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     IPS                                                       Julian Satran
     Internet Draft                                             Daniel Smith
     Document: draft-ietf-ips-iscsi-08.txt                       Kalman Meth
     Category: standards-track                                    Ofer Biran
                                                                  Jim Hafner
                                                                         IBM
     
                                                           Costa Sapuntzakis
                                                                  Mark Bakke
                                                               Cisco Systems
     
                                                                Matt Wakeley
                                                        Agilent Technologies
     
                                                           Luciano Dalle Ore
                                                                     Quantum
     
                                                           Paul Von Stamwitz
                                                                     Adaptec
     
                                                               Randy Haagens
                                                     Mallikarjun Chadalapaka
                                                         Hewlett-Packard Co.
     
                                                                Efri Zeidner
                                                                     SANGate
     
                                                                 Yaron Klein
                                                                      SANRAD
     
     
     
                                      iSCSI
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     Julian Satran    Standards-Track, Expires April 2002                1
     
                                     iSCSI                       30-Sep-01
     
     
     
     Status of this Memo
     
     
        This document is an Internet-Draft and fully conforms to all
        provisions of Section 10 of RFC2026 [1].
     
        Internet-Drafts are working documents of the Internet Engineering
        Task Force (IETF), its areas, and its working groups. Note that other
        groups may also distribute working documents as Internet-Drafts.
        Internet-Drafts are draft documents valid for a maximum of six months
        and may be updated, replaced, or made obsolete by other documents at
        any time. It is inappropriate to use Internet- Drafts as reference
        material or to cite them other than as "work in progress."
        The list of current Internet-Drafts can be accessed at
        http://www.ietf.org/ietf/1id-abstracts.txt
        The list of Internet-Draft Shadow Directories can be accessed at
        http://www.ietf.org/shadow.html.
     
     
     Abstract
     
        The Small Computer Systems Interface (SCSI) is a popular family of
        protocols for communicating with I/O devices, especially storage
        devices.  This memo describes a transport protocol for SCSI that
        operates on top of TCP.  The iSCSI protocol aims to be fully
        compliant with the requirements laid out in the SCSI Architecture
        Model - 2 [SAM2] document.
     
     Acknowledgements
     
        In addition to the authors, a large group of people contributed to
        this work through their review, comments and valuable insights.  We
        are grateful to all of them.  We are especially grateful to those who
        found the time and patience to participate in our weekly phone
        conferences and intermediate meetings in Almaden and Haifa, thus
        helping to shape this document: John Hufferd, Prasenjit Sarkar, Meir
        Toledano, John Dowdy, Steve Legg, Alain Azagury (IBM), Dave Nagle
        (CMU), David Black (EMC), John Matze (Veritas), Steve DeGroote, Mark
        Shrandt (NuSpeed), Gabi Hecht (Gadzoox), Robert Snively (Brocade),
        Nelson Nachum (StorAge), Uri Elzur (Broadcom).  Many more helped
        clean up and improve this document within the IPS working group. We
        are especially grateful to David Robinson and Raghavendra Rao (Sun),
        Charles Monia, Joshua Tseng (Nishan), Somesh Gupta (Silverback
        Systems), Michael Krause, Pierre Labat, Santosh Rao, Matthew
        Burbridge (HP), Stephen Bailey (Sandburst), Robert Elliott (Compaq),
        Steve Senum, Ayman Ghanem (CISCO), Barry Reinhold (Trebia Networks),
     
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        Bob Russell (UNH), Bill Lynn (Adaptec) and Doug Otis (Sanlight),
        Robert Griswold and Bill Moody (Crossroads).  The recovery chapter
        was enhanced with help from Stephen Bailey (Sandburst), Somesh Gupta
        (HP), Venkat Rangan (RhapsodyNetworks), Vince Cavanna, Pat Thaler
        (Agilent), Eddy Quicksall (iVivity, Inc.) - Eddy also contributed
        with some examples.  Last, but not least, thanks to Ralph Weber for
        keeping us in line with T10 (SCSI) standardization.
        We would like to thank Steve Hetzler for his unwavering support and
        for coming up with such a good name for the protocol, Micky Rodeh,
        Jai Menon, Clod Barrera and Andy Bechtolsheim for helping this work
        happen.
     
     
        At the time of the writing, this document has to be considered in
        conjunction with the "Naming & Discovery"[NDT], "Boot"[BOOT] and
        "IPSec"[SEC-IPS] documents.
     
        The "Naming & Discovery" is authored by:
     
           Mark Bakke (Cisco), Joe Czap, Jim Hafner, John Hufferd,
           Kaladhar Voruganti (IBM), Howard Hall (Pirus), Jack Harwood
           (EMC), Yaron Klein (SANRAD), Lawrence Lamers (San Valley
           Systems), Todd Sperry (Adaptec) and Joshua Tseng (Nishan).
     
        The "Boot" is authored by:
     
           Prasenjit Sarkar (IBM), Duncan Missimer (HP) and Costa
           Sapuntzakis (CISCO).
     
        The "IPSec" is authored by:
     
           Bernard Aboba, William Dixon (Microsoft), David Black (EMC),
           Joseph Tardo, Uri Elzur (Broadcom), Mark Bakke, Steve Senum
           (Cisco Systems), Howard Herbert, Jesse Walker (Intel), Julian
           Satran, Ofer Biran and Charles Kunzinger (IBM).
     
     
        We are grateful to all of them for their good work and for helping us
        correlate this document with the ones they produced.
     
     Conventions used in this document
     
     
        In examples, "I->" and "T->" indicate iSCSI PDUs sent by the
        initiator and target respectively.
     
     
     
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        The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
        "SHOULD", "SHOULD NOT", "RECOMMENDED",  "MAY", and "OPTIONAL" in this
        document are to be interpreted as described in RFC2119.
     
     Change Log
     
        The following changes were made from draft-ietf-ips-iSCSI-07 to
        draft-ietf-ips-iSCSI-08:
     
           - Clarified the use of initiator task tag with regard to the
           SCSI tag in 3.2.1.8
           - Added a clarification to 2.2.2.1 - response to a command
           should not precede acknowledgment.
           - Added clarification to 3.7 - good status in Data-In must be
           supported by initiators
           - Clarified InitiatorName is required at login in 5.1
           - Another clarification for SecurityContextComplete in 5.2
           - 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 CopyManager Session types
           - Changed explanation of ExpDataSN
           - Removed/corrected response 05 in 3.4.3
           - Brought 1.2.7 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
           DataSequenceOrder 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 1.2.5
           - Added new Reject reason codes, tabular listing and a pointer
           to 3.17.1
           - Added additional Reject usage semantics on CmdSN and DataSN
           to 3.17.1
           - Added a new Logout Response code for failure
     
     
     
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           - Renamed BUSY as RECOVERY_START, removed RECOVERY_DONE, and
           merged T11 and T14 transitions into T11-(1,2) in section 7.
           - 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 3.6 linking SCSI mode pages to
           Async Messages
           - Changed the ASC/ASCQ values to better mean "not enough
           unsolicited data"
           - Names examples include date
           - Removed references to S bit in 3.4
           - 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 5, changed all examples in Appendix A 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 chapter 4, out DataPDULength,
           DataSequenceOrder
           - Changed all sense keys to aborted command in the table in
           3.4.2
           - Rearranged requests to have all SCSI related grouped etc.
           - Fixed Task Management Function Request ABORT TASK and removed
           the part about it in chapter 9.
           - Reintroduced aliases (the data format) in an Appendix F. The
           aliasing mechanism once part of iSCSI is part of [SPC3]
           - Login negotiations - using only login request response
           (instead of former login and text)
           - F bit in login changed name to T bit
           - Stated defaults for mode parameters in chapter 3
           - Updated chapter 10 to reflect the current consensus on
           security
           - Changed all sense keys to aborted command in the table in
           2.4.2
     
     
     
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           - 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
           clarified language in the same section.
           - Added more description to the session state transitions in
           section 7.3.
           - Several changes in section 8 corresponding to the new task
           management function "reassign".  Other language changes in
           section 8 for better description.  Format errors are mandated
           to cause session failures.
           - Renamed the erstwhile error recovery levels as error recovery
           classes, and renamed "within-session" recovery to "connection
           recovery" to better reflect the mechanics.
           - Added section 8.12 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 3.17 to use the "Invalid SNACK" reason code.
           - Removed a Logout reason code in 3.14 to be consistent with
           section 3.9.
           - Collapsed the two event fields in Async Event and added
           vendor specific event
           - Immediate data can be negotiated anytime (consistency)
           - Removed replay as a protocol notion and all references to it
           - SNACK RunLength 0 means all
           - Cleaning the bookmark mechanism for text
           - New T10 approved ASC/ASQ codes
           - Added a incipient definitions section - thanks to Eddy
           Quicksall
           - Change OpParmReset from yes/no to default/current
           - Added Base64 to encode large strings
           - The 255 limit for key values is now "unless specified
           otherwise"
           - 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:
     
     
     
     
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           - Clarified the "fate" of immediate commands and resources
           mandated (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 exclusively
           with text mode and can be retrieved with either text or Mode-
           SENSE. This enables us to disable their change after the Login
           negotiation. Also added to the negotiation (1.2.4) the value
           "?" with special meaning of enquiry
           - Changed "task" to "command" wherever relevant
           - EMDP usage in line with other SCSI protocols. EMDP governs
           how a target may request data and deliver. Similar to FCP a
           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)
           - Some Task Management commands may require authorization or
           may not be implemented. If not authorized they will return as
           if executed with a qualifier indicating "not authorized" or
           "not implemented" (clear LU and the resets)
           - Task management commands and responses are "generalized" to
           all iSCSI tagged commands (they are named now Task Management
           command and response). Their behavior with respect to their
           CmdSN is clarified and mandated
           - The logic to update ExpCmdSN etc. moved to 1.2.2.1
           - Explicitly specified that a target can "initiate" negotiating
           a parameter (offering)(1.2.4)
           - Returned the "direction" bit and a set of codes similar to
           version 05
           - Introduced a "special" session type (CopyManagerSession) to
           be used between a Copy Manager and all of its target; it may
           help define authentication and limit the type f commands to be
           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
     
     
     
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           - All key=value responses have to be explicit (none, not-
           understood etc.); no more selection by hiatus
           - Targets can also offer key=value pairs (i.e., initiate
           negotiation) stated explicitly in 2.9.3
           - Logout has a CmdSN field
           - The Status SNACK can be discarded if the target has no such
           recovery
           - Some parameters have been removed and replaced by
           "reasonable" defaults (read arbitrary defaults!); many others
           can't be changed anymore while the session is in full-feature
           phase
           - NOP-Out specifies how LUN is generated when used (copied from
           NOP-In)
           - Initial Marker-Less Interval is not a parameter anymore
           - A response with F=1 during negotiation may not contain
           key=value pairs that may require additional answers from the
           initiator
           - Clarified the meaning of the F bit on Write commands with
           regard to immediate and unsolicited data; F bit 0 means that
           unsolicited data will follow while F bit 1 means that this is
           the last of them (if any)
           - You can have both immediate and unsolicited Data-Out PDUs
           - DataPDULength and FirstBurstSize of 0 are allowed and mean
           unlimited length
           - Task management command behavior relative to their own CmdSN
           is now stated in no uncertain terms (they are mandated to
           execute as if issued at CmdSN and, in case of aborts and
           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
           semantics) and SNACK explicitly says that it requests Data or
           R2T.
           - A session can have only one outstanding text request (not
           sequence)
           - Text for Login Response 0301 changed (removed the maintenance
           mention)
           - Clarified when ExpDataSN is reserved in SCSI Response
           - Clarified the text and parameter (timers) for iSCSI event
           - Padding bytes should be 0 (2.1)
           - TotalAHSLength in 2.1.1.1 includes padding
           - DataSegmentLength in 2.1.1.2 excludes padding
           - Clarified bits in AHS type
           - Limit for key/value string lengths (63, 255) in 2.8.3
           - Added an example of SCSI event to Asynchronous Message
           - Changed "Who" to "Who can send" in appendix
     
     
     
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           - Clarified meaning of parameters on 2.18.1 - Asynchronous
           Message - 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
           - Additional Runs (AddRuns) dropped from the SNACK request (too
           complex). With it disappeared also the implicit acknowledgement
           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 connection)
           - Status SNACK for an acknowledged status is a protocol error
           (cause for reject)
           - Reject cause "Command In Progress" when requesting replay
           before status is issued and while command is running
     
     
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           - 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)
           introduced as a replacement to fqn. Iqn prefixes also reversed
           names
           - text in 8.3 revised (task management implementation
           mechanism)
           - Fixed bit 7 byte 1 in Task Management response to 1
           (consistency)
           - Clarified in 1.2.2 behavior when "command window" is 0
           (MaxCmdSN = ExpCmdSN -1)
           - Added state transitions part (new part 6)
           - Refreshed recovery chapter (new part 7)
           - Added an appendix with detailed recovery mechanisms (Appendix
           E)
           - Added session types a brief explanation in part 1
           - Added DiscoverySession key and SendTargets appendix
           - SCSI response made to fit having both a Status and a Response
           field. Needed for target errors that result in a check
           condition and ACA. In line with SAM2 that requires both fields
           (former versions where modeled on FCP).
           - The security appendix list SRP as mandatory to implement
           - Clarified initial CmdSN and the role of TSID as a serializer
           - Long Text Responses - additional fields added to the text
           request and text response
           - Added a SCSI to iSCSI concept mapping section 1.5
           - Clarified SNACK wording to indicate that in general command.
           Request, iSCSI command and iSCSI command have the same meaning.
           Also status, response or numbered response.
           - Changed InitStatSN and clarified how it increases
           - Added requirement for a 0x00 delimiter after each key=value
           - Added binary negotiations (yes|no) explicitly to 1.2.4
           - All keys and values in the spec are case sensitive (stated in
           the text request)
           - Changed the "operational parameters sent before the
           security.. MAY be discarded" into MUST be discarded
           - Changed the login reject 0201 to read - Security Negotiation
           Failed
           - Added to 2.3.1 a paragraph about mandatory consistencies
     
     
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           - 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
           FirstBurstSize and a response (error) for targets not
           supporting less
           - Many more minor editorial changes, clarifications, typos etc.
           - Responses in same position in SCSI response, logout, task
           etc.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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                                Table of Contents
     Status of this Memo...................................................2
     Abstract..............................................................2
     Acknowledgements......................................................2
     Conventions used in this document.....................................3
     Change Log............................................................4
     1. Definitions.......................................................18
     2. Overview..........................................................22
      2.1 SCSI Concepts..................................................22
      2.2 iSCSI Concepts and Functional Overview.........................22
       2.2.1 Layers and Sessions.........................................23
       2.2.2 Ordering and iSCSI Numbering................................24
        2.2.2.1 Command Numbering and Acknowledging......................24
        2.2.2.2 Response/Status Numbering and Acknowledging..............27
        2.2.2.3 Data Sequencing..........................................27
       2.2.3 iSCSI Login.................................................28
       2.2.4 Text Mode Negotiation.......................................29
       2.2.5 iSCSI Full Feature Phase....................................30
       2.2.6 iSCSI Connection Termination................................32
       2.2.7 Naming and Addressing.......................................33
       2.2.8 Persistent State............................................35
       2.2.9 Message Synchronization and Steering........................35
        2.2.9.1 Rationale................................................35
        2.2.9.2 Synchronization (sync) and Steering Functional Model.....36
        2.2.9.3 Sync and Steering and Other Encapsulation Layers.........39
        2.2.9.4 Sync/Steering and iSCSI PDU Size.........................39
      2.3 Third Party Commands...........................................40
      2.4 iSCSI session types............................................40
      2.5 SCSI to iSCSI concepts mapping model...........................40
       2.5.1 iSCSI Architectural Model...................................41
       2.5.2 SCSI Architecture Model.....................................44
       2.5.3 Consequences of the model...................................46
        2.5.3.1 I_T nexus state..........................................47
        2.5.3.2 SCSI Mode Pages..........................................47
     3. iSCSI PDU Formats.................................................48
      3.1 iSCSI PDU Length and Padding...................................48
      3.2 PDU Template, Header and Opcodes...............................48
       3.2.1 Basic Header Segment (BHS)..................................49
        3.2.1.1 X........................................................50
        3.2.1.2 I........................................................50
        3.2.1.3 Opcode...................................................50
        3.2.1.4 Opcode-specific Fields...................................51
        3.2.1.5 TotalAHSLength...........................................51
        3.2.1.6 DataSegmentLength........................................51
     
     
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        3.2.1.7 LUN......................................................51
        3.2.1.8 Initiator Task Tag.......................................51
       3.2.2 Additional Header Segment (AHS).............................52
        3.2.2.1 AHSType..................................................52
        3.2.2.2 AHSLength................................................52
        3.2.2.3 Extended CDB AHS.........................................52
        3.2.2.4 Bidirectional Expected Read-Data Length AHS..............53
       3.2.3 Header Digest and Data Digest...............................53
       3.2.4 Data Segment................................................54
      3.3 SCSI Command...................................................55
       3.3.1 Flags and Task Attributes (byte 1)..........................55
       3.3.2 CRN.........................................................56
       3.3.3 CmdSN - Command Sequence Number.............................56
       3.3.4 ExpStatSN...................................................56
       3.3.5 Expected Data Transfer Length...............................56
       3.3.6 CDB - SCSI Command Descriptor Block.........................57
       3.3.7 Data Segment - Command Data.................................57
      3.4 SCSI Response..................................................58
       3.4.1 Flags (byte 1)..............................................58
       3.4.2 Status......................................................59
       3.4.3 Response....................................................59
       3.4.4 Residual Count..............................................61
       3.4.5 Bidirectional Read Residual Count...........................61
       3.4.6 Data Segment - Sense and Response Data Segment..............62
        3.4.6.1 SenseLength..............................................62
       3.4.7 ExpDataSN...................................................62
       3.4.8 StatSN - Status Sequence Number.............................62
       3.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator..........63
       3.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator....63
      3.5 Task Management Function Request...............................64
       3.5.1 Function....................................................64
       3.5.2 LUN.........................................................66
       3.5.3 Referenced Task Tag.........................................66
       3.5.4 RefCmdSN or ExpDataSN.......................................66
      3.6 Task Management Function Response..............................67
       3.6.1 Response and Qualifier......................................67
       3.6.2 Referenced Task Tag.........................................68
      3.7 SCSI Data-out & SCSI Data-in...................................69
       3.7.1 F (Final) Bit...............................................70
       3.7.2 Target Transfer Tag.........................................71
       3.7.3 StatSN......................................................71
       3.7.4 DataSN......................................................71
       3.7.5 Buffer Offset...............................................72
       3.7.6 DataSegmentLength...........................................72
       3.7.7 Flags (byte 1)..............................................72
      3.8 Ready To Transfer (R2T)........................................74
     
     
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       3.8.1 R2TSN.......................................................75
       3.8.2 StatSN......................................................75
       3.8.3 Desired Data Transfer Length and Buffer Offset..............75
       3.8.4 Target Transfer Tag.........................................76
      3.9 Asynchronous Message...........................................77
       3.9.1 AsyncEvent..................................................78
       3.9.2 AsyncVCode..................................................79
       3.9.3 Sense Data or iSCSI Event Data..............................79
      3.10 Text Request..................................................80
       3.10.1 F (Final) Bit..............................................80
       3.10.2 Initiator Task Tag.........................................81
       3.10.3 Target Transfer Tag........................................81
       3.10.4 Text.......................................................81
      3.11 Text Response.................................................83
       3.11.1 F (Final) Bit..............................................83
       3.11.2 Initiator Task Tag.........................................84
       3.11.3 Target Transfer Tag........................................84
       3.11.4 Text Response Data.........................................84
      3.12 Login Request.................................................86
       3.12.1 X - Restart Connection.....................................86
       3.12.2 I - Immediate..............................................87
       3.12.3 T (Transit) Bit............................................87
       3.12.4 CSG and NSG................................................87
       3.12.5 Version-max................................................88
       3.12.6 Version-min................................................88
       3.12.7 Connection ID - CID........................................88
       3.12.8 ISID.......................................................88
       3.12.9 TSID.......................................................89
       3.12.10 CmdSN.....................................................89
       3.12.11 ExpStatSN.................................................89
       3.12.12 Login Parameters..........................................89
      3.13 Login Response................................................90
       3.13.1 Version-max................................................90
       3.13.2 Version-active.............................................91
       3.13.3 TSID.......................................................91
       3.13.4 StatSN.....................................................91
       3.13.5 Status-Class and Status-Detail.............................91
       3.13.6 T (Transit) bit............................................93
      3.14 Logout Command................................................95
       3.14.1 CID........................................................96
       3.14.2 ExpStatSN..................................................96
       3.14.3 Reason Code................................................96
      3.15 Logout Response...............................................97
       3.15.1 Response...................................................97
       3.15.2 Time2Wait..................................................98
       3.15.3 Time2Retain................................................98
     
     
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      3.16 SNACK Request.................................................99
       3.16.1 Type......................................................100
       3.16.2 BegRun....................................................100
       3.16.3 RunLength.................................................100
      3.17 Reject.......................................................101
       3.17.1 Reason....................................................101
       3.17.2 DataSN....................................................103
       3.17.3 Complete Header of Bad PDU................................103
      3.18 NOP-Out......................................................104
       3.18.1 Initiator Task Tag........................................105
       3.18.2 Target Transfer Tag.......................................105
       3.18.3 Ping Data.................................................105
      3.19 NOP-In.......................................................106
       3.19.1 Target Transfer Tag.......................................107
       3.19.2 LUN.......................................................107
     4. SCSI Mode Parameters for iSCSI...................................108
     5. Login Phase......................................................110
      5.1 Login Phase Start.............................................112
      5.2 iSCSI Security and Integrity Negotiation......................113
      5.3 Operational Parameter Negotiation During the Login Phase......114
     6. Operational Parameter Negotiation Outside the Login Phase........116
     7. State transitions................................................117
      7.1 Standard connection state diagram.............................117
      7.2 Connection recovery state diagram.............................119
      7.3 Session state diagram.........................................122
     8. iSCSI Error Handling and Recovery................................125
      8.1 Retry and Reassign in Recovery................................125
       8.1.1 Usage of Retry.............................................125
       8.1.2 Allegiance Reassignment....................................126
      8.2 Usage Of Reject PDU in Recovery...............................126
      8.3 Format Errors.................................................127
      8.4 Digest Errors.................................................127
      8.5 Sequence Errors...............................................128
      8.6 SCSI Timeouts.................................................129
      8.7 Negotiation failures..........................................129
      8.8 Protocol Errors...............................................129
      8.9 Connection Failures...........................................130
      8.10 Session Errors...............................................130
      8.11 Recovery Classes.............................................131
       8.11.1 Recovery Within-command...................................131
       8.11.2 Recovery Within-connection................................132
       8.11.3 Connection Recovery.......................................133
       8.11.4 Session Recovery..........................................133
      8.12 Error Recovery Hierarchy.....................................134
     9. Notes to Implementers............................................136
      9.1 Multiple Network Adapters.....................................136
     
     
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       9.1.1 iSCSI Name and ISID/TSID use...............................136
      9.2 Autosense and Auto Contingent Allegiance (ACA)................137
      9.3 Task Management Commands and Immediate Delivery...............137
      9.4 Synch and steering layer and performance......................139
      9.5 Unsolicited data and performance..............................140
     10. Security Considerations.........................................141
      10.1 iSCSI Security mechanisms....................................141
      10.2 In-band Initiator-Target Authentication......................141
      10.3 IPSec........................................................142
       10.3.1 Data Integrity and Authentication.........................142
       10.3.2 Confidentiality...........................................143
       10.3.3 Security Associations and Key Management..................143
     11. IANA Considerations.............................................144
     12. References and Bibliography.....................................145
     13. Author's Addresses..............................................147
     Appendix A. iSCSI Security and Integrity...........................150
      01 Security Keys and Values.......................................150
      02 Authentication.................................................152
      03 Login Phase Examples...........................................155
     Appendix B. Examples...............................................167
      04 Read Operation Example.........................................167
      05 Write Operation Example........................................168
      06 R2TSN/DataSN use examples......................................168
      07 CRC Examples...................................................172
     Appendix C. Sync and Steering with Fixed Interval Markers..........174
      08 Markers At Fixed Intervals.....................................174
      09 Initial Marker-less Interval...................................175
     Appendix D. Login/Text Operational Keys............................176
      10 MaxConnections.................................................176
      11 SendTargets....................................................176
      12 TargetName.....................................................176
      13 InitiatorName..................................................177
      14 TargetAlias....................................................177
      15 InitiatorAlias.................................................178
      16 TargetAddress..................................................178
      17 FMarker........................................................179
      18 RFMarkInt......................................................179
      19 SFMarkInt......................................................180
      20 InitialR2T.....................................................180
      21 BidiInitialR2T.................................................181
      22 ImmediateData..................................................181
      23 DataPDULength..................................................182
      24 MaxBurstSize...................................................183
      25 FirstBurstSize.................................................183
      26 LogoutLoginMaxTime.............................................183
      27 MaxOutstandingR2T..............................................184
     
     
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      28 DataPDUInOrder.................................................184
      29 DataSequenceInOrder............................................184
      30 ErrorRecoveryLevel.............................................185
      31 SessionType....................................................185
      32 The Vendor Specific Key Format.................................186
     Appendix E. SendTargets operation..................................187
     Appendix F. SCSI Alias designation formats.........................191
      33 Format codes...................................................191
      34 iSCSI Name designation format..................................192
      35 iSCSI Name with binary IPv4 address designation format.........193
      36 iSCSI Name with IPname designation format......................194
      37 iSCSI Name with binary IPv6 address designation format.........195
     Appendix G. Algorithmic presentation of error recovery classes.....197
      38 General Data structure and procedure description...............197
      39 Within-command error recovery algorithms.......................198
       1  Procedure descriptions........................................198
       2  Initiator algorithms..........................................199
       3  Target algorithms.............................................201
      40 Within-connection recovery algorithms..........................203
       4  Procedure descriptions........................................203
        1. Initiator algorithms.........................................204
        2. Target algorithms............................................206
       5  Connection recovery algorithms................................206
        3. Procedure descriptions.......................................206
        4. Initiator algorithms.........................................207
        5. Target algorithms............................................209
     Full Copyright Statement............................................211
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     1. Definitions
     
        - 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.
     
        - iSCSI Layer: This builds/receives iSCSI PDUs and relays/receives
        them to/from one or more TCP connections that form an initiator-
        target "session".
     
        - 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.
     
        - 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).
     
        - 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
        connections within a session, an initiator sees one "target image".
     
        - 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
        presented to the target during login requests and during logouts that
        close connections.
     
        - ISID (Initiator Session ID): An ID generated by the initiator
        during the leading login for a session. It is used for all additional
        logins for the same session. Between a given iSCSI Initiator and
        iSCSI Target Portal Group (SCSI target port), there can be only one
        session with a given ISID (identifying a SCSI initiator port).
     
        - SSID (Session ID): A session is defined by a session ID that is
        composed of an initiator part (ISID) and a target part (TSID).
     
        - TSID (Target Session ID): The TSID is the target assigned tag for a
        session with a specific named initiator that, together with the ISID
        uniquely identifies a session with that initiator.
        It is given to the target during additional connections for the same
        session to identify the associated session.
     
        - iSCSI Name: The name of an iSCSI initiator or iSCSI target.
     
     
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        - iSCSI Target Name: The iSCSI Target Name specifies the worldwide
        unique name of the target.
     
        - iSCSI Initiator Name: The iSCSI Initiator Name specifies the
        worldwide unique name of the initiator.
     
        - 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 is usable by some iSCSI
        Nodes contained in that Network Entity to gain access to the IP
        network.
     
        - Network Portal: The Network Portal is a component of a Network
        Entity that has a TCP/IP network address and that may be used by an
        iSCSI Node within that Network Entity for the connection(s) within
        one of its iSCSI sessions. A Network Portal in an initiator is
        identified by its IP address. A Network Portal in a target is
        identified by its IP address and its listening TCP port.
     
        - Portal Groups: iSCSI supports multiple connections within the same
        session; some implementations will have the ability to combine
        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 session with
        connections spanning these portals. Not all Network Portals within a
        Portal Group need participate in every session connected through that
        Portal Group. One or more Portal Groups may provide access to an
        iSCSI Node. Each Network Portal as utilized by a given iSCSI Node
        belongs to exactly one portal group within that node.
     
        - Portal Group Tag: This simple integer value between 1 and 65535
        identifies the Portal Group within an iSCSI Node. All Network Portals
        with the same portal group tag in the context of a given iSCSI Node
        are in the same Portal Group.
     
        - iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
        iSCSI target. There are one or more iSCSI Nodes within a Network
        Entity. The iSCSI Node is accessible via one or more Network Portals.
        An iSCSI Node is identified by its iSCSI Name. The separation of the
        iSCSI Name from the addresses used by and for the iSCSI node allows
        multiple iSCSI nodes to use the same addresses, and the same iSCSI
        node to use multiple addresses.  iSCSI nodes also have addresses. An
        iSCSI address specifies a single path to an iSCSI node.
     
        - iSCSI Initiator Node: The "initiator".
     
     
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        - iSCSI Target Node: The "target".
     
        - Alias: An alias string could also be associated with an iSCSI Node.
        The alias allows an organization to associate a user-friendly string
        with the iSCSI Name. However, the alias string is not a substitute
        for the iSCSI Name.
     
        - 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 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).
     
        - SCSI Device: This is the SAM2 term for an entity that contains
        other SCSI entities.  For example, a SCSI Initiator Device contains
        one or more SCSI Initiator Ports and zero or more application
        clients; a SCSI Target Device contains one or more SCSI Target Ports
        and one or more logical units. For iSCSI, the SCSI Device is the
        component within an iSCSI Node that provides the SCSI functionality.
        As such, there can be at most one SCSI Device within a given iSCSI
        Node. Access to the SCSI Device can only be achieved in an iSCSI
        normal operational session. The SCSI Device Name is defined to be the
        iSCSI Name of the node and its use is mandatory in the iSCSI
        protocol.
     
