PDU as a data segment.

   2.5.1.2  SCSI-Response

           The SCSI-Response carries all the SCSI execute command procedure call
           input parameters and the SCSI execute command procedure call return
           value.
           It contains the residual counts from the operation if any, and an
           indication of whether the counts represent an overflow or an under-
           flow, and the SCSI status if the status is valid or a response code (a
           non-zero return value for the execute-command procedure call) if the
           status is not valid.

           For a valid status that indicates that the command is executed but
           resulted in a exception (e.g., a SCSI CHECK CONDITION), the PDU data
           segment contains the associated sense data.

           Some data segment content may also be associated  (in the data seg-
           ment) with a non-zero response code.

           In addition, the SCSI-Response PDU carries information required for
           the proper operation of the iSCSI protocol - the number of Data-In PDU
           that a target has sent (to enable the initiator to check that all
           arrived) - ExpDataSN, the Status Sequence Number on this connection -
           StatSN and the next Expected Command Sequence Number at target - ExpC-
           mdSN, the Maximum CmdSN acceptable at target from this initiator.

   2.5.1.3  Task Management Function Request

           The task management function request provides an initiator with a way
           to explicitly control the execution of one or more SCSI Tasks or iSCSI
           functions. The PDU carries a function identifier (which task manage-
           ment function to perform) and enough information to unequivocally
           identify the task or task-set on which to perform the action even if
           the task(s) to act upon has not yet arrived or has been discarded due
           to an error.

           The referenced tag identifies an individual task if the function
           refers to an individual task.

           The I_T_L nexus identifies task sets and is carried by the LUN (and
           implied by the session identification).


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           For task sets, the CmdSN of the task management function request helps
           identify the tasks upon which to act, namely all tasks associated with
           a LUN and having a CmdSN preceding the task management function
           request CmdSN.

           The task management function request execution is completely per-
           formed at the target, (i.e., any coordination between responses to the
           tasks affected and the task management function request response is
           done by the target).

   2.5.1.4  Task Management Function Response

           The Task Management Function Response carries an indication of func-
           tion completion for a Task Management Function Request including how
           it completed (response and qualifier) and additional information for
           failure responses (Referenced Task Tag - if an abort task failed).

           After the task management response indicating task management func-
           tion completion, the initiator will not receive any additional
           responses from the affected tasks.

   2.5.1.5  SCSI Data-out and SCSI Data-in

           The SCSI Data-out and SCS SCSI Data-in are the main vehicles by which
           SCSI data payload is carried between initiator and target. Data pay-
           load is associated with a specific SCSI command through the Initiator
           Task Tag. For the target, convenience, outgoing solicited data also
           carries a Target Transfer Tag (copied from R2T) and the LUN.
           Each PDU contains the payload length and the data offset relative to
           the buffer address contained in the SCSI exec command procedure call.

           In each direction, the data transfer is split into "sequences". An
           end-of-sequence is indicated by the F bit.

           An outgoing sequence is either unsolicited (only the first sequence
           can be unsolicited) or is a complete payload sent in response to an
           R2T "prompt".

           Input sequences are built to enable the direction switching for bidi-
           rectional commands.

           For input the target may request positive acknowledgement of input
           data. This is limited to sessions that support error recovery and is
           implemented through the A bit in the SCSI Data-in PDU header.

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           Data-in and Data-out PDUs also carry the DataSN to enable the initia-
           tor and target to detect missing PDUs (discarded due to an error).

           StatSN is also carried by the Data-In PDUs.

           To enable a SCSI command to be executed involving a minimum number of
           messages, the last SCSI Data-in PDU passed for a command may also con-
           tain the status if the status indicated termination with no exceptions
           (no sense or response involved).


   2.5.1.6  Ready To Transfer (R2T)

           R2T is the mechanism by which the SCSI target "prompts" the initiator
           for output data. R2T passes the offset of the requested data relative
           of the buffer address from the execute command procedure call and the
           length of the solicited data to the initiator.

           To help the SCSI target to associate resulting Data-out with an R2T,
           the R2T carries the Target Transfer Tag copied by the initiator in the
           solicited SCSI Data-out PDUs. There are no protocol specific require-
           ments with regard to the value of these tags, but it is assumed that
           together with the LUN, they will enable the target to associate data
           with an R2T.

           R2T also carries information required for proper operation of the
           iSCSI protocol, such as an R2TSN (to enable an initiator to detect a
           missing R2T), StatSN, ExpCmdSN and MaxCmdSN.

   2.5.2  Requests/Responses carrying SCSI and iSCSI Payload

   2.5.2.1  Asynchronous Message

           Asynchronous Messages are used to carry SCSI asynchronous events
           (AEN) and iSCSI asynchronous messages.

           When carrying an AEN, the event details are reported as sense data in
           the data segment.





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   2.5.3  Requests/Responses carrying iSCSI Only Payload

   2.5.3.1  Text Request and Text Response

           Text requests and responses are designed as a parameter negotiation
           vehicle and as a vehicle for future extension.

           In the data segment key=value, Text Requests/Responses carry text
           information with a simple syntax.

           Text Request/Responses may form extended sequences using the same
           Initiator Task Tag. The initiator uses the F (Final) flag bit in the
           text request header to indicate its readiness to terminate a sequence.
           The target uses the F (Final) flag bit in the text response header to
           indicate its consent to sequence termination.

           Text Request/Responses also use the Target Transfer Tag to indicate
           continuation of an operation or a new beginning. A target that wishes
           to continue an operation will set the Target Transfer Tag in a Text
           Response to a value different from the default 0xffffffff. An initia-
           tor willing to continue will copy this value into the Target Transfer
           Tag of the next Text Request. If the initiator wants to reset the tar-
           get (start fresh) it will set the Target Transfer Tag to 0xffffffff.

           Although a complete exchange is always started by the initiator, spe-
           cific parameter negotiations may be initiated by the initiator or tar-
           get.

   2.5.3.2  Login Request and Login Response

           Login Requests and Responses are used exclusively during the login
           phase of each connection to set up the session and connection parame-
           ters (the login phase consists of a sequence of login requests and
           responses carrying the same Initiator Task Tag).

           A connection is identified by an arbitrarily selected connection-ID
           (CID) that is unique within a session.

           Similar to the Text Requests and Responses, Login Requests/Responses
           carry  key=value text information with a simple syntax in the data
           segment.

           The Login phase proceeds through several stages (security negotia-
           tion, operational parameter negotiation) that are selected with two

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           binary coded fields in the header - the "current stage" (CSG) and the
           "next stage" (NSG) with the appearance of the later being signaled by
           the "transit" flag (T).

           The first login phase of a session plays a special role (it is called
           the leading login) and some header fields are determined by the lead-
           ing login (e.g., the version number, the maximum number of connec-
           tions, the session identification etc.).

           The command counting initial value is also set by the leading login.

           Status counting for each connection is initiated by the connection
           login.

           Login Requests are always immediate.

           A login request may indicate an implied logout (cleanup) of the con-
           nection to be logged in (we call this a connection restart) through
           the X flag in the first login request header.

   2.5.3.3  Logout Request and Response

           Logout Requests and Responses are used for the orderly closing of con-
           nections for recovery or maintenance. The logout request may be issued
           following a target prompt (through an asynchronous message) or at an
           initiators initiative. When issued on the connection to be logged out
           no other request may follow it.

           The Logout response indicates that the connection or session cleanup
           is completed and no other responses will arrive on the connection (if
           received on the logging-out connection). The Logout Response indi-
           cates also how long the target will keep on holding resources for
           recovery (e.g., command execution that continues on a new connection)
           in Time2Retain and how long the initiator must wait before proceeding
           with recovery in Time2Wait.

   2.5.3.4   SNACK Request

           With the SNACK Request, the initiator requests retransmission of num-
           bered-responses or data from the target. A single SNACK request covers
           a contiguous set of missing items called a run of a given type of
           items (the type is indicate in a type field in the PDU header). The
           run is composed of an initial item (StatSN, DataSN, R2TSN) and the
           number of additional missed Status, Data, or R2T PDUs (0 means only

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           the initial). For long data-in sequences, the target may request (at
           predefined minimum intervals) a positive acknowledgement for the data
           sent. A SNACK request with a type field that indicates ACK and the
           number of Data-In PDUs acknowledged conveys this positive acknowl-
           edgement.

   2.5.3.5  Reject

           Reject enables the target to report an iSCSI error condition (proto-
           col, unsupported option etc.) that uses a Reason field in the PDU
           header and includes the complete header of the bad PDU in the Reject
           PDU data segment.


   2.5.3.6  NOP-Out Request and NOP-In Response

           This request/response pair may be used by an initiator and target as a
           "ping" mechanism to verify that a connection/session is still active
           and all its components are operational. Such a ping may be triggered
           by the initiator or target. The triggering party indicates that it
           wants a reply by setting a value different from the default 0xffffffff
           in the corresponding Initiator/Target Transfer Tag.

           NOP-In/NOP-Out may also be used "unidirectional" to convey to the ini-
           tiator/target command, status or data counter values when there is no
           other "carrier" and there is a need to update the initiator/target.











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   3. SCSI Mode Parameters for iSCSI

           There are no iSCSI specific mode pages.





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   4. Login and Full Feature Phase Negotiation

   4.1  Text Format

           The initiator and target send a set of key=value or key=list pairs
           encoded in UTF-8 Unicode. All the text keys and text values specified
           in this document are to be presented and interpreted in the case they
           appear in this document. They are case sensitive. Text keys and values
           MUST ONLY contain letters (a-z, A-Z), digits (0-9), space (0x20),
           point (.), minus (-), plus (+), commercial at (@) and underscore (_).
           The key and value are separated by a '=' (0x3d) delimiter. Every
           key=value pair (including the last or only pair) MUST be followed by
           one null (0x00) delimiter.  A list is a set of values separated by
           comma (0x2c). Text values may also contain colon (:) and brackets ([
           and ]).

           Character strings are represented as plain text. Binary items can be
           encoded using their decimal representation (with or without leading
           zeros) or hexadecimal representation (e.g., 8190 is 0x1ffe).  Upper
           and lower case letters may be used interchangeably in hexadecimal
           notation (i.e., 0x1aBc, 0x1AbC, 0X1aBc, and 0x1ABC are equivalent).
           Binary items can also be encoded using the more compact Base64 encod-
           ing as specified by [RFC2045] preceded by the 0b.  Key names MUST NOT
           exceed 63 bytes.

           If not otherwise specified, the maximum length of an individual value
           (not its encoded representation) is 255 bytes not including the delim-
           iter (comma or null).

   4.2  Text Mode Negotiation

           During login, and thereafter, some session or connection parameters
           are negotiated through an exchange of textual information.

           The initiator starts the negotiation through a Text/Login request and
           indicates when it is ready for completion (by setting to 1 and keeping
           to 1 the F bit in a Text Request or the T bit in the Login Request).

           The general format of text negotiation is:

                 Originator-> <key>=<valuex>
                 Responder-> <key>=<valuey>|NotUnderstood|Irrelevant|Reject



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           The originator can either be the initiator or the target and the
           responder can either be the target or initiator, respectively. Target
           requests are not limited to respond to key=value pairs as offered by
           the initiator. The target may offer key=value pairs of its own.

           All negotiations are stateless and explicit (i.e., the result MUST be
           based only on newly exchanged values). There is no such thing as
           implicit offers. If an explicit offer is not made then a reply cannot
           be expected.

           The value offered can be an integer, a range defined by lower and
           upper value - both integers separated by a comma, a single literal
           constant a Boolean value (Yes or No), or a list of comma separated,
           literal constant values. A selected value can be an integer, a single
           literal constant or a Boolean value.

           In literal list negotiation, the originator sends a list of options
           (literal constants which may include "None") for each key in its order
           of preference.

           The responding party answers with the first value that it supports and
           is allowed to use for the specific originator selected from the orig-
           inator list.

           The constant "None" MUST always be used to indicate a missing func-
           tion. However, None is a valid selection only if it is explicitly
           offered.

           If a responder does not understand any particular value in a list it
           MUST ignore it. If a responder does not support, does not understand
           or is not allowed to use all of the offered options with a specific
           originator, it MAY use the constant "Reject".  The selection of a
           value not admissible under the selection rules is considered a negoti-
           ation failure and is handled accordingly.


           For numerical, numerical range and single literal negotiations, the
           responding party MUST respond with the required key. The value it
           selects, based on the selection rule specific to the key, becomes the
           negotiation result. For a numerical range the value selected must be
           an integer within the offered range or "Reject" (if the range is unac-
           ceptable).


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           An offer of a value not admissible MAY be answered with the constant
           "Reject". The selection of a value not admissible under the selection
           rules is considered a negotiation failure and is handled accordingly.

           For Boolean negotiations (keys taking the values Yes or No), the
           responding party MUST respond with the required key and the result of
           the negotiation when the received value does not determine that result
           by itself. The last value transmitted becomes the negotiation result.
           The rules for selecting the value with which to respond are expressed
           as Boolean functions of the value received and the value that the
           responding party would select in the absence of knowledge of the
           received value.

           Specifically, the two cases in which responses are OPTIONAL are:

                 - The Boolean function is "AND" and the value "No" is received.
                      The outcome of the negotiation is "No".
                 - The Boolean function is "OR" and the value "Yes" is received.
                      The outcome of the negotiation is "Yes".

           Responses are REQUIRED in all other cases, and the value chosen and
           sent by the responder becomes the outcome of the negotiation.

           An offer of a value not admissible MAY be answered with the constant
           "Reject". The selection of a value not admissible under the selection
           rules is considered a negotiation failure and is handled accordingly.

           If a specific key is not relevant for the current negotiation, the
           responder may answer with the constant "Irrelevant" for all types of
           negotiation.  However the negotiation is not considered as failed if
           the response is Irrelevant.

           Any other key not understood by the responder may be ignored by the
           responder without affecting the basic function. However, the Text
           Response for a key not understood MUST be key=NotUnderstood.

           The constants "None", "Reject", "Irrelevant", and "NotUnderstood" are
           reserved and must only be used as described here.

           Some basic key=value pairs are described in Chapter 11. All keys in
           Chapter 11, except for the X- extension format, MUST be supported by
           iSCSI initiators and targets and MUST NOT be answered with
           NotUnderstood.


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           Manufacturers may introduce new keys by prefixing them with X- fol-
           lowed by their (reversed) domain name. For example the company owning
           the domain acme.com can issue:

                 X-com.acme.bar.foo.do_something=3

   4.3  Login Phase

           The login phase establishes an iSCSI session between an initiator and
           a target. It sets the iSCSI protocol parameters, security parameters,
           and authenticates the initiator and target to each other.

           The login phase is implemented via login request and responses only.
           The whole login phase is considered as a single task and has a single
           Initiator Task Tag (similar to the linked SCSI commands).

           The default MaxRecvPDULength is used during Login.

           The login phase sequence of commands and responses proceeds as fol-
           lows:

                 - Login initial request
                 - Login partial response (optional)
                 - More Login requests and responses (optional)
                 - Login Final-Response (mandatory)

           The initial login request of any connection MUST include the Initia-
           torName key=value pair. The initial login request of the first connec-
           tion of a session MAY also include the SessionType key=value pair. For
           any connection within a session whose type is not "Discovery", the
           first login request MUST also include the key=value pair TargetName.

           The Login Final-response accepts or rejects the Login Command.

           The Login Phase MAY include a SecurityNegotiation stage and a LoginOp-
           erationalNegotiation stage and MUST include at least one of them, but
           the included stage MAY be empty except for the mandatory names.

           The login requests and responses contain a field that indicates the
           negotiation stage (SecurityNegotiation or LoginOperationalNegotia-
           tion). If both stages are used, the SecurityNegotiation MUST precede
           the LoginOperationalNegotiation.



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           Some operational parameters can be negotiated outside login through
           text request/response.

           Security MUST be completely negotiated within the Login Phase (using
           underlying IPsec security is specified in Chapter 7) and in [SEC-
           IPS]).

           In some environments, a target or an initiator is not interested in
           authenticating its counterpart. It is possible to bypass authentica-
           tion through the Login request and response.

           The initiator and target MAY want to negotiate authentication parame-
           ters. Once this negotiation is completed, the channel is considered
           secure.

           Most of the negotiation keys are only allowed in a specific stage. The
           SecurityNegotiation keys appear in Chapter 10 and the LoginOperation-
           alNegotiation keys appear in Chapter 11.
           Only a limited set of keys (marked as Declarative in Chapter 11) may
           be used in any of the two stages.

           Neither the initiator nor the target should attempt to negotiate a
           parameter more than once during any login stage. Attempting to do so
           will result in the termination of the login and connection.

           Any given Login request or response belongs to a specific stage; this
           determines the negotiation keys allowed with the command or response.

           Stage transition is performed through a command exchange (request/
           response) that carries the T bit and the same current stage code. Dur-
           ing this exchange, the next stage is selected by the target and MUST
           NOT exceed the value stated by the initiator. The initiator can
           request a transition whenever it is ready, but a target can respond
           with a transition only after one is offered by the initiator.

           In a negotiation sequence, the T bit settings in one pair of login
           request-responses have no bearing on the T bit settings of the next
           pair. An initiator that has a T bit set to 1 in one pair and is
           answered with a T bit setting of 0 may issue the next request with T
           bit set to 0.

           Targets MUST NOT submit parameters that require an additional initia-
           tor login request in a login response with the T bit set to 1.

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           Stage transitions during login (including entering and exit) are pos-
           sible only as outlined in the following table:

           +-----------------------------------------------------------+
           |From     To ->   | Security    | Operational | FullFeature |
           |  |              |             |             |             |
           |  V              |             |             |             |
           +-----------------------------------------------------------+
           | (start)         |  yes        |  yes        |  no         |
           +-----------------------------------------------------------+
           | Security        |  no         |  yes        |  yes        |
           +-----------------------------------------------------------+
           | Operational     |  no         |  no         |  yes        |
           +-----------------------------------------------------------+

           The Login Final-Response that accepts a Login Command can come only as
           a response to a Login command with the T bit set to 1, and both the
           command and response MUST have FullFeaturePhase in the NSG field.

   4.3.1  Login Phase Start

           The login phase starts with a login request from the initiator to the
           target. The initial login request includes:

                 -Protocol version supported by the initiator.
                 -Session and connection Ids.
                 -The negotiation stage that the initiator is ready to enter.

           Optionally, the login request may include:

                 -Security parameters OR
                 -iSCSI operational parameters AND/OR
                 -The next negotiation stage that the initiator is ready to
                      enter.

           The target can answer the login in the following ways:

                 -Login Response with Login Reject. This is an immediate rejec-
                      tion from the target that causes the connection to terminate
                      and the session to terminate if this is the first (or only)
                      connection of a new session. The T bit and the CSG and NSG
                      fields are reserved.
                 -Login Response with Login Accept as a final response (T bit set
                      to 1 and the NSG in both command and response are set to Full-

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                      FeaturePhase). The response includes the protocol version sup-
                      ported by the target and the session ID, and may include iSCSI
                      operational or security parameters (that depend on the current
                      stage).
                 -Login Response with Login Accept as a partial response (NSG not
                      set to FullFeaturePhase in both request and response) that
                      indicates the start of a negotiation sequence. The response
                      includes the protocol version supported by the target and
                      either security or iSCSI parameters (when no security mecha-
                      nism is chosen) supported by the target.

           If the initiator decides to forego the SecurityNegotiation stage, it
           issues the Login with the CSG set to LoginOperationalNegotiation and
           the target may reply with a Login Response that indicates that it is
           unwilling to accept the connection without SecurityNegotiation and
           will terminate the connection.

           If the initiator is willing to negotiate security, but is unwilling to
           make the initial parameter offer and may accept a connection without
           security, it issues the Login with the T bit set to 1, the CSG set to
           SecurityNegotiation, and NSG set to LoginOperationalNegotiation. If
           the target is also ready to forego security, the Login response is
           empty and has T bit set to 1, the CSG set to SecurityNegotiation, and
           NSG set to LoginOperationalNegotiation.

           An initiator that can operate without security and with all the oper-
           ational parameters taking the default values issues the Login with the
           T bit set to 1, the CSG set to LoginOperationalNegotiation, and NSG
           set to FullFeaturePhase. If the target is also ready to forego secu-
           rity and can finish its LoginOperationalNegotiation, the Login
           response has T bit set to 1, the CSG set to LoginOperationalNegotia-
           tion, and NSG set to FullFeaturePhase in the next stage.

   4.3.2  iSCSI Security Negotiation

           The security exchange sets the security mechanism and authenticates
           the initiator user and the target to each other. The exchange proceeds
           according authentication method chosen in the negotiation phase and
           is conducted using the login requests and responses key=value parame-
           ters.

           An initiator directed negotiation proceeds as follows:

                 -The initiator sends a login request with an ordered list of the
                      options it supports (authentication algorithm). The options

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                      are listed in the initiator's order of preference. The initi-
                      ator MAY also send proprietary options.
                 -The target MUST reply with the first option in the list it sup-
                      ports and is allowed to use for the specific initiator unless
                      it does not support any in which case it MUST answer with
                      "Reject" (see also Section 4.2 Text Mode Negotiation). The
                      parameters are encoded in UTF8 as key=value. For security
                      parameters, see Chapter 10.

                 -The initiator must be aware of the imminent completion of the
                      SecurityNegotiation stage and MUST set the T bit to 1 and the
                      NSG to what it would like the next stage to be. The target
                      will answer with a Login response with the T bit set to 1 and
                      the NSG to what it would like the next stage to be. The next
                      stage selected will be the one the target selected. If the
                      next stage is FullFeaturePhase, the target MUST respond with a
                      Login Response with the Session ID and the protocol version.


           If the security negotiation fails at the target, then the target MUST
           send the appropriate Login Response PDU. If the security negotiation
           fails at the initiator, the initiator SHOULD close the connection.

           It should be noted that the negotiation might also be directed by the
           target if the initiator does support security, but is not ready to
           direct the negotiation (offer options).


   4.3.3  Operational Parameter Negotiation During the Login Phase

           Operational parameter negotiation during the login MAY be done:

                 - Starting with the first Login request if the initiator does
                      not offer any security/ integrity option.
                 - Starting immediately after the security negotiation if the
                      initiator and target perform such a negotiation.

           Operational parameter negotiation MAY involve several Login request-
           response exchanges started and terminated by the initiator. The ini-
           tiator MUST indicate its intent to terminate the negotiation by set-
           ting the T bit to 1; the target sets the T bit to 1 on the last
           response.

           If the target responds to a Login request with the T bit set to 1 with
           a Login response with the T bit set to 0, the initiator should keep
           sending the Login request (even empty) with the T bit set to 1, while


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           it still wants to switch stage, until it receives the Login Response
           with the T bit set to 1.

           Whenever parameter action or acceptance are dependent on other param-
           eters, the dependent parameters MUST be sent after the parameters on
           which they depend. If they are sent within the same command, a
           response for a parameter might imply responses for others.

           Some session specific parameters can be specified only during the
           login phase begun by a login command that contains a null TSID - the
           leading login phase (e.g., the maximum number of connections that can
           be used for this session).

           A session is operational once it has at least one connection in Full-
           FeaturePhase. New or replacement connections can be added to a session
           only after the session is operational.

           For operational parameters, see Chapter 11.

   4.3.4  Connection reinstatement

           Connection reinstatement is the process of initiator logging in with a
           ISID-TSID-CID combination that is possibly active from the target‚ÇÖs
           perspective - thus implicitly logging out the connection state
           machine corresponding to the CID and reinstating a new full-feature
           phase iSCSI connection in its place (with the same CID).  Thus, the
           TSID in the Login PDU MUST be non-zero and CID does not change during
           a connection reinstatement.  The Login command  performs the logout
           function of the old connection if an explicit logout was not performed
           earlier. In sessions with a single connection, this may imply the
           opening of a second connection with the sole purpose of cleaning up
           the first. Targets should support opening a second connection even
           when they do not support multiple connections in full feature phase.

           If the operational ErrorRecoveryLevel is 2, connection reinstatement
           enables future task reassignment.  If the operational ErrorRecovery-
           Level is less than 2, connection reinstatement is the replacement of
           the old CID without enabling task reassignment.  In this case, all the
           tasks that were active on the old CID are internally terminated.

           The initiator connection state MUST be CLEANUP_WAIT (section 5.1) for
           attempting a connection reinstatement.



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   4.3.5  Session reinstatement

           Session reinstatement is the process of initiator logging in with an
           ISID that is possibly active from the target‚ÇÖs perspective - thus
           implicitly logging out the session state machine corresponding to the
           ISID and reinstating a new iSCSI session in its place (with the same
           ISID).  Thus, the TSID in the Login PDU MUST be zero to signal session
           reinstatement.  All the tasks that were active on the old session are
           internally terminated on a session reinstatement.

           The initiator session state MUST be FAILED (Section 5.3 Session State
           Diagrams) for attempting a session reinstatement.

   4.3.6  Session Continuation, closure and failure

           Session continuation is the process by which the state of a pre-exist-
           ing session is continued to be in use by either connection reinstate-
           ment (Section 4.3.4 Connection reinstatement), or by adding a
           connection with a new CID. Either of these actions associates the new
           transport connection with the pre-existing session state.

           Session closure is an event defined to be either of the following -
                 - a successful "session close" logout
                 - a successful "connection close" logout for the last full-fea-
                      ture phase connection when no associated connection states are
                      waiting for cleanup (Section 5.2 Connection Cleanup State Dia-
                      gram for Initiators and Targets) and no associated task states
                      are waiting for reassignment.

           Session failure is an event where the last full-feature phase connec-
           tion reaches the CLEANUP_WAIT (Section 5.2 Connection Cleanup State
           Diagram for Initiators and Targets) state, or completes a successful
           recovery logout thus causing all active tasks (that are formerly alle-
           giant to the connection) to start waiting for task reassignment.

   4.4  Operational Parameter Negotiation Outside the Login Phase

           Some operational parameters MAY be negotiated outside (after) the
           login phase.

           Parameter negotiation in full feature phase is done through Text
           requests and responses. Operational parameter negotiation MAY involve
           several text request-response exchanges, which the indicator always
           starts and terminates and uses the same Initiator Task Tag. The initi-


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           ator MUST indicate its intent to terminate the negotiation by setting
           the F bit to 1; the target sets the F bit to 1 on the last response.

           If to a text request with the F bit set to 1 the target responds with
           a text response with the F bit set to 0, the initiator should keep
           sending the text request (even empty) with the F bit set to 1, while
           it still wants to finish the negotiation, until it receives the text
           response with the F bit set to 1. Responding to a text request with
           the F bit set to 1 with an empty (no key=value pairs) response with
           the F bit set to 0 is not an error but is discouraged.

           Targets MUST NOT submit parameters that require an additional initia-
           tor text request in a text response with the F bit set to 1.

           In a negotiation sequence, the F bit settings in one pair of text
           request-responses have no bearing on the F bit settings of the next
           pair. An initiator that has the F bit set to 1 in a request and being
           answered with an F bit setting of 0 may have the next request issued
           with the F bit set to 0.

           Whenever parameter action or acceptance is dependent on other parame-
           ters, the dependent parameters MUST be sent after the parameters on
           which they depend; if sent within the same command, a response for a
           parameter might imply responses for others.

           Whenever the target responds with the F bit set to 0, it MUST set the
           Target Transfer Tag to a value other than the default 0xffffffff.

           An initiator MAY reset an operational parameter negotiation by issu-
           ing a Text request with the Target Transfer Tag set to the value
           0xffffffff after receiving a response with the Target Transfer Tag set
           to a value other than 0xffffffff. A target may reset an operational
           parameter negotiation by answering a Text request with a Reject.

           Neither the initiator nor the target should attempt to negotiate a
           parameter more than once during any negotiation sequence without an
           intervening reset. If detected by the target this MUST result in a
           Reject with a reason of "protocol error". The initiator MUST reset the
           negotiation as outlined above.





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   5. State Transitions

           iSCSI connections and iSCSI sessions go through several well-defined
           states from the time they are created to the time they are cleared.

           An iSCSI connection is a transport connection used for carrying out
           iSCSI activity.  The connection state transitions are described in two
           separate, but dependent state diagrams for ease in understanding.  The
           first diagram, "standard connection state diagram", describes the
           connection state transitions when the iSCSI connection is not waiting
           for or undergoing a cleanup by way of an explicit or implicit Logout.
           The second diagram, "connection cleanup state diagram", describes the
           connection state transitions while performing the iSCSI connection
           cleanup.

           The "session state diagram" describes the state transitions an iSCSI
           session would go through during its lifetime, and it depends on the
           states of possibly multiple iSCSI connections that participate in the
           session.

   5.1  Standard Connection State Diagrams

   5.1.1  Standard Connection State Diagram for an Initiator

           Symbolic names for States:

                  S1: FREE
                  S2: XPT_WAIT
                  S4: IN_LOGIN
                  S5: LOGGED_IN (full-feature phase)
                  S6: IN_LOGOUT
                  S7: LOGOUT_REQUESTED
                  S8: CLEANUP_WAIT

           The state diagram is as follows:





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                               -------<-------------+
                   +--------->/ S1    \<----+       |
                T13|       +->\       /<-+   \      |
                   |      /    ---+---    \   \     |
                   |     /        |     T2 \   |    |
                   |  T8 |        |T1       |  |    |
                   |     |        |        /   |T7  |
                   |     |        |       /    |    |
                   |     |        |      /     |    |
                   |     |        V     /     /     |
                   |     |     ------- /     /      |
                   |     |    / S2    \     /       |
                   |     |    \       /    /        |
                   |     |     ---+---    /         |
                   |     |        |T4    /          |
                   |     |        V     /           | T18
                   |     |     ------- /            |
                   |     |    / S4    \             |
                   |     |    \       /             |
                   |     |     ---+---              |         T15
                   |     |        |T5      +--------+---------+
                   |     |        |       /T16+-----+------+  |
                   |     |        |      /   -+-----+--+   |  |
                   |     |        |     /   /  S7   \  |T12|  |
                   |     |        |    / +->\       /<-+   V  V
                   |     |        |   / /    -+-----       -------
                   |     |        |  / /T11   |T10        /  S8   \
                   |     |        V / /       V  +----+   \       /
                   |     |      ---+-+-      ----+--  |    -------
                   |     |     / S5    \T9  / S6    \<+    ^
                   |     +-----\       /--->\       / T14  |
                   |            -------      --+----+------+T17
                   +---------------------------+

           The following state transition table represents the above diagram.
           Each row represents the starting state for a given transition, which
           after taking a transition marked in a table cell would end in the
           state represented by the column of the cell. For example, from state
           S1, the connection takes the T1 transition to arrive at state S2. The
           fields marked "-" correspond to undefined transitions.



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              +-----+---+---+---+---+----+---+
              |S1   |S2 |S4 |S5 |S6 |S7  |S8 |
           ---+-----+---+---+---+---+----+---+
            S1| -   |T1 | - | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S2|T2   |-  |T4 | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S4|T7   |-  |-  |T5 | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S5|T8   |-  |-  | - |T9 |T11 |T15|
           ---+-----+---+---+---+---+----+---+
            S6|T13  |-  |-  | - |T14|-   |T17|
           ---+-----+---+---+---+---+----+---+
            S7|T18  |-  |-  | - |T10|T12 |T16|
           ---+-----+---+---+---+---+----+---+
            S8| -   |-  |-  | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+

   5.1.2  Standard Connection State Diagram for a Target

           Symbolic names for States:
                  S1: FREE
                  S3: XPT_UP
                  S4: IN_LOGIN
                  S5: LOGGED_IN (full-feature phase)
                  S6: IN_LOGOUT
                  S7: LOGOUT_REQUESTED
                  S8: CLEANUP_WAIT

           The state diagram is as follows:





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                               -------<-------------+
                   +--------->/ S1    \<----+       |
                T13|       +->\       /<-+   \      |
                   |      /    ---+---    \   \     |
                   |     /        |     T6 \   |    |
                   |  T8 |        |T3       |  |    |
                   |     |        |        /   |T7  |
                   |     |        |       /    |    |
                   |     |        |      /     |    |
                   |     |        V     /     /     |
                   |     |     ------- /     /      |
                   |     |    / S3    \     /       |
                   |     |    \       /    /        | T18
                   |     |     ---+---    /         |
                   |     |        |T4    /          |
                   |     |        V     /           |
                   |     |     ------- /            |
                   |     |    / S4    \             |
                   |     |    \       /             |
                   |     |     ---+---         T15  |
                   |     |        |T5      +--------+---------+
                   |     |        |       /T16+-----+------+  |
                   |     |        |      /  -+-----+---+   |  |
                   |     |        |     /   /  S7   \  |T12|  |
                   |     |        |    / +->\       /<-+   V  V
                   |     |        |   / /    -+-----       -------
                   |     |        |  / /T11   |T10        /  S8   \
                   |     |        V / /       V           \       /
                   |     |      ---+-+-      -------       -------
                   |     |     / S5    \T9  / S6    \        ^
                   |     +-----\       /--->\       /        |
                   |            -------      --+----+--------+T17
                   +---------------------------+


           The following state transition table represents the above diagram,
           and follows the conventions described for the initiator diagram.





