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                              iSCSI                    19-January-03



   IP Storage Working Group                          Julian Satran
   Internet Draft                                      Kalman Meth
   draft-ietf-ips-iscsi-20.txt                                 IBM
   Category: standards-track
                                                 Costa Sapuntzakis
                                                     Cisco Systems

                                            Mallikarjun Chadalapaka
                                               Hewlett-Packard Co.

                                                       Efri Zeidner
                                                            SANGate





                            iSCSI









































































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Status of this Memo

   This document is an Internet-Draft and fully conforms to all
   provisions of Section 10 of RFC2026.

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


Abstract

   The Small Computer Systems Interface (SCSI) is a popular family of
   protocols that enable systems to communicate with I/O devices,
   especially storage devices. SCSI protocols are request/response
   application protocols with a common standardized architecture model
   and basic command set as well as standardized command sets for
   different device classes (disks, tapes, media-changers etc.).

   As system interconnects move from the classical bus structure to a
   network structure SCSI has to be mapped to network transport
   protocols.  IP networks now meet the performance requirements of
   fast system interconnects and as such are good candidates to "carry"
   SCSI.

   This document describes a transport protocol for SCSI that works on
   top of TCP. The iSCSI protocol aims to be fully compliant with the
   standardized SCSI architectural model.

Acknowledgements

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

   Furthermore, a large group of people contributed to this work
   through their review, comments, and valuable insights. We are
   grateful to all of them. We especially thank those people who found
   the time and patience to take part in our weekly phone conferences
   and intermediate meetings in Almaden and Haifa, which helped shape
   this document: Prasenjit Sarkar, Meir Toledano, John Dowdy, Steve
   Legg, Alain Azagury (IBM), Dave Nagle (CMU), David Black (EMC), John
   Matze (Veritas - now Okapi Software), Steve DeGroote, Mark Schrandt
   (Cisco), Gabi Hecht (Gadzoox), Robert Snively and Brian Forbes
   (Brocade), Nelson Nachum (StorAge), and Uri Elzur (Broadcom). Many
   others helped edit and improve this document within the IPS working


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   group. We are especially grateful to David Robinson and Raghavendra
   Rao (Sun), Charles Monia, Joshua Tseng (Nishan), Somesh Gupta
   (Silverback), Michael Krause, Pierre Labat, Santosh Rao, Matthew
   Burbridge, Bob Barry, Robert Elliott, Nick Martin (HP), Stephen
   Bailey (Sandburst), Steve Senum, Ayman Ghanem, Dave Peterson
   (Cisco), Barry Reinhold (Trebia Networks), Bob Russell (UNH), Eddy
   Quicksall (iVivity, Inc.), Bill Lynn and Michael Fischer (Adaptec),
   Vince Cavanna, Pat Thaler (Agilent), Jonathan Stone (Stanford),
   Luben Tuikov (Splentec), Paul Koning (EqualLogic), Michael Krueger
   (Windriver), Martins Krikis (Intel), Doug Otis (Sanlight), John
   Marberg (IBM), Robert Griswold and Bill Moody (Crossroads), Bill
   Studenmund (Wasabi Systems), Elizabeth Rodriguez (Brocade) and Yaron
   Klein (Sanrad). The recovery chapter was enhanced with the help of
   Stephen Bailey (Sandburst), Somesh Gupta (Silverback), and Venkat
   Rangan (Rhapsody Networks). Eddy Quicksall contributed some examples
   and began the Definitions section. Michael Fischer and Bob Barry
   started the Acronyms section. Last, but not least, we thank 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, and Micky
   Rodeh, Jai Menon, Clod Barrera, and Andy Bechtolsheim for helping
   make this work happen.

   In addition to this document, we recommend you acquaint yourself
   with the following in order to get a full understanding of the iSCSI
   specification: "iSCSI Naming & Discovery"[NDT], "Bootstrapping
   Clients using the iSCSI Protocol" [BOOT], "Securing Block Storage
   Protocols over IP"[SEC-IPS] documents, and "iSCSI Requirements and
   Design Considerations" [RFC3347].

   The "iSCSI Naming & Discovery" document is authored by:

        Mark Bakke (Cisco), Jim Hafner, John Hufferd, Kaladhar Voruganti
          (IBM), and Marjorie Krueger (HP).


   The "Bootstrapping Clients using the iSCSI Protocol" document is
   authored by:

        Prasenjit Sarkar (IBM), Duncan Missimer (HP), and Costa
          Sapuntzakis (Cisco).

   The "Securing Block Storage Protocols over IP" document is authored
   by:

        Bernard Aboba (Microsoft), Joshua Tseng (Nishan), Jesse Walker
          (Intel), Venkat Rangan (Rhapsody Networks), and Franco
          Travostino (Nortel Networks).

   The "iSCSI Requirements and Design Considerations" document is
   authored by:

        Marjorie Krueger, Randy Haagens (HP), Costa Sapuntzakis, and
          Mark Bakke (Cisco).



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











































































































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 Status of this Memo  . . . . . . . . . . . . . . . . . . . . . . .  2
 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  2
 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . .  2
1. Introduction   . . . . . . . . . . . . . . . . . . . . . . . . . 13
2. Definitions and Acronyms   . . . . . . . . . . . . . . . . . . . 14
  2.1 Definitions   . . . . . . . . . . . . . . . . . . . . . . . . 14
  2.2 Acronyms  . . . . . . . . . . . . . . . . . . . . . . . . . . 18
  2.3 Conventions   . . . . . . . . . . . . . . . . . . . . . . . . 19
    2.3.1 Word Rule   . . . . . . . . . . . . . . . . . . . . . . . 20
    2.3.2 Half-Word Rule  . . . . . . . . . . . . . . . . . . . . . 20
    2.3.3 Byte Rule   . . . . . . . . . . . . . . . . . . . . . . . 20
3. Overview   . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
  3.1 SCSI Concepts   . . . . . . . . . . . . . . . . . . . . . . . 21
  3.2 iSCSI Concepts and Functional Overview  . . . . . . . . . . . 21
    3.2.1 Layers and Sessions   . . . . . . . . . . . . . . . . . . 22
    3.2.2 Ordering and iSCSI Numbering  . . . . . . . . . . . . . . 23
      3.2.2.1 Command Numbering and Acknowledging   . . . . . . . . 23
      3.2.2.2 Response/Status Numbering and Acknowledging   . . . . 26
      3.2.2.3 Data Sequencing   . . . . . . . . . . . . . . . . . . 26
    3.2.3 iSCSI Login   . . . . . . . . . . . . . . . . . . . . . . 27
    3.2.4 iSCSI Full Feature Phase  . . . . . . . . . . . . . . . . 28
      3.2.4.1 Command Connection Allegiance   . . . . . . . . . . . 28
      3.2.4.2 Data Transfer Overview  . . . . . . . . . . . . . . . 29
      3.2.4.3 Tags and Integrity Checks   . . . . . . . . . . . . . 30
      3.2.4.4 Task Management   . . . . . . . . . . . . . . . . . . 30
    3.2.5 iSCSI Connection Termination  . . . . . . . . . . . . . . 31
    3.2.6 iSCSI Names   . . . . . . . . . . . . . . . . . . . . . . 31
      3.2.6.1 iSCSI Name Properties   . . . . . . . . . . . . . . . 31
      3.2.6.2 iSCSI Name Encoding   . . . . . . . . . . . . . . . . 33
      3.2.6.3 iSCSI Name Structure  . . . . . . . . . . . . . . . . 33
        3.2.6.3.1 Type "iqn." (iSCSI Qualified Name)  . . . . . . . 34
        3.2.6.3.2 Type "eui." (IEEE EUI-64 format)  . . . . . . . . 35
    3.2.7 Persistent State  . . . . . . . . . . . . . . . . . . . . 35
    3.2.8 Message Synchronization and Steering  . . . . . . . . . . 36
      3.2.8.1 Sync/Steering and iSCSI PDU Length  . . . . . . . . . 37
  3.3 iSCSI Session Types   . . . . . . . . . . . . . . . . . . . . 37
  3.4 SCSI to iSCSI Concepts Mapping Model  . . . . . . . . . . . . 37
    3.4.1 iSCSI Architecture Model  . . . . . . . . . . . . . . . . 38
    3.4.2 SCSI Architecture Model   . . . . . . . . . . . . . . . . 40
    3.4.3 Consequences of the Model   . . . . . . . . . . . . . . . 42
      3.4.3.1 I_T Nexus State   . . . . . . . . . . . . . . . . . . 43
  3.5 Request/Response Summary  . . . . . . . . . . . . . . . . . . 43
    3.5.1 Request/Response Types Carrying SCSI Payload  . . . . . . 43
      3.5.1.1 SCSI-Command  . . . . . . . . . . . . . . . . . . . . 43
      3.5.1.2 SCSI-Response   . . . . . . . . . . . . . . . . . . . 43
      3.5.1.3 Task Management Function Request  . . . . . . . . . . 44
      3.5.1.4 Task Management Function Response   . . . . . . . . . 44
      3.5.1.5 SCSI Data-out and SCSI Data-in  . . . . . . . . . . . 45


















