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                                 iSCSI                     1-July-02



  IPS                                                     Julian Satran
  Internet Draft                                           Kalman Meth
  draft-ietf-ips-iscsi-14.txt                                       IBM
  Category: standards-track
                                                      Costa Sapuntzakis
                                                         Cisco Systems

                                                Mallikarjun Chadalapaka
                                                    Hewlett-Packard Co.

                                                           Efri Zeidner
                                                                SANGate





                                 iSCSI





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                                iSCSI                        1-July-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 at most 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 mate-
   rial or to cite them except as "work in progress."
   The list of 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 document describes a transport protocol for SCSI that
   works on top of TCP. The iSCSI protocol aims to be fully compliant
   with the rules laid out in the SCSI Architecture Model - 2 [SAM2]
   document. The current version of iSCSI is 0.

Acknowledgements

   This protocol was developed by a design team that, beside the
   authors, included Daniel Smith, Ofer Biran, Jim Hafner and John
   Hufferd (IBM), Mark Bakke (Cisco), Randy Haagens (HP), Matt Wakeley
   (Agilent, now Sierra Logic), Luciano Dalle Ore (Quantum), Paul Von
   Stamwitz (Adaptec, now TrueSAN Networks).

   Also, a large group of people contributed to this work through their
   review, comments and valuable insights. We are grateful to all them.
   We are especially grateful to those who found the time and patience
   to take part in our weekly phone conferences and intermediate meet-
   ings in Almaden and Haifa, so helping to shape this document: Prasen-
   jit Sarkar, Meir Toledano, John Dowdy, Steve Legg, Alain Azagury
   (IBM), Dave Nagle (CMU), David Black (EMC), John Matze (Veritas - now
   with Okapi Software), Steve DeGroote, Mark Schrandt (NuSpeed), Gabi
   Hecht (Gadzoox), Robert Snively and Brian Forbes (Brocade), Nelson

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                                      iSCSI                             1-July-02

  Nachum (StorAge), Uri Elzur (Broadcom).  Many more helped clean and
  improve this document within the IPS working group. We are espe-
  cially grateful to David Robinson and Raghavendra Rao (Sun), Charles
  Monia, Joshua Tseng (Nishan), Somesh Gupta (Silverback), Michael
  Krause, Pierre Labat, Santosh Rao, Matthew Burbridge, Bob Barry, Rob-
  ert Elliott, Nick Martin (HP), Stephen Bailey (Sandburst),  Steve
  Senum, Ayman Ghanem, Dave Peterson (Cisco), Barry Reinhold (Trebia
  Networks), Bob Russell (UNH), Eddy Quicksall (iVivity, Inc.), Bill
  Lynn and Michael Fischer (Adaptec), Vince Cavanna, Pat Thaler (Agi-
  lent), Jonathan Stone (Stanford), Luben Tuikov (Splentec), Paul Konig
  (?), Michael Krueger (Windriver), Martins Krikis (Intel), Doug Otis
  (Sanlight), Robert Griswold and Bill Moody (Crossroads), Yaron Klein
  (Sanrad). The recovery chapter was enhanced with help from Stephen
  Bailey (Sandburst), Somesh Gupta (Silverback) and Venkat Rangan
  (Rhapsody Networks). Eddy Quicksall contributed some examples and
  began the Definitions Section.  Michael Fischer and Bob Barry started
  the Acronyms Section.  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
  happen.

  This document has to be considered together with the "Naming & Dis-
  covery"[NDT], "Boot"[BOOT] and "Securing iSCSI, iFCP and FCIP"[SEC-
  IPS] documents.

  The "Naming & Discovery" document is authored by:

       Mark Bakke (Cisco), Jim Hafner, John Hufferd, Kaladhar Voru-
         ganti (IBM), Marjorie Krueger (Hewlett-Packard).
       .

  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(Microsoft), Joshua Tseng (Nishan), Jesse Walker
         (Intel), Venkat Rangan (Rhapsody Networks), Franco Travos-
         tino (Nortel Networks).

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                                 iSCSI                          1-July-02



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

Change Log

   The following changes were made from draft-ietf-ips-iSCSI-13 to
   draft-ietf-ips-iSCSI-14:

     - Text cleanup
     - Clarification on COLD RESET - required by SAM
     - fixed in 9.5 recommendation on empty data (was inconsistent
       with R2T)
     - 9.4.6.2 text reffers only to firstburstsize changed error
       code to "incorrect amount of data"
     - changed size to length everywhere
     - Reinstated I bit in text request (typo)
     - StatSN is retransmitted R2T should be the new value
     - Fixed DefaultTime2Wait and changed selection function format
       in Section 11

   The following changes were made from draft-ietf-ips-iSCSI-12 to
   draft-ietf-ips-iSCSI-13:

     - Text cleanup
     - Limited decimal encoding to 64 bit integers
     - Logout Request reason code moved to byte 1
     - Renamed MaxRecvPDULength to MaxRecvDataSegmentLength
     - Large Numbers allowed only if explicitely stated
     - CHAP is the mandatory to implement in-band authentication and
       SRP is optional
     - A negotiation answer is permitted only if all key=value pairs
       are complete. A flag indicates completion.
     - Clearing effects appendix simplified - SCSI effects are now
       part of [SPC3]
     - Made explicit a rule a bout checking when committing a nego-
       tiation
     - Added code 4 for Asynch Message - request negotiation

   The following changes were made from draft-ietf-ips-iSCSI-11 to
   draft-ietf-ips-iSCSI-12:

     - Clarify the use of A bit and DataACK at the end of data
     - Clarified checking to be done for abort task and removed Ref-
       erenced task tag from task management response
     - Range separator is tilde.


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                                iSCSI                           1-July-02

     - Fixed the paragraph numbering in the appendices.
     - Clarified the expected target behavior in a lost F-bit sce-
       nario when responding to Abort Task Set/Clear Task Set.
     - Added the TargetPortalGroupTag key as a Login/operational
       key, and its usage semantics were added to Section 4.3 Login
       Phase.
     - Clarified the language in Section 6.1.2 Allegiance Reassign-
       ment and Section 6.2 Usage Of Reject PDU in Recovery.
     - Clarified the states corresponding to full-feature phase
       operation in connection and session state diagrams in Chap-
       ter 5.
     - Delivering all negotiated unsolicited data are mandatory
     - Delivering all the data for an R2T is mandatory
     - Added a timeout guidance section to Chapter 8
     - Added normative naming text (previously in NDT)
     - Clarified no duplicate parameter for login
     - Added a minimum required to support to text length (16k/64k)
     - Changed the name of TSID to TSIH to better reflect its mean-
       ing
     - Security - IPsec transport mode is MAY and authentication
       MUST be used when encryption is used
     - Added to logout a section clarifying the actions to be taken
       on task termination by the target
     - Removed CRN
     - Changed default time2wait & retain to better express typical
       ratio
     - Changes SCSI port element separator to comma
     - Async Event data format same as for SCSI response

  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, a restart 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
       timeout management.


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                                  iSCSI                         1-July-02

     - The LogoutLoginMinTime and LogoutLoginMaxTime keys are
       respectively renamed to DefaultTime2Wait and
       DefaultTime2Retain, because 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 NextC-
       mdSN 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.  Add-
       ing 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.
     - Added a new Section 9.6.2 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 back to 00



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                                  iSCSI                     1-July-02

  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 chap-
       ter  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 receiv-
       ing a smaller write data sequence than was asked for in an
       R2T.
     - 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" because the invalid SNACK is already covered under
       "Protocol error".  Also treating DataSN and R2TSN equiva-
       lently 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/ses-
       sion can't 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
       DataSequenceInOrder=Yes
     - Alias designation format appendix is again out(!) - T10 has
       decided it will go in SPC
     - Task Management synchronization moved to the target (task
       management response given after task management action and
       confirmed delivery of all previous responses)
     - Removed the don't 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

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                                  iSCSI                         1-July-02

     - 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
     - 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 - stan-
       dard 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.

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                                   iSCSI                      1-July-02

     - 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 2.2.6 iSCSI Names 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
     - Changed name of DataOrder and DataDeliveryOrder to DataSe-
       quenceOrder 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
       2.2.4 iSCSI Full Feature Phase
     - Added new Reject reason codes, tabular listing and a pointer
       to Section 9.14.4 Implicit termination of tasks
     - Added additional Reject usage semantics on CmdSN and DataSN
       to Section 9.14.4 Implicit termination of tasks
     - 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"

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                                 iSCSI                       1-July-02

     - 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
       Section 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.
     - Reintroduced aliases (the data format) in an appendix. The
       aliasing mechanism once part of iSCSI is part of [SPC]
     - 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 secu-
       rity
     - 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 recov-
       ery classes, and renamed "within-session" recovery to "con-
       nection 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" rea-
       son code.

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                                  iSCSI                            1-July-02

     - 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 ven-
          dor 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
     - 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
          statement 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 exclu-
          sively 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
          separate (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)

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                                   iSCSI                     1-July-02

     - 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 Manage-
       ment 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" negotiat-
       ing 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 executed 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
     - 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 nego-
       tiation) 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 "reason-
       able" 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
       execute as if issued at CmdSN and, in case of aborts and


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                                   iSCSI                        1-July-02

       clear/reset no additional response/status is expected for
       those commands 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 mainte-
       nance 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
       sending other commands) and how one expects the TCP close to
       be performed in 2.14
     - 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
       Quicksall)
     - 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


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                                iSCSI                           1-July-02

     - 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
       command allegiance change (command retry on another connec-
       tion)
     - 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
     - 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 mecha-
       nism)
     - 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 (Appen-
       dix 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


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     - 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 secu-
       rity. 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 First-
       BurstSize 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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                                iSCSI                        1-July-02

 Status of this Memo . . . . . . . . . . . . . . . . . . . . . . . . . 2
 Abstract  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Definitions and Acronyms  . . . . . . . . . . . . . . . . . . . . .24
  1.1 Definitions  . . . . . . . . . . . . . . . . . . . . . . . . . .24
  1.2 Acronyms   . . . . . . . . . . . . . . . . . . . . . . . . . . .28
  1.3 Conventions used in this document  . . . . . . . . . . . . . . .30
     1.3.1 Word Rule   . . . . . . . . . . . . . . . . . . . . . . . .30
     1.3.2 Half-Word Rule  . . . . . . . . . . . . . . . . . . . . . .31
     1.3.3 Byte Rule   . . . . . . . . . . . . . . . . . . . . . . . .31
2. Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
  2.1 SCSI Concepts  . . . . . . . . . . . . . . . . . . . . . . . . .32
  2.2 iSCSI Concepts and Functional Overview   . . . . . . . . . . . .33
     2.2.1 Layers and Sessions   . . . . . . . . . . . . . . . . . . .33
     2.2.2 Ordering and iSCSI Numbering  . . . . . . . . . . . . . . .34
        2.2.2.1 Command Numbering and Acknowledging  . . . . . . . . .35
        2.2.2.2 Response/Status Numbering and Acknowledging  . . . . .38
        2.2.2.3 Data Sequencing  . . . . . . . . . . . . . . . . . . .39
     2.2.3 iSCSI Login   . . . . . . . . . . . . . . . . . . . . . . .39
     2.2.4 iSCSI Full Feature Phase  . . . . . . . . . . . . . . . . .40
     2.2.5 iSCSI Connection Termination  . . . . . . . . . . . . . . .43
     2.2.6 iSCSI Names   . . . . . . . . . . . . . . . . . . . . . . .43
        2.2.6.1 iSCSI Name Requirements  . . . . . . . . . . . . . . .44
        2.2.6.2 iSCSI Name Encoding  . . . . . . . . . . . . . . . . .46
        2.2.6.3 iSCSI Name Structure   . . . . . . . . . . . . . . . .46
          2.2.6.3.1 Type "iqn." (iSCSI Qualified Name)   . . . . . . .47
          2.2.6.3.2 Type "eui." (IEEE EUI-64 format)   . . . . . . . .48
     2.2.7 Persistent State  . . . . . . . . . . . . . . . . . . . . .49
     2.2.8 Message Synchronization and Steering  . . . . . . . . . . .49
        2.2.8.1 Rationale  . . . . . . . . . . . . . . . . . . . . . .49
        2.2.8.2 Synchronization (sync) and Steering Functional Model  50
        2.2.8.3 Sync and Steering and Other Encapsulation Layers   . .52
        2.2.8.4 Sync/Steering and iSCSI PDU Length   . . . . . . . . .53
  2.3 iSCSI Session Types  . . . . . . . . . . . . . . . . . . . . . .54
  2.4 SCSI to iSCSI Concepts Mapping Model   . . . . . . . . . . . . .54
     2.4.1 iSCSI Architecture Model  . . . . . . . . . . . . . . . . .55
     2.4.2 SCSI Architecture Model   . . . . . . . . . . . . . . . . .57
     2.4.3 Consequences of the Model   . . . . . . . . . . . . . . . .59
        2.4.3.1 I_T Nexus State  . . . . . . . . . . . . . . . . . . .60
        2.4.3.2 SCSI Mode Pages  . . . . . . . . . . . . . . . . . . .60
  2.5 Request/Response Summary   . . . . . . . . . . . . . . . . . . .61
     2.5.1 Request/Response types carrying SCSI payload  . . . . . . .61

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        2.5.1.1 SCSI-Command   . . . . . . . . . . . . . . . . . . . .61
        2.5.1.2 SCSI-Response  . . . . . . . . . . . . . . . . . . . .62
        2.5.1.3 Task Management Function Request   . . . . . . . . . .62
        2.5.1.4 Task Management Function Response  . . . . . . . . . .63
        2.5.1.5 SCSI Data-out and SCSI Data-in   . . . . . . . . . . .63
        2.5.1.6 Ready To Transfer (R2T)  . . . . . . . . . . . . . . .64
     2.5.2 Requests/Responses carrying SCSI and iSCSI Payload  . . . .64
        2.5.2.1 Asynchronous Message   . . . . . . . . . . . . . . . .64
     2.5.3 Requests/Responses carrying iSCSI Only Payload  . . . . . .65
        2.5.3.1 Text Request and Text Response   . . . . . . . . . . .65
        2.5.3.2 Login Request and Login Response   . . . . . . . . . .65
        2.5.3.3 Logout Request and Response  . . . . . . . . . . . . .66
        2.5.3.4  SNACK Request   . . . . . . . . . . . . . . . . . . .66
        2.5.3.5 Reject   . . . . . . . . . . . . . . . . . . . . . . .67
        2.5.3.6 NOP-Out Request and NOP-In Response  . . . . . . . . .67
3. SCSI Mode Parameters for iSCSI  . . . . . . . . . . . . . . . . . .68
4. Login and Full Feature Phase Negotiation  . . . . . . . . . . . . .69
  4.1 Text Format  . . . . . . . . . . . . . . . . . . . . . . . . . .69
  4.2 Text Mode Negotiation  . . . . . . . . . . . . . . . . . . . . .72
     4.2.1 List negotiations   . . . . . . . . . . . . . . . . . . . .74
     4.2.2 Simple-value negotiations   . . . . . . . . . . . . . . . .75
  4.3 Login Phase  . . . . . . . . . . . . . . . . . . . . . . . . . .76
     4.3.1 Login Phase Start   . . . . . . . . . . . . . . . . . . . .78
     4.3.2 iSCSI Security Negotiation  . . . . . . . . . . . . . . . .80
     4.3.3 Operational Parameter Negotiation During the Login Phase  .81
     4.3.4 Connection reinstatement  . . . . . . . . . . . . . . . . .82
     4.3.5 Session reinstatement, closure and timeout  . . . . . . . .83
        4.3.5.1 Loss of Nexus notification   . . . . . . . . . . . . .83
     4.3.6 Session continuation and failure  . . . . . . . . . . . . .84
  4.4 Operational Parameter Negotiation Outside the Login Phase  . . .84
5. State Transitions   . . . . . . . . . . . . . . . . . . . . . . . .86
  5.1 Standard Connection State Diagrams   . . . . . . . . . . . . . .86
     5.1.1 Standard Connection State Diagram for an Initiator  . . . .86
     5.1.2 Standard Connection State Diagram for a Target  . . . . . .88
     5.1.3 State Descriptions for Initiators and Targets   . . . . . .90
     5.1.4 State Transition Descriptions for Initiators and Targets  .91
  5.2 Connection Cleanup State Diagram for Initiators and Targets  . .95
     5.2.1 State Descriptions for Initiators and Targets   . . . . . .96
     5.2.2 State Transition Descriptions for Initiators and Targets  .97
  5.3 Session State Diagrams   . . . . . . . . . . . . . . . . . . . .98
     5.3.1 Session State Diagram for a Target  . . . . . . . . . . . .99
     5.3.2 State Descriptions for Initiators and Targets   . . . . . 101
     5.3.3 State Transition Descriptions for Initiators and Targets  101

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6. iSCSI Error Handling and Recovery   . . . . . . . . . . . . . . . 103
  6.1 Retry and Reassign in Recovery   . . . . . . . . . . . . . . . 103
     6.1.1 Usage of Retry  . . . . . . . . . . . . . . . . . . . . . 103
     6.1.2 Allegiance Reassignment   . . . . . . . . . . . . . . . . 104
  6.2 Usage Of Reject PDU in Recovery  . . . . . . . . . . . . . . . 105
  6.3 Connection timeout management  . . . . . . . . . . . . . . . . 105
     6.3.1 Timeouts on transport exception events  . . . . . . . . . 106
     6.3.2 Timeouts on planned decommissioning   . . . . . . . . . . 106
  6.4 Format Errors  . . . . . . . . . . . . . . . . . . . . . . . . 106
  6.5 Digest Errors  . . . . . . . . . . . . . . . . . . . . . . . . 107
  6.6 Sequence Errors  . . . . . . . . . . . . . . . . . . . . . . . 108
  6.7 SCSI Timeouts  . . . . . . . . . . . . . . . . . . . . . . . . 109
  6.8 Negotiation Failures   . . . . . . . . . . . . . . . . . . . . 109
  6.9 Protocol Errors  . . . . . . . . . . . . . . . . . . . . . . . 110
  6.10 Connection Failures   . . . . . . . . . . . . . . . . . . . . 110
  6.11 Session Errors  . . . . . . . . . . . . . . . . . . . . . . . 111
  6.12 Recovery Classes  . . . . . . . . . . . . . . . . . . . . . . 112
     6.12.1 Recovery Within-command  . . . . . . . . . . . . . . . . 112
     6.12.2 Recovery Within-connection   . . . . . . . . . . . . . . 113
     6.12.3 Connection Recovery  . . . . . . . . . . . . . . . . . . 114
     6.12.4 Session Recovery   . . . . . . . . . . . . . . . . . . . 114
  6.13 Error Recovery Hierarchy  . . . . . . . . . . . . . . . . . . 115
7. Security Considerations   . . . . . . . . . . . . . . . . . . . . 118
  7.1 iSCSI Security Mechanisms  . . . . . . . . . . . . . . . . . . 118
  7.2 In-band Initiator-Target Authentication  . . . . . . . . . . . 119
     7.2.1 CHAP Considerations   . . . . . . . . . . . . . . . . . . 120
     7.2.2 SRP Considerations  . . . . . . . . . . . . . . . . . . . 120
  7.3 IPsec  . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
     7.3.1 Data Integrity and Authentication   . . . . . . . . . . . 121
     7.3.2 Confidentiality   . . . . . . . . . . . . . . . . . . . . 121
     7.3.3 Policy, Security Associations and Key Management  . . . . 122
8. Notes to Implementers   . . . . . . . . . . . . . . . . . . . . . 124
  8.1 Multiple Network Adapters  . . . . . . . . . . . . . . . . . . 124
     8.1.1 Conservative Reuse of ISIDs   . . . . . . . . . . . . . . 124
     8.1.2 iSCSI Name, ISID and TPGT Use   . . . . . . . . . . . . . 125
  8.2 Autosense and Auto Contingent Allegiance (ACA)   . . . . . . . 127
  8.3 iSCSI timeouts   . . . . . . . . . . . . . . . . . . . . . . . 127
  8.4 Command Retry and Cleaning Old Command Instances   . . . . . . 127
  8.5 Synch and Steering Layer and Performance   . . . . . . . . . . 127
  8.6 Considerations for State-dependent devices   . . . . . . . . . 128
     8.6.1 Determining the proper ErrorRecoveryLevel   . . . . . . . 128
9. iSCSI PDU Formats   . . . . . . . . . . . . . . . . . . . . . . . 130
  9.1 iSCSI PDU Length and Padding   . . . . . . . . . . . . . . . . 130