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              +-----+---+---+---+---+----+---+
              |S1   |S3 |S4 |S5 |S6 |S7  |S8 |
           ---+-----+---+---+---+---+----+---+
            S1| -   |T3 | - | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S3|T6   |-  |T4 | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S4|T7   |-  |-  |T5 | - | -  | - |
           ---+-----+---+---+---+---+----+---+
            S5|T8   |-  |-  | - |T9 |T11 |T15|
           ---+-----+---+---+---+---+----+---+
            S6|T13  |-  |-  | - |-  |-   |T17|
           ---+-----+---+---+---+---+----+---+
            S7|T18  |-  |-  | - |T10|T12 |T16|
           ---+-----+---+---+---+---+----+---+
            S8| -   |-  |-  | - | - | -  | - |
           ---+-----+---+---+---+---+----+---+

   5.1.3  State Descriptions for Initiators and Targets

           State descriptions for the standard connection state diagram are as
           follows:
           -S1: FREE
                           -initiator: State on instantiation, or after successful con-
                                nection closure.
                           -target: State on instantiation, or after successful connec-
                                tion closure.
           -S2: XPT_WAIT
                           -initiator: Waiting for a response to its transport connection
                                establishment request.
                           -target: Illegal
           -S3: XPT_UP
                           -initiator: Illegal
                           -target: Waiting for the Login process to commence.
           -S4: IN_LOGIN
                           -initiator: Waiting for the Login process to conclude, possi-
                                bly involving several PDU exchanges.
                           -target: Waiting for the Login process to conclude, possibly
                                involving several PDU exchanges.
           -S5: LOGGED_IN
                           -initiator: In full-feature phase, waiting for all internal,
                                iSCSI, and transport events.



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                           -target: In full-feature phase, waiting for all internal,
                                iSCSI, and transport events.
           -S6: IN_LOGOUT
                           -initiator: Waiting for a Logout response.
                           -target: Waiting for an internal event signaling completion of
                                logout processing.
           -S7: LOGOUT_REQUESTED
                           -initiator: Waiting for an internal event signaling readiness
                                to proceed with Logout.
                           -target: Waiting for the Logout process to start after having
                                requested a Logout via an Async Message.
           -S8: CLEANUP_WAIT
                           -initiator: Waiting for the context and/or resources to ini-
                                tiate the cleanup processing for this CSM.
                           -target: Waiting for the cleanup process to start for this
                                CSM.
   5.1.4  State Transition Descriptions for Initiators and Targets

           -T1:
                           -initiator: Transport connect request was made (ex: TCP SYN
                                sent).
                           -target: Illegal
           -T2:
                           -initiator: Transport connection request timed out, or a
                                transport reset was received, or an internal event of receiv-
                                ing a Logout response (success) on another connection for a
                                "close the session"  Logout command was received.
                           -target:Illegal
           -T3:
                           -initiator: Illegal
                           -target: Received a valid transport connection request that
                                establishes the transport connection.
           -T4:
                           -initiator: Transport connection established, thus prompting
                                the initiator to start the iSCSI Login.
                           -target: Initial iSCSI Login command was received.
           -T5:
                           -initiator: The final iSCSI Login response with a Status-Class
                                of zero was received.
                           -target: The final iSCSI Login command to conclude the Login
                                phase was received, thus prompting the target to send the
                                final iSCSI Login response with a Status-Class of zero.
           -T6:


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                           -initiator: Illegal
                           -target: Timed out waiting for an iSCSI Login, or transport
                                disconnect indication was received, or transport reset was
                                received, or an internal event indicating a transport time-
                                out was received. In all these cases, the connection is to be
                                closed.
           -T7:
                           -initiator: The final iSCSI Login response was received with a
                                non-zero Status-Class, or Login timed out, or transport dis-
                                connect indication was received, or transport reset was
                                received, or an internal event indicating a transport time-
                                out was received, or an internal event of receiving a Logout
                                response (success) on another connection for a  "close the
                                session"  Logout command was received. In all these cases,
                                the transport connection is closed.
                           -target: The final iSCSI Login command to conclude the Login
                                phase was received, prompting the target to send the final
                                iSCSI Login response with a non-zero Status-Class, or Login
                                timed out, or transport disconnect indication was received,
                                or transport reset was received, or an internal event indi-
                                cating a transport timeout was received, or an internal event
                                of sending a Logout response (success) on another connection
                                for a  "close the session"  Logout command was received. In
                                all these cases, the connection is to be closed.
           -T8:
                           -initiator: An internal event of receiving a Logout response
                                (success) on a another connection for a  "close the session"
                                Logout command was received, thus closing this connection
                                requiring no further cleanup.
                           -target: An internal event of sending a Logout response (suc-
                                cess) on another connection for a "close the session" Logout
                                command was received, or an internal event of a successful
                                connection/session reinstatement is received, thus prompting
                                the target to close this connection cleanly.
           -T9, T10:
                           -initiator: An internal event that indicates the readiness to
                                start the Logout process was received, thus prompting an
                                iSCSI Logout to be sent by the initiator.
                           -target: An iSCSI Logout command was received.
           -T11, T12:
                           -initiator: Async PDU with AsyncEvent "Request Logout" was
                                received.


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                           -target: An internal event that requires the decommissioning
                                of the connection is received, thus causing an Async PDU with
                                an AsyncEvent "Request Logout" to be sent.
           -T13:
                           -initiator: An iSCSI Logout response (success) was received,
                                or an internal event of receiving a Logout response (success)
                                on another connection for a  "close the session"  Logout com-
                                mand was received.
                           -target: An internal event was received that indicates suc-
                                cessful processing of the Logout, which prompts an iSCSI
                                Logout response (success) to be sent, or an internal event of
                                sending a Logout response (success) on another connection
                                for a "close the session" Logout command was received, or an
                                internal event of a successful connection/session reinstate-
                                ment is received. In all these cases, the transport connec-
                                tion is closed.

           -T14:
                           -initiator: Async PDU with AsyncEvent "Request Logout" was
                                received again.
                           -target: Illegal
           -T15, T16:
                           -initiator: One or more of the following events caused this
                                transition:
                               -Internal event that indicates a transport connection tim-
                                eout was received thus prompting transport RESET or trans-
                                port connection closure.
                               -A transport RESET.
                               -A transport disconnect indication.
                               -Async PDU with AsyncEvent "Drop connection" (for this
                                CID).
                               -Async PDU with AsyncEvent "Drop all connections".
                           -target: One or more of the following events caused this tran-
                                sition:
                               -Internal event that indicates a transport connection tim-
                                eout was received, thus prompting transport RESET or trans-
                                port connection closure.
                               -An internal event of a failed connection/session rein-
                                statement is received.
                               -A transport RESET.
                               -A transport disconnect indication.



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                               -Internal emergency cleanup event was received which
                                prompts an Async PDU with AsyncEvent "Drop connection" (for
                                this CID), or event "Drop all connections".

           -T17:
                           -initiator: One or more of the following events caused this
                                transition:
                               -Logout response (failure, i.e. a non-zero status) was
                                received, or Logout timed out.
                               -Any of the events specified for T15 and T16.
                           -target:  One or more of the following events caused this
                                transition:
                               -Internal event that indicates a failure of the Logout
                                processing was received, which prompts a Logout response
                                (failure, i.e. a non-zero status) to be sent.
                               -Any of the events specified for T15 and T16.
           -T18:
                           -initiator: An internal event of receiving a Logout response
                                (success) on another connection for a "close the session"
                                Logout command was received.

                           -target: An internal event of sending a Logout response (suc-
                                cess) on another connection for a "close the session"  Logout
                                command was received, or an internal event of a successful
                                connection/session reinstatement is received.  In both these
                                cases, the connection is closed.



           The CLEANUP_WAIT state (S8) implies that there are possible iSCSI
           tasks that have not reached conclusion and are still considered busy.

   5.2  Connection Cleanup State Diagram for Initiators and Targets

           Symbolic names for states:

                 R1: CLEANUP_WAIT (same as S8)
                 R2: IN_CLEANUP
                 R3: FREE (same as S1)

           Whenever a connection state machine (e.g., CSM-C) enters the
           CLEANUP_WAIT state (S8), it must go through the state transitions
           additionally described in the connection cleanup state diagram either
           a) using a separate full-feature phase connection (let‚ÇÖs call it CSM-

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           E) in the LOGGED_IN state in the same session, or b) using a new
           transport connection (let‚ÇÖs call it CSM-I) in the FREE state that is
           to be added to the same session. In the CSM-E case, an explicit logout
           for the CID that corresponds to CSM-C (either as a connection or ses-
           sion logout) needs to be performed to complete the cleanup. In the
           CSM-I case, an implicit logout for the CID that corresponds to CSM-C
           needs to be performed by way of connection reinstatement (section
           4.3.4) for that CID. In either case, the protocol exchanges on CSM-E
           or CSM-I to determine the state transitions for CSM-C. Therefore, this
           cleanup state diagram is applicable only to the instance of the con-
           nection in cleanup (i.e., CSM-C). In the case of an implicit logout
           for example, CSM-C reaches FREE (R3) at the time CSM-I reaches
           LOGGED_IN. In the case of an explicit logout, CSM-C reaches FREE (R3)
           when CSM-E receives a successful logout response while continuing to
           be in the LOGGED_IN state.


           The following state diagram applies to both initiators and targets.





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                               -------
                              / R1    \
                           +--\       /<-+
                          /    ---+---    \
                         /        |        \ M3
                      M1 |        |M2       |
                         |        |        /
                         |        |       /
                         |        |      /
                         |        V     /
                         |     ------- /
                         |    / R2    \
                         |    \       /
                         |     -------
                         |        |
                         |        |M4
                         |        |
                         |        |
                         |        |
                         |        V
                         |      -------
                         |     / R3    \
                         +---->\       /
                                -------

           The following state transition table represents the above diagram,
           and follows the same conventions as in earlier sections.

                +----+----+----+
                |R1  |R2  |R3  |
           -----+----+----+----+
            R1  | -  |M2  |M1  |
           -----+----+----+----+
            R2  |M3  | -  |M4  |
           -----+----+----+----+
            R3  | -  | -  | -  |
           -----+----+----+----+

   5.2.1  State Descriptions for Initiators and Targets

           -R1: CLEANUP_WAIT (Same as S8)
                           -initiator: Waiting for the internal event to initiate the
                                cleanup processing for CSM-C.


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                           -target: Waiting for the cleanup process to start for CSM-C.
           -R2: IN_CLEANUP
                           -initiator: Waiting for the connection cleanup process to con-
                                clude for CSM-C.
                           -target: Waiting for the connection cleanup process to con-
                                clude for CSM-C.
           -R3: FREE (Same as S1)
                           -initiator: End state for CSM-C.
                           -target: End state for CSM-C.

   5.2.2  State Transition Descriptions for Initiators and Targets

           -M1:  One or more of the following events was received:
                           -initiator:
                               -An internal event that indicates connection state time-
                                out.
                               -An internal event of receiving a successful Logout
                                response on a different connection for a "close the session"
                                Logout.
                           -target:
                               -An internal event that indicates connection state time-
                                out.
                               -An internal event of sending a Logout response (success)
                                on a different connection for a "close the session" Logout
                                command.

           -M2:  An implicit/explicit logout process was initiated by the initi-
           ator.
                           -In CSM-I usage:
                               -initiator: An internal event requesting the connection
                                (or session) reinstatement was received, thus prompting a
                                connection (or session) reinstatement Login to be sent tran-
                                sitioning CSM-I to state IN_LOGIN.
                               -target: A connection/session reinstatement Login was
                                received while in state XPT_UP.
                           -In CSM-E usage:
                               -initiator: An internal event that indicates that an
                                explicit logout was sent for this CID in state LOGGED_IN.
                               -target: An explicit logout was received for this CID in
                                state LOGGED_IN.
           -M3: Logout failure detected
                           -In CSM-I usage:



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                               -initiator: CSM-I failed to reach LOGGED_IN and arrived
                                into FREE instead.
                               -target: CSM-I failed to reach LOGGED_IN and arrived into
                                FREE instead.
                           -In CSM-E usage:
                               -initiator: CSM-E either moved out of LOGGED_IN, or Logout
                                timed out and/or aborted, or Logout response (failure) was
                                received.
                               -target: CSM-E either moved out of LOGGED_IN, or Logout
                                timed out and/or aborted, or an internal event that indicates
                                a failed Logout processing was received.  A Logout response
                                (failure) was sent in the last case.


           -M4: Successful implicit/explicit logout was performed.
                           - In CSM-I usage:
                               -initiator: CSM-I reached state LOGGED_IN, or an internal
                                event of receiving a Logout response (success) on another
                                connection for a "close the session" Logout command was
                                received.
                               -target: CSM-I reached state LOGGED_IN, or an internal
                                event of sending a Logout response (success) on a different
                                connection for a "close the session" Logout command was
                                received.
                           - In CSM-E usage:
                               -initiator: CSM-E stayed in LOGGED_IN and received a
                                Logout response (success), or an internal event of receiving
                                a Logout response (success) on another connection for a
                                "close the session" Logout command was received.
                               -target: CSM-E stayed in LOGGED_IN and an internal event
                                indicating a successful Logout processing was received, or
                                an internal event of sending a Logout response (success) on a
                                different connection for a "close the session" Logout com-
                                mand was received.

   5.3  Session State Diagrams

           Session State Diagram for an Initiator

           Symbolic Names for States:

                 Q1: FREE
                 Q3: LOGGED_IN
                 Q4: FAILED

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           The state diagram is as follows:

                                    -------
                                   / Q1    \
                           +------>\       /<-+
                          /         ---+---   |
                         /             |      |N3
                     N6 |              |N1    |
                        |              |      |
                        |    N4        |      |
                        |  +--------+  |     /
                        |  |        |  |    /
                        |  |        |  |   /
                        |  |        V  V  /
                       -+--+--      -----+-
                      / Q4    \ N5 / Q3    \
                      \       /<---\       /
                       -------      -------

           State transition table:

                +----+----+----+
                |Q1  |Q3  |Q4  |
           -----+----+----+----+
            Q1  | -  |N1  | -  |
           -----+----+----+----+
            Q3  |N3  | -  |N5  |
           -----+----+----+----+
            Q4  |N6  |N4  | -  |
           -----+----+----+----+

   5.3.1  Session State Diagram for a Target

           Symbolic Names for States:

                 Q1: FREE
                 Q2: ACTIVE
                 Q3: LOGGED_IN
                 Q4: FAILED
                 Q5: IN_CONTINUE

           The state diagram is as follows:


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                                              -------
                         +------------------>/ Q1    \
                        /    +-------------->\       /<-+
                        |    |                ---+---   |
                        |    |                ^  |      |N3
                     N6 |    |N11           N9|  V N1   |
                        |    |                +------   |
                        |    |               / Q2    \  |
                        |    |               \       /  |
                        |  --+----            +--+---   |
                        | / Q5    \              |      |
                        | \       / N10          |      |
                        |  +-+---+------------+  |N2   /
                        |  ^ |                |  |    /
                        |N7| |N8              |  |   /
                        |  | |                |  V  /
                       -+--+-V                V----+-
                      / Q4    \ N5           / Q3    \
                      \       /<-------------\       /
                       -------                -------

           State transition table:

                +----+----+----+----+----+
                |Q1  |Q2  |Q3  |Q4  |Q5  |
           -----+----+----+----+----+----+
            Q1  | -  |N1  | -  | -  | -  |
           -----+----+----+----+----+----+
            Q2  |N9  | -  |N2  | -  | -  |
           -----+----+----+----+----+----+
            Q3  |N3  | -  | -  |N5  | -  |
           -----+----+----+----+----+----+
            Q4  |N6  | -  | -  | -  |N7  |
           -----+----+----+----+----+----+
            Q5  |N11 | -  |N10 |N8  | -  |
           -----+----+----+----+----+----+


   5.3.2  State Descriptions for Initiators and Targets

           -Q1: FREE
                           -initiator: State on instantiation or after cleanup.
                           -target: State on instantiation or after cleanup.


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           -Q2: ACTIVE
                           -initiator: Illegal
                           -target: The first iSCSI connection in the session transi-
                                tioned to IN_LOGIN, waiting for it to complete the login pro-
                                cess.
           -Q3: LOGGED_IN
                           -initiator: Waiting for all session events.
                           -target: Waiting for all session events.
           -Q4: FAILED
                           -initiator: Waiting for session recovery or session continua-
                                tion.
                           -target: Waiting for session recovery or session continua-
                                tion.
           -Q5: IN_CONTINUE
                           -initiator: Illegal
                           -target: Waiting for session continuation attempt to reach a
                                conclusion.


   5.3.3  State Transition Descriptions for Initiators and Targets

           -N1:
                           -initiator: At least one transport connection reached the
                                LOGGED_IN state.
                           -target: The first iSCSI connection in the session had reached
                                the IN_LOGIN state.
           -N2:
                           -initiator: Illegal
                           -target: At least one transport connection reached the
                                LOGGED_IN state.
           -N3:
                           -initiator: Graceful closing of the session via session clo-
                                sure (Section 4.3.6 Session Continuation, closure and fail-
                                ure).
                           -target: Graceful closing of the session via session closure
                                (Section 4.3.6 Session Continuation, closure and failure).
                                Or a successful session reinstatement cleanly closed the
                                session.
           -N4:
                           -initiator: A session continuation attempt succeeded.
                           -target: Illegal
           -N5:



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                           -initiator: Session failure (Section 4.3.6 Session Continua-
                                tion, closure and failure) occurred.
                           -target: Session failure (Section 4.3.6 Session Continuation,
                                closure and failure) occurred.
           -N6:
                           -initiator: Session state timeout occurred, or a session rein-
                                statement cleared this session instance.  This results in the
                                freeing of all associated resources and the session state is
                                discarded.
                           -target: Session state timeout occurred, or a session rein-
                                statement cleared this session instance.  This results in the
                                freeing of all associated resources and the session state is
                                discarded.
           -N7:
                           -initiator: Illegal
                           -target: A session continuation attempt is initiated.
           -N8:
                           -initiator: Illegal
                           -target: The last session continuation attempt failed.
           -N9:
                           -initiator: Illegal
                           -target: Login attempt on the leading connection failed.
           -N10:
                           -initiator: Illegal
                           -target: A session continuation attempt succeeded.
           -N11:
                           -initiator: Illegal
                           -target: A successful session reinstatement cleanly closed
                                the session.







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   6. iSCSI Error Handling and Recovery

           For any outstanding SCSI command, it is assumed that iSCSI, in con-
           junction with SCSI at the initiator, is able to keep enough informa-
           tion to be able to rebuild the command PDU, and that outgoing data is
           available (in host memory) for retransmission while the command is
           outstanding.  It is also assumed that at target, incoming data (read
           data) MAY be kept for recovery or it can be re-read from a device
           server.

           It is further assumed that a target will keep the "status & sense" for
           a command it has executed if it supports status retransmission.

           Many of the recovery details in an iSCSI implementation are a local
           matter, beyond the scope of protocol standardization. However, some
           external aspects of the processing must be standardized to ensure
           interoperability. This section describes a general model for recovery
           in support of interoperability. See Appendix E. - Algorithmic Presen-
           tation of Error Recovery Classes - for further detail. Compliant
           implementations do not have to match the implementation details of
           this model as presented, but the external behavior of such implementa-
           tions must correspond to the externally observable characteristics of
           the presented model.

   6.1  Retry and Reassign in Recovery

           This section summarizes two important and somewhat related iSCSI pro-
           tocol features used in error recovery.

   6.1.1  Usage of Retry

           By resending the same iSCSI command PDU ("retry") in the absence of a
           command acknowledgement or response, an initiator attempts to "plug"
           (what it thinks are) the discontinuities in CmdSN ordering on the tar-
           get end.  Discarded command PDUs, due to digest errors, may have cre-
           ated these discontinuities.

           Retry MUST NOT be used for reasons other than plugging command
           sequence gaps.  In particular, all PDU retransmission (for data, or
           status) requests for a currently allegiant command in progress must be
           conveyed to the target using only the SNACK mechanism already
           described.  This, however, does not constitute a requirement on initi-
           ators to use SNACK.


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           If initiators, as part of plugging command sequence gaps as described
           above, inadvertently issue retries for allegiant commands already in
           progress (i.e., targets did not see the discontinuities in CmdSN
           ordering), targets MUST silently discard the duplicate requests if
           the CmdSN window had not advanced by then.  Targets MUST support the
           retry functionality described above.

           When an iSCSI command is retried, the command PDU MUST carry the orig-
           inal Initiator Task Tag and the original operational attributes
           (e.g., flags, function names, LUN, CDB etc.) as well as the original
           CmdSN. The command being retried MUST be sent on the same connection
           as the original command unless the original connection was already
           successfully logged out.

   6.1.2  Allegiance Reassignment

           By issuing a "task reassign" task management command (Section 9.5.1
           Function), the initiator signals its intent to continue an already
           active command (but with no current connection allegiance) as part of
           connection recovery. This means that a new connection allegiance is
           established for the command, that associates it to the connection on
           which the task management command is being issued.

           In reassigning connection allegiance for a command, the targets
           SHOULD continue the command from its current state, for example taking
           advantage of ExpDataSN in the iSCSI command PDU for read commands
           (which must be set to zero if there was no data transfer) and bring it
           to completion by sending (or resending) the status.  However, targets
           MAY choose to send/receive the entire data on a reassignment of con-
           nection allegiance, and it is not considered an error.  For all types
           of commands, a reassignment request implies that the task is still
           considered in progress by the initiator and the target must conclude
           the task appropriately.  This might possibly involve retransmission
           of data/R2T/status PDUs as necessary.


           It is optional for targets to support the allegiance reassignment.
           This capability is negotiated via the ErrorRecoveryLevel text key at
           the login time.  When a target does not support allegiance reassign-
           ment, it MUST respond with a task management response code of "Task
           failover not supported".  If allegiance reassignment is supported by
           the target, but the task is still allegiant to a different connection,


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           the target MUST respond with a task management response code of "Task
           still allegiant".

   6.2  Usage Of Reject PDU in Recovery

           Targets MUST NOT implicitly terminate an active task by sending a
           Reject PDU for any PDU exchanged during the life of the task.  If the
           target decides to terminate the task, a Response PDU (SCSI, Text, Task
           etc.) must be returned by the target to conclude the task.  If the
           task had never been active before the Reject (i.e., the Reject is on
           the command PDU), targets should not send any further responses since
           the command itself is being discarded.

           The above rule means that the initiators can eventually expect a
           response even on Rejects, if the Reject is not for the command itself.
           The non-command Rejects only have diagnostic value in logging the
           errors, and they can be used for retransmission decisions by the ini-
           tiators.

           The CmdSN of the rejected PDU (if it carried one) MUST NOT be consid-
           ered received by the target (i.e., a command sequence gap must be
           assumed for the CmdSN).  This is true even when the CmdSN can be reli-
           ably ascertained, as in the case of a data digest error on immediate
           data.  However, when the DataSN of a rejected data PDU can be ascer-
           tained, a target MUST advance ExpDataSN for the current burst if a
           recovery R2T is being generated.  The target MAY advance its ExpDataSN
           if it does not attempt to recover the lost data PDU.

   6.3  Connection timeout management

           iSCSI defines two session-global timeout values (in seconds) -
           Time2Wait and Time2Retain - that are applicable when an iSCSI full-
           feature phase connection is taken out of service either intentionally
           or on an exception. Time2Wait is the initial "respite time" before
           attempting an explicit/implicit Logout for the CID in question or task
           reassignment for the affected tasks (if any). Time2Retain is the max-
           imum time after the initial respite interval that the task and/or con-
           nection state(s) is/are guaranteed to be maintained on the target to
           cater to a possible recovery attempt.

   6.3.1  Timeouts on transport exception events

           A transport connection shutdown or a transport reset without any
           preceding iSCSI protocol interactions informing of the fact causes a

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           full-feature phase iSCSI connection to be abruptly terminated. The
           timeout values to be used in this case are the negotiated values of
           DefaultTime2Wait (Appendix 11.15 - DefaultTime2Wait -) and
           DefaultTime2Retain (Appendix 11.16 - DefaultTime2Retain -) text keys
           for the session.

   6.3.2  Timeouts on planned decommissioning

           Any planned decommissioning of a full-feature phase iSCSI connection
           is preceded by either a Logout Response PDU, or an Async Message PDU.
           The Time2Wait and Time2Retain field values (section 9.15)in a Logout
           Response PDU, and the Parameter2 and Parameter3 fields of an Async
           Message (AsyncEvent types "drop the connection" or "drop all the con-
           nections"; section 9.9.1) specify the timeout values to be used in
           each of these cases.

           These timeout values are applicable only for the affected connection,
           and the tasks active on that connection.  These timeout values have no
           bearing on initiator timers (if any) that are already running on con-
           nections or tasks associated with that session.

   6.4  Format Errors

           Explicit violations of the PDU layout rules stated in this document
           are format errors.  Violations, when detected, usually indicate a
           major implementation flaw in one of the parties.

           When a target or an initiator receives an iSCSI PDU with a format
           error, it MUST immediately terminate all transport connections in the
           session either with a connection close or with a connection reset and
           escalate the format error to session recovery (see Section 6.12.4 Ses-
           sion Recovery).

   6.5  Digest Errors

           The discussion of the legal choices in handling digest errors below
           excludes session recovery as an explicit option, but either party
           detecting a digest error may choose to escalate the error to session
           recovery.

           When a target receives any iSCSI PDU with a header digest error, it
           MUST silently discard the PDU.



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           When a target receives any iSCSI PDU with a payload digest error, it
           MUST answer with a Reject iSCSI PDU with a Reason-code of Data-Digest-
           Error and discard the PDU.

                 - If the discarded PDU is a solicited or unsolicited iSCSI data
                       PDU (for immediate data in a command PDU, non-data PDU rule
                       below applies), the target MUST do one of the following:
                  a)  Request retransmission with a recovery R2T. [OR]
                  b)  Terminate the task with a response PDU with the reason "proto-
                  col service CRC error" (Section 9.4.3 Response). If the target
                  chooses to implement this option, it MUST wait to receive all the
                  data (signaled by a Data PDU with the final bit set for all out-
                  standing R2Ts) before sending the response PDU. A task management
                  command (similar to an abort task) from the initiator during this
                  wait may also conclude the task.
                 - No further action is necessary for targets if the discarded
                       PDU is a non-data PDU.

           When an initiator receives any iSCSI PDU with a header digest error,
           it MUST discard the PDU.

           When an initiator receives any iSCSI PDU with a payload digest error,
           it MUST discard the PDU.

                 - If the discarded PDU is an iSCSI data PDU, the initiator MUST
                       do one of the following:
                  a)  Request the desired data PDU through SNACK. In its turn,   the
                  target MUST either resend the data PDU or, reject the SNACK with a
                  Reject PDU with a reason-code of "Data-SNACK Reject" in which case
                  -
                            i)  if the status had not already been sent for the com-
                                          mand, the target MUST terminate the command with an
                                          iSCSI response reason(Section 9.4.3 Response) of "SNACK
                                          rejected".
                            ii)  if the status was already sent, no further action is
                                          necessary for the target.  Initiator in this case MUST
                                          internally signal the completion with the "SNACK
                                          rejected" reason (Section 9.4.3 Response) disregarding
                                          any received status PDU, but must wait for the status to
                                          be received before doing so.       [OR]
                  b)  Abort the task and terminate the command with an error.

                 - If the discarded PDU is a response PDU, the initiator MUST do
                       one of the following:

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                  a)  Request PDU retransmission with a status SNACK. [OR]
                  b)  Logout the connection for recovery and continue the tasks on a
                  different connection instance as described in Section 6.1 Retry
                  and Reassign in Recovery. [OR]
                  c)  Logout to close the connection (abort all the commands associ-
                  ated with the connection).

                 - No further action is necessary for initiators if the discarded
                      PDU is an unsolicited PDU (e.g., Async, Reject).

   6.6  Sequence Errors

           When an initiator receives an iSCSI R2T/data PDU with an out-of-order
           R2TSN/DataSN or a SCSI response PDU with an ExpDataSN that implies
           missing data PDU(s), it means that the initiator must have hit a
           header or payload digest error on one or more earlier R2T/data PDUs.
           The initiator MUST address these implied digest errors as described in
           Section 6.5 Digest Errors. When a target receives a data PDU with an
           out-of-order DataSN, it means that the target must have hit a header
           or payload digest error on at least one of the earlier data PDUs. Tar-
           get MUST address these implied digest errors as described in Section
           6.5 Digest Errors.

           When an initiator receives an iSCSI status PDU with an out-of-order
           StatSN that implies missing responses, it MUST address the one or more
           missing status PDUs as described in Section 6.5 Digest Errors. As a
           side effect of receiving the missing responses, the initiator may dis-
           cover missing data PDUs. If the initiator wants to recover the missing
           data for a command, it MUST NOT acknowledge the received responses
           that start from the StatSN of the interested command, until it has
           completed receiving all the data PDUs of the command.

           When an initiator receives duplicate R2TSNs (due to proactive
           retransmission of R2Ts by the target) or duplicate DataSNs (due to
           proactive SNACKs by the initiator), it MUST discard the duplicates.

   6.7  SCSI Timeouts

           An iSCSI initiator MAY attempt to plug a command sequence gap on the
           target end (in the absence of an acknowledgement of the command by way
           of ExpCmdSN) before the ULP timeout by retrying the unacknowledged
           command, as described in Section 6.1 Retry and Reassign in Recovery.



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           On a ULP timeout for a command (that carried a CmdSN of n), the iSCSI
           initiator MUST abort the command by either using the Abort Task task
           management function request, or a "close the connection" Logout if it
           intends to continue the session.  In using an explicit Abort, if the
           ExpCmdSN is still less than (n+1), the target may see the abort
           request while missing the original command itself due to one of the
           following reasons:

                 - The original command was dropped due to digest error.
                 - The connection on which the original command was sent was suc-
                      cessfully logged out (on logout, the unacknowledged commands
                      issued on the connection being logged out are discarded).

           If the abort request is received and the original command is missing,
           targets MUST consider the original command with that RefCmdSN to be
           received and issue a task management response with the response code:
           "Task does not exist". This response concludes the task on both ends.

   6.8  Negotiation Failures

           Text request and response sequences, when used to set/negotiate oper-
           ational parameters, constitute the negotiation/parameter setting.  A
           negotiation failure is considered one or more of the following:

                 - None of the choices or the stated value is acceptable to one
                      negotiating side.
                 - The text request timed out, and possibly aborted.
                 - The text request was answered with a reject.


           The following two rules are to be used to address negotiation fail-
           ures:

                 - During Login, any failure in negotiation MUST be considered a
                      login process failure and the login phase must be terminated,
                      and with it the connection. If the target detects the failure,
                      it must terminate the login with the appropriate login
                      response code.

                 - A failure in negotiation, while in the full-feature phase,
                      will terminate the entire negotiation sequence that may con-
                      sist of a series of text requests that use the same Initiator
                      Task Tag.  The operational parameters of the session or the
                      connection MUST continue to be the values agreed upon during
                      an earlier successful negotiation (i.e., any partial results
                      of this unsuccessful negotiation must be undone).


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   6.9  Protocol Errors

           The authors recognize that mapping framed messages over a "stream"
           connection, such as TCP, make the proposed mechanisms vulnerable to
           simple software framing errors. On the other hand, the introduction of
           framing mechanisms to limit the effects of these errors may be onerous
           on performance for simple implementations.  Command Sequence Numbers
           and the above mechanisms for connection drop and re-establishment
           help handle this type of mapping errors.

           All violations of iSCSI PDU exchange sequences specified in this draft
           are also protocol errors.  This category of errors can be only be
           addressed by fixing the implementations; iSCSI defines Reject and
           response codes to enable this.

   6.10  Connection Failures

           iSCSI can keep a session in operation if it is able to keep/establish
           at least one TCP connection between the initiator and the target in a
           timely fashion.  It is assumed that targets and/or initiators recog-
           nize a failing connection by either transport level means (TCP), a gap
           in the command, a response stream that is not filled for a long time,
           or by a failing iSCSI NOP (ping). The latter MAY be used periodically
           by highly reliable implementations.  Initiators and targets MAY also
           use the keep-alive option on the TCP connection to enable early link
           failure detection on otherwise idle links.

           On connection failure, the initiator and target MUST do one of the
           following:

                 - Attempt connection recovery within the session (Section 6.12.3
                      Connection Recovery).
                 - Logout the connection with the reason code "closes the connec-
                      tion" (Section 9.14.3 Reason Code), re-issue missing commands,
                      and implicitly terminate all active commands. This option
                      requires support for the within-connection recovery class
                      (Section 6.12.2 Recovery Within-connection).
                 - Perform session recovery (Section 6.12.4 Session Recovery).

           Either side may choose to escalate to session recovery, and the other
           side MUST give it precedence.  On a connection failure, a target MUST
           terminate and/or discard all the active immediate commands regardless
           of which of the above options is used (i.e., immediate commands are
           not recoverable across connection failures).