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      3.5.1.6 Ready To Transfer (R2T)   . . . . . . . . . . . . . . 45
    3.5.2 Requests/Responses carrying SCSI and iSCSI Payload  . . . 46
      3.5.2.1 Asynchronous Message  . . . . . . . . . . . . . . . . 46
    3.5.3 Requests/Responses Carrying iSCSI Only Payload  . . . . . 46
      3.5.3.1 Text Request and Text Response  . . . . . . . . . . . 46
      3.5.3.2 Login Request and Login Response  . . . . . . . . . . 46
      3.5.3.3 Logout Request and Response   . . . . . . . . . . . . 47
      3.5.3.4  SNACK Request  . . . . . . . . . . . . . . . . . . . 47
      3.5.3.5 Reject  . . . . . . . . . . . . . . . . . . . . . . . 47
      3.5.3.6 NOP-Out Request and NOP-In Response   . . . . . . . . 48
4. SCSI Mode Parameters for iSCSI   . . . . . . . . . . . . . . . . 49
5. Login and Full Feature Phase Negotiation   . . . . . . . . . . . 50
  5.1 Text Format   . . . . . . . . . . . . . . . . . . . . . . . . 51
  5.2 Text Mode Negotiation   . . . . . . . . . . . . . . . . . . . 54
    5.2.1 List negotiations   . . . . . . . . . . . . . . . . . . . 56
    5.2.2 Simple-value Negotiations   . . . . . . . . . . . . . . . 56
  5.3 Login Phase   . . . . . . . . . . . . . . . . . . . . . . . . 57
    5.3.1 Login Phase Start   . . . . . . . . . . . . . . . . . . . 59
    5.3.2 iSCSI Security Negotiation  . . . . . . . . . . . . . . . 61
    5.3.3 Operational Parameter Negotiation During the Login Phase  62
    5.3.4 Connection Reinstatement  . . . . . . . . . . . . . . . . 63
    5.3.5 Session Reinstatement, Closure, and Timeout   . . . . . . 63
      5.3.5.1 Loss of Nexus Notification  . . . . . . . . . . . . . 64
    5.3.6 Session Continuation and Failure  . . . . . . . . . . . . 64
  5.4 Operational Parameter Negotiation Outside the Login Phase   . 64
6. iSCSI Error Handling and Recovery  . . . . . . . . . . . . . . . 66
  6.1 Overview  . . . . . . . . . . . . . . . . . . . . . . . . . . 66
    6.1.1 Background  . . . . . . . . . . . . . . . . . . . . . . . 66
    6.1.2 Goals   . . . . . . . . . . . . . . . . . . . . . . . . . 66
    6.1.3 Protocol Features and State Expectations  . . . . . . . . 67
    6.1.4 Recovery Classes  . . . . . . . . . . . . . . . . . . . . 67
      6.1.4.1 Recovery Within-command   . . . . . . . . . . . . . . 68
      6.1.4.2 Recovery Within-connection  . . . . . . . . . . . . . 69
      6.1.4.3 Connection Recovery   . . . . . . . . . . . . . . . . 69
      6.1.4.4 Session Recovery  . . . . . . . . . . . . . . . . . . 70
    6.1.5 Error Recovery Hierarchy  . . . . . . . . . . . . . . . . 70
  6.2 Retry and Reassign in Recovery  . . . . . . . . . . . . . . . 72
    6.2.1 Usage of Retry  . . . . . . . . . . . . . . . . . . . . . 72
    6.2.2 Allegiance Reassignment   . . . . . . . . . . . . . . . . 73
  6.3 Usage Of Reject PDU in Recovery   . . . . . . . . . . . . . . 74
  6.4 Connection Timeout Management   . . . . . . . . . . . . . . . 74
    6.4.1 Timeouts on Transport Exception Events  . . . . . . . . . 74
    6.4.2 Timeouts on Planned Decommissioning   . . . . . . . . . . 75
  6.5 Implicit Termination of Tasks   . . . . . . . . . . . . . . . 75
  6.6 Format Errors   . . . . . . . . . . . . . . . . . . . . . . . 76
  6.7 Digest Errors   . . . . . . . . . . . . . . . . . . . . . . . 76
  6.8 Sequence Errors   . . . . . . . . . . . . . . . . . . . . . . 77
  6.9 SCSI Timeouts   . . . . . . . . . . . . . . . . . . . . . . . 78


















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  6.10 Negotiation Failures   . . . . . . . . . . . . . . . . . . . 78
  6.11 Protocol Errors  . . . . . . . . . . . . . . . . . . . . . . 79
  6.12 Connection Failures  . . . . . . . . . . . . . . . . . . . . 79
  6.13 Session Errors   . . . . . . . . . . . . . . . . . . . . . . 80
7. State Transitions  . . . . . . . . . . . . . . . . . . . . . . . 81
  7.1 Standard Connection State Diagrams  . . . . . . . . . . . . . 81
    7.1.1 State Descriptions for Initiators and Targets   . . . . . 81
    7.1.2 State Transition Descriptions for Initiators and Targets  82
    7.1.3 Standard Connection State Diagram for an Initiator  . . . 85
    7.1.4 Standard Connection State Diagram for a Target  . . . . . 87
  7.2 Connection Cleanup State Diagram for Initiators and Targets   89
    7.2.1 State Descriptions for Initiators and Targets   . . . . . 90
    7.2.2 State Transition Descriptions for Initiators and Targets  91
  7.3 Session State Diagrams  . . . . . . . . . . . . . . . . . . . 92
    7.3.1 Session State Diagram for an Initiator  . . . . . . . . . 92
    7.3.2 Session State Diagram for a Target  . . . . . . . . . . . 93
    7.3.3 State Descriptions for Initiators and Targets   . . . . . 94
    7.3.4 State Transition Descriptions for Initiators and Targets  94
8. Security Considerations  . . . . . . . . . . . . . . . . . . . . 96
  8.1 iSCSI Security Mechanisms   . . . . . . . . . . . . . . . . . 96
  8.2 In-band Initiator-Target Authentication   . . . . . . . . . . 96
    8.2.1 CHAP Considerations   . . . . . . . . . . . . . . . . . . 97
    8.2.2 SRP Considerations  . . . . . . . . . . . . . . . . . . . 99
  8.3 IPsec   . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
    8.3.1 Data Integrity and Authentication   . . . . . . . . . . . 99
    8.3.2 Confidentiality   . . . . . . . . . . . . . . . . . . . .100
    8.3.3 Policy, Security Associations, and Cryptographic Key
Management  . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
9. Notes to Implementers  . . . . . . . . . . . . . . . . . . . . .102
  9.1 Multiple Network Adapters   . . . . . . . . . . . . . . . . .102
    9.1.1 Conservative Reuse of ISIDs   . . . . . . . . . . . . . .102
    9.1.2 iSCSI Name, ISID, and TPGT Use  . . . . . . . . . . . . .103
  9.2 Autosense and Auto Contingent Allegiance (ACA)  . . . . . . .104
  9.3 iSCSI Timeouts  . . . . . . . . . . . . . . . . . . . . . . .104
  9.4 Command Retry and Cleaning Old Command Instances  . . . . . .105
  9.5 Synch and Steering Layer and Performance  . . . . . . . . . .105
  9.6 Considerations for State-dependent Devices and Long-lasting SCSI
Operations  . . . . . . . . . . . . . . . . . . . . . . . . . . . .105
    9.6.1 Determining the Proper ErrorRecoveryLevel   . . . . . . .106
10. iSCSI PDU Formats   . . . . . . . . . . . . . . . . . . . . . .107
  10.1 iSCSI PDU Length and Padding   . . . . . . . . . . . . . . .107
  10.2 PDU Template, Header, and Opcodes  . . . . . . . . . . . . .107
    10.2.1 Basic Header Segment (BHS)   . . . . . . . . . . . . . .108
      10.2.1.1 I  . . . . . . . . . . . . . . . . . . . . . . . . .108
      10.2.1.2 Opcode   . . . . . . . . . . . . . . . . . . . . . .108
      10.2.1.3 Final (F) bit  . . . . . . . . . . . . . . . . . . .109
      10.2.1.4 Opcode-specific Fields   . . . . . . . . . . . . . .109
      10.2.1.5 TotalAHSLength   . . . . . . . . . . . . . . . . . .109


















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      10.2.1.6 DataSegmentLength  . . . . . . . . . . . . . . . . .110
      10.2.1.7 LUN  . . . . . . . . . . . . . . . . . . . . . . . .110
      10.2.1.8 Initiator Task Tag   . . . . . . . . . . . . . . . .110
    10.2.2 Additional Header Segment (AHS)  . . . . . . . . . . . .110
      10.2.2.1 AHSType  . . . . . . . . . . . . . . . . . . . . . .110
      10.2.2.2 AHSLength  . . . . . . . . . . . . . . . . . . . . .111
      10.2.2.3 Extended CDB AHS   . . . . . . . . . . . . . . . . .111
      10.2.2.4 Bidirectional Expected Read-Data Length AHS  . . . .111
    10.2.3 Header Digest and Data Digest  . . . . . . . . . . . . .111
    10.2.4 Data Segment   . . . . . . . . . . . . . . . . . . . . .112
  10.3 SCSI Command . . . . . . . . . . . . . . . . . . . . . . . .113
    10.3.1 Flags and Task Attributes (byte 1)   . . . . . . . . . .113
    10.3.2 CmdSN - Command Sequence Number  . . . . . . . . . . . .114
    10.3.3 ExpStatSN  . . . . . . . . . . . . . . . . . . . . . . .114
    10.3.4 Expected Data Transfer Length  . . . . . . . . . . . . .114
    10.3.5 CDB - SCSI Command Descriptor Block  . . . . . . . . . .115
    10.3.6 Data Segment - Command Data  . . . . . . . . . . . . . .115
  10.4 SCSI Response  . . . . . . . . . . . . . . . . . . . . . . .116
    10.4.1 Flags (byte 1)   . . . . . . . . . . . . . . . . . . . .116
    10.4.2 Status   . . . . . . . . . . . . . . . . . . . . . . . .117
    10.4.3 Response   . . . . . . . . . . . . . . . . . . . . . . .117
    10.4.4 SNACK Tag  . . . . . . . . . . . . . . . . . . . . . . .118
    10.4.5 Residual Count   . . . . . . . . . . . . . . . . . . . .118
    10.4.6 Bidirectional Read Residual Count  . . . . . . . . . . .118
    10.4.7 Data Segment - Sense and Response Data Segment   . . . .119
      10.4.7.1 SenseLength  . . . . . . . . . . . . . . . . . . . .119
      10.4.7.2 Sense Data   . . . . . . . . . . . . . . . . . . . .119
    10.4.8 ExpDataSN  . . . . . . . . . . . . . . . . . . . . . . .120
    10.4.9 StatSN - Status Sequence Number  . . . . . . . . . . . .120
    10.4.10 ExpCmdSN - Next Expected CmdSN from this Initiator  . .120
    10.4.11 MaxCmdSN - Maximum CmdSN from this Initiator  . . . . .120
  10.5 Task Management Function Request . . . . . . . . . . . . . .121
    10.5.1 Function   . . . . . . . . . . . . . . . . . . . . . . .121
    10.5.2 TotalAHSLength and DataSegmentLength   . . . . . . . . .124
    10.5.3 LUN  . . . . . . . . . . . . . . . . . . . . . . . . . .124
    10.5.4 Referenced Task Tag  . . . . . . . . . . . . . . . . . .124
    10.5.5 RefCmdSN   . . . . . . . . . . . . . . . . . . . . . . .124
    10.5.6 ExpDataSN  . . . . . . . . . . . . . . . . . . . . . . .124
  10.6 Task Management Function Response  . . . . . . . . . . . . .126
    10.6.1 Response   . . . . . . . . . . . . . . . . . . . . . . .126
    10.6.2 Task Management Actions on Task Sets   . . . . . . . . .127
    10.6.3 TotalAHSLength and DataSegmentLength   . . . . . . . . .128
  10.7 SCSI Data-out & SCSI Data-in . . . . . . . . . . . . . . . .129
    10.7.1 F (Final) Bit  . . . . . . . . . . . . . . . . . . . . .130
    10.7.2 A (Acknowledge) bit  . . . . . . . . . . . . . . . . . .131
    10.7.3 Flags (byte 1)   . . . . . . . . . . . . . . . . . . . .131
    10.7.4 Target Transfer Tag and LUN  . . . . . . . . . . . . . .132
    10.7.5 DataSN   . . . . . . . . . . . . . . . . . . . . . . . .132


