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  9.2 PDU Template, Header, and Opcodes  . . . . . . . . . . . . . . 130
    9.2.1 Basic Header Segment (BHS)  . . . . . . . . . . . . . . . 131
       9.2.1.1 I  . . . . . . . . . . . . . . . . . . . . . . . . . 132
       9.2.1.2 Opcode   . . . . . . . . . . . . . . . . . . . . . . 132
       9.2.1.3 Opcode-specific Fields   . . . . . . . . . . . . . . 133
       9.2.1.4 TotalAHSLength   . . . . . . . . . . . . . . . . . . 133
       9.2.1.5 DataSegmentLength  . . . . . . . . . . . . . . . . . 133
       9.2.1.6 LUN  . . . . . . . . . . . . . . . . . . . . . . . . 134
       9.2.1.7 Initiator Task Tag   . . . . . . . . . . . . . . . . 134
    9.2.2 Additional Header Segment (AHS)   . . . . . . . . . . . . 134
       9.2.2.1 AHSType  . . . . . . . . . . . . . . . . . . . . . . 134
       9.2.2.2 AHSLength  . . . . . . . . . . . . . . . . . . . . . 135
       9.2.2.3 Extended CDB AHS   . . . . . . . . . . . . . . . . . 135
       9.2.2.4 Bidirectional Expected Read-Data Length AHS  . . . . 135
    9.2.3 Header Digest and Data Digest   . . . . . . . . . . . . . 136
    9.2.4 Data Segment  . . . . . . . . . . . . . . . . . . . . . . 136
  9.3 SCSI Command . . . . . . . . . . . . . . . . . . . . . . . . . 137
    9.3.1 Flags and Task Attributes (byte 1)  . . . . . . . . . . . 137
    9.3.2 CmdSN - Command Sequence Number   . . . . . . . . . . . . 138
    9.3.3 ExpStatSN   . . . . . . . . . . . . . . . . . . . . . . . 138
    9.3.4 Expected Data Transfer Length   . . . . . . . . . . . . . 138
    9.3.5 CDB - SCSI Command Descriptor Block   . . . . . . . . . . 139
    9.3.6 Data Segment - Command Data   . . . . . . . . . . . . . . 139
  9.4 SCSI Response  . . . . . . . . . . . . . . . . . . . . . . . . 140
    9.4.1 Flags (byte 1)  . . . . . . . . . . . . . . . . . . . . . 140
    9.4.2 Status  . . . . . . . . . . . . . . . . . . . . . . . . . 141
    9.4.3 Response  . . . . . . . . . . . . . . . . . . . . . . . . 142
    9.4.4 Residual Count  . . . . . . . . . . . . . . . . . . . . . 142
    9.4.5 Bidirectional Read Residual Count   . . . . . . . . . . . 143
    9.4.6 Data Segment - Sense and Response Data Segment  . . . . . 143
       9.4.6.1 SenseLength  . . . . . . . . . . . . . . . . . . . . 143
       9.4.6.2 Sense Data   . . . . . . . . . . . . . . . . . . . . 144
    9.4.7 ExpDataSN   . . . . . . . . . . . . . . . . . . . . . . . 144
    9.4.8 StatSN - Status Sequence Number   . . . . . . . . . . . . 145
    9.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator  . . . 145
    9.4.10 MaxCmdSN - Maximum CmdSN from this Initiator   . . . . . 145
  9.5 Task Management Function Request . . . . . . . . . . . . . . . 146
    9.5.1 Function  . . . . . . . . . . . . . . . . . . . . . . . . 146
    9.5.2 LUN   . . . . . . . . . . . . . . . . . . . . . . . . . . 149
    9.5.3 Referenced Task Tag   . . . . . . . . . . . . . . . . . . 149
    9.5.4 RefCmdSN  . . . . . . . . . . . . . . . . . . . . . . . . 149
    9.5.5 ExpDataSN   . . . . . . . . . . . . . . . . . . . . . . . 149
  9.6 Task Management Function Response  . . . . . . . . . . . . . . 151

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    9.6.1 Response  . . . . . . . . . . . . . . . . . . . . . . . . 151
    9.6.2 Task Management actions on task sets  . . . . . . . . . . 153
  9.7 SCSI Data-out & SCSI Data-in . . . . . . . . . . . . . . . . . 154
    9.7.1 F (Final) Bit   . . . . . . . . . . . . . . . . . . . . . 156
    9.7.2 A (Acknowledge) bit   . . . . . . . . . . . . . . . . . . 156
    9.7.3 Target Transfer Tag   . . . . . . . . . . . . . . . . . . 157
    9.7.4 StatSN  . . . . . . . . . . . . . . . . . . . . . . . . . 157
    9.7.5 DataSN  . . . . . . . . . . . . . . . . . . . . . . . . . 157
    9.7.6 Buffer Offset   . . . . . . . . . . . . . . . . . . . . . 158
    9.7.7 DataSegmentLength   . . . . . . . . . . . . . . . . . . . 158
    9.7.8 Flags (byte 1)  . . . . . . . . . . . . . . . . . . . . . 158
  9.8 Ready To Transfer (R2T)  . . . . . . . . . . . . . . . . . . . 160
    9.8.1 R2TSN   . . . . . . . . . . . . . . . . . . . . . . . . . 161
    9.8.2 StatSN  . . . . . . . . . . . . . . . . . . . . . . . . . 161
    9.8.3 Desired Data Transfer Length and Buffer Offset  . . . . . 162
    9.8.4 Target Transfer Tag   . . . . . . . . . . . . . . . . . . 162
  9.9 Asynchronous Message . . . . . . . . . . . . . . . . . . . . . 163
    9.9.1 AsyncEvent  . . . . . . . . . . . . . . . . . . . . . . . 164
    9.9.2 AsyncVCode  . . . . . . . . . . . . . . . . . . . . . . . 165
    9.9.3 Sense Data and iSCSI Event Data   . . . . . . . . . . . . 165
       9.9.3.1 SenseLength  . . . . . . . . . . . . . . . . . . . . 166
  9.10 Text Request  . . . . . . . . . . . . . . . . . . . . . . . . 167
    9.10.1 F (Final) Bit  . . . . . . . . . . . . . . . . . . . . . 168
    9.10.2 C (Continue) Bit   . . . . . . . . . . . . . . . . . . . 168
    9.10.3 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 168
    9.10.4 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 168
    9.10.5 Text   . . . . . . . . . . . . . . . . . . . . . . . . . 169
  9.11 Text Response . . . . . . . . . . . . . . . . . . . . . . . . 171
    9.11.1 F (Final) Bit  . . . . . . . . . . . . . . . . . . . . . 171
    9.11.2 C (Continue) Bit   . . . . . . . . . . . . . . . . . . . 172
    9.11.3 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 172
    9.11.4 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 172
    9.11.5 StatSN   . . . . . . . . . . . . . . . . . . . . . . . . 173
    9.11.6 Text Response Data   . . . . . . . . . . . . . . . . . . 173
  9.12 Login Request . . . . . . . . . . . . . . . . . . . . . . . . 174
    9.12.1 T (Transit) Bit  . . . . . . . . . . . . . . . . . . . . 175
    9.12.2 C (Continue) Bit   . . . . . . . . . . . . . . . . . . . 175
    9.12.3 CSG and NSG  . . . . . . . . . . . . . . . . . . . . . . 175
    9.12.4 Version-max  . . . . . . . . . . . . . . . . . . . . . . 175
    9.12.5 Version-min  . . . . . . . . . . . . . . . . . . . . . . 175
    9.12.6 ISID   . . . . . . . . . . . . . . . . . . . . . . . . . 176
    9.12.7 TSIH   . . . . . . . . . . . . . . . . . . . . . . . . . 177
    9.12.8 Connection ID - CID  . . . . . . . . . . . . . . . . . . 177

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     9.12.9 CmdSN  . . . . . . . . . . . . . . . . . . . . . . . . . 178
     9.12.10 ExpStatSN   . . . . . . . . . . . . . . . . . . . . . . 178
     9.12.11 Login Parameters  . . . . . . . . . . . . . . . . . . . 178
  9.13 Login Response  . . . . . . . . . . . . . . . . . . . . . . . 180
     9.13.1 Version-max  . . . . . . . . . . . . . . . . . . . . . . 180
     9.13.2 Version-active   . . . . . . . . . . . . . . . . . . . . 181
     9.13.3 TSIH   . . . . . . . . . . . . . . . . . . . . . . . . . 181
     9.13.4 StatSN   . . . . . . . . . . . . . . . . . . . . . . . . 181
     9.13.5 Status-Class and Status-Detail   . . . . . . . . . . . . 181
     9.13.6 T (Transit) bit  . . . . . . . . . . . . . . . . . . . . 184
     9.13.7 C (Continue) Bit   . . . . . . . . . . . . . . . . . . . 184
     9.13.8 Login Parameters   . . . . . . . . . . . . . . . . . . . 185
  9.14 Logout Request  . . . . . . . . . . . . . . . . . . . . . . . 186
     9.14.1 Reason Code  . . . . . . . . . . . . . . . . . . . . . . 188
     9.14.2 CID  . . . . . . . . . . . . . . . . . . . . . . . . . . 189
     9.14.3 ExpStatSN  . . . . . . . . . . . . . . . . . . . . . . . 189
     9.14.4 Implicit termination of tasks  . . . . . . . . . . . . . 189
  9.15 Logout Response . . . . . . . . . . . . . . . . . . . . . . . 190
     9.15.1 Response   . . . . . . . . . . . . . . . . . . . . . . . 190
     9.15.2 Time2Wait  . . . . . . . . . . . . . . . . . . . . . . . 191
     9.15.3 Time2Retain  . . . . . . . . . . . . . . . . . . . . . . 191
  9.16  SNACK Request  . . . . . . . . . . . . . . . . . . . . . . . 193
     9.16.1 Type   . . . . . . . . . . . . . . . . . . . . . . . . . 194
     9.16.2 BegRun   . . . . . . . . . . . . . . . . . . . . . . . . 195
     9.16.3 RunLength  . . . . . . . . . . . . . . . . . . . . . . . 195
  9.17 Reject  . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
     9.17.1 Reason   . . . . . . . . . . . . . . . . . . . . . . . . 198
     9.17.2 DataSN   . . . . . . . . . . . . . . . . . . . . . . . . 199
     9.17.3 StatSN, ExpCmdSN and MaxCmdSN  . . . . . . . . . . . . . 199
     9.17.4 Complete Header of Bad PDU   . . . . . . . . . . . . . . 199
  9.18 NOP-Out . . . . . . . . . . . . . . . . . . . . . . . . . . . 200
     9.18.1 Initiator Task Tag   . . . . . . . . . . . . . . . . . . 201
     9.18.2 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 201
     9.18.3 Ping Data  . . . . . . . . . . . . . . . . . . . . . . . 201
  9.19 NOP-In  . . . . . . . . . . . . . . . . . . . . . . . . . . . 202
     9.19.1 Target Transfer Tag  . . . . . . . . . . . . . . . . . . 203
     9.19.2 StatSN   . . . . . . . . . . . . . . . . . . . . . . . . 203
     9.19.3 LUN  . . . . . . . . . . . . . . . . . . . . . . . . . . 203
10. iSCSI Security Keys and Authentication Methods   . . . . . . . . 204
  10.1 AuthMethod  . . . . . . . . . . . . . . . . . . . . . . . . . 204
  10.2 Kerberos  . . . . . . . . . . . . . . . . . . . . . . . . . . 205
  10.3 Simple Public-Key Mechanism (SPKM)  . . . . . . . . . . . . . 206
  10.4 Secure Remote Password (SRP)  . . . . . . . . . . . . . . . . 207

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  10.5 Challenge Handshake Authentication Protocol (CHAP)  . . . . . 208
11. Login/Text Operational Keys  . . . . . . . . . . . . . . . . . . 210
  11.1 HeaderDigest and DataDigest   . . . . . . . . . . . . . . . . 210
  11.2 MaxConnections  . . . . . . . . . . . . . . . . . . . . . . . 212
  11.3 SendTargets   . . . . . . . . . . . . . . . . . . . . . . . . 212
  11.4 TargetName  . . . . . . . . . . . . . . . . . . . . . . . . . 212
  11.5 InitiatorName   . . . . . . . . . . . . . . . . . . . . . . . 213
  11.6 TargetAlias   . . . . . . . . . . . . . . . . . . . . . . . . 213
  11.7 InitiatorAlias  . . . . . . . . . . . . . . . . . . . . . . . 214
  11.8 TargetAddress   . . . . . . . . . . . . . . . . . . . . . . . 214
  11.9 TargetPortalGroupTag  . . . . . . . . . . . . . . . . . . . . 215
  11.10 InitialR2T   . . . . . . . . . . . . . . . . . . . . . . . . 215
  11.11 BidiInitialR2T   . . . . . . . . . . . . . . . . . . . . . . 216
  11.12 ImmediateData  . . . . . . . . . . . . . . . . . . . . . . . 217
  11.13 MaxRecvDataSegmentLength   . . . . . . . . . . . . . . . . . 218
  11.14 MaxBurstLength   . . . . . . . . . . . . . . . . . . . . . . 218
  11.15 FirstBurstLength   . . . . . . . . . . . . . . . . . . . . . 219
  11.16 DefaultTime2Wait   . . . . . . . . . . . . . . . . . . . . . 219
  11.17 DefaultTime2Retain   . . . . . . . . . . . . . . . . . . . . 220
  11.18 MaxOutstandingR2T  . . . . . . . . . . . . . . . . . . . . . 220
  11.19 DataPDUInOrder   . . . . . . . . . . . . . . . . . . . . . . 221
  11.20 DataSequenceInOrder  . . . . . . . . . . . . . . . . . . . . 221
  11.21 ErrorRecoveryLevel   . . . . . . . . . . . . . . . . . . . . 222
  11.22 SessionType  . . . . . . . . . . . . . . . . . . . . . . . . 222
  11.23 The Vendor Specific Key Format   . . . . . . . . . . . . . . 223
12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . . 224
 References and Bibliography . . . . . . . . . . . . . . . . . . . . 225
 Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 227
Appendix A. Sync and Steering with Fixed Interval Markers  . . . . . 229
   A.1 Markers At Fixed Intervals  . . . . . . . . . . . . . . . . . 229
   A.2 Initial Marker-less Interval  . . . . . . . . . . . . . . . . 230
   A.3 Negotiation   . . . . . . . . . . . . . . . . . . . . . . . . 230
  OFMarker, IFMarker 230
  OFMarkInt, IFMarkInt 231
Appendix B. Examples   . . . . . . . . . . . . . . . . . . . . . . . 233
   B.2 Write Operation Example   . . . . . . . . . . . . . . . . . . 234
   B.3 R2TSN/DataSN use Examples   . . . . . . . . . . . . . . . . . 234
   B.4 CRC Examples  . . . . . . . . . . . . . . . . . . . . . . . . 238
Appendix C. Login Phase Examples   . . . . . . . . . . . . . . . . . 240
Appendix D. SendTargets Operation  . . . . . . . . . . . . . . . . . 249
Appendix E. Algorithmic Presentation of Error Recovery Classes   . . 254
   E.2 Within-command Error Recovery Algorithms  . . . . . . . . . . 255
  Procedure Descriptions 255

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  Initiator Algorithms 256
  Target Algorithms 258
   E.3 Within-connection Recovery Algorithms   . . . . . . . . . . . 260
  Procedure Descriptions 260
  Initiator Algorithms 261
  Target Algorithms 264
   E.4 Connection Recovery Algorithms  . . . . . . . . . . . . . . . 264
  Procedure Descriptions 264
  Initiator Algorithms 265
  Target Algorithms 267
Appendix F. Clearing effects of various events on targets  . . . . . 269
   F.1 Clearing effects on iSCSI objects   . . . . . . . . . . . . . 269
   F.2 Clearing effects on SCSI objects  . . . . . . . . . . . . . . 274
 Full Copyright Statement  . . . . . . . . . . . . . . . . . . . . . 276





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1. Definitions and Acronyms

1.1  Definitions

   - Alias: An alias string can 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
   session for the initiator. It is generated by the initiator and pre-
   sented to the target during login requests and during logouts that
   close connections.

   - Connection: A connection is a TCP 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 Device: A SCSI Device using an iSCSI delivery subsystem

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


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  - iSCSI Target Node: The "target".

  - 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 conjunc-
  tion 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).

  - 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 iden-
  tified 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
  communications 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-

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  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-
  tions spanning these portals. Not all Network Portals within a Portal
  Group need participate in every session connected through that Por-
  tal 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 unsigned-integer between 1 and 65535
  identifies the Portal Group within an iSCSI Node. All Network Por-
  tals 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 cli-
  ents; a SCSI Target Device contains one or more SCSI Target Ports and
  one or more logical units. For iSCSI, the SCSI Device is the compo-
  nent 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 between an iSCSI initiator and an
  iSCSI target is defined by a session ID that is a tuple composed of
  an initiator part (ISID) and a target part (Target Portal Group Tag).
  The ISID is explicitly specified by the initiator at session estab-
  lishment. The Target Portal Group Tag is implied by the initiator
  through the selection of the TCP end-point at connection establish-

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  ment. The TargetPortalGroupTag key may also be returned by the tar-
  get as a confirmation during session establishment.

  - 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
  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 Initiator Port and the SCSI Target Port are different.

  - SCSI Port Name: A name made up as UTF-8 characters and includes 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 por-
  tal group tag.

  - Target Portal Group Tag: a numerical identifier (16 bit) for an
  iSCSI Target Portal Group

  - TSIH (Target Session Identifying Handle): The TSIH is a target
  assigned tag for a session with a specific named initiator. The tar-
  get generates it during session establishment and its internal for-
  mat 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 ses-
  sion. It is given to the target during additional connection estab-
  lishment for the same session.





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1.2  Acronyms

   Acronym       Definition
   --------------------------------------------------------------
   3DES       Triple Data Encryption Standard
   ACA           Auto Contingent Allegiance
   AEN           Asynchronous Event Notification
   AES           Advanced Encryption Standard
   AH            Additional Header
   AHS           Additional Header Segment
   API           Application Programming Interface
   ASC           Additional Sense Code
   ASCII      American Standard Code for Information Interchange
   ASCQ          Additional Sense Code Qualifier
   BHS           Basic Header Segment
   CBC           Cipher Block Chaining
   CDB           Command Descriptor Block
   CHAP       Challenge Handshake Authentication Protocol
   CID           Connection ID
   CO            Connection Only
   CRC           Cyclic Redundancy Check
   CRL           Certificate Revocation List
   CSG           Current Stage
   CSM           Connection State Machine
   DES           Data Encryption Standard
   DNS           Domain Name Server
   DOI           Domain of Interpretation
   ESP           Encapsulating Security Payload
   EUI           Extended Unique Identifier
   FFP           Full Feature Phase
   FFPO       Full Feature Phase Only
   Gbps          GigaBits per Second
   HBA           Host Bus Adapter
   HMAC          Hashed Message Authentication
   IANA          Internet Assigned Numbers Authority
   ID            Identifier
   IDN           Internationalized Domain Name
   IEEE       Institute of Electrical & Electronics Engineers
   IETF       Internet Engineering Task Force
   IKE           Internet Key Exchange
   I/O           Input - Output
   IO            Initialize Only
   IP            Internet Protocol


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  IPsec     Internet Protocol Security
  IPv4      Internet Protocol Version 4
  IPv6      Internet Protocol Version 6
  IQN       iSCSI Qualified Name
  ISID      Initiator Session ID
  ITN       Initiator Task Name
  ITT       Initiator Task Tag
  KRB5      Kerberos V5
  LFL       Lower Functional Layer
  LTDS      Logical-Text-Data-Segment
  LO        Leading Only
  LU        Logical Unit
  LUN       Logical Unit Number
  MAC       Message Authentication Codes
  NA        Not Applicable
  NIC       Network Interface Card
  NOP       No Operation
  NSG       Next Stage
  OS        Operating System
  PDU       Protocol Data Unit
  PKI       Public Key Infrastructure
  R2T       Ready To Transfer
  R2TSN     Ready To Transfer Sequence Number
  RDMA      Remote Direct Memory Access
  SAM       SCSI Architecture Model
  SAM2      SCSI Architecture Model - 2
  SAN       Storage Area Network
  SCSI      Small Computer Systems Interface
  SN        Sequence Number
  SNACK     Selective Negative Acknowledgment - also
            Sequence Number Acknowledgement for data
  SPKM      Simple Public-Key Mechanism
  SRP       Secure Remote Password
  SSID      Session ID
  SW        Session Wide
  TCB       Task Control Block
  TCP       Transmission Control Protocol
  TPGT      Target Portal Group Tag
  TSIH      Target Session Identifying Handle
  TTT       Target Transfer Tag
  UFL       Upper Functional Layer
  ULP       Upper Level Protocol
  URN       Uniform Resource Names

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   UTF          Universal Transformation Format
   WG           Working Group

1.3  Conventions used in this document

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

   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.

   iSCSI messages - PDUs - are represented by diagrams as in the follow-
   ing example:


   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0| Basic Header Segment (BHS)                                    |
     +---------------+---------------+---------------+---------------+
   ----------
    +|                                                               |
     +---------------+---------------+---------------+---------------+


   The diagrams include byte and bit numbering.