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   6.11  Session Errors

           If all the connections of a session fail and cannot be re-established
           in a short time, or if initiators detect protocol errors repeatedly,
           an initiator may choose to terminate a session and establish a new
           session.
           The initiator takes the following actions:

                 - It resets or closes all the transport connections.
                 - It terminates all outstanding requests with an appropriate
                      response before initiating a new session.

           When the session timeout (the connection state timeout for the last
           failed connection) happens on the target, it takes the following
           actions:

                 - Resets or closes the TCP connections (closes the session).
                 - Aborts all Tasks in the task set for the corresponding initi-
                      ator.

   6.12  Recovery Classes

           iSCSI enables the following classes of recovery (in the order of
           increasing scope of affected iSCSI tasks):

                 - Within a command (i.e., without requiring command restart).
                 - Within a connection (i.e., without requiring the connection to
                      be rebuilt, but perhaps requiring command restart).
                 - Connection recovery (i.e., perhaps requiring connections to be
                      rebuilt and commands to be reissued).
                 - Session recovery.

           The recovery scenarios detailed in the rest of this section are repre-
           sentative rather than exclusive. In every case, they detail the lowest
           class recovery that MAY be attempted. The implementer is left to
           decide under which circumstances to escalate to the next recovery
           class and/or what recovery classes to implement.  Both the iSCSI tar-
           get and initiator MAY escalate the error handling to an error recovery
           class, which impacts a larger number of iSCSI tasks in any of the
           cases identified in the following discussion.

           In all classes, the implementer has the choice of deferring errors to
           the SCSI initiator (with an appropriate response code), in which case



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           the task, if any, has to be removed from the target and all the side-
           effects, such as ACA, must be considered.

           Use of within-connection and within-command recovery classes MUST NOT
           be attempted before the connection is in full feature phase.

   6.12.1  Recovery Within-command

           At the target, the following cases lend themselves to within-command
           recovery:

                 - Lost data PDU - realized through one of the following:
                  a)  Data digest error - dealt with as specified in Section 6.5
                  Digest Errors, using the option of a recovery R2T.
                  b)  Sequence reception timeout (no data or partial-data-and-no-F-
                  bit) - considered an implicit sequence error and dealt with as
                  specified in Section 6.6 Sequence Errors, using the option of a
                  recovery R2T.
                  c)  Header digest error, which manifests as a sequence reception
                  timeout, or a sequence error - dealt with as specified in Section
                  6.6 Sequence Errors, using the option of a recovery R2T.

           At the initiator, the following cases lend themselves to within-com-
           mand recovery:

                 Lost data PDU or lost R2T - realized through one of the follow-
                      ing:
                  a)  Data digest error - dealt with as specified in Section 6.5
                  Digest Errors, using the option of a SNACK.
                  b)  Sequence reception timeout (no status) - dealt with as speci-
                  fied in Section 6.6 Sequence Errors, using the option of a SNACK.
                  c)  Header digest error, which manifests as a sequence reception
                  timeout, or a sequence error - dealt with as specified in Section
                  6.6 Sequence Errors, using the option of a SNACK.

           To avoid a race with the target, which may already have a recovery R2T
           or a termination response on its way, an initiator SHOULD NOT origi-
           nate a SNACK for an R2T based on its internal timeouts (if any).
           Recovery in this case is better left to the target.

           The timeout values used by the initiator and target are outside the
           scope of this document.  Sequence reception timeout is generally a
           large enough value to allow the data sequence transfer to be complete.


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   6.12.2  Recovery Within-connection

           At the initiator, the following cases lend themselves to within-con-
           nection recovery:

                 - Requests not acknowledged for a long time. Requests are
                      acknowledged explicitly through ExpCmdSN or implicitly by
                      receiving data and/or status. The initiator MAY retry non-
                      acknowledged commands as specified in Section 6.1 Retry and
                      Reassign in Recovery.

                 - Lost iSCSI numbered Response. It is recognized by either iden-
                      tifying a data digest error on a Response PDU or a Data-In PDU
                      carrying the status, or by receiving a Response PDU with a
                      higher StatSN than expected. In the first case, digest error
                      handling is done as specified in Section 6.5 Digest Errors
                      using the option of a SNACK. In the second case, sequence
                      error handling is done as specified in Section 6.6 Sequence
                      Errors, using the option of a SNACK.

           At the target, the following cases lend themselves to within-connec-
           tion recovery:

                 - Status/Response not acknowledged for a long time. The target
                      MAY issue a NOP-IN (with a valid Target Transfer Tag or other-
                      wise) that carries the next status sequence number it is going
                      to use in the StatSN field.  This helps the initiator detect
                      any missing StatSN(s) and issue a SNACK for the status.

           The timeout values used by the initiator and the target are outside
           the scope of this document.

   6.12.3  Connection Recovery

           At an iSCSI initiator, the following cases lend themselves to connec-
           tion recovery:

                 - TCP connection failure. The initiator MUST close the connec-
                      tion. It then MUST either Logout the failed connection, or
                      Login with an implied Logout, and reassign connection alle-
                      giance for all commands still in progress associated with the
                      failed connection on another connection (that MAY be a newly
                      established connection) using the "Task reassign" task manage-
                      ment function (see Section 9.5.1 Function). Note that for an
                      initiator a command is in progress as long as it has not
                      received for a response or a Data-In PDU including status.



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                 - N.B. The logout function is mandatory, while a new connection
                      establishment is mandatory only if the failed connection was
                      the last or only connection in the session.

                 - Receiving an Asynchronous Message that indicates one or all
                      connections in a session has been dropped.  The initiator MUST
                      handle it as a TCP connection failure for the connection(s)
                      referred to in the Message.

           At an iSCSI target, the following cases lend themselves to connection
           recovery:

                 - TCP connection failure. The target MUST close the connection
                      and if more than one connection is available, the target
                      SHOULD send an Asynchronous Message that indicates it has
                      dropped the connection. Then, the target will wait for the
                      initiator to continue recovery.

   6.12.4  Session Recovery

           Session recovery should be performed when all other recovery attempts
           have failed.  Very simple initiators and targets MAY perform session
           recovery on all iSCSI errors and therefore, place the burden of recov-
           ery on the SCSI layer and above.

           Session recovery implies the closing of all TCP connections, inter-
           nally aborting all executing and queued tasks for the given initiator
           at the target, terminating all outstanding SCSI commands with an
           appropriate SCSI service response at the initiator, and restarting a
           session on a new set of connection(s) (TCP connection establishment
           and login on all new connections).

           Reserve-Release managed SCSI reservations ("Regular" reservations)
           that are secured during an iSCSI session persist until they are
           cleared using regular SCSI means. When the session object is cleared,
           i.e. when the session object reaches the FREE state, iSCSI layer
           informs SCSI layer of the fact and expects the SCSI layer to initiate
           clearing actions (if any) that it deems appropriate.  If the iSCSI
           session is reconstructed (thus between the same SCSI ports with the
           same nexus identifier - see Section 4.3.6 Session Continuation, clo-
           sure and failure), any existing regular reservations may be automati-
           cally associated to this new session if they where not cleared by the
           SCSI layer.



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           Persistent SCSI reservations are not affected by iSCSI session fail-
           ures, and only the regular SCSI means can be used to handle these res-
           ervations when the session is reconstructed (necessarily between the
           same SCSI ports and so with the same nexus identifier).

   6.13  Error Recovery Hierarchy

           The error recovery classes and features described are organized into a
           hierarchy for ease in understanding and to limit the myriad of imple-
           mentation possibilities, with hopes that this significantly contrib-
           utes to highly interoperable implementations.  The attributes of this
           hierarchy are as follows:

                  a)  Each level is a superset of the capabilities of the previous
                  level. For example, Level 1 support implies supporting all capa-
                  bilities of Level 0 and more.
                  b)  As a corollary, supporting a higher error recovery level means
                  increased sophistication and possibly an increase in resource
                  requirement.
                  c)  Supporting error recovery level "n" is advertised and negoti-
                  ated by each iSCSI entity by exchanging the text key "ErrorRecov-
                  eryLevel=n".  The lower of the two exchanged values is the
                  operational ErrorRecoveryLevel for the session.

           The following diagram represents the error recovery hierarchy.

                                      +
                                     / \
                                    / 2 \       <-- Connection recovery
                                   +-----+
                                  /   1   \     <-- Digest failure recovery
                                 +---------+
                                /     0     \   <-- Session failure recovery
                               +-------------+

           The following table lists the error recovery capabilities expected
           from the implementations that support each error recovery level.





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           +-------------------+--------------------------------------------+
           |ErrorRecoveryLevel |  Associated Error recovery capabilities    |
           +-------------------+--------------------------------------------+
           |        0          |  Session recovery class                    |
           |                   |  (Section 6.12.4 Session Recovery)         |
           +-------------------+--------------------------------------------+
           |        1          |  Digest failure recovery (See Note below.)      |
           +-------------------+--------------------------------------------+
           |        2          |  Connection recovery class                 |
           |                   |  (Section 6.12.3 Connection Recovery)      |
           +-------------------+--------------------------------------------+

           Note: Digest failure recovery is comprised of two recovery classes:
           Within-Connection recovery class (Section 6.12.2 Recovery Within-con-
           nection) and Within-Command recovery class (Section 6.12.1 Recovery
           Within-command).

           Supporting error recovery level "0" is mandatory, while the rest are
           optional to implement.  In implementation terms, the above striation
           means that the following incremental sophistication with each level
           is required.

           +-------------------+---------------------------------------------+
           |Level transition   |  Incremental requirement                    |
           +-------------------+---------------------------------------------+
           |        0->1       |  PDU retransmissions on the same connection |
           +-------------------+---------------------------------------------+
           |        1->2       |  Retransmission across connections and      |
           |                   |  allegiance reassignment                    |
           +-------------------+---------------------------------------------+





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   7. Security Considerations

           Historically, native storage systems have not had to consider secu-
           rity because their environments offered minimal security risks. That
           is, these environments consisted of storage devices either directly
           attached to hosts or connected via a subnet distinctly separate from
           the communications network. The use of storage protocols, such as
           SCSI, over IP networks requires that security concerns be addressed.
           iSCSI implementations MUST provide means of protection against active
           attacks (e.g., pretending to be another identity, message insertion,
           deletion, modification, and replaying) and passive attacks
           (e.g.,eavesdropping, gaining advantage by analyzing the data sent
           over the line).

           Although technically possible, iSCSI SHOULD NOT be configured without
           security. iSCSI without security should be confined, in extreme
           cases, to closed environments without any security risk.

           The following section describes the security mechanisms provided by
           an iSCSI implementation.

   7.1  iSCSI Security Mechanisms

           The entities involved in iSCSI security are the initiator, target, and
           the IP communication end points. iSCSI scenarios where multiple ini-
           tiators or targets share a single communication end point are
           expected. To accommodate such scenarios, iSCSI uses two separate
           security mechanisms: In-band authentication between the initiator and
           the target at the iSCSI connection level (carried out by exchange of
           iSCSI Login PDUs), and packet protection (integrity, authentication,
           and confidentiality) by IPsec at the IP level. The two security mech-
           anisms complement each other: The in-band authentication provides
           end-to-end trust (at login time) between the iSCSI initiator and the
           target, while IPsec provides a secure channel between the IP communi-
           cation end points.

           Further details on typical iSCSI scenarios and the relation between
           the initiators, targets, and the communication end points can be found
           in [SEC-IPS].





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   7.2  In-band Initiator-Target Authentication

           With this mechanism, the target authenticates the initiator and the
           initiator optionally authenticates the target. The authentication is
           performed on every new iSCSI connection by an exchange of iSCSI Login
           PDUs using a negotiated authentication method.

           The authentication method cannot assume an underlying IPsec protec-
           tion, since IPsec is optional to use. An attacker should gain as lit-
           tle advantage as possible by inspecting the authentication phase
           PDUs. Therefore, a method using clear text (or equivalent) passwords
           is not acceptable; on the other hand, identity protection is not
           strictly required.

           This mechanism protects against an unauthorized login to storage
           resources by using a false identity (spoofing). Once the authentica-
           tion phase is completed, if the underlying IPsec is not used, all PDUs
           are sent and received in clear. This mechanism alone (without underly-
           ing IPsec) should only be used when there is no risk of eavesdropping,
           message insertion, deletion, modification, and replaying.

           The CHAP authentication method (see Chapter 10) is vulnerable to an
           off-line dictionary attack. In environments where this attack is a
           concern, CHAP SHOULD NOT be used without additional protection.
           Underlying IPsec encryption provides protection against this attack.


           The strength of the SRP authentication method (specified in Chapter
           13) is dependent on the characteristics of the group being used (i.e.,
           the prime modulus N and generator g). As described in [RFC2945], N is
           required to be a Sophie-German prime (of the form N = 2q + 1, where q
           is also prime) and the generator g is a primitive root of GF(n). In
           iSCSI authentication, the prime modulus N MUST be at least 768 bits.

           Upon receiving N and g from the Target, the Initiator MUST verify that
           they satisfy the above requirements (and otherwise, abort the connec-
           tion). This verification MAY start by trying to match N and g with a
           well-known group that satisfies the above requirements.
           Well-known SRP groups are provided in [SEC-IPS].

           Compliant iSCSI initiators and targets MUST at least implement the SRP
           authentication method [RFC2945] (see Chapter 10).



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   7.3  IPsec

           The IPsec mechanism is used by iSCSI for packet protection (crypto-
           graphic integrity, authentication, and confidentiality) at the IP
           level between the iSCSI communicating end points. The following sec-
           tions describe the IPsec protocols that must be implemented for data
           integrity and authentication, confidentiality, and key management.

           Detailed considerations and recommendations for using IPsec for iSCSI
           are provided in [SEC-IPS].

   7.3.1  Data Integrity and Authentication

           Data authentication and integrity is provided by a keyed Message
           Authentication Code in every sent packet. This code protects against
           message insertion, deletion, and modification.  Protection against
           message replay is realized by using a sequence counter.

           An iSCSI compliant initiator or target MUST provide data integrity and
           authentication by implementing IPsec [RFC2401] with ESP in tunnel
           mode [RFC2406] with the following iSCSI specific requirements:

                 - HMAC-SHA1 MUST be implemented [RFC2404].
                 - AES CBC MAC with XCBC extensions SHOULD be implemented
                      [AESCBC].

           If the IPsec implementation of an iSCSI initiator or target conforms
           to the [RFC2401] definition of a host, then to comply with section 4.1
           of [RFC2401] it MUST also implement ESP in transport mode (with the
           same requirements above).

           The ESP anti-replay service MUST also be implemented.

           At the high speeds iSCSI is expected to operate, a single IPsec SA
           could rapidly cycle through the 32-bit IPsec sequence number space.
           In view of this, in the future it may be desirable for an iSCSI imple-
           mentation that operates at speeds of 1 Gbps or faster to implement the
           IPsec sequence number extension [SEQ-EXT].

   7.3.2  Confidentiality

           Confidentiality is provided by encrypting the data in every packet.
           Confidentiality SHOULD always be used together with data integrity


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           and authentication to provide comprehensive protection against eaves-
           dropping, message insertion, deletion, modification, and replaying.

           An iSCSI compliant initiator or target MUST provide confidentiality
           by implementing IPsec [RFC2401] with ESP in tunnel mode [RFC2406] with
           the following iSCSI specific requirements:

                 - 3DES in CBC mode MUST be implemented [RFC2451].
                 - AES in Counter mode SHOULD be implemented [AESCTR] (NOTE: This
                      is still subject to the IPsec WG's standardization plans).

           If the IPsec implementation of an iSCSI initiator or target conforms
           to the [RFC2401] definition of a host, then to comply with section 4.1
           of [RFC2401] it MUST also implement ESP in transport mode (with the
           same requirements above).

           DES in CBC mode SHOULD NOT be used due to its inherent weakness.
           The NULL encryption algorithm MUST also be implemented.

   7.3.3  Policy, Security Associations and Key Management

           A compliant iSCSI implementation MUST meet the key management
           requirements of the IPsec protocol suite. Authentication, security
           association negotiation, and key management MUST be provided by
           implementing IKE [RFC2409] using the IPsec DOI [RFC2407] with the fol-
           lowing iSCSI specific requirements:

                 - Peer authentication using a pre-shared key MUST be supported.
                      Certificate-based peer authentication using digital signa-
                      tures MAY be supported. Peer authentication using the public
                      key encryption methods outlined in IKE sections 5.2 and 5.3[7]
                      SHOULD NOT be used.

                 - When digital signatures are used to achieve authentication, an
                      IKE negotiator SHOULD use IKE Certificate Request Payload(s)
                      to specify the certificate authority. IKE negotiators SHOULD
                      check the pertinent Certificate Revocation List (CRL) before
                      accepting a PKI certificate for use in IKE authentication pro-
                      cedures.

                 - Both IKE Main Mode and Aggressive Mode MUST be supported. IKE
                      main mode with pre-shared key authentication method SHOULD NOT
                      be used when either the initiator or the target uses dynami-
                      cally assigned IP addresses. While pre-shared keys in many
                      cases offer good security, situations where dynamically
                      assigned addresses are used force the use of a group pre-


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                      shared key, which creates vulnerability to a man-in-the-middle
                      attack.

                 - In the IKE Phase 2 Quick Mode exchanges for creating the Phase
                      2 SA, the Identity Payload fields MUST be present.
                      ID_IPV4_ADDR, ID_IPV6_ADDR (if the protocol stack supports
                      IPv6) and ID_FQDN Identity payloads MUST be supported;
                      ID_USER_FQDN MAY be supported. The IP Subnet, IP Address
                      Range, ID_DER_ASN1_DN, ID_DER_ASN1_GN formats SHOULD NOT be
                      used. The ID_KEY_ID Identity Payload MUST NOT be used.

           Manual keying MUST NOT be used since it does not provide the necessary
           re-keying support.


           When IPsec is used the receipt of an IKE Phase 2 delete message SHOULD
           NOT be interpreted as a reason for tearing down the iSCSI TCP connec-
           tion. If additional traffic is sent on it, a new IKE Phase 2 SA will
           be created to protect it.



           The method used by the initiator to determine whether the target
           should be connected using IPsec is regarded as an issue of IPsec pol-
           icy administration, and thus not defined in the iSCSI standard. How-
           ever, as iSCSI has an is an in-band discovery mechanism (discovery
           session and SendTargets), the use or non-use of IPsec in any opera-
           tional session is assumed to be identical to that of the discovery
           session.

           If an iSCSI target is discovered via a SendTargets request in a dis-
           covery session not using IPsec, the initiator should assume that it
           does not need IPsec to establish a session to that target.  If an
           iSCSI target is discovered using a discovery session that does use
           IPsec, the initiator should use IPsec when establishing a session to
           that target.





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   8. Notes to Implementers

           This section notes some of the performance and reliability consider-
           ations of the iSCSI protocol.  This protocol was designed to allow
           efficient silicon and software implementations. The iSCSI tag mecha-
           nism was designed to enable RDMA at the iSCSI level or lower.

           The guiding assumption made throughout the design of this protocol is
           that targets are resource constrained relative to initiators.

           Implementers are also advised to consider the implementation conse-
           quences of the iSCSI to SCSI mapping model as outlined in Section
           2.4.3 Consequences of the Model.

   8.1  Multiple Network Adapters

           The iSCSI protocol allows multiple connections, not all of which need
           to go over the same network adapter. If multiple network connections
           are to be utilized with hardware support, the iSCSI protocol command-
           data-status allegiance to one TCP connection ensures that there is no
           need to replicate information across network adapters or otherwise
           require them to cooperate.

           However, some task management commands may require some loose form of
           cooperation or replication at least on the target.

   8.1.1  Conservative Reuse of ISIDs

           Historically, the SCSI model (and implementations and applications
           based on that model) has assumed that SCSI ports are static, physical
           entities. Recent extensions to the SCSI model have taken advantage of
           persistent worldwide unique names for these ports. In iSCSI however,
           the SCSI initiator ports are the endpoints of dynamically created ses-
           sions, so the presumption of "static and physical" does not apply. In
           any case, the model clauses (particularly, Section 2.4.2 SCSI Archi-
           tecture Model) provide for persistent, reusable names for the iSCSI-
           type SCSI initiator ports even though there does not need to be any
           physical entity bound to these names.

           To both minimize the disruption of legacy applications and to better
           facilitate the SCSI features that rely on persistent names for SCSI
           ports, iSCSI implementations should attempt to provide a stable pre-
           sentation of SCSI Initiator Ports (both to the upper OS-layers and to


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           the targets to which they connect). This can be achieved in an initi-
           ator implementation by conservatively reusing ISIDs. In other words,
           the same ISID should be used in the Login process to multiple target
           portal groups (of the same iSCSI Target or different iSCSI Targets).
           The ISID RULE (Section 2.4.3 Consequences of the Model) only prohibits
           reuse to the same target portal group. It does not "preclude" reuse to
           other target portal groups.
           The principle of conservative reuse "encourages" reuse to other tar-
           get portal groups.  When a SCSI target device sees the same (Initia-
           torName, ISID) pair in different sessions to different target portal
           groups, it can identify the underlying SCSI Initiator Port on each
           session as the same SCSI port. In effect, it can recognize multiple
           paths from the same source.

   8.1.2  iSCSI Name and ISID/TSID Use

           The designers of the iSCSI protocol envisioned there being
           one iSCSI Initiator Node Name per operating system image on a machine.
           This enables SAN resource configuration and authentication schemes
           based on a system's identity.  It supports the notion that it should
           be possible to assign access to storage resources based on "initiator
           device" identity.

           When there are multiple hardware or software components coordinated
           as a single iSCSI Node, there must be some (logical) entity that rep-
           resents the iSCSI Node that makes the iSCSI Node Name available to all
           components involved in session creation and login. Similarly, this
           entity that represents the iSCSI Node must be able to coordinate ses-
           sion identifier resources (ISID for initiators and TSID for targets)
           to enforce both the ISID and TSID RULES (see Section Section 2.4.3
           Consequences of the Model).

           For targets, because of the closed environment, implementation of
           this entity should be straightforward. However, vendors of iSCSI
           hardware (e.g., NICs or HBAs) intended for targets, should provide
           mechanisms for configuration of the iSCSI Node Name and for configura-
           tion and/or coordination of TSIDs across the portal groups instanti-
           ated by multiple instances of these components within a target. One
           mechanism is to allow for static or dynamic partitioning of the TSID
           namespace among the portal groups. Such a partitioning allows each
           portal group to act independently of other portal groups when assign-
           ing TSIDs, and facilitates enforcement of the TSID RULE (Section 2.4.3
           Consequences of the Model).


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           For initiators, in the long term, it is expected that operating system
           vendors will take on the role of this entity and provide standard APIs
           that can inform components of their iSCSI Node Name and can configure
           and/or coordinate ISID allocation, use and reuse.

           Recognizing that such initiator APIs are not available today, other
           implementations of the role of this entity are possible.
           For example, a human may instantiate the (common) Node name as part of
           the installation process of each iSCSI component involved in session
           creation and login. This may be done either by pointing the component
           to a vendor-specific location for this datum or to a system-wide loca-
           tion. The structure of the ISID namespace (see Section 9.12.5 ISID and
           [NDT]) facilitates implementation of the ISID coordination by allow-
           ing each component vendor to independently (of other vendor's compo-
           nents) coordinate allocation and use and reuse its own partition of
           the ISID namespace in a vendor-specific manner. Partitioning of the
           ISID namespace within initiator portal groups managed by that vendor
           allows each such initiator portal group to act independently of all
           other portal groups when selecting an ISID for a login; this facili-
           tates enforcement of the ISID RULE (see Section 2.4.3 Consequences of
           the Model) at the initiator.

           A vendor of iSCSI hardware (e.g., NICs or HBAs) intended for use in
           the initiators must allow, in addition to a mechanism for configuring
           the iSCSI Node Name, for a mechanism to configure and/or coordinate
           ISIDs for all sessions managed by multiple instances of that hardware
           within a given iSCSI Node.  Such configuration might be either perma-
           nently pre-assigned at the factory (in a necessarily globally unique
           way), statically assigned (e.g., partitioned across all the NICs at
           initialization in a locally unique way), or dynamically assigned
           (e.g., on-line allocator, also in a locally unique way).  In the lat-
           ter two cases, the configuration may be via public APIs (perhaps
           driven by an independent vendor's SW, such as the OS vendor) or via
           private APIs driven by the vendor's own SW.

   8.2  Autosense and Auto Contingent Allegiance (ACA)

           Autosense refers to the automatic return of sense data to the initia-
           tor in case a command did not complete successfully. iSCSI initiators
           and targets MUST support autosense.




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           ACA helps preserve ordered command execution in the presence of
           errors.  As iSCSI can have many commands in-flight between initiator
           and target, iSCSI initiators and targets SHOULD support ACA.

   8.3  Command Retry and Cleaning Old Command Instances

           To avoid having old, retried command instances appear in a valid com-
           mand window after a command sequence number wrap around, the protocol
           requires (see Section 2.2.2.1 Command Numbering and Acknowledging)
           that on every connection on which a retry has been issued, a non-imme-
           diate command be issued and acknowledged within a 2**31-1 commands
           interval since the retry was issued. This requirement can be fulfilled
           by an implementation in several ways.

           The simplest technique to use is to send a (non-retry) non-immediate
           SCSI command (or a NOP if no SCSI command is available for a while)
           after every command retry on the connection on which the retry was
           attempted.  As errors are deemed rare events, this technique is prob-
           ably the most effective, as it does not involve additional checks at
           the initiator when issuing commands.

   8.4  Synch and Steering Layer and Performance

           While a synch and steering layer is optional, an initiator/target that
           does not have it working against a target/initiator that demands synch
           and steering may experience performance degradation caused by packet
           reordering and loss.  Providing a synch and steering mechanism is rec-
           ommended for all high-speed implementations.

   8.5  Unsolicited Data and Performance

           Unsolicited data on write are meant to reduce the effect of latency on
           throughput (no R2T is needed to start sending data).  In addition,
           immediate data are meant to reduce the protocol overhead (both band-
           width and execution time).

           However, negotiating an amount of unsolicited data for writes and
           sending less than the negotiated amount when the total data amount to
           be sent by a command is larger than the negotiated amount may nega-
           tively impact performance and may not be supported by all the targets.





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   8.6  Considerations for State-dependent devices

           Sequential access devices operate on the principle that the position
           of the device is based on the last command processed. As such, command
           processing order and knowledge of whether or not the previous command
           was processed is of the utmost importance to maintain data integrity.
           As an example, inadvertent retries of SCSI commands when it is not
           known if the previous SCSI command was processed is a potential data
           integrity risk.

           For a sequential access device, consider the scenario where a SCSI
           SPACE command to backspace one filemark is issued and then re-issued
           due to no status received for the command. If the first SPACE command
           was actually processed, the re-issued SPACE command, if processed,
           will cause the position to change. Thus, a subsequent write operation
           will write data to the wrong position and any previous data at that
           position will be overwritten.

           For a medium changer device, consider the scenario where an EXCHANGE
           MEDIUM command (the SOURCE ADDRESS and DESTINATION ADDRESS are the
           same thus performing a swap) is issued and then re-issued due to no
           status received for the command. If the first EXCHANGE MEDIUM command
           was actually processed, the re-issued EXCHANGE MEDIUM command, if
           processed, will perform the swap again. The net effect is no swap was
           performed thus leaving a data integrity exposure.

           All commands that change the state of the device (as in SPACE commands
           for sequential access devices, and EXCHANGE MEDIUM for medium changer
           device), MUST be issued as non-immediate commands for deterministic
           and in order delivery to iSCSI targets.

           For many of those state changing commands the execution model also
           assumes  that the command is executed exactly once.  For those com-
           mands a retry at SCSI level is not feasible or very difficult and
           error recovery at iSCSI level is advisable.

   8.6.1  Determining the proper ErrorRecoveryLevel


           The implementation and usage of a specific ErrorRecoveryLevel should
           be determined based on the deployment scenarios of a given iSCSI
           implementation.  Generally, the following factors must be
           considered before deciding on the proper level of recovery:


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                  a)  Application resilience to I/O failures.
                  b)  Required level of availability in the face of transport connec-
                  tion failures.
                  c)  Probability of transport layer "checksum escape" frequency.
                  This in turn decides the iSCSI digest failure frequency, and thus
                  the criticality of iSCSI-level error recovery.  The details of
                  estimating this probability are outside the scope of this docu-
                  ment.

           A consideration of the above factors for SCSI tape devices as an exam-
           ple suggests that implementations SHOULD use ErrorRecoveryLevel=1
           when transport connection failure is not a concern, and ErrorRecov-
           eryLevel=2 when the connection failure is also of high likelihood dur-
           ing a backup/retrieval.





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   9. iSCSI PDU Formats

           All multi-byte integers that are specified in formats defined in this
           document are to be represented in network byte order (i.e., big
           endian).  Any field that appears in this document assumes that the
           most significant byte is the lowest numbered byte and the most signif-
           icant bit (within byte or field) is the highest numbered bit unless
           specified otherwise.

           Any compliant sender MUST set all bits not defined and all reserved
           fields to zero unless specified otherwise.  Any compliant receiver
           MUST ignore any bit not defined and all reserved fields unless speci-
           fied otherwise.

           Reserved fields are marked by the word "reserved", some abbreviation
           of "reserved" or by "." for individual bits when no other form of
           marking is technically feasible.

   9.1  iSCSI PDU Length and Padding

           iSCSI PDUs are padded to the closest integer number of four byte
           words. The padding bytes SHOULD be 0.

   9.2  PDU Template, Header, and Opcodes

           All iSCSI PDUs have one or more header segments and, optionally, a
           data segment.  After the entire header segment group  a header-digest
           may follow. The data segment MAY also be followed by a data-digest.

           The Basic Header Segment (BHS) is the first segment in all of the
           iSCSI PDUs.  The BHS is a fixed-length 48-byte header segment.  It may
           be followed by Additional Header Segments (AHS), a Header-Digest, a
           Data Segment, and/or a Data-Digest.

           The overall structure of an iSCSI  PDU is as follows:





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           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0/ Basic Header Segment (BHS)                                    /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48/ Additional Header Segment (AHS)  (optional)                   /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           ----
             +---------------+---------------+---------------+---------------+
            k/ Header-Digest (optional)                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
            l/ Data Segment(optional)                                        /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
            m/ Data-Digest (optional)                                        /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

           All PDU segments and digests are padded to an integer number of four
           byte words. The padding bytes SHOULD be sent as 0.

           iSCSI response PDUs do not have AH Segments.

   9.2.1  Basic Header Segment (BHS)

           The BHS is 48 bytes long.  The Opcode and DataSegmentLength fields
           appear in all iSCSI PDUs. In addition, when used, the Initiator Task
           Tag and Logical Unit Number always appear in the same location in the
           header.

           The format of the BHS is:





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           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| Opcode    | Opcode-specific fields                        |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Opcode-specific fields                                 |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag or Opcode-specific fields                  |
             +---------------+---------------+---------------+---------------+
           20/ Opcode-specific fields                                        /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48

   9.2.1.1  I

           For request PDUs, the I bit set to 1 is an immediate delivery marker.

   9.2.1.2  Opcode

           The Opcode indicates the type of iSCSI PDU the header encapsulates.

           The Opcodes are divided into two categories: initiator opcodes and
           target opcodes. Initiator opcodes are in PDUs sent by the initiators
           (request PDUs). Target opcodes are in PDUs sent by the target
           (response PDUs).

           Initiators MUST NOT use target opcodes and targets MUST NOT use initi-
           ator opcodes.

           Initiator opcodes defined in this specification are:


                 0x00 NOP-Out
                 0x01 SCSI Command (encapsulates a SCSI Command Descriptor Block)
                 0x02 SCSI Task Management Function Request
                 0x03 Login Command
                 0x04 Text request
                 0x05 SCSI Data-out (for WRITE operations)


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                 0x06 Logout Command
                 0x10 SNACK Request
                 0x1c-0x1e Vendor specific codes

           Target opcodes are:


                 0x20 NOP-In
                 0x21 SCSI Response -contains SCSI status and possibly sense
                      information or other response information.
                 0x22 SCSI Task Management Function Response
                 0x23 Login Response
                 0x24 Text Response
                 0x25 SCSI Data-in -for READ operations.
                 0x26 Logout Response
                 0x31 Ready To Transfer (R2T) - sent by target when it is ready
                      to receive data.
                 0x32 Asynchronous Message -sent by target to indicate certain
                      special conditions.
                 0x3c-0x3e Vendor specific codes
                 0x3f Reject

           All other opcodes are reserved.

   9.2.1.3  Opcode-specific Fields

           These fields have different meanings for different opcode types.

   9.2.1.4  TotalAHSLength

           Total length of all AHS header segments in four byte words including
           padding, if any.

           The TotalAHSLength is used only in PDUs that have an AHS and MUST be 0
           in all other PDUs.