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    10.7.6 Buffer Offset  . . . . . . . . . . . . . . . . . . . . .132
    10.7.7 DataSegmentLength  . . . . . . . . . . . . . . . . . . .133
  10.8 Ready To Transfer (R2T)  . . . . . . . . . . . . . . . . . .134
    10.8.1 TotalAHSLength and DataSegmentLength   . . . . . . . . .135
    10.8.2 R2TSN  . . . . . . . . . . . . . . . . . . . . . . . . .135
    10.8.3 StatSN   . . . . . . . . . . . . . . . . . . . . . . . .135
    10.8.4 Desired Data Transfer Length and Buffer Offset   . . . .135
    10.8.5 Target Transfer Tag  . . . . . . . . . . . . . . . . . .136
  10.9 Asynchronous Message . . . . . . . . . . . . . . . . . . . .137
    10.9.1 AsyncEvent   . . . . . . . . . . . . . . . . . . . . . .137
    10.9.2 AsyncVCode   . . . . . . . . . . . . . . . . . . . . . .139
    10.9.3 LUN  . . . . . . . . . . . . . . . . . . . . . . . . . .139
    10.9.4 Sense Data and iSCSI Event Data  . . . . . . . . . . . .139
      10.9.4.1 SenseLength  . . . . . . . . . . . . . . . . . . . .139
  10.10 Text Request  . . . . . . . . . . . . . . . . . . . . . . .141
    10.10.1 F (Final) Bit   . . . . . . . . . . . . . . . . . . . .141
    10.10.2 C (Continue) Bit  . . . . . . . . . . . . . . . . . . .142
    10.10.3 Initiator Task Tag  . . . . . . . . . . . . . . . . . .142
    10.10.4 Target Transfer Tag   . . . . . . . . . . . . . . . . .142
    10.10.5 Text  . . . . . . . . . . . . . . . . . . . . . . . . .143
  10.11 Text Response . . . . . . . . . . . . . . . . . . . . . . .144
    10.11.1 F (Final) Bit   . . . . . . . . . . . . . . . . . . . .144
    10.11.2 C (Continue) Bit  . . . . . . . . . . . . . . . . . . .145
    10.11.3 Initiator Task Tag  . . . . . . . . . . . . . . . . . .145
    10.11.4 Target Transfer Tag   . . . . . . . . . . . . . . . . .145
    10.11.5 StatSN  . . . . . . . . . . . . . . . . . . . . . . . .145
    10.11.6 Text Response Data  . . . . . . . . . . . . . . . . . .145
  10.12 Login Request . . . . . . . . . . . . . . . . . . . . . . .147
    10.12.1 T (Transit) Bit   . . . . . . . . . . . . . . . . . . .147
    10.12.2 C (Continue) Bit  . . . . . . . . . . . . . . . . . . .147
    10.12.3 CSG and NSG   . . . . . . . . . . . . . . . . . . . . .148
    10.12.4 Version   . . . . . . . . . . . . . . . . . . . . . . .148
      10.12.4.1 Version-max   . . . . . . . . . . . . . . . . . . .148
      10.12.4.2 Version-min   . . . . . . . . . . . . . . . . . . .148
    10.12.5 ISID  . . . . . . . . . . . . . . . . . . . . . . . . .148
    10.12.6 TSIH  . . . . . . . . . . . . . . . . . . . . . . . . .150
    10.12.7 Connection ID - CID   . . . . . . . . . . . . . . . . .150
    10.12.8 CmdSN   . . . . . . . . . . . . . . . . . . . . . . . .150
    10.12.9 ExpStatSN   . . . . . . . . . . . . . . . . . . . . . .151
    10.12.10 Login Parameters   . . . . . . . . . . . . . . . . . .151
  10.13 Login Response  . . . . . . . . . . . . . . . . . . . . . .152
    10.13.1 Version-max   . . . . . . . . . . . . . . . . . . . . .152
    10.13.2 Version-active  . . . . . . . . . . . . . . . . . . . .152
    10.13.3 TSIH  . . . . . . . . . . . . . . . . . . . . . . . . .153
    10.13.4 StatSN  . . . . . . . . . . . . . . . . . . . . . . . .153
    10.13.5 Status-Class and Status-Detail  . . . . . . . . . . . .153
    10.13.6 T (Transit) bit   . . . . . . . . . . . . . . . . . . .156
    10.13.7 C (Continue) Bit  . . . . . . . . . . . . . . . . . . .156


















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    10.13.8 Login Parameters  . . . . . . . . . . . . . . . . . . .156
  10.14 Logout Request  . . . . . . . . . . . . . . . . . . . . . .157
    10.14.1 Reason Code   . . . . . . . . . . . . . . . . . . . . .158
    10.14.2 TotalAHSLength and DataSegmentLength  . . . . . . . . .159
    10.14.3 CID   . . . . . . . . . . . . . . . . . . . . . . . . .159
    10.14.4 ExpStatSN   . . . . . . . . . . . . . . . . . . . . . .159
    10.14.5 Implicit termination of tasks   . . . . . . . . . . . .159
  10.15 Logout Response . . . . . . . . . . . . . . . . . . . . . .161
    10.15.1 Response  . . . . . . . . . . . . . . . . . . . . . . .161
    10.15.2 TotalAHSLength and DataSegmentLength  . . . . . . . . .161
    10.15.3 Time2Wait   . . . . . . . . . . . . . . . . . . . . . .162
    10.15.4 Time2Retain   . . . . . . . . . . . . . . . . . . . . .162
  10.16  SNACK Request  . . . . . . . . . . . . . . . . . . . . . .163
    10.16.1 Type  . . . . . . . . . . . . . . . . . . . . . . . . .164
    10.16.2 Data Acknowledgement  . . . . . . . . . . . . . . . . .164
    10.16.3 Resegmentation  . . . . . . . . . . . . . . . . . . . .164
    10.16.4 Initiator Task Tag  . . . . . . . . . . . . . . . . . .165
    10.16.5 Target Transfer Tag or SNACK Tag  . . . . . . . . . . .165
    10.16.6 BegRun  . . . . . . . . . . . . . . . . . . . . . . . .165
    10.16.7 RunLength   . . . . . . . . . . . . . . . . . . . . . .166
  10.17 Reject  . . . . . . . . . . . . . . . . . . . . . . . . . .167
    10.17.1 Reason  . . . . . . . . . . . . . . . . . . . . . . . .167
    10.17.2 DataSN/R2TSN  . . . . . . . . . . . . . . . . . . . . .169
    10.17.3 StatSN, ExpCmdSN and MaxCmdSN   . . . . . . . . . . . .169
    10.17.4 Complete Header of Bad PDU  . . . . . . . . . . . . . .169
  10.18 NOP-Out . . . . . . . . . . . . . . . . . . . . . . . . . .170
    10.18.1 Initiator Task Tag  . . . . . . . . . . . . . . . . . .170
    10.18.2 Target Transfer Tag   . . . . . . . . . . . . . . . . .171
    10.18.3 Ping Data   . . . . . . . . . . . . . . . . . . . . . .171
  10.19 NOP-In  . . . . . . . . . . . . . . . . . . . . . . . . . .172
    10.19.1 Target Transfer Tag   . . . . . . . . . . . . . . . . .173
    10.19.2 StatSN  . . . . . . . . . . . . . . . . . . . . . . . .173
    10.19.3 LUN   . . . . . . . . . . . . . . . . . . . . . . . . .173
11. iSCSI Security Text Keys and Authentication Methods   . . . . .174
  11.1 AuthMethod   . . . . . . . . . . . . . . . . . . . . . . . .174
    11.1.1 Kerberos   . . . . . . . . . . . . . . . . . . . . . . .176
    11.1.2 Simple Public-Key Mechanism (SPKM)   . . . . . . . . . .176
    11.1.3 Secure Remote Password (SRP)   . . . . . . . . . . . . .177
    11.1.4 Challenge Handshake Authentication Protocol (CHAP)   . .178
12. Login/Text Operational Text Keys  . . . . . . . . . . . . . . .180
  12.1 HeaderDigest and DataDigest  . . . . . . . . . . . . . . . .180
  12.2 MaxConnections   . . . . . . . . . . . . . . . . . . . . . .182
  12.3 SendTargets  . . . . . . . . . . . . . . . . . . . . . . . .182
  12.4 TargetName   . . . . . . . . . . . . . . . . . . . . . . . .182
  12.5 InitiatorName  . . . . . . . . . . . . . . . . . . . . . . .183
  12.6 TargetAlias  . . . . . . . . . . . . . . . . . . . . . . . .183
  12.7 InitiatorAlias   . . . . . . . . . . . . . . . . . . . . . .184
  12.8 TargetAddress  . . . . . . . . . . . . . . . . . . . . . . .184


