   The following representation and ordering rules are observed in this
   document:

         - Word Rule
         - Half-word Rule
         - Byte Rule


1.3.1  Word Rule

   A word holds 4 consecutive bytes and whenever having a numeric con-
   tent the word is considered an unsigned number in base 2 positional
   representation with the lowest numbered byte (e.g., byte 0) bit 0
   representing 2**31, bit 1 representing 2**30 and through Lowest num-
   bered byte + 3 (e.g., byte 3) bit 7 representing 2**0.

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  Decimal and hexadecimal representation of word values map this repre-
  sentation to decimal or hexadecimal positional notation.

1.3.2  Half-Word Rule

  A half-word holds 2 consecutive bytes and whenever having a numeric
  content the half-word is considered an unsigned number in base 2
  positional representation with the lowest numbered byte (e.g., byte
  0) bit 0 representing 2**16, bit 1 representing 2**15 and through
  Lowest numbered byte + 1 (e.g., byte 1) bit 7 representing 2**0.

  Decimal and hexadecimal representation of word values map this repre-
  sentation to decimal or hexadecimal positional notation.

1.3.3  Byte Rule

  For every PDU bytes are sent and received in increasing numbering
  order (network order).

  Whenever a byte has a numerical content it is considered an unsigned
  number in base 2 positional representation with bit 0 representing
  2**7, bit 1 representing 2**6 and through bit 7 representing 2**0.





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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 famil-
   iarize 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 spe-
   cific 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 tar-
   get 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 initia-
   tor provided "task tag" to distinguish between tasks. Only one com-
   mand 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 ter-
   minates 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 spe-
   cific 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 "tar-
   get" refer to "iSCSI initiator node" and "iSCSI target node", respec-
   tively (see Section 2.4.1 iSCSI Architecture Model) unless otherwise
   qualified.

   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
   target, and data and responses may be shipped together from targets.

   The iSCSI transfer direction is defined with respect to the initia-
   tor. Outbound or outgoing transfers are transfers from an initiator
   to a target, while inbound or incoming transfers are from a target to
   an 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 session 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 "tar-
   get image". All target identifying elements, such as LUN, are the
   same.  A target also sees one "initiator image" across all connec-
   tions within a session. Initiator identifying elements, such as the
   Initiator Task Tag are global across the session regardless of the
   connection on which they are sent or received.

   iSCSI targets and initiators MUST support at least one TCP connec-
   tion and MAY support several connections in a session. For error
   recovery purposes, targets and initiators that support a single
   active connection 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 sequenc-
   ing scheme.

   Command numbering is session-wide and is used for ordered command
   delivery over multiple connections. It can also be used as a mecha-
   nism 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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   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 NOP-Out/In PDUs may be utilized
   to synchronize the command and status ordering counters of the tar-
   get 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 iden-
   tified 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 PDUs
   carry this number. The iSCSI initiator allocates CmdSNs with a 32-bit
   unsigned counter (modulo 2**32). Comparisons and arithmetic on CmdSN
   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 connec-
   tion) and command numbers are incremented by 1 for every non-immedi-
   ate command issued afterwards.

   If immediate delivery is used with task management commands, these
   commands may reach the target before the tasks on which they are sup-
   posed to act. For this reason the task management command MUST carry
   the current CmdSN as a marker of their position in the stream of com-
   mands. 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.  Whenever CmdSN for an
   outgoing PDU is not specified by an explicit rule CmdSN will carry
   the current value of the local CmdSN register (see later in this sec-
   tion).




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                                  iSCSI                        1-July-02

  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 are beyond the scope of this document.

  The number of commands used for immediate delivery is not limited and
  their delivery to execution is not acknowledged through the number-
  ing scheme. Immediate commands can be rejected by the iSCSI target
  due to lack of resources. An iSCSI target MUST be able to handle at
  least one immediate task management command and one immediate non-
  task-management iSCSI command 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 retrans-
  mitted 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 imme-
        diate 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 execu-
        tion 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.


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                                   iSCSI                      1-July-02

  ExpCmdSN and MaxCmdSN are derived from target-to-initiator PDU
  fields. Comparisons and arithmetic on ExpCmdSN and MaxCmdSN MUST use
  Serial Number Arithmetic as defined in [RFC1982] where SERIAL_BITS =
  32.

  The target MUST NOT transmit a MaxCmdSN that is less than ExpCmdSN-1.
  For non-immediate commands, the CmdSN field can take any value from
  ExpCmdSN to MaxCmdSN inclusive. The target MUST silently ignore any
  non-immediate command outside of this range or non-immediate dupli-
  cates within the range. Note that the CmdSN carried by immediate com-
  mands may lie outside the ExpCmdSN to MaxCmdSN range (e.g., if the
  initiator has previously sent a non-immediate command carrying the
  CmdSN equal to MaxCmdSN - i.e., target window is closed). For group
  task management commands issued as immediate commands CmdSN indi-
  cates the scope of the group action (e.g., on ABORT TASK SET - what
  commands get aborted).

  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 greater than the local MaxCmdSN (in
         Serial Arithmetic Sense) it updates the local MaxCmdSN; oth-
         erwise, it is ignored.
     -If the PDU ExpCmdSN is greater than the local ExpCmdSN (in
         Serial Arithmetic Sense) it updates the local ExpCmdSN; oth-
         erwise, it is ignored.

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

  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 reis-
  sued (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 (represented by
  identifying the Initiator Task Tag) is assumed to precede any other
  action at the target, and is followed by ordering and delivery if no
  execution state is found or delivery if an execution state is found.

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                                iSCSI                          1-July-02


   If an initiator issues a command retry for a command with CmdSN R on
   a connection when the session CmdSN register is Q, it MUST NOT
   advance the CmdSN past R + 2**31 -1 unless the connection is no
   longer operational (has returned to the FREE state - see Section 5.1
   Standard Connection State Diagrams), or the connection has been rein-
   stated (see Section 4.3.4 Connection reinstatement), or a non-immedi-
   ate command with CmdSN equal or greater than Q was issued on the same
   connection and the reception of the command is acknowledged by the
   target (see Section 8.4 Command Retry and Cleaning Old Command
   Instances).

   A target MUST NOT issue a command response or DATA-In PDU with sta-
   tus 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 32-
   bit unsigned-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 Exp-
   StatSN.

   A large absolute difference between StatSN and ExpStatSN may indi-
   cate 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.




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                                   iSCSI                     1-July-02

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 output data PDUs, DataSN starts with 0 for the first data PDU of
   a 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
   bidirectional 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 read or bidirectional command, a target MUST issue less
   than 2**32 combined R2T and Data-In PDUs. Any output data sequence
   MUST contain less than 2**32 Data-Out 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 parame-
   ters 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.


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                                   iSCSI                     1-July-02

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

   The iSCSI Login Phase is carried through Login requests and
   responses. Once suitable authentication has occurred and operational
   parameters have been set, the initiator may start to send SCSI com-
   mands. 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 the ISID part of the session ID (SSID). The
   target portal group servicing the login is implied by the selection
   of the connection end-point. For a new session, the TSIH is zero. As
   part of the response, the target generates a TSIH.

   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 section).
   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 persistent 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. Login requests and responses MUST be used
   exclusively during Login.  On any connection the login phase MUST
   immediately succeed TCP connection establishment and a single Login
   Phase is allowed before tearing down a connection.

2.2.4  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)
   connection of a session.  A connection is in Full Feature Phase if


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                                 iSCSI                        1-July-02

  the session 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 performed 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 connec-
  tion. We call this "connection allegiance". If the original connec-
  tion fails before the command is completed, the connection allegiance
  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 the command MUST be sent over the
  same TCP connection to which the SCSI command is currently alle-
  giant, 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 over the same TCP connection that was
  used to deliver the SCSI 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. Solic-
  ited data are sent in response to R2T PDUs. Unsolicited data can be
  sent as part of an iSCSI command PDU ("immediate data") or in sepa-

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                               iSCSI                        1-July-02

  rate iSCSI data PDUs. An initiator may send unsolicited data up to
  FirstBurstLength as immediate (up to the negotiated maximum PDU
  length), in a separate PDU sequence or both. All subsequent data MUST
  be solicited. The maximum length of an individual data PDU or the
  immediate-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. The maximum amount of unsolicited data that can
  be sent with a command is negotiated at login. A target MAY sepa-
  rately enable immediate data without enabling the more general (sepa-
  rate data PDUs) form of unsolicited data.

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

  An iSCSI initiator MAY choose to send no unsolicited data, only imme-
  diate data or FirstBurstLength bytes of unsolicited data with a com-
  mand. If any non-immediate unsolicited data are sent, the total
  unsolicited data MUST be either the negotiated amount or all the data
  if the total amount is less than the negotiated amount for unsolic-
  ited data.

  An initiator MUST honor an R2T data request for a valid outstanding
  command (i.e., carrying a valid Initiator Task Tag) and deliver all
  the requested data provided the command is supposed to deliver outgo-
  ing data and the R2T specifies data within the command bounds. The
  initiator actions on receiving an R2T request that specifies data all
  or part outside the command bounds is unspecified.

  It is considered an error for an initiator to send unsolicited data
  PDUs to a target that operates in R2T mode (only solicited data are
  allowed). It is also an error for an initiator to send more data,
  whether immediate or as separate PDUs, than the iSCSI limit for first
  burst.

  A target SHOULD NOT silently discard data and then request retrans-
  mission 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


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                                 iSCSI                       1-July-02

   implicitly solicited. SCSI data packets are matched to their corre-
   sponding SCSI commands 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 target tags are used by the target to tag (alone or
   in combination with the LUN) the solicited data. Target tags are gen-
   erated by the target and "echoed" by the initiator. The above mecha-
   nisms 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 which commands were sent. A target that receives data out of order
   MAY terminate the session.

2.2.5  iSCSI Connection Termination

   An iSCSI connection may be terminated by use of a transport connec-
   tion 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 Asyn-
   chronous Message PDU.  Connection termination with outstanding com-
   mands may require recovery actions.

   If a connection is terminated while in Full Feature Phase, connec-
   tion 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.

2.2.6  iSCSI Names

   Both targets and initiators require names for the purpose of identi-
   fication, and so that iSCSI storage resources can be managed regard-
   less of location (address).  An iSCSI node name is also the SCSI
   device name of an iSCSI device.  The iSCSI name of a SCSI device is
   the principal object used in authentication of targets to initiators
   and initiators to targets.  This name is also used to identify and
   manage iSCSI storage resources.

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                                  iSCSI                        1-July-02


   iSCSI names must be unique within the operation domain of the end
   user. However, because the operation domain of an IP network is
   potentially worldwide, the iSCSI name formats are architected to be
   world wide unique.  To assist naming authorities in the construction
   of world wide unique names, iSCSI provides two name formats for dif-
   ferent types of naming authorities.

   iSCSI names are associated with iSCSI nodes, not iSCSI network
   adapter cards, to ensure the replacement of network adapter cards
   does not require reconfiguration of all SCSI and iSCSI resource allo-
   cation information.

   Some SCSI commands require that protocol-specific identifiers be com-
   municated within SCSI CDBs. See Section 2.4.2 SCSI Architecture Model
   for the definition of the SCSI port name/identifier for iSCSI ports.

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

2.2.6.1  iSCSI Name Requirements

   Each iSCSI node, whether an initiator or target, MUST have an iSCSI
   name.

   Initiators and targets MUST support the receipt of iSCSI names of up
   to the maximum length of 255 bytes.

   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 or connection. The only exception is if a
   discovery session (see Section 2.3 iSCSI Session Types) is to be
   established; the iSCSI Initiator Name is still required, but the
   iSCSI Target Name may be ignored.

   iSCSI names must adhere to the following requirements:

        a)  iSCSI names must be globally unique.  No two initiators or
        targets should have the same name.
        b)  iSCSI names must be permanent.  An iSCSI initiator or target
        has the same name for its lifetime.



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                                    iSCSI                           1-July-02

         c)  iSCSI names do not imply a location or address.  An iSCSI ini-
         tiator or target can move, or have multiple addresses.  A change
         of address does not imply a change of name.
         d)  iSCSI names must not rely on a central name broker; the nam-
         ing authority must be distributed.
         e)  iSCSI names must support integration with existing unique nam-
         ing schemes.
         f)  iSCSI names must rely on existing naming authorities.  iSCSI
         does not have to create its own naming authority.

  The encoding of an iSCSI name also has some requirements:

         a)  iSCSI names must have a single encoding method when transmit-
         ted over various protocols.
         b)  iSCSI names must be relatively simple to compare.  The algo-
         rithm for comparing two iSCSI names for equivalence must not rely
         on any external server.
         c)  iSCSI names must be composed of displayable characters only.
         iSCSI names should be kept as simple as possible.  They must pro-
         vide for the use of international character sets, and must not be
         case sensitive.  Whitespace characters are not allowed.
         d)  iSCSI names must be transport-friendly.  They must be trans-
         ported using both binary and ASCII-based protocols.

  An iSCSI name really names a logical software entity, and is not tied
  to a port or other hardware that can be changed.  For instance, an
  initiator name should name the iSCSI initiator node, not a particu-
  lar NIC or HBA.  When multiple NICs are used, they should generally
  all present the same iSCSI initiator name to the targets, because
  they are just paths to the same SCSI layer.  In most operating sys-
  tems, the named entity is the operating system image.

  A target name should similarly not be tied to hardware interfaces
  which can be changed.  A target name should identify the logical tar-
  get, and must be the same for the target regardless of the physical
  portion being addressed.  This assists iSCSI initiators in determin-
  ing that two targets it has discovered are really two paths to the
  same target.

  The iSCSI name is designed to fulfill the functional requirements for
  Uniform Resource Names (URN) [RFC1737].  For example, it is required
  that the name have a global scope, independent of address or loca-
  tion, and that it be persistent and globally unique.  Names must be

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                                         iSCSI                        1-July-02

   extensible, and scale with the use of naming authorities.  The encod-
   ing of the name should be readable by a human, as well as be machine-
   readable.  See [RFC1737] for further requirements.

2.2.6.2  iSCSI Name Encoding

   An iSCSI name MUST be a UTF-8 encoding of a string of Unicode charac-
   ters,  with the following properties:

        - it is in Normalization Form C (see "Unicode Normalization
             Forms" [UNICODE])
        - it contains only the following characters:

                 - ASCII dash ('-'=U+002d)
                 - ASCII dot ('.'=U+002e)
                 - ASCII colon (':'=U+003a)
                 - Any character allowed by the output of the iSCSI
                 stringprep template (described in [STPREP-iSCSI])

        - when encoded in UTF-8, it is no larger than 255 bytes

   The stringprep process is described in [STPREP]; iSCSI's use of the
   stringprep process is described in [STPREP-iSCSI].  Stringprep is a
   method designed by the Internationalized Domain Name (IDN) working
   group to translate human-typed strings into a format that can be com-
   pared as opaque strings.  Strings must not include punctuation, spac-
   ing, diacritical marks, or other characters that could get in the way
   of readability. The stringprep process also converts strings into
   equivalent strings of lower-case characters.

   Note that in most cases, the Stringprep process does not need to be
   implemented if the names are generated using only lower-case (any
   character set) alpha-numeric characters.

   Once iSCSI names encoded in UTF-8 are "normalized" (there is one and
   only one representation for each possible name), they may be safely
   compared byte-for-byte.

2.2.6.3  iSCSI Name Structure

   An iSCSI name consists of two parts - a type designator followed by a
   unique name string.




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                                       iSCSI                    1-July-02

   The iSCSI name does not define any new naming authorities.  Instead,
   it supports two existing ways of designating naming authorities: an
   iSCSI-Qualified Name, using domain names to identify a naming author-
   ity, and the EUI format, where the IEEE Registration Authority
   assists in the formation of world wide unique names (EUI-64 format).

   The type designator strings that may currently be used are:

     iqn.       - iSCSI Qualified name
     eui.       - Remainder of the string is an IEEE EUI-64 identi-
           fier, in ASCII-encoded hexadecimal.

   As these two naming authority designators will suffice in nearly
   every case for both software and hardware-based entities, the cre-
   ation of additional type designators is prohibited.  One of these two
   type strings MUST be used when constructing an iSCSI name; any type
   string not listed here is not allowed, as they cannot be guaranteed
   to be unique.

2.2.6.3.1  Type "iqn." (iSCSI Qualified Name)

   This iSCSI name type can be used by any organization which owns a
   domain name.  This naming format is useful when an end user or ser-
   vice provider wishes to assign iSCSI names for targets and/or initia-
   tors.

   To generate names of this type, the person or organization generat-
   ing the name must own a DNS domain name.  This domain name does not
   have to be active, and does not have to resolve to an address; it
   just needs to be reserved to prevent others from generating iSCSI
   names using the same domain name.

   Because a domain name can expire, be acquired by another entity, and
   might be used to generate iSCSI names by both owners, the domain name
   must be additionally qualified by a date during which the naming
   authority owned the domain name.  A date code is provided as part of
   the "iqn." format for this reason.

   The iSCSI qualified name string consists of:

     -  The string "iqn.", used to distinguish these names from
           "eui." formatted names.
     -  A date code, in yyyy-mm format.  This date MUST be a date
           during which the naming authority owned the domain name used

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                                   iSCSI                          1-July-02

           in this format, and SHOULD be the date on which the domain
           name was acquired by this naming authority.  This date code
           uses the Gregorian calendar.  All four digits in the year
           must be present.  Both digits of the month must be present,
           with January == "01" and December == "12".  The dash must be
           included.
        -  Another ".".
        -  The reversed domain name of the naming authority (person or
           organization) creating this iSCSI name.
        -  Another ".".
        -  Any string, within the character set and length boundaries,
           that the owner of the domain name deems appropriate.  This
           may contain product types, serial numbers, host identifiers,
           software keys, or anything else that makes sense to uniquely
           identify the initiator or target.  Everything after the
           reversed domain name, followed by another dot ".", can be
           assigned as desired by the owner of the domain name.  It is
           the responsibility of the entity that is the naming author-
           ity to ensure that the iSCSI names it assigns are world wide
           unique. For example, "ACME Storage Arrays, Inc.", might own
           the domain name "acme.com".

   The following are examples of iSCSI qualified names that might be
   generated by "ACME Storage Arrays, Inc."

                  Organization    Subgroup Naming Authority
                      Naming      and/or string defined by
        Type  Date     Auth       "acme.com" Naming Authority
        +--++-----+ +------+ +--------------------------------+
        |  ||     | |      | |                                |

        iqn.2001-04.com.acme.diskarrays-sn-a8675309
        iqn.2001-04.com.acme.storage:tape.sys1.xyz
        iqn.2001-04.com.acme.storage.tape:sys1.xyz

2.2.6.3.2  Type "eui." (IEEE EUI-64 format)


   The IEEE Registration Authority provides a service for assigning glo-
   bally unique identifiers [EUI].  The EUI-64 format is in use as a
   global identifier in other network protocols such as Fibre Channel.
   See http://standards.ieee.org/regauth/oui/index.shtml - for more
   information on registering for EUI identifiers.

   The format is "eui." followed by an EUI-64 identifier (16 ASCII-
   encoded hexidecimal digits).

   Example iSCSI name :

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                                  iSCSI                          1-July-02


      Type  EUI-64 identifier (ASCII-encoded hexadecimal)
      +--++--------------+
      |  ||              |
      eui.02004567A425678D

   The IEEE EUI-64 iSCSI name format might be used when a manufacturer
   is already registered with the IEEE Registration Authority and uses
   EUI-64 formatted world wide unique names for its products.

   More examples of name construction are discussed in [NDT].


2.2.7  Persistent State

   iSCSI does not require any persistent state maintenance across ses-
   sions. However in some cases, SCSI requires persistent identifica-
   tion 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,
   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 9.5 Task Man-
   agement Function Request.)

2.2.8  Message Synchronization and Steering

2.2.8.1  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


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                                   iSCSI                         1-July-02

   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 pro-
   cessed 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 segments arrive, upon which the data must be copied to the appli-
   cation 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 dedicated reassembly buffers as well as the latency and
   bandwidth related to extra copies.

   Relying solely on the "message length" information from the iSCSI
   message header may make it impossible to find iSCSI message bound-
   aries 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). Because 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 -. To make these schemes work, iSCSI implemen-
   tations have to make sure that the appropriate protocol layers are
   provided with enough information to implement a synchronization and/
   or data steering mechanism.

2.2.8.2  Synchronization (sync) and Steering Functional Model

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





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       +------------------------+
       |        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
  boundaries. 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,

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                                 iSCSI                       1-July-02

   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 are 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 identi-
   cal 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-
   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.

2.2.8.3  Sync and Steering and Other Encapsulation Layers

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



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                                  iSCSI                      1-July-02

        +----------------------------------+
        |             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, compres-
   sion, padding 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 per-
   form on the stream.

   This makes implementation of Sync and Steering in the presence of
   otherwise opaque UFLs less attractive.