   9.2.1.5  DataSegmentLength

           This is the data segment payload length in bytes (excluding padding).
           The DataSegmentLength MUST be 0 whenever the PDU has no data segment

   9.2.1.6  LUN

           Some opcodes operate on a specific Logical Unit. The Logical Unit Num-
           ber (LUN) field identifies which Logical Unit.  If the opcode does not
           relate to a Logical Unit, this field is either ignored or may be used
           in an opcode specific way.  The LUN field is 64-bits and should be

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           formatted in accordance with [SAM2] i.e., LUN[0] from [SAM2] is BHS
           byte 8 and so on up to LUN[8] from [SAM2] that is BHS byte 15..

   9.2.1.7  Initiator Task Tag

           The initiator assigns a Task Tag to each iSCSI task it issues. While a
           task exists, this tag MUST uniquely identify it session-wide.
           SCSI may also use the initiator task tag as part of the SCSI task
           identifier when the time span during which an iSCSI initiator task tag
           must be unique extends over the time span during which a SCSI task tag
           must be unique.  However, the iSCSI Initiator Task Tag has to exist
           and be unique even for untagged SCSI commands.

   9.2.2  Additional Header Segment (AHS)

           The general format of an AHS is:

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0| AHSLength                     | AHSType       | AHS-Specific  |
             +---------------+---------------+---------------+---------------+
            4/ AHS-Specific                                                  /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
            x

   9.2.2.1  AHSType

           The AHSType field is coded as follows:

                 bit 7-6 - Reserved

                 bit 5-0 - AHS code

                  0 - Reserved
                  1 - Extended CDB
                  2 - Expected Bidirectional Read Data Length
                  3 - 59 Reserved
                  60- 63 Non-iSCSI extensions





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   9.2.2.2  AHSLength

           This field contains the effective length in bytes of the AHS excluding
           AHSType and AHSLength (not including padding). The AHS is padded to
           the smallest integer number of 4 byte words (i.e., from 0 up to 3 pad-
           ding bytes).

   9.2.2.3  Extended CDB AHS

           The format of the Extended CDB AHS is:

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0| AHSLength (CDBLength-15)      | 0x01          | Reserved      |
             +---------------+---------------+---------------+---------------+
            4/ ExtendedCDB...+padding                                        /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
            x


   9.2.2.4  Bidirectional Expected Read-Data Length AHS

           The format of the Bidirectional Read Expected Data Transfer Length AHS
           is:

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0| AHSLength (0x0005)            | 0x02          | Reserved      |
             +---------------+---------------+---------------+---------------+
            4| Expected Read-Data Length                                     |
             +---------------+---------------+---------------+---------------+
            8

   9.2.3  Header Digest and Data Digest

           Optional header and data digests protect the integrity of the header
           and data, respectively. The digests, if present, are located, respec-
           tively, after the header and PDU-specific data and include the padding
           bytes.

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           The digest types are negotiated during the login phase.

           The separation of the header and data digests is useful in iSCSI rout-
           ing applications, where only the header changes when a message is for-
           warded. In this case, only the header digest should be re-calculated.

           Digests are not included in data or header length fields.

           A zero-length Data Segment also implies a zero-length data-digest.

   9.2.4  Data Segment

           The (optional) Data Segment contains PDU associated data. Its payload
           effective length is provided in the BHS field - DataSegmentLength. The
           Data Segment is also padded to an integer number of 4 byte words.





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   9.3  SCSI Command

           The format of the SCSI Command PDU is:

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| 0x01      |F|R|W|0 0|ATTR | Reserved      | CRN or Rsvd   |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| Logical Unit Number (LUN)                                     |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Expected Data Transfer Length                                 |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32/ SCSI Command Descriptor Block (CDB)                           /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| AHS (if any), Header Digest (if any)                          |
             +---------------+---------------+---------------+---------------+
             / (DataSegment - Command Data + Data Digest (if any))(optional) /
            +/                                                               /
             +---------------+---------------+---------------+---------------+


   9.3.1  Flags and Task Attributes (byte 1)

                 The flags for a SCSI Command are:

                 bit 7   (F) set to 1 when no unsolicited SCSI Data-Out PDUs fol-
                      low this PDU.  For a write, if Expected Data Transfer Length
                      is larger than the DataSegmentLength the target may solicit
                      additional data through R2T.

                 bit 6   (R) set to 1 when input data is expected.


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                 bit 5   (W) set to 1 when output data is expected.

                 bit 4-3 Reserved

                 bit 2-0 contains Task Attributes.

           Task Attributes (ATTR) have one of the following integer values (see
           [SAM2] for details):

                 0 - Untagged
                 1 - Simple
                 2 - Ordered
                 3 - Head of Queue
                 4 - ACA
                 5-7 - Reserved

           Setting both the W and the F bit to 0 is an error.
           The R and W MAY both be 1 when the corresponding Expected Data Trans-
           fer Lengths are 0, but they  CANNOT both be 0 when the corresponding
           Expected Data Transfer Lengths are not 0.


   9.3.2  CRN

           SCSI command reference number - if present in the SCSI execute command
           arguments (according to [SAM2]).

   9.3.3  CmdSN - Command Sequence Number

           Enables ordered delivery across multiple connections in a single ses-
           sion.

   9.3.4  ExpStatSN

           Command responses up to ExpStatSN-1 (mod 2**32) have been received
           (acknowledges status) on the connection.

   9.3.5  Expected Data Transfer Length

           For unidirectional operations, the Expected Data Transfer Length
           field contains the number of bytes of data involved in this SCSI oper-
           ation.  For a unidirectional write operation (W flag set to 1 and R
           flag set to 0), the initiator uses this field to specify the number of
           bytes of data it expects to transfer for this operation.  For a unidi-
           rectional read operation (W flag set to 0 and R flag set to 1), the
           initiator uses this field to specify the number of bytes of data it

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           expects the target to transfer to the initiator.  It corresponds to
           the SAM2 byte count.

           For bidirectional operations (both R and W flags are set to 1), this
           field contains the number of data bytes involved in the write trans-
           fer. For bidirectional operations, an additional header segment MUST
           be present in the header sequence that indicates the Bidirectional
           Read Expected Data Transfer Length.  The Expected Data Transfer Length
           field and the Bidirectional Read Expected Data Transfer Length field
           correspond to the SAM2 byte count

           If the Expected Data Transfer Length for a write and the length of the
           immediate data part that follows the command (if any) are the same,
           then no more data PDUs are expected to follow.  In this case, the F
           bit MUST be set to 1.

           If the Expected Data Transfer Length is higher than the FirstBurstSize
           (the negotiated maximum amount of unsolicited data the target will
           accept), the initiator SHOULD send the maximum size of unsolicited
           data.  The target MAY terminate a command in error for which the
           Expected Data Transfer Length is higher than the FirstBurstSize and
           for which the initiator sent less than the FirstBurstSize unsolicited
           data.

           Upon completion of a data transfer, the target informs the initiator
           (through residual counts) of how many bytes were actually processed
           (sent and/or received) by the target.

   9.3.6  CDB - SCSI Command Descriptor Block

           There are 16 bytes in the CDB field to accommodate the commonly used
           CDBs.  Whenever the CDB is larger than 16 bytes, an Extended CDB AHS
           MUST be used to contain the CDB spillover.

   9.3.7  Data Segment - Command Data

           Some SCSI commands require additional parameter data to accompany the
           SCSI command. This data may be placed beyond the boundary of the iSCSI
           header in a data segment.  Alternatively, user data (for example, from
           a WRITE operation) can be placed in the same PDU (both cases are
           referred to as immediate data). These data are governed by the general
           rules for solicited vs. unsolicited data.



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   9.4  SCSI Response

           The format of the SCSI Response PDU is:

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x21      |1 . .|o|u|O|U|.| Response      | Status        |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| Reserved                                                      |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| ExpDataSN or Reserved                                         |
             +---------------+---------------+---------------+---------------+
           40| Bidirectional Read Residual Count                             |
             +---------------+---------------+---------------+---------------+
           44| Residual Count                                                |
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / Data Segment (Optional)                                       /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

   9.4.1  Flags (byte 1)

                 bit 6-5 Reserved

                 bit 4 - (o) set for Bidirectional Read Residual Overflow. In
                      this case, the b Bidirectional Read Residual Count indicates

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                      the number of bytes that were not transferred to the initiator
                      because the initiator's Expected Bidirectional Read Data
                      Transfer Length was not sufficient.

                 bit 3 - (u) set for Bidirectional Read Residual Underflow. In
                      this case, the Bidirectional Read Residual Count indicates the
                      number of bytes that were not transferred to the initiator out
                      of the number of bytes expected to be transferred.

                 bit 2 - (O) set for Residual Overflow. In this case, the Resid-
                      ual Count indicates the number of bytes that were not trans-
                      ferred because the initiator's Expected Data Transfer length
                      was not sufficient. For a bidirectional operation, the Resid-
                      ual Count contains the residual for the write operation.

                 bit 1 - (U) set for Residual Underflow. In this case, the Resid-
                      ual Count indicates the number of bytes that were not trans-
                      ferred out of the number of bytes that expected to be
                      transferred. For a bidirectional operation, the Residual Count
                      contains the residual for the write operation.

                 bit 0 - (0) Reserved

           Bits O and U and bits o and u are mutually exclusive.
           For a response other than "Command Completed at Target" bit 4-1 MUST
           be 0.

   9.4.2  Status

           The Status field is used to report the SCSI status of the command (as
           specified in [SAM2]) and is valid only if the Response Code is Command
           Completed at target.

           Some of the status codes defined in [SAM2] are:

                 0x00 GOOD
                 0x02 CHECK CONDITION
                 0x08 BUSY
                 0x18 RESERVATION CONFLICT
                 0x28 TASK SET FULL
                 0x30 ACA ACTIVE
                 0x40 TASK ABORTED

           See [SAM2] for the complete list and definitions.

           If a SCSI device error is detected while data from the initiator is
           still expected (the command PDU did not contain all the data and the


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           target has not received a Data PDU with the final bit Set), the target
           MUST wait until it receives a Data PDU with the F bit set in the last
           expected sequence, before sending the Response PDU.

   9.4.3  Response

           This field contains the iSCSI service response.

           iSCSI service response codes defined in this specification are:

                 0x00 - Command Completed at Target
                 0x01 - Target Failure
                 0x80-0xff - Vendor specific

           The Response is used to report a Service Response. The exact mapping
           of the iSCSI response codes to SAM service response symbols is outside
           the scope of this document.

           Certain iSCSI conditions result in the command being terminated at the
           target (response Command Completed at Target) with a SCSI Check Condi-
           tion Status as outlined in the next table:

           +--------------------------+----------+---------------------------+
           | Reason                   |Sense     | Additional Sense Code &   |
           |                          |Key       | Qualifier                 |
           +--------------------------+----------+---------------------------+
           | Unexpected unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0c    |
           | data                     |Command-0B| Write Error               |
           +--------------------------+----------+---------------------------+
           | Not enough unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0d    |
           | data                     |Command-0B| Write Error               |
           +--------------------------+----------+---------------------------+
           | Protocol Service CRC     |Aborted   | ASC = 0x47 ASCQ = 0x05    |
           | error                    |Command-0B| CRC Error Detected        |
           +--------------------------+----------+---------------------------+
           | SNACK rejected           |Aborted   | ASC = 0x11 ASCQ = 0x13    |
           |                          |Command-0B| Read Error                |
           +--------------------------+----------+---------------------------+

           The target reports the "Not enough unsolicited data" condition only if
           it does not support output (write) operations in which the total data
           length is higher than FirstBurstSize, but the initiator sent less than
           FirstBurstSize amount of unsolicited data, and out-of-order R2Ts can-
           not be used.

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   9.4.4  Residual Count

           The Residual Count field is only valid in the case where either the U
           bit or the O bit is set. If neither bit is set, the Residual Count
           field SHOULD be zero. If the O bit is set, the Residual Count indi-
           cates the number of bytes that were not transferred because the initi-
           ator's Expected Data Transfer Length was not sufficient. If the U bit
           is set, the Residual Count indicates the number of bytes that were not
           transferred out of the number of bytes expected to be transferred.

   9.4.5  Bidirectional Read Residual Count

           The Bidirectional Read Residual Count field is only valid in the case
           where either the u bit or the o bit is set. If neither bit is set, the
           Bidirectional Read Residual Count field SHOULD be zero. If the o bit
           is set, the Bidirectional Read Residual Count indicates the number of
           bytes that were not transferred to the initiator because the initia-
           tor's Expected Bidirectional Read Transfer Length was not sufficient.
           If the u bit is set, the Bidirectional Read Residual Count indicates
           the number of bytes that were not transferred to the initiator out of
           the number of bytes expected to be transferred.

   9.4.6  Data Segment - Sense and Response Data Segment

           iSCSI targets MUST support and enable autosense.  If Status is CHECK
           CONDITION (0x02), then the Data Segment contains sense data for the
           failed command.

           For some iSCSI responses, the response data segment MAY contain some
           response related information, (e.g., for a target failure, it may con-
           tain a vendor specific detailed description of the failure).

           If the DataSegmentLength is not 0, the format of the Data Segment is
           as follows:





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           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|SenseLength                    | Sense Data                    |
             +---------------+---------------+---------------+---------------+
            x/ Sense Data                                                    /
             +---------------+---------------+---------------+---------------+
            y/ Response Data                                                 /
             /                                                               /
             +---------------+---------------+---------------+---------------+
            z|

   9.4.6.1  SenseLength

           Length of Sense Data.

   9.4.7  ExpDataSN

           The number of Data-In (read) PDUs the target has sent for the command.

           This field is reserved if the response code is not Command Completed
           at Target or the command is a write command.

   9.4.8  StatSN - Status Sequence Number

           StatSN is a Sequence Number that the target iSCSI layer generates per
           connection and that in turn, enables the initiator to acknowledge sta-
           tus reception. StatSN is incremented by 1 for every response/status
           sent on a connection except for responses sent as a result of a retry
           or SNACK.  In the case of responses sent due to a retransmission
           request, the StatSN MUST be the same as the first time the PDU was
           sent unless the connection has since been restarted.

   9.4.9  ExpCmdSN - Next Expected CmdSN from this Initiator

           ExpCmdSN is a Sequence Number that the target iSCSI returns to the
           initiator to acknowledge command reception. It is used to update a
           local register with the same name. An ExpCmdSN equal to MaxCmdSN+1
           indicates that the target cannot accept new commands.





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   9.4.10  MaxCmdSN - Maximum CmdSN from this Initiator

           MaxCmdSN is a Sequence Number that the target iSCSI returns to the
           initiator to indicate the maximum CmdSN the initiator can send. It is
           used to update a local register with the same name. If MaxCmdSN is
           equal to ExpCmdSN-1, this indicates to the initiator that the target
           cannot receive any additional commands.  When MaxCmdSN changes at the
           target while the target has no pending PDUs to convey this information
           to the initiator, it MUST generate a NOP-IN to carry the new MaxCmdSN.





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   9.5  Task Management Function Request

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| x02       |1| Function    | Reserved                      |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| Logical Unit Number (LUN) or Reserved                         |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Referenced Task Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32| RefCmdSN or ExpDataSN                                         |
             +---------------+---------------+---------------+---------------+
           36/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48

   9.5.1  Function

           The Task Management functions provide an initiator with a way to
           explicitly control the execution of one or more Tasks (SCSI and iSCSI
           tasks). The Task Management functions are listed below. For a more
           detailed description of SCSI task management, see [SAM2].

                 1    ABORT TASK - aborts the task identified by the Referenced
                      Task Tag field.

                 2    ABORT TASK SET - aborts all Tasks issued via this session
                      on the logical unit.

                 3    CLEAR ACA - clears the Auto Contingent Allegiance condi-
                      tion.


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                 4    CLEAR TASK SET - aborts all Tasks for the Logical Unit.

                 5    LOGICAL UNIT RESET

                 6    TARGET WARM RESET

                 7    TARGET COLD RESET

                 8    TASK REASSIGN - reassigns connection allegiance for the
                      task identified by the Initiator Task Tag field to this con-
                      nection, thus resuming the iSCSI exchanges for the task.

           For all these functions, the Task Management Function Response MUST be
           returned as detailed in Section 9.6 Task Management Function
           Response. All these functions apply to the referenced tasks regard-
           less of whether they are proper SCSI tasks or tagged iSCSI operations.
           Task management requests must act on all the commands having a CmdSN
           lower than the task management CmdSN. If the task management request
           is marked for immediate delivery it must be considered immediately for
           execution but the operations involved (all or part of them) may be
           postponed to allow the target to receive all relevant tasks. According
           to [SAM2] for all the tasks covered by the task management response
           (i.e., with CmdSN not higher than the task management command CmdSN),
           additional responses MUST NOT be delivered to the SCSI layer after the
           task management response. The iSCSI initiator MAY deliver to the SCSI
           layer all responses received before the task management response
           (i.e., it is a matter of implementation if the SCSI responses -
           received before the task management response but after the task man-
           agement request was issued - are delivered to the SCSI layer by the
           iSCSI layer in the initiator). The iSCSI target MUST ensure that no
           responses for the tasks covered by a task management function are
           delivered to the iSCSI initiator after the task management response.

           For ABORT TASK SET and CLEAR TASK SET, the issuing initiator MUST con-
           tinue to respond to all valid target transfer tags (received via R2T,
           Text Response, NOP-In, or SCSI Data-in PDUs) related to the affected
           task set, even after issuing the task management request.  The issuing
           initiator SHOULD however terminate (i.e. by setting the F-bit to 1)
           these response sequences as quickly as possible, and it is recommended
           to terminate all responses with no data.  The target on its part, MUST
           wait for responses on all affected target transfer tags before acting
           on either of these two task management requests.

           If the connection is still active (it is not undergoing an implicit or
           explicit logout), ABORT TASK MUST be issued on the same connection to

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           which the task to be aborted is allegiant at the time the Task Manage-
           ment Request is issued. If the connection is being implicitly or
           explicitly logged out (i.e., no other request will be issued on the
           failing connection and no other response will be received on the fail-
           ing connection), then an ABORT TASK function request may be issued on
           another connection. This Task Management request will then establish
           a new allegiance for the command to be aborted as well as abort it
           (i.e., the task to be aborted will not have to be retried or reas-
           signed, and its status, if issued but not acknowledged, will be reis-
           sued followed by the task management response).

           For the LOGICAL UNIT RESET function, the target MUST behave as dic-
           tated by the Logical Unit Reset function in [SAM2].

           The TARGET RESET function (WARM and COLD) implementation is OPTIONAL
           and when implemented, should act as described below. Target Reset MAY
           also be subject to SCSI access controls for the requesting initiator.
           When authorization fails at the target, the appropriate response as
           described in Section 9.6 Task Management Function Response must be
           returned by the target.

           For the TARGET WARM RESET and TARGET COLD RESET functions, the target
           cancels all pending operations. Both functions are equivalent to the
           Target Reset function specified by [SAM2]. They can affect many other
           initiators.

           In addition, for the TARGET COLD RESET, the target MUST then terminate
           all of its TCP connections to all initiators (all sessions are termi-
           nated).

           For the TASK REASSIGN function, the target should reassign the connec-
           tion allegiance to this new connection (and thus resume iSCSI
           exchanges for the task). TASK REASSIGN MUST be received by the target
           ONLY after the connection on which the command was previously execut-
           ing has been successfully logged-out. For additional usage semantics
           see Section 6.1 Retry and Reassign in Recovery.


           TASK REASSIGN MUST be issued as an immediate command.





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   9.5.2  LUN

           This field is required for functions that address a specific LU (ABORT
           TASK, CLEAR TASK SET, ABORT TASK SET, CLEAR ACA, LOGICAL UNIT RESET)
           and is reserved in all others.

   9.5.3  Referenced Task Tag

           The Initiator Task Tag of the task to be aborted for the ABORT TASK
           function or reassigned for the TASK REASSIGN function.
           For all the other functions this field is reserved.

   9.5.4  RefCmdSN or ExpDataSN

           For ABORT TASK, this is the task CmdSN of the task to be aborted. If
           RefCmdSN does not match the CmdSN of the command to be aborted at the
           target, the abort action MUST NOT be performed and the response MUST
           be ‚ÇÖfunction rejected‚ÇÖ.

           If the function is TASK REASSIGN, which establishes a new connection
           allegiance for a previously issued Read or Bidirectional command,
           this field will contain the next consecutive input DataSN number
           expected by the initiator (no gaps) for the referenced command in a
           previous execution. The initiator MUST discard any discontiguous data
           PDUs from the previous execution and the target MUST retransmit all
           data previously transmitted in Data-in PDUs (if any) starting with
           ExpDataSN.  The number of retransmitted PDUs, may or may not be the
           same as the original transmission, depending on if there was a change
           in MaxRecvPDULength in the reassignment.


           Otherwise, this field is reserved.





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   9.6  Task Management Function Response


           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x22      |1| Reserved    | Response      | Reserved      |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------------------------------------------------------+
            8/ Reserved                                                      /
             /                                                               /
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Referenced Task Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digest (if any)                                               |
             +---------------------------------------------------------------+

           For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
           SET, LOGICAL UNIT RESET, and TARGET WARM RESET, the target performs
           the requested Task Management function and sends a Task Management
           Response back to the initiator.

   9.6.1  Response

           The target provides a Response, which may take on the following val-
           ues:

                  a)    0 - Function Complete
                  b)    1 - Task does not exist
                  c)    2 - LUN does not exist.
                  d)    3 - Task still allegiant.

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                  e)    4 - Task failover not supported.
                  f)    5 - Task management function not supported.
                  g)    6 - Function authorization failed.
                  h)  255 - Function Rejected.

           All other values are reserved.

           For a discussion on usage of response codes 3 and 4, see Section 6.1.2
           Allegiance Reassignment.

           For the TARGET COLD RESET and TARGET WARM RESET functions, the target
           cancels all pending operations.  For the TARGET COLD RESET function,
           the target MUST then close all of its TCP connections to all initia-
           tors (terminates all sessions).

           The mapping of the response code into a SCSI service response code, if
           needed, is outside the scope of this document.

           The response to ABORT TASK SET and CLEAR TASK SET MUST be issued by
           the target only after all the commands affected have been received by
           the target, the corresponding task management functions have been
           executed by the SCSI target and the delivery of all responses deliv-
           ered until the task management function completion have been con-
           firmed (acknowledged through ExpStatSN) by the initiator on all
           connections of this session.  For the exact timeline of events, refer
           Section 9.6.3 Task Management actions on task sets.

   9.6.2  Referenced Task Tag

           If the Request was ABORT TASK and the Response is "task does not
           exist", the Referenced Task Tag contains the Initiator Task Tag of the
           task that was to be aborted. In other cases, it MUST be set to
           0xffffffff.

   9.6.3  Task Management actions on task sets

           The execution of ABORT TASK SET and CLEAR TASK SET task management
           function requests consists of the following sequence of events in the
           specified order on each of the entities.

           The initiator:

                         a)  issues ABORT TASK SET/CLEAR TASK SET request.


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                         b)  continues to respond to each target transfer tag received
                                  for the affected task set.
                         c)  receives any responses for the tasks in the affected task
                                  set (may process them as usual since they are guaranteed to
                                  be valid).
                         d)  receives the task set management response, thus concluding
                                  all the tasks in the affected task set.

           The target:

                         a)  receives the ABORT TASK SET/CLEAR TASK SET request.
                         b)  waits for all target transfer tags to be responded and also
                                  for all affected tasks in the task set to be received.
                         c)  propagates the command up to and receives the response from
                                  the target SCSI layer.
                         d)  takes note of last-sent StatSN on each of the connections in
                                  the session, and waits for acknowledgement of each StatSN
                                  (may solicit for acknowledgement by way of a NOP-In).
                         e)  sends the task set management response.





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   9.7  SCSI Data-out & SCSI Data-in

           The SCSI Data-out PDU for WRITE operations has the following format:


           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x05      |F| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           36| DataSN                                                        |
             +---------------+---------------+---------------+---------------+
           40| Buffer Offset                                                 |
             +---------------+---------------+---------------+---------------+
           44| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment                                                   /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

           The SCSI Data-in PDU for READ operations has the following format:





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           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x25      |F|A|0 0 0|O|U|S| Reserved      |Status or Rsvd |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| StatSN or Reserved                                            |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| DataSN                                                        |
             +---------------+---------------+---------------+---------------+
           40| Buffer Offset                                                 |
             +---------------+---------------+---------------+---------------+
           44| Residual Count                                                |
             +---------------+---------------+---------------+---------------+
           48| Header Digest (if any)                                        |
             +---------------+---------------+---------------+---------------+
             / DataSegment (and digest if any)                               /
            +/                                                               /
             +---------------+---------------+---------------+---------------+


           Status can accompany the last Data-in PDU if the command did not end
           with an exception (i.e., the status is "good status" - GOOD, CONDITION
           MET or INTERMEDIATE CONDITION MET).  The presence of status (and of a
           residual count) is signaled though the S flag bit.  Although targets
           MAY choose to send even non-exception status in separate responses,
           initiators MUST support non-exception status in Data-In PDUs.



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   9.7.1  F (Final) Bit

           For outgoing data, this bit is 1 for the last PDU of unsolicited data
           or the last PDU of a sequence that answers an R2T.

           For incoming data, this bit is 1 for the last input (read) data PDU of
           a sequence.  Input can be split into several sequences, each having
           its own F bit. Splitting the data stream into sequences does not
           affect DataSN counting on Data-In PDUs. It MAY be used as a "change
           direction" indication for Bidirectional operations that need such a
           change.

           For Bidirectional operations, the F bit is 1 for both the end of the
           input sequences as well as the end of the output sequences.

   9.7.2  A (Acknowledge) bit

           For sessions with ErrorRecoveryLevel 1 or higher, the target sets this
           bit to 1 to indicate that it requests a positive acknowledgement from
           the initiator for the data received.  The target should use the A bit
           moderately; it MAY set the A bit to 1 only once every MaxBurstSize
           bytes and MUST NOT do so more frequently than this.

           On receiving a Data-In PDU with the A bit set to 1, the initiator MUST
           issue a SNACK of type DataACK.  If the initiator has detected holes in
           the input sequence, it MUST postpone issuing the SNACK of type DataACK
           until the holes are filled.

   9.7.3  Target Transfer Tag

           On outgoing data, the Target Transfer Tag is provided to the target if
           the transfer is honoring an R2T. In this case, the Target Transfer Tag
           field is a replica of the Target Transfer Tag provided with the R2T.

           On incoming data, the Target Transfer Tag MUST be provided by the tar-
           get if the A bit is set to 1. The Target Transfer Tag and LUN are cop-
           ied by the initiator in the SNACK of  type DataACK that it issues as a
           result of receiving a SCSI Data-in PDU with the A bit set to 1.

           The Target Transfer Tag values are not specified by this protocol
           except that the value 0xffffffff is reserved and means that the Target
           Transfer Tag is not supplied.  If the Target Transfer Tag is provided,
           then the LUN field MUST hold a valid value and be consistent with


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           whatever was specified with the command; otherwise, the LUN field is
           reserved.

   9.7.4  StatSN

           This field MUST ONLY be set if the S bit is set to 1.

   9.7.5  DataSN

           For input (read) data PDUs, the DataSN is the data PDU number (start-
           ing with 0) within the data transfer for the command identified by the
           Initiator Task Tag.

           For output (write) data PDUs, the DataSN is the data PDU number
           (starting with 0) within the current output sequence. The current out-
           put sequence is either identified by the Initiator Task Tag (for unso-
           licited data) or is a data sequence generated for one R2T (for data
           solicited through R2T).

           Any input or output data sequence MUST contain less than 2**32 num-
           bered PDUs.


   9.7.6  Buffer Offset

           The Buffer Offset field contains the offset of this PDU payload data
           within the complete data transfer. The sum of the buffer offset and
           length should not exceed the expected transfer length for the command.

           The order of data PDUs within a sequence is determined by DataPDUInOr-
           der. When set to Yes, it means that PDUs have to be in increasing
           Buffer Offset order and overlays are forbidden.

           The ordering between sequences is determined by DataSequenceInOrder.
           When set to Yes, it means that sequences have to be in increasing
           Buffer Offset order and overlays are forbidden.

   9.7.7  DataSegmentLength

           This is the data payload length of a SCSI Data-In or SCSI Data-Out
           PDU. The sending of 0 length data segments should be avoided, but ini-
           tiators and targets MUST be able to properly receive 0 length data
           segments.


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           The Data Segments of Data-in and Data-out PDUs SHOULD be filled to the
           integer number of 4 byte words (real payload) unless the F bit is set
           to 1.

   9.7.8  Flags (byte 1)

           The last SCSI Data packet sent from a target to an initiator for a
           SCSI command that completed successfully (with a status of GOOD, CON-
           DITION MET, INTERMEDIATE or INTERMEDIATE CONDITION MET) may also
           optionally contain the Status for the data transfer.  In this case,
           Sense Data cannot be sent together with the Command Status.  If the
           command is completed with an error, then the response and sense data
           MUST be sent in a SCSI Response PDU (i.e., MUST NOT be sent in a SCSI
           Data packet). For Bidirectional commands, the status MUST be sent in a
           SCSI Response PDU.

                 bit 3-5 - not used (should be set to 0).

                 bit 1-2 - used the same as in a SCSI Response.

                 bit 0 S (status)- set to indicate that the Command Status field
                      contains status. If this bit is set to 1 the F bit MUST also
                      be set to 1.


           The fields StatSN, Status and Residual Count have meaningful content
           only if the S bit is set to 1 and they values are as define in Section
           9.4 SCSI Response.





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   9.8  Ready To Transfer (R2T)

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x31      |1| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag                                           |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| R2TSN                                                         |
             +---------------+---------------+---------------+---------------+
           40| Buffer Offset                                                 |
             +---------------+---------------+---------------+---------------+
           44| Desired Data Transfer Length                                  |
             +---------------------------------------------------------------+
           48| Digest (if any)                                               |
             +---------------------------------------------------------------+


           When an initiator has submitted a SCSI Command with data that passes
           from the initiator to the target (WRITE), the target may specify which
           blocks of data it is ready to receive. The target may request that the
           data blocks be delivered in whichever order is convenient for the tar-
           get at that particular instant. This information is passed from the
           target to the initiator in the Ready To Transfer (R2T) PDU.

           In order to allow write operations without an explicit initial R2T,
           the initiator and target MUST have agreed by sending the InitialR2T=No


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                                                                  iSCSI            1-March-02

           key-pair to each other, which occurs either during Login or through
           the Text request/Response mechanism.

           An R2T MAY be answered with one or more SCSI Data-out PDUs with a
           matching Target Transfer Tag. If an R2T is answered with a single
           Data-out PDU, the Buffer Offset in the Data PDU MUST be the same as
           the one specified by the R2T. The data length of the Data PDU MUST not
           exceed the Desired Data Transfer Length specified in the R2T. If the
           R2T is answered with a sequence of Data PDUs, the Buffer Offset and
           Length MUST be within the range of those specified by R2T, and the
           last PDU SHOULD have the F bit set to 1. If the last PDU (marked with
           the F bit) is received before the Desired Data Transfer Length is
           transferred, a target MAY choose to Reject that PDU with "Protocol
           error" reason code.  DataPDUInOrder governs the Data-Out PDU order-
           ing. If DataPDUInOrder is set to Yes, the Buffer Offsets and Lengths
           for consecutive PDUs MUST form a continuous non-overlapping range and
           the PDUs MUST be sent in increasing offset order.

           The target may send several R2T PDUs (up to a negotiated number).  It,
           therefore, can have a number of pending data transfers.  Within a con-
           nection, outstanding R2Ts MUST be fulfilled by the initiator in the
           order in which they were received.

           DataSequenceInOrder governs the buffer offset ordering in consecutive
           R2Ts. If DataSequenceInOrder is Yes, then consecutive R2Ts SHOULD
           refer to continuous non-overlapping ranges.

   9.8.1  R2TSN

           R2TSN is the R2T PDU number (starting with 0) within the command iden-
           tified by the Initiator Task Tag.

           The number of R2Ts in a command MUST be less than 2**32-1.

   9.8.2  StatSN

           The StatSN field will contain the next StatSN. The StatSN for this
           connection is not advanced.

   9.8.3  Desired Data Transfer Length and Buffer Offset

           The target specifies how many bytes it wants the initiator to send
           because of this R2T PDU.  The target may request the data from the
           initiator in several chunks, not necessarily in the original order of

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                                                                  iSCSI            1-March-02

           the data.  The target, therefore, also specifies a Buffer Offset that
           indicates the point at which the data transfer should begin, relative
           to the beginning of the total data transfer. The Desired Data Transfer
           Length SHOULD not be 0 and MUST not exceed MaxBurstSize.

   9.8.4  Target Transfer Tag

           The target assigns its own tag to each R2T request that it sends to
           the initiator. This tag can be used by the target to easily identify
           the data it receives.  The Target Transfer Tag and LUN are copied in
           the outgoing data PDUs and are used by the target only. There is no
           protocol rule about the Target Transfer Tag, but it is assumed that it
           is used to tag the response data to the target (alone or in combina-
           tion with the LUN).





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   9.9  Asynchronous Message

           An Asynchronous Message may be sent from the target to the initiator
           without corresponding to a particular command. The target specifies
           the reason for the event and sense data.