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  12.9 TargetPortalGroupTag   . . . . . . . . . . . . . . . . . . .185
  12.10 InitialR2T  . . . . . . . . . . . . . . . . . . . . . . . .185
  12.11 ImmediateData   . . . . . . . . . . . . . . . . . . . . . .186
  12.12 MaxRecvDataSegmentLength  . . . . . . . . . . . . . . . . .186
  12.13 MaxBurstLength  . . . . . . . . . . . . . . . . . . . . . .187
  12.14 FirstBurstLength  . . . . . . . . . . . . . . . . . . . . .187
  12.15 DefaultTime2Wait  . . . . . . . . . . . . . . . . . . . . .188
  12.16 DefaultTime2Retain  . . . . . . . . . . . . . . . . . . . .188
  12.17 MaxOutstandingR2T   . . . . . . . . . . . . . . . . . . . .188
  12.18 DataPDUInOrder  . . . . . . . . . . . . . . . . . . . . . .189
  12.19 DataSequenceInOrder   . . . . . . . . . . . . . . . . . . .189
  12.20 ErrorRecoveryLevel  . . . . . . . . . . . . . . . . . . . .189
  12.21 SessionType   . . . . . . . . . . . . . . . . . . . . . . .190
  12.22 The Private or Public Extension Key Format  . . . . . . . .190
13. IANA Considerations   . . . . . . . . . . . . . . . . . . . . .192
  13.1 Naming Requirements  . . . . . . . . . . . . . . . . . . . .193
  13.2 Mechanism Specification Requirements   . . . . . . . . . . .193
  13.3 Publication Requirements   . . . . . . . . . . . . . . . . .193
  13.4 Security Requirements  . . . . . . . . . . . . . . . . . . .193
  13.5 Registration Procedure   . . . . . . . . . . . . . . . . . .194
    13.5.1 Present the iSCSI extension item to the Community  . . .194
    13.5.2 iSCSI extension item review and IESG approval  . . . . .194
    13.5.3 IANA Registration  . . . . . . . . . . . . . . . . . . .194
    13.5.4 Standard iSCSI extension item-label format   . . . . . .194
  13.6 IANA Procedures for Registering iSCSI extension items  . . .195
 References and Bibliography  . . . . . . . . . . . . . . . . . .  196
 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .  198
Appendix A. Sync and Steering with Fixed Interval Markers   . . . .199
   A.1 Markers At Fixed Intervals   . . . . . . . . . . . . . . . .199
   A.2 Initial Marker-less Interval   . . . . . . . . . . . . . . .200
   A.3 Negotiation  . . . . . . . . . . . . . . . . . . . . . . . .200
      A.3.1 OFMarker, IFMarker  . . . . . . . . . . . . . . . . . .200
      A.3.2 OFMarkInt, IFMarkInt  . . . . . . . . . . . . . . . . .201
Appendix B. Examples  . . . . . . . . . . . . . . . . . . . . . . .202
   B.1 Read Operation Example   . . . . . . . . . . . . . . . . . .202
   B.2 Write Operation Example  . . . . . . . . . . . . . . . . . .202
   B.3 R2TSN/DataSN Use Examples  . . . . . . . . . . . . . . . . .202
   B.4 CRC Examples   . . . . . . . . . . . . . . . . . . . . . . .205
Appendix C. Login Phase Examples  . . . . . . . . . . . . . . . . .207
Appendix D. SendTargets Operation   . . . . . . . . . . . . . . . .215
Appendix E. Algorithmic Presentation of Error Recovery Classes  . .219
   E.1 General Data Structure and Procedure Description   . . . . .219
   E.2 Within-command Error Recovery Algorithms   . . . . . . . . .220
      E.2.1 Procedure Descriptions  . . . . . . . . . . . . . . . .220
      E.2.2 Initiator Algorithms  . . . . . . . . . . . . . . . . .221
      E.2.3 Target Algorithms   . . . . . . . . . . . . . . . . . .223
   E.3 Within-connection Recovery Algorithms  . . . . . . . . . . .225
      E.3.1 Procedure Descriptions  . . . . . . . . . . . . . . . .225


















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      E.3.2 Initiator Algorithms  . . . . . . . . . . . . . . . . .226
      E.3.3 Target Algorithms   . . . . . . . . . . . . . . . . . .228
   E.4 Connection Recovery Algorithms   . . . . . . . . . . . . . .229
      E.4.1 Procedure Descriptions  . . . . . . . . . . . . . . . .229
      E.4.2 Initiator Algorithms  . . . . . . . . . . . . . . . . .229
      E.4.3 Target Algorithms   . . . . . . . . . . . . . . . . . .232
Appendix F. Clearing Effects of Various Events on Targets   . . . .234
   F.1 Clearing Effects on iSCSI Objects  . . . . . . . . . . . . .234
   F.2 Clearing Effects on SCSI Objects   . . . . . . . . . . . . .237
 Full Copyright Statement . . . . . . . . . . . . . . . . . . . .  238
 Notice of Intellectual Property Rights . . . . . . . . . . . . .  238

























































































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1. Introduction

   The Small Computer Systems Interface (SCSI) is a popular family of
   protocols for communicating with I/O devices, especially storage
   devices. SCSI is a client-server architecture. Clients of a SCSI
   interface are called "initiators". Initiators issue SCSI "commands"
   to request services from components, logical units, of a server
   known as a "target". A "SCSI transport" maps the client-server SCSI
   protocol to a specific interconnect. Initiators are one endpoint of
   a SCSI transport and targets are the other endpoint.

   The SCSI protocol has been mapped over various transports, including
   Parallel SCSI, IPI, IEEE-1394 (firewire) and Fibre Channel.  These
   transports are I/O specific and have limited distance capabilities.

   The iSCSI protocol defined in this document describes a means of
   transporting of the SCSI packets over TCP/IP, providing for an
   interoperable solution which can take advantage of existing Internet
   infrastructure, Internet management facilities and address distance
   limitations.







































































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2. Definitions and Acronyms

2.1  Definitions

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

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

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

   - iSCSI Device: A SCSI Device using an iSCSI service delivery
   subsystem. Service Delivery Subsystem is defined by [SAM2] as a
   transport mechanism for SCSI commands and responses.

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

   - iSCSI Initiator Node: The "initiator".

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

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

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

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

   - iSCSI Target Node: The "target".

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

   - iSCSI Transfer Direction: The iSCSI transfer direction is defined
   with regard to the initiator. Outbound or outgoing transfers are






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   transfers from the initiator to the target, while inbound or incoming
   transfers are from the target to the initiator.

   - ISID: The initiator part of the Session Identifier. It is
   explicitly specified by the initiator during Login.

   - 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).

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

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

   - Originator: In a negotiation or exchange, the party that initiates
   the negotiation or exchange.

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

   - Portal Groups: iSCSI supports multiple connections within the same
   session; some implementations will have the ability to combine
   connections in a session across multiple Network Portals. A Portal
   Group defines a set of Network Portals within an iSCSI Network
   Entity 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 16-bit quantity identifies a 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.

   - Recovery R2T: An R2T generated by a target upon detecting the loss
   of one or more Data-Out PDUs through one of the following means: a






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   digest error, a sequence error, or a sequence reception timeout. A
   recovery
   R2T carries the next unused R2TSN, but requests all or part of the
   data burst that an earlier R2T (with a lower R2TSN) had already
   requested.

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

   - SCSI Device: This is the SAM2 term for an entity that contains one
   or more SCSI ports that are connected to a service delivery
   subsystem and supports a SCSI application protocol. For example, a
   SCSI Initiator Device contains one or more SCSI Initiator Ports and
   zero or more application clients. A Target Device contains one or
   more SCSI Target Ports and one or more device servers and associated
   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.

   - SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
   Blocks) and relays/receives them with the remaining command execute
   [SAM2] parameters to/from the iSCSI Layer.

   - Session: The group of TCP connections that link an initiator with
   a target form a session (loosely equivalent to a SCSI I-T nexus).
   TCP connections can be added and removed from a session. Across all
   connections within a session, an initiator sees one and the same
   target.

   - SSID (Session ID): A session between an iSCSI initiator and an
   iSCSI target is defined by a session ID that is a tuple composed of
   an initiator part (ISID) and a target part (Target Portal Group
   Tag). The ISID is explicitly specified by the initiator at session
   establishment. The Target Portal Group Tag is implied by the
   initiator through the selection of the TCP endpoint at connection
   establishment. The TargetPortalGroupTag key must also be returned by
   the target as a confimation during connection establishment.

   - 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 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. For iSCSI, the definition of the SCSI Initiator
   Port and the SCSI Target Port are different.