        - SCSI 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 SCSI
        Initiator Port and SCSI Target Port are different.
     
        - SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
        operational session. An iSCSI normal operational session is
        negotiated through the login process between an iSCSI initiator node
        and an iSCSI target node. At successful completion of this process, a
        SCSI Initiator Port is created within the SCSI Initiator Device. The
        SCSI Initiator Port Name and SCSI Initiator Port 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 Target Port: This maps to an iSCSI Target Portal Group.
     
     
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        - SCSI Port Name: A name made up as UTF-8 characters and is basically
        the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.
     
        - SCSI Target Port Name and SCSI Target Port Identifier: These are
        both defined to be the iSCSI Target Name together with (a) a label
        that identifies it as a target port name/identifier and (b) the
        portal group tag.
     
        - 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 initiator to target, while inbound or incoming
        transfers are from target to initiator.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     2. Overview
     
     2.1 SCSI Concepts
     
        The SCSI Architecture Model-2 [SAM2] describes in detail the
        architecture of the SCSI family of I/O protocols. This section
        provides a brief background to familiarize readers with the
        terminology of the SCSI architecture.
     
        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
        individual 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
        service from a logical unit. The "device server" on the logical unit
        accepts SCSI commands and processed them.
     
        A "SCSI transport" maps the client-server SCSI protocol to a specific
        interconnect. Initiators are one endpoint of a SCSI transport. The
        "target" is the other endpoint. A target can contain multiple Logical
        Units (LUs). Each Logical Unit has an address within a target called
        a Logical Unit Number (LUN).
     
        A SCSI task is a SCSI command or possibly a linked set of SCSI
        commands. Some LUs support multiple pending (queued) tasks but the
        queue of tasks is managed by the target. The target uses an initiator
        provided "task tag" to distinguish between tasks. Only one command in
        a task can be outstanding at any given time.
     
        Each SCSI command results in an optional data phase and a required
        response phase. In the data phase, information can travel from the
        initiator to target (e.g., WRITE), target to initiator (e.g., READ),
        or in both directions. In the response phase, the target returns the
        final status of the operation, including any errors. A response
        terminates a SCSI command.
     
        Command Descriptor Blocks (CDB) is the data structure used to contain
        the command parameters that are to be handed by an initiator to a
        target. The CDB content and structure is defined by [SAM] and device-
        type specific SCSI standards.
     
     
     2.2 iSCSI Concepts and Functional Overview
     
     
     
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        The iSCSI protocol is a mapping of the SCSI remote procedure
        invocation model (see [SAM]) over the TCP protocol.
     
        In the rest of this document, the terms "initiator" and "target"
        refer to "iSCSI initiator node" and "iSCSI target node", respectively
        (see 2.5.1) 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 regard to the initiator.
        Outbound or outgoing transfers are transfers from initiator to
        target, while inbound or incoming transfers are from target to
        initiator.
     
        An iSCSI task is an iSCSI request for which a response is expected.
     
        In this document "iSCSI request", "iSCSI command", request or
        (unqualified) command have the same meaning.  Also, unless specified
        otherwise, status, response or numbered response have the same
        meaning.
     
     2.2.1 Layers and Sessions
     
        To specify initiator and target actions and how they relate to
        transmitted and received Protocol Data Units the following conceptual
        layering model is used:
     
           -the SCSI layer builds/receives SCSI CDBs (Command Descriptor
           Blocks) and relays/receives them with the remaining command
           execute parameters (cf. SAM2) to/from ->
           -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 2.5.2). A session is defined by a session ID that is composed
     
     
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        of an initiator part and a target part. TCP connections can be added
        and removed from a session.  Connections within a session are
        identified by a connection ID (CID).
     
        Across all connections within a session, an initiator sees one
        "target image". All target identifying elements, like LUN, are the
        same. In addition, across all connections within a session, a target
        sees one "initiator image". Initiator identifying elements like the
        Initiator Task Tag, can be used to identify the same entity
        regardless of the connection on which they are sent or received.
     
        iSCSI targets and initiators MUST support at least one TCP connection
        and MAY support several connections in a session. For error recovery
        purposes even targets and initiators supporting 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 sequencing
        scheme.
     
        Command numbering is session-wide and is used for ordered command
        delivery over multiple connections.  It can also be used as a
        mechanism for command flow control over a session.
     
        Status numbering is per connection and is used to enable missing
        status 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.
     
        Normally, 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 target
        and initiator.
     
     2.2.2.1 Command Numbering and Acknowledging
     
        iSCSI supports ordered command delivery within a session.  All
        commands (initiator-to-target PDUs) are numbered.
     
        Many SCSI activities are related to a task (SAM2). The task is
        identified by the Initiator Task Tag for the life of the task.
     
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        Commands in transit from the initiator to the target layer are
        numbered by iSCSI; the number is carried by the iSCSI PDU as CmdSN
        (Command-Sequence-Number).  The numbering is session-wide.  Outgoing
        iSCSI request PDUs  carry this number. The iSCSI initiator allocates
        CmdSNs with a 32-bit unsigned counter (modulo 2**32). Comparisons and
        arithmetic on CmdSN SHOULD use Serial Number Arithmetic as defined in
        [RFC1982] where SERIAL_BITS = 32.
     
        Commands meant for immediate delivery are marked as such through an
        immediate delivery flag. They too carry CmdSN, but CmdSN does not
        advance for commands marked for immediate delivery.
     
        Command numbering starts with the first login request on the first
        connection of a session (the leading login on the leading connection)
        and includes every non-immediate command issued afterwards.
     
        If immediate delivery is used with task management commands, these
        commands may reach the target task management before the tasks they
        are supposed to act upon.  However, their CmdSN is a marker of their
        position in the stream of commands.  The task management command MUST
        carry the CmdSN that would be given to the next non-immediate
        command.  The initiator and target must ensure that the task
        management commands act as specified by SAM2 - i.e., both commands
        and responses appear as if delivered in order.
     
        Not covered in this document are the means by which one may request
        immediate delivery for a command or by which iSCSI will decide by
        itself to mark a PDU for immediate delivery.
     
        Please note that the number of commands used for immediate delivery
        is not limited and their delivery to execution is not acknowledged
        through the numbering scheme.  Immediate commands can be rejected by
        the iSCSI target due to 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 request per connection at any
        time.
     
        Except for 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 command for execution if so
        required by some prior SCSI or iSCSI action (e.g., clear task set
        Task Management request received before all the commands it was
        supposed to act on).  Delivery for execution means delivery to the
     
     
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        SCSI execution engine or an iSCSI-SCSI protocol specific execution
        engine (e.g., for text requests).
     
        The initiator and target are assumed to have three registers, unique
        session wide, that define the numbering mechanism:
     
            - CmdSN - the current command Sequence Number advanced by 1 on
           each command shipped except for commands marked for immediate
           delivery.
            - ExpCmdSN - the next expected command by the target. The
           target acknowledges all commands up to but not including this
           number and 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 is able to deliver for
           execution plus 1 (no holes in the CmdSN sequence).
            - MaxCmdSN - the maximum number to be shipped. The queuing
           capacity of the receiving iSCSI layer is MaxCmdSN - ExpCmdSN +
           1.
     
        ExpCmdSN and MaxCmdSN are derived from target-to-initiator PDU
        fields.
     
        MaxCmdSN and ExpCmdSN fields are processed as follows:
     
           -if the PDU MaxCmdSN is less than the PDU ExpCmdSN-1 (in Serial
           Arithmetic Sense and with a difference bounded by 2**31-1),
           they are both ignored
           -if the PDU MaxCmdSN is less than the local MaxCmdSN (in Serial
           Arithmetic Sense and with a difference bounded by 2**31-1), it
           is ignored; else it updates the local MaxCmdSN
           -if the PDU ExpCmdSN is less than the local ExpCmdSN (in Serial
           Arithmetic Sense and with a difference bounded by 2**31-1), it
           is ignored; else it updates the local ExpCmdSN
     
        This sequence is required as updates may arrive out of order because
        they travel on different TCP connections.
     
        The target MUST NOT transmit a MaxCmdSN that is more than 2**31 - 1
        above the last ExpCmdSN.  For non-immediate commands, the CmdSN field
        can take any value from ExpCmdSN to MaxCmdSN. The target MUST
        silently ignore any non-immediate command outside this range or non-
        immediate duplicates within the range that have not been flagged with
        the retry bit (the X bit in the opcode).
     
     
     
     
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        iSCSI initiators and targets MUST support the command numbering
        scheme.
     
        A numbered iSCSI request will not change its allocated CmdSN
        regardless of the number of times and circumstances in which it is
        reissued.  At the target, it is assumed that CmdSN is relevant only
        while the command has not created any execution state (can't find the
        Initiator Task Tag).  Afterwards CmdSN becomes irrelevant.  Testing
        for execution state 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 execution state is found.
     
        A target MUST NOT issue a command response or DATA-In PDU with status
        before acknowledging the command. However, the acknowledgement can be
        included in the response or Data-in PDU itself.
     
     2.2.2.2 Response/Status Numbering and Acknowledging
     
        Responses in transit from the target to the initiator are numbered.
        The StatSN (Status Sequence Number) is used for this purpose. StatSN
        is a counter maintained per connection.  ExpStatSN is used by the
        initiator to acknowledge status.
     
        Status numbering starts with the Login response to the first Login
        request (C=0) of the connection. The Login response includes an
        initial value for status numbering.
     
        To enable command recovery the target MAY maintain enough state
        information to enable data and status recovery after a connection
        failure.  A target can discard all the state information maintained
        for recovery after the status delivery is acknowledged through
        ExpStatSN.
     
        A large difference between StatSN and ExpStatSN may indicate a failed
        connection. Initiators MUST undertake recovery actions if the
        difference is greater than 2**31-1.
     
        Initiators and Targets MUST support the response-numbering scheme.
     
     2.2.2.3 Data Sequencing
     
        Data and R2T PDUs, transferred as part of some command execution,
        MUST be sequenced. The DataSN field is used for data sequencing. For
        input (read) data PDUs DataSN starts with 0 for the first data PDU of
        an input command and advances by 1 for each subsequent data PDU.  For
        output data PDUs, DataSN starts with 0 for the first data PDU of a
        sequence (the initial unsolicited sequence or any data PDU sequence
     
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        issued to satisfy an R2T) and advances by 1 for each subsequent data
        PDU. R2Ts are also sequenced per command - i.e. the first R2T has an
        R2TSN of 0 and advances by 1 for each subsequent R2T. Unlike command
        and status, the data PDUs and R2Ts are not acknowledged except as
        implied by status. The DataSN/R2TSN field is meant to enable the
        initiator to detect missing data PDUs and simplify this operation at
        the target.
     
        For any given write command a target must have issued less than
        2**32-1 R2Ts. Any input or output data sequence MUST contain less
        than 2**32-1 numbered PDUs.
     
     
     2.2.3 iSCSI Login
     
        The purpose of the iSCSI login is to enable a TCP connection for
        iSCSI use, authenticate the parties, negotiate the session's
        parameters, open a security association protocol, and mark the
        connection as belonging to an iSCSI session.
     
        A session is used to identify to a target all the connections with a
        given initiator that belong to the same I_T nexus (See 2.5.2 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
        connecting to one of these TCP ports.
     
        As part of the login process, the initiator and target MAY wish to
        authenticate each other and set a security association protocol for
        the session. This can occur in many different ways and is subject to
        negotiation.
     
        In order to protect the TCP connection, an IPSec security association
        MAY be established before the Login request. Using IPSec security for
        iSCSI is specified in chapter 10 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
        commands. How the target chooses to authorize an initiator is beyond
        the scope of this document. A more detailed description of the Login
        Phase can be found in chapter 5.
     
     
     
     
     
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        The login PDU includes a session ID that is composed of an initiator
        part ISID and a target part TSID. For a new session, the TSID is
        null. As part of the response, the target generates a TSID.
     
        During session establishment, the target identifies the SCSI
        initiator port (the "I" in the "I_T nexus") through the value pair
        InitiatorName and ISID (InitiatorName is described later in this
        part). Any persistent state (e.g., persistent reservations) on the
        target 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 2.5.1) and internally in an implementation
        dependent way. As ISID is used to identify persistent state, it is
        subject to reuse restrictions (see 2.5.3).
     
        Before full feature phase is established, only Login PDUs are
        allowed. Any other PDU, when received at initiator or target, is a
        protocol error and MUST result in the connection being terminated.
     
     
     2.2.4 Text Mode Negotiation
     
        During login and thereafter some session or connection parameters are
        negotiated through an exchange of textual information.
     
        In "list" negotiation, the offering party sends for each key a list
        of values (which may include "none") in its order of preference.
     
        The responding party answers with the first value from the list it
        supports and is allowed to use for the specific initiator.
     
        The value "none" MUST always be used to indicate a missing function.
        However, none is a valid selection only if it is explicitly offered.
     
        If a target is not supporting, or not allowed to use with a specific
        initiator, any of the offered options, it may use the value "reject".
        The values "none" and "reject" are reserved and must be used only as
        described here.  Any key not understood is answered with
        "NotUnderstood".
     
        The general format of text negotiation is:
     
           Offer-> <key>=<value1>,<value2>,...,<valuen>
           Answer-> <key>=<valuex>|reject|NotUnderstood
     
     
     
     
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        In "numerical" negotiations, the offering and responding party state
        a numerical value. The result of the negotiation is key dependent;
        frequently the lower or the higher of the two values is used.
     
        For numerical negotiations, the responding party MUST respond with
        the required key.
     
        Binary negotiations (for keys taking the values yes or no) are a
        restricted form of numerical negotiations and the result is a key
        dependent Boolean function of the two inputs. The negotiation MAY
        proceed only up to the point where both parties can unequivocally
        compute the result; continuing beyond this point is OPTIONAL (e.g.,
        if the function is AND and one of the parties says "no" then this may
        end the negotiation).
     
        The value "?" with any key has the meaning of enquiry and should be
        answered with the current value or "NotUnderstood".
     
        The target may offer key=value pairs of its own. Target requests are
        not limited to matching key=value pairs as offered by the initiator.
        However, only the initiator can initiate the negotiation start
        (through the first Text request) and completion (by setting to 1 and
        keeping to 1 the F bit in a Text request).
     
     2.2.5 iSCSI Full Feature Phase
     
        Once the initiator is authorized to do so, the iSCSI session is in
        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 the
        session is in full feature phase and the connection login has
        completed successfully. An iSCSI connection is not in full feature
        phase a) either 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 on it or the connection is
        currently logged out.  In normal full feature phase the initiator may
        send SCSI commands and data to the various LUs on the target by
        wrapping them in iSCSI PDUs that go over the established iSCSI
        session.
     
        For an iSCSI request issued over a TCP connection, the corresponding
        response and/or requested PDU(s) MUST be sent over the same
        connection by default. We call this "connection allegiance". If the
        original connection 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
        8.1.
     
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        As an illustration of the above rule, SCSI commands that require data
        and/or parameter transfer, the (optional) data and the status for a
        command MUST be sent over the same TCP connection to which the SCSI
        command is currently allegiant.
     
        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 and 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) as well as 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
        commands, their SCSI Data and responses, over the session.
     
        Outgoing SCSI data (initiator to target user data or command
        parameters) is sent as either solicited data or unsolicited data.
        Solicited data is sent in response to R2T PDUs. Unsolicited data can
        be sent as part of an iSCSI command PDU ("immediate data") or in
        separate iSCSI data PDUs.  An initiator may send unsolicited data as
        immediate up to the negotiated maximum PDU size or in a separate PDU
        sequence (up to the mode page limit). All subsequent data MUST be
        solicited.  The maximum size of an individual data PDU or the
        immediate-part of the first unsolicited burst MAY be negotiated at
        login.  FirstBurstSize is an iSCSI specific mode page value that can
        be set and enquired according with SCSI commands.
     
        Targets operate in either solicited (R2T) data mode or unsolicited
        (non R2T) data mode.  In unsolicited mode, an initial R2T allowing
        transfer up to the FirstBurstSize is implied. A target MAY separately
        enable immediate data without enabling the more general (separate
        data PDUs) form of unsolicited data.
     
        An initiator SHOULD honor an R2T data request for a valid outstanding
        command (i.e., carrying a valid Initiator Task Tag) provided the
        command is supposed to deliver outgoing data and the R2T specifies
        data within the command bounds.
     
     
     
     
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        It is considered an error for an initiator to send unsolicited data
        PDUs to a target operating in R2T mode (only solicited data is
        allowed).  It is also an error for an initiator to send more data,
        whether immediate or as separate PDUs, than the SCSI limit for first
        burst.  At login, an initiator MAY request to send data blocks and a
        first burst of any size; in this case, the target MUST indicate the
        size of the first burst and of the immediate and data blocks that it
        is ready to accept.  The agreed upon limits for the first burst as
        well as the maximum data PDU are recorded in (and are retrievable
        from) the disconnect-reconnect mode page.
     
        A target SHOULD NOT silently discard data and request retransmission
        through R2T.  Initiators SHOULD NOT do any scoreboarding for data -
        targets perform residual count calculation.  Incoming data for
        initiators is always implicitly solicited. SCSI data packets are
        matched to their corresponding SCSI commands by using Tags that are
        specified in the protocol.
     
        Initiator tags for pending commands are unique initiator-wide for a
        session.  Target tags are not strictly specified by the protocol. It
        is assumed that these tags are used by the target to tag (alone or in
        combination with the LUN) the solicited data. Target tags are
        generated by the target and "echoed" by the initiator. The above
        mechanisms are designed to accomplish efficient data delivery and a
        large degree of control over the data flow.
     
        iSCSI initiators and targets MUST also enforce some ordering rules to
        achieve deadlock-free operation.  Unsolicited data MUST be sent on
        every connection in the same order in which commands were sent. A
        target receiving data out of order SHOULD terminate the session.
     
     2.2.6 iSCSI Connection Termination
     
        Connection termination is assumed to be an exceptional event.
        Graceful TCP connection shutdowns are done by sending TCP FINs.
        Graceful connection shutdowns MUST only occur when there are no
        outstanding tasks that have allegiance to the connection and when the
        connection is not in full-feature phase.  A target SHOULD respond
        rapidly to a FIN from the initiator by closing its half of the
        connection after waiting for all outstanding commands that have
        allegiance to the connection to conclude and send their status.
        Connection termination with outstanding commands may require recovery
        actions.
     
        Connection termination is also required as a prelude to recovery.  By
        terminating a connection before starting recovery, the initiator and
     
     
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        target can avoid having stale PDUs being received after recovery.  In
        this case, the initiator sends a Logout request on any of the
        operational connections of a session indicating what connection
        should be terminated.
     
        Logout can also be issued by an initiator at the explicit request of
        a target (through an Asynchronous Message PDU) or  the connection can
        be autonomously terminated by the target after announcing it to the
        initiator (through an Asynchronous Message PDU).
     
     
     2.2.7 Naming and Addressing
     
        All iSCSI initiators and targets are named.  Each target or initiator
        is known by an iSCSI Name.  The iSCSI Name is independent of the
        location of the initiator and target; two formats are provided that
        allow the use of existing naming authorities when generating them.
        One of these formats allows the use of a registered domain name as a
        naming authority; it is important not to confuse this with an
        address.  The iSCSI Name is a UTF-8 text string, and is defined in
        [NDT].
     
        iSCSI Names are used to provide:
     
           - an initiator identifier for configurations that provide
           multiple initiators behind a single IP address
           - a target identifier for configurations that present multiple
           targets behind a single IP address and port.
           - a method to recognize multiple paths to the same device on
           different IP addresses and ports.
           - an identifier for source and destination targets for use in
           third party commands.
           - an identifier for initiators and targets to enable them to
           recognize each other regardless of IP address and port mapping
           on intermediary firewalls.
     
        The initiator MUST present both its iSCSI Initiator Name and the
        iSCSI Target Name to which it wishes to connect in the first login
        request of a new session.  The only exception is if a discovery
        session (see 2.4) is to be established; the iSCSI Initiator Name is
        still required, but the iSCSI Target Name may be ignored.  The key
        "SessionType=discovery" is sent by the initiator at login to indicate
        a discovery session.
     
        The default name "iSCSI" is reserved, and is not used as an
        individual initiator or target name.
     
     
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        iSCSI Names do not require special handling within iSCSI layer; they
        are opaque and case-sensitive for the purposes of comparison.
     
        Examples of iSCSI Names:
     
           iqn.1998-03.com.disk-vendor.diskarrays.sn.45678
           iqn.2000-01.com.gateways.yourtargets.24
           iqn.1987-06.com.os-vendor.plan9.cdrom.12345
           iqn.2001-03.com.service-provider.users.customer235.host90
           eui.02004567A425678D
     
        iSCSI nodes also have addresses.  An iSCSI address specifies a single
        path to an iSCSI node.
     
           <domain-name>[:<port>]
     
        Where <domain-name> is one of:
     
           - IPv4 address, in dotted decimal notation.  Assumed if the
           name contains exactly four numbers, separated by dots (.),
           where each number is in the range 0..255.
           - IPv6 address, in colon-separated hexadecimal notation, as
           specified in [RFC2373] and enclosed in "[" and "]" characters,
           as specified in [RFC2732].
           - Fully Qualified Domain Name (host name).  Assumed if the
           <domain-name> is neither an IPv4 nor an IPv6 address.
     
        For iSCSI targets, the <port> in the address is optional; if
        specified it is the TCP port on which the target is listening for
        connections.  If the <port> is not specified, a default port, to be
        assigned by IANA, will be assumed.  For iSCSI initiators, the <port>
        is omitted.
     
        Examples of addresses:
     
           10.40.1.2
           [FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
           [FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
           [1080:0:0:0:8:800:200C:417A]
           [3ffe:2a00:100:7031::1]
           [1080::8:800:200C:417A]
           [::192.9.5.5]
           mydisks.example.com
     
     
     
     
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        To assist in providing a more human-readable user interface for
        devices containing iSCSI targets and initiators, a target or
        initiator may also provide an alias.  This alias is a simple UTF-8
        string, is not globally unique, and is never interpreted or used to
        identify an initiator or device within the iSCSI protocol.  Its use
        is described in [NDT].
     
        Third party commands require that protocol-specific addresses be
        communicated within SCSI CDBs.  The iSCSI protocol-specific address
        consists of an iSCSI name, or an iSCSI name + TCP address.
     
        An initiator may discover the iSCSI Target Names to which it has
        access, along with their addresses, using the SendTargets text
        request, or by other techniques discussed in [NDT].
     
     2.2.8 Persistent State
     
        iSCSI does not require any persistent state maintenance across
        sessions. However, SCSI requires, in some cases, persistent
        identification of the SCSI initiator port name (for iSCSI, the
        InitiatorName plus the ISID of the session) (See 2.5.2 and 2.5.3).
     
        iSCSI sessions do not persist through power cycles and boot
        operations.
     
        All iSCSI session and connection parameters are reinitialized on
        session and connection creation.
     
        Commands persist beyond connection termination if the session
        persists and command recovery within session is supported.  However
        command execution as perceived by iSCSI (i.e., involving iSCSI
        protocol exchanges for the affected task) is suspended when a
        connection is dropped until a new allegiance is established by the
        'task reassign' task management function (section 3.5)
     
     2.2.9 Message Synchronization and Steering
     
     2.2.9.1 Rationale
     
        iSCSI presents a mapping of the SCSI protocol onto TCP.  This
        encapsulation is accomplished by sending iSCSI PDUs that are of
        varying length. Unfortunately, TCP does not have a built-in mechanism
        for signaling message boundaries at the TCP layer.  iSCSI overcomes
        this obstacle by placing the message length in the iSCSI message
        header. This serves to delineate the end of the current message as
        well as the beginning of the next message.
     
     
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        In situations where IP packets are delivered in order from the
        network, iSCSI message framing is not an issue; messages are
        processed one after the other. In the presence of IP packet
        reordering (e.g., 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 application buffers.  In iSCSI it is desirable to steer the SCSI
        data within these out of order TCP segments into the pre-allocated
        SCSI buffers rather than store them in temporary buffers. This
        decreases the need for 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
        boundaries in subsequent TCP segments due to the loss of a TCP
        segment containing the iSCSI message length. The missing TCP
        segment(s) must be received before any of the following segments can
        be steered to the correct SCSI buffers (due to the inability to
        determine the iSCSI message boundaries).  Since these segments cannot
        be steered to the correct location, they must be saved in temporary
        buffers that must then be copied to the SCSI buffers.
     
        Different schemes can be used to recover synchronization. One of
        these schemes is detailed in an Appendix C.  To make those schemes
        work iSCSI implementations have to make sure that the appropriate
        protocol layers are provided with enough information to implement a
        synchronization and/or data steering mechanism.
     
     2.2.9.2 Synchronization (sync) and Steering Functional Model
     
        We assume that iSCSI is implemented according to the following
        layering 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. Note that an implementation may choose to place
        Sync and Steering somewhere else in the stack if it can translate the
        information kept by iSCSI in terms valid for the chosen layer.
     
        According to our model of layering, 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
        infinitely 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 doe not need to examine the stream content to discover the PDU
        boundaries. If a specific implementation does 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
        understandable to the Sync and Steering Layer.
     
        The Sync and Steering Layer (which itself 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,
        additional information including identifying tags and buffer offsets
        MUST also be retained for every sent PDU. The Sync and Steering Layer
     
     
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        is required to add to every sent data item (IP packet, TCP packet or
        some other superstructure) enough information 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
        transmission stream is built statically, the Sync and Steering
        information is inserted in the transmission stream.
     
        The retained information can be released whenever the transmitted
        data is acknowledged by the receiver (in 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
        outgoing 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. Then it helps steer
        (place) the data stream to its final location and/or recover iSCSI
        PDU boundaries when some TCP packets are lost or received out of
        order.  The data stream seen by the receiving iSCSI layer is
        identical to the data stream that left the sending iSCSI layer.  The
        Sync and Steering information is kept until the PDUs it refers to 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
        placements, 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
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     2.2.9.3 Sync and Steering and Other Encapsulation Layers
     
     
        We recognize that in many environments the following is a more
        appropriate layering model:
     
             +----------------------------------+
             |             SCSI                 |
             +----------------------------------+
             |            iSCSI                 |
             +----------------------------------+
             |   Upper Functional Layers (UFL)  |
             +----------------------------------+
             |     Sync and Steering            |
             |  +-----------------------------+ |
             |  |            TCP              | |
             |  +-----------------------------+ |
             +----------------------------------+
             |   Lower Functional Layers (LFL)  |
             +----------------------------------+
             |              IP                  |
             +----------------------------------+
             |             Link                 |
             +----------------------------------+
     
        In this model, UFL can be TLS (see[RFC2246]) or some other transport
        conversion mechanism (a mechanism changing the TCP stream but
        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
        has to be left out of any UFL transformation (encryption,
        compression, 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
        perform on the stream.
     
        This makes implementation of Sync and Steering in the presence of
        otherwise opaque UFLs less attractive.
     
     2.2.9.4 Sync/Steering and iSCSI PDU Size
     
        When a large iSCSI message is sent, the TCP segment(s) that contain
        the iSCSI header may be lost.  The remaining TCP segment(s) up to the
        next iSCSI message need to be buffered (in temporary buffers) since
        the iSCSI header that indicates what SCSI buffers the data is to be
     
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        steered to was lost.  To minimize the amount of buffering, it is
        recommended that the iSCSI PDU size be restricted to a small value
        (perhaps a few TCP segments in length). During login, each end of the
        iSCSI session specifies the maximum size of an iSCSI PDU it will
        accept.
     
     2.3 Third Party Commands
     
        SCSI allows every addressable entity to be either an initiator or a
        target. In host-to-host communication, each such entity can take on
        the initiator role.  In typical I/O operations between a host and a
        peripheral subsystem, the host plays the initiator role and the
        peripheral subsystem plays the target role.
     
        For EXTENDED COPY and other third party SCSI commands, that involve
        device-to-device communication, such as (EXTENDED) COPY and COMPARE,
        SCSI defines a copy-manager. The copy-manager takes on the role of
        initiator in the device-to-device communication.  The copy-manager is
        the "original-target" of the command and acts as initiator for a
        (variable) number of the devices, which are called sources and
        destinations. Sources and destinations act as targets.
        The copy operation is described in one CDB to the copy-manager, along
        with a series of descriptor blocks.  Each descriptor block addresses
        source and destination target, LU, and a description of the work to
        be done in terms of blocks or bytes as required by the device types.
        The relevant SCSI standards do not require full support of the
        (EXTENDED) COPY or COMPARE, nor do they provide a detailed execution
        model.
     
     2.4 iSCSI session types
     
        iSCSI defines two types of sessions:
     
                normal operational session - an unrestricted session
                discovery-session - a session opened only for target
                discovery; the target MAY accept only text requests with
                the SendTargets key
     
        The session type is defined during login with key=value parameter in
        the login command.
     
     2.5 SCSI to iSCSI concepts mapping model
     
        The following diagram shows an example of how multiple iSCSI Nodes
        (targets in this case) can co-exist within the same Network Entity
        and can share Network Portals (IP addresses and TCP ports).  Other
     
     
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        more complex configurations are also possible. Detailed descriptions
        of the components of these diagrams are given in 2.5.1.
     