2.2.8.4  Sync/Steering and iSCSI PDU Length

   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) because
   the iSCSI header that indicates to which SCSI buffers the data are to
   be steered was lost. To minimize the amount of buffering, it is rec-
   ommended that the iSCSI PDU length be restricted to a small value



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                                   iSCSI                      1-July-02

   (perhaps a few TCP segments in length). During login, each end of the
   iSCSI session specifies the maximum iSCSI PDU length 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 discov-
      ery; the target MAY accept only text requests with the SendTar-
      gets 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 3260| | TCP Port 3260| |
                 | +--------------+ +--------------+ |
                 |        |               |          |
                 |        -----------------          |
                 |           |         |             |
                 |  +-------------+ +--------------+ |
                 |  | 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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                               iSCSI                        1-July-02

     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 Sec-
     tion 2.2.6 iSCSI Names and Chapter 11). 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.

     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
     substitute 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
     Portals within a Portal Group need to participate in every ses-
     sion 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 unsigned-integer
     between 1 and 65535 (see Section 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 8.1.1 Conser-
     vative Reuse of ISIDs  for references to the Initiator Portal
     Groups.


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                                    iSCSI                           1-July-02

      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) | |
   |   |                            |  |                             | |
   |   |       (TSIH = 56)          |  |       (TSIH = 48)           | |
   |   +----------------------------+  +-----------------------------+ |
   |                                                                   |
   |                      iSCSI Target Node                            |
   |              (within Network Entity, not shown)                   |
   +-------------------------------------------------------------------+

2.4.2  SCSI Architecture Model

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

   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.



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                                iSCSI                           1-July-02

  The following list outlines mappings of SCSI architectural elements
  to iSCSI.

     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 mandatory 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 ser-
       vice delivery subsystem or transport. For iSCSI, the defini-
       tion of SCSI Initiator Port and SCSI Target Port are
       different.

      SCSI Initiator Port: This maps to one endpoint of an iSCSI
       normal 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 pro-
       cess, a SCSI Initiator Port is created within the SCSI Initi-
       ator 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 identifies it as an ini-
       tiator 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 Identi-
       fier 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 MUST be encoded as:
      - The iSCSI Name in UTF-8 format, followed by
      - a comma separator (1 byte), followed by
      - the ASCII character 'i' (for SCSI Initiator Port) or the
       ASCII character 't' (for SCSI Target Port), followed by
      - a comma separator (1 byte), 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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                                    iSCSI                    1-July-02

      - 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 multi-
       ple 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 pro-
       vides the interpretation and length of the remaining six
       bytes (initiator) 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
       relationship 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
       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).


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. Between a given SCSI initiator port and a
   given SCSI target port, only one I_T nexus (session) can exist. That
   is, no more than one nexus relationship (parallel nexus) is allowed.
   Therefore, between a given iSCSI initiator node and an iSCSI target
   node, at any given time, only one session can exist with the same
   session identifier (SSID).

   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
   9.12.6 ISID.

   The structure of the ISID that contains a naming authority component
   (see Section 9.12.6 ISID and [NDT]) provides a mechanism to facili-
   tate compliance with the ISID rule (See also Section 8.1.1 Conserva-
   tive Reuse of ISIDs).

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                                   iSCSI                     1-July-02


   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 differ-
   ent Target Portal Groups on the same iSCSI target or on other iSCSI
   targets (see Section 8.1.1 Conservative Reuse of ISIDs). Allowing
   this would be analogous to a single SCSI Initiator Port having rela-
   tionships (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 session 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 dif-
   ferent 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.

   TSIH RULE: The iSCSI Target selects a non-zero value for the TSIH at
   session creation (when an initiator presents a 0 value at Login).
   After being selected the same TSIH value MUST be used whenever initi-
   ator or target refer to the given session and a TSIH is required.

2.4.3.1  I_T Nexus State

   Certain nexus relationships contain an explicit state (e.g., initia-
   tor-specific mode pages) that may need to be preserved 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 fail-
   ures). In order for that state to be restored, the iSCSI initiator
   should re-establish its session (re-login) to the same Target Portal
   Group using the previous ISID. That is, it should perform session
   recovery as described in Chapter 6. This is because the SCSI initia-
   tor port identifier and the SCSI target port identifier (or relative
   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


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   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 Target 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 (see [SAM2]) IN arguments such as task
   attributes, Command Sequence Number, Expected Data Transfer Length
   for one or both transfer directions (the latter 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
   number (CmdSN) and the expected status number on the connection it is
   issued (ExpStatSN).

   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 seg-
   ment.





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2.5.1.2  SCSI-Response

   The SCSI-Response carries all the SCSI execute-command procedure call
   (see [SAM2]) OUT arguments 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
   PDUs that a target has sent (to enable the initiator to check that
   all have arrived) - ExpDataSN, the Status Sequence Number on this
   connection - StatSN and the next Expected Command Sequence Number at
   the target - ExpCmdSN, the Maximum CmdSN acceptable at the 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
   management function to perform) and enough information to unequivo-
   cally 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 dis-
   carded 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 associ-
   ated 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.

   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 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 Initia-
   tor 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
   contain the status if the status indicates termination with no excep-
   tions (no sense or response involved).


2.5.1.6  Ready To Transfer (R2T)

   R2T is the mechanism by which the SCSI target "prompts" the initia-
   tor for output data. R2T passes the offset of the requested data rel-
   ative to 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
   requirements 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 Trans-
   fer Tag of the next Text Request. If the initiator wants to reset the
   target (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
   target.

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.



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   The Login Phase proceeds through several stages (security negotia-
   tion, operational parameter negotiation) that are selected with two
   binary coded fields in the header - the "current stage" (CSG) and the
   "next stage" (NSG) with the appearance of the latter 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.

   A login request may indicate an implied logout (cleanup) of the con-
   nection to be logged in (we call this a connection restart) by using
   the same Connection ID (CID) as an existing connection, in the login
   request header, as well as the same session identifying elements of
   the session to which the old connection was associated.

2.5.3.3  Logout Request and Response

   Logout Requests and Responses are used for the orderly closing of
   connections 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 connec-
   tion) in Time2Retain and how long the initiator must wait before pro-
   ceeding 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 cov-
   ers a contiguous set of missing items called a run of a given type of
   items (the type is indicated in a type field in the PDU header). The

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   run is composed of an initial item (StatSN, DataSN, R2TSN) and the
   number of missed Status, Data, or R2T PDUs. 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 acknowl-
   edged conveys this positive acknowledgement.

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
   initiator/target command, status or data counter values when there is
   no other "carrier" and there is a need to update the initiator/tar-
   get.











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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 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.

   The following character symbols are used in this document for text
   items:

   (a-z, A-Z) - letters
   (0-9) - digits
   " " (0x20) - space
   "." (0x2e) - dot
   "-" (0x2d) - minus
   "+" (0x2b) - plus
   "@" (0x40) - commercial at
   "_" (0x5f) - underscore
   "=" (0x3d) - equal
   ":" (0x3a) - colon
   "/" (0x2f) - solidus or slash
   "[" (0x5b) - left bracket
   "]" (0x5d) - right bracket
   nul (0x00) - nul separator
   "," (0x2c) - comma
   "~" (0x7e) - tilde

   Key=value pairs may span PDU boundaries. An initiator or target that
   sends partial key=value text within a PDU indicates that more text
   follows by setting the C bit in the Text/Login Request or Text/Login
   Response to 1. Data segments in a series of PDUs having the C bit set
   to 1 and ending with a PDU having the C bit set to 0 or including a
   single PDU having the C bit set to 0 have to be considered as form-
   ing a single logical-text-data-segment (LTDS).

   Every key=value pair, including the last or only pair in a LTDS, MUST
   be followed by one null (0x00) delimiter.

   A key-name is whatever precedes the first = in the key=value pair.
   The term key is used frequently in this document with the meaning of
   key-name.


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  A value is whatever follows the first = in the key=value pair up to
  the end of the key=value pair.

  The following definitions will be used in the rest of this document:

     key-name: a string of one or more characters consisting of let-
       ters, digits, dot, minus, plus, commercial at, and under-
       score, A key-name MUST begin with a capital letter an must
       not exceed 63 characters.

     text-value: a string of 0 or more characters consisting of let-
       ters, digits, dot, minus, plus, commercial at, underscore,
       slash, left bracket, right bracket and colon.

     iSCSI-name-value: a string of one or more characters consist-
       ing of minus, dot, colon and any character allowed by the
       output of the iSCSI string-prep template as specified in
       [STPREP-iSCSI] (see also Section 2.2.6.2 iSCSI Name Encod-
       ing).

     iSCSI-local-name-value: an UTF-8 string; no nul characters are
       allowed in the string. This encoding is to be used for local-
       ized (internationalized) aliases.

     boolean-value: the string "Yes" or "No".

     hex-constant: hexadecimal constant encoded as a string start-
       ing with "0x" or "0X" followed by 1 or more digits or the
       letters a, b, c, d, e, f, A, B, C, D, E and F. Hex-constants
       are used to encode numerical values or binary strings. When
       used to encode numerical values the excessive use of leading
       0 digits is discouraged and the string following 0X (or 0x)
       represents a base16 number starting with the most signifi-
       cant base16 digit, followed by all other digits in decreas-
       ing significance order and ending with the least-significant
       base16 digit. When used to encode binary strings hexadecimal
       constants have an implicit byte-length that includes 4 bits
       for every hexadecimal digit of the constant, including lead-
       ing zeroes (i.e., a hex-constant of n hexadecimal digits has
       a byte-length of (the integer part of) (n+1)/2).

     decimal-constant: an unsigned decimal number - the digit 0 or a
       string of 1 or more digits starting with a non-zero digit.
       This encoding is not used for numerical values equal or
       greater than 2**64. Decimal-constants are used to encode
       numerical values or binary strings. When used to encode
       binary strings decimal constants have an implicit byte-length


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       that is the minimum number of bytes needed to represent the
       base2 encoding of the decimal number.

     base64-constant: base64 constant encoded as a string starting
       with "0b" or "0B" followed by 1 or more digits or letters or
       plus or slash or equal. The encoding is done according to
       [RFC2045] and each character, except equal, represents a
       base64 digit or a 6-bit binary string. Base64-constants are
       used to encode numerical-values or binary strings. When used
       to encode numerical values the excessive use of leading 0
       digits (encoded a A) is discouraged and the string following
       0B (or 0b) represents a base64 number starting with the most
       significant base64 digit, followed by all other digits in
       decreasing significance order and ending with the least-sig-
       nificant base64 digit; the least significant base64 digit may
       be optionally followed by pad digits (encoded as equal) that
       are not considered as part of the number. When used to encode
       binary strings base64-constants have an implicit byte-length
       that includes 6 bits for every character of the constant
       excluding trailing equals (i.e., a base64-constant of n
       base64 characters excluding the trailing equals has a byte-
       length of ((the integer part of) (n*3/4)). N.B. correctly
       encoded base64 strings cannnot have n values of 1, 5 ...
       k*4+1.

     numerical-value: an unsigned integer less than 2**64 encoded as
       a decimal-constant or a hex constant. Unsigned integer arith-
       metic applies to numeric-values.


     large-numerical-value: an unsigned integer larger than or equal
       to 2**64 encoded as a hex constant, or base64-constant.
       Unsigned integer arithmetic applies to large-numeric-values.

     numeric-range: two numerical-values separated by a tilde where
       the value to the right of tilde must not be lower that the
       value to the left.

     regular-binary-value: a binary string less than 64 bits encoded
       as a decimal constant, hex constant or base64-constant. The
       length of the string is either specified by the key defini-
       tion or is implicit byte-length of the encoded string.

     large-binary-value: a binary string encoded as a hex-constant
       or base64-constant. The length of the string is either speci-
       fied by the key definition or is implicit byte-length of the
       encoded string.

     binary-value: a regular-binary-value or a large-binary-value.
       Operations on binary values are key specific.

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     simple-value: text-value, iSCSI-name-value, boolean-value,
       numeric-value, a numeric-range or a binary-value.

     list-of-values: a sequence of text-values separated by comma.


   If not otherwise specified, the maximum length of a simple-value (not
   its encoded representation) is 255 bytes not including the delimiter
   (comma or zero byte).

   Any iSCSI target or initiator MUST support receiving at least 16384
   bytes of key=value data in a negotiation sequence except when indi-
   cating support for very long authentication items by offering or
   selecting authentication methods such as public key certificates in
   which case they MUST support receiving at least 64 kilobytes of
   key=value data.

4.2  Text Mode Negotiation

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

   The initiator starts the negotiation and/or declaration 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). As negotiation text may span PDU bound-
   aries a Text/Login Request or Text/Login Response PDU having the C
   bit set to 1 MUST NOT have the F/T bit set to 1.

   A target or initiator receiving a Text/Login Request respective Text/
   Login Response with the C bit set to 1 MUST answer with a Text/Login
   Response or Text/Login Request with no data segment (DataSeg-
   mentLength 0).

   A target or initiator SHOULD NOT use a Text/Login Response or Text/
   Login Request with no data segment (DataSegmentLength 0) unless
   explicitly required by a general or a key-specific negotiation rule.

   The format of a declaration is:

     Declarer-> <key>=<valuex>


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  The general format of text negotiation is:

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

  The originator or declarer can either be the initiator or the target
  and the responder can either be the target or initiator, respec-
  tively. Targets 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 explicit (i.e., the result MUST be based only on
  newly exchanged or declared values). There are no implicit offers. If
  an explicit offer is not made then a reply cannot be expected. Con-
  servative design requires also that default values should not be
  relied upon when use of some other value has serious consequences.

  The value offered or declared can be a numerical-value, a numerical-
  range defined by lower and upper value - both integers separated by
  tilde, a binary value, a text-value, a iSCSI-name-value, an iSCSI-
  local-name-value, a boolean-value (Yes or No), or a list of comma
  separated text-values. A range or a large-numerical-value MAY ONLY be
  offered if it is explicitly allowed for a key. An iSCSI-name-value
  and an iSCSI-local-name-value can be used only where explicitly
  allowed. A selected value can be an numerical-value, a large-numeri-
  cal-value, a text-value or a boolean-value.

  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 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.

  Reject or Irrelevant are legitimate negotiation options where allowed
  but their excessive use is discouraged. A negotiation is considered
  complete when the responder has sent the key value pair even if the



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   value is "Reject", "Irrelevant", or "NotUnderstood. Sending the key
   again would be a re-negotiation

   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 NotUnder-
   stood.

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

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

   Whenever parameter action or acceptance are dependent on other param-
   eters, the dependency rules and parameter sequence must be specified
   with the parameters.

   Negotiations MUST be handled as atomic operations - i.e., all negoti-
   ated values get into effect after the negotiation concludes in agree-
   ment or are ignored if the negotiation fails.

   Some parameters may be subject to integrity rules (e.g., parameter-x
   must not exceed parameter-y or parameter-u not 1 implies parameter-v
   to be Yes). Whenever required integrity rules are specified with the
   keys. Checking for compliance with the integrity rule MUST NOT be
   performed before all the negotiation parameters are available (the
   existent and newly negotiated). An iSCSI target MUST perform integ-
   rity checking before committing new values for parameters. An initia-
   tor MAY perform integrity checking.


4.2.1  List negotiations

   In list negotiation, the originator sends a list of values (which may
   include "None") in its order of preference.

   The responding party MUST respond with the same key and the first
   value that it supports (and is allowed to use for the specific origi-
   nator) selected from the originator list.





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   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 support, understand or is allowed
   to use none of the offered options with a specific originator, it may
   use the constant "Reject" or terminate the negotiation. The selec-
   tion of a value not offered is considered a negotiation failure and
   is handled as a protocol error.

4.2.2  Simple-value negotiations

   For simple-value negotiations, the responding party MUST respond with
   the same key. The value it selects, based on the selection rule spe-
   cific 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 unacceptable). An offer of a value not
   admissible (e.g., not within the specified bounds) MAY be answered
   with the constant "Reject" or the responder MAY select an admissible
   value. The selection, by the responder, of a value not admissible
   under the selection rules is considered a negotiation failure and is
   handled accordingly. The selection rules are key-specific.

   For boolean negotiations (keys taking the values Yes or No), the
   responding party MUST respond with the same 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 have selected if given a choice.

   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.




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4.3  Login Phase

   The Login Phase establishes an iSCSI session between an initiator and
   a target. It sets the iSCSI protocol parameters, security parame-
   ters, 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 sin-
   gle Initiator Task Tag (similar to the linked SCSI commands).

   The default MaxRecvDataSegmentLength is used during Login.

   The Login Phase sequence of requests 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 con-
   nection 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 TargetName key=value
   pair.

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

   The Login Phase MAY include a SecurityNegotiation stage and a Login-
   OperationalNegotiation 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.

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

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

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  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 LoginOpera-
  tionalNegotiation keys appear in Chapter 11. Only a limited set of
  keys (marked as Any-Stage in Chapter 11) may be used in any of the
  two stages.

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

  Stage transition is performed through a command exchange (request/
  response) that carries the T bit and the same current stage code.
  During 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.

  When a transition is requested by the initiator and acknowledged by
  the target both initiator and target switch to the selected stage.

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

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





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   +-----------------------------------------------------------+
   |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 Request can come only
   as a response to a Login request with the T bit set to 1, and both
   the request and response MUST have FullFeaturePhase in the NSG field.

   Neither the initiator nor the target should attempt to declare or
   negotiate a parameter more than once during login except for
   responses to specific keys that explicitly allow repeated key decla-
   rations (e.g. TargetAddress). If detected by the target this MUST
   result in a Login reject (initiator error). The initiator MUST drop
   the connection

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.
        -iSCSI Initiator Name and iSCSI Target Name
        -ISID, TSIH and connection Ids.
        -The negotiation stage that the initiator is ready to enter.

   A login may create a new session or it may add a connection to an
   existing session. Between a given iSCSI Initiator Node (selected only
   by an InitiatorName) and a given iSCSI target defined by an iSCSI
   TargetName and a Target Portal Group Tag login results are defined by
   the following table:





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  +-------------------------------------------------------------------+
  |ISID       | TSIH        | CID    |     Target action              |
  +-------------------------------------------------------------------+
  |new        | non-zero    | any    |     fail the login             |
  |           |             |        |     ("session does not exist") |
  +-------------------------------------------------------------------+
  |new        | zero        | any    |     instantiate a new session  |
  +-------------------------------------------------------------------+
  |existing   | zero        | any    |     do session reinstatement   |
  +-------------------------------------------------------------------+
  |existing   | valid       | new    |     add a new connection to    |
  |           | existing    |        |     the session                |
  +-------------------------------------------------------------------+
  |existing   | valid       |existing|     do connection reinstatement|
  |           | existing    |        |                                |
  +-------------------------------------------------------------------+
  |existing   | invalid     | any    |         fail the login         |
  |           |             |        |     ("session does not exist") |
  +-------------------------------------------------------------------+


  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 request and response are set to
       FullFeaturePhase). The response includes the protocol ver-
       sion supported 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 tar-

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       get and either security or iSCSI parameters (when no secu-
       rity mechanism 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 with-
   out security, it issues the Login with the T bit set to 1, the CSG
   set to SecurityNegotiation, and NSG set to LoginOperationalNegotia-
   tion. 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 SecurityNe-
   gotiation, 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
   security 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.

   The first Login Response PDU during the Login Phase from the iSCSI
   target SHOULD return the TargetPortalGroupTag key that contains the
   tag value of the iSCSI portal group servicing the Login Request PDU.
   If the iSCSI target implementation supports altering the portal group
   configuration (including adding, deleting, and swapping of portals in
   a portal group), it MUST return the TargetPortalGroupTag key carry-
   ing the tag value of the servicing portal group. If the reconfigura-
   tion of iSCSI portal groups is a concern in a given environment, the
   iSCSI initiator MUST use this key to ascertain that it had indeed
   initiated the Login Phase with the intended target portal group.

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 pro-
   ceeds according to the authentication method chosen in the negotia-
   tion phase and is conducted using the login requests' and responses'
   key=value parameters.


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   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 are listed in the initiator's order of preference.
       The initiator MAY also send proprietary options.
     -The target MUST reply with the first option in the list it
       supports 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 secu-
       rity parameters, see Chapter 10.

     -When the initiator considers that it ready to conclude the
       SecurityNegotiation stage it sets the T bit to 1 and the NSG
       to what it would like the next stage to be. The target will
       then set the T bit to 1 and set NSG to the next stage in the
       Login response where it finishes sending its security keys.
       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 TSIH value.

   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.



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   If the target responds to a Login request having the T bit set to 1
   with a Login response having the T bit set to 0, the initiator should
   keep sending the Login request (even empty) with the T bit set to 1,
   while it still wants to switch stage, until it receives the Login
   Response having the T bit set to 1.