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x32      |1| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN                                                           |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Reserved - 0xffffffff                                         |
             +---------------+---------------+---------------+---------------+
           20| Reserved                             |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| AsyncEvent    | AsyncVCode    | Parameter1 or Reserved        |
             +---------------+---------------+---------------+---------------+
           40| Parameter2 or Reserved        | Parameter3 or Reserved        |
             +---------------+---------------+---------------+---------------+
           44| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment - Sense Data or iSCSI Event Data                  /
            +/                                                               /
             +---------------+---------------+---------------+---------------+


           Some Asynchronous Messages are strictly related to iSCSI while others
           are related to SCSI [SAM2].


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           StatSN counts this PDU as an acknowledgeable event (StatSN is
           advanced), which allows for initiator and target state synchroniza-
           tion.

   9.9.1  AsyncEvent

           The codes used for iSCSI Asynchronous Messages (Events) are:

                 0 - a SCSI Asynchronous Event is reported in the sense data.
                      Sense Data that accompanies the report, in the data segment,
                      identifies the condition. The sending of a SCSI Event (Asyn-
                      chronous Event Notification in SCSI terminology) is controlled
                      by a SCSI Control Mode Page bit.

                 1 - target requests Logout. This Async Message MUST be sent on
                      the same connection as the one requesting to be logged out.
                      The initiator MUST honor this request by issuing a Logout as
                      early as possible, but no later than Parameter3 seconds.
                      Initiator MUST send a Logout with a reason code of "Close the
                  connection" (if not the only connection) OR "Close the session"
                  (if using multiple connections). Once this message is received,
                      the initiator SHOULD NOT issue new iSCSI commands.  The target
                      MAY reject any new I/O requests that it receives after this
                      Message with the reason code "Waiting for Logout".  If the
                      initiator does not Logout in Parameter3 seconds, the target
                      should send an Async PDU with iSCSI event code "Dropped the
                      connection" if possible, or simply terminate the transport
                      connection. Parameter1 and Parameter2 are reserved.

                 2 - target indicates it will drop the connection.
                      The Parameter1 field indicates the CID of the connection going
                      to be dropped.
                      The Parameter2 field (Time2Wait) indicates, in seconds, the
                      minimum time to wait before attempting to reconnect or reas-
                      sign.
                      The Parameter3 field (Time2Retain) indicates the maximum time
                      allowed to reconnect and/or reassign commands after the ini-
                      tial wait (in Parameter2).
                      If the initiator does not attempt to reconnect and/or reassign
                      the outstanding commands within the time specified by
                      Parameter3, or if Parameter3 is 0, the target will terminate
                      all outstanding commands on this connection; no other
                      responses should be expected from the target for the outstand-
                      ing commands on this connection in this case.
                      A value of 0 for Parameter2 indicates that reconnect can be
                      attempted immediately.



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                 3 - target indicates it will drop all the connections of this
                      session.
                      Parameter1 field is reserved.
                      The Parameter2 field (Time2Wait) indicates, in seconds, the
                      minimum time to wait before attempting to reconnect.
                      The Parameter3 field (Time2Retain) indicates the maximum time
                      allowed to reconnect and/or reassign commands after the ini-
                      tial wait (in Parameter2).
                      If the initiator does not attempt to reconnect and/or reassign
                      the outstanding commands within the time specified by
                      Parameter3, or if Parameter3 is 0, the session is terminated.
                      In this case, the target will terminate all outstanding com-
                      mands in this session; no other responses should be expected
                      from the target for the outstanding commands in this session.
                      A value of 0 for Parameter2 indicates that reconnect can be
                      attempted immediately.

                 255 - vendor specific iSCSI Event. The AsyncVCode details the
                      vendor code, and data MAY accompany the report.

           All other event codes are reserved.

   9.9.2  AsyncVCode

           AsyncVCode is a vendor specific detail code that is valid only if the
           AsyncEvent field indicates a vendor specific event. Otherwise, it is
           reserved.

   9.9.3  Sense Data or iSCSI Event Data

           For a SCSI Event, this data accompanies the report in the data segment
           and identifies the condition.

           For an iSCSI Event, additional vendor-unique data MAY accompany the
           Async event.  Initiators MAY ignore the data when not understood while
           processing the rest of the PDU.





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   9.10  Text Request

           The Text Request is provided to allow for the exchange of information
           and for future extensions. It permits the initiator to inform a target
           of its capabilities or to request some special operations.

           An initiator MUST have only one outstanding Text Request on a connec-
           tion at any given time.

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| 0x04      |F| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digests if any                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment (Text)                                            /
            +/                                                               /
             +---------------+---------------+---------------+---------------+


   9.10.1  F (Final) Bit

           When set to 1,  indicates that this is the last or only text request
           in a sequence of commands; otherwise, it indicates that more commands
           will follow.

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   9.10.2  Initiator Task Tag

           The initiator assigned identifier for this Text Request.
           If the command is sent as part of a sequence of text requests and
           responses, the Initiator Task Tag MUST be the same for all the
           requests within the sequence (similar to linked SCSI commands).

   9.10.3  Target Transfer Tag

           When the Target Transfer Tag is set to the reserved value 0xffffffff,
           it tells the target that this is a new request and the target should
           reset any internal state associated with the Initiator Task Tag.

           The target sets the Target Transfer Tag in a text response to a value
           other than the reserved value 0xffffffff whenever it indicates that it
           has more data to send or more operations to perform that are associ-
           ated with the specified Initiator Task Tag. It MUST do so whenever it
           sets the F bit to 0 in the response. By copying the Target Transfer
           Tag from the response to the next Text Request, the initiator tells
           the target to continue the operation for the specific Initiator Task
           Tag. The initiator MUST ignore the Target Transfer Tag in the Text
           Response when the F bit is set to 1.

           This mechanism allows the initiator and target to transfer a large
           amount of textual data over a sequence of text-command/text-response
           exchanges or to perform extended negotiation sequences.

           If the Target Transfer Tag is not 0xffffffff the LUN field must be the
           one sent by the target in the Text Response.

           A target MAY reset its internal state if an exchange is stalled by the
           initiator for a long time or if it is running out of resources.

           Long text responses are handled as in the following example:

                 I->T Text SendTargets=all (F=1,TTT=0xffffffff)
                 T->I Text <part 1> (F=0,TTT=0x12345678)
                 I->T Text <empty> (F=1, TTT=0x12345678)
                 T->I Text <part 2> (F=0, TTT=0x12345678)
                 I->T Text <empty> (F=1, TTT=0x12345678)
                 ...
                 T->I Text <part n> (F=1, TTT=0xffffffff)



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   9.10.4  Text

           The data lengths of a text request MUST NOT exceed the iSCSI target
           MaxRecvPDULength (a per connection and per direction negotiated
           parameter).  The text format is specified in Section 4.2 Text Mode
           Negotiation.

           Chapter 10 and Chapter 11 list some basic Text key=value pairs, some
           of which can be used in Login Request/Response and some in Text
           Request/Response.

           A Key=value pair can span Text request or response boundaries (i.e., a
           key=value pair can start in one PDU and continue on the next).

           The target responds by sending its response back to the initiator. The
           response text format is similar to the request text format.

           As text for text requests and responses can span several PDUs (e.g.,
           if the PDU length does not allow the whole text to be contained in a
           single PDU), the text response MAY refer to key=value pairs presented
           in an earlier text request and the text in the request may refer to
           earlier responses.

           Text operations are usually meant for parameter setting/negotiations,
           but can also be used to perform some long lasting operations.

           Text operations that take a long time should be placed in their own
           Text request.





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   9.11  Text Response

           The Text Response PDU contains the target's responses to the initia-
           tor's Text request. The format of the Text field matches that of the
           Text request.

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x24      |F| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment (Text)                                            /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

   9.11.1  F (Final) Bit

           When set to 1, in response to a text request with the Final bit set to
           1, the F bit indicates that the target has finished the whole opera-
           tion.  Otherwise, if set to 0 in response to a text request with the
           Final Bit set to 1, it indicates that the target has more work to do
           (invites a follow-on text request).  A text response with the F bit

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           set to 1 in response to a text request with the F bit set to 0 is a
           protocol error.

           A text response with the F bit set to 1 MUST NOT contain key=value
           pairs that may require additional answers from the initiator.

           A text response with the F bit set to 1 MUST have a Target Transfer
           Tag field set to the reserved value of 0xffffffff.

           A text response with the F bit set to 0 MUST have a Target Transfer
           Tag field set to a value other than the reserved 0xffffffff.

   9.11.2  Initiator Task Tag

           The Initiator Task Tag matches the tag used in the initial Text
           request.

   9.11.3  Target Transfer Tag

           When a target has more work to do (e.g., cannot transfer all the
           remaining text data in a single Text response or has to continue the
           negotiation) and has enough resources to proceed, it MUST set the Tar-
           get Transfer Tag to a value other than the reserved value of
           0xffffffff.  Otherwise the Target Transfer Tag MUST be set to
           0xffffffff.

           When the Target Transfer Tag is not 0xffffffff the LUN field may be
           significant.

           The initiator MUST copy the Target Transfer Tag and LUN in its next
           request to indicate that it wants the rest of the data.

           If the target receives a Text Request with the Target Transfer Tag set
           to the reserved value of 0xffffffff, it discards its internal informa-
           tion (resets state) associated with the given Initiator Task Tag.

           When a target cannot finish the operation in a single text response,
           and does not have enough resources to continue it rejects the Text
           request with the appropriate Reject code. A target may reset its
           internal state associated with an Initiator Task Tag, state expressed
           through the Target Transfer Tag if the initiator fails to continue the
           exchange for some time. The target may reject subsequent Text requests
           with the Target Transfer Tag set to the "stale" value.


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   9.11.4  Text Response Data

           The data lengths of a text response MUST NOT exceed the iSCSI initia-
           tor MaxRecvPDULength (a per connection and per direction negotiated
           parameter).  The text format is specified in Section 4.2 Text Mode
           Negotiation.

           Chapter 10 and Chapter 11 list some basic Text key=value pairs, some
           of which can be used in Login Request/Response and some in Text
           Request/Response.

           As text for text requests and responses can span several PDUs (e.g.,
           if the PDU length does not allow the whole text to be contained in a
           single PDU) the text response MAY refer to key=value pairs presented
           in an earlier text request.

           Although the initiator is the requesting party and controls the
           request-response initiation and termination, the target can offer
           key=value pairs of its own as part of a sequence and not only in
           response to the initiator.





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   9.12  Login Request

           After establishing a TCP connection between an initiator and a target,
           the initiator MUST start a Login phase to gain further access to the
           target's resources.

           The Login Phase (see Chapter 4) consists of a sequence of Login
           requests and responses that carry the same Initiator Task Tag.

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x03      |T|0|0 0|CSG|NSG| Version-max   | Version-min   |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| ISID                                                          |
             +                               +---------------+---------------+
           12|                               |TSID                           |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| CID                           | Reserved                      |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN   or   Reserved                                     |
             +---------------+---------------+---------------+---------------+
           32| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           36| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           40/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48/ DataSegment - Login Parameters in Text request Format         /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

   9.12.1  T (Transit) Bit

           If set to 1, indicates that the initiator is ready to transit to the
           next stage.

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           If the T bit is set to 1 and NSG is FullFeaturePhase, then this also
           indicates that the initiator is ready for the Final Login Response
           (see Chapter 4).

   9.12.2  CSG and NSG

           Through these fields, Current Stage (CSG) and Next Stage (NSG), the
           Login negotiation commands and responses are associated with a spe-
           cific stage in the session (SecurityNegotiation, LoginOperationalNe-
           gotiation, FullFeaturePhase) and may indicate the next stage they
           want to move to (see Chapter 4).
           The next stage value is valid only when the T bit is 1; otherwise, it
           is reserved.

           The stage codes are:

                 - 0 - SecurityNegotiation
                 - 1 - LoginOperationalNegotiation
                 - 3 - FullFeaturePhase

   9.12.3  Version-max

           Maximum Version number supported.

           All Login requests within the Login phase MUST carry the same Version-
           max.

           The target MUST use the value presented with the first login request.

   9.12.4  Version-min

           Minimum Version supported. The version number of the current draft is
           0x00.

           All Login requests within the Login phase MUST carry the same Version-
           min. The target MUST use the value presented with the first login
           request.

   9.12.5  ISID

           This is an initiator-defined component of the session identifier
           (SSID) and is structured as follows (see [NDT] and Section 8.1.1 Con-
           servative Reuse of ISIDs for details):


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           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0| T |    A      |               B               |      C        |
             +---------------+---------------+---------------+---------------+
            4|               D               |
             +---------------+---------------+

           The T field identifies the format and usage of A, B, C & D as indi-
           cated bellow:

                 T

                 00b     OUI-format
                         A&B are a 22 bit OUI
                         (the I/G & U/L omitted)
                         C&D 24 bit qualifier
                 01b     EN - format (IANA Enterprise Number)
                         A - reserved
                         B&C EN (IANA Enterprise Number)
                         D - Qualifier
                 10b     "Random"
                         A - reserved
                         B&C Random
                         D - Qualifier
                 11b     A,B,C&D Reserved

           For the T field values 00b and 01b a combination of A and B (for 00b)
           or B and C (for 01b) identifies the vendor or organization whose com-
           ponent (software or hardware) generates this ISID.  A vendor or orga-
           nization with one or more OUIs, or one or more Enterprise Numbers,
           MUST use at least one of these numbers and select the appropriate
           value for the T field when its components generate ISIDs.  An OUI or
           EN MUST be set in the corresponding fields in network byte order (byte
           big-endian).

           If the T field is 10b, B and C are set to a random  24bit unsigned
           integer value in network byte order (byte big-endian).  See [NDT] for
           how this affects the principle of "conservative reuse".

           The Qualifier field is a 16 or 24 bit unsigned integer value that pro-
           vides a range of possible values for the ISID within the selected
           namespace. It may be set to any value, within the constraints speci-


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                                                                  iSCSI            1-March-02

           fied in the iSCSI protocol (see Section 2.4.3 Consequences of the
           Model and Section 8.1.1 Conservative Reuse of ISIDs).

           The T field of 11 is reserved.

           If the ISID is derived from something assigned to a hardware adapter
           or interface by a vendor, as a preset default value, it MUST be con-
           figurable to a value assigned according to the SCSI port behavior
           desired by the system in which it is installed (see Section 8.1.1 Con-
           servative Reuse of ISIDs and Section 8.1.2 iSCSI Name and ISID/TSID
           Use) and the resultant ISID MUST also be persistent over power cycles,
           reboot, card swap etc..

   9.12.6  TSID

           The TSID is the target assigned component of the session identifier
           (SSID).  Together with the ISID, provided by the initiator, TSID
           uniquely identifies the session from that specific target with that
           initiator.

           On a Login request, a TSID value of 0 indicates a request to open a
           new session.

           A non-zero TSID indicates a request to add a connection to an existing
           session.

   9.12.7  Connection ID - CID

           A unique ID for this connection within the session.

           All Login requests within the Login phase MUST carry the same CID.

           The target MUST use the value presented with the first login request.

           A Login request with a non-zero TSID and a CID equal to that of an
           existing connection implies a logout of the connection followed by a
           Login (see Section 4.3.4 Connection reinstatement).

   9.12.8  CmdSN

           CmdSN is either the initial command sequence number of a session (for
           the first Login request of a session - the "leading" login) or the
           command sequence number in the command stream (e.g., if the leading


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           login carries the CmdSN 123 all other Login requests carry the CmdSN
           123 and the first non-immediate command also carries the CmdSN 123).

           The target MUST use the value presented with the first login request.

   9.12.9  ExpStatSN

           This is ExpStatSN for the old connection.

           This field is valid only if the Login request restarts a connection
           (see Section 4.3.4 Connection reinstatement).

   9.12.10  Login Parameters

           The initiator MAY provide some basic parameters in order to enable the
           target to determine if the initiator may use the target's resources
           and the initial text parameters for the security exchange.
           All the rules specified in Section 9.10.4 Text for text requests/
           responses also hold for login requests/responses.   Keys and their
           explanations are listed in Chapter 10 (security negotiation keys) and
           Chapter 11 (operational parameter negotiation keys). All keys in
           Chapter 11, except for the X- extension format, MUST be supported by
           iSCSI initiators and targets. Keys in Chapter 10, only need to be sup-
           ported when the function to which they refer is mandatory to imple-
           ment.





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   9.13  Login Response

           The Login Response indicates the progress and/or end of the login
           phase.

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x23      |T|0 0 0|CSG|NSG| Version-max   | Version-active|
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| ISID                                                          |
             +                               +---------------+---------------+
           12|                               |TSID                           |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| Status-Class  | Status-Detail | Reserved                      |
             +---------------+---------------+---------------+---------------+
           40/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48/ DataSegment - Login Parameters in Text request Format         /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

   9.13.1  Version-max

           This is the highest version number supported by the target.

           All Login responses within the Login phase MUST carry the same Ver-
           sion-max.



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           The initiator MUST use the value presented as a response to the first
           login request.

   9.13.2  Version-active

           Indicates the highest version supported by the target and initiator.
           If the target does not support a version within the range specified by
           the initiator, the target rejects the login and this field indicates
           the lowest version supported by the target.

           All Login responses within the Login phase MUST carry the same Ver-
           sion-active.

           The initiator MUST use the value presented as a response to the first
           login request.

   9.13.3  TSID

           The TSID is the target assigned component of the session identifier
           (SSID).  TSID MUST be valid only in the final response.  The target is
           generating and using it and its internal format and content are not
           defined by this protocol except for the value 0 that is reserved and
           used by the initiator to indicate a new session.  It is given to the
           target, during additional connection establishment for the same ses-
           sion, to identify the associated session for the target.

   9.13.4  StatSN

           For the first Login Response (the response to the first Login
           Request), this is the starting status Sequence Number for the connec-
           tion. The next response of any kind, including the next login
           response, if any, in the same login phase, will carry this number + 1.
           This field is valid only if the Status-Class is 0.

   9.13.5  Status-Class and Status-Detail

           The Status returned in a Login Response indicates the execution status
           of the login phase. The status includes:

                 Status-Class
                 Status-Detail

           0 Status-Class indicates success.



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           A non-zero Status-Class indicates an exception. In this case, Status-
           Class is sufficient for a simple initiator to use when handling
           errors, without having to look at the Status-Detail.  The Status-
           Detail allows finer-grained error recovery for more sophisticated
           initiators, as well as better information for error logging.

           The status classes are as follows:

                 0 - Success - indicates that the iSCSI target successfully
                      received, understood, and accepted the request. The numbering
                      fields (StatSN, ExpCmdSN, MaxCmdSN) are valid only if Status-
                      Class is 0.

                 1 - Redirection - indicates that the initiator must take further
                      action to complete the request. This is usually due to the
                      target moving to a different address. All of the redirection
                      status class responses MUST return one or more text key param-
                      eters of the type "TargetAddress", which indicates the tar-
                      get's new address.

                 2 - Initiator Error (not a format error) - indicates that the
                      initiator most likely caused the error. This MAY be due to a
                      request for a resource for which the initiator does not have
                      permission.  The request should not be tried again.

                 3 - Target Error - indicates that the target sees no errors in
                      the initiator's login request, but is currently incapable of
                      fulfilling the request.  The client may re-try the same login
                      request later.

           The table below shows all of the currently allocated status codes.
           The codes are in hexadecimal; the first byte is the status class and
           the second byte is the status detail.





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                                                                  iSCSI            1-March-02

           -----------------------------------------------------------------
           Status        | Code | Description
                         |(hex) |
           -----------------------------------------------------------------
           Success       | 0000 | Login is proceeding OK (*1).
           -----------------------------------------------------------------
           Target Moved  | 0101 | The requested iSCSI Target Name (ITN)
           Temporarily   |      |  has temporarily moved
                         |      |  to the address provided.
           -----------------------------------------------------------------
           Target Moved  | 0102 | The requested ITN has permanently moved
           Permanently   |      |  to the address provided.
           -----------------------------------------------------------------
           Initiator     | 0200 | Miscellaneous iSCSI initiator
           Error         |      | errors.
           ----------------------------------------------------------------
           Authentication| 0201 | The initiator could not be
           Failure       |      | successfully authenticated.
           -----------------------------------------------------------------
           Authorization | 0202 | The initiator is not allowed access
           Failure       |      | to the given target.
           -----------------------------------------------------------------
           Not Found     | 0203 | The requested ITN does not
                         |      | exist at this address.
           -----------------------------------------------------------------
           Target Removed| 0204 | The requested ITN has been removed and
                         |      |no forwarding address is provided.
           -----------------------------------------------------------------
           Unsupported   | 0205 | The requested iSCSI version range is
           Version       |      | not supported by the target.
           -----------------------------------------------------------------
           Too many      | 0206 | No more connections are accepted on this SID.
           connections   |      |
           -----------------------------------------------------------------
           Missing       | 0207 | Missing parameters (e.g., iSCSI
           parameter     |      | Initiator and/or Target Name).
           -----------------------------------------------------------------
           Can't include | 0208 | Target does not support session
           in session    |      | spanning to this connection (address)
           -----------------------------------------------------------------
           Session type  | 0209 | Target does not support this type of
           Not supported |      | of session or not from this Initiator.
           -----------------------------------------------------------------

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                                                                  iSCSI            1-March-02

           Session does  | 020a | Attempt to add a connection
           not exist     |      | to an inexistent session
           -----------------------------------------------------------------
           Invalid during| 020b | Invalid Request type during Login
           login         |      |
           -----------------------------------------------------------------
           Target Error  | 0300 | Target hardware or software error.
           -----------------------------------------------------------------
           Service       | 0301 | The iSCSI service or target is not
           Unavailable   |      | currently operational.
           -----------------------------------------------------------------
           Out of        | 0302 | The target has insufficient session,
           Resources     |      | connection, or other resources.
           -----------------------------------------------------------------

           (*1)If the response T bit is 1 and the NSG is FullFeaturePhase in both
           the request and the response the login phase is finished and the ini-
           tiator may proceed to issue SCSI commands.

           If the Status Class is not 0, the initiator and target MUST close the
           TCP connection.

           If the target wishes to reject the login request for more than one
           reason, it should return the primary reason for the rejection.

   9.13.6  T (Transit) bit

           The T bit is set to 1 as an indicator of the end of the stage. If the
           T bit is set to 1 and NSG is FullFeaturePhase, then this is also the
           Final Login Response (see Chapter 4). A T bit of 0 indicates a "par-
           tial" response, which means "more negotiation needed".

           A login response with a T bit set to 1 MUST NOT contain key=value
           pairs that may require additional answers from the initiator within
           the same stage.

           If the status class is 0, the T bit MUST NOT be set to 1 if the T bit
           in the request was set to 0.





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                                                                  iSCSI            1-March-02

   9.14  Logout Request

           The Logout request is used to perform a controlled closing of a con-
           nection.

           An initiator MAY use a logout command to remove a connection from a
           session or to close an entire session.

           After sending the Logout PDU, an initiator MUST NOT send any new iSCSI
           commands on the closing connection. If the Logout is intended to close
           the session, new iSCSI commands MUST NOT be sent on any of the connec-
           tions participating in the session.

           When receiving a Logout request with the reason code of "close the
           connection" or "close the session", the target MUST abort all pending
           commands, whether acknowledged or not, on that connection or session
           respectively. When receiving a Logout request with the reason code
           "remove connection for recovery", the target MUST discard all
           requests not yet acknowledged that were issued on the specified con-
           nection and suspend all data/status/R2T transfers on behalf of pend-
           ing commands on the specified connection.  The target then issues the
           Logout response and half-closes the TCP connection (sends FIN).  After
           receiving the Logout response and attempting to receive the FIN (if
           still possible), the initiator MUST completely close the logging-out
           connection. For the aborted commands, no additional responses should
           be expected.

           A Logout for a CID may be performed on a different transport connec-
           tion when the TCP connection for the CID has already been terminated.
           In such a case, only a logical "closing" of the iSCSI connection for
           the CID is implied with a Logout.

           All commands that were not aborted or not completed (with status) and
           acknowledged when the connection is closed completely can be reas-
           signed to a new connection if the target supports connection recovery.

           If an initiator intends to start recovery for a failing connection, it
           MUST use either the Logout command to "clean-up" the target end of a
           failing connection and enable recovery to start, or use the restart
           option of the Login command for the same effect.  In sessions with a
           single connection, this may imply the opening of a second connection
           with the sole purpose of cleaning-up the first. In this case, the
           restart option of the Login should be used.


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                                                                  iSCSI            1-March-02


           Sending a logout request with the reason code of "close the connec-
           tion" or "remove the connection for recovery" may result in the dis-
           carding of some unacknowledged commands. Those holes in command
           sequence numbers will have to be handled by appropriate recovery (see
           Chapter 6) unless the session is also closed.


           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| 0x06      |1| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------------------------------------------------------+
            8/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           12| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| CID or Reserved               | Reserved      |Reason Code    |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digest (if any)                                               |
             +---------------------------------------------------------------+

   9.14.1  CID

           This is the connection ID of the connection to be closed (including
           closing the TCP stream). This field is valid only if the reason code
           is not "close the session".

   9.14.2  ExpStatSN

           This is the last ExpStatSN value for the connection to be closed.

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   9.14.3  Reason Code

           Indicates the reason for Logout:

                 0 - closes the session. All commands associated with the session
                      (if any) are aborted.

                 1 - closes the connection. All commands associated with connec-
                      tion (if any) are aborted.

                 2 - removes the connection for recovery. Connection is closed
                      and all commands associated with it, if any, are to be pre-
                      pared for a new allegiance.





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                                                                  iSCSI            1-March-02

   9.15  Logout Response

           The logout response is used by the target to indicate if the cleanup
           operation for the connection(s) has completed.

           After Logout, the TCP connection referred by the CID MUST be closed at
           both ends (or all connections must be closed if the logout reason was
           session close).

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x26      |1| Reserved    | Response      | Reserved      |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------------------------------------------------------+
            8/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag                                            |
             +---------------+---------------+---------------+---------------+
           20| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| Reserved                                                      |
             +---------------------------------------------------------------+
           40| Time2Wait                     | Time2Retain                   |
             +---------------+---------------+---------------+---------------+
           44| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           48| Digest (if any)                                               |
             +---------------------------------------------------------------+

   9.15.1  Response

           Logout response:

                 0 - connection or session closed successfully.

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                 1 - CID not found.

                 2 - connection recovery not supported (if Logout reason code was
                      recovery and target does not support it- as indicated by the
                      ErrorRecoveryLevel.

                 3 - cleanup failed for various reasons.

   9.15.2  Time2Wait

           If the Logout response code is 0 and if the operational ErrorRecovery-
           Level is 2, this is the minimum amount of time, in seconds, to wait
           before attempting task reassignment.  If the Logout response code is 0
           and if the operational ErrorRecoveryLevel is less than 2, this field
           is to be ignored.

           This field is invalid if the Logout response code is 1.

           If the Logout response code is 2 or 3, this field specifies the mini-
           mum time to wait before attempting a new implicit or explicit logout.

           If Time2Wait is 0, the reassignment or a new Logout may be attempted
           immediately.

   9.15.3  Time2Retain

           If the Logout response code is 0 and if the operational ErrorRecovery-
           Level is 2, this is the maximum amount of time, in seconds, after the
           initial wait (Time2Wait), the target waits for the allegiance reas-
           signment for any active task after which the task state is discarded.
           If the Logout response code is 0 and if the operational ErrorRecovery-
           Level is less than 2, this field is to be ignored.

           This field is invalid if the Logout response code is 1.

           If the Logout response code is 2 or 3, this field specifies the maxi-
           mum amount of time, in seconds, after the initial wait (Time2Wait),the
           target waits for a new implicit or explicit logout.

           If it is the last connection of a session, the whole session state is
           discarded after Time2Retain.




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                                                                  iSCSI            1-March-02

           If Time2Retain is 0, the target had already discarded the connection
           (and possibly the session) state along with the task states.  No reas-
           signment or Logout is required in this case.





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                                                                  iSCSI            1-March-02

   9.16   SNACK Request

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x10      |1|Rsrvd| Type  | Reserved                      |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag or 0xffffffff                              |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           40| BegRun                                                        |
             +---------------------------------------------------------------+
           44| RunLength                                                     |
             +---------------------------------------------------------------+
           48| Digest (if any)                                               |
             +---------------------------------------------------------------+

           Support for SNACK is optional.

           The SNACK request is used to request the retransmission of numbered-
           responses, data, or R2T PDUs from the target.  The SNACK request indi-
           cates the missed numbered-response or data "run" to the target, where
           the run starts with the first missed StatSN, DataSN, or R2TSN and
           indicates also the number of missed Status, Data, or R2T PDUs (0 has
           the special meaning of "all after the initial").

           The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
           delivered as exact replicas of the ones the initiator missed and MUST


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                                                                  iSCSI            1-March-02

           include all its flags. However, the fields ExpCmdSN, MaxCmdSN and Exp-
           DataSN MUST carry the current values.

           The numbered Data-In PDUs, requested by a SNACK with a RunLength dif-
           ferent from 0, have to be delivered as exact replicas of the ones the
           initiator missed and MUST include all its flags. However, the fields
           ExpCmdSN and MaxCmdSN MUST carry the current values.  Data-In PDUs
           requested with RunLength 0 (meaning all PDUs after this number) may be
           different from the ones originally sent, in order to reflect changes
           in MaxRecvPDULength.

           Any SNACK that requests a numbered-response, Data, or R2T that was not
           sent by the target MUST be rejected with a reason code of "Protocol
           error".

   9.16.1  Type

           This field encodes the SNACK function as follows:

                 0-Data/R2T SNACK - requesting retransmission of a Data-In or R2T
                      PDU.

                 1-Status SNACK - requesting retransmission of a numbered
                      response.

                 2-DataACK - positively acknowledges Data-In PDUs.

           All other values are reserved.

           Data/R2T SNACK for a command MUST precede status acknowledgement for
           the given command.

           For Status SNACK, the Initiator Task Tag is reserved. In all other
           cases, the Initiator Task Tag field MUST be set to the Initiator Task
           Tag of the referenced command.

           For DataACK, the Target Transfer Tag has to contain a copy of the Tar-
           get Transfer Tag and LUN provided with the SCSI Data-In PDU with the A
           bit set to 1. In all other cases, the Target Transfer Tag field MUST
           be set to the reserved value of 0xffffffff.

           An iSCSI target that does not support recovery within connection MAY
           discard the status SNACK. If the target supports recovery within con-
           nection, it MAY discard the SNACK after which it MUST issue an Asyn-


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                                                                  iSCSI            1-March-02

           chronous Message PDU with an iSCSI event that indicates "Request
           Logout".

           If an initiator operates at ErrorRecoveryLevel 1 or higher, it MUST
           issue a SNACK of type DataACK after receiving a Data-In PDU with the A
           bit set to 1.  However, if the initiator has detected holes in the
           input sequence, it MUST postpone issuing the SNACK of type DataACK
           until the holes are filled. An initiator MAY ignore the A bit if it
           deems that the bit is being set aggressively by the target (i.e.,
           before the MaxBurstSize limit is reached).

           The DataACK is used to free resources at the target and not to request
           or imply data retransmission.

   9.16.2  BegRun

           The first missed DataSN, R2TSN, or StatSN or the next expected DataSN
           for a DataACK type SNACK request.

   9.16.3  RunLength

           The number of sequential missed DataSN, R2TSN or StatSN. RunLength of
           "0" signals that all Data-In, R2T or Response PDUs carrying the num-
           bers equal to or greater to BegRun have to be resent.

           The first data SNACK, issued after initiator‚ÇÖs MaxRecvPDULength
           decreased, for a command issued on the same connection before the
           change in MaxRecvPDULength, MUST use RunLength "0" to request
           retransmission of any number of PDUs (including one).  The number of
           retransmitted PDUs in this case, may or may not be the same as the
           original transmission, depending on whether loss was before or after
           the MaxRecvPDULength was changed at the target.





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                                                                  iSCSI            1-March-02

   9.17  Reject

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x3f      |1| Reserved    | Reason        | Reserved      |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           16| Reserved - 0xffffffff                                         |
             +---------------+---------------+---------------+---------------+
           20| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36| DataSN or Reserved                                            |
             +---------------+---------------+---------------+---------------+
           40| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           44| Reserved                                                      |
             +---------------+---------------+---------------+---------------+
           48| Digest (if any)                                               |
             +---------------+---------------+---------------+---------------+
           xx/ Complete Header of Bad PDU                                    /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           yy/Vendor specific data (if any)                                  /
             /                                                               /
             +---------------+---------------+---------------+---------------+
           zz| Digest (if any)                                               |
             +---------------+---------------+---------------+---------------+

           Reject is used to indicate an iSCSI error condition (protocol, unsup-
           ported option etc.).