                      +-----------------------------------+
                      |  Network Entity (iSCSI Client)    |
                      |                                   |
                      |         +-------------+           |
                      |         | iSCSI Node  |           |
                      |         | (Initiator) |           |
                      |         +-------------+           |
                      |            |       |              |
                      | +--------------+ +--------------+ |
                      | |Network Portal| |Network Portal| |
                      | |   10.1.30.4  | |   10.1.40.6  | |
                      +-+--------------+-+--------------+-+
                               |               |
                               |  IP Networks  |
                               |               |
                      +-+--------------+-+--------------+-+
                      | |Network Portal| |Network Portal| |
                      | |  10.1.30.21  | |   10.1.40.3  | |
                      | |  TCP Port 4  | |  TCP Port 4  | |
                      | +--------------+ +--------------+ |
                      |        |               |          |
                      |        -----------------          |
                      |           |         |             |
                      |  +-------------+ +--------------+ |
                      |  | iSCSI Node  | | iSCSI Node   | |
                      |  |  (Target)   | |  (Target)    | |
                      |  +-------------+ +--------------+ |
                      |                                   |
                      |   Network Entity (iSCSI Server)   |
                      +-----------------------------------+
     
     2.5.1 iSCSI Architectural Model
     
        This section describes that part of the iSCSI architecture model that
        has the most bearing on the relationship between iSCSI and the SCSI
        Architecture Model.
     
     
     
     
     
     
     
     
     
     
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                a) 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 (see
                item (c)), each of which is usable by some iSCSI Nodes
                (see item (b)) contained in that Network Entity to gain
                access to the IP network.
     
                b) iSCSI Node - The iSCSI Node represents a single iSCSI
                initiator or iSCSI target.  There are one or more iSCSI
                Nodes within a Network Entity.  The iSCSI Node is
                accessible via one or more Network Portals (see item (c)).
                An iSCSI Node is identified by its iSCSI Name (see 2.2.7
                and Appendix D).  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.
     
                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.
     
                c) Network Portal - The Network Portal is a component of a
                Network Entity that has a TCP/IP network address and that
                may be used by an iSCSI Node within that Network Entity
                for the connection(s) within one of its iSCSI sessions.  A
                Network Portal in an initiator is identified by its IP
                address.  A Network Portal in a target is identified by
                its IP address and its listening TCP port.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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                d) Portal Groups - iSCSI supports multiple connections
                within the same session; some implementations will have
                the ability to combine 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 session with
                connections spanning these portals.  Not all Network
                Portals within a Portal Group need participate in every
                session connected through that Portal Group.  One or more
                Portal Groups may provide access to an iSCSI Node.  Each
                Network Portal as utilized by a given iSCSI Node belongs
                to exactly one portal group within that node. Portal
                Groups are identified within an iSCSI Node by a portal
                group tag, a simple integer value between 1 and 65535 (see
                SendTargets in Appendix D, item 11).  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 Appendix E).  See 9.1.1 for references to the
                Initiator Portal Groups.
     
                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
                2.5.3.2 SCSI Mode Pages)
     
        The following diagram shows an example of one such configuration on a
        target and how a session may be established that shares Network
        Portals within a Portal Group.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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           ----------------------------IP Network---------------------
                 |               |                    |
        +--------|---------------|--------------------|---------------------+
        |   +----|---------------|-----+         +----|---------+           |
        |   | +---------+  +---------+ |         | +---------+  |           |
        |   | | Network |  | Network | |         | | Network |  |           |
        |   | | Portal  |  | Portal  | |         | | Portal  |  |           |
        |   | +--|------+  +---------+ |         | +---------+  |           |
        |   |    |               |     |         |    |         |           |
        |   |    |    Portal     |     |         |    | Portal  |           |
        |   |    |    Group 1    |     |         |    | Group 2 |           |
        |   +--------------------------+         +--------------+           |
        |        |               |                    |                     |
        |   +----------------------------+  +-----------------------------+ |
        |   | iSCSI Session (Target side)|  | iSCSI Session (Target side) | |
        |   |                            |  |                             | |
        |   |  (iSCSI Name + TSID=2)     |  | (iSCSI Name + TSID=1)       | |
        |   +----------------------------+  +-----------------------------+ |
        |                                                                   |
        |                      iSCSI Target Node                            |
        |              (within Network Entity, not shown)                   |
        +-------------------------------------------------------------------+
     
     2.5.2 SCSI Architecture Model
     
        This part describes the relationship between the SCSI Architecture
        Model [SAM2] constructs of 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 2.5.3.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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           a) SCSI Device - This is the SAM2 term for an entity that
           contains other SCSI entities.  For example, a SCSI Initiator
           Device contains one or more SCSI Initiator Ports and zero or
           more application clients; a SCSI Target Device contains one or
           more SCSI Target Ports and one or more logical units.  For
           iSCSI, the SCSI Device is the component within an iSCSI Node
           that provides the SCSI functionality.  As such, there can be at
           most one SCSI Device within a given iSCSI Node.  Access to the
           SCSI Device can only be achieved in an iSCSI normal operational
           session (see 2.4).  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 - 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 SCSI Initiator Port and SCSI Target Port are
           different.
     
           SCSI Initiator Port: this maps to the endpoint of an iSCSI
           normal operational session (see 2.4).  An iSCSI normal
           operational session is negotiated through the login process
           between an iSCSI initiator node and an iSCSI target node.  At
           successful completion of this process, a SCSI Initiator Port is
           created within the SCSI Initiator Device.  The SCSI Initiator
           Port Name and SCSI Initiator Port 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 Target Port: this maps to an iSCSI target Portal Group.
           The SCSI Target Port Name and the SCSI Target Port Identifier
           are both defined to be the iSCSI Target Name together with (a)
           a label that identifies it as a target port name/identifier and
           (b) the portal group tag.
     
           The SCSI Port Name is mandatory in iSCSI.  When used in SCSI
           parameter data, the SCSI port name shall be formatted as
           - the iSCSI Name in UTF-8 format, followed by
           - a null terminator (1byte), followed by
           - the ASCII character 'i' (for SCSI Initiator Port) or the
           ASCII character 't' (for SCSI Target Port), followed by
           - a null terminator (1byte), followed by
           - zero to 3 null pad bytes so that the complete format is a
           multiple of 4 bytes long, followed by
     
     
     
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           - the 2byte value of ISID (for SCSI initiator port) or portal
           group tag (for SCSI target port)in network byte order
           (BigEndian).
              SCSI port names have a maximum length of 260 bytes and must
              be     a multiple of 4 bytes long.  The ASCII character 'i'
              or 't' is       the label that identifies this as either a
              SCSI Initiator Port     or a SCSI Target Port name, and so
              also provides the interpretation of the value of the final
              two bytes as either an     ISID or a portal group tag.
     
           c) 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 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).
     
     
     2.5.3 Consequences of the model
     
        This section describes implementation and behavioral requirements
        that result from the mapping of SCSI constructs to iSCSI constructs
        defined above.  Two assumptions are at the basis of the requirements
        stated here.
     
                a) Between a given iSCSI Initiator and iSCSI Target, at
                any given    time there can exist only one session with a
                given session identifier (SSID).
     
                b) Between a given SCSI initiator port and SCSI target
                port, there can be only one I_T nexus (session); that is,
                no more than one nexus relationship (parallel nexus) is
                allowed.
     
        These assumptions lead to the following conclusions and requirements.
     
        ISID RULE: Between a given iSCSI Initiator and iSCSI Target Portal
        Group (SCSI target port), then can be only one session with a given
        ISID (identifying a SCSI initiator port).  See 3.12.8.
     
     
     
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        The iSCSI Initiator Node is expected to manage the assignment of
        ISIDs prior to session initiation. The "ISID rule" does not preclude
        the use of the same ISID from the same iSCSI Initiator with different
        Target Portal Groups on the same iSCSI target or on other iSCSI
        targets - this would be analogous to a single SCSI Initiator Port
        having conversations with multiple ports on the same target or ports
        on other targets.  It is also possible to have multiple sessions with
        different ISIDs to the same Target Portal Group.  The same ISID may
        be used by a different iSCSI Initiator, because it is the iSCSI Name
        together with the ISID that identifies the SCSI initiator port.
     
        NOTE: A consequence of the ISID RULE and the specification for the
        I_T nexus identifier, two nexuses with the same identifier should
        never occur.
     
        TSID RULE: The iSCSI Target SHALL NOT select a TSID for a given login
        request if the resulting SSID is already in use by an existing
        session between that the target and the requesting iSCSI Initiator.
        See 9.1.1.
     
     2.5.3.1 I_T nexus state
     
        Certain nexus relationships contain explicit state (e.g., initiator-
        specific mode pages or reservation state) that may need to be
        preserved by the target (actually, the device server in a logical
        unit) through changes or failures in the iSCSI layer (e.g., session
        failures).  In order for that state to be restored, the iSCSI
        initiator should re-establish its session (re-login) to the same
        Target Portal Group using the previous ISID. That is, it should do
        session recovery as described in section 8.  This is because the SCSI
        initiator 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.
     
     2.5.3.2 SCSI Mode Pages
     
        If the SCSI logical unit device server does not maintain initiator-
        specific mode pages, and an initiator makes changes to port-specific
        mode pages, the changes may affect all other initiators logged in to
        that iSCSI Target through the same Target Portal Group.
     
        Changes via mode pages to the behavior of a portal group via one
        iSCSI node should not affect the behavior of this portal group with
        respect to other iSCSI Target Nodes, even if the underlying
        implementation of a portal group serves multiple iSCSI Target Nodes
        in the same Network Entity.
     
     
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     3. 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 appearing in this document assumes that the most
        significant byte is the lowest numbered byte and the most significant
        bit (within byte or field) is the highest numbered bit unless
        specified otherwise.
     
        Any bits not defined MUST be set to zero. Any reserved fields and
        values MUST be 0 unless specified otherwise.
     
     3.1 iSCSI PDU Length and Padding
     
        iSCSI PDUs are padded to an integer number of 4 byte words. The
        padding bytes SHOULD be 0.
     
     3.2 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 there MAY be a
        header-digest. The data segment MAY also be followed by a data-
        digest.
     
        The Basic Header Segment (BHS) is the first segment in all 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 a PDU is as follows:
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
        0 / Basic Header Segment (BHS)                                    /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48/ Additional Header Segment (AHS)  (optional)                   /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        ----
          +---------------+---------------+---------------+---------------+
         k/ Header-Digest (optional)                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
         l/ Data Segment(optional)                                        /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
         m/ Data-Digest (optional)                                        /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
        All PDU segments and digests are padded to an integer number of 4
        byte words. The padding bytes SHOULD be sent as 0.
     
     3.2.1 Basic Header Segment (BHS)
     
        The BHS is 48 bytes long.  The Opcode, TotalAHSLength and
        DataSegmentLength fields appear in all iSCSI PDUs. In addition, the
        Initiator Task Tag and Logical Unit Number when used, always appear
        in the same location in the header.
     
        The format of the BHS is:
     
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| Opcode    | Opcode-specific fields                        |
          +---------------+---------------+---------------+---------------+
         4|TotalAHSLength | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
     
     
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         8| LUN or Opcode-specific fields                                 |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag or Opcode-specific fields                  |
          +---------------+---------------+---------------+---------------+
        20/ Opcode-specific fields                                        /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48
     
     3.2.1.1 X
     
        For request PDUs (PDUs from initiator to target) the X bit set to 1
        is a Retry/Restart indicator. This bit is always 1 for response PDUs
        (PDUs from target to initiator).
     
     3.2.1.2 I
     
        For request PDUs the I bit set to 1 is an immediate delivery marker.
        This bit is always 1 for response PDUs (PDUs from target to
        initiator).
     
     3.2.1.3 Opcode
     
        The Opcode indicates what 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), and target opcodes are in PDUs sent by the target
        (response PDUs).
     
        Initiators MUST NOT use target opcodes and targets MUST NOT use
        initiator opcodes.
     
        Initiator opcodes defined in this specification are:
     
     
           0x00 NOP-Out
           0x01 SCSI Command (encapsulates a SCSI Command Descriptor
           Block)
           0x02 SCSI Task Management Function Request
           0x03 Login Command
           0x04 Text request
           0x05 SCSI Data-out (for WRITE operations)
           0x06 Logout Command
           0x10 SNACK Request
     
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           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.
     
     3.2.1.4 Opcode-specific Fields
     
        These fields have different meanings for different opcode types.
     
     3.2.1.5 TotalAHSLength
     
        Total length of all AHS header segments in 4 byte words including
        padding if any.
     
     3.2.1.6 DataSegmentLength
     
        This is the data segment payload length in bytes (excluding padding).
     
     3.2.1.7 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 either is ignored or may be
        used in an opcode specific way.  The LUN field is 64-bits and it is
        to be formatted in accordance with [SAM2].
     
     3.2.1.8 Initiator Task Tag
     
        The initiator assigns a Task Tag to each iSCSI task that it issues.
        While a task exists, this tag MUST uniquely identify it session-wide.
     
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        The initiator task tag may be used by SCSI too as part of the SCSI
        task identifier as the time span during which an iSCSI initiator task
        tag has to be unique extends over the time span during which a SCSI
        task tag has to be unique.  However, the iSCSI Initiator Task Tag has
        to exist and be unique even for untagged SCSI commands.
     
     3.2.2 Additional Header Segment (AHS)
     
        The general format of an AHS is:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0| AHSLength                     | AHSType       | AHS-Specific  |
          +---------------+---------------+---------------+---------------+
         4/ AHS-Specific                                                  /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
         x
     
     3.2.2.1 AHSType
     
        The AHSType field is coded as follows:
     
           bit 7 - Drop Bit - if set to 1 this AHS may be ignored if not
           understood; if set to 0 this AHS must be rejected if not
           understood.
           bit 6 - Reserved
           bit 5-0 - AHS code
               0 - Reserved
               1 - Extended CDB
               2 - Expected Bidirectional Read Data Length
               3-59 Reserved
               60-63 Non-iSCSI extensions
     
     
     3.2.2.2 AHSLength
     
        This field contains the effective length in bytes of the AHS
        excluding AHSType and AHSLength (not including padding). The AHS is
        padded to an integer number of 4 byte words.
     
     
     3.2.2.3 Extended CDB AHS
     
        The format of the Extended CDB AHS is:
     
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        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0| AHSLength (CDBLength-15)      | 0x01          | Reserved      |
          +---------------+---------------+---------------+---------------+
         4/ ExtendedCDB...+padding                                        /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
         x
     
     
     3.2.2.4 Bidirectional Expected Read-Data Length AHS
     
        The format of the Bidirectional Read Expected Data Transfer Length
        AHS is:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0| AHSLength (0x0005)            | 0x02          | Reserved      |
          +---------------+---------------+---------------+---------------+
         4| Expected Read-Data Length                                     |
          +---------------+---------------+---------------+---------------+
         8
     
     3.2.3 Header Digest and Data Digest
     
        Optional header and data digests protect the integrity of header and
        data, respectively. The digests, if present, are located,
        respectively, after the header and PDU-specific data and include 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-
        calculated.
     
        Digests are not included in data or header length fields.
     
        A zero-length Data Segment implies also a zero-length data-digest.
     
     
     
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     3.2.4 Data Segment
     
        The (optional) Data Segment contains PDU associated data. Its payload
        effective length is given in the BHS field - Data Segment Length and.
        The Data Segment is also padded to an integer number of 4 byte words.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.3 SCSI Command
     
        The format of the SCSI Command PDU is:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| 0x01      |F|R|W|0 0|ATTR | Reserved      | CRN or Rsvd   |
          +---------------+---------------+---------------+---------------+
         4|TotalAHSLength | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Logical Unit Number (LUN)                                     |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Expected Data Transfer Length                                 |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32/ SCSI Command Descriptor Block (CDB)                           /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| AHS (if any), Header Digest (if any)                          |
          +---------------+---------------+---------------+---------------+
          / DataSegment - Command Data (optional)                         /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
     3.3.1 Flags and Task Attributes (byte 1)
     
           The flags for a SCSI Command are:
     
           bit 7   (F) set to 1 when no unsolicited SCSI Data-Out PDUs
           follow this PDU.  For a write, if Expected Data Transfer Length
           is larger than the DataSegmentLength the target may solicit
           additional data through R2T.
           bit 6   (R) set to 1 when input data is expected
           bit 5   (W) set to 1 when output data is expected
           bit 4-3 Reserved
     
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           bit 2-0 contain Task Attributes
     
        The Task Attributes (ATTR) has 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
     
        Having both the W and the F bit set to 0 is an error.
        The R and W MAY both be 1 while the corresponding Expected Data
        Transfer Lengths are 0 but they MUST NOT both be 0 when the
        corresponding Expected Data Transfer Lengths are not 0.
     
     
     3.3.2 CRN
     
        SCSI command reference number - if present in the SCSI execute
        command arguments (according to [SAM2]).
     
     3.3.3 CmdSN - Command Sequence Number
     
        Enables ordered delivery across multiple connections in a single
        session.
     
     3.3.4 ExpStatSN
     
        Command responses up to ExpStatSN-1 (mod 2**32) have been received
        (acknowledges status) on the connection.
     
     3.3.5 Expected Data Transfer Length
     
        For unidirectional operations, the Expected Data Transfer Length
        field contains the number of bytes of data involved in this SCSI
        operation.  For a unidirectional write (W flag set to 1 and R flag
        set to 0) operation, the initiator uses this field to specify the
        number of bytes of data it expects to transfer for this operation.
        For a unidirectional read (W flag set to 0 and R flag set to 1)
        operation, the initiator uses this field to specify the number of
        bytes of data it expects the target to transfer to the initiator.  It
        corresponds to the SAM2 byte count.
     
        For bidirectional operations (both R and W flags are set to 1), this
        field contains the number of data bytes involved in the write
     
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        transfer. For bidirectional operations, an additional header segment
        MUST be present in the header sequence indicating 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
        immediate data part that follows the command (if any) are the same
        then no more data PDUs are expected to follow.  In this case, the F
        bit MUST be set to 1.
     
        If the Expected Data Transfer Length is higher than the
        FirstBurstSize (the negotiated maximum amount of unsolicited data the
        target will accept) the initiator SHOULD send the maximum size of
        unsolicited data.  The target MAY terminate in error a command for
        which the Expected Data Transfer Length is higher than the
        FirstBurstSize and for which the initiator sent less than
        FirstBurstSize unsolicited data.
     
        Upon completion of a data transfer, the target informs the initiator
        of how many bytes were actually processed (sent and/or received) by
        the target.  This is done through residual counts.
     
     3.3.6 CDB - SCSI Command Descriptor Block
     
        There are 16 bytes in the CDB field to accommodate the commonly used
        CDBs.  Whenever the CDB is larger than 16 bytes, an Extended CDB AHS
        MUST be used to contain the CDB spillover.
     
     3.3.7 Data Segment - Command Data
     
        Some SCSI commands require additional parameter data to accompany the
        SCSI command. This data may be placed beyond the boundary of the
        iSCSI header in a data segment.  Alternatively, user data (as from a
        WRITE operation) can be placed in the same PDU (both cases referred
        to as immediate data). Those data are governed by the general rules
        for solicited vs. unsolicited data.
     
     
     
     
     
     
     
     
     
     
     
     
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     3.4 SCSI Response
     
        The format of the SCSI Response PDU is:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x21      |1 0 0|o|u|O|U|0| Response      | Status        |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Reserved                                                      |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Residual Count                                                |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| ExpDataSN or Reserved                                         |
          +---------------+---------------+---------------+---------------+
        40| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        44| Bidirectional Read Residual Count                             |
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / Data Segment - Sense Data and Response Data (optional)        /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     3.4.1 Flags (byte 1)
     
           bit 7-5 Reserved
           bit 4   (o) same as bit 2 but for the read operation of a bi-
           directional operation
           bit 3   (u) same as bit 1 but for the read-part of a
           bidirectional operation
     
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           bit 2   (O) set for Residual Overflow. In this case, the
           Residual Count indicates how many bytes could not be
           transferred because the initiator's Expected Data Transfer
           Length was too small. For a bidirectional operation, contains
           the residual for the write operation.
           bit 1   (U) set for Residual Underflow. In this case, the
           Residual Count indicates how many bytes were not transferred
           out of those expected to be transferred. For a bidirectional
           operation, contains the residual for the write operation.
           bit 0   (0) Reserved
     
        Bits O and U are mutually exclusive and so are bits o and u.
        For a response other than "Command Completed at Target" bit 4-1 MUST
        be 0.
     
     3.4.2 Status
     
        The Status field is used to report the SCSI status of the command (as
        specified in [SAM2]) and is valid only if the Response Code is
        Command Completed at target.
     
        Some of the status codes defined in SAM2 are:
     
           0x00 GOOD
           0x02 CHECK CONDITION
           0x08 BUSY
           0x18 RESERVATION CONFLICT
           0x28 TASK SET FULL
           0x30 ACA ACTIVE
           0x40 TASK ABORTED
     
        See [SAM2] for the complete list and definitions.
     
        If a SCSI device error is detected while data from the initiator is
        still expected (the command PDU did not contain all the data and the
        target has not received a Data PDU with the final bit Set) the target
        MUST wait until it receives a Data PDU with the F bit set, in the
        last expected sequence, before sending the Response PDU.
     
     3.4.3 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
     
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           0x80-0xff - Vendor specific
     
        The Response is used to report a Service Response. The exact mapping
        of the iSCSI response codes to SAM service response symbols is
        outside the scope of this document.
     
        Certain iSCSI conditions result in the command being terminated at
        the target (response Command Completed at Target) with a SCSI Check
        Condition Status as outlined in the next table:
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        +--------------------------+----------+---------------------------+
        | Reason                   |Sense     | Additional Sense Code &   |
        |                          |Key       | Qualifier                 |
        +--------------------------+----------+---------------------------+
        | Unexpected unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0c    |
        | data                     |Command-0B| Write Error               |
        +--------------------------+----------+---------------------------+
        | Not enough unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0d    |
        | data                     |Command-0B| Write Error               |
        +--------------------------+----------+---------------------------+
        | Protocol Service CRC     |Aborted   | ASC = 0x47 ASCQ = 0x05    |
        | error                    |Command-0B| CRC Error Detected        |
        +--------------------------+----------+---------------------------+
        | SNACK rejected           |Aborted   | ASC = 0x11 ASCQ = 0x13    |
        |                          |Command-0B| Read Error                |
        +--------------------------+----------+---------------------------+
     
        "Not enough unsolicited data" condition is reported by the target
        only if it does not support output (write) operations in which the
        total data length is higher than FirstBurstSize but the initiator
        sent less than FirstBurstSize amount of unsolicited data, and out-of-
        order R2Ts can't be used.
     
     3.4.4 Residual Count
     
        The Residual Count field is valid only 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 U bit is set, the Residual Count
        indicates how many bytes were not transferred out of those expected
        to be transferred.  If the O bit is set, the Residual Count indicates
        how many bytes could not be transferred because the initiator's
        Expected Data Transfer Length was too small.
     
     3.4.5 Bidirectional Read Residual Count
     
        The Bidirectional Read Residual Count field is valid only 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 u
        bit is set, the Bidirectional Read Residual Count indicates how many
        bytes were not transferred to the initiator out of those expected to
        be transferred.  If the o bit is set, the Bidirectional Read Residual
        Count indicates how many bytes could not be transferred to the
        initiator because the initiator's Expected Bidirectional Read
        Transfer Length was too small.
     
     
     
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     3.4.6 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:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|SenseLength                    | Sense Data                    |
          +---------------+---------------+---------------+---------------+
         x/ Sense Data                                                    /
          +---------------+---------------+---------------+---------------+
         y/ Response Data                                                 /
          +                                                               +
          /                                                               /
          +---------------+---------------+---------------+---------------+
         z|
     
     
     3.4.6.1 SenseLength
     
        Length of Sense Data.
     
     3.4.7 ExpDataSN
     
        The number of Data-In (read) PDUs the target has sent for the
        command.
     
        This field is reserved if the response code is not Command Completed
        at Target.
     
     
     3.4.8 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/status sent on a connection except for responses sent as a
     
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        result of a retry or SNACK.  In case of responses sent because of a
        retransmission request the StatSN used MUST be the same as the first
        time the PDU was sent unless the connection was restarted since then.
     
     3.4.9 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.
     
     3.4.10 MaxCmdSN - Maximum CmdSN Acceptable 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 that indicates to the initiator that the target
        can't receive any additional commands.  When MaxCmdSN changes at the
        target while the target has no pending PDUs to convey this
        information to the initiator it MUST generate a NOP-IN to carry the
        new MaxCmdSN.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.5 Task Management Function Request
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| x02       |0| Function    | Reserved                      |
          +---------------+---------------+---------------+---------------+
         4| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
         8| Logical Unit Number (LUN) or Reserved                         |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Referenced Task Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32| RefCmdSN or ExpDataSN                                         |
          +---------------+---------------+---------------+---------------+
        36/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48
     
     3.5.1 Function
     
        The Task Management functions provide an initiator with a way to
        explicitly control the execution of one or more Tasks (SCSI and iSCSI
        tasks). The Task Management functions are (for a more detailed
        description of SCSI task management see [SAM2]):
     
           1    ABORT TASK - aborts the task identified by the Referenced
           Task Tag field.
           2    ABORT TASK SET - aborts all Tasks issued by this initiator
           on the Logical Unit.
           3    CLEAR ACA - clears the Auto Contingent Allegiance
           condition.
           4    CLEAR TASK SET - Aborts all Tasks (from all initiators)
           for the Logical Unit.
           5    LOGICAL UNIT RESET
           6    TARGET WARM RESET
     
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           7   TARGET COLD RESET
           8   TASK REASSIGN - reassign connection allegiance for the
               task identified by the Initiator Task Tag field on this
               connection, thus resuming the iSCSI exchanges for the task
     
        For all these functions, if executed, the Task Management Function
        Response MUST be returned using the Initiator Task Tag to identify
        the operation for which it is responding. All those functions apply
        to the referenced tasks regardless if they are proper SCSI tasks or
        tagged iSCSI operations.  Task management commands must be executed
        as if all the commands having a CmdSN lower or equal to the task
        management CmdSN have been received by the target (i.e., have to be
        executed as if received for ordered delivery even when marked for
        immediate delivery).  For all the tasks covered by the task
        management response (i.e., with CmdSN not higher than the task
        management command CmdSN), additional responses MUST NOT be delivered
        to the SCSI layer after the task management response.
     
        ABORT TASK MUST be issued on the same connection to which the task to
        be aborted is allegiant at the time the Task Management Request is
        issued if the connection is still active (it is not undergoing an
        implicit or explicit logout).  If the connection is being implicitly
        or explicitly logged out (i.e., no other request will be issued on
        the failing connection and no other response will be received on the
        failing connection) then an ABORT TASK function request may be issued
        on another connection. This Task Management request will then both
        establish a new allegiance for the command to be aborted, and abort
        it as well (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). For the ABORT TASK function, the target MUST NOT deliver
        additional responses after sending the task management response. In
        case both responses were delivered, whether the initiator should
        deliver task responses before delivering the task management response
        or not while an ABORT TASK is executing is a matter of
        implementation.
     
        For the LOGICAL UNIT RESET function, the target MUST behave as
        dictated by the Logical Unit Reset function in [SAM2].
     
        The TARGET RESET function (WARM and COLD) implementation is OPTIONAL
        and when implemented should act as described below.  Target Reset MAY
        be also subject to SCSI access controls for the requesting initiator.
        When not implemented or when authorization fails at target, Target
        Reset functions should end as if the function was executed
        successfully and the response qualifier will detail what was
        executed.
     
     
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        For the TARGET WARM RESET and TARGET COLD RESET functions, the target
        cancels all pending operations and are both equivalent to the Target
        Reset function specified by [SAM2].  They can both affect many other
        initiators.
     
        In addition, for the TARGET COLD RESET the target then MUST terminate
        all of its TCP connections to all initiators (all sessions are
        terminated).
     
        For the TASK REASSIGN function, the target should reassign the
        connection allegiance to this new connection (and thus resume iSCSI
        exchanges for the task).  TASK REASSIGN MUST be received by the
        target ONLY after the connection on which the command was previously
        executing has been successfully logged-out.  For additional usage
        semantics, see section 8.1.
     
     
        TASK REASSIGN MUST be issued as an immediate command.
     
     
     3.5.2 LUN
     
        This field is required for functions addressing a specific LU (ABORT
        TASK, CLEAR TASK SET, ABORT TASK SET, CLEAR ACA, LOGICAL UNIT RESET)
        and is reserved in all others.
     
     3.5.3 Referenced Task Tag
     
        Initiator Task Tag of the task to be aborted or reassigned.
     
     3.5.4 RefCmdSN or ExpDataSN
     
        For ABORT TASK the task CmdSN to enable task removal. If RefCmdSN
        does not match the CmdSN of the command to be aborted at the target,
        the abort action MUST NOT be performed and the response MUST be
        function rejected.
     
        If the function is TASK REASSIGN establishing 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.
     
        Otherwise, this field is reserved.
     
     
     
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     3.6 Task Management Function Response
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x22      |1| Reserved    | Response      | Qualifier     |
          +---------------+---------------+---------------+---------------+
         4/ Reserved                                                      /
          /                                                               /
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Referenced Task Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48
     
        For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
        SET, LOGICAL UNIT RESET, TARGET WARM RESET, the target performs the
        requested Task Management function and sends a Task Management
        Response back to the initiator.
     
     3.6.1 Response and Qualifier
     
        The target provides a Response, which may take on the following
        values:
     
                0 - Function Complete
                1 - Task specified in the Referenced Task Tag field was
                not in task set
                2 - LUN does not exist
                3 - Task still allegiant
                4 - Task failover not supported
           255   Function Rejected
     
        All other values are reserved.
     
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        The Qualifier field provides additional information about the
        Response.
     
        For a Response of "Function Complete" the valid Qualifiers are:
     
           0 - Function Executed
           1 - Not Authorized
     
        For a discussion on usage of response codes 3 and 4, see section
        8.1.2.
     