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

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

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

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

   - TSIH (Target Session Identifying Handle): A target assigned tag
   for a session with a specific named initiator. The target generates
   it during session establishment. Its internal format and content are
   not defined by this protocol except for the value 0 that is reserved
   and used by the initiator to indicate a new session. It is given to
   the target during additional connection establishment for the same
   session.







































































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2.2  Acronyms

   AcronymDefinition
   --------------------------------------------------------------
   3DES          Triple Data Encryption Standard
   ACA           Auto Contingent Allegiance
   AEN           Asynchronous Event Notification
   AES           Advanced Encryption Standard
   AH            Additional Header (not the IPsec AH!)
   AHS           Additional Header Segment
   API           Application Programming Interface
   ASC           Additional Sense Code
   ASCII         American Standard Code for Information Interchange
   ASCQ          Additional Sense Code Qualifier
   BHS           Basic Header Segment
   CBC           Cipher Block Chaining
   CD            Compact Disk
   CDB           Command Descriptor Block
   CHAP          Challenge Handshake Authentication Protocol
   CID           Connection ID
   CO            Connection Only
   CRC           Cyclic Redundancy Check
   CRL           Certificate Revocation List
   CSG           Current Stage
   CSM           Connection State Machine
   DES           Data Encryption Standard
   DNS           Domain Name Server
   DOI           Domain of Interpretation
   DVD           Digital Versatile Disk
   ESP           Encapsulating Security Payload
   EUI           Extended Unique Identifier
   FFP           Full Feature Phase
   FFPO          Full Feature Phase Only
   FIM           Fixed Interval Marker
   Gbps          Gigabits per Second
   HBA           Host Bus Adapter
   HMAC          Hashed Message Authentication Code
   I_T           Initiator_Target
   I_T_L         Initiator_Target_LUN
   IANA          Internet Assigned Numbers Authority
   ID            Identifier
   IDN           Internationalized Domain Name
   IEEE          Institute of Electrical & Electronics Engineers
   IETF          Internet Engineering Task Force
   IKE           Internet Key Exchange
   I/O           Input - Output
   IO            Initialize Only
   IP            Internet Protocol
   IPsec         Internet Protocol Security
   IPv4          Internet Protocol Version 4
   IPv6          Internet Protocol Version 6
   IQN           iSCSI Qualified Name
   ISID          Initiator Session ID
   ITN           iSCSI Target Name
   ITT           Initiator Task Tag
   KRB5          Kerberos V5


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   LFL           Lower Functional Layer
   LTDS          Logical-Text-Data-Segment
   LO            Leading Only
   LU            Logical Unit
   LUN           Logical Unit Number
   MAC           Message Authentication Codes
   NA            Not Applicable
   NIC           Network Interface Card
   NOP           No Operation
   NSG           Next Stage
   OS            Operating System
   PDU           Protocol Data Unit
   PKI           Public Key Infrastructure
   R2T           Ready To Transfer
   R2TSN         Ready To Transfer Sequence Number
   RDMA          Remote Direct Memory Access
   RFC           Request For Comments
   SAM           SCSI Architecture Model
   SAM2          SCSI Architecture Model - 2
   SAN           Storage Area Network
   SCSI          Small Computer Systems Interface
   SN            Sequence Number
   SNACK         Selective Negative Acknowledgment - also
             Sequence Number Acknowledgement for data
   SPKM          Simple Public-Key Mechanism
   SRP           Secure Remote Password
   SSID          Session ID
   SW            Session Wide
   TCB           Task Control Block
   TCP           Transmission Control Protocol
   TPGT          Target Portal Group Tag
   TSIH          Target Session Identifying Handle
   TTT           Target Transfer Tag
   UFL           Upper Functional Layer
   ULP           Upper Level Protocol
   URN           Uniform Resource Names
   UTF           Universal Transformation Format
   WG            Working Group

2.3  Conventions

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

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

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











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


   The diagrams include byte and bit numbering.

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

     - Word Rule
     - Half-word Rule
     - Byte Rule


2.3.1  Word Rule

   A word holds four consecutive bytes. Whenever a word has numeric
   content, it is considered an unsigned number in base 2 positional
   representation with the lowest numbered byte (e.g., byte 0) bit 0
   representing 2**31 and bit 1 representing 2**30 through lowest
   numbered byte + 3 (e.g., byte 3) bit 7 representing 2**0.

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

2.3.2  Half-Word Rule

   A half-word holds two consecutive bytes. Whenever a half-word has
   numeric content it is considered an unsigned number in base 2
   positional representation with the lowest numbered byte (e.g., byte
   0) bit 0 representing 2**15 and bit 1 representing 2**14  through
   lowest numbered byte + 1 (e.g., byte 1) bit 7 representing 2**0.

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

2.3.3  Byte Rule

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

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









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3. Overview

3.1  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 of the SCSI architecture and is intended
   to familiarize readers with its terminology.

   At the highest level, SCSI is a family of interfaces for requesting
   services from I/O devices, including hard drives, tape drives, CD
   and DVD drives, printers, and scanners. In SCSI terminology, an
   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
   services from components, logical units, of a server known as a
   "target". The "device server" on the logical unit accepts SCSI
   commands and processes them.

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

   A SCSI task is a SCSI command or possibly a linked set of SCSI
   commands. Some LUs support multiple pending (queued) tasks, but the
   queue of tasks is managed by the logical unit. 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.

   Command Descriptor Blocks (CDB) are the data structures used to
   contain the command parameters that an initiator sends to a target.
   The CDB content and structure is defined by [SAM2] and device-type
   specific SCSI standards.


3.2  iSCSI Concepts and Functional Overview

   The iSCSI protocol is a mapping of the SCSI remote procedure
   invocation model (see [SAM2]) over the TCP protocol. SCSI commands
   are carried by iSCSI requests and SCSI responses and status are
   carried by iSCSI responses. iSCSI also uses the request response
   mechanism for iSCSI protocol mechanisms.

   For the remainder of this document, the terms "initiator" and
   "target" refer to "iSCSI initiator node" and "iSCSI target node",
   respectively (see Section 3.4.1 iSCSI Architecture Model) unless
   otherwise qualified.


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

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

   The iSCSI transfer direction is defined with respect to the
   initiator. Outbound or outgoing transfers are transfers from an
   initiator to a target, while inbound or incoming transfers are from
   a target to an initiator.

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

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

3.2.1  Layers and Sessions

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

      a)  the SCSI layer builds/receives SCSI CDBs (Command
      Descriptor Blocks) and passes/receives them with the remaining
      command execute parameters ([SAM2]) to/from
      b)  the iSCSI layer that builds/receives iSCSI PDUs and relays/
      receives them to/from one or more TCP connections; the group of
      connections form an initiator-target "session".

   Communication between the initiator and target occurs over one or
   more TCP connections. The TCP connections carry control messages,
   SCSI commands, parameters, and data within iSCSI Protocol Data Units
   (iSCSI PDUs). The group of TCP connections that link an initiator
   with a target form a session (loosely equivalent to a SCSI I_T
   nexus, see Section 3.4.2 SCSI Architecture Model). A session is
   defined by a session ID that is composed of an initiator part and a
   target part. TCP connections can be added and removed from a
   session. Each connections within a session is identified by a
   connection ID (CID).

   Across all connections within a session, an initiator sees one
   "target image". All target identifying elements, such as LUN, are
   the same. A target also sees one "initiator image" across all
   connections within a session. Initiator identifying elements, such
   as the Initiator Task Tag, are global across the session regardless
   of the connection on which they are sent or received.

   iSCSI targets and initiators MUST support at least one TCP
   connection and MAY support several connections in a session. For
   error recovery purposes, targets and initiators that support a




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   single active connection in a session SHOULD support two connections
   during recovery.

3.2.2  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.

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

3.2.2.1  Command Numbering and Acknowledging

   iSCSI performs ordered command delivery within a session. All
   commands (initiator-to-target PDUs) in transit from the initiator to
   the target are numbered.

   iSCSI considers a task to be instantiated on the target in response
   to every request issued by the initiator. A set of task management
   operations including abort and reassign (see Section 10.5 Task
   Management Function Request) may be performed on any iSCSI task.
   Some iSCSI tasks are SCSI tasks, and many SCSI activities are
   related to a SCSI task ([SAM2]). In all cases, the task is
   identified by the Initiator Task Tag for the life of the task.

   The command number is carried by the iSCSI PDU as CmdSN (Command-
   Sequence-Number). The numbering is session-wide. Outgoing iSCSI PDUs
   carry this number. The iSCSI initiator allocates CmdSNs with a 32-
   bit unsigned counter (modulo 2**32). Comparisons and arithmetic on
   CmdSN use Serial Number Arithmetic as defined in [RFC1982] where
   SERIAL_BITS = 32.

   Commands meant for immediate delivery are marked with an immediate
   delivery flag; they MUST also carry the current CmdSN. CmdSN does
   not advance after a command marked for immediate delivery is sent.

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



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   If immediate delivery is used with task management commands, these
   commands may reach the target before the tasks on which they are
   supposed to act. However their CmdSN serves as a marker of their
   position in the stream of commands. The initiator and target must
   ensure that the task management commands act as specified by [SAM2].
   For example, both commands and responses appear as if delivered in
   order. Whenever CmdSN for an outgoing PDU is not specified by an
   explicit rule, CmdSN will carry the current value of the local CmdSN
   variable (see later in this section).

   The means by which an implementation decides to mark a PDU for
   immediate delivery or by which iSCSI decides by itself to mark a PDU
   for immediate delivery are beyond the scope of this document.

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

   In this document, delivery for execution means delivery to the SCSI
   execution engine or an iSCSI protocol specific execution engine
   (e.g., for text requests with public or private extension keys
   involving an execution component). With the exception of the
   commands marked for immediate delivery, the iSCSI target layer MUST
   deliver the commands for execution in the order specified by CmdSN.
   Commands marked for immediate delivery may be delivered by the iSCSI
   target layer for execution as soon as detected. iSCSI may avoid
   delivering some commands to the SCSI target layer if required by a
   prior SCSI or iSCSI action (e.g., CLEAR TASK SET Task Management
   request received before all the commands on which it was supposed to
   act).

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

   For the numbering mechanism, the initiator and target maintain the
   following three variables for each session:

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



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

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

   MaxCmdSN and ExpCmdSN fields are processed by the initiator as
   follows:

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

   This sequence is required because updates may arrive out of order
   (e.g., the updates are sent on different TCP connections).

   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 (see Section 6.2.1 Usage of Retry). At the target, CmdSN is
   only relevant when the command has not created any state related to
   its execution (execution state); afterwards, CmdSN becomes
   irrelevant. Testing for the execution state (represented by
   identifying the Initiator Task Tag) MUST precede any other action at
   the target. If no execution state is found, it is followed by
   ordering and delivery. If an execution state is found, it is
   followed by delivery.