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                                                                  iSCSI            1-March-02

   9.17.1  Reason

           The reject Reason is coded as follows:

           +------+-----------------------------------------+------------------+
           | Code | Explanation                             | Can the original |
           | (hex)|                                         | PDU be re-sent?  |
           +------+-----------------------------------------+------------------+
           | 0x01 | Reserved                                | no               |
           |      |                                         |                  |
           | 0x02 | Data (payload) Digest Error             | yes  (Note 1)    |
           |      |                                         |                  |
           | 0x03 | Data-SNACK Reject                       | yes              |
           |      |                                         |                  |
           | 0x04 | Protocol Error (e.g., SNACK request for | no               |
           |      | a status that was already acknowledged  |                  |
           |      |                                         |                  |
           | 0x05 | Command not supported in this session   | no               |
           |      | type                                    |                  |
           |      |                                         |                  |
           | 0x06 | Immediate Command Reject - too many     | yes              |
           |      | immediate commands                      |                  |
           |      |                                         |                  |
           | 0x07 | Task in progress                        | no               |
           |      |                                         |                  |
           | 0x08 | Invalid Data ACK                        | no               |
           |      |                                         |                  |
           | 0x09 | Invalid PDU field                       | no   (Note 2)    |
           |      |                                         |                  |
           | 0x0a | Long Operation Reject - Can't generate  | yes              |
           |      | Target Transfer Tag - out of resources  |                  |
           |      |                                         |                  |
           | 0x0b | Negotiation Reset                       | no               |
           |      |                                         |                  |
           | 0x0c | Waiting for Logout                      | no               |
           +------+-----------------------------------------+------------------+

           Note 1: For iSCSI Data-Out PDU retransmission is done only if the tar-
           get requests retransmission with a recovery R2T. However, if this is
           the data digest error on immediate data, the initiator may choose to
           retransmit the whole PDU including the immediate data.




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                                                                  iSCSI            1-March-02

           Note 2: A target should use this reason code for all invalid values of
           PDU fields that are meant to describe a task or a data transfer.  Some
           examples are invalid TTT/ITT, buffer offset, LUN qualifying a TTT.

           All other values for Reason are reserved.

           In all the cases in which a pre-instantiated SCSI task is terminated
           because of the reject, the target must issue a proper SCSI command
           response with CHECK CONDITION as described in Section 9.4.3 Response.
           In those cases in which a status for the SCSI task was already sent
           before the reject no additional status is required. If the error is
           detected while data from the initiator is still expected (the command
           PDU did not contain all the data and the target has not received a
           Data-out PDU with the Final bit 1), the target MUST wait until it
           receives the Data-out PDU with the F bit set to 1 before sending the
           Response PDU.

           For additional usage semantics of Reject PDU, see Section 6.2 Usage Of
           Reject PDU in Recovery.

   9.17.2  DataSN

           This field is valid only if the Reason code is "Protocol error" and
           the SNACK was a Data/R2T SNACK.  The DataSN/R2TSN is the last valid
           sequence number that the target sent for the task.

   9.17.3  StatSN, ExpCmdSN and MaxCmdSN

           Those fields carry their usual values and are not related to the
           rejected command

   9.17.4  Complete Header of Bad PDU

           The target returns the header (not including digest) of the PDU in
           error as the data of the response.





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                                                                  iSCSI            1-March-02

   9.18  NOP-Out

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|I| 0x00      |1| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag or 0xffffffff                              |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| CmdSN                                                         |
             +---------------+---------------+---------------+---------------+
           28| ExpStatSN                                                     |
             +---------------+---------------+---------------+---------------+
           32/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment - Ping Data (optional)                            /
            +/                                                               /
             +---------------+---------------+---------------+---------------+

           A NOP-Out may be used by an initiator as a "ping command" to verify
           that a connection/session is still active and all its components are
           operational.  The NOP-In response is the "ping echo".

           A NOP-Out is also sent by an initiator in response to a NOP-In.

           A NOP-Out may also be used to confirm a changed ExpStatSN if another
           PDU will not be available for a long time.

           When used as a ping command, the Initiator Task Tag MUST be set to a
           valid value (not the reserved 0xffffffff).



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                                                                  iSCSI            1-March-02

           Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
           value (not the reserved 0xffffffff), the initiator MUST respond with a
           NOP-Out. In this case, the NOP-Out Target Transfer Tag MUST contain a
           copy of the NOP-In Target Transfer Tag.

           When a target receives the NOP-Out with a valid Initiator Task Tag, it
           MUST respond with a Nop-In Response (see NOP-In).

   9.18.1  Initiator Task Tag

           An initiator assigned identifier for the operation.

           The NOP-Out must have the Initiator Task Tag set to a valid value only
           if a response in the form of NOP-In is requested.

           If the Initiator Task Tag contains 0xffffffff, the CmdSN field con-
           tains the next CmdSN. However, CmdSN is not advanced and the I bit
           must be set to 1.

   9.18.2  Target Transfer Tag

           A target assigned identifier for the operation.

           The NOP-Out MUST have the Target Transfer Tag set only if it is issued
           in response to a NOP-In with a valid Target Transfer Tag. In this
           case, it copies the Target Transfer Tag from the NOP-In PDU.

           When the Target Transfer Tag is set, the LUN field MUST also be copied
           from the NOP-In.

   9.18.3  Ping Data

           Ping data is reflected in the NOP-In Response. The length of the
           reflected data is limited to MaxRecvPDULength. The length of ping data
           is indicated by the Data Segment Length.  0 is a valid value for the
           Data Segment Length and indicates the absence of ping data.





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                                                                  iSCSI            1-March-02

   9.19  NOP-In

           Byte /    0       |       1       |       2       |       3       |
              /              |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0|.|.| 0x20      |1| Reserved                                    |
             +---------------+---------------+---------------+---------------+
            4|TotalAHSLength | DataSegmentLength                             |
             +---------------+---------------+---------------+---------------+
            8| LUN or Reserved                                               |
             +                                                               +
           12|                                                               |
             +---------------+---------------+---------------+---------------+
           16| Initiator Task Tag or 0xffffffff                              |
             +---------------+---------------+---------------+---------------+
           20| Target Transfer Tag or 0xffffffff                             |
             +---------------+---------------+---------------+---------------+
           24| StatSN                                                        |
             +---------------+---------------+---------------+---------------+
           28| ExpCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           32| MaxCmdSN                                                      |
             +---------------+---------------+---------------+---------------+
           36/ Reserved                                                      /
            +/                                                               /
             +---------------+---------------+---------------+---------------+
           48| Digests if any...                                             |
             +---------------+---------------+---------------+---------------+
             / DataSegment - Return Ping Data                                /
            +/                                                               /
             +---------------+---------------+---------------+---------------+


           NOP-In is either sent by a target as a response to a NOP-Out, as a
           "ping" to an initiator or as a means to carry a changed ExpCmdSN and/
           or MaxCmdSN if another PDU will not be available for a long time (as
           determined by the target).

           When a target receives the NOP-Out with a valid Initiator Task Tag
           (not the reserved value 0xffffffff), it MUST respond with a NOP-In
           with the same Initiator Task Tag that was provided in the NOP-Out Com-
           mand. It MUST also duplicate up to the first MaxRecvPDULength bytes of


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           the initiator provided Ping Data.  For such a response, the Target
           Transfer Tag MUST be 0xffffffff.

           When a target send a NOP-In as a "ping" (the Initiator Task Tag is
           0xffffffff) it MUST NOT send any data in the data segment (DataSeg-
           mentLength MUST be 0).

   9.19.1  Target Transfer Tag

           A target assigned identifier for the operation.

           If the target is responding to a NOP-Out, this is set to the reserved
           value 0xffffffff.

           If the target is sending a NOP-In as a Ping (intending to receive a
           corresponding NOP-Out), this field is set to a valid value (not the
           reserved 0xffffffff).

           If the target is initiating a NOP-In without wanting to receive a cor-
           responding NOP-Out, this field MUST hold the reserved value of
           0xffffffff.

           Whenever the NOP-In is sent as a "ping" to an initiator (not as a
           response to a NOP-Out), the StatSN field will contain the next StatSN.
           However, StatSN for this connection is not advanced.

   9.19.2  LUN

           A LUN MUST be set to a correct value when the Target Transfer Tag is
           valid (not the reserved value 0xffffffff).





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   10. iSCSI Security Keys and Values

           The following keys can only be used during the SecurityNegotiation
           stage of the Login Phase:

                 SessionType
                 InitiatorName
                 TargetName
                 InitiatorAlias
                 TargetAlias
                 AuthMethod and all keys listed under AuthMethod along with all
                      of their associated keys.

           SessionType, InitiatorName, TargetName, InitiatorAlias and Tar-
           getAlias are described in Chapter 11 as they can be used also in the
           OperationalNegotiation stage.

           All security keys have connection-wide applicability.

   10.1  AuthMethod

           Use: During Login - Security Negotiation
           Senders: Initiator and Target
           Scope: connection

           AuthMethod = <list-of-options>

           The  main item of security negotiation is the authentication method
           (AuthMethod).

           The authentication methods that can be used (appear in the list-of-
           options) are either those listed in the following table or are vendor-
           unique methods:





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           +------------------------------------------------------------+
           | Name          | Description                                |
           +------------------------------------------------------------+
           | KRB5          | Kerberos V5                                |
           +------------------------------------------------------------+
           | SPKM1         | Simple Public-Key GSS-API Mechanism        |
           +------------------------------------------------------------+
           | SPKM2         | Simple Public-Key GSS-API Mechanism        |
           +------------------------------------------------------------+
           | SRP           | Secure Remote Password                     |
           +------------------------------------------------------------+
           | CHAP          | Challenge Handshake Authentication Protocol|
           +------------------------------------------------------------+
           | None          | No authentication                          |
           +------------------------------------------------------------+

           KRB5 is defined in [RFC1510].
           SPKM1 and SPKM2 are defined in [RFC2025].
           SRP is defined in [RFC2945] and CHAP is defined in [RFC1994].

           The AuthMethod selection is followed by an "authentication exchange"
           specific to the authentication method selected.

           The authentication exchange authenticates the initiator to the tar-
           get, and optionally, the target to the initiator.  Authentication is
           not mandatory to use but must be supported by the target and initia-
           tor.

           The initiator and target MUST implement SRP.

   10.2  Kerberos

           For KRB5 (Kerberos V5) [RFC1510], the initiator MUST use:

               KRB_AP_REQ=<KRB_AP_REQ>

           where KRB_AP_REQ is the client message as defined in [RFC1510].

           If the initiator authentication fails, the target MUST answer with a
           Login reject with "Authentication Failure" status. Otherwise, if the
           initiator has selected the mutual authentication option (by setting
           MUTUAL-REQUIRED in the ap-options field of the KRB_AP_REQ), the tar-
           get MUST reply with:


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               KRB_AP_REP=<KRB_AP_REP>

           where KRB_AP_REP is the server's response message as defined in
           [RFC1510].

           If mutual authentication was selected and target authentication
           fails, the initiator MUST close the connection.

           KRB_AP_REQ and KRB_AP_REP are large binary items and their binary
           length (not the length of the character string that represents them in
           encoded form) MUST not exceed 65536 bytes.

   10.3  Simple Public-Key Mechanism (SPKM)


           For SPKM1 and SPKM2 [RFC2025], the initiator MUST use:

               SPKM_REQ=<SPKM-REQ>

           where SPKM-REQ is the first initiator token as defined in [RFC2025].

           [RFC2025] defines situations where each side may send an error token
           that may cause the peer to re-generate and resend its last token. This
           scheme is followed in iSCSI, and the error token syntax is:

               SPKM_ERROR=<SPKM-ERROR>

           However, SPKM-DEL tokens that are defined by [RFC2025] for fatal
           errors will not be used by iSCSI. If the target needs to send a SPKM-
           DEL token(by[RFC2025], it will, instead, send a Login "login reject"
           message with the "Authentication Failure" status and terminate the
           connection. If the initiator needs to send a SPKM-DEL token, it will
           close the connection.

           In the following sections, we assume that no SPKM-ERROR tokens are
           required.

           If the initiator authentication fails, the target MUST return an
           error. Otherwise, if the AuthMethod is SPKM1 or if the initiator has
           selected the mutual authentication option (by setting mutual-state
           bit in the options field of the REQ-TOKEN in the SPKM-REQ), the target
           MUST reply with:


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               SPKM_REP_TI=<SPKM-REP-TI>

           where SPKM-REP-TI is the target token as defined in [RFC2025].

           If mutual authentication was selected and target authentication
           fails, the initiator MUST close the connection. Otherwise, if the
           AuthMethod is SPKM1, the initiator MUST continue with:

               SPKM_REP_IT=<SPKM-REP-IT>

           where SPKM-REP-IT is the second initiator token as defined in
           [RFC2025]. If the initiator authentication fails, the target MUST
           answer with a Login reject with "Authentication Failure" status.

           All the SPKM-* tokens are large binary items and their binary length
           (not the length of the character string that represents them in
           encoded form) MUST not exceed 65536 bytes.

   10.4  Secure Remote Password (SRP)


           For SRP [RFC2945], the initiator MUST use:

              SRP_U=<user> TargetAuth=Yes   /* or TargetAuth=No */

           The target MUST answer with a Login reject with the "Authorization
           Failure" status or reply with:

              SRP_N=<N> SRP_g=<g> SRP_s=<s>

           The initiator MUST either close the connection or continue with:

              SRP_A=<A>

           The target MUST answer with a Login reject with the "Authentication
           Failure" status or reply with:

              SRP_B=<B>

           The initiator MUST close the connection or continue with:

              SRP_M=<M>


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           If the initiator authentication fails, the target MUST answer with a
           Login reject with "Authentication Failure" status. Otherwise, if the
           initiator sent TargetAuth=Yes in the first message (requiring target
           authentication), the target MUST reply with:

             SRP_HM=<H(A | M | K)>

           If the target authentication fails, the initiator MUST close the con-
           nection.

           Where U, N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945]
           (using the SHA1 hash function, i.e., SRP-SHA1), U is a text string,
           N,g,s,A,B,M, and H(A | M | K) are binary items, and their binary
           length (not the length of the character string that represents them in
           encoded form) MUST not exceed 1024 bytes. Further restrictions on
           allowed N,g values are specified in Section 7.2 In-band Initiator-
           Target Authentication.

   10.5  Challenge Handshake Authentication Protocol (CHAP)

           For CHAP [RFC1994], the initiator MUST use:

              CHAP_A=<A1,A2...>

           Where A1,A2... are proposed algorithms, in order of preference.

           The target MUST answer with a Login reject with the "Authentication
           Failure" status or reply with:

              CHAP_A=<A> CHAP_I=<I> CHAP_C=<C>

           Where A is one of A1,A2... that were proposed by the initiator.

           The initiator MUST continue with:

              CHAP_N=<N> CHAP_R=<R>

           or, if it requires target authentication, with:

              CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>




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           If the initiator authentication fails, the target MUST answer with a
           Login reject with "Authentication Failure" status. Otherwise, if the
           initiator required target authentication, the target MUST reply with

              CHAP_N=<N> CHAP_R=<R>

           If target authentication fails, the initiator MUST close the connec-
           tion.

           Where N, (A,A1,A2), I, C, and R are (correspondingly) the Name, Algo-
           rithm, Identifier, Challenge, and Response as defined in [RFC1994], N
           is a text string, A,A1,A2, and I are numbers, and C and R are binary
           items and their binary length (not the length of the character string
           that represents them in encoded form) MUST not exceed 1024 bytes.

           For the Algorithm, as stated in [RFC1994], one value is required
           to be implemented:

          5       (CHAP with MD5)

           To guarantee interoperability, initiators SHOULD always offer it as
           one of the proposed algorithms.





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   11. Login/Text Operational Keys

           The ISID and TSID collectively form the SSID (session id).  A TSID of
           zero indicates a leading connection. Some session specific parameters
           MUST only be carried on the leading connection and cannot be changed
           after the leading connection login (e.g., MaxConnections, the maximum
           number of connections).  This holds for a single connection session
           with regard to connection restart. The keys that fall into this cate-
           gory have the use LO (Leading Only).

           Keys that can be used only during login have the use IO (initialize
           only) while those that can be used in both the login phase and full
           feature phase have the use ALL.

           Keys that can only be used during full feature phase use FFPO (full
           feature phase only).

           Keys marked as "declarative" may appear also in the SecurityNegotia-
           tion stage while all other keys described in this chapter are opera-
           tional keys.

           Key scope is indicated as session-wide (SW) or connection-only (CO).

   11.1  HeaderDigest and DataDigest

           Use: IO
           Senders: Initiator and Target
           Scope: CO

           HeaderDigest = <list-of-options>
           DataDigest = <list-of-options>

           Digests enable the checking of end-to-end non-cryptographic data
           integrity beyond the integrity checks provided by the link layers and
           the covering of the whole communication path including all elements
           that may change the network level PDUs such as routers, switches, and
           proxies.

           The following table lists cyclic integrity checksums that can be nego-
           tiated for the digests and that MUST be implemented by every iSCSI
           initiator and target.  These digest options only have error detection
           significance.



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           +---------------------------------------------+
           | Name          | Description     | Generator |
           +---------------------------------------------+
           | CRC32C        | 32 bit CRC      |0x11edc6f41|
           +---------------------------------------------+
           | None          | no digest                   |
           +---------------------------------------------+

           The generator polynomial for this digest is given in hex-notation, for
           example 0x3b stands for 0011 1011. The polynomial x**5+X**4+x**3+x+1.

           When the Initiator and Target agree on a digest, this digest MUST be
           used for every PDU in Full Feature Phase.

           Padding bytes, when present, in a segment covered by a CRC, should be
           set to 0 and are included in the CRC. The CRC should be calculated as
           follows:

                 - Data bits are assumed to form a serial bit stream in the num-
                      bering order that appears in the draft and starts with byte 0
                      bit 0 to 7 continues with byte 1 bit 0 etc. (Big Endian on
                      bytes / Little Endian on bits). This bit-stream has no rela-
                      tion to the physical bit stream and is used to associate the
                      data bits with specific coefficients of a binary polynomial.

                 - The first 32 bits of the bit-stream are complemented.

                 - The n bits of the bit-stream are considered coefficients of a
                      polynomial M(x) of order n-1, with bit 0 of byte 0 being x^(n-
                      1).

                 - The polynomial is multiplied by x^32 then divided by G(x). The
                      generator polynomial produces a remainder R(x) of degree <=
                      31.

                 - The coefficients of R(x) are considered a 32 bit sequence.

                 - The bit sequence is complemented and the result is the CRC.

                 - The CRC bits appear after the message bits with x^31 first
                      followed by x^30 etc. (when examples are provided, the value
                      to be specified in the examples follows the same rules of
                      ordering as the rest of this document).

                 - A receiver of a "good" segment (data or header) including the
                      CRC built using the generator 0x11edc6f41 will get the value


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                      0x1c2d19ed as its CRC (this is a polynomial value and not a
                      word as outlined in this draft).

           Proprietary algorithms MAY also be negotiated for digests. Whenever a
           proprietary algorithm is negotiated, "None" or "CRC32C" should be
           listed as an option in order to guarantee interoperability.

   11.2  MaxConnections

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           MaxConnections=<integer-from-1-to-65535>

           Default is 1.

           Initiator and target negotiate the maximum number of connections
           requested/acceptable.  The lower of the two numbers is selected.

   11.3  SendTargets

           Use: FFPO
           Senders: Initiator
           Scope: SW

           For a complete description, see Appendix D. - SendTargets Operation -.

   11.4  TargetName

           Use: IO by initiator ALL by target, Declarative
           Senders: Initiator and Target
           Scope: SW

           TargetName=<iSCSI-Name>

           Examples:

                 TargetName=iqn.1993-11.com.disk-vendor.diskarrays.sn.45678
                 TargetName=eui.020000023B040506

           The initiator of the TCP connection must provide this key to the
           remote endpoint in the first login request if the initiator is not



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           establishing a discovery session. The iSCSI Target Name specifies the
           worldwide unique name of the target.
           The TargetName key may also be returned by the "SendTargets" text
           request (which is its only use when issued by a target).

   11.5  InitiatorName

           Use: IO, Declarative
           Senders: Initiator
           Scope: SW

           InitiatorName=<iSCSI-Name>

           Examples:

                 InitiatorName=iqn.1992-04.com.os-vendor.plan9.cdrom.12345
                 InitiatorName=iqn.2001-02.com.ssp.users.customer235.host90
                 InitiatorName=iSCSI

           The initiator of the TCP connection must provide this key to the
           remote endpoint at the first Login of the login phase for every con-
           nection. The Initiator key enables the initiator to identify itself to
           the remote endpoint.

   11.6  TargetAlias

           Use: ALL, Declarative
           Senders: Target
           Scope: SW

           TargetAlias=<UTF-8 string>

           Examples:

                 TargetAlias=Bob-s Disk
                 TargetAlias=Database Server 1 Log Disk
                 TargetAlias=Web Server 3 Disk 20

           If a target has been configured with a human-readable name or descrip-
           tion, this name MUST be communicated to the initiator during a Login
           Response PDU.  This string is not used as an identifier, but can be
           displayed by the initiator's user interface in a list of targets to
           which it is connected.



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   11.7  InitiatorAlias

           Use: ALL, Declarative
           Senders: Initiator
           Scope: SW

           InitiatorAlias=<UTF-8 string>

           Examples:

                 InitiatorAlias=Web Server 4
                 InitiatorAlias=spyalley.nsa.gov
                 InitiatorAlias=Exchange Server

           If an initiator has been configured with a human-readable name or
           description, it may be communicated to the target during a Login
           Request PDU.  If not, the host name can be used instead.
           This string is not used as an identifier, but can be displayed by the
           target's user interface in a list of initiators to which it is con-
           nected.

           This key SHOULD be sent by an initiator within the Login phase, if
           available.

   11.8  TargetAddress

           Use: ALL, Declarative
           Senders: Target
           Scope: SW

           TargetAddress=domainname[:port][,portal-group-tag]

           If the TCP port is not specified, it is assumed to be the IANA-
           assigned default port for iSCSI.

           If the TargetAddress is returned as the result of a redirect status in
           a login response, the comma and portal group tag are omitted.

           If the TargetAddress is returned within a SendTargets response, the
           portal group tag is required.

           Examples:

                 TargetAddress=10.0.0.1:5003,1

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                 TargetAddress=[1080:0:0:0:8:800:200C:417A],65
                 TargetAddress=[1080::8:800:200C:417A]:5003,1
                 TargetAddress=computingcenter.acme.com,23

           The TargetAddress key is further described in Appendix D. - SendTar-
           gets Operation -.

   11.9  InitialR2T

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           InitialR2T=<Yes|No>

           Examples:

                 I->InitialR2T=No
                 T->InitialR2T=No

           Default is Yes.
           Result function is OR.

           The InitialR2T key is used to turn off the default use of R2T, thus
           allowing an initiator to start sending data to a target as if it has
           received an initial R2T with Buffer Offset=0 and Desired Data Transfer
           Length=min (FirstBurstSize, Expected Data Transfer Length).  The
           default action is that R2T is required, unless both the initiator and
           the target send this key-pair attribute specifying InitialR2T=No.
           Only the first outgoing data burst (immediate data and/or separate
           PDUs) can be sent unsolicited (i.e., not requiring an explicit R2T).

   11.10  BidiInitialR2T

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           BidiInitialR2T=<Yes|No>

           Examples:

                 I->BidiInitialR2T=No
                 T->BidiInitialR2T=No


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           Default is Yes.
           Result function is OR.

           The BidiInitialR2T key is used to turn off the default use of BiDiR2T,
           thus allowing an initiator to send data to a target without the target
           having sent an R2T to the initiator for the output data (write part)
           of a Bidirectional command (having both the R and the W bits set).
           The default action is that R2T is required, unless both the initiator
           and the target send this key-pair attribute specifying
           BidiInitialR2T=No.  Only the first outgoing data burst (immediate
           data and/or separate PDUs) can be sent unsolicited by an R2T.

   11.11  ImmediateData

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           ImmediateData=<Yes|No>

           Default is Yes.
           Result function is AND.

           The initiator and target negotiate support for immediate data. To turn
           immediate data off, the initiator or target must state its desire to
           do so.  ImmediateData can be turned on if both the initiator and tar-
           get have ImmediateData=Yes.

           If ImmediateData is set to Yes and InitialR2T is set to Yes (default),
           then only immediate data are accepted in the first burst.

           If ImmediateData is set to No and InitialR2T is set to Yes, then the
           initiator MUST NOT send unsolicited data and the target MUST reject
           them with the corresponding response code.

           If ImmediateData is set to No and InitialR2T is set to No, then the
           initiator MUST NOT send unsolicited immediate data, but MAY send one
           unsolicited burst of Data-OUT PDUs.

           If ImmediateData is set to Yes and InitialR2T is set to No, then the
           initiator MAY send unsolicited immediate data and/or one unsolicited
           burst of Data-OUT PDUs.



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           The following table is a summary of unsolicited data options:


           +----------+-------------+---------------------------------------+
           |InitialR2T|ImmediateData| Result (up to FirstBurstSize)         |
           +----------+-------------+---------------------------------------+
           |  No      |    No       | Unsolicited data in data PDUs only.   |
           +----------+-------------+---------------------------------------+
           |  No      |    Yes      | Immediate & separate unsolicited data.|
           +----------+-------------+---------------------------------------+
           |  Yes     |    No       | Unsolicited data disallowed.          |
           +----------+-------------+---------------------------------------+
           |  Yes     |    Yes      | Immediate unsolicited data only.      |
           +----------+-------------+---------------------------------------+


   11.12  MaxRecvPDULength

           Use: ALL
           Senders: Initiator and Target
           Scope: CO

           MaxRecvPDULength=<integer-512-to-(2**24-1)>

           Default is 8192 bytes.

           This is a connection specific parameter.
           The initiator or target declares the maximum data segment length in
           bytes they can receive in an iSCSI PDU.

           For a target the value limiting the size of the receive PDUs is the
           lower of the declared MaxRecvPDULength and the negotiated MaxBurst-
           Size for solicited data or FirstBurstSize for unsolicited data.

   11.13  MaxBurstSize

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           MaxBurstSize=<integer-512-to-(2**24-1)>

           Default is 262144 (256 Kbytes).


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           The initiator and target negotiate maximum SCSI data payload in bytes
           in an Data-In or a solicited Data-Out iSCSI sequence. A sequence of
           Data-In or Data-Out PDUs ending with a Data-In or Data-Out PDU with
           the F bit set to one.

           The minimum of the two numbers is selected.

   11.14  FirstBurstSize

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           FirstBurstSize=<integer-512-to-(2**24-1)>

           Default is 65536 (64 Kbytes).

           The initiator and target negotiate the maximum amount in bytes of
           unsolicited data an iSCSI initiator may send to the target, during the
           execution of a single SCSI command. This covers the immediate data (if
           any) and the sequence of unsolicited Data-Out PDUs (if any) that fol-
           low the command.

           The minimum of the two numbers is selected.

           FirstBurstSize MUST NOT exceed MaxBurstSize.

   11.15  DefaultTime2Wait

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           DefaultTime2Wait=<integer-0-to-3600>

           Default is 3.

           The initiator and target negotiate the minimum time, in seconds, to
           wait before attempting an explicit/implicit logout or active task
           reassignment after an unexpected connection termination or a connec-
           tion reset.

           The higher of the two values is selected.


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           A value of 0 indicates that logout or active task reassignment can be
           attempted immediately.

   11.16  DefaultTime2Retain

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           DefaultTime2Retain=<integer-0-to-3600>

           Default is 3.

           The initiator and target negotiate the maximum time, in seconds after
           an initial wait (Time2Wait), before which an explicit/implicit con-
           nection Logout or active task reassignment is still possible after an
           unexpected connection termination or a connection reset.

           This value is also the session state timeout if the connection in
           question is the last LOGGED_IN connection in the session.

           The lesser of the two values is selected.

           A value of 0 indicates that connection/task state is immediately dis-
           carded by the target.

   11.17  MaxOutstandingR2T

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           MaxOutstandingR2T=<integer-from-1-to-65535>

           Default is 1.

           Initiator and target negotiate the maximum number of outstanding R2Ts
           per task, excluding any implied initial R2T that might be part of that
           task.  An R2T is considered outstanding until the last data PDU (with
           the F bit set to 1) is transferred, or a sequence reception timeout
           (section 6.12.1) is encountered for that data sequence.




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                                                                  iSCSI            1-March-02

   11.18  DataPDUInOrder

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           DataPDUInOrder=<Yes|No>

           Default is Yes.
           Result function is OR.

           No is used by iSCSI to indicate that the data PDUs within sequences
           can be in any order. Yes is used to indicate that data PDUs within
           sequences have to be at continuously increasing addresses and over-
           lays are forbidden.

   11.19  DataSequenceInOrder

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           DataSequenceInOrder=<Yes|No>

           Default is Yes.
           Result function is OR.

           A Data Sequence is a sequence of Data-In or Data-Out PDUs ending with
           a Data-In or Data-Out PDU with the F bit set to one. A Data-out
           sequence is sent either unsolicited or in response to an R2T.
           Sequences cover an offset-range.

           If DataSequenceInOrder is set to No, Data PDU sequences may be trans-
           ferred in any order.

           If DataSequenceInOrder is set to Yes, Data Sequences MUST be trans-
           ferred using continuously non-decreasing sequence offsets (R2T buffer
           offset for writes, or the smallest SCSI Data-In buffer offset within a
           read data sequence).

           If ErrorRecoveryLevel is not 0 and if DataSequenceInOrder is set to
           Yes, a target may retry at most the last R2T, and an initiator may at
           most request retransmission for the last read data sequence.
           MaxOustandingR2T MUST be set to 1 in this case.

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                                                                  iSCSI            1-March-02


   11.20  ErrorRecoveryLevel

           Use: LO
           Senders: Initiator and Target
           Scope: SW

           ErrorRecoveryLevel=<0 to 2>

           Default is 0.

           The initiator and target negotiate the recovery level supported.
           The minimum of the two values is selected.

           Recovery levels represent a combination of recovery capabilities.
           Each recovery level includes all the capabilities of the lower recov-
           ery levels and adds some new ones to them.

           In the description of recovery mechanisms, certain recovery classes
           are specified.  Section 6.13 Error Recovery Hierarchy describes the
           mapping between the classes and the levels.

   11.21  SessionType

           Use: LO, Declarative
           Senders: Initiator
           Scope: SW

           SessionType= <Discovery|Normal>

           Default is Normal.

           The Initiator indicates the type of session it wants to create.  The
           target can either accept it or reject it.

           A discovery session indicates to the Target that the only purpose of
           this Session is discovery.  The only requests a target accepts  in
           this type of session are a text request with a SendTargets key and a
           logout request with reason "close the session".

           The discovery session implies MaxConnections = 1 and overrides both
           the default and an explicit setting.



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                                                                  iSCSI            1-March-02

   11.22  The Vendor Specific Key Format

           Use: ALL
           Senders: Initiator and Target
           Scope: specific key dependent

           X-reversed.vendor.dns_name.do_something=

           Keys with this format are used for vendor-specific purposes. These
           keys always start with X-.

           To identify the vendor, we suggest you use the reversed DNS-name as a
           prefix to the key-proper.





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                                                                  iSCSI            1-March-02

   12. IANA Considerations


           The temporary (user) well-known port number for iSCSI connections
           assigned by IANA is 3260.