        For the TARGET COLD RESET and TARGET WARM RESET functions, the target
        cancels all pending operations.  For the TARGET COLD RESET function
        the target MUST then close all of its TCP connections to all
        initiators (terminates all sessions).
     
        The mapping of the response code into a SCSI service response code,
        if needed, is outside the scope of this document.
     
     
     3.6.2 Referenced Task Tag
     
        If the Request was ABORT TASK and the Response is "task not found"
        Referenced Task Tag contains the Initiator Task Tag of the task that
        had to be aborted. It MUST be set to 0xffffffff in other cases.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.7 SCSI Data-out & SCSI Data-in
     
        The SCSI Data-out PDU for WRITE operations has the following format:
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|0|0| 0x05      |F| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| LUN or Reserved                                               |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Target Transfer Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        36| DataSN                                                        |
          +---------------+---------------+---------------+---------------+
        40| Buffer Offset                                                 |
          +---------------+---------------+---------------+---------------+
        44| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment                                                   /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
     
     
     
     
     
     
     
     
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        The SCSI Data-in PDU for READ operations has the following format:
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x25      |F|0 0 0 0|O|U|S| Reserved      |Status or Rsvd |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Reserved                                                      |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Residual Count                                                |
          +---------------+---------------+---------------+---------------+
        24| StatSN or Reserved                                            |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| DataSN                                                        |
          +---------------+---------------+---------------+---------------+
        40| Buffer Offset                                                 |
          +---------------+---------------+---------------+---------------+
        44| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment                                                   /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
        Status can accompany the last Data-in PDU if the command did not end
        with an exception.  Presence of status (and of a residual count) is
        signaled though the S flag bit.  Although targets MAY choose to send
        even non-exception status in separate responses initiators MUST
        support non-exception status in Data-In PDUs.
     
     3.7.1 F (Final) Bit
     
     
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        For outgoing data, this bit is 1 for the last PDU of unsolicited data
        or the last PDU of a sequence answering an R2T.
     
        For incoming data, this bit is 1 for the last input (read) data PDU
        of a sequence.  Input can be split in several sequences each one
        having it's own F bit. Splitting the data stream in 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 and/or end of recoverable sequences by targets with a
        limited retransmission buffer.  A target that implements
        ErrorRecoveryLevel 1 or higher MUST use the F bit to indicate the
        end-of-sequence of Data-In PDUs is it is going to discard.
     
        For Bidirectional operations, the F bit is 1 both for the end of the
        input sequences as well as the end of the output sequences.
     
     3.7.2 Target Transfer Tag
     
        On outgoing data, the Target Transfer Tag is provided to the target
        if the transfer is honoring an R2T. In this case, the Target Transfer
        Tag field is a replica of the Target Transfer Tag provided with the
        R2T.
     
        The Target Transfer Tag values are not specified by this protocol
        except that the value 0xffffffff is reserved and means that the
        Target Transfer Tag is not supplied.  If the Target Transfer Tag is
        provided then the LUN field MUST hold a valid value and be consistent
        with whatever was specified with the command, otherwise the LUN field
        is reserved.
     
     
     3.7.3 StatSN
     
        This field MUST be set only if the S bit is set to 1.
     
     
     3.7.4 DataSN
     
        For input (read) data PDUs, the DataSN is the data PDU number
        (starting with 0) within the data transfer for the command identified
        by the Initiator Task Tag.
     
        For output (write) data PDUs, the DataSN is the data PDU number
        (starting with 0) within the current output sequence. The current
        output sequence is identified by the Initiator Task Tag (for
     
     
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        unsolicited data) or is a data sequence generated for one R2T (for
        data solicited through R2T).
     
        Any input or output data sequence MUST contain less than 2**32-1
        numbered PDUs.
     
     
     3.7.5 Buffer Offset
     
        The Buffer Offset field contains the offset of this PDU payload data
        within the complete data transfer. The sum of the buffer offset and
        length should not exceed the expected transfer length for the
        command.
     
        The order of data PDUs within a sequence is determined by
        DataPDUInOrder (when set to yes it means that PDUs have to be in
        increasing Buffer Offset order and overlays are forbidden).
     
        The ordering between sequences is determined by DataSequenceInOrder
        (when set to yes it means that sequences have to be in increasing
        Buffer Offset order and overlays are forbidden)
     
     3.7.6 DataSegmentLength
     
        This is the data payload length of a SCSI Data-In or SCSI Data-Out
        PDU; 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
        integer number of 4 byte words (real payload) unless the F bit is set
        to 1.
     
     3.7.7 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,
        CONDITION MET, INTERMEDIATE or INTERMEDIATE CONDITION MET) may also
        optionally contain the Status for the data transfer.  In this case,
        Sense Data cannot be sent together with the Command Status.  If the
        command is completed with an error, then the response and sense data
        MUST be sent in a SCSI Response PDU (i.e., MUST NOT be sent in a SCSI
        Data packet). For Bidirectional commands, the status MUST be sent in
        a SCSI Response PDU.
     
           bit 3-6 not used (should be set to 0)
           bit 1-2 as in an SCSI Response
     
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           bit 0   S (status)- set to indicate that the Command Status
           field contains status. If this bit is set to 1 the F bit MUST
           also be set to 1
     
     
        The fields StatSN, Status, Residual Count have meaningful content
        only if the S bit is set to 1.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.8 Ready To Transfer (R2T)
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x31      |1| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        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
     
        When an initiator has submitted a SCSI Command with data passing 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.
     
        In order to allow write operations without an explicit initial R2T,
        the initiator and target MUST have agreed to do so by sending the
        InitialR2T=no key-pair to each other, which happens either during
        Login or through the Text request/Response mechanism.
     
        An R2T MAY be answered with one or more SCSI Data-out PDUs with a
        matching Target Transfer Tag. If an R2T is answered with a single
        Data-out PDU, the Buffer Offset in the Data PDU MUST be the same as
     
     
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        the one specified by the R2T. The data length of the Data PDU MUST
        not exceed the Desired Data Transfer Length specified in the R2T. If
        the R2T is answered with a sequence of Data PDUs the Buffer Offset
        and Length MUST be within the range of those specified by R2T, the
        last PDU SHOULD have the F bit set to 1. The Data-Out PDU ordering is
        governed by DataPDUInOrder. 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) and
        thus have a number of data transfers pending.  Within a connection,
        outstanding R2Ts MUST be fulfilled by the initiator in the order in
        which they were received.
     
        Buffer offset ordering in consecutive R2Ts is governed by
        DataSequenceInOrder.  If DataSequenceInOrder is yes then consecutive
        R2Ts SHOULD refer to continuous non-overlapping ranges.  However,
        even when DataSequenceInOrder is no, a target MAY send out-of-order
        R2Ts (e.g., for recovery) and an initiator MAY choose to terminate a
        command when receiving an out-of-order R2T that it can't fulfill,
        with an appropriate response after aborting the command at the target
        with the appropriate task management command.
     
     3.8.1 R2TSN
     
        R2TSN is the R2T PDU number (starting with 0) within the command
        identified by the Initiator Task Tag.
     
        The number of R2Ts in a command MUST be less than 0xffffffff.
     
     3.8.2 StatSN
     
        The StatSN field will contain as usual the next StatSN but StatSN for
        this connection is not advanced.
     
     3.8.3 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, relative
        to the beginning of the total data transfer. The Desired Data
        Transfer Length SHOULD not be 0 and MUST not exceed MaxBurstSize.
     
     
     
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     3.8.4 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 is copied in the
        outgoing data PDUs and is used by the target only. There is no
        protocol rule about Target Transfer Tag, but it is assumed that it is
        used to tag the response data to the target (alone or in combination
        with the LUN).
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.9 Asynchronous Message
     
        An Asynchronous Message may be sent from the target to the initiator
        without corresponding to a particular command. The target specifies
        the reason for the event and sense data.
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x32      |1| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| LUN                                                           |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| AsyncEvent    | AsyncVCode    | Parameter1 or Reserved        |
          +---------------+---------------+---------------+---------------+
        40| Parameter2 or Reserved        | Parameter3 or Reserved        |
          +---------------+---------------+---------------+---------------+
        44| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment - Sense Data or iSCSI Event Data                  /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
        Some Asynchronous Messages are strictly related to iSCSI while others
        are related to SCSI [SAM2].
     
     
     
     
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        Please note that StatSN counts this PDU as an acknowledgeable event
        (StatSN is advanced), allowing initiator and target state
        synchronization.
     
     3.9.1 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. Sending of a SCSI Event (Asynchronous
           Event Notification in SCSI terminology) is controlled by a SCSI
           Control Mode Page bit.
           1    Target requests Logout. This Async Message MUST be sent on
           the same connection as the one being requested to be logged
           out.  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" to cleanly shutdown the connection.  If the
           initiator does not Logout in Parameter3 seconds, the target
           should send an Async PDU with iSCSI event code "Dropped the
           connection" if possible, or simply terminate the transport
           connection. Parameter1 and Parameter2 are reserved.
           2    Target indicates it will drop the connection.
           The Parameter1 field indicates on what CID the connection will
           dropped.
           The Parameter2 field indicates, in seconds, the minimum time to
           wait before attempting to reconnect.
           Parameter3 indicates the maximum time to reconnect and/or
           restart commands after the initial wait (Parameter2).
           If the initiator does not attempt to reconnect and/or restart
           the outstanding commands, within the time specified by
           Parameter3 or, if Parameter3 is 0, the target will terminate
           all outstanding commands on this connection, no other responses
           should be expected from the target for the outstanding commands
           on this connection.
           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.
           The Parameter2 field indicates, in seconds, the minimum time to
           wait before attempting to reconnect.
     
     
     
     
     
     
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           The Parameter3 field indicates the maximum time to reconnect
           and restart commands after the initial wait (Parameter2).
           If the initiator does not attempt to reconnect within the time
           specified by Parameter 3 or, if Parameter 3 is 0, the session
           is terminated. In this case, the target will terminate all
           outstanding 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
           reconnect can be attempted immediately.
           255 Vendor specific iSCSI Event. The AsyncVCode details the
           vendor code and data MAY accompany the report.
     
        All other event codes are reserved.
     
     3.9.2 AsyncVCode
     
        AsyncVCode is a vendor specific detail code valid only if the
        AsyncEvent field indicates a vendor specific event. Otherwise it is
        reserved.
     
     3.9.3 Sense Data or iSCSI Event Data
     
        For a SCSI Event this data accompanies the report, in the data
        segment, identifies the condition.
     
        For an iSCSI Event additional data that MAY accompany the report
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.10 Text Request
     
        The Text Request is provided to allow the exchange of information and
        for future extensions. It permits the initiator to inform a target of
        its capabilities or to request some special operations.
     
        An initiator MUST have only one outstanding Text Request on a
        connection at any given time.
     
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| 0x04      |F| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Reserved                                                      |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Target Transfer Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment (Text)                                            /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
     3.10.1 F (Final) Bit
     
        When set to 1 it indicates that this is the last or only text request
        in a sequence of commands; otherwise it indicates that more commands
        will follow.
     
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     3.10.2 Initiator Task Tag
     
        The initiator assigned identifier for this Text Request.
        If the command is sent as part of a sequence of text requests and
        responses,  the Initiator Task Tag MUST be the same for all the
        requests within the sequence (similar to linked SCSI commands).
     
     3.10.3 Target Transfer Tag
     
        When the Target Transfer Tag is set to the reserved value 0xffffffff,
        it tells the target that this is a new request and the target should
        reset any internal bookmarks associated with the Initiator Task Tag.
     
        When the target sets in a text response the Target Transfer Tag to a
        value other than the reserved value 0xffffffff it indicates that it
        has more data to send associated with the specified Initiator Task
        Tag (an internal bookmark). By copying the Target Transfer Tag from
        the response to the next Text Request, the initiator tells the target
        to continue from its last bookmark for the specific Initiator Task
        Tag.
     
        This mechanism allows a target to transfer a large amount of textual
        data over a sequence of text-command/text-response exchanges.
     
        A target MAY reject an old Bookmark.
     
        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)
     
     3.10.4 Text
     
        The initiator sends the target a set of key=value or key=list pairs
        encoded in UTF-8 Unicode. All the text keys and text values specified
        in this document are to be presented and interpreted in the case they
        appear in this document (they are case sensitive). The key and value
        are separated by a '=' (0x3d) delimiter. Every key=value pair
        (including the last or only pair) MUST be followed by at least one
     
     
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        null (0x00) delimiter.  A list is a set of values separated by comma
        (0x2c).
     
        Character strings are represented as plain text. Binary items can be
        encoded using their decimal representation (with or without leading
        zeros) or hexadecimal representation (e.g., 8190 is 0x1ffe).  Binary
        items can also be encoded using the more compact Base64 encoding as
        specified by [RFC2045] preceded by the 0b.  Key names MUST NOT exceed
        63 bytes.
     
        If not specified otherwise the maximum length of an individual value
        (not its encoded representation) is 255 bytes not including the
        delimiter (comma or null).
     
        The data lengths of a text request or response MUST NOT exceed 4096
        bytes.
     
        The target responds by sending its response back to the initiator.
        The response text format is similar to the request text format.
     
        Some basic key=value pairs are described in Appendix D. All keys in
        Appendix D, except for the X- extension format, MUST be supported by
        iSCSI initiators and targets.
     
        Manufacturers may introduce new keys by prefixing them with X-
        followed by their (reversed) domain name, for example the company
        owning the domain acme.com can issue:
     
           X-com.acme.bar.foo.do_something=3
     
        Any other key not understood by the target may be ignored by the
        target without affecting basic function. However the Text Response
        for a key that was not understood MUST be key=NotUnderstood.
     
        Text operations are usually meant for parameter setting/negotiations
        but can be used also to perform some long lasting operations.
     
        Text operations that will take a long time should be placed in their
        own Text request.
     
     
     
     
     
     
     
     
     
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     3.11 Text Response
     
        The Text Response PDU contains the target's responses to the
        initiator's Text request. The format of the Text field matches that
        of the Text request.
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x24      |F| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Reserved                                                      |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Target Transfer Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment (Text)                                            /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     3.11.1 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
        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.
     
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        A text response with a F bit set to 1 MUST NOT contain key=value
        pairs that may require additional answers from the initiator.
     
     3.11.2 Initiator Task Tag
     
        The Initiator Task Tag matches the tag used in the initial Text
        request.
     
     3.11.3 Target Transfer Tag
     
        When a target can't transfer all the remaining text data in a single
        Text response, it attempts to set an internal bookmark. If
        successful, the target sets the Target Transfer Tag to the bookmark
        value and associates the bookmark with the Initiator Task Tag.
     
        The initiator MUST copy this Target Transfer Tag in its next request
        to indicate that it wants the rest of the data.
     
        If the target receives a Text Request with the Target Task Tag set to
        the reserved value of 0xffffffff it resets the internal bookmark
        associated with the given Initiator Task Tag.
     
        When a target can't transfer all the text data in a single text
        response and it cannot set an internal bookmark it rejects the Text
        request with an appropriate Reject code. A target may reset its
        internal bookmark(s) after some time in order to reclaim resources
        associated with the bookmark and reject subsequent Text requests with
        the Target Transfer Tag set to a bookmark value.
     
        When all the text data yet to be sent fits in a single Text response
        the Target Transfer Tag of the response is set to 0xffffffff and the
        internal bookmark associated with the Initiator Task Tag is reset.
     
     3.11.4 Text Response Data
     
        The Text Response Data Segment contains responses in the same
        key=value format as the Text request and with the same length and
        coding constraints. Appendix A and Appendix D lists some basic Text
        requests and their Responses.
     
        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 an identical key=value pair offered by the initiator.
     
     
     
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        A Key=value pair must be confined to a given text response even in
        the presence of bookmark - i.e., it must start and end within one
        Text Response.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.12 Login Request
     
        After establishing a TCP connection between an initiator and a
        target, the initiator MUST start a Login phase to gain further access
        to the target's resources.
     
        The Login Phase (see chapter 5) consists of a sequence of Login
        requests and responses that carry the same Initiator Task Tag.
     
     
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| 0x03      |T|0 0 0|CSG|NSG| Version-max   | Version-min   |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| CID                           | Reserved                      |
          +---------------+---------------+---------------+---------------+
        12| ISID                          |TSID                           |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN   or   Reserved                                     |
          +---------------+---------------+---------------+---------------+
        32| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        36| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        40/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48/ DataSegment - Login Parameters in Text request Format         /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     3.12.1 X - Restart Connection
     
        If this bit is set to 1 then this command is an attempt to reinstate
        a failed connection or a failed session.
     
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        If TSID is not 0 then this is a connection restart. CID does not
        change and this command performs first the logout function of the old
        connection if an explicit logout was not performed earlier. In
        sessions with a single connection, this may imply the opening of a
        second connection with the sole purpose of cleaning-up the first.
        Targets should support opening a second connection even when not
        supporting multiple connections in full feature phase.
     
        If TSID is 0 then the X bit MUST be 0.
     
        The X bit MAY be set to 1 ONLY on the first request of the Login
        phase.
     
        Connection reinstatement if the operational ErrorRecoveryLevel is 2,
        is a complete connection recovery which enables task reassignment.
        If the operational ErrorRecoveryLevel is less than 2, connection
        reinstatement refers to a mere replacement of the old CID without
        enabling task reassignment.
     
     3.12.2 I - Immediate
     
        Login MUST be issued as an immediate request (I=1).
     
     3.12.3 T (Transit) Bit
     
        If set to 1 indicates that the initiator is ready to transit to next
        stage.
     
        If the T bit is set to 1 and NSG is FullFeaturePhase then this is
        also indicating that the initiator is ready for the Final Login
        Response (see chapter 5).
     
        The target MAY answer with a Login response with the T bit set to 1
        ONLY if the T is set to 1 in the request.
     
     3.12.4 CSG and NSG
     
        Through these fields, called Current Stage (CSG) and Next Stage
        (NSG), the Login negotiation commands and responses are associated
        with a specific stage in the session (SecurityNegotiation,
        LoginOperationalNegotiation, FullPhaseOperationalNegotiations) and
        may indicate the next stage they want to move to (see chapter 5).
     
        The next stage value is valid only when the T bit is 1 and is
        reserved otherwise.
     
     
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        The stage codes are:
     
           - 0 - SecurityNegotiation
           - 1 - LoginOperationalNegotiation
           - 3 - FullFeaturePhase
     
     3.12.5 Version-max
     
        Maximum Version number supported.
     
        All Login requests within the Login phase MUST carry the same
        Version-max.
     
        The target MUST use the value presented with the first login request.
     
     3.12.6 Version-min
     
        Minimum Version supported.
     
        The version number of the current draft is 0x2.
     
        All Login requests within the Login phase MUST carry the same
        Version-min.
     
        The target MUST use the value presented with the first login request.
     
     3.12.7 Connection ID - CID
     
        This is a unique ID for this connection within the session.
     
        All Login requests within the Login phase MUST carry the same CID.
     
        The target MUST use the value presented with the first login request.
     
     3.12.8 ISID
     
        This is an initiator-defined session-identifier.  It MUST be the same
        for all connections within a session.  A SCSI initiator port is
        uniquely identified by the value pair (InitiatorName, ISID).
     
        When a target detects an attempt to open a new session by the same
        SCSI initiator port (same InitiatorName and ISID) to the same target
        portal group it MUST close the old session and establish a new
        session.
     
        All Login requests within the Login phase MUST carry the same ISID.
     
     
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        The target MUST use the value presented with the login request with
        C=0.
     
     3.12.9 TSID
     
        The TSID is the target assigned tag for a session with a specific
        named initiator that, together with the ISID uniquely identifies a
        session with that initiator.
     
        On a Login request a TSID value of 0 indicates a request to open a
        new session.
     
        A non zero TSID indicates a request to add a connection to an
        existing session.
     
     3.12.10 CmdSN
     
        CmdSN is either the initial command sequence number of a session (for
        the first Login request of a session - the "leading" login) or the
        command sequence number in the command stream (e.g., if the leading
        login carries the CmdSN 123 all other Login requests carry the CmdSN
        123 and the first non-immediate command also carries the CmdSN 123).
     
        The target MUST use the value presented with the first login request.
     
     3.12.11 ExpStatSN
     
        This is ExpStatSN for the old connection.
     
        This field is valid only if the Login request restarts a connection
        (i.e., X bit is 1 and TSID is not zero).
     
     3.12.12 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.
        The format of the parameters is as specified for the Text request.
        Keys and their explanations are listed in the Appendix A (security
        negotiation keys) and Appendix D (operational parameter negotiation
        keys). All keys in Appendix D, except for the X- extension format,
        MUST be supported by iSCSI initiators and targets. Keys in Appendix A
        MUST be supported only when the function they refer to is mandatory
        to implement.
     
     
     
     
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     3.13 Login Response
     
        The Login Response indicates the progress and/or end of the login
        phase.  Note that after security is established, the login response
        is authenticated.
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x23      |T|0 0 0|CSG|NSG| Version-max   | Version-active|
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        12| ISID                          |TSID                           |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| Status-Class  | Status-Detail | Reserved                      |
          +---------------+---------------+---------------+---------------+
        40/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment - Login Parameters in Text request Format         /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
     3.13.1 Version-max
     
        This is the highest version number supported by the target.
     
        All Login responses within the Login phase MUST carry the same
        Version-max.
     
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        The initiator MUST use the value presented as response to the first
        login request.
     
     
     3.13.2 Version-active
     
        Indicates the version supported (the highest version supported by the
        target and initiator). If the target does not support a version
        within the range specified by the initiator, the target rejects the
        login and this field indicates the lowest version supported by the
        target.
     
        All Login responses within the Login phase MUST carry the same
        Version-active.
     
        The initiator MUST use the value presented as response to the first
        login request.
     
     3.13.3 TSID
     
        The TSID is a tag set by the target that together with the
        ISID identifies a unique session with the initiator.
        It MUST be valid only in the final response.
     
     3.13.4 StatSN
     
        For the first Login Response (the response to the first Login
        Request) this is the starting status Sequence Number for the
        connection (the next response of any kind will carry this number +
        1). This field is valid only if the Status Class is 0.
     
     3.13.5 Status-Class and Status-Detail
     
        The Status returned in a Login Response indicates the execution
        status of the login phase. The status includes:
     
           Status-Class
           Status-Detail
     
        A 0 Status-Class indicates success.
     
        A non-zero Status-Class indicates exception. In this case, Status-
        Class is sufficient for a simple initiator to use when handling
        errors, without having to look at the Status-Detail.  The Status-
        Detail allows finer-grained error recovery for more sophisticated
        initiators, as well as better information for error logging.
     
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        For a non-zero Status-Class the T, CSG & NSG  fields MUST be 0.
     
        The status classes are as follows:
     
           0 - Success - indicates that the iSCSI target successfully
           received, understood, and accepted the request. The numbering
           fields (StatSN, ExpCmdSN, MaxCmdSN are valid only if Status-
           Class is 0).
           1 - Redirection - indicates that further action must be taken
           by the initiator to complete the request. This is usually due
           to the target moving to a different address. All of the
           redirection status class responses MUST return one or more text
           key parameters of the type "TargetAddress", which indicates the
           target's new address.
     
           2 - Initiator Error - indicates that the initiator likely
           caused the error. This MAY be due to a request for a resource
           for which the initiator does not have permission.  The request
           should not be tried again.
     
           3 - Target Error - indicates that the target sees no errors in
           the initiator's login request, but is currently incapable of
           fulfilling the request.  The client may re-try the same login
           request later.
     
        The table below shows all of the currently allocated status codes.
        The codes are in hexadecimal; the first byte is the status class and
        the second byte is the status detail.
     
        -----------------------------------------------------------------
        Status        | Code | Description
                      |(hex) |
        -----------------------------------------------------------------
        Success       | 0000 | Login is proceeding OK (*1)
        -----------------------------------------------------------------
        Target Moved  | 0101 | The requested ITN has moved
        Temporarily   |      | temporarily to the address provided.
        -----------------------------------------------------------------
        Target Moved  | 0102 | The requested ITN has moved
        Permanently   |      | permanently to the address provided.
        -----------------------------------------------------------------
        Initiator     | 0200 | Miscellaneous iSCSI initiator
        Error         |      | errors
        ----------------------------------------------------------------
        Authentication| 0201 | The initiator could not be
        Failure       |      | successfully authenticated.
     
     
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        -----------------------------------------------------------------
        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
                      |      | No forwarding address is provided.
        -----------------------------------------------------------------
        Unsupported   | 0205 | The requested iSCSI version range is
        Version       |      | not supported by the target.
        -----------------------------------------------------------------
        Too many      | 0206 | No more connections accepted on this SID
        connections   |      |
        -----------------------------------------------------------------
        Missing       | 0207 | Missing parameters (e.g., iSCSI
        parameter     |      | Initiator and/or Target Name)
        -----------------------------------------------------------------
        Can't include | 0208 | Target does not support session
        in session    |      | spanning to this connection (address)
        -----------------------------------------------------------------
        Session type  | 0209 | Target does not support this type of
        Not supported |      | of session or not from this Initiator
        -----------------------------------------------------------------
        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.
     
     3.13.6 T (Transit) bit
     
     
     
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        T bit is set to 1 as an indicator of end of stage. If the T bit is
        set to 1 and NSG is FullFeaturePhase then this is also the Final
        Login Response (see chapter 5). A T bit of 0 indicates a "partial"
        response, which means "more negotiation needed".
     
        A login response with a T bit set to 1 MUST NOT contain key=value
        pairs that may require additional answers from the initiator within
        the same stage.
     
        If the status class is 0, the T bit MUST NOT be set to 1 if the
        T bit in the request was set to 0.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.14 Logout Command
     
        The Logout command is used to perform a controlled closing of a
        connection.
     
        An initiator MAY use a logout command to remove a connection from a
        session or to close an entire session.
     
        After sending the Logout PDU, an initiator MUST NOT send any new
        iSCSI commands on the closing connection except SNACK and task
        management commands required for recovery.
     
        After receiving the Logout command the target aborts all pending
        commands on that connection/session if the logout reason code is
        "close the connection", " or "close the session" and suspends all
        data/status/R2T transfers on behalf of pending commands if the reason
        code is "remove connection for recovery". The target then issues the
        Logout response and half-closes the TCP connection (sends FIN).
        After receiving the Logout response and attempting to receive the FIN
        (if still possible), the initiator MUST completely close the logging-
        out connection. For the aborted commands, no additional responses
        should be expected after that.
     
        Note that a Logout for a CID may be performed on a different
        transport connection when the TCP connection for the CID had already
        been terminated.  In such a case, only a logical "closing" of the
        iSCSI connection for the CID is implied with a Logout.
     
        All commands that were not aborted or not completed (with status) and
        acknowledged when the connection is closed completely can be
        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 command to "clean-up" the target end of a
        failing connection and enable recovery to start, or use the restart
        option of the Login command for the same effect.  In sessions with a
        single connection, this may imply the opening of a second connection
        with the sole purpose of cleaning-up the first. In this case, the
        restart option of the Login should be used.
     
     
     
     
     
     
     
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        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|0|I| 0x06      |1| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
         8| CID or Reserved               | Reserved      |Reason Code    |
          +---------------+---------------+---------------+---------------+
        12| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48
     
     3.14.1 CID
     
        This is the connection ID of the connection to be closed (including
        closing the TCP stream). This field is valid only if the reason code
        is not "close session".
     
     3.14.2 ExpStatSN
     
        This is the last ExpStatSN value for the connection to be closed.
     
     3.14.3 Reason Code
     
        Indicate the reason for Logout:
     
           0 - closes the session - the session is closed - all commands
           associated with the session (if any) are aborted
           1 - closes the connection - the connection is closed - all
           commands associated with connection (if any) are aborted
           2 - removes the connection for recovery  - connection is closed
           and all commands associated with it (if any) are to be prepared
           for a new allegiance
     
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     3.15 Logout Response
     
        The logout response is used by the target to indicate that the
        cleanup operation for the connection has completed.
     
        After Logout, the TCP connection referred by the CID MUST be closed
        at both ends (or all connections must be closed if the logout reason
        was session close).
     
     
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x26      |1| Reserved    | Response      | Reserved      |
          +---------------+---------------+---------------+---------------+
         4/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag                                            |
          +---------------+---------------+---------------+---------------+
        20| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| Reserved                                                      |
          +---------------------------------------------------------------+
        40| Time2Wait                     | Time2Retain                   |
          +---------------+---------------+---------------+---------------+
        44| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        48
     
     
     
     3.15.1 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
     
     3.15.2 Time2Wait
     
        Minimum time in seconds to wait before Login for adding or
        reinstating a new connection to this session on this target.
     
     3.15.3 Time2Retain
     
        Maximum time to wait for a Login that associates non acknowledged
        status to a new connection.  After this time the status is discarded
        as acknowledged by hiatus.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.16  SNACK Request
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|0|1| 0x10      |1|Rsrvd| Type  | Reserved                      |
          +---------------+---------------+---------------+---------------+
         4/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag or 0xffffffff                              |
          +---------------+---------------+---------------+---------------+
        20| BegRun                                                        |
          +---------------+---------------+---------------+---------------+
        24| RunLength                                                     |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        36| ExpDataSN or Reserved                                         |
          +---------------+---------------+---------------+---------------+
        32/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48
     
        Support for SNACK is optional.
     
        SNACK request is used to request retransmission of numbered-
        responses, data or R2T PDUs from the target.  The SNACK request
        indicates to the target the missed numbered-response or data run,
        where the run is composed of an initial missed StatSN, DataSN or
        R2TSN and the number of additional missed Status, Data or R2T PDUs (0
        means only the initial).
     
        The numbered-response, Data or R2T PDUs requested by a SNACK have to
        be delivered as exact replicas of the ones the initiator missed
        including all its flags.
     