   If an initiator issues a command retry for a command with CmdSN R on
   a connection when the session CmdSN value is Q, it MUST NOT advance
   the CmdSN past R + 2**31 -1 unless the connection is no longer
   operational (i.e., it has returned to the FREE state, see Section
   7.1.3 Standard Connection State Diagram for an Initiator), the
   connection has been reinstated (see Section 5.3.4 Connection
   Reinstatement), or a non-immediate command with CmdSN equal or
   greater than Q was issued subsequent to the command retry on the
   same connection and the reception of that command is acknowledged by



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   the target (see Section 9.4 Command Retry and Cleaning Old Command
   Instances).

   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.

3.2.2.2  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. The status sequence number space is
   32-bit unsigned-integers and the arithmetic operations are the
   regular mod(2**32) arithmetic.

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

   To enable command recovery, the target MAY maintain enough state
   information for data and status recovery after a connection failure.
   A target doing so can safely discard all of the state information
   maintained for recovery of a command after the delivery of the
   status for the command (numbered StatSN) is acknowledged through
   ExpStatSN.

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

   Initiators and Targets MUST support the response-numbering scheme.

3.2.2.3  Data Sequencing

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






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   For any read or bidirectional command, a target MUST issue less than
   2**32 combined R2T and Data-In PDUs. Any output data sequence MUST
   contain less than 2**32 Data-Out PDUs.


3.2.3  iSCSI Login

   The purpose of the iSCSI login is to enable a TCP connection for
   iSCSI use, authentication of the parties, negotiation of the
   session's parameters and marking of 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. (For more details
   on how a session relates to an I_T nexus, see Section 3.4.2 SCSI
   Architecture Model).

   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 SHOULD
   authenticate each other and MAY set a security association protocol
   for the session. This can occur in many different ways and is
   subject to negotiation.

   To protect the TCP connection, an IPsec security association MAY be
   established before the Login request. For information on using IPsec
   security for iSCSI see Chapter 8 and [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 session transitions to Full Feature
   Phase and the initiator may start to send SCSI commands. The
   security policy for whether, and by what means, a target chooses to
   authorize an initiator is beyond the scope of this document. For a
   more detailed description of the Login Phase, see Chapter 5.

   The login PDU includes the ISID part of the session ID (SSID). The
   target portal group that services the login is implied by the
   selection of the connection endpoint. For a new session, the TSIH is
   zero. As part of the response, the target generates a TSIH.

   During session establishment, the target identifies the SCSI
   initiator port (the "I" in the "I_T nexus") through the value pair
   (InitiatorName, ISID). We describe InitiatorName later in this
   section. Any persistent state (e.g., persistent reservations) on the
   target that is associated with a SCSI initiator port is identified
   based on this value pair. Any state associated with the SCSI target
   port (the "T" in the "I_T nexus") is identified externally by the
   TargetName and portal group tag (see Section 3.4.1 iSCSI
   Architecture Model). ISID is subject to reuse restrictions because
   it is used to identify a persistent state (see Section 3.4.3
   Consequences of the Model).




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   Before the Full Feature Phase is established, only Login Request and
   Login Response PDUs are allowed. Login requests and responses MUST
   be used exclusively during Login. On any connection, the login phase
   MUST immediately follow TCP connection establishment and a
   subsequent Login Phase MUST NOT occur before tearing down a
   connection.

   A target receiving any PDU except a Login request before the Login
   phase is started MUST immediately terminate the connection on which
   the PDU was received. Once the Login phase has started, if the
   target receives any PDU except a Login request, it MUST send a Login
   reject (with Status "invalid during login") and then disconnect. If
   the initiator receives any PDU except a Login response, it MUST
   immediately terminate the connection.

3.2.4  iSCSI Full Feature Phase

   Once the initiator is authorized to do so, the iSCSI session is in
   the iSCSI Full Feature Phase. A session is in Full Feature Phase
   after successfully finishing the Login Phase on the first (leading)
   connection of a session. A connection is in Full Feature Phase if
   the session is in Full Feature Phase and the connection login has
   completed successfully. An iSCSI connection is not in Full Feature
   Phase

      a)  when it does not have an established transport connection,
      OR
      b)  when it has a valid transport connection, but a successful
      login was not performed or the connection is currently logged
      out.

   In a normal Full Feature Phase, the initiator may send SCSI commands
   and data to the various LUs on the target by encapsulating them in
   iSCSI PDUs that go over the established iSCSI session.

3.2.4.1  Command Connection Allegiance

   For any iSCSI request issued over a TCP connection, the
   corresponding response and/or other related PDU(s) MUST be sent over
   the same connection. 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
   6.2 Retry and Reassign in Recovery.

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




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   However, consecutive commands that are part of a SCSI linked
   command-chain task (see [SAM2]) 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.

3.2.4.2  Data Transfer Overview

   Outgoing SCSI data (initiator to target user data or command
   parameters) is sent as either solicited data or unsolicited data.
   Solicited data are 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.

   Immediate data are assumed to originate at offset 0 in the initiator
   SCSI write-buffer (outgoing data buffer). All other Data PDUs have
   the buffer offset set explicitly in the PDU header.

   An initiator may send unsolicited data up to FirstBurstLength as
   immediate (up to the negotiated maximum PDU length), in a separate
   PDU sequence or both. All subsequent data MUST be solicited. The
   maximum length of an individual data PDU or the immediate-part of
   the first unsolicited burst MAY be negotiated at login.

   The maximum amount of unsolicited data that can be sent with a
   command is negotiated at login through the FirstBurstLength key. A
   target MAY separately enable immediate data (through the
   ImmediateData key) without enabling the more general (separate data
   PDUs) form of unsolicited data (through the InitialR2T key).

   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 is meant to reduce the protocol overhead (both
   bandwidth and execution time).

   An iSCSI initiator MAY choose not to send unsolicited data, only
   immediate data or FirstBurstLength bytes of unsolicited data with a
   command. If any non-immediate unsolicited data is sent, the total
   unsolicited data MUST be either FirstBurstLength, or all of the data
   if the total amount is less than the FirstBurstLength.

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

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


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   A target SHOULD NOT silently discard data and then request
   retransmission through R2T. Initiators SHOULD NOT keep track of the
   data transferred to or from the target (scoreboarding). SCSI targets
   perform residual count calculation to check how much data was
   actually transferred to or from the device by a command. This may
   differ from the amount the initiator sent and/or received for
   reasons such as retransmissions and errors. Read or bidirectional
   commands implicitly solicit the transmission of the entire amount of
   data covered by the command. SCSI data packets are matched to their
   corresponding SCSI commands by using tags specified in the protocol.

   In addition, iSCSI initiators and targets MUST enforce some ordering
   rules. When unsolicited data is used, the order of the unsolicited
   data on each connection MUST match the order in which the commands
   on that connection are sent. Command and unsolicited data PDUs may
   be interleaved on a single connection as long as the ordering
   requirements of each are maintained (e.g., command N+1 MAY be sent
   before the unsolicited Data-Out PDUs for command N, but the
   unsolicited Data-Out PDUs for command N MUST precede the unsolicited
   Data-Out PDUs of command N+1). A target that receives data out of
   order MAY terminate the session.

3.2.4.3  Tags and Integrity Checks

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

   As the Initiator Task Tag is used to identify a task during its
   execution the iSCSI initiator and target MUST verify that all other
   fields used in task related PDUs have values that are consistent
   with the values used at the task instantiation based on Initiator
   Task Tag (e.g., the LUN used in an R2T PDU MUST be the same as the
   one used in the SCSI command PDU used to instantiate the task).
   Using inconsistent field values is considered a protocol error.

3.2.4.4  Task Management

   SCSI task management assumes that individual tasks and task groups
   can be aborted solely based on the task tags (for individual tasks)
   or the  timing of the task management command (for task groups) and
   that the task management action is executed synchronously - i.e, no
   message involving an aborted task will be seen by the SCSI initiator
   after receiving the task management response. In iSCSI initiators
   and targets interact asynchronously over several connections. iSCSI
   specifies the protocol mechanism and implementation requirements
   needed to present a synchronous view while using an asynchronous
   infrastructure.






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3.2.5  iSCSI Connection Termination

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

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

   If a connection is terminated while in Full Feature Phase,
   connection cleanup (see section 7) is required prior to recovery. By
   doing connection cleanup before starting recovery, the initiator and
   target will avoid receiving stale PDUs after recovery.

3.2.6  iSCSI Names

   Both targets and initiators require names for the purpose of
   identification. In addition, names enable iSCSI storage resources to
   be managed regardless of location (address). An iSCSI node name is
   also the SCSI device name of an iSCSI device. The iSCSI name of a
   SCSI device is the principal object used in authentication of
   targets to initiators and initiators to targets. This name is also
   used to identify and manage iSCSI storage resources.

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

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

   Some SCSI commands require that protocol-specific identifiers be
   communicated within SCSI CDBs. See Section 3.4.2 SCSI Architecture
   Model for the definition of the SCSI port name/identifier for iSCSI
   ports.

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

3.2.6.1  iSCSI Name Properties

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




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   Initiators and targets MUST support the receipt of iSCSI names of up
   to the maximum length of 223 bytes.

   The initiator MUST present both its iSCSI Initiator Name and the
   iSCSI Target Name to which it wishes to connect in the first login
   request of a new session or connection. The only exception is if a
   discovery session (see Section 2.3 iSCSI Session Types) is to be
   established. In this case, the iSCSI Initiator Name is still
   required, but the iSCSI Target Name MAY be omitted.

   iSCSI names have the following properties:

          a)  iSCSI names are globally unique. No two initiators or
          targets can have the same name.
          b)  iSCSI names are permanent. An iSCSI initiator node or
          target node has the same name for its lifetime.
          c)  iSCSI names do not imply a location or address. An iSCSI
          initiator or target can move, or have multiple addresses. A
          change of address does not imply a change of name.
          d)  iSCSI names do not rely on a central name broker; the
          naming authority is distributed.
         e)  iSCSI names support integration with existing unique naming
          schemes.
         f)  iSCSI names rely on existing naming authorities. iSCSI does
          not create any new naming authority.