   Some session specific parameters can be specified only during the
   Login Phase begun by a login request that contains a zero-valued TSIH
   - 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 ses-
   sion 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-TSIH-CID combination that is possibly active from the tar-
   get's 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
   TSIH in the Login PDU MUST be non-zero and CID does not change dur-
   ing a connection reinstatement. The Login request performs the logout
   function of the old connection if an explicit logout was not per-
   formed 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.

   In practical terms, beside the implicit logout connection, reinstate-
   ment is equivalent to a new connection login.


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4.3.5  Session reinstatement, closure and timeout

   Session reinstatement is the process of initiator logging in with an
   ISID that is possibly active from the target's 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 TSIH in the Login PDU MUST be zero to signal ses-
   sion reinstatement. All the tasks that were active on the old ses-
   sion 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.

   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
       Diagram for Initiators and Targets) and no associated task
       states are waiting for reassignment.

   Session timeout is an event defined to occur when the last connec-
   tion state timeout happens and no tasks are waiting for reassign-
   ment. This takes the session to the FREE state (N6 transition in the
   session state diagram).

4.3.5.1  Loss of Nexus notification

   iSCSI Layer provides the SCSI layer with the "I_T nexus loss" notifi-
   cation when any one of the following events happens:

      a)  A successful completion of session reinstatement
      b)  A session closure event
      c)  A session timeout event

   Certain SCSI object clearing actions may result upon this notifica-
   tion in the SCSI end nodes, as documented in Appendix F. - Clearing
   effects of various events on targets -.





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4.3.6  Session continuation and failure

   Session continuation is the process by which the state of a pre-
   existing session is continued to be in use by either connection rein-
   statement (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 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
   allegiant 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 initiator always
   starts and terminates and uses the same Initiator Task Tag. The ini-
   tiator MUST indicate its intent to terminate the negotiation by set-
   ting the F bit to 1; the target sets the F bit to 1 on the last
   response.

   If the target responds with a text response with the F bit set to 0
   to a text request with the F bit set to 1, 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 is
   being answered with an F bit setting of 0 may issue the next request
   with the F bit set to 0.


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  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 opera-
  tional parameter negotiation by answering a Text request with a
  Reject PDU.

  Neither the initiator nor the target should attempt to declare or
  negotiate a parameter more than once during any negotiation sequence
  without an intervening reset except for responses to specific keys
  that explicitly allow repeated key declarations (e.g. TargetAdress).
  If detected by the target this MUST result in a Reject with a reason
  of "protocol error". The initiator MUST reset the negotiation as out-
  lined above.

  Parameters negotiated by a text exchange negotiation sequence become
  effective only after the negotiation sequence is completed.





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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 understand-
   ing.  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 dia-
   gram", 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
         S6: IN_LOGOUT
         S7: LOGOUT_REQUESTED
         S8: CLEANUP_WAIT

   States S5, S6 and S7 constitute the Full Feature Phase operation of
   the connection.

   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
         S6: IN_LOGOUT
         S7: LOGOUT_REQUESTED
         S8: CLEANUP_WAIT

   States S5, S6 and S7 constitute the Full Feature Phase operation of
   the connection.

   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 connec-
               tion 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 readi-
              ness to proceed with Logout.
              -target: Waiting for the Logout process to start after hav-
              ing 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
              receiving a Logout response (success) on another connection
              for a  "close the session"  Logout request 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 request was received.
   -T5:
              -initiator: The final iSCSI Login response with a Status-
              Class of zero was received.
              -target: The final iSCSI Login request 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 - one of the following evens caused the transi-
                 tion:
                 - The final iSCSI Login response was received with a non-
                 zero Status-Class
                 - Login timed out
                 - A transport disconnect indication was received
                 - A transport reset was received
                 - An internal event indicating a transport timeout was
                 received
                 - An internal event of receiving a Logout response (suc-
                 cess) on another connection for a  "close the session"
                 Logout request was received.

             In all these cases, the transport connection is closed.

             -target - one of the following events caused the transition:
                 - The final iSCSI Login request to conclude the Login
                 Phase was received, prompting the target to send the final
                 iSCSI Login response with a non-zero Status-Class
                 - Login timed out
                 - Transport disconnect indication was received
                 - Transport reset was received
                 - An internal event indicating a transport timeout was
                 received
                 - On another connection  a  "close the session"  Logout
                 request was received.

             In all these cases, the connection is to be closed.
  -T8:
             -initiator: An internal event of receiving a Logout response
                 (success) on another connection for a  "close the session"
                 Logout request 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
                 request was received, or an internal event of a successful

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              connection/session reinstatement is received, thus prompt-
              ing 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 request was received.
  -T11, T12:
              -initiator: Async PDU with AsyncEvent "Request Logout" was
              received.
              -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 (suc-
              cess) on another connection for a  "close the session"
              Logout request 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 connec-
              tion for a "close the session" Logout request was received,
              or an internal event of a successful connection/session
              reinstatement is received. In all these cases, the trans-
              port connection 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".


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              -target: 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.
                  -An internal event of a failed connection/session rein-
                  statement is received.
                  -A transport RESET.
                  -A transport disconnect indication.
                  -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 request was received.

              -target: An internal event of sending a Logout response (suc-
                  cess) on another connection for a "close the session"
                  Logout request was received, or an internal event of a suc-
                  cessful 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.




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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's call it CSM-
   E) in the LOGGED_IN state in the same session, or b) using a new
   transport connection (let's 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 session 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 (sec-
   tion 4.3.4) for that CID. In either case, the protocol exchanges on
   CSM-E or CSM-I determine the state transitions for CSM-C. Therefore,
   this cleanup state diagram is applicable only to the instance of the
   connection 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.

   An initiator must initiate an explicit or implicit connection logout
   for a connection in the CLEANUP_WAIT state, if the initiator intends
   to continue using the associated iSCSI session.

   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
                  conclude 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
                  request.

   -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 request 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 request 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 request 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
               request 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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   State Q3 represents the Full Feature Phase operation of the session.

   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

   State Q3 represents the Full Feature Phase operation of the session.

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  The state diagram is as follows:

                                     -------
                +------------------>/ 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  | -  |
  -----+----+----+----+----+----+




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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.
   -Q2: ACTIVE
              -initiator: Illegal
              -target: The first iSCSI connection in the session transi-
              tioned to IN_LOGIN, waiting for it to complete the login
              process.
   -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 iSCSI connection reached the LOGGED_IN
              state.
   -N3:
              -initiator: Graceful closing of the session via session clo-
              sure (Section 4.3.6 Session continuation and failure).
              -target: Graceful closing of the session via session closure
              (Section 4.3.6 Session continuation and failure). Or a suc-
              cessful session reinstatement cleanly closed the session.
   -N4:
              -initiator: A session continuation attempt succeeded.
              -target: Illegal

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  -N5:
             -initiator: Session failure (Section 4.3.6 Session continua-
                 tion and failure) occurred.
             -target: Session failure (Section 4.3.6 Session continuation
                 and failure) occurred.
  -N6:
             -initiator: Session state timeout occurred, or a session
                 reinstatement 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
   are available (in host memory) for retransmission while the command
   is outstanding.  It is also assumed that at the 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 recov-
   ery in support of interoperability. See Appendix E. - Algorithmic
   Presentation of Error Recovery Classes - for further detail. Compli-
   ant implementations do not have to match the implementation details
   of this model as presented, but the external behavior of such imple-
   mentations must correspond to the externally observable characteris-
   tics 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
   target end.  Discarded command PDUs, due to digest errors, may have
   created 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 in Section 2.5.3.4 SNACK Request.  This, however, does not
   constitute a requirement on initiators 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
   original 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 request (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 request is being issued.

   In reassigning connection allegiance for a command, the targets
   SHOULD continue the command from its current state. For example, when
   reassigning read commands, the target SHOULD take advantage of Exp-
   DataSN field provided by the Task Management Function Request (which
   must be set to zero if there was no data transfer) and bring the read
   command to completion by sending the remaining data and sending (or
   resending) the status.  However, targets MAY choose to send/receive
   the entire data on a reassignment of connection 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 nec-
   essary.


   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


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   failover not supported".  If allegiance reassignment is supported by
   the target, but the task is still allegiant to a different connec-
   tion, 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
   because the command itself is being discarded.

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

   The CmdSN of the rejected command PDU (if it carried one) MUST NOT be
   considered received by the target (i.e., a command sequence gap must
   be assumed for the CmdSN), even though the CmdSN can be reliably
   ascertained in this case.

   When a data PDU is rejected and its DataSN can be ascertained, a tar-
   get MUST advance ExpDataSN for the current data 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 intention-
   ally or on an exception. Time2Wait is the initial "respite time"
   before attempting an explicit/implicit Logout for the CID in ques-
   tion or task reassignment for the affected tasks (if any).
   Time2Retain is the maximum time after the initial respite interval
   that the task and/or connection state(s) is/are guaranteed to be
   maintained on the target to cater to a possible recovery attempt. No
   recovery attempt should be made before Time2Wait and task reassign-
   ment has to be done within the Time2Retain.

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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
   Full Feature Phase iSCSI connection to be abruptly terminated. The
   timeout values to be used in this case are the negotiated values of
   DefaultTime2Wait (Section 11.16 DefaultTime2Wait) and
   DefaultTime2Retain (Section 11.17 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 connec-
   tion, and the tasks active on that connection.  These timeout values
   have no bearing on initiator timers (if any) that are already run-
   ning on connections or tasks associated with that session.

6.4  Format Errors

   The following two explicit violations of PDU layout rules are format
   errors:

        a)  illegal contents of the PDU header (except the Opcode) - for
        ex., out-of-range values for certain fields
        b)  inconsistent contents - for ex., value of one field conflicts
        with that of another.

   Format errors indicate a major implementation flaw in one of the par-
   ties.

   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
   Session Recovery).

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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 or an initiator  receives any iSCSI PDU with a header
   digest error, it MUST either discard the header and all data up to
   the beginning of a later PDU or close the connection. Since the
   digest error indicate that the length field of the header may have
   been corrupted, the location of the beginning of a later PDU needs to
   be reliably ascertained by other means (such as the operation of a
   sync and steering layer).

   When a target receives any iSCSI PDU with a payload digest error, it
   MUST answer with a Reject 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 a CHECK CONDITION
         Status and an iSCSI Condition of "protocol service CRC error"
         (Section 9.4.6.2 Sense Data). 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 outstanding 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 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



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      Reject PDU with a reason-code of "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 CHECK CONDI-
      TION Status and an iSCSI Condition of "SNACK rejected" (Section
      9.4.6.2 Sense Data).
                ii)  if the status was already sent, no further action
      is necessary for the target.  Initiator in this case MUST inter-
      nally signal the completion with CHECK CONDITION Status and an
      iSCSI Condition of "protocol service CRC error" (Section 9.4.6.2
      Sense Data) disregarding any received status PDU, but must wait
      for the status to be received before doing so.
      b)  [OR] 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:

      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 dis-
       carded 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. Target 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

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   may discover 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 unacknowl-
   edged command, as described in Section 6.1 Retry and Reassign in
   Recovery.

   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
       successfully logged out (on logout, the unacknowledged com-
       mands issued on the connection being logged out are dis-
       carded).

   If the abort request is received and the original command is miss-
   ing, targets MUST consider the original command with that RefCmdSN to
   be received and issue a task management response with the response
   code: "Function Complete". 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:




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


   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 termi-
       nated, 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 Initia-
       tor 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).

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-estab-
   lishment 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 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/estab-
   lish at least one TCP connection between the initiator and the tar-
   get in a timely fashion.  It is assumed that targets and/or
   initiators recognize 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

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   MAY be used periodically by highly reliable implementations.  Initia-
   tors and targets MAY also use the keep-alive option on the TCP con-
   nection 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 con-
       nection" (Section 9.14.4 Implicit termination of tasks), re-
       issue missing commands, and implicitly terminate all active
       commands. This option requires support for the within-connec-
       tion recovery class (Section 6.12.2 Recovery Within-connec-
       tion).
     - 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 regard-
   less of which of the above options is used (i.e., immediate commands
   are not recoverable across connection failures).

6.11  Session Errors

   If all the connections of a session fail and cannot be re-estab-
   lished in a short time, or if initiators detect protocol errors
   repeatedly, an initiator may choose to terminate a session and estab-
   lish 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.




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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 rep-
   resentative 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 recov-
   ery 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
   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.


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   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) or response reception
      timeout - dealt with as specified 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
   originate 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 com-
   plete.

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
       identifying 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:

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

   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 man-
       agement function (see Section 9.5.1 Function). Note that for
       an initiator a command is in progress as long as it has not
       received a response or a Data-In PDU including status.

       N.B. The logout function is mandatory, while a new connec-
       tion establishment is mandatory only if the failed connec-
       tion 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 connec-
       tion(s) referred to in the Message.

   At an iSCSI target, the following cases lend themselves to connec-
   tion 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

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   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 initia-
   tor 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).

   For possible clearing effects of session recovery on SCSI and iSCSI
   objects, refer to Appendix F. - Clearing effects of various events on
   targets -.

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
   implementation possibilities, with hopes that this significantly con-
   tributes 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
      requirements.
      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.





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                             +
                            / \
                           / 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.

  +-------------------+--------------------------------------------+
  |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 comprises 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 Storage Area Network (SAN) dis-
   tinctly separate from the communications network. The use of storage
   protocols, such as SCSI, over IP-networks requires that security con-
   cerns be addressed. iSCSI implementations MUST provide means of pro-
   tection 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 analyz-
   ing the data sent over the line).

   Although technically possible, iSCSI SHOULD NOT be configured with-
   out 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
   initiators 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

   During login the target authenticates the initiator and the initia-
   tor optionally authenticates the target. The authentication is per-
   formed 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, because IPsec is optional to use. An attacker should gain as
   little 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.

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

   Section 10 iSCSI Security Keys and Authentication Methods defines
   several authentication methods and the exact steps that must be fol-
   lowed in each of them, including the keys and their allowed values in
   each step. Whenever an iSCSI initiator gets a response whose keys, or
   their values, are not according to the step definition, it MUST abort
   the connection. Whenever an iSCSI target gets a response whose keys,
   or their values, are not according to the step definition, it MUST
   answer with a Login reject with the "Initiator Error" or "Missing
   Parameter" status (these statuses are not intended for cryptographi-
   cally incorrect value, e.g., the CHAP response, for which "Authenti-
   cation Failure" status MUST be specified). The importance of this
   rule can be illustrated in CHAP with target authentication (Section
   10.5 Challenge Handshake Authentication Protocol (CHAP)) where the
   initiator would have been able to conduct a reflection attack by
   omitting his response key (CHAP_R), using the same CHAP challenge as
   the target and reflecting the target's response back to the target.
   In CHAP this is prevented since the target must answer the missing
   CHAP_R key with a Login reject with the "Missing Parameter" status.





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7.2.1  CHAP Considerations

   Compliant iSCSI implementation MUST implement the CHAP authentication
   method [RFC1994] (according to Section 10.5 Challenge Handshake
   Authentication Protocol (CHAP) including the target authentication
   option).

   When CHAP is performed over a non-encrypted channel, it is vulnera-
   ble to an off-line dictionary attack. Implementations MUST support
   use of up to 128 bits random CHAP secrets, including the means to
   generate such secrets and to accept them from an external generation
   source. Implementations MUST NOT provide secret generation (or expan-
   sion) means other than random generation.

   An administrative entity of an environment in which CHAP is used with
   a secret that has less than 96 random bits MUST enforce IPsec encryp-
   tion (according to the implementation requirements in Section 7.3.2
   Confidentiality) to protect the connection. Moreover, in this case
   IKE authentication with group pre-shared keys SHOULD NOT be used
   unless it is not essential to protect group members against off-line
   dictionary attacks by other members.

   A compliant implementation SHOULD NOT continue with the login step in
   which it should send a CHAP response (CHAP_R - Section 10.5 Chal-
   lenge Handshake Authentication Protocol (CHAP)) unless it can verify
   that either the CHAP secret is at least 96 bits, or that IPsec
   encryption is being used to protect the connection.

   Originators MUST NOT reuse the CHAP challenge sent by the Responder
   for the other direction of a bidirectional authentication. Respond-
   ers MUST check for this condition and close the iSCSI TCP connection
   if it occurs.

7.2.2  SRP Considerations

   The strength of the SRP authentication method (specified in
   [RFC2945]) 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.



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   Upon receiving N and g from the Target, the Initiator MUST verify
   that they match a well-known group that satisfies the above require-
   ments and abort the connection if they do not match. Well- known SRP
   groups are provided in [SEC-IPS].
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 [RFC2406]
   in tunnel mode and MAY provide data integrity and authentication by
   implementing IPsec with ESP in transport mode. The IPsec implementa-
   tion MUST fulfill the following iSCSI specific requirements:

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

   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
   implementation that operates at speeds of 1 Gbps or faster to imple-
   ment the IPsec sequence number extension [SEQ-EXT].

7.3.2  Confidentiality

   Confidentiality is provided by encrypting the data in every packet.
   When confidentiality is used it MUST be accompanied by data integ-


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   rity and authentication to provide comprehensive protection against
   eavesdropping, message insertion, deletion, modification, and replay-
   ing.

   An iSCSI compliant initiator or target MUST provide confidentiality
   by implementing IPsec [RFC2401] with ESP [RFC2406] in tunnel mode and
   MAY provide confidentiality by implementing IPsec with ESP in trans-
   port mode. 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).

   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
   following iSCSI specific requirements:

     - Peer authentication using a pre-shared key MUST be sup-
           ported. Certificate-based peer authentication using digital
           signatures 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 Pay-
           load(s) to specify the certificate authority. IKE negotia-
           tors SHOULD check the pertinent Certificate Revocation List
           (CRL) before accepting a PKI certificate for use in IKE
           authentication procedures.

     - Conformant iSCSI implementations MUST support IKE Main Mode
           and SHOULD support Aggressive Mode. IKE main mode with pre-
           shared key authentication method SHOULD NOT be used when
           either the initiator or the target uses dynamically 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-shared key, which creates
           vulnerability to a man-in-the-middle attack.


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     - 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 SHOULD 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 because it does not provide the neces-
  sary 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
  connection. 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 in-band discovery mechanism (discovery session
  and SendTargets), the use or non-use of IPsec in any operational ses-
  sion 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 task tag
   mechanism 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, physi-
   cal entities. Recent extensions to the SCSI model have taken advan-
   tage of persistent worldwide unique names for these ports. In iSCSI
   however, the SCSI initiator ports are the endpoints of dynamically
   created sessions, so the presumption of "static and physical" does
   not apply. In any case, the model clauses (particularly, Section
   2.4.2 SCSI Architecture 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 prohib-
   its 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, ISID and TPGT 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 coordi-
   nate session identifier resources (ISID for initiators) to enforce
   both the ISID and TSIH 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 across the por-
   tal groups instantiated by multiple instances of these components
   within a target.

   However, complex targets making use of multiple Target Portal Group
   Tags may reconfigure them to achieve various quality goals.  The ini-
   tiators have two mechanisms at their disposal to discover and/or
   check reconfiguring targets - the discovery session type and a key


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  returned by the target during login to confirm the TPGT.  An initia-
  tor should attempt to "rediscover" the target configuration anytime a
  session is terminated unexpectedly.

  For initiators, in the long term, it is expected that operating sys-
  tem vendors will take on the role of this entity and provide stan-
  dard 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 exam-
  ple, a human may instantiate the (common) Node name as part of the
  installation process of each iSCSI component involved in session cre-
  ation 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 9.12.6 ISID
  and [NDT]) facilitates implementation of the ISID coordination by
  allowing each component vendor to independently (of other vendor's
  components) coordinate allocation and use and reuse its own parti-
  tion 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
  facilitates enforcement of the ISID RULE (see Section 2.4.3 Conse-
  quences 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 configur-
  ing the iSCSI Node Name, for a mechanism to configure and/or coordi-
  nate ISIDs for all sessions managed by multiple instances of that
  hardware within a given iSCSI Node.  Such configuration might be
  either permanently pre-assigned at the factory (in a necessarily glo-
  bally 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 latter two cases, the configuration may be via public APIs (per-
  haps driven by an independent vendor's software, such as the OS ven-
  dor) or via private APIs driven by the vendor's own software.





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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 initia-
   tors and targets MUST support autosense.

   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  iSCSI timeouts

   iSCSI recovery actions are often dependent on iSCSI time-outs being
   recognized and acted upon before SCSI time-outs. Determining the
   right time-outs to use for various iSCSI actions (command acknowl-
   edgements expected, status acknowledgements, etc.) is very much
   dependent on infrastructure (hardware, links, TCP/IP stack, iSCSI
   driver). As a guidance the implementer may use an average Nop-Out/
   Nop-In turnaround delay multiplied by a "safety factor" (2-3) as a
   good estimate for the basic delay of the iSCSI stack for a given con-
   nection.

8.4  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 proto-
   col requires (see Section 2.2.2.1 Command Numbering and
   Acknowledging) that on every connection on which a retry has been
   issued, a non-immediate command be issued and acknowledged within a
   2**31-1 commands interval from the CmdSN of the retried command. 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.