        Any SNACK requesting a numbered-response, Data or R2T that was not
        sent by the target MUST be rejected with a reason code of "Invalid
        SNACK".
     
     
     
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     3.16.1 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
     
        All other values are reserved.
     
        Data/R2T SNACK for a command MUST precede status acknowledgement for
        the given command.
     
        For a Data/R2T SNACK the Initiator Task Tag MUST be set to the
        Initiator Task Tag of the referenced Command. Otherwise, it is
        reserved.
     
        For a Status SNACK the ExpDataSN field is reserved.
     
        An iSCSI target that does not support recovery within connection MAY
        discard status SNACK. If the target supports command recovery within
        session it MAY discard the SNACK after which it MUST issue an
        Asynchronous Message PDU with an iSCSI event indicating "Request
        Logout".
     
     3.16.2 BegRun
     
        First missed DataSN, R2TSN or StatSN
     
     3.16.3 RunLength
     
        RunLength is the number of sequential missed DataSN, R2TSN or StatSN.
        RunLength 0 signals that all Data-In, R2T or Response PDUs carrying
        numbers equal or greater to BegRun have to be resent.
     
     
     
     
     
     
     
     
     
     
     
     
     
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     3.17 Reject
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x3f      |1| Reserved    | Reason        |               |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36| DataSN or Reserved                                            |
          +---------------+---------------+---------------+---------------+
        40| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        44| Reserved                                                      |
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
        xx/ Complete Header of Bad PDU                                    /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        yy
     
     
        Reject is used to indicate an iSCSI error condition (protocol,
        unsupported option etc.).
     
     3.17.1 Reason
     
        The reject Reason is coded as follows:
     
     
     
     
     
     
     
     
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        +------+-----------------------------------------+------------------+
        | Code | Explanation                             | Can the original |
        | (hex)|                                         | PDU be re-sent?  |
        +------+-----------------------------------------+------------------+
        | 0x01 | Full Feature Phase Command before login | no               |
        |      |                                         |                  |
        | 0x02 | Data (payload) Digest Error             | yes  (Note 1)    |
        |      |                                         |                  |
        | 0x03 | Data-SNACK Reject                       | yes              |
        |      |                                         |                  |
        | 0x04 | Protocol Error (e.g., SNACK request for | no               |
        |      | a status that was already acknowledged) |                  |
        |      |                                         |                  |
        | 0x05 | Command not supported in this session   | no               |
        |      | type                                    |                  |
        |      |                                         |                  |
        | 0x06 | Immediate Command Reject - too many     | yes              |
        |      | immediate commands                      |                  |
        |      |                                         |                  |
        | 0x07 | Task in progress                        | no               |
        |      |                                         |                  |
        | 0x08 | Invalid SNACK                           | no               |
        |      |                                         |                  |
        | 0x09 | Bookmark Reject - No bookmark for this  | no               |
        |      | Initiator Task Tag                      |                  |
        |      |                                         |                  |
        | 0x0a | Bookmark Reject - Can't generate        | yes              |
        |      | bookmark - out of resources             |                  |
        |      |                                         |                  |
        | 0x0b | Negotiation Reset                       | no              |
        +------+-----------------------------------------+------------------+
     
        Note 1: For iSCSI data PDUS, this is done only if target requests
        retransmission with a recovery R2T.    However, if this is the data
        digest error on immediate data, no signal from the target is
        necessary for PDU retransmission if desired so by the initiator.
     
        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 3.4.3.  If the
        error is detected while data from the initiator is still expected
        (the command PDU did not contain all the data and the target has not
        received a Data-out PDU with the final bit Set) the target MUST wait
     
     
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        until it receives the Data-out PDU with the F bit set before sending
        the Response PDU.
     
        For additional usage semantics of Reject PDU, please see section
        Error! Reference source not found..
     
     3.17.2 DataSN
     
        This field is valid only if the Reason code is "Invalid SNACK" and
        the SNACK was a data SNACK.  The DataSN is the last sequence number
        that the target sent for the task.
     
     3.17.3 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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     3.18 NOP-Out
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|X|I| 0x00      |1| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| LUN or Reserved                                               |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag or 0xffffffff                              |
          +---------------+---------------+---------------+---------------+
        20| Target Transfer Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| CmdSN                                                         |
          +---------------+---------------+---------------+---------------+
        28| ExpStatSN                                                     |
          +---------------+---------------+---------------+---------------+
        32/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment - Ping Data (optional)                            /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
        A NOP-Out may be used by an initiator as a "ping command", to verify
        that a connection/session is still active and all its components are
        operational.  The NOP-In response is the "ping echo".
     
        A NOP-Out is also sent by an initiator in response to a NOP-In.
     
        A NOP-Out may also be used to confirm a changed ExpStatSN if there is
        no other PDU to carry it for a long time.
     
        When used as a ping command, the Initiator Task Tag MUST be set to
        valid value (not the reserved 0xffffffff).
     
     
     
     
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        Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
        value (not the reserved 0xffffffff), the initiator MUST respond with
        a NOP-Out. In this case, the NOP-Out Target Transfer Tag MUST contain
        a copy of NOP-In Target Task 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).
     
     3.18.1 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
        contains as usual the next CmdSN but CmdSN is not advanced and the I
        bit must be set to 1.
     
     3.18.2 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
        which case it copies the Target Transfer Tag from the NOP-In PDU.
     
        When the Target Transfer Tag is set, the LUN field MUST be also
        copied from the NOP-In.
     
     3.18.3 Ping Data
     
        Ping data is reflected in the NOP-In Response. Note that the length
        of the reflected data is limited to 4096 bytes and the initiator
        should avoid sending more than 4096 bytes. The length of ping data is
        indicated by the Data Segment Length.  0 is a valid value for the
        Data Segment Length - and indicates the absence of ping data.
     
     
     
     
     
     
     
     
     
     
     
     
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     3.19 NOP-In
     
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0|1|1| 0x20      |1| Reserved                                    |
          +---------------+---------------+---------------+---------------+
         4| Reserved      | DataSegmentLength                             |
          +---------------+---------------+---------------+---------------+
         8| LUN or Reserved                                               |
          +                                                               +
        12|                                                               |
          +---------------+---------------+---------------+---------------+
        16| Initiator Task Tag or 0xffffffff                              |
          +---------------+---------------+---------------+---------------+
        20| Target Transfer Tag or 0xffffffff                             |
          +---------------+---------------+---------------+---------------+
        24| StatSN                                                        |
          +---------------+---------------+---------------+---------------+
        28| ExpCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        32| MaxCmdSN                                                      |
          +---------------+---------------+---------------+---------------+
        36/ Reserved                                                      /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
        48| Digests if any...                                             |
          +---------------+---------------+---------------+---------------+
          / DataSegment - Return Ping Data                                /
         +/                                                               /
          +---------------+---------------+---------------+---------------+
     
     
        NOP-In is either sent by a target as a response to a NOP-Out, as a
        "ping" to an initiator, or a means to carry a changed ExpCmdSN and/or
        MaxCmdSN if there is no other PDU to carry them for a long time.
     
        When a target receives the NOP-Out with a valid Initiator Task Tag
        (not the reserved value 0xffffffff), it MUST respond with a NOP-In
        with the same Initiator Task Tag that was provided in the NOP-Out
        Command. It MUST also duplicate up to first 4096 bytes of the
        initiator provided Ping Data.  For such a response, the Target
        Transfer Tag MUST be 0xffffffff.
     
     
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     3.19.1 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.
     
        Whenever the NOP-In is not issued in response to a NOP-Out the StatSN
        field will contain as usual the next StatSN but StatSN for this
        connection is not advanced.
     
     
     3.19.2 LUN
     
        A LUN MUST be set to a correct value when the Target Transfer Tag is
        valid (not the reserved value 0xffffffff).
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     4. SCSI Mode Parameters for iSCSI
     
        There are no iSCSI specific mode pages.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     5. Login Phase
     
        In the rest of this chapter, whenever we mention security we mean
        security and/or data integrity.
     
        The login phase establishes an iSCSI session between initiator and
        target. It sets the iSCSI protocol parameters, security parameters,
        and authenticates the initiator and target to each other.
     
        The login phase is implemented via login request and responses only.
        The whole login phase is considered as a single task and has a single
        Initiator Task Tag (similar to the linked SCSI commands).
     
        The login phase sequence of commands and responses proceeds as
        follows:
     
           - Login initial request
           - Login partial response (optional)
           - More Login requests and responses (optional)
           - Login Final-Response (mandatory)
     
        The initial Login request MUST include the InitiatorName and
        SessionType key=value pairs.  If the SessionType is not "discovery"
        then the initial Login Request MUST also include the key=value pair
        TargetName.
     
        The Login Final-response accepts or rejects the Login Command.
     
        The Login Phase MAY include a SecurityNegotiation stage and a
        LoginOperationalNegotiation stage and MUST include at least one of
        them, but the included stage MAY be empty.
     
        The login requests and responses contain a field that indicates the
        negotiation stage (SecurityNegotiation or
        LoginOperationalNegotiation).  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 (using
        underlying IPSec security is specified in chapter 10 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
        authentication through the Login request and response.
     
        The initiator and target MAY want to negotiate authentication and
        data integrity parameters. Once this negotiation is completed, the
        channel is considered secure.
     
        Most of the negotiation keys are allowed only in a specific stage -
        the SecurityNegotiation keys appear all in Appendix A while the
        LoginOperationalNegotiation keys appear in Appendix D.
        Only a limited set of keys (marked as Declarative in Appendix D) may
        be used in any of the 2 stages.
     
        Any given Login request or response belongs to a specific stage and
        this determines the negotiation keys allowed with the command or
        response.
     
        Stage transition is performed through a command exchange
        (request/response) carrying the T bit and the same current stage
        code.  During this exchange, the next stage selected is the lower of
        the two next stage codes.  The initiator can request a transition
        whenever it is ready but a target can respond with a transition only
        after it is offered one 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 having T bit set to 1 in one pair and being
        answered with an T bit setting of 0 may issue the next request with T
        bit set to 0.
     
        Stage transitions during login (including entering and exit) are
        possible only as outlined in the following table:
     
        +-----------------------------------------------------------+
        |From     To ->   | Security    | Operational | FullFeature |
        |  |              |             |             |             |
        |  V              |             |             |             |
        +-----------------------------------------------------------+
        | (start)         |  yes        |  yes        |  no         |
        +-----------------------------------------------------------+
        | Security        |  no         |  yes        |  yes        |
        +-----------------------------------------------------------+
        | Operational     |  no         |  no         |  yes        |
        +-----------------------------------------------------------+
     
     
     
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        The Login Final-Response that accepts a Login Command can come only
        as a response to a Login command with the T bit set to 1 and both the
        command and response MUST have FullFeaturePhase in the NSG field.
     
     
     5.1 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 (currently 0x'02')
           -Session and connection Ids
           -The negotiation stage that the initiator is ready to enter
     
        Optionally the login request may include:
     
           -Security/Integrity 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
           rejection from the target that causes the session to terminate.
           The T bit of the response MUST be set to 1 and the CSG and NSG
           are ignored
           -Login Response with Login Accept as a final response (T bit
           set to 1 and the NSG in both command a response are set to
           FullFeaturePhase). The response includes the protocol version
           supported by the target  and the session ID and may  include
           iSCSI operational or security parameters (depending on the
           current stage).
           -Login Response with Login Accept as a partial response (T bit
           set to 0 or NSG not set to FullFeaturePhase in both request and
           response) indicating the start of a negotiation sequence.  The
           response includes the protocol version supported by the target
           and either security/integrity parameters or iSCSI parameters
           (when no security/integrity 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 indicating that it is
        unwilling to accept the connection without SecurityNegotiation and
        terminate the connection.
     
     
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        If the initiator is willing to negotiate security but it is unwilling
        to make the initial parameter offer and may accept a connection
        without security it issues the Login with the T bit set to 1, the CSG
        set to SecurityNegotiation and NSG set to
        LoginOperationalNegotiation. If the target is also ready to forego
        security the Login response is empty and has T bit set to 1, the CSG
        set to SecurityNegotiation and NSG set to
        LoginOperationalNegotiation.
     
        An initiator that can operate without security and with all the
        operational 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 LoginOperationalNegotiation the Login response is
        empty and has T bit set to 1, the CSG set to
        LoginOperationalNegotiation and NSG set to FullFeaturePhase in the
        next stage.
     
        The iSCSI Initiator Name MUST be sent in the login command for the
        first connection of a session. The iSCSI Target Name MUST also be
        sent in the login command for the first connection of a session ONLY
        if the session type is normal (i.e., a target can be accessed without
        a Target Name only if the session type is a discovery session). If
        sent on new connections within an existing session the iSCSI Target
        Name and the iSCSI Initiator Name MUST be the same as the one used
        for the leading connection.
     
        The iSCSI Names MUST be in text request format.
     
     5.2 iSCSI Security and Integrity Negotiation
     
        The security exchange sets the security mechanism and authenticates
        the user and the target to each other. The exchange proceeds
        according to the algorithms that were chosen in the negotiation phase
        and is conducted by the login requests and responses key=value
        parameters.
     
        The negotiable security mechanisms include the following modes:
     
           -Initiator-target authentication - the host and the target
           authenticate themselves to each other. A negotiable algorithm
           such as Kerberos provides this feature.
           -PDU integrity - an integrity/authentication digest is attached
           to each packet.  The algorithm is negotiable.
     
     
     
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           Using IPsec for encryption or authentication may eliminate part
           of the security negotiation at the iSCSI level but not
           necessarily all.
     
        If security is established in the login phase then after the security
        negotiation is complete, each iSCSI PDU MUST include the appropriate
        digest field if any.
     
        An initiator directed negotiation proceeds as follows:
     
           -The initiator sends a login request with an ordered list of
           the options it supports for each subject (authentication
           algorithm, iSCSI parameters and so on). The options are listed
           in the initiator's order of preference.
           -The target MUST reply with the first option in the list it
           supports and is allowed for the specific initiator.  The
           parameters are encoded in UTF8 as key=value.  The initiator MAY
           also send proprietary options. The "none" option, if allowed,
           MUST be included in the list, which indicates that no algorithm
           is supported by the target. For a list of security parameters
           see Appendix A.
     
           -The initiator must be aware of the imminent completion of the
           SecurityNegotiation stage and MUST set the T bit to 1 and the
           NSG to what it would like the next stage to be. The target will
           answer with a Login response with the T bit set to 1 and the
           NSG to what it would like the next stage to be. The next stage
           selected will be the "lower" of the two. If the next stage is
           FullFeaturePhase, the target MUST respond with a Login Response
           with the Session ID and the protocol version.
     
     
        All PDUs sent after the security negotiation stage MUST be built
        using the agreed security.
     
        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 shall drop 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).
     
     
     5.3 Operational Parameter Negotiation During the Login Phase
     
     
     
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        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/integrity negotiation
           if the initiator and target perform such a negotiation
     
        An operational parameter negotiation on a connection MUST NOT start
        before the security negotiation if a security negotiation exists.
     
        Operational parameter negotiation MAY involve several Login request-
        response exchanges started and terminated by the initiator. The
        initiator MUST indicate its intent to terminate the negotiation by
        setting the T bit to 1; the target sets the T bit to 1 on the last
        response.
     
        If the target responds to a Login request with the T bit set to 1,
        with a Login response with the T bit set to 0, the initiator must
        keep sending the Login request (even empty) with the T bit set to 1
        until it gets the Login Response with the T bit set to 1.
     
        Whenever parameter action or acceptance is dependent on other
        parameters, the dependent parameters MUST be sent after the
        parameters they depend on.  If they are sent within the same command
        a response for a parameter might imply responses for others.
     
        Session specific parameters can be specified only during the login
        phase begun by a login command containing a null TSID (e.g., the
        maximum number of connections that can be used for this session).
        Connection specific parameters, if any, can be specified during the
        login phase begun by any login command. Thus, a session is
        operational once it has at least one connection.
     
        For a list of operational parameters, see Appendix D.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     6. 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 always started and terminated by the initiator.
        The initiator MUST indicate its intent to terminate the negotiation
        by setting the F bit to 1; the target sets the F bit to 1 on the last
        response.
     
        If the target responds to a text request with the F bit set to 1,
        with a text response with the F bit set to 0, the initiator must keep
        sending the text request (even empty) with the F bit set to 1 until
        it gets 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) is not an error but is discouraged.
     
        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 having the F bit set to 1 in a request and being
        answered with an F bit setting of 0 may have the next request issued
        with the F bit set to 0.
     
        Whenever parameter action or acceptance is dependent on other
        parameters, the dependent parameters MUST be sent after the
        parameters they depend on; if they are sent within the same command a
        response for a parameter might imply responses for others.
     
        An initiator MAY reset an operational parameter negotiation by
        issuing an ABORT TASK Task management request. A target may reset an
        operational parameter negotiation by answering a Text request with a
        Reject.
     
     
     
     
     
     
     
     
     
     
     
     
     
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     7. State transitions
     
        An iSCSI connection and an iSCSI session go through several well-
        defined states from the time the connection and the session are
        created to the time they are cleared.
     
        An iSCSI connection is a transport connection that is used for
        carrying out iSCSI activity.  The connection state transitions are
        described in two separate but dependent state diagrams for ease of
        understanding.  The first of these two is called a "standard
        connection state diagram" and it describes the connection state
        transitions when the iSCSI connection is not in connection recovery
        mode.  The second diagram is called a "connection recovery state
        diagram" which describes the connection state transitions while
        performing connection recovery.
     
        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 are participating
        in the session.
     
     7.1 Standard connection state diagram
     
        Symbolic names for States:
     
           S1:  FREE
           S2:  XPT_WAIT (illegal for target)
           S3:  XPT_UP
           S4:  LOGIN_SENT (initiator)/LOGIN_RCVD (target)
           S5:  FAILED
           S6:  EXITING
           S7:  LOGGED_IN (full-feature phase)
           S8:  LOGO_SENT (initiator)/LOGO_RCVD(target)
           S9:  LOGGED_OUT
           S10: ASYNC_MSG_SENT (target)/ ASYNC_MSG_RCVD(initiator)
           S11: LOGO_FAILED
           S12: XPT_CLEANUP
           S13: RECOVERY_START
     
     
     
     
     
     
     
     
     
     
     
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        Due to the number of states and the transitions involved in the
        description, the standard connection state diagram is defined using
        only a state transition table.  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 T4
        transition to arrive at state S3).  Transitions that take place
        because of the same set of events, and which arrive into the same end
        state (from different starting states), share the same transition
        number, but are given different suffixes.  The fields marked "-"
        correspond to undefined transitions.
     
     
           +-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
           |S1   |S2 |S3 |S4 |S5 |S6  |S7 |S8   |S9  |S10  |S11 |S12  |S13  |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S1| -   |T1 |T4 | - | - | -  | - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S2|T3   |-  |T2 | - | - | -  | - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S3|T21-1|-  |-  |T5 | - |T9-1| - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S4|T21-2|-  |T8 | - |T7 |T9-2|T6 | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S5|T21-3|-  |-  | - | - |T9-3| - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S6|T10  |-  |-  | - | - | -  | - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S7| -   |-  |-  | - | - | -  | - |T11-1| -  |T13-1| -  |T20-1|T19-1|
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S8| -   |-  |-  | - | - | -  | - |T15  |T12 | -   |T16 |T20-2|T19-2|
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
         S9|T21-4|-  |-  | - | - |T9-4| - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
        S10| -   |-  |-  | - | - | -  | - |T11-2| -  |T13-2| -  |T20-3|T19-3|
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
        S11| -   |-  |-  | - | - | -  | - | -   | -  | -   | -  |T17  |T19-4|
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
        S12| -   |-  |-  | - | - | -  | - | -   | -  | -   | -  | -   |T18  |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
        S13| -   |-  |-  | - | - | -  | - | -   | -  | -   | -  | -   | -   |
        ---+-----+---+---+---+---+----+---+-----+----+-----+----+-----+-----+
     
        State transition descriptions:
     
     
     
     
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           T1: Transport connect request was made (ex: TCP SYN sent).
           (Initiator only)
           T2: Transport connection is established. (Initiator only)
           T3: Transport connection request had timed out or failed.
           (Initiator only)
           T4: Transport connection is established. (Target only)
           T5: iSCSI login was sent by the initiator (or was received for
           a target).
           T6: A login success was received/sent
           T7: A login redirection/initiator error/target error was
           received, or login timed out. (Initiator only)
           T8: A login redirection/initiator error/target error was sent.
           (Target only)
           T9-1, T9-2, T9-3, T9-4: Transport disconnect request was
           sent/indication received (ex: TCP FIN received/sent).
           T10: Both sides closed the transport connection.
           T11-1, T11-2: Logout was sent by the initiator (or was received
           for a target).
           T12: Logout Response (success) was received by the initiator
           (or sent by the target)
           T13-1, T13-2: Async PDU with iSCSI event 2 received by the
           initiator (or sent by the target)
           T15: Async PDU with iSCSI event 2 received (initiator only)
           T16: Logout Response (failure) was received by the initiator
           (or sent by the target)
           T17: Transport disconnect request was sent/indication received
           (ex: TCP FIN received/sent).
           T18: Both sides closed the transport connection.
           T19-1, T19-2, T19-3, T19-4: Transport connection deemed non-
           responsive by either end; or transport RESET received by
           either; or Async PDU with iSCSI event 3 (for this CID), or
           event 4 received by the initiator.
           T20-1, T20-2, T20-3: Unexpected transport disconnect indication
           received by either side.
           T21-1, T21-2, T21-3, T21-4: Transport connection deemed non-
           responsive by either end; or transport RESET received by either
           end.
     
        The RECOVERY_START state (S13) implies that there are possibly iSCSI
        tasks that have not reached conclusion and are still considered busy.
     
     7.2 Connection recovery state diagram
     
        Symbolic names for states:
     
           R1: RECOVERY_START (same as S13)
     
     
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           R2: IN_RECOVERY
           R3: FREE (same as S1)
     
        Whenever a connection state machine (say, CSM-R) enters the
        RECOVERY_START state (S13), it must go through the state transitions
        additionally described in the connection recovery state diagram.
        These additional state transitions may be traversed either by using a
        connection in the LOGGED_IN state with an explicit logout (let us
        call it CSM-E), or on a new transport connection in the FREE state
        with an implicit logout (let us call it CSM-I).  This recovery state
        diagram hence is applicable only to the instance of the connection in
        recovery, i.e. CSM-R.  In the case of an implicit logout for example,
        CSM-R reaches FREE at the time CSM-I reaches LOGGED_IN.  In the case
        of an explicit logout, CSM-R reaches FREE when CSM-E receives a
        successful logout response while continuing to be in the LOGGED_IN
        state.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        State diagram -
     
                            -------
                           / R1    \
                        +--\       /<-+
                       /    ---+---    \
                      /        |        \ M3
                   M1 |        |M2       |
                      |        |        /
                      |        |       /
                      |        |      /
                      |        V     /
                      |     ------- /
                      |    / R2    \
                      |    \       /
                      |     -------
                      |        |
                      |        |M4
                      |        |
                      |        |
                      |        |
                      |        V
                      |      -------
                      |     / R3    \
                      +---->\       /
                             -------
     
        State transition table:
     
                +----+----+----+
                |R1  |R2  |R3  |
           -----+----+----+----+
            R1  | -  |M2  |M1  |
           -----+----+----+----+
            R2  |M3  | -  |M4  |
           -----+----+----+----+
            R3  | -  | -  | -  |
           -----+----+----+----+
     
        State transition descriptions:
     
           M1: Connection state timeout happened on either side.
           M2:  An implicit /explicit logout was sent by the initiator (or
           received by the target)
              - In CSM-I case, a recovery login was sent by the initiator
              (or received by the target) in state S1. [OR]
     
     
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              - In CSM-E case, a logout was sent by the initiator (or
              received by the target) in state S7.
           M3: Logout failure detected
              - CSM-I failed to reach S7, instead arrived into S1. [OR]
              - CSM-E either moved out of S7/Logout timed out and/or
              aborted/Logout Response (failure) received by the initiator
              (or sent by the target).
           M4: Successful implicit/explicit logout was performed.
              - CSM-I reached state S7. [OR]
              - CSM-E stayed in S7, and received Logout Response (success)
              by the initiator (or sent by the target).
     
     
     
     7.3 Session state diagram
     
        If any connection participating in a session is LOGGED_IN (S7), the
        session state is LOGGED_IN (Q3 below).  The first connection entering
        into S7 and the last connection leaving S7 toggle the session state.
     
        Symbolic Names for States:
     
           Q1: FREE
           Q2: ACTIVE
           Q3: LOGGED_IN
           Q4: FAILED
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        State diagram:
     
                            -------
                           / Q1    \
                        +->\       /<-+
                       /    ---+---    \
                      /        |        \ N4
                  N6 |         |N1       |
                     |         |        /
                     |         |       /
                     |         |      /
                     |         V     /
                     |      ------- /
                     | N7  / Q2    \
                     |  +->\       /<-+
                     |  |+--+----+-   |
                     |  ||       |    |  N3
                     |  ||N5     |N2  |
                     |  ||       |    |
                     |  ||       |    |
                     |  ||       |    |
                     |  |V       V    |
                    -+--+--      -----+-
                   / Q4    \ N5 / Q3    \
                   \       /<---\       /
                    -------      -------
     
        State transition table:
     
                +----+----+----+----+
                |Q1  |Q2  |Q3  |Q4  |
           -----+----+----+----+----+
            Q1  | -  |N1  | -  | -  |
           -----+----+----+----+----+
            Q2  |N4  | -  |N2  |N5  |
           -----+----+----+----+----+
            Q3  | -  |N3  | -  |N5  |
           -----+----+----+----+----+
            Q4  |N6  |N7  | -  | -  |
           -----+----+----+----+----+
     
        State transition descriptions:
     
           N1: At least one transport connection was established for the
           session.
     
     
     
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           N2: At least one transport connection reached the LOGGED_IN
           state.
           N3: Last LOGGED_IN connection had ceased to be LOGGED_IN.
           N4: Last participating transport connection was dropped.
           N5: Session failure (all connections reported RECOVERY_START,
           or recovery failed)
           N6: Session state timeout happened on either side.
           N7: Connection recovery attempt preserving session state -
           either via connection reinstatement or new CID addition.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     8. iSCSI Error Handling and Recovery
     
        For any outstanding SCSI command, it is assumed that iSCSI in
        conjunction with SCSI at the initiator is able to keep enough
        information to be able to rebuild the command PDU, and that outgoing
        data is available (in host memory) for retransmission while the
        command is outstanding.  It is also assumed that at target, incoming
        data (read data) MAY be kept for recovery or it can be re-read from a
        device server.
     
        It is further assumed that a target will keep the "status & sense"
        for a command it has executed, if it supports status retransmission.
     
        Many of the recovery details in an iSCSI implementation are a local
        matter, beyond the scope of protocol standardization.  However, some
        external aspects of the processing must be standardized, to ensure
        interoperability.  This section (and the corresponding appendix in
        more detail) describes a general model for recovery, in support of
        interoperability.  Compliant implementations need not match details
        of this model as presented, but the external behavior of such
        implementations must correspond to the externally observable
        characteristics model.
     
     8.1 Retry and Reassign in Recovery
     
        This section summarizes two important and somewhat related iSCSI
        protocol features used in error recovery.
     
     8.1.1 Usage of Retry
     
        By setting the Retry bit (X-bit) in the iSCSI command PDU, initiator
        attempts to "plug" (what it thinks are) the discontinuities in CmdSN
        ordering on the target end.  These discontinuities may have been
        created because of discarded command PDUs due to digest errors or
        format errors.  It is illegal to set the X-bit for immediate
        commands.
     
        Note that the X-bit MUST NOT be used for any reasons other than
        plugging command sequence gaps.  In particular, all PDU
        retransmission (for data, or status) requests for a currently
        allegiant command in progress must be conveyed to the target using
        only the SNACK mechanism already described.  This does not however
        constitute a requirement on initiators to use SNACK.
     
        Initiators as part of plugging command sequence gaps described above
        may inadvertently issue retries for allegiant commands already in
        progress at times (i.e. targets did not see the discontinuities in
     
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        CmdSN ordering).  Targets MUST reject such command PDUs with a reason
        code of "Command in progress".  This reason code may be used by
        initiators to tune their command retransmission logic, identify
        inadvertent connection allegiance switching attempts, and to get an
        updated target view of the command.  Targets MUST support the retry
        bit and the associated functionality described above.
     
        When the X-bit is specified, the command PDU MUST carry the original
        Initiator Task Tag and the original operational attributes (ex.
        flags, function names, LUN, CDB etc.).  In addition, it MUST hold the
        original CmdSN.
     
     8.1.2 Allegiance Reassignment
     
        By issuing a "task reassign" task management command (section 3.5.1),
        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 being
        established for the command, associating it to the connection on
        which the task management command is being issued.
     
        In reassigning connection allegiance for a command, the targets
        SHOULD continue the command from its current state, for example
        taking advantage of ExpDataSN in the command PDU for read commands
        (must be set to zero if there had been no data transfer).  However,
        targets MAY choose to send/receive the entire data on a reassignment
        of connection allegiance, and it is not considered an error.
     
        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
        reassignment, it MUST respond with a task management response code of
        "Task failover not supported".  If allegiance reassignment is
        supported by the target but the task is still allegiant to a
        different connection, target MUST respond with a task management
        response code of "Task still allegiant".
     
     8.2 Usage Of Reject PDU in Recovery
     
        Targets MUST NOT implicitly terminate an active task by sending a
        Reject PDU for any PDU exchanged during the life of the task.  If the
        target decides to terminate the task, a Response PDU (SCSI, Text,
        Task etc.) must be returned by the target to conclude the task.  If
        the task had never been active before the Reject (i.e. the Reject is
        on the command PDU), targets should not send any further responses
        since the command itself is being discarded.
     