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                                                                  iSCSI            1-March-02

   References and Bibliography

                 [AC] A Detailed Proposal for Access Control, Jim Hafner, T10/99-
                      245
                 [AESCBC] Frankel, S., Kelly, S., Glenn, R., "The AES Cipher
                      Algorithm and Its Use with IPsec", Internet draft  (work in
                      progress), draft-ietf-ipsec-ciph-aes-cbc-03.txt, November
                      2001.
                 [AESCTR] Walker, J., Moskowitz, R., "The AES128 CTR Mode of
                      Operation and Its Use with IPsec", Internet draft (work in
                      progress), draft-moskowitz-aes128-ctr-00.txt, September 2001.
                 [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-01.txt
                 [CAM] ANSI X3.232-199X, Common Access Method-3.
                 [Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman "Optimi-
                      zation of Cyclic Redundancy-Check Codes with 24 and 32 Parity
                      Bits", IEEE Transact. on Communications, Vol. 41, No. 6, June
                      1993.
                 [COBS] S. Cheshire and M. Baker, Consistent Overhead Byte Stuff-
                      ing, IEEE Transactions on Networking, April 1999.
                 [CRC] ISO 3309, High-Level Data Link Control (CRC 32).
                 [NDT] M. Bakke & team, draft-ietf-ips-iscsi-name-disc-03.txt
                 [RFC790] J. Postel, ASSIGNED NUMBERS, September 1981.
                 [RFC791] INTERNET PROTOCOL, DARPA INTERNET PROGRAM PROTOCOL
                      SPECIFICATION, September 1981.
                 [RFC793] TRANSMISSION CONTROL PROTOCOL, DARPA INTERNET PROGRAM
                      PROTOCOL SPECIFICATION, September 1981.
                 [RFC1035] P. Mockapetris, DOMAIN NAMES - IMPLEMENTATION AND
                      SPECIFICATION, November 1987.
                 [RFC1122] Requirements for Internet Hosts-Communication Layer
                      RFC1122, R. Braden (editor).
                 [RFC1510] J. Kohl, C. Neuman, "The Kerberos Network Authentica-
                      tion Service (V5)", September 1993.
                 [RFC1766] H. Alvestrand, "Tags for the Identification of Lan-
                      guages", March 1995.
                 [RFC1964] J. Linn, "The Kerberos Version 5 GSS-API Mechanism",
                      June 1996.
                 [RFC1982] Elz, R., Bush, R., "Serial Number Arithmetic", RFC
                      1982, August 1996.
                 [RFC1994] "W. Simpson, PPP Challenge Handshake Authentication
                      Protocol (CHAP)", RFC 1994, August 1996.
                 [RFC2025] C. Adams, "The Simple Public-Key GSS-API Mechanism
                      (SPKM)", October 1996.
                 [RFC2026] Bradner, S., "The Internet Standards Process -- Revi-
                      sion 3", RFC 2026, October 1996.
                 [RFC2044] Yergeau, F., "UTF-8, a Transformation Format of Uni-
                      code and ISO 10646", October 1996.
                 [RFC2045] N. Borenstein, N. Freed, "MIME (Multipurpose Internet
                      Mail Extensions) Part One: Mechanisms for Specifying and



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                                                                  iSCSI            1-March-02

                      Describing the Format of Internet Message Bodies", November
                      1996.
                 [RFC2119] Bradner, S. "Key Words for use in RFCs to Indicate
                      Requirement Levels", BCP 14, RFC 2119, March 1997.
                 [RFC2234] D. Crocker, P. Overell Augmented BNF for Syntax Spec-
                      ifications: ABNF.
                 [RFC2246] T. Dierks, C. Allen, " The TLS Protocol Version 1.0.
                 [RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
                      Architecture", RFC 2373, July 1998.
                 [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing
                      an IANA Considerations Section in RFCs.", RFC2434, October
                      1998.
                 [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
                      Internet Protocol", RFC 2401, November 1998.
                  [RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96 within ESP
                  and AH", RFC 2404, November 1998.
                  [RFC2406] S. Kent, R. Atkinson, "IP Encapsulating Security Payload
                  (ESP)", RFC 2406, November 1998.
                  [RFC2407] D. Piper, "The Internet IP Security Domain of Interpre-
                  tation of ISAKMP", RFC 2407, November 1998.
                 [RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange
                      (IKE)", RFC 2409, November 1998.
                  [RFC2451] R. Pereira, R. Adams " The ESP CBC-Mode Cipher Algo-
                  rithms".
                 [RFC2732] R. Hinden, B. Carpenter, L. Masinter, "Format for Lit-
                      eral IPv6 Addresses in URL's", RFC 2732, December 1999.
                      [RFC2945], Wu, T., "The SRP Authentication and Key Exchange
                      System", September 2000.
                 [SAM] ANSI X3.270-1998, SCSI-3 Architecture Model (SAM).
                 [SAM2] T10/1157D, SCSI Architecture Model - 2 (SAM-2).
                 [SBC] NCITS.306-1998, SCSI-3 Block Commands (SBC).
                 [Schneier] B. Schneier, "Applied Cryptography: Protocols, Algo-
                      rithms, and Source Code in C", 2nd edition, John Wiley & Sons,
                      New York, NY, 1996.
                 [SPC] NCITS.351:200, SCSI-3 Primary Commands (SPC).
                 [SEQ-EXT] Kent, S., "IP Encapsulating Security Payload (ESP)",
                      Internet draft (work in progress), draft-ietf-ipsec-esp-v3-
                      01.txt, November 2002.
                 [SEC-IPS] B. Aboba & team "Securing Block Storage Protocols over
                      IP", Internet draft (work in progress), draft-ietf-ips-secu-
                      rity-09.txt, February 2002.
                 [SPC3]T10/1416-D, SCSI-3 Primary Commands (SPC).


   Authors' Addresses

                 Julian Satran

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                                                                  iSCSI            1-March-02

                 IBM, Haifa Research Lab
                 MATAM - Advanced Technology Center
                 Haifa 31905, Israel
                 Phone +972.4.829.6264
                 E-mail: Julian_Satran@vnet.ibm.com

                 Kalman Meth
                 IBM, Haifa Research Lab
                 MATAM - Advanced Technology Center
                 Haifa 31905, Israel
                 Phone +972.4.829.6341
                 E-mail: meth@il.ibm.com

                  Ofer Biran
                 IBM, Haifa Research Lab
                 MATAM - Advanced Technology Center
                 Haifa 31905, Israel
                 Phone +972.4.829.6253
                 E-mail: biran@il.ibm.com

                 Daniel F. Smith
                 IBM Almaden Research Center
                 650 Harry Road
                 San Jose, CA 95120-6099, USA
                 Phone: +1.408.927.2072
                 E-mail: dfsmith@almaden.ibm.com

                 Jim Hafner
                 IBM Almaden Research Center
                 650 Harry Road
                 San Jose, CA 95120
                 Phone: +1.408.927.1892
                 E-mail: hafner@almaden.ibm.com

                 Costa Sapuntzakis
                 Cisco Systems, Inc.
                 170 W. Tasman Drive
                 San Jose, CA 95134, USA
                 Phone: +1.408.525.5497
                 E-mail: csapuntz@cisco.com

                 Mark Bakke
                 Cisco Systems, Inc.
                 6450 Wedgwood Road
                 Maple Grove, MN
                 USA 55311
                 Phone: +1.763.398.1000
                 E-Mail: mbakke@cisco.com

                 Randy Haagens

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                                                                  iSCSI            1-March-02

                 Hewlett-Packard Company
                 8000 Foothills Blvd.
                 Roseville, CA 95747-5668, USA
                 Phone: +1.916.785.4578
                 E-mail: Randy_Haagens@hp.com

                 Matt Wakeley (current address)
                 Sierra Logic, Inc.
                 Phone: +1.916.772.1234 ext 116
                 E-mail: matt_wakeley@sierralogic.com

                 Efri Zeidner
                 SANgate Systems, Inc.
                 41 Hameyasdim Street
                 P.O.B. 1486
                 Even-Yehuda, Israel 40500
                 Phone: +972.9.891.9555
                 E-mail: efri@sangate.com

                 Paul von Stamwitz (current address)
                 TrueSAN Networks, Inc.
                 Phone: +1.408.869.4219
                 E-mail: pvonstamwitz@truesan.com

                 Luciano Dalle Ore
                 Quantum Corp.
                 Phone: +1.408.232.6524
                 E-mail: ldalleore@snapserver.com

                 Mallikarjun Chadalapaka
                 Hewlett-Packard Company
                 8000 Foothills Blvd.
                 Roseville, CA 95747-5668, USA
                 Phone: +1.916.785.5621
                 E-mail: cbm@rose.hp.com



           Comments may be sent to Julian Satran





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                                                                  iSCSI            1-March-02

   Appendix A. Sync and Steering with Fixed Interval Markers

           This appendix presents a simple scheme for synchronization (PDU
           boundary retrieval). It uses markers that include synchronization
           information placed at fixed intervals in the TCP stream.

           A Marker consists of:

           Byte /    0       |       1       |       2       |       3       |
               /             |               |               |               |
             |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
             +---------------+---------------+---------------+---------------+
            0| Next-iSCSI-PDU-start pointer - copy #1                        |
             +---------------+---------------+---------------+---------------+
            4| Next-iSCSI-PDU-start pointer - copy #2                        |
             +---------------+---------------+---------------+---------------+

           The Marker schemes uses payload byte stream counting that includes
           every byte placed by iSCSI in the TCP stream except for the markers
           themselves. It also excludes any bytes that TCP counts but are not
           originated by iSCSI.

           The Marker indicates the offset to the next iSCSI PDU header. The
           Marker is eight bytes in length and contains two 32-bit offset fields
           that indicate how many bytes to skip in the TCP stream in order to
           find the next iSCSI PDU header. The marker uses two copies of the
           pointer so that a marker that spans a TCP packet boundary should leave
           at least one valid copy in one of the packets.

           The inserted value is independent of the marker interval.

           The use of markers is negotiable. The initiator and target MAY indi-
           cate their readiness to receive and/or send markers during login sep-
           arately for each connection. The default is No.

   A.1  Markers At Fixed Intervals

           A marker is inserted at fixed intervals in the TCP byte stream. During
           login, each end of the iSCSI session specifies the interval at which
           it is willing to receive the marker, or it disables the marker alto-
           gether. If a receiver indicates that it desires a marker, the sender
           MAY agree (during negotiation) and provide the marker at the desired
           interval. However, in certain environments, a sender not providing


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                                                                  iSCSI            1-March-02

           markers to a receiver wanting markers may suffer an appreciable per-
           formance degradation.

           The marker interval and the initial marker-less interval are counted
           in terms of the bytes placed in the TCP stream data by iSCSI.

           When reduced to iSCSI terms, markers MUST indicate the offset to a 4-
           byte word boundary in the stream. The last two bits of each marker
           word are reserved and are considered 0 for offset computation.

           Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
           marker manipulation.

   A.2  Initial Marker-less Interval

           To enable the connection setup including the login phase negotiation,
           marking (if any) is started only at the first marker interval after
           the end of the login phase. However, in order to enable the marker
           inclusion and exclusion mechanism to work without knowledge of the
           length of the login phase, the first marker will be placed in the TCP
           stream as if the Marker-less interval had included markers.

           Thus all markers appear in the stream at locations conforming to the
           formula: [(MI + 8) * n - 8] where MI = Marker Interval, n = integer
           number.

           As an example if the marker interval is 512 and the login ended at
           byte 1003 (first iSCSI placed byte is 0) the first marker will be
           inserted after byte 1031 in the stream.

   A.3  Negotiation

           The following operational key=value pairs are used to negotiate the
           fixed interval markers. The direction (output or input) is relative to
           the initiator.

   A.3.1   OFMarker, IFMarker

           Use: IO
           Senders: Initiator and Target
           Scope: CO

           OFMarker=<Yes|No>
           IFMarker=<Yes|No>

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                                                                  iSCSI            1-March-02


           Default is No.

           Result function is AND.

           OFMarker is used to turn on or off the initiator to target markers on
           the connection.  IFMarker is used to turn on or off the target to ini-
           tiator markers on the connection.

           Examples:

                 I->OFMarker=Yes,IFMarker=Yes
                 T->OFMarker=Yes,IFMarker=Yes

           Results in the Marker being used in both directions while

                 I->OFMarker=Yes,IFMarker=Yes
                 T->OFMarker=Yes,IFMarker=No

           Results in Marker being used from the initiator to the target, but not
           from the target to initiator.

   A.3.2   OFMarkInt, IFMarkInt

           Use: IO
           Senders: Initiator and Target
           Scope: CO

           Offering:

           OFMarkInt=<integer-from-1-to-65535>[,<integer-from-1-to-65535>]
           IFMarkInt=<integer-from-1-to-65535>[,<integer-from-1-to-65535>]

           Responding:

           OFMarkInt=<integer-from-1-to-65535>|Reject
           IFMarkInt=<integer-from-1-to-65535>|Reject

           OFMarkInt is used to set the interval for the initiator to target
           markers on the connection.  IFMarkInt is used to set the interval for
           the target to initiator markers on the connection.

           For the offering the initiator or target indicates the minimum to max-
           imum interval (in 4-byte words) it wants the markers for one or both

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                                                                  iSCSI            1-March-02

           directions. In case it only wants a specific value, only a single
           value has to be specified. The responder selects a value within the
           minimum and maximum offered or the only value offered or indicates
           through the xFMarker key=value its inability to set and/or receive
           markers. When the interval is unacceptable the responder answers with
           "Reject".  Reject is resetting the marker function in the specified
           direction (Output or Input) to No.

           The interval is measured from the end of a marker to the beginning of
           the next marker. For example, a value of 1024 means 1024 words (4096
           bytes of iSCSI payload between markers).

           The default is 2048.





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                                                                  iSCSI            1-March-02

   Appendix B. Examples

   B.4  Read Operation Example

           +------------------+-----------------------+----------------------+
           |Initiator Function|    PDU Type           |  Target Function     |
           +------------------+-----------------------+----------------------+
           |  Command request |SCSI Command (READ)>>> |                      |
           |  (read)          |                       |                      |
           +------------------+-----------------------+----------------------+
           |                  |                       | Prepare Data Transfer|
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           +------------------+-----------------------+----------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense |
           +------------------+-----------------------+----------------------+
           | Command Complete |                       |                      |
           +------------------+-----------------------+----------------------+

   B.5  Write Operation Example

           +------------------+-----------------------+---------------------+
           |Initiator Function|    PDU Type           |  Target Function    |
           +------------------+-----------------------+---------------------+
           |  Command request |SCSI Command (WRITE)>>>| Receive command     |
           |  (write)         |                       | and queue it        |
           +------------------+-----------------------+---------------------+
           |                  |                       | Process old commands|
           +------------------+-----------------------+---------------------+
           |                  |                       | Ready to process    |
           |                  |   <<< R2T             | WRITE command       |
           +------------------+-----------------------+---------------------+
           |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
           +------------------+-----------------------+---------------------+
           |                  |   <<< R2T             | Ready for data      |
           +------------------+-----------------------+---------------------+
           |                  |   <<< R2T             | Ready for data      |
           +------------------+-----------------------+---------------------+
           |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |


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                                                                  iSCSI            1-March-02

           +------------------+-----------------------+---------------------+
           |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
           +------------------+-----------------------+---------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense|
           +------------------+-----------------------+---------------------+
           | Command Complete |                       |                     |
           +------------------+-----------------------+---------------------+

   B.6  R2TSN/DataSN use Examples

           Output (write) data DataSN/R2TSN Example

           +------------------+-----------------------+----------------------+
           |Initiator Function|    PDU Type & Content |  Target Function     |
           +------------------+-----------------------+----------------------+
           |  Command request |SCSI Command (WRITE)>>>| Receive command      |
           |  (write)         |                       | and queue it         |
           +------------------+-----------------------+----------------------+
           |                  |                       | Process old commands |
           +------------------+-----------------------+----------------------+
           |                  |   <<< R2T             | Ready for data       |
           |                  |   R2TSN = 0           |                      |
           +------------------+-----------------------+----------------------+
           |                  |   <<< R2T             | Ready for more data  |
           |                  |   R2TSN = 1           |                      |
           +------------------+-----------------------+----------------------+
           |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
           |  for R2TSN 0     |   DataSN = 0, F=0     |                      |
           +------------------+-----------------------+----------------------+
           |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
           |  for R2TSN 0     |   DataSN = 1, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |  Send Data       |   SCSI Data >>>       |   Receive Data       |
           |  for R2TSN 1     |   DataSN = 0, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense |
           |                  |   ExpDataSN = 0       |                      |
           +------------------+-----------------------+----------------------+
           | Command Complete |                       |                      |
           +------------------+-----------------------+----------------------+





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                                                                  iSCSI            1-March-02

            Input (read) data DataSN Example

           +------------------+-----------------------+----------------------+
           |Initiator Function|    PDU Type           |  Target Function     |
           +------------------+-----------------------+----------------------+
           |  Command request |SCSI Command (READ)>>> |                      |
           |  (read)          |                       |                      |
           +------------------+-----------------------+----------------------+
           |                  |                       | Prepare Data Transfer|
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           |                  |   DataSN = 0, F=0     |                      |
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           |                  |   DataSN = 1, F=0     |                      |
           +------------------+-----------------------+----------------------+
           |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           |                  |   DataSN = 2, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense |
           |                  |   ExpDataSN = 3       |                      |
           +------------------+-----------------------+----------------------+
           | Command Complete |                       |                      |
           +------------------+-----------------------+----------------------+


            Bidirectional DataSN Example

           +------------------+-----------------------+----------------------+
           |Initiator Function|    PDU Type           |  Target Function     |
           +------------------+-----------------------+----------------------+
           |  Command request |SCSI Command >>>       |                      |
           |  (Read-Write)    |  Read-Write           |                      |
           +------------------+-----------------------+----------------------+
           |                  |                       | Process old commands |
           +------------------+-----------------------+----------------------+
           |                  |   <<< R2T             | Ready to process     |
           |                  |   R2TSN = 0           | WRITE command        |
           +------------------+-----------------------+----------------------+
           | * Receive Data   |   <<< SCSI Data-in    |   Send Data          |
           |                  |   DataSN = 0, F=0     |                      |
           +------------------+-----------------------+----------------------+
           | * Receive Data   |   <<< SCSI Data-in    |   Send Data          |

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                                                                  iSCSI            1-March-02

           |                  |   DataSN = 1, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |  * Send Data     |   SCSI Data-out >>>   |   Receive Data       |
           |  for R2TSN 0     |   DataSN = 0, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense |
           |                  |   ExpDataSN = 2       |                      |
           +------------------+-----------------------+----------------------+
           | Command Complete |                       |                      |
           +------------------+-----------------------+----------------------+

           *) Send data and Receive Data may be transferred simultaneously as in
           an atomic Read-Old-Write-New or sequential as in an atomic Read-
           Update-Write (in the alter case the R2T may follow the received data).

           Unsolicited and immediate output (write) data with DataSN Example

           +------------------+-----------------------+----------------------+
           |Initiator Function|    PDU Type & Content |  Target Function     |
           +------------------+-----------------------+----------------------+
           |  Command request |SCSI Command (WRITE)>>>| Receive command      |
           |  (write)         |F=0                    | and data             |
           |+ immediate data  |                       | and queue it         |
           +------------------+-----------------------+----------------------+
           | Send Unsolicited |   SCSI Write Data >>> | Receive more Data    |
           |  Data            |   DataSN = 0, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |                  |                       | Process old commands |
           +------------------+-----------------------+----------------------+
           |                  |   <<< R2T             | Ready for more data  |
           |                  |   R2TSN = 0           |                      |
           +------------------+-----------------------+----------------------+
           |  Send Data       |   SCSI Write Data >>> |   Receive Data       |
           |  for R2TSN 0     |   DataSN = 0, F=1     |                      |
           +------------------+-----------------------+----------------------+
           |                  |   <<< SCSI Response   |Send Status and Sense |
           |                  |                       |                      |
           +------------------+-----------------------+----------------------+
           | Command Complete |                       |                      |
           +------------------+-----------------------+----------------------+




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                                                                  iSCSI            1-March-02

   B.7  CRC Examples

           N.B. all Values are Hexadecimal

           32 bytes of zeroes:

             Byte:        0  1  2  3

                0:       00 00 00 00
              ...
               28:       00 00 00 00

              CRC:       aa 36 91 8a

           32 bytes of ones:

             Byte:        0  1  2  3

                0:       ff ff ff ff
              ...
               28:       ff ff ff ff

              CRC:       43 ab a8 62

           32 bytes of incrementing 00..1f:

             Byte:        0  1  2  3

                0:       00 01 02 03
              ...
               28:       1c 1d 1e 1f

              CRC:       4e 79 dd 46

           32 bytes of decrementing 1f..00:

             Byte:        0  1  2  3

                0:       1f 1e 1d 1c
              ...
               28:       03 02 01 00

              CRC:       5c db 3f 11


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   Appendix C. Login Phase Examples

           In the first example, the initiator and target authenticate each other
           via Kerberos:

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=KRB5,SRP,None

                 T-> Login (CSG,NSG=0,0 T=0)
                     AuthMethod=KRB5


                 I-> Login (CSG,NSG=0,1 T=1)
                     KRB_AP_REQ=<krb_ap_req>

                 (krb_ap_req contains the Kerberos V5 ticket and authenticator
                      with MUTUAL-REQUIRED set in the ap-options field)

                 If the authentication is successful, the target proceeds with:

                 T-> Login (CSG,NSG=0,1 T=1)
                     KRB_AP_REP=<krb_ap_rep>

                 (krb_ap_rep is the Kerberos V5 mutual authentication reply)

                 If the authentication is successful, the initiator may proceed
                      with:

                 I-> Login (CSG,NSG=1,0 T=0) FirstBurstSize=0
                 T-> Login (CSG,NSG=1,0 T=0) FirstBurstSize=8192 MaxBurst-
                      Size=8192
                 I-> Login (CSG,NSG=1,0 T=0) MaxBurstSize=8192
                     ... more iSCSI Operational Parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... more iSCSI Operational Parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"

                 If the initiator‚ÇÖs authentication by the target is not success-
                      ful, the target responds with:


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                                                                  iSCSI            1-March-02

                 T-> Login "login reject"

                 instead of the Login KRB_AP_REP message, and terminates the con-
                      nection.

                 If the target‚ÇÖs authentication by the initiator is not success-
                      ful, the initiator terminates the connection (without respond-
                      ing to the Login KRB_AP_REP message).

           In the next example only the initiator is authenticated by the target
           via Kerberos:

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=SRP,KRB5,None

                 T-> Login-PR (CSG,NSG=0,0 T=0)
                     AuthMethod=KRB5

                 I-> Login (CSG,NSG=0,1 T=1)
                     KRB_AP_REQ=krb_ap_req

                 (MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)

                 If the authentication is successful, the target proceeds with:

                 T-> Login (CSG,NSG=0,1 T=1)

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 . . .

                 T-> Login (CSG,NSG=1,3 T=1)"login accept"


           In the next example, the initiator and target authenticate each other
           via SPKM1:

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=SPKM1,KRB5,None

                 T-> Login (CSG,NSG=0,0 T=0)

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                                                                  iSCSI            1-March-02

                     AuthMethod=SPKM1

                 I-> Login (CSG,NSG=0,0 T=0)
                     SPKM_REQ=<spkm-req>

                 (spkm-req is the SPKM-REQ token with the mutual-state bit in the
                      options field of the REQ-TOKEN set)

                 T-> Login (CSG,NSG=0,0 T=0)
                     SPKM_REP_TI=<spkm-rep-ti>

                 If the authentication is successful, the initiator proceeds:

                 I-> Login (CSG,NSG=0,1 T=1)
                     SPKM_REP_IT=<spkm-rep-it>

                 If the authentication is successful, the target proceeds with:

                 T-> Login (CSG,NSG=0,1 T=1)

                 The initiator may proceed:

                 I-> Login  (CSG,NSG=1,0 T=0) ... iSCSI parameters
                 T-> Login  (CSG,NSG=1,0 T=0) ... iSCSI parameters

                 And at the end:

                 I-> Login  (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"


                 If the target‚ÇÖs authentication by the initiator is not success-
                      ful, the initiator terminates the connection (without respond-
                      ing to the Login SPKM_REP_TI message).

                 If the initiator‚ÇÖs authentication by the target is not success-
                      ful, the target responds with:

                 T-> Login "login reject"

                 instead of the Login "proceed and change stage" message, and
                      terminates the connection.


           In the next example, the initiator and target authenticate each other
           via SPKM2:



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                                                                  iSCSI            1-March-02

                 I-> Login (CSG,NSG=0,0 T=0)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                           AuthMethod=SPKM1,SPKM2

                 T-> Login-PR (CSG,NSG=0,0 T=0)
                     AuthMethod=SPKM2

                 I-> Login (CSG,NSG=0,1 T=1)
                     SPKM_REQ=<spkm-req>

                 (spkm-req is the SPKM-REQ token with the mutual-state bit in the
                      options field of the REQ-TOKEN not set)

                 If the authentication is successful, the target proceeds with:

                 T-> Login (CSG,NSG=0,1 T=1)

                 The initiator may proceed:

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login  (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"


           In the next example, the initiator and target authenticate each other
           via SRP:

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=KRB5,SRP,None

                 T-> Login-PR  (CSG,NSG=0,0 T=0)
                     AuthMethod=SRP

                 I-> Login (CSG,NSG=0,0 T=0)
                     SRP_U=<user>
                     TargetAuth=Yes


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                                                                  iSCSI            1-March-02

                 T-> Login (CSG,NSG=0,0 T=0)
                     SRP_N=<N>
                     SRP_g=<g>
                     SRP_s=<s>

                 I-> Login (CSG,NSG=0,0 T=0)
                     SRP_A=<A>

                 T-> Login (CSG,NSG=0,0 T=0)
                     SRP_B=<B>

                 I-> Login (CSG,NSG=0,1 T=1)
                     SRP_M=<M>

                 If the initiator authentication is successful, the target pro-
                      ceeds:

                 T-> Login (CSG,NSG=0,1 T=1)
                     SRP_HM=<H(A | M | K)>

              Where N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945].

                 If the target authentication is not successful, the initiator
                      terminates the connection; otherwise, it proceeds.

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login  (CSG,NSG=1,3 T=1) "login accept"

                 If the initiator authentication is not successful, the target
                      responds with:

                 T-> Login "login reject"

                 Instead of the T-> Login SRP_HM=<H(A | M | K)>  message and ter-
                      minates the connection.

           In the next example, only the initiator is authenticated by the target
           via SRP:



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                                                                  iSCSI            1-March-02

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=KRB5,SRP,None

                 T-> Login-PR (CSG,NSG=0,0 T=0)
                     AuthMethod=SRP

                 I-> Login (CSG,NSG=0,0 T=0)
                     SRP_U=<user>
                     TargetAuth=No

              T-> Login (CSG,NSG=0,0 T=0)
                  SRP_N=<N>
                  SRP_g=<g>
                  SRP_s=<s>

                 I-> Login (CSG,NSG=0,0 T=0)
                     SRP_A=<A>

                 T-> Login (CSG,NSG=0,0 T=0)
                     SRP_B=<B>

                 I-> Login (CSG,NSG=0,1 T=1)
                     SRP_M=<M>

                 If the initiator authentication is successful, the target pro-
                      ceeds:

                 T-> Login (CSG,NSG=0,1 T=1)

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"


           In the next example the initiator and target authenticate each other
           via CHAP:

                 I-> Login (CSG,NSG=0,0 T=0)

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                                                                  iSCSI            1-March-02

                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=KRB5,CHAP,None

                 T-> Login-PR (CSG,NSG=0,0 T=0)
                     AuthMethod=CHAP

                 I-> Login (CSG,NSG=0,0 T=0)
                     CHAP_A=<A1,A2>

              T-> Login (CSG,NSG=0,0 T=0)
                  CHAP_A=<A1>
                  CHAP_I=<I>
                  CHAP_C=<C>

                 I-> Login (CSG,NSG=0,1 T=1)
                     CHAP_N=<N>
                     CHAP_R=<R>
                     CHAP_I=<I>
                     CHAP_C=<C>

                 If the initiator authentication is successful, the target pro-
                      ceeds:

                 T-> Login (CSG,NSG=0,1 T=1)
                     CHAP_N=<N>
                     CHAP_R=<R>

                 If the target authentication is not successful, the initiator
                      aborts the connection; otherwise, it proceeds.

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters
                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"

                 If the initiator authentication is not successful, the target
                      responds with:

                 T-> Login "login reject"



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                                                                  iSCSI            1-March-02

                 Instead of the Login CHAP_R=<response> "proceed and change
                      stage"
                 message and terminates the connection.


           In the next example, only the initiator is authenticated by the target
           via CHAP:

                 I-> Login (CSG,NSG=0,1 T=0)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod=KRB5,CHAP,None

                 T-> Login-PR (CSG,NSG=0,0 T=0)
                     AuthMethod=CHAP

                 I-> Login (CSG,NSG=0,0 T=0)
                     CHAP_A=<A1,A2>

              T-> Login (CSG,NSG=0,0 T=0)
                  CHAP_A=<A1>
                  CHAP_I=<I>
                  CHAP_C=<C>

                 I-> Login (CSG,NSG=0,1 T=1)
                     CHAP_N=<N>
                     CHAP_R=<R>

                 If the initiator authentication is successful, the target pro-
                      ceeds:

                 T-> Login (CSG,NSG=0,1 T=1)

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"




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           In the next example, the initiator does not offer any security param-
           eters. It therefore, may offer iSCSI parameters on the Login PDU with
           the T bit set to 1, and the target may respond with a final Login
           Response PDU immediately:

                 I-> Login (CSG,NSG=1,3 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"
                     ... ISCSI parameters

                 In the next example, the initiator does offer security parame-
                      ters on the Login PDU, but the target does not choose any
                      (i.e., chooses the "None" values):

                 I-> Login (CSG,NSG=0,1 T=1)
                     InitiatorName=iqn.1999-07.com.os.hostid.77
                     TargetName=iqn.1999-07.com.acme.diskarray.sn.88
                     AuthMethod:KRB5,SRP,None

                 T-> Login-PR (CSG,NSG=0,1 T=1)
                     AuthMethod=None

                 I-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 T-> Login (CSG,NSG=1,0 T=0)
                     ... iSCSI parameters

                 And at the end:

                 I-> Login (CSG,NSG=1,3 T=1)
                     optional iSCSI parameters

                 T-> Login (CSG,NSG=1,3 T=1) "login accept"





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                                                                  iSCSI            1-March-02

   Appendix D. SendTargets Operation

           To reduce the amount of configuration required on an initiator, iSCSI
           provides the SendTargets text request.  This initiator sends this com-
           mand to request a list of targets to which it may have access, as well
           as the list of addresses (IP address and TCP port) on which these tar-
           gets may be accessed.

           To make use of SendTargets, an initiator must first establish one of
           two types of sessions.  If the initiator establishes the session using
           the key "SessionType=Discovery", the session is a discovery session,
           and a target name does not need to be specified.  Otherwise, the ses-
           sion is a normal, operational session.  The SendTargets command MUST
           only be sent during the full feature phase of a normal or discovery
           session.

           A system that contains targets MUST support discovery sessions on each
           of its IP addresses, and MUST support the SendTargets command on the
           discovery session.  A target MUST support the SendTargets command on
           operational sessions; these will only return address information
           about the target to which the session is connected, and do not return
           information about other targets.

           An initiator MAY make use of the SendTargets as it sees fit.

           A SendTargets command consists of a single Text request PDU.
           This PDU contains exactly one text key and value.  The text key MUST
           be SendTargets.  The expected response depends upon the value, as well
           as whether the session is a discovery or operational session.

           The value must be one of:

                 all

                 The initiator is requesting that information on all relevant
                      targets known to the implementation be returned.  This value
                      MUST be supported on a discovery session, and MUST NOT be sup-
                      ported on an operational session.

                 <iSCSI-target-name>

                 If an iSCSI target name is specified, the session should respond
                      with addresses for only the named target, if possible.  This
                      value MUST be supported on discovery sessions.  A discovery


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                                                                  iSCSI            1-March-02

                      session MUST be capable of returning addresses for those tar-
                      gets that would have been returned had value=all been desig-
                      nated.

                 <nothing>

                 The session should respond only with addresses for the target to
                      which the session is logged in.  This MUST be supported on
                      operational sessions, and MUST NOT return targets other than
                      the one to which the session is logged in.

           The response to this command is a text response that contains a list
           of zero or more targets and, optionally, their addresses.  Each target
           is returned as a target record.  A target record begins with the Tar-
           getName text key, followed by a list of TargetAddress text keys, and
           bounded by the end of the text response or the next TargetName key,
           which begins a new record.  No text keys other than TargetName and
           TargetAddress are permitted within a SendTargets response.

           For the format of the TargetName, see Section 11.4 TargetName.

           A discovery session MAY respond to a SendTargets request with its com-
           plete list of targets, or with a list of targets that is based on the
           name of the initiator logged in to the session.

           A SendTargets response MUST NOT not contain target names if there are
           no targets for the requesting initiator to access.

           Each target record returned includes zero or more TargetAddress
           fields.

           A SendTargets response MUST NOT contain iSCSI default target names.

           Each target record starts with one text key of the form:

                 TargetName=<target-name-goes-here>

           Followed by zero or more address keys of the form:

                 TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],<portal-
                      group-tag>

           The hostname-or-ipaddress and tcp port are as specified in the  Sec-
           tion 2.2.6 Naming and Addressing.


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           Each TargetAddress belongs to a portal group, identified by its
           numeric, decimal portal group tag.  The iSCSI target name, together
           with this tag, constitutes the SCSI port identifier; the tag need be
           unique only within a given target name's list of addresses.

           Multiple-connection sessions can span iSCSI addresses that belong to
           the same portal group.

           Multiple-connection sessions cannot span iSCSI addresses that belong
           to different portal groups.

           If a SendTargets response reports an iSCSI address for a target, it
           SHOULD also report all other addresses in its portal group in the same
           response.

           A SendTargets text response can be longer than a single Text Response
           PDU, and makes use of the long text responses as specified.

           After obtaining a list of targets from the discovery target session,
           an iSCSI initiator may initiate new sessions to log in to the discov-
           ered targets for full operation.  The initiator MAY keep the session
           to a default target open, and MAY send subsequently SendTargets com-
           mands to discover new targets.

           Examples:


           This example is the SendTargets response from a single target that has
           no other interface ports.

           Initiator sends text request that contains:

                 SendTargets=all

           Target sends a text response that contains:

                 TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309

           All the target  had to return in the simple case was the target name.
           It is assumed by the initiator that the IP address and TCP port for
           this target are the same as used on the current connection to the
           default iSCSI target.