8.5  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

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   packet reordering and loss.  Providing a synch and steering mecha-
   nism is recommended for all high-speed implementations.

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, com-
   mand 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 com-
   mand was actually processed, the re-issued SPACE command, if pro-
   cessed, 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 com-
   mand 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 com-
   mands for sequential access devices, and EXCHANGE MEDIUM for medium
   changer device), MUST be issued as non-immediate commands for deter-
   ministic 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





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  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:

     a)  Application resilience to I/O failures.
     b)  Required level of availability in the face of transport con-
     nection 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
  example suggests that implementations SHOULD use ErrorRecovery-
  Level=1 when transport connection failure is not a concern, and
  ErrorRecoveryLevel=2 when the connection failure is also of high
  likelihood during 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 sig-
   nificant bit (within byte or field) is the lowest 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0/ Basic Header Segment (BHS)                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Additional Header Segment 1 (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     / Additional Header Segment 2 (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   ----
     +---------------+---------------+---------------+---------------+
     / Additional Header Segment n (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   ----
     +---------------+---------------+---------------+---------------+
    k/ Header-Digest (optional)                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    l/ Data Segment(optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    m/ Data-Digest (optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

   All PDU segments and digests are padded to the closest integer num-
   ber of four byte words - i.e., all PDU segments and the digests start
   at a four byte word boundary and the padding ranges from 0 to 3
   bytes. 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.


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   The format of the BHS is:


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

   Initiator opcodes defined in this specification are:


         0x00 NOP-Out


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     0x01 SCSI Command (encapsulates a SCSI Command Descriptor
       Block)
     0x02 SCSI Task Management Function Request
     0x03 Login Request
     0x04 Text Request
     0x05 SCSI Data-out (for WRITE operations)
     0x06 Logout Request
     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 pad-
   ding). The DataSegmentLength MUST be 0 whenever the PDU has no data
   segment.

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9.2.1.6  LUN

   Some opcodes operate on a specific Logical Unit. The Logical Unit
   Number (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 formatted in accordance with [SAM2] i.e., LUN[0] from [SAM2] is
   BHS byte 8 and so on up to LUN[7] 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 the task 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0| AHSLength                     | AHSType       | AHS-Specific  |
     +---------------+---------------+---------------+---------------+
    4/ AHS-Specific                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    x

9.2.2.1  AHSType

   The AHSType field is coded as follows:

         bit 0-1 - Reserved

         bit 2-7 - AHS code

          0 - Reserved
          1 - Extended CDB

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          2 - Expected Bidirectional Read Data Length
          3 - 59 Reserved
          60- 63 Non-iSCSI extensions


9.2.2.2  AHSLength

   This field contains the effective length in bytes of the AHS exclud-
   ing 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
   padding bytes).

9.2.2.3  Extended CDB AHS

   The format of the Extended CDB AHS is:

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




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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 cover both the
   proper data as well as the padding bytes.

   The digest types are negotiated during the Login Phase.

   The separation of the header and data digests is useful in iSCSI
   routing applications, where only the header changes when a message is
   forwarded. In this case, only the header digest should be re-calcu-
   lated.

   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 pay-
   load effective length is provided in the BHS field - DataSeg-
   mentLength. 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x01      |F|R|W|0 0|ATTR | Reserved                      |
     +---------------+---------------+---------------+---------------+
    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)                                                  /
     +---------------+---------------+---------------+---------------+
    x/ Header Digest (if any)                                        /
     +---------------+---------------+---------------+---------------+
    y/ (DataSegment, Command Data) (if any)                          /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    z/ Data Digest (if any)                                          /
     +---------------+---------------+---------------+---------------+

9.3.1  Flags and Task Attributes (byte 1)

     The flags for a SCSI Command are:

     bit 0   (F) set to 1 when no unsolicited SCSI Data-Out PDUs
       follow this PDU.  For a write, if Expected Data Transfer


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       Length is larger than the DataSegmentLength the target may
       solicit additional data through R2T.

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

     bit 2   (W) set to 1 when the command is expected to output
       data.

     bit 3-4 Reserved

     bit 5-7 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 Length and Bidirectional Read Expected Data
   Transfer Length are not 0.


9.3.2  CmdSN - Command Sequence Number

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

9.3.3  ExpStatSN

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

9.3.4  Expected Data Transfer Length

   For unidirectional operations, the Expected Data Transfer Length
   field contains the number of bytes of data involved in this SCSI
   operation.  For a unidirectional write operation (W flag set to 1 and
   R flag set to 0), the initiator uses this field to specify the num-


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   ber of bytes of data it expects to transfer for this operation.  For
   a unidirectional 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 expects the target to transfer to the initiator.  It corre-
   sponds 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 FirstBurst-
   Length (the negotiated maximum amount of unsolicited data the target
   will accept), the initiator MUST send the maximum length of unsolic-
   ited data OR ONLY the immediate 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.

9.3.5  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.

9.3.6  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 exam-
   ple, from a WRITE operation) can be placed in the data segment (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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / Data Segment (Optional)                                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

9.4.1  Flags (byte 1)

     bit 1-2 Reserved


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     bit 3 - (o) set for Bidirectional Read Residual Overflow. In
       this case, the Bidirectional Read Residual Count indicates
       the number of bytes that were not transferred to the initia-
       tor because the initiator's Expected Bidirectional Read Data
       Transfer Length was not sufficient.

     bit 4 - (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 initia-
       tor out of the number of bytes expected to be transferred.

     bit 5 - (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 6 - (U) set for Residual Underflow. In this case, the
       Residual Count indicates the number of bytes that were not
       transferred out of the number of bytes that were expected to
       be transferred. For a bidirectional operation, the Residual
       Count contains the residual for the write operation.

     bit 7 - (0) Reserved

   Bits O and U and bits o and u are mutually exclusive.
   For a response other than "Command Completed at Target" bits 3-6 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 Com-
   mand 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.



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   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
   target has not received a Data PDU with the final bit Set), the tar-
   get 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

   All other response codes are reserved.

   The Response is used to report a Service Response. The mapping of the
   response code into a SCSI service response code value, if needed, is
   outside the scope of this document. However, in symbolic terms
   response value 0x00 maps to the SCSI service response of TASK COM-
   PLETE or LINKED COMMAND COMPLETE. All other Response values map to
   the SCSI service response of SERVICE DELIVERY OR TARGET FAILURE.

   If a SCSI Response PDU does not arrive before the session is termi-
   nated, the SCSI service response is SERVICE DELIVERY OR TARGET FAIL-
   URE.


   As non-zero response field indicates a failure to execute the com-
   mand in which case the Status and Sense fields are undefined.

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 ini-
   tiator'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 trans-
   ferred.


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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 num-
   ber of bytes that were not transferred to the initiator because the
   initiator's Expected Bidirectional Read Transfer Length was not suf-
   ficient. If the u bit is set, the Bidirectional Read Residual Count
   indicates the number of bytes that were not transferred to the initi-
   ator 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
   contain a vendor specific detailed description of the failure).

   If the DataSegmentLength is not 0, the format of the Data Segment is
   as follows:
   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|SenseLength                    | Sense Data                    |
     +---------------+---------------+---------------+---------------+
    x/ Sense Data                                                    /
     +---------------+---------------+---------------+---------------+
    y/ Response Data                                                 /
     /                                                               /
     +---------------+---------------+---------------+---------------+
    z|


9.4.6.1  SenseLength

   Length of Sense Data.




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9.4.6.2  Sense Data

   The Sense Data contain detailed information about a check condition
   and [SPC] specifies the format and content of the Sense Data.

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

   +--------------------------+----------+---------------------------+
   | iSCSI Condition          |Sense     | Additional Sense Code &   |
   |                          |Key       | Qualifier                 |
   +--------------------------+----------+---------------------------+
   | Unexpected unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0c    |
   | data                     |Command-0B| Write Error               |
   +--------------------------+----------+---------------------------+
   | Incorrect amount of data |Aborted   | ASC = 0x0c ASCQ = 0x0d    |
   |                          |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 "Incorrect amount of data" condition if dur-
   ing data output the total data length to output is greater than
   FirstBurstLength and the initiator sent unsolicited non-immediate
   data but the total amount of unsolicited data is different than
   FirstBurstLength. The target reports the same error when the amount
   of data sent as a reply to an R2T does not match the amount
   requested.


9.4.7  ExpDataSN

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

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



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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
   status reception. StatSN is incremented by 1 for every response/sta-
   tus 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 retransmis-
   sion 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.

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 informa-
   tion 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x02      |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 Reserved                                          |
     +---------------+---------------+---------------+---------------+
   36| ExpDataSN or Reserved                                         |
     +---------------+---------------+---------------+---------------+
   40/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

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 function codes are listed below. For a
   more detailed description of SCSI task management, see [SAM2].

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

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

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

     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 opera-
  tions.  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 imme-
  diately 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 man-
  agement response (i.e., with CmdSN not higher than the task manage-
  ment command CmdSN), additional responses MUST NOT be delivered to
  the SCSI layer after the task management response. The iSCSI initia-
  tor 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 management 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 manage-
  ment function are delivered to the iSCSI initiator after the task
  management response.

  For ABORT TASK SET and CLEAR TASK SET, the issuing initiator MUST
  continue 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.  The
  target on its part MUST wait for responses on all affected target

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  transfer tags before acting on either of these two task management
  requests.  In case all or part of the response sequence is not
  received (due to digest errors) for a valid TTT, the target MAY treat
  it as a case of within-command error recovery class (section 6.12.1)
  if it is supporting ErrorRecoveryLevel >= 1, or alternatively may
  drop the connection to complete the requested task set function.

  If the connection is still active (it is not undergoing an implicit
  or explicit logout), ABORT TASK MUST be issued on the same connec-
  tion to which the task to be aborted is allegiant at the time the
  Task Management Request is issued. If the connection is 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
  failing 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
  reassigned, and its status, if issued but not acknowledged, will be
  reissued 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 implementation of the TARGET WARM RESET function and the TARGET
  COLD RESET function is OPTIONAL and when implemented, should act as
  described below. The TARGET WARM RESET function MAY also be subject
  to SCSI access controls (see [SPC3]) on 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.  The TARGET COLD RESET function is not sub-
  ject to SCSI access controls, but its execution privileges may be
  managed by iSCSI
  mechanisms such as login authentication.

  When executing the TARGET WARM RESET and TARGET COLD RESET func-
  tions, the target cancels all pending operations. Both functions are
  equivalent to the Target Reset function specified by [SAM2]. They can
  affect many other initiators logged in with the servicing SCSI tar-
  get port.

  The target MUST treat the TARGET COLD RESET function additionally as
  a power on event, thus terminating all of its TCP connections to all
  initiators (all sessions are terminated).  For this reason, the Ser-

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   vice Response (defined by [SAM2]) for this SCSI task management func-
   tion may not be reliably delivered to the issuing initiator port.

   For the TASK REASSIGN function, the target should reassign the con-
   nection allegiance to this new connection (and thus resume iSCSI
   exchanges for the task). TASK REASSIGN MUST be received by the tar-
   get ONLY after the connection on which the command was previously
   executing 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.

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 MUST be set to the reserved
   value 0xffffffff.

9.5.4  RefCmdSN

   For the ABORT TASK function, initiators MUST always set this to the
   CmdSN of the task identified by the Referenced Task Tag field. Tar-
   gets must use this field as described in section 9.6.1 when the task
   identified by the Referenced Task Tag field is not with the target.

   Otherwise this field is reserved.

9.5.5  ExpDataSN

   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

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  same as the original transmission, depending on if there was a change
  in MaxRecvDataSegmentLength in the reassignment.

  Otherwise, this field is reserved.





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9.6  Task Management Function Response


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

   For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
   SET, LOGICAL UNIT RESET, TARGET COLD 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 tar-
  get cancels all pending operations.  For the TARGET COLD RESET func-
  tion, the target MUST then close all of its TCP connections to all
  initiators (terminates all sessions).

  The mapping of the response code into a SCSI service response code
  value, if needed, is outside the scope of this document. However, in
  symbolic terms Response value 0 maps to the SCSI service response
  of FUNCTION COMPLETE.  All other Response values map to the SCSI ser-
  vice response of FUNCTION REJECTED. If a Task Management Function
  Response PDU does not arrive before the session is terminated, the
  SCSI service response is SERVICE DELIVERY OR TARGET FAILURE

  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 9.6.2 Task Management actions on task sets.

  For the ABORT TASK function,

     a)  if the Referenced Task Tag identifies a valid task leading to
     a successful termination, targets must return the "Function com-
     plete" response.
     b)  if the Referenced Task Tag does not identify an existing task
     but if the CmdSN indicated by the RefCmdSN field in the task man-
     agement function request is within the valid CmdSN window (between
     MaxCmdSN and ExpCmdSN), targets must consider the CmdSN received
     and return the "Function complete" response.


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      c)  if the Referenced Task Tag does not identify an existing task
      and if the CmdSN indicated by the RefCmdSN field in the task man-
      agement function request is outside the valid CmdSN window, tar-
      gets must return the "Task does not exist" response.

9.6.2  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.
         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 because 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment                                                   /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

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



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  Byte/     0       |       1       |       2       |       3       |
     /              |               |               |               |
    |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
    +---------------+---------------+---------------+---------------+
   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 (Optional)                                      |
    +---------------+---------------+---------------+---------------+
    / DataSegment                                                   /
   +/                                                               /
    +---------------+---------------+---------------+---------------+
    | Data-Digest (Optional)                                        |
    +---------------+---------------+---------------+---------------+


  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, CONDI-
  TION 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


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   responses, initiators MUST support non-exception status in Data-In
   PDUs.

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 hav-
   ing 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.

   DataSegmentLength MUST not exceed MaxRecvDataSegmentLength for the
   direction it is sent and the total of all the DataSegmentLength of
   all PDUs in a sequence MUST not exceed MaxBurstLength (or FirstBurst-
   Length for unsolicited data).  However the number of individual PDUs
   in a sequence (or in total) may be higher than the MaxBurstLength (or
   FirstBurstLength) to MaxRecvDataSegmentLength ratio (as PDUs may be
   limited in length by the sender capabilities).  Using DataSeg-
   mentLength of 0 may increase beyond what is reasonable the number of
   PDUs and should therefore be avoided.

   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 acknowledge-
   ment 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 Max-
   BurstLength bytes or on the last Data-In PDU that concludes the
   entire requested read data transfer for the task from the target's
   perspective, and MUST NOT do so more frequently than this.

   On receiving a Data-In PDU with the A bit set to 1, if there are no
   holes in the read data until that Data-In PDU, the initiator MUST
   issue a SNACK of type DataACK except when it is able to acknowledge
   the status for the task immediately via ExpStatSN on other outbound
   PDUs if the status for the task is also received; in this latter case
   (acknowledgement through ExpStatSN) sending a SNACK of type DataACK

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   in response to the A bit is not mandatory but if it is done it must
   not be sent after the status acknowledgement through ExpStatSN.  If
   the initiator has detected holes in the read data until that Data-In
   PDU, it MUST postpone issuing the SNACK of type DataACK until the
   holes are filled. An initiator also MUST NOT acknowledge the status
   for the task before those holes are filled.  A status acknowledge-
   ment for a task that generated the Data-In PDUs is considered by the
   target as an implicit acknowledgement of the Data-In PDUs if such an
   acknowledgement was requested by the target.

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 Trans-
   fer 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
   target if the A bit is set to 1. The Target Transfer Tag and LUN are
   copied 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 Tar-
   get Transfer Tag is not supplied.  If the Target Transfer Tag is pro-
   vided, then the LUN field MUST hold a valid value and be consistent
   with 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) or bidirectional Data-In PDUs, the DataSN is the
   input PDU number within the data transfer for the command identified
   by the Initiator Task Tag.

   R2T and Data-In PDUs, in the context of bidirectional commands, share
   the numbering sequence (see Section 2.2.2.3 Data Sequencing).

   For output (write) data PDUs, the DataSN is the Data-Out PDU number
   within the current output sequence. The current output sequence is

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   either identified by the Initiator Task Tag (for unsolicited data) or
   is a data sequence generated for one R2T (for data solicited through
   R2T).

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 com-
   mand.

   The order of data PDUs within a sequence is determined by DataPDU-
   InOrder. When set to Yes, it means that PDUs have to be in increas-
   ing 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
   initiators and targets MUST be able to properly receive 0 length data
   segments.

   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 2-3 - Reserved


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     bit 5-6 - used the same as in a SCSI Response. Those bits are
       valid only when S is set to 1.

     bit 7 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 their values are defined in Sec-
  tion 9.4 SCSI Response.





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9.8  Ready To Transfer (R2T)

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x31      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN                                                           |
     +                                                               +
   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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+


   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 target at that particular instant. This information is passed
   from the target to the initiator in the Ready To Transfer (R2T) PDU.





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   In order to allow write operations without an explicit initial R2T,
   the initiator and target MUST have negotiated the key InitialR2T to
   No during Login.

   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 and the data length of the Data PDU MUST
   be the same as the Desired Data Transfer Length specified in the R2T.
   If the R2T is answered with a sequence of Data PDUs, the Buffer Off-
   set and Length MUST be within the range of those specified by R2T,
   and the last PDU MUST 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 ordering. 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
   connection, outstanding R2Ts MUST be fulfilled by the initiator in
   the order in which they were received.

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

9.8.1  R2TSN

   R2TSN is the R2T PDU input PDU number within the command identified
   by the Initiator Task Tag.

   For bidirectional commands R2T and Data-In PDUs share the input PDU
   numbering sequence (see Section 2.2.2.3 Data Sequencing).

9.8.2  StatSN

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





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

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 except that the value
   0xffffffff is reserved and MUST never be sent by a target in an
   R2T.





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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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x32      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN                                                           |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| 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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Sense Data and iSCSI Event Data                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+




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   Some Asynchronous Messages are strictly related to iSCSI while oth-
   ers are related to SCSI [SAM2].

   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 Reporting in SCSI terminology) is dependent on
       the target support for SCSI asynchronous event reporting (see
       [SAM2]) as indicated in the standard INQUIRY data (see
       [SPC]). Its use may be enabled by parameters in the SCSI Con-
       trol mode page (see [SPC]).

     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 ses-
       sion" to close all the connections (if using multiple connec-
       tions). 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 possi-
       ble, 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 reassign commands after the initial wait (in
       Parameter2).
       If the initiator does not attempt to reconnect and/or reas-
       sign 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

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       responses should be expected from the target for the out-
       standing commands on this connection in this case.
       A value of 0 for Parameter2 indicates that reconnect can be
       attempted immediately.

     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 reassign commands after the initial wait (in
       Parameter2).
       If the initiator does not attempt to reconnect and/or reas-
       sign the outstanding commands within the time specified by
       Parameter3, or if Parameter3 is 0, the session is termi-
       nated. In this case, the target will terminate all outstand-
       ing commands 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 recon-
       nect can be attempted immediately.

     4 - target requests parameter negotiation on this connection.
       The initiator MUST honor this request by issuing a Text
       Request (that can be empty) on the same connection as early
       as possible, but no later than Parameter3 seconds, unless a
       Text Request is already pending on the connection, or by
       issuing a Logout Request. If the initiator does not issue a
       Text Request the target may reissue the Asynchronous Message
       requesting parameter negotiation.

     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 and iSCSI Event Data

   For a SCSI Event, this data accompanies the report in the data seg-
   ment and identifies the condition.




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   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.

   If the DataSegmentLength is not 0, the format of the DataSegment is
   as follows:
   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|SenseLength                    | Sense Data                    |
     +---------------+---------------+---------------+---------------+
    x/ Sense Data                                                    /
     +---------------+---------------+---------------+---------------+
    y/ iSCSI Event Data                                              /
     /                                                               /
     +---------------+---------------+---------------+---------------+
    z|

9.9.3.1  SenseLength

   Length of Sense Data.





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9.10  Text Request

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


   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x04      |F|C| 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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment (Text)                                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+


   An initiator MUST have at most one outstanding Text Request on a con-
   nection at any given time.




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   On a connection failure, an initiator must either explicitly abort
   any active allegiant text negotiation task or must cause such a task
   to be implicitly terminated by the target.

9.10.1  F (Final) Bit

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

9.10.2  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Text Request is not complete (it will be continued on subse-
   quent Text Requests); otherwise, it indicates that this Text Request
   ends a set of key=value pairs. A Text Request with the C bit set to 1
   MUST have the F bit set to 0.

9.10.3  Initiator Task Tag

   The initiator assigned identifier for this Text Request. If the com-
   mand 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). The I bit for all
   requests in a sequence also MUST be the same.

9.10.4  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 resets
   any internal state associated with the Initiator Task Tag (resets the
   current negotiation state).

   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 asso-
   ciated 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 Trans-
   fer Tag from the response to the next Text Request, the initiator
   tells the target to continue the operation for the specific Initia-
   tor Task Tag. The initiator MUST ignore the Target Transfer Tag in
   the Text Response when the F bit is set to 1.