     
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        The above rule means that the initiators can eventually expect a
        response even on seeing Rejects, if the Reject is not for the command
        itself.  The non-command Rejects only have diagnostic value in
        logging the errors, and they may be used for retransmission decisions
        as well by the initiators.
     
        It should also be noted that the CmdSN of the rejected 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).  This is true
        even when the CmdSN can be reliably ascertained as in the case of a
        data digest error on immediate data.  However, when the DataSN of a
        rejected data PDU can be ascertained, a target MUST advance ExpDataSN
        for the current burst if a recovery R2T is being generated.  Target
        MAY advance its ExpDataSN if it does not attempt to recover the lost
        data PDU.
     
     8.3 Format Errors
     
        Explicit violations of the PDU layout rules stated in this document
        are format errors.  This when detected, usually indicates a major
        implementation flaw in one of the parties.
     
        When a target or an initiator receives an iSCSI PDU with a format
        error, it MUST reset all transport connections in the session
        immediately and escalate the format error to session recovery
        (section 8.11.4).
     
     8.4 Digest Errors
     
        When a target receives any iSCSI PDU with a header digest error, it
        MUST silently discard the PDU.
     
        When a target receives any iSCSI PDU with a payload digest error, it
        MUST answer with a Reject iSCSI PDU with a Reason-code of Data-
        Digest-Error and discard the PDU.
     
             - If the discarded PDU is an solicited/unsolicited iSCSI data
             (for immediate data in a command PDU, non-data PDU rule below
             applies) PDU, target MUST do one of the following:
             a) Request retransmission with an R2T. [OR]
             b) Terminate the task with a command response PDU with the
               reason "delivery subsystem failure" (section 3.4.3).  If
               the target chooses to implement this, 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
               command response PDU.
     
     
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             - No further action is necessary for targets if the discarded
             PDU is a non-data PDU.
     
        When an initiator receives any iSCSI PDU with a header digest error,
        it MUST discard the PDU.
     
        When an initiator receives any iSCSI PDU with a payload digest error,
        it MUST discard the PDU.
     
             - If the discarded PDU is an iSCSI data PDU, initiator MUST
             do one of the following -
             a) Request the desired data PDU through SNACK. In its turn,
               the target MUST either reject the SNACK with a Reject PDU
               with a reason-code of "Data-SNACK Reject" in which case
               the target MUST terminate the command with an iSCSI
               command response reason of "SNACK rejected", or resend the
               data PDU. [OR]
             b) Abort the task and terminate the command with an error.
     
             - If the discarded PDU is a response PDU, 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 7.1. [OR]
                       c) Logout to close the connection (abort all the
                          commands associated with the connection)
             - No further action is necessary for initiators if the
             discarded PDU is an unsolicited PDU.
     
     8.5 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 implying
        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.
        Initiator MUST address these implied digest errors as described in
        section 8.4.  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 8.4.
     
        When an initiator receives an iSCSI status PDU with an out-of-order
        StatSN implying missing responses, it MUST address the one or more
        missing status PDUs as described in section 8.4.  As a side effect of
     
     
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        receiving the missing responses, the initiator may discover missing
        data PDUs. The initiator MUST NOT acknowledge the received responses
        until it has completed receiving all the data PDUs of a SCSI command.
     
     8.6 SCSI Timeouts
     
        An iSCSI initiator SHOULD 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 re-transmitting the
        unacknowledged command with the retry bit set, as described in
        section 8.1.
     
        On a ULP timeout for a command that carried a CmdSN of n, if the
        ExpCmdSN is still less than (n+1) on ULP timeout, the iSCSI initiator
        MUST assume a session failure and take the appropriate actions as
        described in section 8.11.4.
     
     8.7 Negotiation failures
     
        Text request and response sequences when used to set/negotiate
        operational parameters constitute the negotiation/parameter setting.
        A negotiation failure is considered one or both of the following:
     
           - None of the choices or the stated value is acceptable to one
           negotiating side.
           - The text request timed out, and possibly aborted.
           - A text request is answered with a reject
     
        The following two rules are to be used to address negotiation
        failures.
     
           - During Login, any failure in negotiation MUST be considered
           as the login process failure and the connection must be
           dropped.
           - A failure in negotiation while in the full-feature phase MUST
           terminate the entire negotiation sequence possibly consisting
           of a series of text requests using the same Initiator Task Tag.
           The operational parameters of the session or the connection
           MUST continue to be the values agreed upon during an earlier
           successful negotiation - i.e. any partial results of this
           unsuccessful negotiation must be undone.
     
     8.8 Protocol Errors
     
        The authors recognize that mapping framed messages over a "stream"
        connection, such as TCP, makes the proposed mechanisms vulnerable to
        simple software framing errors. On the other hand, the introduction
     
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        of framing mechanisms to limit the effects of those errors may be
        onerous for performance and bandwidth.  Command Sequence Numbers and
        the above mechanisms for connection drop and reestablishment help
        handle this type of mapping errors.
     
        All violations of iSCSI PDU exchange sequences specified in this
        draft are also protocol errors.  This category of errors can be
        addressed only by fixing the implementations; iSCSI defines Reject
        and response codes to enable this.
     
     8.9 Connection Failures
     
        iSCSI can keep a session in operation if it is able to keep/establish
        at least one TCP connection between the initiator and target 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 or response stream that is not filled for a long
        time, or by a failing iSCSI NOP-ping. The latter MAY be used
        periodically by highly reliable implementations.  Initiators and
        targets MAY also use the keep-alive option on the TCP connection to
        enable early link failure detection on otherwise idle links.
     
        On connection failure, the initiator and target MUST do one of the
        following:
     
         a) Attempt connection recovery within the session (section 8.11.3)
           [OR]
         b) Logout the connection with the reason code "closes the
           connection" (section 3.14.3) and re-issue missing commands, and
           implicitly terminate all active commands.  Note that this option
           requires support for the within-connection recovery class
           (section 8.11.2) [OR]
         c) Perform session recovery (section 8.11.4).
     
        Either side may choose to escalate to session recovery, and the other
        side MUST give precedence to it.  On a connection failure, a target
        MUST terminate and/or discard all the active immediate commands
        regardless of which of the above options is used - i.e. immediate
        commands are not recoverable across connection failures.
     
     8.10 Session Errors
     
        If all the connections of a session fail and cannot be reestablished
        in a short time or if initiators detect protocol errors repeatedly,
        an initiator may choose to terminate a session and establish a new
        session. It terminates all outstanding requests with an appropriate
     
     
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        response before initiating a new session.  The target takes the
        following actions:
     
           - Resets the TCP connections (closes the session).
           - Aborts all Tasks in the task set for the corresponding
           initiator.
     
     8.11 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
        representative 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
        target and initiator MAY escalate the error handling to an error
        recovery class impacting 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 (like ACA) have to be considered.
     
        Usage of within a connection and within a command recovery classes
        MUST NOT be attempted before the connection is in full feature phase.
     
     8.11.1 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) a data digest error - to be dealt with as specified in
             section 8.4
          b) a sequence reception timeout (no data or partial-data-and-no-
             F-bit) - to be dealt with as specified in section 8.5
     
     
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          c) a header digest error which manifests as a sequence reception
             timeout, or a sequence error - to be dealt with as specified
             in section 8.5
     
        At the initiator, the following cases lend themselves to within-
        command recovery:
     
           Lost data PDU or lost R2T - realized through one of the
           following:
          a) a data digest error - to be dealt with as specified in
             section 8.4
          b) a sequence reception timeout (no status) - to be dealt with
             as specified in section 8.5
          c) a header digest error which manifests as a sequence reception
             timeout, or a sequence error - to be dealt with as specified
             in section 8.5
     
           Please Note that an initiator SHOULD NOT request a missing R2T
           by a SNACK after a timeout to avoid a race; this action is
           better left to the target.
     
     
        Both the timeout values to be used by the initiator and target are
        outside the scope of this document.
     
     8.11.2 Recovery Within-connection
     
        At the initiator, the following cases lend themselves to within-
        connection recovery:
     
          a) Requests not acknowledged for a long time. Requests are
             acknowledged explicitly through ExpCmdSN or implicitly by
             receiving data and/or status. The initiator MAY reissue non-
             acknowledged commands as specified in section 8.1.
          b) Lost iSCSI numbered Response recognized by either receiving
             it with a data digest error or receiving a Response PDU with
             a higher StatSN than expected. In the first case, digest
             error handling is done as specified in section 8.4, and in
             the second case, sequence error handling is done as specified
             in section 8.5.
     
        At the target, the following cases lend themselves to within-
        connection recovery:
     
     
     
     
     
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          a) Status/Response not acknowledged for a long time. The target
             MAY issue a NOP-IN, with the P bit set to 1 or 0, which
             indicates in the StatSN field the next status number it is
             going to issue.  This helps the initiator detect missing
             StatSN and issue a SNACK-status.
     
        Both the timeout values to be used by the initiator and target are
        outside the scope of this document.
     
     8.11.3 Connection Recovery
     
        At an iSCSI initiator, the following cases lend themselves to
        connection recovery:
     
           a) TCP connection failure. The initiator MUST close the
             connection following which it MUST either Logout the failed
             connection, or Login with an implied Logout, and reassign
             connection allegiance for all commands associated with the
             failed connection on another connection (that MAY be a newly
             established connection) using the "Task reassign" task
             management function (section 3.5.1).
     
           N.B. The logout function is mandatory, while a new connection
           establishment is mandatory only if the failed connection was
           the last or only connection in the session
     
           N.B. As an alternative to Logout and reissue commands, the
           initiator MAY instead reset the target and terminate all
           outstanding commands with a service response indicating
           Delivery Subsystem Failure. The initiator MUST perform one of
           the two actions.
     
          b) Receiving an Asynchronous Message indicating one or all
             connections in a session had been dropped.  The initiator
             MUST handle it as a TCP connection failure for the
             connection(s) referred to in the Message.
     
        At an iSCSI target, the following cases lend themselves to connection
        recovery -
     
          a) TCP connection failure. The target MUST close the connection
             and then, if more than one connection is available, the
             target SHOULD send an Asynchronous Message indicating it has
             dropped the connection. Following that, the target will wait
             for the initiator to continue recovery.
     
     8.11.4 Session Recovery
     
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        Session recovery is to be performed when all other recovery attempts
        have failed.  Very simple initiators and targets MAY perform session
        recovery on all iSCSI errors and therefore place the burden of
        recovery on the SCSI layer and above.
     
        Session recovery implies closing of all TCP connections, aborting at
        target all executing and queued tasks for the given initiator,
        terminating at initiator all outstanding SCSI commands with an
        appropriate SCSI service response and restarting a session on a new
        connection set (TCP connection establishment and login on all new
        connections).  It is to be noted that neither Reserve-Release managed
        SCSI reservations ("Regular" reservations) nor Persistent SCSI
        reservations are affected by session failures.  Regular SCSI means
        are to be used to handle these reservations.
     
     8.12 Error Recovery Hierarchy
        The error recovery classes and features described so far are
        organized into a hierarchy for ease of understanding and to limit the
        myriad of implementation possibilities, thus significantly
        contributing to highly interoperable implementations.  The attributes
        of this hierarchy are:
     
               a) Each level is a superset of the capabilities of the
                  previous level.   For example, Level 1 support implies
                  supporting all capabilities of Level 0 and more.
               b) As a corollary, supporting a higher error recovery
                  level means increased sophistication and possibly an
                  increase in resource requirement.
               c) Supporting error recovery level "n" is advertised and
                  negotiated by each iSCSI entity by exchanging the text
                  key "ErrorRecoveryLevel=n".  The lower of the two
                  exchanged values is the operational ErrorRecoveryLevel
                  for the session.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        The following picture represents the error recovery hierarchy.
     
                                   +
                                  / \
                                 / 2 \       <-- Connection recovery
                                +-----+
                               /   1   \     <-- Digest failure recovery
                              +---------+
                             /     0     \   <-- Session failure recovery
                            +-------------+
     
        The following table lists the error recovery capabilities expected of
        implementations supporting each error recovery level.
     
        +-------------------+--------------------------------------------+
        |ErrorRecoveryLevel |  Associated Error recovery capabilities    |
        +-------------------+--------------------------------------------+
        |        0          |  Session recovery class (8.11.4)           |
        +-------------------+--------------------------------------------+
        |        1          |  Digest failure recovery (Note below)      |
        +-------------------+--------------------------------------------+
        |        2          |  Connection recovery class (8.11.3)        |
        +-------------------+--------------------------------------------+
     
        Note: Digest failure recovery is comprised of two recovery classes -
        Within-Connection recovery class (8.11.2) and Within-Command recovery
        class (8.11.1).
     
        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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     9. Notes to Implementers
     
        This section notes some of the performance and reliability
        considerations of the iSCSI protocol.  This protocol was designed to
        allow efficient silicon and software implementations. The iSCSI tag
        mechanism was designed to enable RDMA at the iSCSI level or lower.
     
        The guiding assumption made throughout the design of this protocol
        was that targets are resource constrained relative to initiators.
     
        Implementers are also advised to consider the implementation
        consequences of the iSCSI to SCSI mapping model as outlined in 2.5.3.
     
     9.1 Multiple Network Adapters
     
        The iSCSI protocol allows multiple connections, not all of which need
        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 insure 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.
     
     9.1.1 iSCSI Name and ISID/TSID use
     
        The designers of the iSCSI protocol envision there should be 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.  This 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 that are
        coordinated as a single iSCSI Node, it is expected that an entity
        representing the iSCSI Node should manage session identifier
        resources (to enforce both the TSID and ISID RULES). This assignment
        can be accomplished in a number of ways.  For iSCSI initiator
        devices, it is expected that operating systems will provide standard
        APIs that will inform these devices of the iSCSI Node Name and manage
        ISIDs for the purpose of coordination of sessions.
     
        Recognizing that these APIs are not available today, the following
        are recommendations for separate session coordinators within a node
        ("Session coordinators" are the components, either hardware or
        software, that handle session semantics within Portal Groups).
     
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        Because all portal groups of one iSCSI Node (initiator or target)
        must share the same name, the iSCSI Name should be a configurable
        parameter to the session coordinators across all portal groups of
        that node.  A session coordinator is responsible for presenting the
        iSCSI Name of the node at login and in response to certain SCSI
        inquiries.
     
        For an iSCSI Initiator, the ISID values used by the session
        coordinators should be configurable parameters and the ISID namespace
        should be partitioned among the Initiator Portal Groups.  This allows
        each Initiator Portal Group to act independently of other portal
        groups when selecting an ISID for a login; this facilitates
        enforcement of the ISID RULE (see 2.5.3) at the initiator.
     
        For an iSCSI Target, the TSID values used by the session coordinators
        should be configurable parameters and the TSID namespace should be
        partitioned among the Target Portal Groups. This allows each Target
        Portal Group to act independently of other portal groups when
        selecting a TSID for a login response; this best facilitates the
        enforcement of the TSID RULE (see 2.5.3) at the target.
     
     9.2 Autosense and Auto Contingent Allegiance (ACA)
     
        Autosense refers to the automatic return of sense data to the
        initiator in case a command did not complete successfully. iSCSI
        mandates support for autosense.
     
        ACA helps preserve ordered command execution in presence of errors.
        As iSCSI can have many commands in-flight between initiator and
        target iSCSI mandates support for ACA.
     
     9.3 Task Management Commands and Immediate Delivery
     
        A task management command may reach the target and, in the case
        immediate delivery was requested, be executed before all of the tasks
        it was meant to act upon have been delivered or even reached the
        target.
     
        It is assumed that, while pending delivery from iSCSI to SCSI at the
        target, commands are kept in an iSCSI queue at both the initiator and
        the target and that the target queue contains both commands and
        "holes" (placeholders for commands not received yet).
     
        The following general mechanism can be used to achieve the effect of
        ordered delivery for task management commands while enabling the
        "urgent" delivery that some of them imply and immediate execution of
     
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        the task management commands.  The mechanism manages discarding
        commands while they are in the iSCSI layer at the target and prevents
        these discarded commands from being delivered to the target's SCSI
        layer.  The initiator must keep a record of these commands to
        determine which will not receive a response.  The target does not
        generate a response to a command that is aborted while in the iSCSI
        layer.  The "barrier list" described in the following sections is a
        list containing information relating to all task management commands
        marked for immediate delivery.
     
           At the Initiator when a relevant task management command marked
           for immediate delivery is issued:
     
              a) if ExpCmdSN is equal to CmdSN (there are no commands in
              the queue) skip to step c;
              b) mark all pending commands with a CmdSN field between the
              current ExpCmdSN and the current CmdSN as candidates for
              cleanup and retain CmdSN of the task management command in a
              "barrier list";
              c) send the task management command for immediate delivery
              to the target.
     
     
           Note: for clarity, the barrier list contains "items" and the
           command queue contains "entries"
     
           At initiator when updating ExpCmdSN:
     
              a) if the "barrier list" is empty or ExpCmdSN is less than
                the CmdSN of the oldest item in the barrier list then
                skip to step d;
              b) remove the oldest barrier list item, and remove and
                silently discard all entries marked for cleanup having a
                CmdSN field less than ExpCmdSN;
              c) go to step a;
              d) release all queued entries between the old and new
                ExpCmdSN from the queue. Note: Any entries that had been
                marked as a candidate for cleanup have now been delivered
                by the target to its SCSI layer.  The SCSI layer will
                have to determine if they are to be aborted.
     
           At the target when receiving a relevant task management command
           for immediate delivery:
     
              a) if ExpCmdSN is equal to CmdSN skip to step c;
     
     
     
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              b) mark all pending entries (commands received and
              placeholders) with a CmdSN field between ExpCmdSN and the
              current CmdSN as candidates for cleanup and retain CmdSN in
              a "barrier list" including the referenced LUN (or an ALL
              marker);
              c) send the task management command to SCSI for immediate
              execution.
     
           At target when updating ExpCmdSN (releasing ordered commands to
           SCSI):
     
              a) if the "barrier list" is empty or ExpCmdSN is less than
                the oldest item in the barrier list then skip to step d;
              b) remove the oldest barrier list item and evaluate all
                queued entries that have a CmdSN field less than
                ExpCmdSN, removing and silently discarding each queued
                command that meets the criteria for cleanup candidacy (as
                specified by the task management function);
              c) go to step a;
              d) release all queued entries between the old and new
                ExpCmdSN from the queue.
     
        Note that this scheme will withstand connection recovery.
     
        The following table details the candidates for cleanup:
     
        +---+------------------+------------------------------------------+
        |No | Function         | Candidacy Selection                      |
        +---+------------------+------------------------------------------+
        | 1 | Abort Task       | The task that are identified by the      |
        |   |                  | Referenced Task Tag Field and initiator  |
        +---+------------------+------------------------------------------+
        | 2 | Abort Task Set   | All tasks associated with the specified  |
        |   |                  | LUN and initiator.                       |
        +---+------------------+------------------------------------------+
        | 3 | Clear ACA        | No entries are marked for candidacy.     |
        +---+------------------+------------------------------------------+
        | 4 | Clear Task Set   | All tasks associated with the specified  |
        |   |                  | LUN and initiator. For all other         |
        |   |                  | initiators all tasks at LUN with no      |
        |   |                  | regard to order.                         |
        +---+------------------+------------------------------------------+
     
     
     9.4 Synch and steering layer and performance
     
     
     
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        Although a synch and steering layer is optional, an initiator/target
        without synch and steering working against a target/initiator
        demanding synch and steering may experience performance degradation
        caused by packet reordering and loss.  Providing a synch and steering
        mechanism is recommended for all high-speed implementations.
     
     9.5 Unsolicited data and performance
     
        Unsolicited data on write are meant to reduce the effect of latency
        on throughput (no R2T is needed to start sending data).  In addition,
        immediate data are meant to reduce the protocol overhead (both
        bandwidth and execution time).
     
        However, negotiating an amount of unsolicited data for writes and
        sending less than the negotiated amount when the total data amount to
        be sent by a command is larger than the negotiated amount may
        negatively impact performance and may not be supported by all the
        targets.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     10. Security Considerations
     
        Historically, native storage systems have not had to consider
        security because their environments offered minimal security risks.
        That is, these environments consisted of storage devices either
        directly attached to hosts or connected via a subnet distinctly
        separate from the communications network. The use of storage
        protocols, such as SCSI, over IP networks requires that security
        concerns be addressed. iSCSI implementations MUST provide means of
        protection against active attacks (pretending as another identity,
        message insertion, deletion, modification and replaying) and passive
        attacks (eavesdropping, gaining advantage by analyzing the data sent
        over the line).
     
        Although technically possible, iSCSI SHOULD NOT be configured without
        security.  iSCSI without security should be confined, in extreme
        cases, to closed environments without any security risk.
     
        The following section describes the security mechanisms to be
        provided by an iSCSI implementation.
     
     10.1 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
        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
        mechanisms complement each other: the in-band authentication provides
        end-to-end trust (at login time) between the iSCSI initiator and
        target, while IPSec provides a secure channel between the IP
        communication 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].
     
     
     10.2 In-band Initiator-Target Authentication
     
        With this mechanism, the target authenticates the initiator and the
        initiator optionally authenticates the target. The authentication is
        performed on every new iSCSI connection, by an exchange of iSCSI
        Login PDUs and using a negotiated authentication method.
     
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        The authentication method cannot assume an underlying IPSec
        protection, since IPSec is optional to use. An attacker should gain
        as minimal advantage as possible by inspecting the authentication
        phase PDUs. In this spirit, a method using clear text (or equivalent)
        passwords is not acceptable; on the other hand, identity protection
        is not strictly required.
     
        This mechanism protects against an unauthorized login to storage
        resources by using a false identity (spoofing). Once the
        authentication phase is completed, if underlying IPSec is not used -
        all PDUs are sent and received in clear. This mechanism alone
        (without underlying IPSec) should only be used when there is no risk
        of eavesdropping, message insertion, deletion, modification and
        replaying.  In addition, the CHAP authentication method (specified in
        Appendix A) is vulnerable to off-line dictionary attack. CHAP SHOULD
        NOT is used without additional protection in environments where this
        attack is a concern.  Underlying IPsec, encryption provides
        protection against this attack.
     
        Compliant iSCSI initiators and targets MUST implement at least the
        SRP authentication method [RFC2945] (see Appendix A).
     
     
     10.3 IPSec
     
       The IPSec mechanism is used by iSCSI for packet protection
       (cryptographic integrity, authentication and confidentiality) at the
       IP level between the iSCSI communicating end points. The following
       sections describe the IPSec protocols that must be implemented for
       data integrity and authentication, confidentiality and key
       management.
     
       Detailed considerations and recommendations on using IPSec for iSCSI
       are given in [SEC-IPS].
     
     10.3.1 Data Integrity and Authentication
     
        Data authentication and integrity is provided by usage of a keyed
        Message Authentication Code in every sent packet. This 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]
        with the following iSCSI specific requirements:
     
     
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           - HMAC-SHA1 MUST be implemented [RFC2404].
           - AES CBC MAC with XCBC extensions SHOULD be implemented [AES],
           [XCBC] (NOTE - this is still subject to the IETF-IPSec WG's
           standardization plans).
     
        The ESP anti-replay service MUST also be implemented.
     
     10.3.2 Confidentiality
     
        Confidentiality is provided by encrypting the data in every packet.
        Confidentiality SHOULD always be used together with data integrity
        and authentication to provide comprehensive protection against
        eavesdropping, message insertion, deletion, modification and
        replaying.
     
        An iSCSI compliant initiator or target MUST provide confidentiality
        by implementing IPSec [RFC2401] with ESP [RFC2406] with the following
        iSCSI specific requirements:
     
           - 3DES in CBC mode MUST be implemented [RFC2451].
           - AES in Counter mode SHOULD be implemented [AESCTR] (NOTE -
           this is still subject to the IPSec WG's standardization plans).
     
        The NULL encryption algorithm MUST also be implemented.
     
     10.3.3 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].
     
        When IPSec is used, each iSCSI TCP connection within an iSCSI
        session MUST be protected by a separate IKE Phase 2 SA.
        In the IKE Phase 2 Quick Mode exchanges for creating the Phase 2 SA,
        the Identity Payload fields MUST be present, and MUST carry
        individual addresses (MUST NOT use the IP Subnet or IP Address Range
        formats).
     
        IKE main mode with pre-shared key authentication method SHOULD NOT
        be used (the only practical usage under this configuration is a
        group pre-shared key which creates vulnerability to man-in-the-
        middle attack).
     
     
     
     
     
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     11. IANA Considerations
     
        There will be a well-known port for iSCSI connections.  This well-
        known port will be registered with IANA.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     12. References and Bibliography
     
           [AC]  A Detailed Proposal for Access Control, Jim Hafner,
           T10/99-245
           [AES] J. Daemen, V. Rijman, "AES Proposal: Rijndael" NIST
           AES proposal,
           http://csrc.nist.gov/encryption/aes/rijndael/Rijndael.pdf ,
           September 1999.
           [XCBC] J. Black, P. Rogaway "Comments to NIST concerning AES
           Modes of Operations: A Suggestion for Handling Arbitrary-Length
           Messages with the CBC MAC",
           http://csrc.nist.gov/encryption/modes/proposedmodes/xcbc-
           mac/xcbc-mac-spec.pdf , NIST proposed modes of operations, August
           2001.
           [AESCTR] J. Etienne, "The counter-mode and its use with ESP",
           Internet draft (work in progress), draft-etienne-ipsec-esp-ctr-
           mode-00.txt,  May 2001.
           [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-01.txt
           [CAM]  ANSI X3.232-199X, Common Access Method-3 (Cam)
           [Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman
           "Optimization of Cyclic Redundancy-Check Codes with 24 and 32
           Parity 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-03.txt
           [RFC790] J. Postel, ASSIGNED NUMBERS, September 1981
           [RFC791] INTERNET PROTOCOL, DARPA INTERNET PROGRAM PROTOCOL
           SPECIFICATION, September 1981
           [RFC793]  TRANSMISSION CONTROL PROTOCOL, DARPA INTERNET PROGRAM
           PROTOCOL SPECIFICATION, September 1981
           [RFC1035] P. Mockapetris, DOMAIN NAMES - IMPLEMENTATION AND
           SPECIFICATION, November 1987
           [RFC1122] Requirements for Internet Hosts-Communication Layer
           RFC1122, R. Braden (editor)
           [RFC1510] J. Kohl, C. Neuman, "The Kerberos Network
           Authentication Service (V5)", September 1993.
           [RFC1766] H. Alvestrand, "Tags for the Identification of
           Languages", 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.
     
     
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           [RFC2026] Bradner, S., "The Internet Standards Process --
           Revision 3", RFC 2026, October 1996.
           [RFC2044] Yergeau, F., "UTF-8, a Transformation Format of
           Unicode and ISO 10646", October 1996.
           [RFC2045] N. Borenstein, N. Freed, "MIME (Multipurpose Internet
           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.
           [RFC2234] D. Crocker, P. Overell Augmented BNF for Syntax
           Specifications: ABNF
           [RFC2246] T. Dierks, C. Allen, " The TLS Protocol Version 1.0
           [RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
           Architecture", RFC 2373, July 1998.
           [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing
           an IANA Considerations Section in RFCs.", RFC2434, October
           1998.
           [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
           Internet Protocol", RFC 2401, November 1998
           [RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96 within
           ESP and AH", RFC 2404, November 1998.
           [RFC2406] S. Kent, R. Atkinson, "IP Encapsulating Security
           Payload (ESP)", RFC 2406, November 1998
           [RFC2407] D. Piper, "The Internet IP Security Domain of
           Interpretation 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
           Algorithms"
           [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)
           [Schneier] B. Schneier, "Applied Cryptography: Protocols,
           Algorithms, and Source Code in C", 2nd edition, John Wiley &
           Sons, New York, NY, 1996.
           [SEC-IPS] B. Aboba & team "Securing iSCSI, iFCP and FCIP"  -
           draft-ietf-ips-security-01.txt
           [SPC] NCITS.351:200, SCSI-3 Primary Commands (SPC)
           [SPC3]T10/1416-D, SCSI-3 Primary Commands (SPC)
     
     
     
     
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     13. Author's Addresses
     
             Julian Satran
             IBM, Haifa Research Lab
             MATAM - Advanced Technology Center
             Haifa 31905, Israel
             Phone +972.4.829.6264
             E-mail: Julian_Satran@vnet.ibm.com
     
             Kalman Meth
             IBM, Haifa Research Lab
             MATAM - Advanced Technology Center
             Haifa 31905, Israel
             Phone +972.4.829.6341
             E-mail: meth@il.ibm.com
     
             Ofer Biran
             IBM, Haifa Research Lab
             MATAM - Advanced Technology Center
             Haifa 31905, Israel
             Phone +972.4.829.6253
             E-mail: biran@il.ibm.com
     
             Daniel F. Smith
             IBM Almaden Research Center
             650 Harry Road
             San Jose, CA 95120-6099, USA
             Phone: +1.408.927.2072
             E-mail: dfsmith@almaden.ibm.com
     
             Jim Hafner
             IBM Almaden Research Center
             650 Harry Road
             San Jose, CA 95120
             Phone: +1.408.927.1892
             E-mail: hafner@almaden.ibm.com
     
             Costa Sapuntzakis
             Cisco Systems, Inc.
             170 W. Tasman Drive
             San Jose, CA 95134, USA
             Phone: +1.408.525.5497
             E-mail: csapuntz@cisco.com
     
             Mark Bakke
             Cisco Systems, Inc.
     