   The encoding of an iSCSI name has the following properties:

         a)  iSCSI names have the same encoding method regardless of the
          underlying protocols.
         b)  iSCSI names are relatively simple to compare. The algorithm
          for comparing two iSCSI names for equivalence does not rely on
          an external server.
          c)  iSCSI names are composed only of displayable characters.
          iSCSI names allow the use of international character sets but
          are not case sensitive. No whitespace characters are used in
          iSCSI names.
         d)  iSCSI names may be transported using both binary and ASCII-
          based protocols.

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

   Similarly, a target name should not be tied to hardware interfaces
   that can be changed. A target name should identify the logical
   target and must be the same for the target regardless of the










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   physical portion being addressed. This assists iSCSI initiators in
   determining that the two targets it has discovered are really two
   paths to the same target.

   The iSCSI name is designed to fulfill the functional requirements
   for Uniform Resource Names (URN) [RFC1737]. For example, it is
   required that the name have a global scope, be independent of
   address or location, and be persistent and globally unique. Names
   must be extensible and scalable with the use of naming authorities.
   The name encoding should be both human and machine readable. See
   [RFC1737] for further requirements.

3.2.6.2  iSCSI Name Encoding

   An iSCSI name MUST be a UTF-8 encoding of a string of Unicode
   characters with the following properties:
     - It is in Normalization Form C (see "Unicode Normalization
             Forms" [UNICODE]).
        - It only contains characters allowed by the output of the iSCSI
             stringprep template (described in [STPREP-iSCSI]).
        - The following characters are used for formatting iSCSI names:

                  - dash ('-'=U+002d)
                  - dot ('.'=U+002e)
                  - colon (':'=U+003a)

        - The UTF-8 encoding of the name is not larger than 223 bytes.

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

   The stringprep process does not need to be implemented if the names
   are only generated using numeric and lower-case (any character set)
   alphabetic characters.

   Once iSCSI names encoded in UTF-8 are "normalized" they may be
   safely compared byte-for-byte.

3.2.6.3  iSCSI Name Structure

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

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






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   The type designator strings currently defined are:

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

   These two naming authority designators were considered sufficient at
   the time of writing this document.  The creation of additional
   naming type designators for iSCSI may be considered by the IETF and
   detailed in separate RFCs.

3.2.6.3.1  Type "iqn." (iSCSI Qualified Name)

   This iSCSI name type can be used by any organization that owns a
   domain name. This naming format is useful when an end user or
   service provider wishes to assign iSCSI names for targets and/or
   initiators.

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

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

   The iSCSI qualified name string consists of:

     - The string "iqn.", used to distinguish these names from "eui."
           formatted names.
     - A date code, in yyyy-mm format. This date MUST be a date
           during which the naming authority owned the domain name used
           in this format, and SHOULD be the first month in which the
          domain name was owned by this naming authority at 00:01 GMT of
           the first day of the month. This date code uses the Gregorian
           calendar. All four digits in the year must be present. Both
           digits of the month must be present, with January == "01" and
           December == "12". The dash must be included.
     - A dot "."
     - The reversed domain name of the naming authority (person or
           organization) creating this iSCSI name.
     - An optional, colon (:) prefixed, string within the character
           set and length boundaries that the owner of the domain name
           deems appropriate. This may contain product types, serial
           numbers, host identifiers, or software keys (e.g, it may
           include colons to separate organization boundaries). With the
           exception of the colon prefix, the owner of the domain name
           can assign everything after the reversed domain name as
           desired. It is the responsibility of the entity that is the
          naming authority to ensure that the iSCSI names it assigns are



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          worldwide unique. For example, "Example Storage Arrays, Inc.",
           might own the domain name "example.com".

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

                     Naming     String defined by
        Type  Date    Auth      "example.com" naming authority
       +--++-----+ +---------+ +--------------------------------+
       |  ||     | |         | |                                |

       iqn.2001-04.com.example:storage:diskarrays-sn-a8675309
       iqn.2001-04.com.example
       iqn.2001-04.com.example:storage.tape1.sys1.xyz
       iqn.2001-04.com.example:storage.disk2.sys1.xyz

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


   The IEEE Registration Authority provides a service for assigning
   globally unique identifiers [EUI]. The EUI-64 format is used to
   build a global identifier in other network protocols. For example,
   Fibre Channel defines a method of encoding it into a WorldWideName.
   For more information on registering for EUI identifiers, see [OUI].

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

   Example iSCSI name:

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

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

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


3.2.7  Persistent State

   iSCSI does not require any persistent state maintenance across
   sessions. However, in some cases, SCSI requires persistent
   identification of the SCSI initiator port name (See Section 3.4.2
   SCSI Architecture Model and Section 3.4.3 Consequences of the
   Model).

   iSCSI sessions do not persist through power cycles and boot
   operations.

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



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   Commands persist beyond connection termination if the session
   persists and command recovery within the session is supported.
   However, when a connection is dropped, command execution, as
   perceived by iSCSI (i.e., involving iSCSI protocol exchanges for the
   affected task), is suspended until a new allegiance is established
   by the 'task reassign' task management function. (See Section 10.5
   Task Management Function Request.)

3.2.8  Message Synchronization and Steering

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

   In situations where IP packets are delivered in order from the
   network, iSCSI message framing is not an issue and messages are
   processed one after the other. In the presence of IP packet
   reordering (i.e., frames being dropped), legacy TCP implementations
   store the "out of order" TCP segments in temporary buffers until the
   missing TCP 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 that contains the iSCSI message length. The missing TCP
   segment(s) must be received before any of the following segments can
   be steered to the correct SCSI buffers (due to the inability to
   determine the iSCSI message boundaries). Since these segments cannot
   be steered to the correct location, they must be saved in temporary
   buffers that must then be copied to the SCSI buffers.

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

   The Fixed Interval Markers (FIM) scheme works by inserting markers
   in the payload stream at fixed intervals that contain the offset to
   the start of the next iSCSI PDU.

   Under normal circumstances (no PDU loss or data reception out of
   order), iSCSI data steering can be accomplished by using the
   identifying tag and the data offset fields in the iSCSI header in
   addition to the TCP sequence number from the TCP header. The
   identifying tag helps associate the PDU with a SCSI buffer address


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   while the data offset and TCP sequence number are used to determine
   the offset within the buffer.

   When the part of the TCP data stream containing an iSCSI PDU header
   is delayed or lost, markers may be used to minimize the damage as
   follows:

     - Markers indicate where the next iSCSI PDU starts and enable
       continued processing when iSCSI headers have to be dropped due
       to data errors discovered at iSCSI level (e.g., iSCSI header
       CRC errors).
     - Markers help minimize the amount of data that has to be kept
       by the TCP/iSCSI layer while waiting for a late TCP packet
       arrival or recovery, because later they might help find iSCSI
       PDU headers and use the information contained in those to
       steer data to SCSI buffers.


3.2.8.1  Sync/Steering and iSCSI PDU Length

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

3.3  iSCSI Session Types

   iSCSI defines two types of sessions:

      a)  Normal operational session - an unrestricted session.
      b)  Discovery-session - a session only opened for target
      discovery. The target MUST ONLY accept text requests with the
      SendTargets key and a logout request with reason "close the
      session". All other requests MUST be rejected.

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

3.4  SCSI to iSCSI Concepts Mapping Model

   The following diagram shows an example of how multiple iSCSI Nodes
   (targets in this case) can coexist within the same Network Entity
   and can share Network Portals (IP addresses and TCP ports). Other
   more complex configurations are also possible. For detailed
   descriptions of the components of these diagrams, see Section 3.4.1
   iSCSI Architecture Model .









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                 +-----------------------------------+
                 |  Network Entity (iSCSI Client)    |
                 |                                   |
                 |         +-------------+           |
                 |         | iSCSI Node  |           |
                 |         | (Initiator) |           |
                 |         +-------------+           |
                 |            |       |              |
                 | +--------------+ +--------------+ |
                 | |Network Portal| |Network Portal| |
                 | |   10.1.30.4  | |   10.1.40.6  | |
                 +-+--------------+-+--------------+-+
                          |               |
                          |  IP Networks  |
                          |               |
                 +-+--------------+-+--------------+-+
                 | |Network Portal| |Network Portal| |
                 | |  10.1.30.21  | |   10.1.40.3  | |
                 | | TCP Port 3260| | TCP Port 3260| |
                 | +--------------+ +--------------+ |
                 |        |               |          |
                 |        -----------------          |
                 |           |         |             |
                 |  +-------------+ +--------------+ |
                 |  | iSCSI Node  | | iSCSI Node   | |
                 |  |  (Target)   | |  (Target)    | |
                 |  +-------------+ +--------------+ |
                 |                                   |
                 |   Network Entity (iSCSI Server)   |
                 +-----------------------------------+

3.4.1  iSCSI Architecture Model

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

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

      b)  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 d). An iSCSI Node is identified by its iSCSI
      Name (see Section 3.2.6 iSCSI Names and Chapter 12). 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.










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

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

      e)  Portal Groups - iSCSI supports multiple connections within
      the same session; some implementations will have the ability to
      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 that span these
      portals. Not all Network Portals within a Portal Group need to
      participate in every session connected through that Portal
      Group. One or more Portal Groups may provide access to an iSCSI
      Node. Each Network Portal, as utilized by a given iSCSI Node,
      belongs to exactly one portal group within that node. Portal
      Groups are identified within an iSCSI Node by a portal group
      tag, a simple unsigned-integer between 0 and 65535 (see Section
      12.3 SendTargets). All Network Portals with the same portal
      group tag in the context of a given iSCSI Node are in the same
      Portal Group.