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   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 negotiation 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)

9.10.5  Text

   The data lengths of a text request MUST NOT exceed the iSCSI target
   MaxRecvDataSegmentLength (a per connection and per direction negoti-
   ated 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 - in
   other words the end of a PDU does not necessarily signal the end of a
   key value pair).

   The target responds by sending its response back to the initiator.
   The response text format is similar to the request text format.
   The text response MAY refer to key=value pairs presented in an ear-
   lier text request and the text in the request may refer to earlier
   responses.

   Chapter 4 details the rules for the Text Requests and Responses.


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  Text operations are usually meant for parameter setting/negotia-
  tions, 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x24      |F|C| 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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment (Text)                                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

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
   operation.  Otherwise, if set to 0 in response to a Text Request with

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   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 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  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Text Response is not complete (it will be continued on subse-
   quent Text Responses); otherwise, it indicates that this Text
   Response  ends a set of key=value pairs. A Text Response with the C
   bit set to 1 MUST have the F bit set to 0.

9.11.3  Initiator Task Tag

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

9.11.4  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
   Target 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.

   When the target receives a Text Request with the Target Transfer Tag
   set to the reserved value of 0xffffffff, it resets its internal

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   information (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 (the current negotiation state), 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.

9.11.5  StatSN

   The target StatSN register is advanced by each Text Response.

9.11.6  Text Response Data

   The data lengths of a text request MUST NOT exceed the iSCSI initia-
   tor MaxRecvDataSegmentLength (a per connection and per direction
   negotiated parameter).

   The text in the Text Response Data is governed by the same rules as
   the text in the Text Request Data (see Section 9.10.5 Text).

   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 tar-
   get, 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.

   Login requests are always considered as immediate.

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x03      |T|C|.|.|CSG|NSG| Version-max   | Version-min   |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| ISID                                                          |
     +                               +---------------+---------------+
   12|                               | TSIH                          |
     +---------------+---------------+---------------+---------------+
   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         /
    +/                                                               /
     +---------------+---------------+---------------+---------------+




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9.12.1  T (Transit) Bit

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

   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  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Login Request is not complete (it will be continued on subse-
   quent Login Requests); otherwise, it indicates that this Login
   Request  ends a set of key=value pairs. A Login Request with the C
   bit set to 1 MUST have the T bit set to 0.

9.12.3  CSG and NSG

   Through these fields, Current Stage (CSG) and Next Stage (NSG), the
   Login negotiation requests 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

9.12.4  Version-max

   Maximum Version number supported.

   All Login requests within the Login Phase MUST carry the same Ver-
   sion-max.

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

9.12.5  Version-min

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

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

9.12.6  ISID

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


   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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

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   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
   provides a range of possible values for the ISID within the selected
   namespace. It may be set to any value, within the constraints speci-
   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
   Conservative Reuse of ISIDs and Section 8.1.2 iSCSI Name, ISID and
   TPGT Use) and the resultant ISID MUST also be persistent over power
   cycles, reboot, card swap etc..

9.12.7  TSIH

   TSIH must be set in the first Login Request.  The reserved value 0
   MUST be used on the first connection for a new session.  Otherwise
   the TSIH sent by the target at the conclusion of successful login of
   the first connection for this session MUST be used.  The TSIH identi-
   fies to the target the associated existing session for this new con-
   nection.

   All Login requests within a Login Phase MUST carry the same TSIH.

   The target MUST check the value presented with the first login
   request and act as specified in Section 4.3.1 Login Phase Start.




9.12.8  Connection ID - CID

   A unique ID for this connection within the session.


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   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 TSIH 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).

9.12.9  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 if the login is for a
   new connection in an existing session.

   Examples:

        - A leading login phase - if the leading login carries the
         CmdSN 123 all other login requests in the same login phase
         carry the CmdSN 123 and the first non-immediate command in
         FullFeaturePhase also carries the CmdSN 123.

        - A non-leading login phase - if the current CmdSN at the time
         the first login on the connection is issued is 500 - the
         login request carries CmdSN=500 the second login request car-
         ries a CmdSN not lower than 500 (higher if non-immediate
         requests where issued in the session between the first and
         the second request in the new login phase) etc..

   If the login request is a leading login request the target MUST use
   the value presented in CmdSN as the target value for ExpCmdSN.

9.12.10  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).

9.12.11  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.



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  All the rules specified in Section 9.10.5 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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x23      |T|C|.|.|CSG|NSG| Version-max   | Version-active|
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| ISID                                                          |
     +                               +---------------+---------------+
   12|                               | TSIH                          |
     +---------------+---------------+---------------+---------------+
   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 indi-
   cates 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  TSIH

   The TSIH is the target assigned session identifying handle and its
   internal format and content are not defined by this protocol except
   for the value 0 that is reserved. For a new session, the target MUST
   generate a non-zero TSIH and return it in the Login Final-Response
   (see Section 4.3 Login Phase). In all other cases, this field should
   be set to the TSIH provided by the initiator in the Login Request.

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 sta-
   tus 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
  exceptions, without having to look at the Status-Detail.  The Status-
  Detail allows finer-grained exception handling for more sophisti-
  cated initiators, as well as better information for logging.

  The status classes are as follows:

     0 - Success - indicates that the iSCSI target successfully
          received, understood, and accepted the request. The number-
          ing fields (StatSN, ExpCmdSN, MaxCmdSN) are valid only if
          Status-Class is 0.

     1 - Redirection - indicates that the initiator must take fur-
          ther action to complete the request. This is usually due to
          the target moving to a different address. All of the redirec-
          tion status class responses MUST return one or more text key
          parameters of the type "TargetAddress", which indicates the
          target'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 initiator 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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  -----------------------------------------------------------------
  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 | Too many connections on this SSID
  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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   Session does  | 020a | Attempt to add a connection
   not exist     |      | to an non-existent 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
   initiator 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.

9.13.7  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Login Response is not complete (it will be continued on subse-
   quent Login Responses); otherwise, it indicates that this Login

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   Response  ends a set of key=value pairs. A Login Response with the C
   bit set to 1 MUST have the T bit set to 0.

9.13.8  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 9.11.5 StatSN 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
   supported when the function to which they refer is mandatory to
   implement.





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9.14  Logout Request

   The Logout request is used to perform a controlled closing of a con-
   nection.

   An initiator MAY use a logout request 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 requests on the closing connection. If the Logout is intended
   to close the session, new iSCSI requests MUST NOT be sent on any of
   the connections 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 pend-
   ing commands, whether acknowledged or not, on that connection or ses-
   sion 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 terminated 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 termi-
   nated.  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 terminated or not completed (with status)
   and acknowledged when the connection is closed completely can be
   reassigned 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 request to "clean-up" the target end of
   a failing connection and enable recovery to start, or use the Login
   request with a non-zero TSIH and the same CID on a new connection for
   the same effect (see Section 9.14.2 CID).  In sessions with a single



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  connection, the connection can be closed then a new connection
  reopened and a restart login can be used for recovery.

  A successful completion of a logout request with the reason code of
  "close the connection" or "remove the connection for recovery"
  results in the discarding of all tasks waiting in the command reor-
  dering queue that are allegiant to the connection being logged out.
  Those holes in command sequence numbers will have to be handled by
  appropriate recovery (see Chapter 6) unless the session is also
  closed.

  The entire logout discussion in this section is completely applica-
  ble also for an implicit Logout effected by way of a connection rein-
  statement or session reinstatement.  The Logout reason codes for
  implicit Logout are specified as below:

     Reason code        Type of implicit Logout
         0              session reinstatement
         1              connection reinstatement when
                     the operational ErrorRecoveryLevel < 2
         2              connection reinstatement when
                     the operational ErrorRecoveryLevel = 2





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  Byte/     0       |       1       |       2       |       3       |
     /              |               |               |               |
    |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
    +---------------+---------------+---------------+---------------+
   0|.|I| 0x06      |1| Reason Code | Reserved                      |
    +---------------+---------------+---------------+---------------+
   4|TotalAHSLength | DataSegmentLength                             |
    +---------------------------------------------------------------+
   8/ Reserved                                                      /
   +/                                                               /
    +---------------+---------------+---------------+---------------+
  16| Initiator Task Tag                                            |
    +---------------+---------------+---------------+---------------+
  20| CID or Reserved               | Reserved                      |
    +---------------+---------------+---------------+---------------+
  24| CmdSN                                                         |
    +---------------+---------------+---------------+---------------+
  28| ExpStatSN                                                     |
    +---------------+---------------+---------------+---------------+
  32/ Reserved                                                      /
   +/                                                               /
    +---------------+---------------+---------------+---------------+
  48| Header-Digest (Optional)                                      |
    +---------------+---------------+---------------+---------------+

9.14.1  Reason Code

  Reason Code indicates the reason for Logout as follows:

     0 - closes the session. All commands associated with the ses-
          sion (if any) are terminated.

     1 - closes the connection. All commands associated with connec-
          tion (if any) are terminated.

     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.

  All other values are reserved.





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9.14.2  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".

9.14.3  ExpStatSN

   This is the last ExpStatSN value for the connection to be closed.

9.14.4  Implicit termination of tasks

   A target implicitly terminates the active tasks in three cases due to
   iSCSI protocol:

      a)  When a connection is implicitly or explicitly logged out with
      the Reason code of "Closes the connection" and there are active
      tasks allegiant to that connection.

      b)  When a connection fails and eventually the connection state
      times out (state transition M1 in Section 5.2.2 State Transition
      Descriptions for Initiators and Targets) and there are active
      tasks allegiant to that connection.

      c)  When a successful recovery Logout is performed while there are
      active tasks allegiant to that connection, and those tasks eventu-
      ally time out after the Time2Wait and Time2Retain periods without
      allegiance reassignment.

   If the tasks terminated in any of the above cases are SCSI tasks,
   they MUST be internally terminated with CHECK CONDITION status with a
   sense key of unit attention and ASC/ASCQ values of 0x6E/0x00 (COM-
   MAND TO LOGICAL UNIT FAILED).  Note that this status is meaningful
   only for appropriately handling the internal SCSI state aspects such
   as queued commands because this status is never communicated back as
   a terminating status to the initiator.





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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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

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 ErrorRecov-
   eryLevel 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 ErrorRecov-
   eryLevel is 2, this is the maximum amount of time, in seconds, after
   the initial wait (Time2Wait), the target waits for the allegiance
   reassignment for any active task after which the task state is dis-
   carded.  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 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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  If Time2Retain is 0, the target had already discarded the connection
  (and possibly the session) state along with the task states.  No
  reassignment or Logout is required in this case.





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9.16   SNACK Request

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

   Support for SNACK is mandatory only if the supported ErrorRecovery-
   Level of the implementation is greater than zero.

   The SNACK request is used to request the retransmission of numbered-
   responses, data, or R2T PDUs from the target.  The SNACK request
   indicates 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").




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   The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
   delivered as exact replicas of the ones the initiator missed except
   for the fields ExpCmdSN, MaxCmdSN and ExpDataSN which MUST carry the
   current values. R2T(s)requested by SNACK MUST carry also the current
   value of StatSN.

   The numbered Data-In PDUs, requested by a SNACK with a RunLength dif-
   ferent from 0, MUST be delivered as exact replicas of the ones the
   initiator missed except the fields ExpCmdSN and MaxCmdSN which MUST
   carry the current values.

   If the initiator MaxRecvDataSegmenTLength changed 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 MaxRecvDataSegmentLength. Their DataSN starts with the
   requested number and is increased by 1 for each resent Data-In PDU.
   If DataSN numbers change and a SCSI-Reponse PDU was sent reflecting
   the DataSN before retransmission it MUST be resent to reflect the new
   numbers.

   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 "Proto-
   col 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 and DataACK, the Initiator Task Tag MUST be set to
   the reserved value 0xffffffff. In all other cases, the Initiator Task



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   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
   Target 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
   reject the status SNACK with a Reject PDU. If the target supports
   recovery within connection, it MAY reject the SNACK after which it
   MUST issue an Asynchronous Message PDU with an iSCSI event that indi-
   cates "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 MaxBurstLength 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 car-
   rying the numbers equal to or greater than BegRun have to be resent.

   The RunLength MUST also be 0 for a DataACK SNACK.

   The first data SNACK issued after initiator's MaxRecvDataSeg-
   mentLength decreased, for a command issued on the same connection
   before the change in MaxRecvDataSegmentLength, 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

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  as the original transmission, depending on whether loss was before or
  after the MaxRecvDataSegmentLength was changed at the target.





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9.17  Reject

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x3f      |1| Reserved    | Reason        | Reserved      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| 0xffffffff                                                    |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| DataSN or Reserved                                            |
     +---------------+---------------+---------------+---------------+
   40| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   44| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
   xx/ Complete Header of Bad PDU                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   yy/Vendor specific data (if any)                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   zz| Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+


   Reject is used to indicate an iSCSI error condition (protocol, unsup-
   ported option etc.).


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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 | SNACK Reject                            | yes              |
   |      |                                         |                  |
   | 0x04 | Protocol Error (e.g., SNACK request for | no               |
   |      | a status that was already acknowledged) |                  |
   |      |                                         |                  |
   | 0x05 | Command not supported                   | no               |
   |      |                                         |                  |
   | 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
   target 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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   Note 2: A target should use this reason code for all invalid values
   of PDU fields that are meant to describe a task,  a response or a
   data transfer.  Some examples are invalid TTT/ITT, buffer offset, LUN
   qualifying a TTT, an invalid sequence number in a SNACK.

   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 com-
   mand PDU did not contain all the data and the target has not received
   a Data-out PDU with the Final bit 1 for the unsolicted data - if any
   and all outstanding R2Ts - if any), the target MUST wait until it
   receives the last expected Data-out PDUs 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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9.18  NOP-Out

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Ping Data (optional)                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

   A NOP-Out may be used by an initiator as a "ping request" 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.




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   When used as a ping request, the Initiator Task Tag MUST be set to a
   valid value (not the reserved 0xffffffff).

   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 con-
   tain 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 cop-
   ied from the NOP-In.

9.18.3  Ping Data

   Ping data are reflected in the NOP-In Response. The length of the
   reflected data are limited to MaxRecvDataSegmentLength. The length of
   ping data are indicated by the DataSegmentLength.  0 is a valid value
   for the Data Segment Length and indicates the absence of ping data.





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9.19  NOP-In

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    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| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Return Ping Data                                /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+


   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


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   with the same Initiator Task Tag that was provided in the NOP-Out
   request. It MUST also duplicate up to the first MaxRecvDataSeg-
   mentLength bytes of the initiator provided Ping Data.  For such a
   response, the Target Transfer Tag MUST be 0xffffffff.

   When a target sends a NOP-In with the Initiator Task Tag set to
   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
   corresponding NOP-Out, this field MUST hold the reserved value of
   0xffffffff.

9.19.2  StatSN

   The StatSN field will contain always the next StatSN. However, when
   the Initiator Task Tag is set to 0xffffffff StatSN for the connec-
   tion is not advanced.

9.19.3  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 Authentication Methods

   Only the following keys can be used during the SecurityNegotiation
   stage of the Login Phase:

     SessionType
     InitiatorName
     TargetName
     InitiatorAlias
     TargetAlias
     TargetPortalGroupTag
     AuthMethod and all keys listed under AuthMethod along with all
       of their associated keys.

   SessionType, InitiatorName, TargetName, InitiatorAlias, TargetAlias
   and TargetPortalGroupTag 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 ven-
   dor-unique methods:





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   +------------------------------------------------------------+
   | Name          | Description                                |
   +------------------------------------------------------------+
   | KRB5          | Kerberos V5 - defined in [RFC1510]         |
   +------------------------------------------------------------+
   | SPKM1         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SPKM2         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SRP           | Secure Remote Password                     |
   |               | defined in [RFC2945]                       |
   +------------------------------------------------------------+
   | CHAP          | Challenge Handshake Authentication Protocol|
   |               | defined in [RFC1944]                       |
   +------------------------------------------------------------+
   | None          | No authentication                          |
   +------------------------------------------------------------+


   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 CHAP.

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 respond with a
   Login reject with "Authentication Failure" status. Otherwise, if the
   initiator has selected the mutual authentication option (by setting



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   MUTUAL-REQUIRED in the ap-options field of the KRB_AP_REQ), the tar-
   get MUST reply with:

       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-values 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, 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 con-
   nection.

   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


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   bit in the options field of the REQ-TOKEN in the SPKM-REQ), the tar-
   get MUST reply with:

       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-values 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:


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      SRP_M=<M>

   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-values. The length of
   N,g,s,A,B,M in binary form (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-
   values 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

   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 category 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 Any-Stage may appear also in the SecurityNegotiation
   stage while all other keys described in this chapter are operational
   keys.

   Keys that do not require an answer are marked as Declarative

   Key scope is indicated as session-wide (SW) or connection-only (CO).

   Result function wherever mentioned states the function that can be
   applied to check the validity of the responder selection.  Minimum
   means that the selected value cannot exceed the offered value. Maxi-
   mum means that the selected value cannot be lower than the offered
   value.

11.1  HeaderDigest and DataDigest

   Use: IO
   Senders: Initiator and Target
   Scope: CO

   HeaderDigest = <list-of-options>
   DataDigest = <list-of-options>

   Default is None for both HeaderDigest and DataDigest.

   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


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  that may change the network level PDUs such as routers, switches, and
  proxies.

  The following table lists cyclic integrity checksums that can be
  negotiated for the digests and that MUST be implemented by every
  iSCSI initiator and target. These digest options only have error
  detection significance.

  +---------------------------------------------+
  | Name          | Description     | Generator |
  +---------------------------------------------+
  | CRC32C        | 32 bit CRC      |0x11edc6f41|
  +---------------------------------------------+
  | None          | no digest                   |
  +---------------------------------------------+

  The generator polynomial for this digest is given in hex-nota-
  tion(e.g., 0x3b stands for 0011 1011 and the polynomial is
  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 MUST be calculated by a method that produces the same results
  as the following process:

     - The PDU bits are considered as the coefficients of a polyno-
       mial M(x) of degree n-1; bit 7 of the lowest numbered byte is
       considered the most significant bit (x^n-1), followed by bit
       6 of the lowest numbered byte and through bit 0 of the high-
       est numbered byte (x^0).

     - The most significant 32 bits are complemented.

     - 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.


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     - the CRC bits are mapped into the digest word - the x^31 coef-
       ficient in bit 7 of the lowest numbered byte of the digest
       continuing to through the byte up to the x^24 coefficient in
       bit 0 of the lowest numbered byte, continuing with the x^23
       coefficient in bit 7 of next byte through x^0 in bit 0 of the
       highest numbered byte.

     - Computing the CRC over any segment (data or header) extended
       to include the CRC built using the generator 0x11edc6f41 will
       get always the value 0x1c2d19ed as its final remainder
       (R(x)). This value is given here in its polynomial form -
       i.e. not mapped as the digest word

   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=<numerical-value-from-1-to-65535>

   Default is 1.
   Result function is Minimum.

   Initiator and target negotiate the maximum number of connections
   requested/acceptable.

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, Any-Stage
   Senders: Initiator and Target
   Scope: SW

   TargetName=<iSCSI-name-value>

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   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
   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, Any-Stage
   Senders: Initiator
   Scope: SW

   InitiatorName=<iSCSI-name-value>

   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, Any-Stage
   Senders: Target
   Scope: SW

   TargetAlias=<iSCSI-local-name-value>

   Examples:

        TargetAlias=Bob-s Disk


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     TargetAlias=Database Server 1 Log Disk
     TargetAlias=Web Server 3 Disk 20

   If a target has been configured with a human-readable name or
   description, 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.

11.7  InitiatorAlias

   Use: ALL, Declarative, Any-Stage
   Senders: Initiator
   Scope: SW

   InitiatorAlias=<iSCSI-local-name-value>

   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 connected.

   This key SHOULD be sent by an initiator within the Login Phase, if
   available.

11.8  TargetAddress

   Use: ALL, Declarative, Any-Stage
   Senders: Target
   Scope: SW

   TargetAddress=domainname[:port][,portal-group-tag]

   The domainname can be specified as either a DNS host name, a dotted-
   decimal IPv4 address, or a bracketed IPv6 address as specified in
   [RFC2732].



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   If the TCP port is not specified, it is assumed to be the IANA-
   assigned default port for iSCSI (3260).

   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
     TargetAddress=[1080:0:0:0:8:800:200C:417A],65
     TargetAddress=[1080::8:800:200C:417A]:5003,1
     TargetAddress=computingcenter.acme.com,23

   Use of the portal-group-tag is described in Appendix D. - SendTar-
   gets Operation.