     
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             6450 Wedgwood Road
             Maple Grove, MN
             USA 55311
             Phone:  +1.763.398.1000
             E-Mail: mbakke@cisco.com
     
             Randy Haagens
             Hewlett-Packard Company
             8000 Foothills Blvd.
             Roseville, CA 95747-5668, USA
             Phone: +1.916.785.4578
             E-mail: Randy_Haagens@hp.com
     
             Matt Wakeley (current address)
             Sierra Logic, Inc.
             Phone: +1.916.772.1234 ext 116
             E-mail: matt_wakeley@sierralogic.com
     
             Efri Zeidner
             SANgate Systems, Inc.
             41 Hameyasdim Street
             P.O.B. 1486
             Even-Yehuda, Israel 40500
             Phone: +972.9.891.9555
             E-mail: efri@sangate.com
     
             Paul von Stamwitz (current address)
             TrueSAN Networks, Inc.
             Phone: +1.408.869.4219
             E-mail: pvonstamwitz@truesan.com
     
             Luciano Dalle Ore
             Quantum Corp.
             Phone: +1.408.232.6524
             E-mail: ldalleore@snapserver.com
     
             Mallikarjun Chadalapaka
             Hewlett-Packard Company
             8000 Foothills Blvd.
             Roseville, CA 95747-5668, USA
             Phone: +1.916.785.5621
             E-mail: cbm@rose.hp.com
     
             Yaron Klein
             SANRAD
             24 Raul Valenberg St.
     
     
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             Tel-Aviv, 69719 Israel
             Phone: +972.3.765.9998
             E-mail: klein@sanrad.com
     
     
        Comments may be sent to Julian Satran
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Appendix A. iSCSI Security and Integrity
     
     01 Security Keys and Values
     
        The parameters (keys) negotiated for security are:
     
           - Digests (HeaderDigest, DataDigest)
           - Authentication method (AuthMethod)
     
        Digests enable checking end-to-end data integrity beyond the
        integrity checks provided by the link layers and covering the whole
        communication path including all elements that may change the network
        level PDUs like routers, switches, proxies, etc.
     
     
        The following table lists cyclic integrity checksums that can be
        negotiated for the digests and MUST be implemented by every iSCSI
        initiator and target. Note that these digest options have only error
        detection significance.
     
        +---------------------------------------------+
        | Name          | Description     | Generator |
        +---------------------------------------------+
        | CRC32C        | 32 bit CRC      |0x11edc6f41|
        +---------------------------------------------+
        | none          | no digest                   |
        +---------------------------------------------+
     
        The generator polynomial for this digest is given in hex-notation,
        for example 0x3b stands for 0011 1011 - the polynomial
        x**5+X**4+x**3+x+1.
     
     
        Padding bytes, when present, in a segment covered by a CRC, should be
        set to 0 and are included in the CRC. The CRC should be calculated as
        follows:
     
           - data are assumed to be  in the numbering order that appears
           in the draft - start with byte 0 bit 0 continue byte 1 bit 0
           etc. (Big Endian on bytes / Little Endian on bits)
           - the CRC register is initialized with all 1s (equivalent to
           complementing the first 32 bits of the message)
           - the n PDU bits are considered coefficients of a polynomial
           M(x) of order n-1, with bit 0 of byte 0 being x^(n-1)
           - the polynomial is multiplied by x^32 and divided by G(x)- the
           generator polynomial - producing a remainder R(x) of degree <=
           31
     
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           - the coefficients of R(x) are considered a 32 bit sequence
           - the bit sequence is complemented and the result is the CRC
           - after the last bit of the original segment the CRC bits are
           transmitted with x^31 first followed by x^30 etc. ( whenever
           examples are given the value to be specified in examples
           follows the same rules of representation as the rest of this
           document)
           - a receiver of a "good" segment (data or header) built using
           the generator 0x11edc6f41 will end-up having in the CRC
           register the value 0x1c2d19ed (this a register value and not a
           word as outlined in this draft)
     
        Proprietary algorithms MAY also be negotiated for data authentication
        and integrity digests.
     
        The following table details authentication methods:
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        +------------------------------------------------------------+
        | Name          | Description                                |
        +------------------------------------------------------------+
        | KRB5          | Kerberos V5                                |
        +------------------------------------------------------------+
        | SPKM1         | Simple Public-Key GSS-API Mechanism        |
        +------------------------------------------------------------+
        | SPKM2         | Simple Public-Key GSS-API Mechanism        |
        +------------------------------------------------------------+
        | SRP           | Secure Remote Password                     |
        +------------------------------------------------------------+
        | CHAP          | Challenge Handshake Authentication Protocol|
        +------------------------------------------------------------+
        | none          | No authentication                          |
        +------------------------------------------------------------+
     
        KRB5 is defined in [RFC1510], SPKM1, SPKM2 are defined in
        [RFC2025], SRP is defined in [RFC2945] and CHAP is defined in
        [RFC1994].
     
        Initiator and target MUST implement SRP.
     
     02 Authentication
     
        The authentication exchange authenticates the initiator to the
        target, and optionally the target to the initiator.  Authentication
        is not mandatory and is distinct from the data integrity exchange.
     
        The authentication methods to be used are KRB5, SPKM1, SPKM2, SRP,
        CHAP, or proprietary.
     
        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 return an
        error. Otherwise, if the initiator has selected the mutual
        authentication option (by setting MUTUAL-REQUIRED in the ap-options
        field of the KRB_AP_REQ), the target MUST reply with:
     
            KRB_AP_REP=<KRB_AP_REP>
     
        where KRB_AP_REP is the server's response message as defined in
     
     
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        [RFC1510].
     
        KRB_AP_REQ, KRB_AP_REP are large binary items.
     
     
        For SPKM1,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
        which may cause the peer to re-generate and resend his 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 (by
        [RFC2025]) to send SPKM-DEL token, it will, instead, send a Login
        "login reject" message and terminate the connection. If the initiator
        needs to send SPKM-DEL token, it will just abort the connection.
     
        In what follows, we assume that no SPKM-ERROR tokens are required:
     
        If the initiator authentication fails, the target MUST return an
        error. Otherwise, if the AuthMethod is SPKM1 or if the initiator has
        selected the mutual authentication option (by setting mutual-state
        bit in the options field of the REQ-TOKEN in the SPKM-REQ), the
        target MUST reply with:
     
            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 abort 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].
     
        All the SPKM-* tokens are large binary items and their binary length
        (not the encoded length) MUST not exceed 2048 bytes.
     
     
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        For SRP [RFC2945], the initiator MUST use:
     
           SRP_U=<user> TargetAuth=yes   /* or TargetAuth=no */
     
        The target MUST either return an error or reply with:
     
           SRP_N=<N> SRP_g=<g> SRP_s=<s>
     
        The initiator MUST continue with:
     
           SRP_A=<A>
     
        The target MUST either return an error or reply with:
     
           SRP_B=<B>
     
        The initiator MUST either abort or continue with:
     
           SRP_M=<M>
     
        If the initiator authentication fails, the target MUST return an
        error. 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)>
     
     
        Where U, N, g, s, A, B, M and H(A | M | K) are defined in [RFC2945].
        U is a text string, N,g,s,A,B,M and H(A | M | K) are numbers.
     
     
        For CHAP [RFC1994], the initiator MUST use:
     
           CHAP_A=<A1,A2...>
     
        Where A1,A2... are proposed algorithms, in order of preference.
     
        The target MUST either return an error 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 either with:
     
     
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           CHAP_N=<N> CHAP_R=<R>
     
        or, if he requires target authentication, with:
     
           CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>
     
        If the initiator authentication fails, the target MUST return an
        error. Otherwise, if the initiator required target authentication,
        the target MUST reply with
     
           CHAP_N=<N> CHAP_R=<R>
     
        Where N, (A,A1,A2), I, C, R are (correspondingly) the Name,
        Algorithm, Identifier, Challenge and Response as defined in
        [RFC1994]. N is a text string, A,A1,A2,I are numbers and C,R are
        large binaries encoded as hexadecimal strings.
     
        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.
     
     03 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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=KRB5,SRP,none
     
           T-> Login (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=KRB5
     
     
           I-> Login (CSG,NSG=0,1 T=1)
               KRB_AP_REQ=<krb_ap_req>
     
     
     
     
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           (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 proceeds.
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           The initiator may proceed:
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI Operational Parameters
     
           T-> Login (CSG,NSG=1,3 T=0)
               ... 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 authentication by the target is not
           successful, the target responds with:
     
           T-> Login "login reject"
     
           instead of the Login KRB_AP_REP message, and terminates the
           connection.
     
           If the target authentication by the initiator is not
           successful, 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 target
        via Kerberos:
     
           I-> Login (CSG,NSG=0,1 T=1)
     
     
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               InitiatorName=iqn.1999-07.com.os.hostid.77
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=SRP,KRB5,none
     
           T-> Login-PR (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               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)
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           T-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           . . .
     
           T-> Login (CSG,NSG=1,3 T=1)"login accept"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
        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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C, none
               AuthMethod=SPKM1,KRB5,none
     
           T-> Login (CSG,NSG=0,1 T=0)
     
     
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               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=SPKM1
     
           I-> Login (CSG,NSG=0,1 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=0,1 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)
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           The initiator may proceed:
     
           I-> Login  (CSG,NSG=1,3 T=0) ... iSCSI parameters
           T-> Login  (CSG,NSG=1,3 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
           If the target authentication by the initiator is not
           successful, the initiator terminates the connection (without
           responding to the Login SPKM_REP_TI message).
     
           If the initiator authentication by the target is not
           successful, the target responds with:
     
     
     
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           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:
     
           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
         HeaderDigest= CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=SPKM1,SPKM2
     
           T-> Login-PR (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               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)
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           The initiator may proceed:
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           T-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           And at the end:
     
           I-> Login  (CSG,NSG=1,3 T=1)
               optional iSCSI parameters
     
     
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           T-> Login (CSG,NSG=1,3 T=1) "login accept"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
        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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=KRB5,SRP,none
     
           T-> Login-PR  (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=SRP
     
           I-> Login (CSG,NSG=0,1 T=0)
               SRP_U=<user>
               TargetAuth=yes
     
           T-> Login (CSG,NSG=0,1 T=0)
               SRP_N=<N>
               SRP_g=<g>
               SRP_s=<s>
     
           I-> Login (CSG,NSG=0,1 T=0)
               SRP_A=<A>
     
           T-> Login (CSG,NSG=0,1 T=0)
               SRP_B=<B>
     
           I-> Login (CSG,NSG=0,1 T=1)
               SRP_M=<M>
     
           If the initiator authentication is successful, the target
           proceeds:
     
           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].
     
     
     
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           If the target authentication is not successful, the initiator
           terminates the connection. Otherwise it proceeds.
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           T-> Login (CSG,NSG=1,3 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
           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 target
        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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=KRB5,SRP,none
     
           T-> Login-PR (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=SRP
     
           I-> Login (CSG,NSG=0,1 T=0)
               SRP_U=<user>
               TargetAuth=no
     
     
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           T-> Login (CSG,NSG=0,1 T=0)
               SRP_N=<N>
               SRP_g=<g>
               SRP_s=<s>
     
           I-> Login (CSG,NSG=0,1 T=0)
               SRP_A=<A>
     
           T-> Login (CSG,NSG=0,1 T=0)
               SRP_B=<B>
     
           I-> Login (CSG,NSG=0,1 T=1)
               SRP_M=<M>
     
           If the initiator authentication is successful, the target
           proceeds:
     
           T-> Login (CSG,NSG=0,1 T=1)
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           T-> Login (CSG,NSG=1,3 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
        In the next example the initiator and target authenticate each other
        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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
     
     
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               AuthMethod=KRB5,CHAP,none
     
           T-> Login-PR (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=CHAP
     
           I-> Login (CSG,NSG=0,1 T=0)
               CHAP_A=<A1,A2>
     
           T-> Login (CSG,NSG=0,1 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
           proceeds:
     
           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.
     
           From this point on, any Login command and each PDU thereafter
           MUST have CRC32C digests for the header and the data.
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
           T-> Login (CSG,NSG=1,3 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
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           If the initiator authentication is not successful, the target
           responds with:
     
           T-> Login "login reject"
     
           Instead of the Login CHAP_R=<response> "proceed and change
           stage"
           message and terminates the connection.
     
     
        In the next example only the initiator is authenticated by the target
        via CHAP:
     
           I-> Login (CSG,NSG=0,1 T=0)
               InitiatorName=iqn.1999-07.com.os.hostid.77
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod=KRB5,CHAP,none
     
           T-> Login-PR (CSG,NSG=0,1 T=0)
               HeaderDigest=CRC32C
               DataDigest=CRC32C
               AuthMethod=CHAP
     
           I-> Login (CSG,NSG=0,1 T=0)
               CHAP_A=<A1,A2>
     
           T-> Login (CSG,NSG=0,1 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
           proceeds:
     
           T-> Login (CSG,NSG=0,1 T=1)
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
     
     
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           T-> Login (CSG,NSG=1,3 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
        In the next example, the initiator does not offer any
        security/integrity parameters, so it may offer iSCSI parameters on
        the Login PDU with the F 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
               ... ISCSI parameters
     
        In the next example, the initiator does offer security/integrity
        parameters 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
               HeaderDigest=CRC32C,none
               DataDigest=CRC32C,none
               AuthMethod:KRB5,SRP,none
     
           T-> Login-PR (CSG,NSG=0,1 T=1)
               HeaderDigest=none
               DataDigest=none
               AuthMethod=none
     
           I-> Login (CSG,NSG=1,3 T=0)
               ... iSCSI parameters
     
           T-> Login (CSG,NSG=1,3 T=0)
     
     
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               ... 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"
               TargetName=iqn.1999-07.com.acme.diskarray.sn.88
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Appendix B. Examples
     
     04 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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     05 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 |                       |                     |
        +------------------+-----------------------+---------------------+
     
     06 R2TSN/DataSN use examples
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        Output (write) data DataSN/R2TSN Example
     
        +------------------+-----------------------+----------------------+
        |Initiator Function|    PDU Type & Content |  Target Function     |
        +------------------+-----------------------+----------------------+
        |  Command request |SCSI Command (WRITE)>>>| Receive command      |
        |  (write)         |                       | and queue it         |
        +------------------+-----------------------+----------------------+
        |                  |                       | Process old commands |
        +------------------+-----------------------+----------------------+
        |                  |   <<< R2T             | Ready for data       |
        |                  |   R2TSN = 0           |                      |
        +------------------+-----------------------+----------------------+
        |                  |   <<< R2T             | Ready for more data  |
        |                  |   R2TSN = 1           |                      |
        +------------------+-----------------------+----------------------+
        |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
        |  for R2TSN 0     |   DataSN = 0, F=0     |                      |
        +------------------+-----------------------+----------------------+
        |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
        |  for R2TSN 0     |   DataSN = 1, F=1     |                      |
        +------------------+-----------------------+----------------------+
        |  Send Data       |   SCSI Data >>>       |   Receive Data       |
        |  for R2TSN 1     |   DataSN = 0, F=1     |                      |
        +------------------+-----------------------+----------------------+
        |                  |   <<< SCSI Response   |Send Status and Sense |
        |                  |   ExpDataSN = 0       |                      |
        +------------------+-----------------------+----------------------+
        | Command Complete |                       |                      |
        +------------------+-----------------------+----------------------+
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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         Input (read) data DataSN Example
     
        +------------------+-----------------------+----------------------+
        |Initiator Function|    PDU Type           |  Target Function     |
        +------------------+-----------------------+----------------------+
        |  Command request |SCSI Command (READ)>>> |                      |
        |  (read)          |                       |                      |
        +------------------+-----------------------+----------------------+
        |                  |                       | Prepare Data Transfer|
        +------------------+-----------------------+----------------------+
        |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
        |                  |   DataSN = 0, F=0     |                      |
        +------------------+-----------------------+----------------------+
        |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
        |                  |   DataSN = 1, F=0     |                      |
        +------------------+-----------------------+----------------------+
        |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
        |                  |   DataSN = 2, F=1     |                      |
        +------------------+-----------------------+----------------------+
        |                  |   <<< SCSI Response   |Send Status and Sense |
        |                  |   ExpDataSN = 3       |                      |
        +------------------+-----------------------+----------------------+
        | Command Complete |                       |                      |
        +------------------+-----------------------+----------------------+
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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         Bidirectional DataSN Example
     
        +------------------+-----------------------+----------------------+
        |Initiator Function|    PDU Type           |  Target Function     |
        +------------------+-----------------------+----------------------+
        |  Command request |SCSI Command >>>       |                      |
        |  (Read-Write)    |  Read-Write           |                      |
        +------------------+-----------------------+----------------------+
        |                  |                       | Process old commands |
        +------------------+-----------------------+----------------------+
        |                  |   <<< R2T             | Ready to process     |
        |                  |   R2TSN = 0           | WRITE command        |
        +------------------+-----------------------+----------------------+
        | * Receive Data   |   <<< SCSI Data-in    |   Send Data          |
        |                  |   DataSN = 0, F=0     |                      |
        +------------------+-----------------------+----------------------+
        | * Receive Data   |   <<< SCSI Data-in    |   Send Data          |
        |                  |   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)
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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        Unsolicited and immediate output (write) data with DataSN Example
     
        +------------------+-----------------------+----------------------+
        |Initiator Function|    PDU Type & Content |  Target Function     |
        +------------------+-----------------------+----------------------+
        |  Command request |SCSI Command (WRITE)>>>| Receive command      |
        |  (write)         |F=0                    | and data             |
        |+ immediate data  |                       | and queue it         |
        +------------------+-----------------------+----------------------+
        | Send Unsolicited |   SCSI Write Data >>> | Receive more Data    |
        |  Data            |   DataSN = 0, F=1     |                      |
        +------------------+-----------------------+----------------------+
        |                  |                       | Process old commands |
        +------------------+-----------------------+----------------------+
        |                  |   <<< R2T             | Ready for more data  |
        |                  |   R2TSN = 0           |                      |
        +------------------+-----------------------+----------------------+
        |  Send Data       |   SCSI Write Data >>> |   Receive Data       |
        |  for R2TSN 0     |   DataSN = 0, F=1     |                      |
        +------------------+-----------------------+----------------------+
        |                  |   <<< SCSI Response   |Send Status and Sense |
        |                  |   ExpDataSN = 0       |                      |
        +------------------+-----------------------+----------------------+
        | Command Complete |                       |                      |
        +------------------+-----------------------+----------------------+
     
     07 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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           ...
            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. Sync and Steering with Fixed Interval Markers
     
        This appendix presents a simple scheme for synchronization (PDU
        boundary retrieval).  It uses markers including synchronization
        information placed at fixed intervals in the TCP stream.
     
        A Marker consists of:
     
        Byte /    0       |       1       |       2       |       3       |
           /              |               |               |               |
          |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
          +---------------+---------------+---------------+---------------+
         0| Next-iSCSI-PDU-start pointer - copy #1                        |
          +---------------+---------------+---------------+---------------+
         4| Next-iSCSI-PDU-start pointer - copy #2                        |
          +---------------+---------------+---------------+---------------+
     
        The Marker 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 offset is counted from
        the marker end to the beginning of the next header.  The marker uses
        two copies of the pointer so that a marker spanning a TCP packet
        boundary should leave at least one valid copy in one of the packets.
     
        The offset to the next iSCSI PDU header is counted in terms of the
        TCP stream data. Anything counted in the TCP sequence-number is
        counted for the offset. Specifically this includes any bytes
        "inserted" in the TCP stream by an UFL and it excludes any other
        markers inserted between the one we are examining and the next PDU
        header. The inserted value is independent of the marker interval.
     
        The use of markers is negotiable. The initiator and target MAY
        indicate their readiness to receive and/or send markers during login
        separately for each connection.  The default is NO. In certain
        environments a sender not willing to supply markers to a receiver
        willing to accept markers MAY suffer from a considerable performance
        degradation.
     
     08 Markers At Fixed Intervals
     
        At fixed intervals in the TCP byte stream, a marker is inserted.
        Each end of the iSCSI session specifies during login the interval at
        which it is willing to receive the marker or disables the marker
        altogether. If a receiver indicates that it desires a marker, the
        sender SHOULD agree (during negotiation) and provide the marker at
        the desired interval.
     
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        The marker interval and the initial marker-less interval are counted
        in terms of the TCP stream data. Anything counted in the TCP
        sequence-number is counted for the interval and the initial marker-
        less interval. Specifically this includes any bytes "inserted" in the
        TCP stream by an UFL.
     
        When reduced to iSCSI terms markers MUST indicate the offset to a 4-
        byte word boundary in the stream.  The last 2 bits of each marker
        word are reserved and are considered 0 for offset computation.
     
        Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
        marker manipulation.
     
     
     
     09 Initial Marker-less Interval
     
        To enable the connection setup including the login phase negotiation,
        marking (if any) is started only at the first marker interval after
        the end of the login phase.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Appendix D. Login/Text Operational Keys
     
        ISID and TSID form collectively the SSID (session id). A TSID of zero
        indicates a leading connection. Some session specific parameters MUST
        be carried only on the leading connection and cannot be changed after
        the leading connection login (e.g., MaxConnections, the maximum
        number of connections).  This holds even for a single connection
        session with regard to connection restart. The keys that fall into
        this category have the use defined as LO (Leading Only).
     
        Keys that can be used only during login have the use defined as IO
        (initialize only) while those that can be used in both the login
        phase and full feature phase have the use defined as ALL.
     
        Keys that can be used only during full feature phase have the use
        defined as FFPO (full feature phase only).
     
        Unless explicitly stated otherwise, all key=value pairs specified
        here are session specific.
     
     
     10 MaxConnections
     
        Use: LO
        Who can send: Initiator and Target
     
        MaxConnections=<number-from-1-to-65535>
     
        Default is 1.
     
        Initiator and target negotiate the maximum number of connections
        requested/acceptable.  The lower of the 2 numbers is selected.
     
     
     11 SendTargets
     
        Use: FFPO
        Who can send: Initiator
     
        For a complete description see Appendix E.
     
     
     12 TargetName
     
        Use: LO by initiator ALL by target, Declarative
        Who can send: Initiator and Target
     
     
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        TargetName=<iSCSI-Name>
     
        Examples:
     
           TargetName=iqn.1993-11.com.disk-vendor.diskarrays.sn.45678
           TargetName=eui.020000023B040506
     
        This key MUST be provided by the initiator of the TCP connection to
        the remote endpoint before the end of the login phase. The iSCSI
        Target Name specifies the worldwide unique name of the target.
        The TargetName key may also be returned by the "SendTargets" text
        request (and that is its only use when issued by a target).
     
     13 InitiatorName
     
        Use: LO, Declarative
        Who can send: Initiator
     
        InitiatorName=<iSCSI-Name>
     
        Examples:
     
           InitiatorName=iqn.1992-04.com.os-vendor.plan9.cdrom.12345
           InitiatorName=iqn.2001-02.com.ssp.users.customer235.host90
           InitiatorName=iSCSI
     
        This key MUST be provided by the initiator of the TCP connection to
        the remote endpoint before the end of the login phase. The Initiator
        key enables the initiator to identify itself to the remote endpoint.
        The use of the group name "iSCSI" is interpreted as "other side of
        TCP connection". The target may silently ignore this key if it does
        not support it, and does not need to track or verify which initiators
        use it.  A target that supports this field may use it to allow or
        deny access to an initiator.
     
     14 TargetAlias
     
        Use: ALL
        Who can send: Target
     
        TargetAlias=<UTF-8 string>
     
        Examples:
     
           TargetAlias=Bob's Disk
           TargetAlias=Database Server 1 Log Disk
     
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           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.
     
     15 InitiatorAlias
     
        Use: ALL
        Who can send: Initiator
     
        InitiatorAlias=<UTF-8 string>
     
        Examples:
     
           InitiatorAlias=Web Server 4
           InitiatorAlias=spyalley.nsa.gov
           InitiatorAlias=Exchange Server
     
        If an initiator has been configured with a human-readable name or
        description, it may be communicated to the target during a Login
        Request PDU.  If not, the host name can be used instead.
        This string is not used as an identifier, but can be displayed by the
        target's user interface in a list of initiators to which it is
        connected.
     
        This key SHOULD be sent by an initiator within the Login phase if
        available.
     
     16 TargetAddress
     
        Use: ALL
        Who can send: Target
     
        TargetAddress=domainname[:port][,portal-group-tag]
     
        If the TCP port is not specified, it is assumed to be the IANA-
        assigned default port for iSCSI.
     
        If the TargetAddress is being returned in a login response as the
        result of a redirect status, the comma and portal group tag are
        omitted.
     
        If the TargetAddress is being returned within a SendTargets response,
        the portal group tag is required.
     
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        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
     
        The TargetAddress key is more fully described in Appendix E.
     
     17 FMarker
     
        Use: IO
        Who can send: Initiator and Target
     
        FMarker=<send|receive|send-receive|no>
     
        Default is no.
     
        This is a connection specific parameter.
     
        Examples:
     
           I->FMarker=send-receive
           T->FMarker=send-receive
     
        results in Marker being used in both directions while
     
           I->FMarker=send-receive
           T->FMarker=receive
     
        results in Marker being used from the initiator to the target but not
        from the target to initiator.
     
     
     18 RFMarkInt
     
        Use: IO
        Who can send: Initiator and Target
     
        RFMarkInt=<number-from-1-to-65535>[,<number-from-1-to-65535>]
     
        This is a connection specific parameter.
     
        The receiver indicates the minimum to maximum interval (in 4-byte
        words) the receiver wants the markers. In case the receiver wants
        only a specific value, only a single value has to be specified. The
     
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        sender selects a value within the minimum and maximum the receiver
        requires (or the only value the receiver requires) or indicates
        through the FMarker key=value its inability to set markers. 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 "pure" payload between markers). Whenever FMarker and
        RFMarkInt are both sent they MUST appear on the same Login
        Request/Response.
     
        Default is 2048.
     
     19 SFMarkInt
     
        Use: IO
        Who can send: Initiator and Target
     
        SFMarkInt=<number-from-1-to-65535>
     
        This is a connection specific parameter.
     
        Indicates at what interval (in 4-byte words) the sender accepts to
        send the markers. The number MUST be within the range required by the
        receiver.  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 "pure" payload between markers).
     
        Default is 2048.
     
     20 InitialR2T
     
        Use: ALL
        Who can send: Initiator and Target
     
        InitialR2T=<yes|no>
     
        Examples:
     
           I->InitialR2T=no
           T->InitialR2T=no
     
        Default is yes.
        Result function is OR.
     
        The InitialR2T key is used to turn off the default use of R2T, thus
        allowing an initiator to start sending data to a target as if it has
        received an initial R2T with Buffer Offset=0 and Desired Data
        Transfer Length=min (FirstBurstSize, Expected Data Transfer Length).
     
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        The default action is that R2T is required, unless both the initiator
        and the target send this key-pair attribute specifying InitialR2T=no.
        Once InitialR2T has been set to 'no', it cannot be set back to 'yes'.
        Note that only the first outgoing data burst (immediate data and/or
        or separate PDUs) can be sent unsolicited by an R2T.
     
     21 BidiInitialR2T
     
        Use: ALL
        Who can send: Initiator and Target
     
        BidiInitialR2T=<yes|no>
     
        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
        (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.  Once BidiInitialR2T has been set to 'no', it
        cannot be set back to 'yes'.  Note that only the first outgoing data
        burst (immediate data and/or or separate PDUs) can be sent
        unsolicited by an R2T.
     
     22 ImmediateData
     
        Use: ALL
        Who can send: Initiator and Target
     
        ImmediateData=<yes|no>
     
        Default is yes.
        Result function is AND.
     
        Initiator and target negotiate support for immediate data.  If
        initiator or target wants to turn immediate data off they have to
        state that. ImmediateData can be turned on if both initiator and
        target have ImmediateData=yes.
     
     
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        If ImmediateData is set to yes and InitialR2T is set to yes (default)
        then only immediate data are accepted in the first burst.
     
        If ImmediateData is set to no and InitialR2T is set to yes then the
        initiator MUST NOT send unsolicited data and the target MUST reject
        them with the corresponding response code.
     
        If ImmediateData is set to no and InitialR2T is set to no then the
        initiator MUST NOT send unsolicited immediate data but MAY send one
        unsolicited burst of Data-OUT PDUs.
     
        If ImmediateData is set to yes and InitialR2T is set to no then the
        initiator MAY send unsolicited immediate data and/or one unsolicited
        burst of Data-OUT PDUs.
     
        The following table is a summary of unsolicited data options:
     
     
        +----------+-------------+--------------------------------------+
        |InitialR2T|ImmediateData| Result (up to FirstBurstSize)        |
        +----------+-------------+--------------------------------------+
        |  no      |    no       | Unsolicited data in data PDUs only   |
        +----------+-------------+--------------------------------------+
        |  no      |    yes      | Immediate & separate unsolicited data|
        +----------+-------------+--------------------------------------+
        |  yes     |    no       | Unsolicited data disallowed          |
        +----------+-------------+--------------------------------------+
        |  yes     |    yes      | Immediate unsolicited data only      |
        +----------+-------------+--------------------------------------+
     
     
     23 DataPDULength
     
        Use: LO
        Who can send: Initiator and Target
     
        DataPDULength=<number-0-to-(2**15-1)>
     
        Default is 16 units.
     
        Initiator and target negotiate the maximum data payload supported for
        SCSI command or data PDUs in units of 512 bytes. The minimum of the 2
        numbers is selected.
     
        A value of 0 indicates no limit.
     
     
     
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     24 MaxBurstSize
     
        Use: LO
        Who can send: Initiator and Target
     
        MaxBurstSize=<number-0-to-(2**15-1)>
     
        Default is 512 units.
     
        Initiator and target negotiate maximum SCSI data payload in an 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) in units of 512 bytes.
     
        A value of 0 indicates no limit (the largest possible number).
     
        The minimum of the 2 numbers is selected.
     
     
     25 FirstBurstSize
     
        Use: LO
        Who can send: Initiator and Target
     
        FirstBurstSize=<number-from-0-to-(2**15-1)>
     
        Default is 128 units.
     