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                                                                  iSCSI            1-March-02

           The next example has two internal iSCSI targets, each accessible via
           two different ports with different IP addresses.  The following is the
           text response:

                 TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
                 TargetAddress=10.1.0.45:3000,1
                 TargetAddress=10.1.1.45:3000,2
                 TargetName=iqn.1993-11.com.acme.diskarray.sn.1234567
                 TargetAddress=10.1.0.45:3000,1
                 TargetAddress=10.1.1.45:3000,2

           Both targets share both addresses; the multiple addresses are likely
           used to provide multi-path support.  The initiator may connect to
           either target name on either address.  Each of the addresses has its
           own portal group tag; they do not support spanning multiple-connec-
           tion sessions with each other.  Keep in mind also that the portal
           group tags for the two named targets are independent of one another;
           portal group "1" on the first target is not necessarily the same as
           portal group "1" on the second.

           In the above example, a DNS host name could have been returned instead
           of an IP address, and that an IPv6 addresses (5 to 16 dotted-decimal
           numbers) could have also been returned.

           The next text response shows a target that supports spanning sessions
           across multiple addresses, which indicates the use of the portal group
           tags:

                 TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
                 TargetAddress=10.1.0.45:3000,1
                 TargetAddress=10.1.1.46:3000,1
                 TargetAddress=10.1.0.47:3000,2
                 TargetAddress=10.1.1.48:3000,2
                 TargetAddress=10.1.1.49:3000,3

           In this example, any of the target addresses can be used to reach the
           same target.  A single-connection session can be established to any of
           these TCP addresses.  A multiple-connection session could span
           addresses .45 and .46 or .47 and .48, but cannot span any other combi-
           nation.  A TargetAddress with its own tag (.49), cannot be combined
           with any other address within the same session.

           This SendTargets response does not indicate whether .49 supports mul-
           tiple connections per session; it communicated via the MaxConnections
           text key upon login to the target.

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   Appendix E. Algorithmic Presentation of Error Recovery Classes

           This appendix illustrates the error recovery classes using a pseudo-
           programming-language.  The procedure names are chosen to be obvious to
           most implementers. Each of the recovery classes described has initia-
           tor procedures as well as target procedures.   These algorithms focus
           on outlining the mechanics of error recovery classes, and ignore all
           other aspects/cases. Examples of this approach are:

                 - Handling for only certain Opcode types is shown.

                 - Only certain reason codes (for example, Recovery in Logout
                      command) are outlined.

                 - Resultant cases, such as recovery of Synchronization on a
                      header digest error are considered out-of-scope in these algo-
                      rithms.  In this particular example a header digest error may
                      lead to connection recovery if some type of sync and steering
                      layer is not implemented.

           These algorithms strive to convey the iSCSI error recovery concepts in
           the simplest terms, and are not designed to be optimal.

   E.8  General Data Structure and Procedure Description

           This section defines the procedures and data structures that are com-
           monly used by all the error recovery algorithms. The structures may
           not be the exhaustive representations of what is required for a typi-
           cal implementation.

           Data structure definitions -
           struct TransferContext {
                   int TargetTransferTag;
                   int ExpectedDataSN;
           };

           struct TCB {              /* task control block */
                   Boolean SoFarInOrder;
                   int ExpectedDataSN; /* used for both R2Ts, and Data */
                   int MissingDataSNList[MaxMissingDPDU];
                   Boolean FbitReceived;
                   Boolean StatusXferd;
                   Boolean CurrentlyAllegiant;
                   int ActiveR2Ts;


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                   int Response;
                   char *Reason;
                   struct TransferContext
                               TransferContextList[MaxOutStandingR2T];
                   int InitiatorTaskTag;
                   int CmdSN;
           };

           struct Connection {
                   struct Session SessionReference;
                   Boolean SoFarInOrder;
                   int CID;
                   int State;
                   int ExpectedStatSN;
                   int MissingStatSNList[MaxMissingSPDU];
                   Boolean PerformConnectionCleanup;
           };

           struct Session {
                   int NumConnections;
                   int CmdSN;
                   int Maxconnections;
                   int ErrorRecoveryLevel;
                   struct iSCSIEndpoint OtherEndInfo;
                   struct Connection ConnectionList[MaxSupportedConns];
           };

           Procedure descriptions -
           Receive-a-In-PDU(transport connection, inbound PDU);
           check-basic-validity(inbound PDU);
           Start-Timer(timeout handler, argument, timeout value);
           Build-And-Send-Reject(transport connection, bad PDU, reason code);

   E.9  Within-command Error Recovery Algorithms

   E.9.1   Procedure Descriptions

           Recover-Data-if-Possible(last required DataSN, task control block);
           Build-And-Send-DSnack(task control block);
           Build-And-Send-Abort(task control block);
           SCSI-Task-Completion(task control block);
           Build-And-Send-a-Data-Burst(transport connection, R2T PDU,
                                                         task control block);
           Build-And-Send-R2T(transport connection, description of data,

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                                                        task control block);
           Build-And-Send-Status(transport connection, task control block);
           Transfer-Context-Timeout-Handler(transfer context);

           Implementation-specific tunables -
           InitiatorDataSNACKEnabled, TargetDataSNACKSupported,
           TargetRecoveryR2TEnabled.

           Notes:

                 - Some procedures used in this section, including: Recover-Sta-
                      tus-if-Possible, Handle-Status-SNACK-request, Evaluate-a-
                      StatSN are defined in Within-connection recovery algorithms.

                 - The Response processing pseudo-code, shown in the target algo-
                      rithms, applies to all solicited PDUs that carry StatSN - SCSI
                      Response, Text Response etc.

   E.9.2   Initiator Algorithms

           Recover-Data-if-Possible(LastRequiredDataSN, TCB)
           {
               if (InitiatorDataSNACKEnabled) {
                    if (# of missing PDUs is trackable) {
                          Note the missing DataSNs in TCB.
                          Build-And-Send-DSnack(TCB);
                    } else {
                        TCB.Reason = "Protocol service CRC error";
                          }
               } else {
                     TCB.Reason = "Protocol service CRC error";
               }
               if (TCB.Reason = "Protocol service CRC error") {
                     Clear the missing PDU list in the TCB.
                     if (TCB.StatusXferd is not TRUE)
                        Build-And-Send-Abort(TCB);
               }
           }

           Receive-a-In-PDU(Connection, CurrentPDU)
           {
              check-basic-validity(CurrentPDU);
              if (Header-Digest-Bad) discard, return;
              Retrieve TCB for CurrentPDU.InitiatorTaskTag.


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              if ((CurrentPDU.type = Data)
                          or (CurrentPDU.type = R2T)) {
                 if (Data-Digest-Bad) {
                         send-data-SNACK = TRUE;
                   LastRequiredDataSN = CurrentPDU.DataSN;
                       } else {
                       if (TCB.SoFarInOrder = TRUE) {
                           if (current DataSN is expected) {
                                Increment TCB.ExpectedDataSN.
                           } else {
                                   TCB.SoFarInOrder = FALSE;
                                   send-data-SNACK = TRUE;
                                            }
                       } else {
                                 if (current DataSN was considered missing) {
                                               remove current DataSN from missing PDU list.
                                 } else if (current DataSN is higher than expected) {
                                       send-data-SNACK = TRUE;
                                            } else {
                                                  discard, return;
                                            }
                                            Adjust TCB.ExpectedDataSN if appropriate.
                       }
                       LastRequiredDataSN = CurrentPDU.DataSN - 1;
                       }
                       if (send-data-SNACK is TRUE and
                           task is not already considered failed) {
                       Recover-Data-if-Possible(LastRequiredDataSN, TCB);
                 }
                       if (missing data PDU list is empty) {
                          TCB.SoFarInOrder = TRUE;
                       }
                 if (CurrentPDU.type = R2T) {
                    Increment ActiveR2Ts for this task.
                    Build-And-Send-A-Data-Burst(Connection, CurrentPDU, TCB);
                 }
              } else if (CurrentPDU.type = Response) {
                 if (Data-Digest-Bad) {
                          send-status-SNACK = TRUE;
                       } else {
                    TCB.StatusXferd = TRUE;
                    Store the status information in TCB.
                    if (ExpDataSN does not match) {

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                         TCB.SoFarInOrder = FALSE;
                         Recover-Data-if-Possible(current DataSN, TCB);
                    }
                          if (missing data PDU list is empty) {
                               TCB.SoFarInOrder = TRUE;
                          }
                    send-status-SNACK = Evaluate-a-StatSN(Connection,
                                                 CurrentPDU.StatSN);
                 }
                 if (send-status-SNACK is TRUE)
                    Recover-Status-if-Possible(Connection, CurrentPDU);
              } else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN */
              }
              if ((TCB.SoFarInOrder is TRUE) and
                                                           (TCB.StatusXferd is TRUE)) {
                 SCSI-Task-Completion(TCB);
              }
           }

   E.9.3   Target Algorithms

           Receive-a-In-PDU(Connection, CurrentPDU)
           {
             check-basic-validity(CurrentPDU);
             if (Header-Digest-Bad) discard, return;
             Retrieve TCB for CurrentPDU.InitiatorTaskTag.
             if (CurrentPDU.type = Data) {
                 Retrieve TContext from CurrentPDU.TargetTransferTag;
                 if (Data-Digest-Bad) {
                          Build-And-Send-Reject(Connection, CurrentPDU,
                                         Payload-Digest-Error);
                    Note the missing data PDUs in MissingDataRange[].
                          send-recovery-R2T = TRUE;
                       } else {
                    if (current DataSN is not expected) {
                        Note the missing data PDUs in MissingDataRange[].
                              send-recovery-R2T = TRUE;
                          }
                    if (CurrentPDU.Fbit = TRUE) {
                        if (current PDU is solicited) {
                               Decrement TCB.ActiveR2Ts.
                        }
                        if ((current PDU is unsolicited and


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                               data received is less than I/O size and
                                 data received is less than FirstBurstSize)
                            or {current PDU is solicited and the size of
                                 this burst is less than expected)) {
                            send-recovery-R2T = TRUE;
                            Note the missing data in MissingDataRange[].
                        }
                          }
                       }
                       Increment TContext.ExpectedDataSN.
                 if (send-recovery-R2T is TRUE  and
                           task is not already considered failed) {
                    if (TargetRecoveryR2TEnabled is TRUE) {
                        Increment TCB.ActiveR2Ts.
                        Build-And-Send-R2T(Connection, MissingDataRange, TCB);
                    } else {
                         if (current PDU is the last unsolicited)
                             TCB.Reason = "Not enough unsolicited data";
                         else
                             TCB.Reason = "Protocol service CRC error";
                    }
                 }
                 if (TCB.ActiveR2Ts = 0) {
                    Build-And-Send-Status(Connection, TCB);
                 }
             } else if (CurrentPDU.type = SNACK) {
                 snack-failure = FALSE;
                 if (this is data retransmission request) {
                    if (TargetDataSNACKSupported) {
                         if (the request is satisfiable) {
                               Build-And-Send-A-Data-Burst(CurrentPDU, TCB);
                         } else {
                               snack-failure = TRUE;
                         }
                    } else {
                         snack-failure = TRUE;
                    }
                    if (snack-failure is TRUE) {
                         Build-And-Send-Reject(Connection, CurrentPDU,
                                                             Data-SNACK-Reject);
                         if (TCB.StatusXferd is not TRUE) {
                              TCB.Reason = "SNACK Rejected";
                              Build-And-Send-Status(Connection, TCB);

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                         }
                    }
                 } else {
                     Handle-Status-SNACK-request(Connection, CurrentPDU);
                 }
             } else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN */
             }
           }

           Transfer-Context-Timeout-Handler(TContext)
           {
             Retrieve TCB and Connection from TContext.
             Decrement TCB.ActiveR2Ts.
             if (TargetRecoveryR2TEnabled is TRUE and
                           task is not already considered failed) {
                 Note the missing data PDUs in MissingDataRange[].
                 Build-And-Send-R2T(Connection, MissingDataRange, TCB);
             } else {
                 TCB.Reason = "Protocol service CRC error";
                 if (TCB.ActiveR2Ts = 0) {
                    Build-And-Send-Status(Connection, TCB);
                 }
             }
           }

   E.10  Within-connection Recovery Algorithms

   E.10.1   Procedure Descriptions

           Procedure descriptions:
           Recover-Status-if-Possible(transport connection,
                                               currently received PDU);
           Evaluate-a-StatSN(transport connection, current StatSN);
           Retransmit-Command-if-Possible(transport connection, CmdSN);
           Build-And-Send-SSnack(transport connection);
           Build-And-Send-Command(transport connection, task control block);
           Command-Acknowledge-Timeout-Handler(task control block);
           Status-Expect-Timeout-Handler(transport connection);
           Build-And-Send-Nop-Out(transport connection);
           Handle-Status-SNACK-request(transport connection, status SNACK PDU);
           Retransmit-Status-Burst(status SNACK, task control block);
           Is-Acknowledged(beginning StatSN, run size);

           Implementation-specific tunables:

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           InitiatorCommandRetryEnabled, InitiatorStatusExpectNopEnabled, Initi-
           atorProactiveSNACKEnabled, InitiatorStatusSNACKEnabled, TargetSta-
           tusSNACKSupported.

           Notes:
                 - The initiator algorithms only deal with unsolicited Nop-In
                      PDUs for generating status SNACKs.  Solicited Nop-In PDU has
                      an assigned StatSN, which, when out-of-order, could trigger
                      the out-of-order StatSN handling in Within-command algo-
                      rithms, again leading to Recover-Status-if-Possible.

                 - The pseudo-code shown may result in the retransmission of
                      unacknowledged commands in more cases than necessary.  This
                      will not however affect the correctness of the operation since
                      the target is required to discard the duplicate CmdSNs.

                 - The procedure Build-And-Send-Async is defined in the Connec-
                      tion recovery algorithms.

                 - The procedure Status-Expect-Timeout-Handler describes how
                      initiators may proactively attempt to retrieve the Status if
                      they so choose. This procedure is assumed to be triggered much
                      before the standard ULP timeout.

   E.10.1.1 Initiator Algorithms

           Recover-Status-if-Possible(Connection, CurrentPDU)
           {
               if ((Connection.state = LOGGED_IN) and
                                         connection is not already considered failed) {
                  if (InitiatorStatusSNACKEnabled) {
                     if (# of missing PDUs is trackable) {
                             Note the missing StatSNs in Connection;
                       Build-And-Send-SSnack(Connection);
                           } else {
                             Connection.PerformConnectionCleanup = TRUE;
                     }
                  } else {
                           Connection.PerformConnectionCleanup = TRUE;
                  }
                  if (Connection.PerformConnectionCleanup is TRUE) {
                     Start-Timer(Connection-Cleanup-Handler, Connection, 0);
                        }
               }
           }


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           Retransmit-Command-if-Possible(Connection, CmdSN)
           {
               if (InitiatorCommandRetryEnabled) {
                  Retrieve the InitiatorTaskTag, and thus TCB for the CmdSN.
                  Build-And-Send-Command(Connection, TCB);
               }
           }

           Evaluate-a-StatSN(Connection, StatSN)
           {
               send-status-SNACK = FALSE;
               if (Connection.SoFarInOrder is TRUE) {
                  if (current StatSN is the expected) {
                       Increment Connection.ExpectedStatSN.
                  } else {
                             Connection.SoFarInOrder = FALSE;
                             send-status-SNACK = TRUE;
                        }
               } else {
                  if (current StatSN was considered missing) {
                       remove current StatSN from the missing list.
                  } else {
                             if (current StatSN is higher than expected){
                                 send-status-SNACK = TRUE;
                             } else {
                           discard, return;
                       }
                  }
                  Adjust Connection.ExpectedStatSN if appropriate.
                  if (missing StatSN list is empty) {
                       Connection.SoFarInOrder = TRUE;
                        }
               }
               return send-status-SNACK;
           }

           Receive-a-In-PDU(Connection, CurrentPDU)
           {
               check-basic-validity(CurrentPDU);
               if (Header-Digest-Bad) discard, return;
               Retrieve TCB for CurrentPDU.InitiatorTaskTag.
               if (CurrentPDU.type = Nop-In) {
                     if (the PDU is unsolicited) {

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                           if (current StatSN is not expected) {
                                             Recover-Status-if-Possible(Connection, CurrentPDU);
                           }
                           if (current ExpCmdSN is not Session.CmdSN) {
                               Retransmit-Command-if-Possible(Connection,
                                              CurrentPDU.ExpCmdSN);
                           }
                     }
               } else if (CurrentPDU.type = Reject) {
                     if (it is a data digest error on immediate data) {
                           Retransmit-Command-if-Possible(Connection,
                                              CurrentPDU.BadPDUHeader.CmdSN);
                     }
               } else if (CurrentPDU.type = Response) {
                    send-status-SNACK = Evaluate-a-StatSN(Connection,
                                                   CurrentPDU.StatSN);
                    if (send-status-SNACK is TRUE)
                        Recover-Status-if-Possible(Connection, CurrentPDU);
               } else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOVERY,
                         * NOT SHOWN */
               }
           }

           Command-Acknowledge-Timeout-Handler(TCB)
           {
               Retrieve the Connection for TCB.
               Retransmit-Command-if-Possible(Connection, TCB.CmdSN);
           }

           Status-Expect-Timeout-Handler(Connection)
           {
               if (InitiatorStatusExpectNopEnabled) {
                   Build-And-Send-Nop-Out(Connection);
               } else if (InitiatorProactiveSNACKEnabled){
                   if ((Connection.state = LOGGED_IN) and
                                         connection is not already considered failed) {
                        Build-And-Send-SSnack(Connection);
                   }
               }
           }

   E.10.1.2 Target Algorithms


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           Handle-Status-SNACK-request(Connection, CurrentPDU)
           {
               if (TargetStatusSNACKSupported) {
                  if (request for an acknowledged run) {
                      Build-And-Send-Reject(Connection, CurrentPDU,
                                                        Protocol-Error);
                  } else if (request for an untransmitted run) {
                      discard, return;
                  } else {
                      Retransmit-Status-Burst(CurrentPDU, TCB);
                  }
               } else {
                  Build-And-Send-Async(Connection, DroppedConnection,
                                          DefaultTime2Wait, DefaultTime2Retain);
               }
           }

   E.10.2   Connection Recovery Algorithms

   E.10.2.1 Procedure Descriptions

           Build-And-Send-Async(transport connection, reason code,
                                              minimum time, maximum time);
           Pick-A-Logged-In-Connection(session);
           Build-And-Send-Logout(transport connection, logout connection
                             identifier, reason code);
           PerformImplicitLogout(transport connection, logout connection
                             identifier, target information);
           PerformLogin(transport connection, target information);
           CreateNewTransportConnection(target information);
           Build-And-Send-Command(transport connection, task control block);
           Connection-Cleanup-Handler(transport connection);
           Connection-Resource-Timeout-Handler(transport connection);
           Quiesce-And-Prepare-for-New-Allegiance(session, task control block);
           Build-And-Send-Logout-Response(transport connection,
                                    CID of connection in recovery, reason code);
           Build-And-Send-TaskMgmt-Response(transport connection,
                                  task mgmt command PDU, response code);
           Establish-New-Allegiance(task control block, transport connection);
           Schedule-Command-To-Continue(task control block);

           Notes:
                 - Transport exception conditions, such as unexpected connection
                      termination, connection reset, and hung connection while the

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                      connection is in the full-feature phase, are all assumed to be
                      asynchronously signaled to the iSCSI layer using the
                      Transport_Exception_Handler procedure.

   E.10.2.2 Initiator Algorithms


           Receive-a-In-PDU(Connection, CurrentPDU)
           {
               check-basic-validity(CurrentPDU);
               if (Header-Digest-Bad) discard, return;
               Retrieve TCB from CurrentPDU.InitiatorTaskTag.
               if (CurrentPDU.type = Async) {
                   if (CurrentPDU.AsyncEvent = ConnectionDropped) {
                      Retrieve the AffectedConnection for CurrentPDU.Parameter1.
                     AffectedConnection.State = CLEANUP_WAIT;
                   } else if (CurrentPDU.AsyncEvent = LogoutRequest)) {
                      Retrieve the AffectedConnection for CurrentPDU.Parameter1.
                     AffectedConnection.State = LOGOUT_REQUESTED;
                     AffectedConnection.PerformConnectionCleanup = TRUE;
                     Start-Timer(Connection-Cleanup-Handler,
                                   AffectedConnection, CurrentPDU.Parameter2);
                   } else if (CurrentPDU.AsyncEvent = SessionDropped)) {
                     for (each Connection) {
                         Connection.state = CLEANUP_WAIT;
                     }
                     Session.state = FAILED;
                     Start-Timer(Session-Continuation-Handler,
                                   Session, CurrentPDU.Parameter2);
                   }

               } else if (CurrentPDU.type = LogoutResponse) {
                   Retrieve the CleanupConnection for CurrentPDU.CID.
                   if (CurrentPDU.Response = failure) {
                      CleanupConnection.State = CLEANUP_WAIT;
                   } else {
                       CleanupConnection.State = FREE;
                   }
               } else if (CurrentPDU.type = LoginResponse) {
                    if (this is a response to an implicit Logout) {
                       Retrieve the CleanupConnection.
                       if (successful) {
                           CleanupConnection.State = FREE;
                           Connection.State = LOGGED_IN;

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                       } else {
                            CleanupConnection.State = CLEANUP_WAIT;
                            DestroyTransportConnection(Connection);
                       }
                    }
               } else { /* REST UNRELATED TO CONNECTION-RECOVERY,
                         * NOT SHOWN */
               }
               if (CleanupConnection.State = FREE) {
                  for (each command that was active on CleanupConnection) {
                  /* Establish new connection allegiance */
                       NewConnection = Pick-A-Logged-In-Connection(Session);
                       Build-And-Send-Command(NewConnection, TCB);
                   }
               }
           }

           Connection-Cleanup-Handler(Connection)
           {
               Retrieve Session from Connection.
               Start-Timer(Connection-Resource-Timeout-Handler,
                         Connection, DefaultTime2Retain);
               if (Connection can still exchange iSCSI PDUs) {
                   NewConnection = Connection;
               } else {
                   if (there are other logged-in connections) {
                        NewConnection = Pick-A-Logged-In-Connection(Session);
                   } else {
                        NewConnection =
                             CreateTransportConnection(Session.OtherEndInfo);
                        Initiate an implicit Logout on NewConnection for
                                                          Connection.CID.
                        return;
                   }
               }
               Build-And-Send-Logout(NewConnection, Connection.CID,
                                                   RecoveryRemove);
           }

           Transport_Exception_Handler(Connection)
           {
               Connection.PerformConnectionCleanup = TRUE;
               if (the event is an unexpected transport disconnect) {

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                   Connection.State = CLEANUP_WAIT;
                   Start-Timer(Connection-Cleanup-Handler, Connection,
                                                     LogooutLoginMinTime);

               } else {
                   Connection.State = FREE;
               }
           }

   E.10.2.3 Target Algorithms

           Receive-a-In-PDU(Connection, CurrentPDU)
           {
               check-basic-validity(CurrentPDU);
               if (Header-Digest-Bad) discard, return;
               else if (Data-Digest-Bad) {
                       Build-And-Send-Reject(Connection, CurrentPDU,
                                                 Payload-Digest-Error);
                       discard, return;
               }
               Retrieve TCB and Session.
               if (CurrentPDU.type = Logout) {
                  if (CurrentPDU.ReasonCode = RecoveryRemove) {
                      Retrieve the CleanupConnection from CurrentPDU.CID).
                      for (each command active on CleanupConnection) {
                           Quiesce-And-Prepare-for-New-Allegiance(Session, TCB);
                           TCB.CurrentlyAllegiant = FALSE;
                      }
                      Cleanup-Connection-State(CleanupConnection);
                      if ((quiescing successful) and (cleanup successful)) {
                           Build-And-Send-Logout-Response(Connection,
                                               CleanupConnection.CID, Success);
                      } else {
                           Build-And-Send-Logout-Response(Connection,
                                               CleanupConnection.CID, Failure);
                      }
                  }
               } else if (CurrentPDU.type = TaskManagement) {
                    if (CurrentPDU.function = "TaskReassign") {
                          if (Session.ErrorRecoveryLevel < 2) {
                             Build-And-Send-TaskMgmt-Response(Connection,
                                  CurrentPDU, "Task failover not supported");
                          } else if (task is not found) {


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                             Build-And-Send-TaskMgmt-Response(Connection,
                                  CurrentPDU, "Task not in task set");
                          } else if (task is currently allegiant) {
                             Build-And-Send-TaskMgmt-Response(Connection,
                                       CurrentPDU, "Task still allegiant");
                          } else {
                             Establish-New-Allegiance(TCB, Connection);
                             TCB.CurrentlyAllegiant = TRUE;
                             Schedule-Command-To-Continue(TCB);
                          }
                    }
               } else { /* REST UNRELATED TO CONNECTION-RECOVERY,
                         * NOT SHOWN */
               }
           }

           Transport_Exception_Handler(Connection)
           {
               Connection.PerformConnectionCleanup = TRUE;
               if (the event is an unexpected transport disconnect) {
                   Connection.State = CLEANUP_WAIT;
                    Start-Timer(Connection-Resource-Timeout-Handler, Connection,
                                         (DefaultTime2Wait+DefaultTime2Retain));
                   if (this Session has full-feature phase connections left) {
                       DifferentConnection =
                          Pick-A-Logged-In-Connection(Session);
                        Build-And-Send-Async(DifferentConnection,
                              DroppedConnection, DefaultTime2Wait,
                                DefaultTime2Retain);
                  }
               } else {
                   Connection.State = FREE;
               }
           }





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   Appendix F. Clearing effects on various events on targets

           The following tables describes the target behavior on receiving the
           events specified in the rows of the table.  The second table is merely
           an extension of the first table and defines clearing actions for more
           objects on the same events.  The legend is:

                 Y   = Yes (cleared/discarded/reset on the event specified in the
                      row).  Unless noted otherwise, the clearing action is applica-
                      ble only for the issuing initiator port.
                 N   = No  (not affected on the event specified in the row, i.e.
                      stays at previous value).
                 NA  = Not Applicable, or Not Defined.





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                                                                  iSCSI            1-March-02

                                 +-----+-----+-----+-----+-----+-----+-----+
                                 |IT(1)|IC(2)|RR(3)|PR(4)|CT(5)|ST(6)|PP(7)|
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |connection failure(8)|Y    |Y    |N    |N    |N    |N    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |connection state     |NA   |NA   |N    |N    |Y    |N    |NA   |
           |timeout (9)          |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |session timeout/     |Y    |Y    |N    |N    |Y    |Y    |Y(14)|
           |closure/reinstatement|     |     |     |     |     |     |     |
           |(10)                 |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |session continuation |NA   |NA   |N    |N    |N(11)|N    |NA   |
           |(12)                 |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |successful connection|Y    |Y   |N    |N    |Y    |N    |Y(13)|
           |close logout         |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |session failure (18) |Y    |Y    |N   |N    |N    |N    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |successful recovery  |Y    |Y    |N    |N    |N    |N    |Y(13)|
           |Logout               |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |failed Logout        |Y    |Y    |N    |N    |N    |N    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |connection Login     |NA   |NA   |N   |N    |NA   |Y(15)|NA   |
           |(leading)            |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |connection Login     |NA   |NA  |N    |N    |N(11)|N    |Y    |
           |(non-leading)        |     |     |     |     |     |     |     |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |target cold reset(16)|Y    |Y    |Y    |Y(17)|Y    |Y    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |target warm reset(16)|Y    |Y    |Y    |N    |Y    |Y    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |LU reset(19)         |Y    |Y    |Y    |N    |Y    |Y    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+
           |powercycle(16)       |Y    |Y    |Y    |Y(17)|Y    |Y    |Y    |
           +---------------------+-----+-----+-----+-----+-----+-----+-----+

           1.Incomplete TTTs - Target Transfer Tags on which the target is still
           expecting PDUs to be received. Examples include TTTs received via R2T,
           NOP-IN etc.

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           2.Immediate Commands - immediate commands but waiting for execution
           on a target, for ex., Abort Task Set.

           3.Regular Reservations - these are the SCSI reservations managed by
           the SCSI Reserve and Release commands.

           4.Persistent Reservations - the objects that are covered in this col-
           umn are registration information, and the persistent reservation
           information.

           5.Connection Tasks - tasks that are active on the iSCSI connection in
           question.

           6.Session Tasks - tasks that are active on the entire iSCSI session,
           so is a union of ‚Çÿconnection tasks‚ÇÖ on all participating connections.

           7.Partial PDUs (if any) - PDUs that are partially sent and waiting for
           transport window credit to complete the transmission.

           8.Connection failure is a connection exception condition -one of
           transport connection shutdown, transport connection reset, or trans-
           port connection timeout abruptly terminating the iSCSI full-feature
           phase connection. A connection failure always takes the connection
           state machine to the CLEANUP_WAIT state.

           9.Connection state timeout happens if a connection spends more time
           than agreed upon during Login negotiation in the CLEANUP_WAIT state,
           and this takes the connection to the FREE state (M1 transition in con-
           nection cleanup state diagram).

           10.Session state timeout happens when the last connection state time-
           out happens and no tasks are waiting for reassignment.  This takes the
           session to the FREE state (N6 transition in the session state dia-
           gram).  Session closure and reinstatement are defined

           11.This clearing effect is however "Y" only if it is a connection
           reinstatement and the operational ErrorRecoveryLevel is less than 2.

           12.Session continuation is as defined in Section 4.3.6 Session Con-
           tinuation, closure and failure.



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                                                                  iSCSI            1-March-02

           13.This clearing effect is valid only if the connection is being
           logged-out on a different connection and when the connection being
           logged out on the target may have some partial PDUs pending to be
           sent.  In all other cases, the effect is "NA".

           14.This clearing effect is valid only for a "close the session" logout
           in a multi-connection session.  In all other cases, the effect is
           "NA".

           15.Applicable only if this leading connection login is a session rein-
           statement. If that is not the case, this is "NA".

           16.This operation affects all logged-in initiators.

           17.Only if the SCSI APTPL bit (SPC-2) was not used in the registration
           (Note that iSCSI defines target cold reset as protocol-equivalent to a
           target powercycle). If APTPL was used, this is "N".

           18.Session failure is as defined in Section 4.3.6 Session Continua-
           tion, closure and failure.

           19.This operation affects all logged-in initiators and the clearing
           effects are only applicable to the LU being reset.





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                                                                  iSCSI            1-March-02

                                 +-----+-----+-----+-----+-----+------+
                                 |DC(1)|DD(2)|SS(3)|CS(4)|DS(5)|CRN(6)|
           +---------------------+-----+-----+-----+-----+-----+------+
           |connection failure   |N    |Y    |N    |N    |N    |N     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |connection state     |Y    |NA   |Y    |N    |NA   |N     |
           |timeout              |     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |session timeout/     |Y    |Y    |Y(7) |Y    |NA   |NA    |
           |closure/reinstatement|     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |session continuation |N(11)|NA*12|NA   |N    |NA*13|N     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |successful connection|Y    |Y    |Y   |N    |NA   |N     |
           |close Logout         |     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |session failure      |N    |Y    |N    |N    |N    |N     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |successful recovery  |Y    |Y    |Y    |N    |N    |N     |
           |Logout               |     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |failed Logout        |N    |Y(9) |N    |N    |N    |N     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |connection Login     |NA   |NA   |N(8) |N(8) |NA   |Y     |
           |(leading             |     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |connection Login     |N(11)|NA*12|N(8) |N    |NA*13|N     |
           |(non-leading)        |     |     |     |     |     |      |
           +---------------------+-----+-----+-----+-----+-----+------+
           |target cold reset    |Y    |Y    |Y    |Y(10)|NA   |Y     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |target warm reset    |Y    |Y    |N    |N    |NA   |Y     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |LU reset             |N    |Y    |N    |N    |N    |Y     |
           +---------------------+-----+-----+-----+-----+-----+------+
           |powercycle           |Y    |Y    |Y    |Y(10)|NA   |Y     |
           +---------------------+-----+-----+-----+-----+-----+------+

           1.Discontiguous Commands - commands allegiant to the connection in
           question and waiting to be reordered in the iSCSI layer. All ‚Ç£Y‚Ç¥s in
           this column assume that the task causing the event (if indeed the
           event is the result of a task) is issued as an immediate command,
           since the discontiguities can be ahead of the task.

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                                                                  iSCSI            1-March-02


           2.Discontiguous Data - data PDUs received for the task in question and
           waiting to be reordered due to prior discontiguities in DataSN.

           3.StatSN

           4.CmdSN

           5.DataSN

           6.Command Reference Number - defined by SAM-2, and follows the reset
           rules defined by SAM-2.

           7.It clears the StatSN on all the connections.

           8.This sequence number is instantiated on this event.

           9.A logout failure drives the connection state machine to the
           CLEANUP_WAIT state, similar to the connection failure event. Hence,
           it has a similar effect on this and several other protocol aspects.

           10.This is cleared by virtue of the fact that all sessions with all
           initiators are terminated.

           11.This clearing effect is "Y" if it is a connection reinstatement.

           12.This clearing effect is "Y" only if it is a connection reinstate-
           ment and the operational ErrorRecoveryLevel is 2.

           13.This clearing effect is "N" only if it is a connection reinstate-
           ment and the operational ErrorRecoveryLevel is 2.





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                                                                  iSCSI            1-March-02

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