11.9  TargetPortalGroupTag

   Use: IO by target, Declarative, Any-Stage
   Senders: Target
   Scope: SW

   TargetPortalGroupTag=<numerical-value-from-1-to-65535>

   Examples:
   TargetPortalGroupTag=1

   Target portal group tag is a 16-bit numerical-value that uniquely
   identifies a portal group within an iSCSI target node. This key car-
   ries the value of the tag of the portal group that is servicing the
   Login request. The iSCSI target returns this key to the initiator in
   the Login Response PDU to the first Login Request PDU that has the C
   bit set to 0.

   For the complete usage expectations of this key see Section 4.3 Login
   Phase.


11.10  InitialR2T

   Use: LO

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   Senders: Initiator and Target
   Scope: SW

   InitialR2T=<boolean-value>

   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=Immediate Data Length and
   Desired Data Transfer Length=(min(FirstBurstLength, Expected
   DataTransfer Length) - Received Immediate Data Length).

   The default action is that R2T is required, unless both the initia-
   tor 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).

11.11  BidiInitialR2T

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   BidiInitialR2T=<boolean-value>

   Examples:

     I->BidiInitialR2T=No
     T->BidiInitialR2T=No

   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

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   (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.

11.12  ImmediateData

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   ImmediateData=<boolean-value>

   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 initia-
   tor and target 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
   unsolicited data 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.

   The following table is a summary of unsolicited data options:





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   +----------+-------------+------------------+--------------+
   |InitialR2T|ImmediateData|    Unsolicited   |Immediate Data|
   |          |             |   Data Out PDUs  |              |
   +----------+-------------+------------------+--------------+
   | No       | No          | Yes              | No           |
   +----------+-------------+------------------+--------------+
   | No       | Yes         | Yes              | Yes          |
   +----------+-------------+------------------+--------------+
   | Yes      | No          | No               | No           |
   +----------+-------------+------------------+--------------+
   | Yes      | Yes         | No               | Yes          |
   +----------+-------------+------------------+--------------+


11.13  MaxRecvDataSegmentLength

   Use: ALL, Declarative
   Senders: Initiator and Target
   Scope: CO

   MaxRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)>

   Default is 8192 bytes.

   The initiator or target declares the maximum data segment length in
   bytes it can receive in an iSCSI PDU.

   The transmitter (initiator or target) is required to send PDUs with a
   data segment not exceeding MaxRecvDataSegmentLength of the receiver.

   A target receiver is additionally limited by MaxBurstLength for
   solicited data and FirstBurstLength for unsolicited data and an ini-
   tiator MUST NOT send solicited PDUs exceeding MaxBurstLength nor
   unsolicited PDUs exceeding FirstBurstLength (or FirstBurstLength-
   Immediate Data Length if immediate data where sent).

11.14  MaxBurstLength

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   MaxBurstLength=<numerical-value-512-to-(2**24-1)>

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   Default is 262144 (256 Kbytes).
   Result function is Minimum.

   The initiator and target negotiate maximum SCSI data payload in bytes
   in a 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.

11.15  FirstBurstLength

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   FirstBurstLength=<numerical-value-512-to-(2**24-1)>

   Default is 65536 (64 Kbytes).
   Result function is Minimum.

   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
   follow the command.

   FirstBurstLength MUST NOT exceed MaxBurstLength.

11.16  DefaultTime2Wait

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   DefaultTime2Wait=<numerical-value-0-to-3600>

   Default is 2.
   Result function is Maximum.

   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.


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   A value of 0 indicates that logout or active task reassignment can be
   attempted immediately.

11.17  DefaultTime2Retain

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   DefaultTime2Retain=<numerical-value-0-to-3600>

   Default is 20.
   Result function is Minimum.

   The initiator and target negotiate the maximum time, in seconds after
   an initial wait (Time2Wait), before which an active task reassign-
   ment 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.

   A value of 0 indicates that connection/task state is immediately dis-
   carded by the target.

11.18  MaxOutstandingR2T

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   MaxOutstandingR2T=<numerical-value-from-1-to-65535>

   Default is 1.
   Result function is Minimum.

   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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11.19  DataPDUInOrder

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   DataPDUInOrder=<boolean-value>

   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.

11.20  DataSequenceInOrder

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   DataSequenceInOrder=<boolean-value>

   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 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. For this reason if ErrorRecoveryLevel is not


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   0 and DataSequenceInOrder is set to Yes then MaxOustandingR2T MUST be
   set to 1.

11.21  ErrorRecoveryLevel

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   ErrorRecoveryLevel=<numerical-value-0-to-2>

   Default is 0.
   Result function is Minimum.

   The initiator and target negotiate the recovery level supported.

   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.

11.22  SessionType

   Use: LO, Declarative, Any-Stage
   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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11.23  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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12. IANA Considerations


   The temporary (user) well-known port number for iSCSI connections
   assigned by IANA is 3260.





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References and Bibliography

   Normative References

     [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.
     [CAM] ANSI X3.232-199X, Common Access Method-3.
     [EUI] "Guidelines for 64-bit Global Identifier (EUI-64)",
       http://standards.ieee.org/regauth/oui/tutorials/EUI64.html
     [OUI] "IEEE OUI and Company_Id Assignments", http://stan-
       dards.ieee.org/regauth/oui/index.shtml
     [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.
     [RFC1737] K. Sollins, L. Masinter "Functional Requirements for
       Uniform Resource Names".
     [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 Inter-
       net Mail Extensions) Part One: Mechanisms for Specifying and
       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.


Julian Satran              Expires February 2003                      225


                                   iSCSI                       1-July-02

     [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.
     [RFC2396] T. Berners-Lee, R. Fielding, L. Masinter "Uniform
       Resource Identifiers".
     [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
       Literal 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).
     [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-
       security-09.txt, February 2002.
     [SPC]T10/1416-D, SCSI-3 Primary Commands.
     [SPC3]T10/1416-D, SCSI Primary Commands-3.
     [STPREP] P. Hoffman, M. Blanchet, "Preparation of Internation-
       alized Strings", draft-hoffman-stringprep-00.txt, September,
       2001.
     [STPREP-iSCSI] M. Bakke, "String Profile for iSCSI Names",
       draft-ietf-ips-iscsi-string-prep-00.txt, November 2001.
     [UNICODE] Unicode Standard Annex #15, "Unicode Normalization
       Forms", http://www.unicode.org/unicode/reports/15

  Informative References:



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                                   iSCSI                        1-July-02

     [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-03.txt (work
       in progress)
     [COBS] S. Cheshire and M. Baker, Consistent Overhead Byte
       Stuffing, IEEE Transactions on Networking, April 1999.
     [Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman "Opti-
       mization of Cyclic Redundancy-Check Codes with 24 and 32 Par-
       ity Bits", IEEE Transact. on Communications, Vol. 41, No. 6,
       June 1993.
     [CRC] ISO 3309, High-Level Data Link Control (CRC 32).
     [NDT] M. Bakke & team, draft-ietf-ips-iscsi-name-disc-05.txt
       (work in progress)
     [Schneier] B. Schneier, "Applied Cryptography: Protocols, Algo-
       rithms, and Source Code in C", 2nd edition, John Wiley &
       Sons, New York, NY, 1996.


Authors' Addresses

     Julian Satran
     IBM, Haifa Research Lab
     Haifa University Campus - Mount Carmel
     Haifa 31905, Israel
     Phone +972.4.829.6264
     E-mail: Julian_Satran@il.ibm.com

     Kalman Meth
     Haifa University Campus - Mount Carmel
     MATAM - Advanced Technology Center
     Haifa 31905, Israel
     Phone +972.4.829.6341
     E-mail: meth@il.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

     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

     Mallikarjun Chadalapaka
     Hewlett-Packard Company
     8000 Foothills Blvd.

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                                 iSCSI           1-July-02

     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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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       |
       /             |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0| Next-iSCSI-PDU-start pointer - copy #1                        |
     +---------------+---------------+---------------+---------------+
    4| Next-iSCSI-PDU-start pointer - copy #2                        |
     +---------------+---------------+---------------+---------------+

   The Marker scheme 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. Dur-
   ing login, each end of the iSCSI session specifies the interval at
   which it is willing to receive the marker, or it disables the marker
   altogether. 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 pro-


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                                    iSCSI                    1-July-02

   viding markers to a receiver wanting markers may suffer an apprecia-
   ble performance 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 least significant two bits of
   each marker word are reserved and are considered 0 for offset compu-
   tation.

   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 negotia-
   tion, 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 bytes 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=<boolean-value>

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                                    iSCSI                       1-July-02

   IFMarker=<boolean-value>

   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
   initiator 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=<numeric-range-from-1-to-65535>
   IFMarkInt=<numeric-range-from-1-to-65535>

   Responding:

   OFMarkInt=<numeric-value-from-1-to-65535>|Reject
   IFMarkInt=<numeric-value-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.



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  For the offering the initiator or target indicates the minimum to
  maximum interval (in 4-byte words) it wants the markers for one or
  both directions. In case it only wants a specific value, only a sin-
  gle value has to be specified. The responder selects a value within
  the minimum and maximum offered or the only value offered or indi-
  cates 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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Appendix B. Examples

B.1  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 |                       |                      |
   +------------------+-----------------------+----------------------+





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B.2  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      |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense|
   +------------------+-----------------------+---------------------+
   | Command Complete |                       |                     |
   +------------------+-----------------------+---------------------+

B.3  R2TSN/DataSN use Examples

   Output (write) data DataSN/R2TSN Example





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                               iSCSI                        1-July-02

  +------------------+-----------------------+----------------------+
  |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 |                       |                      |
  +------------------+-----------------------+----------------------+



   Input (read) data DataSN Example





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                                   iSCSI                    1-July-02

  +------------------+-----------------------+----------------------+
  |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





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                               iSCSI                        1-July-02

  +------------------+-----------------------+----------------------+
  |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          |
  |                  |   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





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                                 iSCSI                       1-July-02

   +------------------+-----------------------+----------------------+
   |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 |                       |                      |
   +------------------+-----------------------+----------------------+

B.4  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


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                               iSCSI            1-July-02

     ...
      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) FirstBurstLength=0
     T-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=8192 MaxBurst-
          Length=8192
     I-> Login (CSG,NSG=1,0 T=0) MaxBurstLength=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's authentication by the target is not success-
          ful, the target responds with:


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                                   iSCSI                      1-July-02

     T-> Login "login reject"

     instead of the Login KRB_AP_REP message, and terminates the
       connection.

     If the target's authentication by the initiator is not success-
       ful, the initiator terminates the connection (without
       responding to the Login KRB_AP_REP message).

  In the next example only the initiator is authenticated by the tar-
  get 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-July-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's authentication by the initiator is not success-
          ful, the initiator terminates the connection (without
          responding to the Login SPKM_REP_TI message).

     If the initiator's 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-July-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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     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
       terminates the connection.

  In the next example, only the initiator is authenticated by the tar-
  get via SRP:



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     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-July-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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     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 tar-
  get 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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Appendix D. SendTargets Operation

   To reduce the amount of configuration required on an initiator, iSCSI
   provides the SendTargets text request.  The initiator uses the Send-
   Targets request to get 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 targets 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.  Other-
   wise, the session 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 iSCSI IP address-port pairs, and MUST support the Send-
   Targets command on the discovery session.  A target MUST return all
   path information (IP address-port pairs and portal group tags) for
   the targets for which the requesting initiator is authorized.

   A target MUST support the SendTargets command on operational ses-
   sions; these will only return path information about the target to
   which the session is connected, and need not return information about
   other target names that may be defined in the responding system.

   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
        supported on an operational session.

      <iSCSI-target-name>

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     If an iSCSI target name is specified, the session should
       respond with addresses for only the named target, if possi-
       ble.  This value MUST be supported on discovery sessions.  A
       discovery session MUST be capable of returning addresses for
       those targets that would have been returned had value=all
       been designated.

     <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 tar-
  get is returned as a target record.  A target record begins with the
  TargetName 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
  complete 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.

  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 contains a domain name, IPv4 address, or
  IPv6 address, as specified for the TargetAddress key.

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  Each TargetAddress belongs to a portal group, identified by its
  numeric portal group tag (as in Section 11.9 TargetPortalGroupTag).
  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 discov-
  ery session open, and MAY send subsequent SendTargets commands 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



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  this target are the same as used on the current connection to the
  default iSCSI target.

  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 or an IPv6 address could have
  been returned instead of an IPv4 address.

  The next text response shows a target that supports spanning ses-
  sions across multiple addresses, and illustrates further 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 com-
  bination.  A TargetAddress with its own tag (.49) cannot be combined
  with any other address within the same session.



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  This SendTargets response does not indicate whether .49 supports mul-
  tiple connections per session; it communicated via the MaxConnec-
  tions 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 ini-
   tiator 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
          algorithms.  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.1  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 CurrentTimeout;
           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.2  Within-command Error Recovery Algorithms

E.2.1   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);

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   Build-And-Send-R2T(transport connection, description of data,
                                                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
         algorithms, applies to all solicited PDUs that carry StatSN -
         SCSI Response, Text Response etc.

E.2.2   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;


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     Retrieve TCB for CurrentPDU.InitiatorTaskTag.
     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.

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            if (ExpDataSN does not match) {
                 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.2.3   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.


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               }
               if ((current PDU is unsolicited and
                      data received is less than I/O length and
                        data received is less than FirstBurstLength)
                   or {current PDU is solicited and the length 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) {

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                      TCB.Reason = "SNACK Rejected";
                      Build-And-Send-Status(Connection, TCB);
                 }
            }
         } 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.3  Within-connection Recovery Algorithms

E.3.1   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 length);

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   Implementation-specific tunables:
   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
          because the target is required to discard the duplicate Cmd-
          SNs.

         - 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.3.2   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;

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      Retrieve TCB for CurrentPDU.InitiatorTaskTag.
      if (CurrentPDU.type = Nop-In) {
            if (the PDU is unsolicited) {
                  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);
          }
      }
  }

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E.3.3   Target Algorithms

   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.4  Connection Recovery Algorithms

E.4.1   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);


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   Notes:
        - Transport exception conditions, such as unexpected connec-
         tion termination, connection reset, and hung connection while
         the 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.4.2   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.AsyncEvent = ConnectionDropped) {
              Retrieve the AffectedConnection for CurrentPDU.Parameter1.
              AffectedConnection.CurrentTimeout = CurrentPDU.Parameter3;
             AffectedConnection.State = CLEANUP_WAIT;
             Start-Timer(Connection-Cleanup-Handler,
                           AffectedConnection, CurrentPDU.Parameter2);
           } else if (CurrentPDU.AsyncEvent = LogoutRequest)) {
             AffectedConnection = Connection;
             AffectedConnection.State = LOGOUT_REQUESTED;
             AffectedConnection.PerformConnectionCleanup = TRUE;
                AffectedConnection.CurrentTimeout = CurrentPDU.Parameter3;
             Start-Timer(Connection-Cleanup-Handler,
                           AffectedConnection, 0);
           } else if (CurrentPDU.AsyncEvent = SessionDropped)) {
             for (each Connection) {
                 Connection.State = CLEANUP_WAIT;
                 Connection.CurrentTimeout = CurrentPDU.Parameter3;
                 Start-Timer(Connection-Cleanup-Handler,
                           Connection, CurrentPDU.Parameter2);
             }
             Session.state = FAILED;
           }

       } else if (CurrentPDU.type = LogoutResponse) {
           Retrieve the CleanupConnection for CurrentPDU.CID.
           if (CurrentPDU.Response = failure) {
              CleanupConnection.State = CLEANUP_WAIT;
           } else {
               CleanupConnection.State = FREE;

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          }
      } 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;
              } 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.
      if (Connection can still exchange iSCSI PDUs) {
          NewConnection = Connection;
      } else {
          Start-Timer(Connection-Resource-Timeout-Handler,
                Connection, Connection.CurrentTimeout);
          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,

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                                           RecoveryRemove);
   }

   Transport_Exception_Handler(Connection)
   {
       Connection.PerformConnectionCleanup = TRUE;
       if (the event is an unexpected transport disconnect) {
           Connection.State = CLEANUP_WAIT;
           Connection.CurrentTimeout = DefaultTime2Retain;
           Start-Timer(Connection-Cleanup-Handler, Connection,
                                             DefaultTime2Wait);

       } else {
           Connection.State = FREE;
       }
   }

E.4.3   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);


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             }
         }
      } 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) {
                    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 of various events on targets

F.1  Clearing effects on iSCSI objects

   The following tables describe 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
       applicable 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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                        +-----+-----+-----+-----+-----+
                        |IT(1)|IC(2)|CT(5)|ST(6)|PP(7)|
  +---------------------+-----+-----+-----+-----+-----+
  |connection failure(8)|Y    |Y    |N    |N    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |connection state     |NA   |NA   |Y    |N    |NA   |
  |timeout (9)          |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session timeout/     |Y    |Y    |Y    |Y    |Y(14)|
  |closure/reinstatement|     |     |     |     |     |
  |(10)                 |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session continuation |NA   |NA   |N(11)|N    |NA   |
  |(12)                 |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |successful connection|Y    |Y    |Y    |N    |Y(13)|
  |close logout         |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session failure (18) |Y    |Y    |N    |N    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |successful recovery  |Y    |Y    |N    |N    |Y(13)|
  |Logout               |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |failed Logout        |Y    |Y    |N    |N    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |connection Login     |NA   |NA   |NA   |Y(15)|NA   |
  |(leading)            |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |connection Login     |NA   |NA   |N(11)|N    |Y    |
  |(non-leading)        |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |target cold reset(16)|Y    |Y    |Y    |Y    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |target warm reset(16)|Y    |Y    |Y    |Y    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |LU reset(19)         |Y    |Y    |Y    |Y    |Y    |
  +---------------------+-----+-----+-----+-----+-----+
  |powercycle(16)       |Y    |Y    |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.

  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 `connection tasks' 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
  connection cleanup state diagram).

  10.These are defined in Section 4.3.5 Session reinstatement, closure
  and timeout.

  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 and failure.

  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".



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  15.Applicable only if this leading connection login is a session
  reinstatement. If that is not the case, this is "NA".

  16.This operation affects all logged-in initiators.

  18.Session failure is as defined in Section 4.3.6 Session continua-
  tion 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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                        +-----+-----+-----+-----+-----+
                        |DC(1)|DD(2)|SS(3)|CS(4)|DS(5)|
  +---------------------+-----+-----+-----+-----+-----+
  |connection failure   |N    |Y    |N    |N    |N    |
  +---------------------+-----+-----+-----+-----+-----+
  |connection state     |Y    |NA   |Y    |N    |NA   |
  |timeout              |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session timeout/     |Y    |Y    |Y(7) |Y    |NA   |
  |closure/reinstatement|     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session continuation |N(11)|NA*12|NA   |N    |NA*13|
  +---------------------+-----+-----+-----+-----+-----+
  |successful connection|Y    |Y    |Y    |N    |NA   |
  |close Logout         |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |session failure      |N    |Y    |N    |N    |N    |
  +---------------------+-----+-----+-----+-----+-----+
  |successful recovery  |Y    |Y    |Y    |N    |N    |
  |Logout               |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |failed Logout        |N    |Y(9) |N    |N    |N    |
  +---------------------+-----+-----+-----+-----+-----+
  |connection Login     |NA   |NA   |N(8) |N(8) |NA   |
  |(leading             |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |connection Login     |N(11)|NA*12|N(8) |N    |NA*13|
  |(non-leading)        |     |     |     |     |     |
  +---------------------+-----+-----+-----+-----+-----+
  |target cold reset    |Y    |Y    |Y    |Y(10)|NA   |
  +---------------------+-----+-----+-----+-----+-----+
  |target warm reset    |Y    |Y    |N    |N    |NA   |
  +---------------------+-----+-----+-----+-----+-----+
  |LU reset             |N    |Y    |N    |N    |N    |
  +---------------------+-----+-----+-----+-----+-----+
  |powercycle           |Y    |Y    |Y    |Y(10)|NA   |
  +---------------------+-----+-----+-----+-----+-----+

  1.Discontiguous Commands - commands allegiant to the connection in
  question and waiting to be reordered in the iSCSI layer. All "Y"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,
  because the discontiguities can be ahead of the task.

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   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

   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.

F.2  Clearing effects on SCSI objects

   The only iSCSI protocol action that can effect clearing actions on
   SCSI objects is the "I_T nexus loss" notification (Section 4.3.5.1
   Loss of Nexus notification). [SPC3] describes the clearing effects of
   this notification on a variety of SCSI attributes. In addition, SCSI
   standards documents (such as [SAM2] and [SBC]) define additional
   clearing actions that may take place for several SCSI objects on SCSI
   events such as LU resets and power-on resets.

   Note that because iSCSI defines target cold reset as protocol-equiva-
   lent to a target power-cycle, the iSCSI target cold reset must also
   be considered as the power-on reset event in interpreting the actions
   defined in the SCSI standards.


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  When the iSCSI session is reconstructed (thus between the same SCSI
  ports with the same nexus identifier) establishing the same I_T nexus
  again, all SCSI objects that are defined to not clear on the "I_T
  nexus loss" notification event, such as persistent reservations, are
  automatically associated to this new session.





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