        Initiator and target negotiate the maximum amount of unsolicited data
        an iSCSI initiator may send to the target, during the execution of a
        single SCSI command, in units of 512 bytes.
     
        A value of 0 indicates no limit (the largest possible number).
     
        The minimum of the 2 numbers is selected.
     
        FirstBurstSize MUST NOT exceeds MaximumBurstSize.
     
     
     26 LogoutLoginMaxTime
     
        Use: LO
        Who can send: Initiator and Target
     
        LogoutLoginMaxTime=<number-from-2-3600>
     
        Default is 3.
     
     
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        Initiator and target negotiate the maximum time in seconds before
        which connection reinstatement is still possible after a connection
        termination, or a connection reset.
        This value is also the session state timeout if the connection in
        question is the last LOGGED_IN connection in the session.
     
        The minimum of the 2 values is selected.
     
     27 MaxOutstandingR2T
     
        Use: LO
        Who can send: Initiator and Target
     
        MaxOutstandingR2T=<number-from-1-to-65535>
     
        The default is 1.
     
        Initiator and target negotiate the maximum number of outstanding R2Ts
        per task. The minimum of the two values is selected.
     
     28 DataPDUInOrder
     
        Use: LO
        Who can send: Initiator and Target
     
        DataPDUInOrder=<yes|no>
     
        The 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
        overlays are forbidden.
     
     29 DataSequenceInOrder
     
        Use: LO
        Who can send: Initiator and Target
     
        DataSequenceInOrder=<yes|no>
     
        The 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
     
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        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
        transferred in any order.  If DataSequenceInOrder is set to no, Data
        Sequences MUST be transferred using continuously increasing offsets
        except for error recovery.
     
     30 ErrorRecoveryLevel
     
        Use: LO
        Who can send: Initiator and Target
     
        ErrorRecoveryLevel=<0 to 2>
     
        Default is 0.
     
        Initiator and target negotiate the recovery level supported.
        The minimum of the two values is selected.
     
        Recovery levels represent a combination of recovery capabilities.
        Each recovery level includes all the capabilities of the lower
        recovery levels and adds to them some new ones.
     
        In the description of recovery mechanisms, certain recovery classes
        are specified.  Section 8.12 describes the mapping between the
        classes and the levels.
     
     31 SessionType
     
        Use: LO, Declarative
        Who can send: Initiator
     
        SessionType= <discovery|normal>
     
        Default is Normal.
     
        The Initiator indicates the type of session it wants to create.  The
        target can accept or reject it.
     
        A discovery session indicates to the Target that the only purpose of
        this Session is discovery.  The only command accepted by a target in
        this type of session is a text request with a SendTargets key.
     
        Discovery session implies MaxConnections = 1 and overrides both the
        default and an explicit setting.
     
     
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     32 The Vendor Specific Key Format
     
        Use: ALL
        Who can send: Initiator and Target
     
        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 it is suggested to use the reversed DNS-name
        as a prefix to the key-proper.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Appendix E. SendTargets operation
     
        To reduce the amount of configuration required on an initiator, iSCSI
        provides the SendTargets text request.  This command is sent by the
        initiator to request a list of targets to which it may have access,
        as well as the list of addresses (IP address and TCP port) on which
        these 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 need not be specified.  Otherwise, the
        session is a normal, operational session.  The SendTargets command
        MUST be sent only during the full feature phase of a normal or
        discovery session.
     
        A system containing targets MUST support discovery sessions on each
        of its IP addresses, and MUST support the SendTargets command on the
        discovery session.  A target MUST support the SendTargets command on
        operational sessions; these will only return address information
        about the target to which the session is connected, and do not return
        information about other targets.
     
        An initiator MAY make use of the SendTargets as it sees fit.
     
        A SendTargets command consists of a single Text request PDU.
        This PDU contains exactly one text key and value.  The text key shall
        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 MAY 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
             possible.  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>
     
             If no target name is specified, the session should respond
             with addresses only for the target to which the session is
             logged in.  This MUST be supported on operational sessions,
             and MAY NOT return targets other than the one to which the
             session is logged in.
     
        The response to this command is a text response containing a list of
        targets and their addresses.  Each target 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 Appendix D-12.
     
        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 MAY contain no target names, if there are no
        targets for the requesting initiator to access.
     
        Each target record returned includes zero or more TargetAddress
        fields.
     
        A SendTargets response MUST NOT contain iSCSI default target names.
     
        Each target record starts with one text key of the form:
     
           TargetName=<target-name-goes-here>
     
        Followed by zero or more address keys of the form:
     
           TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],<portal-
           group-tag>
     
     
     
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        The hostname-or-ipaddress and tcp port are as specified in the
        "Naming and Addressing" section.
     
        Each TargetAddress belongs to a portal group, identified by its
        numeric, decimal portal group tag.  The iSCSI target name, together
        with this tag, constitutes the SCSI port identifier; the tag need be
        unique only within a given target name's list of addresses.
        iSCSI addresses belonging with the same portal group tag support
        spanning multiple-connection sessions across this set of addresses.
        iSCSI addresses that do not support multiple-connection sessions with
        other addresses must have their own unique portal group tag.
     
        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
        discovered targets for full operation.  The initiator MAY keep the
        session to a default target 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 containing:
     
           SendTargets=all
     
        Target sends text response containing:
     
           TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
     
        Note that all it really had to return in the simple case was the
        target name.  It is assumed by the initiator that the IP address and
        TCP port for this target are the same as used on the current
        connection to the default iSCSI target.
     
     
     
     
     
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        The next example has two internal iSCSI targets, each accessible via
        two different ports with different IP addresses.  Here's 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
     
        Note that 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-connection 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.
     
        Also note that in the above example, a DNS host name could have been
        returned instead of an IP address, and that an IPv6 addresses (5 to
        16 dotted-decimal numbers) could have been returned as well.
     
        The next text response shows a target that supports spanning sessions
        across multiple addresses, indicating this using 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
        combination.  A TargetAddress with its own tag (.49) cannot be
        combined with any other address within the same session.
     
        Note that this SendTargets response does not indicate whether .49
        supports multiple connections per session; this is communicated via
        the MaxConnections text key upon login to the target.
     
     
     
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     Appendix F. SCSI Alias designation formats
     
     33 Format codes
     
        The SCSI command set (see [SPC3]) defines an alias mechanism (CHANGE
        ALIASES and REPORT ALIASES commands) for mapping long identifiers
        (such as iSCSI Names) into shorter values for use in parameter data,
        such as third party commands.
     
        This clause defines the alias entry formats and codes used in these
        commands to designate iSCSI devices or ports.  As noted in Error!
        Reference source not found., the protocol identifier used in these
        formats shall be set to 0x05 (see [SPC3]) and the format code values
        are defined in the following table:
     
        ------------------------------------------------------------------
        Format | Description | Max     | Content
        Code   |             | Length  |
               |             | (bytes) |
        ------------------------------------------------------------------
        00h    | iSCSI Name  | 256     | Name in UTF-8 format (null
               |             |         | terminated with pad). See Y.2.
        ------------------------------------------------------------------
        01h    | iSCSI Name  | 268     | Name in UTF-8 format (null
               | with IPv4   |         | terminated with pad), binary IPv4
               | address     |         | address, binary TCP port, binary
               |             |         | Internet Protocol Number. See Y.3
        ------------------------------------------------------------------
        02h    | iSCSI Name  | 520     | Name in UTF-8 format (null
               | with IPName |         | terminated), IPName (null
               |             |         | terminated with pad), binary
               |             |         | TCP port, binary Internet
               |             |         | Protocol Number. See Y.4
        ------------------------------------------------------------------
        01h    | iSCSI Name  | 268     | Name in UTF-8 format (null
               | with IPv6   |         | terminated with pad), binary IPv6
               | address     |         | address, binary TCP port, binary
               |             |         | Internet Protocol Number. See Y.5
        ------------------------------------------------------------------
        04-FFh | reserved    | n/a     | n/a
        ------------------------------------------------------------------
     
        In all cases, if the length is not a multiple of 4, then zero to
        three pad bytes are added (as indicated).
     
        A designation that contains no IP addressing information or contains
        IP addressing information that does not address the named SCSI device
     
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        may require the SCSI logical unit device server to have access to a
        name server or to other discovery protocols to resolve the given
        iSCSI Name to an IP address through which the device server may
        establish iSCSI Login.
     
     34 iSCSI Name designation format
     
        The following table describes the iSCSI Name designation format.
     
         Byte /    0       |       1       |       2       |       3       |
            /              |               |               |               |
           |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
           +---------------+---------------+---------------+---------------+
          0| iSCSI Name + Null (00h) + pad (0) (if necessary)              |
          +/                                                               /
           +---------------+---------------+---------------+---------------+
          x
     
        The iSCSI Name field shall contain the iSCSI Name of an iSCSI Node.
     
        A Null (00h) byte shall terminate the iSCSI Name.
     
        Zero to three bytes set to zero shall be appended as padding so that
        the total length of the designation is a multiple of four. The pad
        field shall be ignored.
     
        An iSCSI Name designation is valid if the device server has access to
        a SCSI domain containing an IP network and there exists an iSCSI Node
        on that network with the specified iSCSI Name.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     35 iSCSI Name with binary IPv4 address designation format
     
        The following table describes the iSCSI Name with IPv4 address
        designation format.
     
          Byte /    0       |       1       |       2       |       3       |
             /              |               |               |               |
            |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
            +---------------+---------------+---------------+---------------+
           0| iSCSI Name + Null (00h) + pad (0) (if necessary)              |
           +/                                                               /
            +---------------+---------------+---------------+---------------+
           x| IPv4 address                                                  |
            +---------------+---------------+---------------+---------------+
         x+4| Reserved                      | Port Number                   |
            +---------------+---------------+---------------+---------------+
         x+8| Reserved                      | Internet Protocol Number      |
            +---------------+---------------+---------------+---------------+
        x+12
     
     
        The iSCSI Name field shall contain the iSCSI Name of an iSCSI Node.
     
        A Null (00h) byte shall terminate the iSCSI Name.
     
        Zero to three bytes set to zero shall be appended as padding so that
        the total length of the designation is a multiple of four. The pad
        field shall be ignored.
     
        The IPv4 Address field shall contain an IPv4 address. See [RFC791]
        for a description of IPv4 addresses.
     
        The Port Number field shall contain a port number. See [RFC790] for a
        description of port numbers.
     
        The internet protocol number field shall contain an Internet protocol
        number. See [RFC790] for a description of Internet protocol numbers.
     
        An iSCSI Name with IPv4 address designation is valid if the device
        server has access to a SCSI domain containing an IP network and there
        exists an iSCSI Node on that network with the specified iSCSI Name.
        The IPv4 address, port number and internet protocol number provided
        in the designation may be used by a device server for addressing to
        discover and establish communication with the named iSCSI Node.
     
     
     
     
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        Alternatively, the device server may use other protocol specific or
        vendor specific methods to discover and establish communication with
        the named iSCSI Node.
     
     36 iSCSI Name with IPname designation format
     
        The following table describes the iSCSI Name with IPname designation
        format.
     
          Byte /    0       |       1       |       2       |       3       |
             /              |               |               |               |
            |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
            +---------------+---------------+---------------+---------------+
           0| iSCSI Name + Null (00h) + IPname + Null (00h) +               |
           +/       pad (0) (if necessary)                                  /
            +---------------+---------------+---------------+---------------+
           x| Reserved                      | Port Number                   |
            +---------------+---------------+---------------+---------------+
         x+4| Reserved                      | Internet Protocol Number      |
            +---------------+---------------+---------------+---------------+
         x+8
     
        The iSCSI name field shall contain the iSCSI Name of an iSCSI Node.
        See [NDT] for a description of iSCSI Names. The iSCSI name field
        shall not include a byte set to 00h.
     
        A Null (00h) byte shall terminate the iSCSI Name.
     
        The IPname field shall contain a Internet protocol domain name. See
        [RFC1035] for a description of domain names.
     
        A Null (00h) byte shall terminate the Internet protocol domain name.
     
        Zero to three bytes set to zero shall be appended as padding so that
        the total length of the designation is a multiple of four. The pad
        field shall be ignored.
     
        An iSCSI Name with IPname designation is valid if the device server
        has access to a SCSI domain containing an IP network and there exists
        an iSCSI Node on that network with the specified iSCSI Name. The
        domain name, port number and internet protocol number provided in the
        designation may be used by a device server for addressing to discover
        and establish communication with the named iSCSI Node. Alternatively,
        the device server may use other protocol specific or vendor specific
        methods to discover and establish communication with the named iSCSI
        Node.
     
     
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     37 iSCSI Name with binary IPv6 address designation format
     
        The following table describes the iSCSI Name with IPv6 address
        designation format.
     
          Byte /    0       |       1       |       2       |       3       |
             /              |               |               |               |
            |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
            +---------------+---------------+---------------+---------------+
           0| iSCSI Name + Null (00h) + pad (0) (if necessary)              |
           +/                                                               /
            +---------------+---------------+---------------+---------------+
           x| IPv6 address                                                  |
           +/                                                               /
            +---------------+---------------+---------------+---------------+
        x+16| Reserved                      | Port Number                   |
            +---------------+---------------+---------------+---------------+
        x+20| Reserved                      | Internet Protocol Number      |
            +---------------+---------------+---------------+---------------+
        x+24
     
     
        The iSCSI Name field shall contain the iSCSI Name of an iSCSI Node.
     
        A Null (00h) byte shall terminate the iSCSI Name.
     
        Zero to three bytes set to zero shall be appended as padding so that
        the total length of the designation is a multiple of four. The pad
        field shall be ignored.
     
        The IPv6 Address field shall contain an IPv6 address. See [RFC2373]
        for a description of IPv6 addresses.
     
        The Port Number field shall contain a port number. See [RFC790] for a
        description of port numbers.
     
        The Internet Protocol Number field shall contain an Internet protocol
        number. See [RFC790] for a description of Internet protocol numbers.
     
        An iSCSI Name with IPv6 address designation is valid if the device
        server has access to a SCSI domain containing an IP network and there
        exists an iSCSI Node on that network with the specified iSCSI Name.
        The IPv6 address, port number and internet protocol number provided
        in the designation may be used by a device server for addressing to
        discover and establish communication with the named iSCSI Node.
     
     
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        Alternatively, the device server may use other protocol specific or
        vendor specific methods to discover and establish communication with
        the named iSCSI Node.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Appendix G. 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, and each of the recovery classes described has
        initiator procedures as well as target procedures.  Readers may
        please note that 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 like recovery of Synchronization on a
             header digest error are considered out-of-scope in these
             algorithms.  In this particular example, header digest error
             may lead to connection recovery if sync and steering layer is
             not implemented.
     
        It may also be noted that these algorithms strive to convey the iSCSI
        error recovery concepts in simplest terms, and are not designed to be
        optimal.
     
     38 General Data structure and procedure description
     
        This section defines the procedures and data structures that are
        commonly used by all the error recovery algorithms.  Please note that
        the structures may not be the exhaustive representations of what is
        required for a typical implementation.
     
        Data structure definitions -
        struct TransferContext {
                int TargetTransferTag;
                int ExpectedDataSN;
        };
     
        struct TCB {
                Boolean SoFarInOrder;
                int ExpectedDataSN; /* used for both R2Ts, and Data */
                int MissingDataSNList[MaxMissingDPDU];
                Boolean FbitReceived;
                Boolean StatusXferd;
                Boolean CurrentlyAllegiant;
                int ActiveR2Ts;
                int Response;
                char *Reason;
                struct TransferContext
     
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                            TransferContextList[MaxOutStandingR2T];
                int InitiatorTaskTag;
                int CmdSN;
        };
     
        struct Connection {
                struct Session SessionReference;
                Boolean SoFarInOrder;
                int CID;
                int State;
                int ExpectedStatSN;
                int MissingStatSNList[MaxMissingSPDU];
                Boolean PerformConnectionRecovery;
        };
     
        struct Session {
                int NumConnections;
                int ISID;
                int TSID;
                int NextCmdSN;
                int Maxconnections;
                Boolean FailoverSupport;
                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);
     
     39 Within-command error recovery algorithms
     
     1  Procedure descriptions
     
        Recover-Data-if-Possible(last required DataSN, task control block);
        Build-And-Send-DSnack(task control block);
        Build-And-Send-Abort(task control block);
        SCSI-Task-Completion(task control block);
        Build-And-Send-a-Data-Burst(transport connection, R2T PDU,
                                                      task control block);
        Build-And-Send-R2T(transport connection, description of data,
                                                     task control block);
        Build-And-Send-Status(transport connection, task control block);
        Transfer-Context-Timeout-Handler(transfer context);
     
     
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        Implementation-specific tunables -
        InitiatorDataSNACKEnabled, TargetDataSNACKSupported,
        TargetRecoveryR2TEnabled.
     
        Notes:
     
             - Some procedures used in this section - Recover-Status-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 carrying StatSN -
               SCSI Response, Text Response etc.
     
     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 = "Delivery subsystem failure";
                 }
            } else {
                  TCB.Reason = "Delivery subsystem failure";
            }
            if (TCB.Reason = "Delivery subsystem failure") {
                  Clear the missing PDU list in the TCB.
                  if (TCB.StatusXferd is not TRUE)
                     Build-And-Send-Abort(TCB);
            }
        }
     
        Receive-a-In-PDU(Connection, CurrentPDU)
        {
           check-basic-validity(CurrentPDU);
           if (Header-Digest-Bad) discard, return;
           Retrieve TCB for CurrentPDU.InitiatorTaskTag.
           if ((CurrentPDU.type = Data)
                       or (CurrentPDU.type = R2T)) {
              if (Data-Digest-Bad) {
                send-data-SNACK = TRUE;
                LastRequiredDataSN = CurrentPDU.DataSN;
              } else {
                    if (TCB.SoFarInOrder = TRUE) {
     
     
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                        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 (current PDU has F-bit set) {
                  TCB.FbitReceived = TRUE;
              }
              if (send-data-SNACK is TRUE and
                        task is not already considered failed) {
                    Recover-Data-if-Possible(LastRequiredDataSN, TCB);
              }
              if (missing data PDU list is empty) {
                 TCB.SoFarInOrder = TRUE;
              }
              if (CurrentPDU.type = R2T) {
                 Increment ActiveR2Ts for this task.
                 Build-And-Send-A-Data-Burst(Connection, CurrentPDU, TCB);
              }
           } else if (CurrentPDU.type = Response) {
              if (Data-Digest-Bad) {
                 send-status-SNACK = TRUE;
              } else {
                 TCB.StatusXferd = TRUE;
                 Store the status information in TCB.
                 if (ExpDataSN does not match) {
                      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,
     
     
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                                              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 ) {
                  if (TCB.StatusXferd is TRUE and
                       (TCB.FbitReceived is TRUE or
                                task is already considered failed)) {
                             SCSI-Task-Completion(TCB);
                  }
           }
        }
     
     3  Target algorithms
     
        Receive-a-In-PDU(Connection, CurrentPDU)
        {
          check-basic-validity(CurrentPDU);
          if (Header-Digest-Bad) {
              Build-And-Send-Reject(Connection, CurrentPDU,
                                           Header-Digest-Error);
              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) {
                     Decrement TCB.ActiveR2Ts.
                     if (current PDU is unsolicited and
                            data received is less than I/O size and
                              data received is less than FirstBurstSize) {
                         send-recovery-R2T = TRUE;
                         Note the missing data PDUs in MissingDataRange[].
     
     
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                     }
                 }
              }
              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 = "Delivery subsystem failure";
                 }
              }
              if (TCB.ActiveR2Ts = 0) {
                 Build-And-Send-Status(Connection, TCB);
              }
          } else if (CurrentPDU.type = SNACK) {
              if (this is data retransmission request) {
                 if (TargetDataSNACKSupported) {
                      if (the request is satisfiable) {
                            Build-And-Send-A-Data-Burst(CurrentPDU, TCB);
                      } else {
                            TCB.Reason = "SNACK Rejected";
                      }
                 } else {
                      TCB.Reason = "SNACK Rejected";
                 }
                 if (TCB.Reason = "SNACK Rejected") {
                      Build-And-Send-Reject(Connection, CurrentPDU,
                                                          Data-SNACK-Reject);
                      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.
     
     
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          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 = "Delivery subsystem failure";
              if (TCB.ActiveR2Ts = 0) {
                 Build-And-Send-Status(Connection, TCB);
              }
          }
        }
     
     40 Within-connection recovery algorithms
     
     4  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,
                                            Retrybit);
        Command-Acknowledge-Timeout-Handler(task control block);
        Status-Expect-Timeout-Handler(transport connection);
        Build-And-Send-Nop-Out(transport connection);
        Handle-Status-SNACK-request(transport connection, status SNACK PDU);
        Retransmit-Status-Burst(status SNACK, task control block);
        Is-Acknowledged(beginning StatSN, run size);
     
        Implementation-specific tunables -
        InitiatorCommandRetryEnabled, InitiatorStatusExpectNopEnabled,
        InitiatorProactiveSNACKEnabled, InitiatorStatusSNACKEnabled,
        TargetStatusSNACKSupported.
     
        Notes:
        The initiator algorithms deal only 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 algorithms, again leading to Recover-
        Status-if-Possible.
        The pseudo-code shown may result in retransmission of unacknowledged
        commands in more cases than is necessary.  This will not however
        affect the correctness of operation since the target is required to
        discard the duplicate CmdSNs.
     
     
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        The procedure Build-And-Send-Async is defined in Connection recovery
        algorithms.
        The procedure Status-Expect-Timeout-Handler describes how initiators
        may proactively attempt to retrieve Status if they choose to. This
        procedure is assumed to be triggered much before the standard ULP
        timeout.
     
     1. Initiator algorithms
     
        Recover-Status-if-Possible(Connection, CurrentPDU)
        {
            if ((Connection.state = LOGGED_IN) and
                     connection is not already considered failed) {
               if (InitiatorStatusSNACKEnabled) {
                  if (# of missing PDUs is trackable) {
                    Note the missing StatSNs in Connection;
                    Build-And-Send-SSnack(Connection);
                  } else {
                    Connection.PerformConnectionRecovery = TRUE;
                  }
               } else {
                  Connection.PerformConnectionRecovery = TRUE;
               }
               if (Connection.PerformConnectionRecovery is TRUE) {
                  Start-Timer(Connection-Recovery-Handler, Connection, 0);
               }
            }
        }
     
        Retransmit-Command-if-Possible(Connection, CmdSN)
        {
            if (InitiatorCommandRetryEnabled) {
               Retrieve the InitiatorTaskTag, and thus TCB for the CmdSN.
               Build-And-Send-Command(Connection, TCB, Retrybit);
            }
        }
     
        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;
     
     
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               }
            } else {
               if (current StatSN was considered missing) {
                    remove current StatSN from the missing list.
               } else {
                    if (current StatSN is higher than expected){
                        send-status-SNACK = TRUE;
                    } else {
                        discard, return;
                    }
               }
               Adjust Connection.ExpectedStatSN if appropriate.
               if (missing StatSN list is empty) {
                    Connection.SoFarInOrder = TRUE;
               }
            }
            return send-status-SNACK;
        }
     
        Receive-a-In-PDU(Connection, CurrentPDU)
        {
            check-basic-validity(CurrentPDU);
            if (Header-Digest-Bad) discard, return;
            Retrieve TCB for CurrentPDU.InitiatorTaskTag.
            if (CurrentPDU.type = Nop-In) {
                  if (the PDU is unsolicited) {
                        if (current StatSN is not expected) {
                         Recover-Status-if-Possible(Connection, CurrentPDU);
                        }
                        if (current ExpCmdSN is not our NextCmdSN) {
                            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 */
     
     
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            }
        }
     
        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);
                }
            }
        }
     
     2. 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,
                                         0, TargetConnectionRecoveryTimeout);
            }
        }
     
     5  Connection recovery algorithms
     
     3. Procedure descriptions
     
        Build-And-Send-Async(transport connection, reason code,
                                           minimum time, maximum time);
        Pick-A-Logged-In-Connection(session);
     
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        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,
                                                       bits to set);
        Connection-Recovery-Handler(transport connection);
        Connection-Resource-Timeout-Handler(transport connection);
        Quiesce-And-Prepare-for-New-Allegiance(session, task control block);
        Build-And-Send-Logout-Response(transport connection,
                                 CID of connection in recovery, reason code);
        Build-And-Send-TaskMgmt-Response(transport connection,
                               task mgmt command PDU, response code);
        Establish-New-Allegiance(task control block, transport connection);
        Schedule-Command-To-Continue(task control block);
        Notes:
        Transport exception conditions such as unexpected connection
        termination, connection reset, hung connection while the connection
        is in the full-feature phase, are all assumed to be asynchronously
        signaled to iSCSI layer using the Transport_Exception_Handler
        procedure.
     
     4. Initiator algorithms
     
        Receive-a-In-PDU(Connection, CurrentPDU)
        {
            check-basic-validity(CurrentPDU);
            if (Header-Digest-Bad) discard, return;
            Retrieve TCB from CurrentPDU.InitiatorTaskTag.
            if (CurrentPDU.type = Async) {
                if ((CurrentPDU.iSCSIEvent = LogoutRequest) or
                        (CurrentPDU.iSCSIEvent = ConnectionDropped)) {
                  Retrieve the AffectedConnection for CurrentPDU.Parameter1.
                  AffectedConnection.State = ASYNC_MSG_RCVD;
                  AffectedConnection.PerformConnectionRecovery = TRUE;
                  Start-Timer(Connection-Recovery-Handler,
                                AffectedConnection, CurrentPDU.Parameter2);
                }
            } else if (CurrentPDU.type = LogoutResponse) {
                Retrieve the RecoveryConnection for CurrentPDU.CID.
                if (CurrentPDU.Response = failure) {
                   RecoveryConnection.State = RECOVERY_START;
                   Start-Timer(Connection-Resource-Timeout-Handler,
                               RecoveryConnection, InitiatorRecoveryTimeout);
     
     
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                } else {
                    RecoveryConnection.State = FREE;
                }
            } else if (CurrentPDU.type = LoginResponse) {
                 if (this is a response to an implicit Logout) {
                    Retrieve the RecoveryConnection.
                    if (successful) {
                        RecoveryConnection.State = FREE;
                        Connection.State = LOGGED_IN;
                    } else {
                         RecoveryConnection.State = RECOVERY_START;
                         DestroyTransportConnection(Connection);
                         Start-Timer(Connection-Resource-Timeout-Handler,
                               RecoveryConnection, InitiatorRecoveryTimeout);
                    }
                 }
            } else { /* REST UNRELATED TO CONNECTION-RECOVERY,
                      * NOT SHOWN */
            }
            if (RecoveryConnection.State = FREE) {
               for (each command that was active on RecoveryConnection) {
                    NewConnection = Pick-A-Logged-In-Connection(Session);
                    Build-And-Send-Command(NewConnection, TCB, Retrybit);
                }
            }
        }
     
        Connection-Recovery-Handler(Connection)
        {
            Retrieve Session from Connection.
            if (Connection can still exchange iSCSI PDUs) {
                NewConnection = Connection;
            } else {
                if (there are other logged-in connections) {
                     NewConnection = Pick-A-Logged-In-Connection(Session);
                } else {
                     NewConnection =
                          CreateTransportConnection(Session.OtherEndInfo);
                     Initiate an implicit Logout on NewConnection for
                                                       Connection.CID.
                     return;
                }
            }
            Build-And-Send-Logout(NewConnection, Connection.CID,
                                                RecoveryRemove);
        }
     
     
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        Transport_Exception_Handler(Connection)
        {
            Connection.PerformConnectionRecovery = TRUE;
            if (the event is an unexpected transport disconnect) {
                Connection.State = XPT_CLEANUP;
            } else {
                Connection.State = RECOVERY_START;
            }
            Start-Timer(Connection-Recovery-Handler, Connection, 0);
        }
     
     5. Target algorithms
     
        Receive-a-In-PDU(Connection, CurrentPDU)
        {
            check-basic-validity(CurrentPDU);
            if (Header-Digest-Bad) {
              Build-And-Send-Reject(Connection, CurrentPDU,
                                              Header-Digest-Error);
              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 RecoveryConnection from CurrentPDU.CID).
                   for (each command active on RecoveryConnection) {
                        Quiesce-And-Prepare-for-New-Allegiance(Session, TCB);
                        TCB.CurrentlyAllegiant = FALSE;
                   }
                   Cleanup-Connection-State(RecoveryConnection);
                   if ((quiescing successful) and (cleanup successful)) {
                        Build-And-Send-Logout-Response(Connection,
                                            RecoveryConnection.CID, Sucess);
                   } else {
                        Build-And-Send-Logout-Response(Connection,
                                            RecoveryConnection.CID, Failure);
                   }
               }
            } else if (CurrentPDU.type = TaskManagement) {
                 if (CurrentPDU.function = "TaskReassign") {
                       if (Session.FailoverSupport is not TRUE) {
     
     
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                                     iSCSI                       30-Sep-01
     
     
                          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.PerformConnectionRecovery = TRUE;
            if (the event is an unexpected transport disconnect) {
                Connection.State = XPT_CLEANUP;
            } else {
                Connection.State = RECOVERY_START;
            }
            Start-Timer(Connection-Resource-Timeout-Handler, Connection,
                                      TargetConnectionRecoveryTimeout);
            if (this Session has full-feature phase connections left) {
                 DifferentConnection = Pick-A-Logged-In-Connection(Session);
                 Build-And-Send-Async(DifferentConnection, DroppedConnection,
                                         0, TargetConnectionRecoveryTimeout);
            }
        }
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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     Full Copyright Statement
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        The limited permissions granted above are perpetual and will not be
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        This document and the information contained herein is provided on an
        "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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     Satran, J.       Standards-Track, Expires April 2002              211
     

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