      Both iSCSI Initiators and iSCSI Targets have portal groups,
      though only the iSCSI Target Portal Groups are used directly in
      the iSCSI protocol (e.g., in SendTargets). For references to
      the Initiator Portal Groups, see Section 9.1.1 Conservative
      Reuse of ISIDs.

      f)  Portals within a Portal Group should support similar
      session parameters, because they may participate in a common
      session

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



























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

3.4.2  SCSI Architecture Model

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

   This relationship implies implementation requirements in order to
   conform to the SAM2 model and other SCSI operational functions.
   These requirements are detailed in Section 3.4.3 Consequences of the
   Model.

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

      a)  SCSI Device - the SAM2 term for an entity that contains one
      or more SCSI ports that are connected to a service delivery
      subsystem and supports a SCSI application protocol. For
      example, a SCSI Initiator Device contains one or more SCSI
      Initiator Ports and zero or more application clients. A SCSI
      Target Device contains one or more SCSI Target Ports and one or
      more logical units. For iSCSI, the SCSI Device is the component
      within an iSCSI Node that provides the SCSI functionality. As
      such, there can be one SCSI Device, at most, within an iSCSI
      Node. Access to the SCSI Device can only be achieved in an
      iSCSI normal operational session (see Section 3.3 iSCSI Session
      Types). The SCSI Device Name is defined to be the iSCSI Name of
      the node and MUST be used in the iSCSI protocol.








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

      SCSI Initiator Port: This maps to one endpoint of an iSCSI
      normal operational session (see Section 3.3 iSCSI Session
      Types). An iSCSI normal operational session is negotiated
      through the login process between an iSCSI initiator node and
      an iSCSI target node. At successful completion of this process,
      a SCSI Initiator Port is created within the SCSI Initiator
      Device. The SCSI Initiator Port Name and SCSI Initiator Port
      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 MUST be used in iSCSI. When used in SCSI
      parameter data, the SCSI port name MUST be encoded as:
            - The iSCSI Name in UTF-8 format, followed by
            - a comma separator (1 byte), followed by
            - the ASCII character 'i' (for SCSI Initiator Port) or
            the ASCII character 't' (for SCSI Target Port) (1 byte),
            followed by
            - a comma separator (1 byte), followed by
            - a text encoding as a hex-constant (see Section 5.1 Text
            Format) of the ISID (for SCSI initiator port) or the
            portal group tag (for SCSI target port) including the
            initial 0X or 0x and the terminating null (14 bytes).

            The ASCII character 'i' or 't' is the label that
            identifies this port as either a SCSI Initiator Port or a
            SCSI Target Port.

      c)  I_T nexus - a relationship between a SCSI Initiator Port
      and a SCSI Target Port, according to [SAM2]. For iSCSI, this
      relationship is a session, defined as a relationship between an
      iSCSI Initiator's end of the session (SCSI Initiator Port) and
      the iSCSI Target's Portal Group. The I_T nexus can be
      identified by the conjunction of the SCSI port names or by the
      iSCSI session identifier SSID. iSCSI defines the I_T nexus


















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      identifier to be 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).

3.4.3  Consequences of the Model

   This section describes implementation and behavioral requirements
   that result from the mapping of SCSI constructs to the iSCSI
   constructs defined above. Between a given SCSI initiator port and a
   given SCSI target port, only one I_T nexus (session) can exist. No
   more than one nexus relationship (parallel nexus) is allowed by
   [SAM2]. Therefore, between a given iSCSI initiator node and an iSCSI
   target node, at any given time, only one session can exist with the
   same session identifier (SSID).

   These assumptions lead to the following conclusions and
   requirements:

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

   The structure of the ISID that contains a naming authority component
   (see Section 10.12.5 ISID and [NDT]) provides a mechanism to
   facilitate compliance with the ISID rule. (See Section 9.1.1
   Conservative Reuse of ISIDs.)

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

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

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






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3.4.3.1  I_T Nexus State

   Certain nexus relationships contain an explicit state (e.g.,
   initiator-specific mode pages) that may need to be preserved by the
   device server [SAM2] 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 reestablish its session
   (re-login) to the same Target Portal Group using the previous ISID.
   That is, it should perform session recovery as described in Chapter
   6. This is because the SCSI 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.

3.5  Request/Response Summary

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

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

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

3.5.1  Request/Response Types Carrying SCSI Payload

3.5.1.1  SCSI-Command

   This request carries the SCSI CDB and all the other SCSI execute
   command procedure call (see [SAM2]) IN arguments such as task
   attributes, Expected Data Transfer Length for one or both transfer
   directions (the latter for bidirectional commands), and Task Tag (as
   part of the I_T_L_x nexus). The I_T_L nexus is derived by the
   initiator and target from the LUN field in the request and the I_T
   nexus is implicit in the session identification.

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

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

3.5.1.2  SCSI-Response

   The SCSI-Response carries all the SCSI execute-command procedure
   call (see [SAM2]) OUT arguments and the SCSI execute-command
   procedure call return value.

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


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   For a valid status that indicates that the command has been
   processed, but resulted in an exception (e.g., a SCSI CHECK
   CONDITION), the PDU data segment contains the associated sense data.
   The use of Autosense ([SAM2]) is REQUIRED by iSCSI.

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

   In addition, the SCSI-Response PDU carries information required for
   the proper operation of the iSCSI protocol:

     - The number of Data-In PDUs that a target has sent (to enable
       the initiator to check that all have arrived).
     - StatSN - the Status Sequence Number on this connection.
     - ExpCmdSN - the next Expected Command Sequence Number at the
       target.
     - MaxCmdSN - the maximum CmdSN acceptable at the target from
       this initiator.

3.5.1.3  Task Management Function Request

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

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

   The I_T_L nexus identifies task sets. In iSCSI the I_T_L nexus is
   identified by the LUN and the session identification (the session
   identifies an I_T nexus).

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

   For a Task Management function the coordination between responses to
   the tasks affected and the Task Management function response is done
   by the target.

3.5.1.4  Task Management Function Response

   The Task Management function response carries an indication of
   function completion for a Task Management function request including
   how it completed (response and qualifier) and additional information
   for failure responses.

   After the Task Management response indicates Task Management
   function completion, the initiator will not receive any additional
   responses from the affected tasks.


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3.5.1.5  SCSI Data-out and SCSI Data-in

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

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

   An outgoing sequence is either unsolicited (only the first sequence
   can be unsolicited) or consists of all the Data-Out PDUs sent in
   response to an R2T.

   Input sequences are built to enable the direction switching for
   bidirectional commands.

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

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

   In addition, StatSN is carried by the Data-In PDUs.

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


3.5.1.6  Ready To Transfer (R2T)

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

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

   R2T also carries information required for proper operation of the
   iSCSI protocol, such as:

     - R2TSN (to enable an initiator to detect a missing R2T)
     - StatSN


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     - ExpCmdSN
     - MaxCmdSN

3.5.2  Requests/Responses carrying SCSI and iSCSI Payload

3.5.2.1  Asynchronous Message

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

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

3.5.3  Requests/Responses Carrying iSCSI Only Payload

3.5.3.1  Text Request and Text Response

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

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

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

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

   Although a complete exchange is always started by the initiator,
   specific parameter negotiations may be initiated by the initiator or
   target.

3.5.3.2  Login Request and Login Response

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

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

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



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

   The first Login Phase of a session plays a special role, called the
   leading login, which determines some header fields (e.g., the
   version number, the maximum number of connections, and the session
   identification).

   The CmdSN initial value is also set by the leading login.

   StatSN for each connection is initiated by the connection login.

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

3.5.3.3  Logout Request and Response

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

   The Logout response indicates that the connection or session cleanup
   is completed and no other responses will arrive on the connection
   (if received on the logging out connection). In addition, the Logout
   Response indicates how long the target will continue to hold
   resources for recovery (e.g., command execution that continues on a
   new connection) in the text key Time2Retain and how long the
   initiator must wait before proceeding with recovery in the text key
   Time2Wait.

3.5.3.4   SNACK Request

   With the SNACK Request, the initiator requests retransmission of
   numbered-responses or data from the target. A single SNACK request
   covers a contiguous set of missing items, called a run, of a given
   type of items. The type is indicated in a type field in the PDU
   header. The run is composed of an initial item (StatSN, DataSN,
   R2TSN) and the number of missed Status, Data, or R2T PDUs. For long
   data-in sequences, the target may request (at predefined minimum
   intervals) a positive acknowledgement for the data sent. A SNACK
   request with a type field that indicates ACK and the number of Data-
   In PDUs acknowledged conveys this positive acknowledgement.

3.5.3.5  Reject

   Reject enables the target to report an iSCSI error condition (e.g.,
   protocol, unsupported option) that uses a Reason field in the PDU



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   header and includes the complete header of the bad PDU in the Reject
   PDU data segment.


3.5.3.6  NOP-Out Request and NOP-In Response

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

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








































































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4. SCSI Mode Parameters for iSCSI

   There are no iSCSI specific mode pages.









































































































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5. Login and Full Feature Phase Negotiation

   iSCSI parameters are negotiated at session or connection
   establishment by using Login Requests and Responses (see Section
   3.2.3 iSCSI Login) and during Full Feature Phase (Section 3.2.4
   iSCSI Full Feature Phase) by using Text Requests and Responses. In
   both cases the mechanism used is an exchange of iSCSI-text-key=value
   pairs. For brevity iSCSI-text-keys are called just keys in the rest
   of this document.

   Keys are either declarative or require negotiation and the key
   description indicates if the key is declarative or requires
   negotiation.

   For the declarative keys the declaring party sets a value for the
   key. The key specification indicates if the key can be declared by
   the initiator, target or both.

   For the keys that require negotiation one of the parties (the
   proposing party) proposes a value or set of values by including the
   key=value in the data part of a Login or Text Request or Response.
   The other party (the accepting party) makes a selection based on the
   value or list of values proposed and includes the selected value in
   a key=value in the data part of the following Login or Text Response
   or Request. For most of the keys both the initiator and target can
   be proposing parties.

   The Login process proceeds in two stages - the security negotiation
   stage and the operational parameter negotiation stage. Both stages
   are optional but at least one of them has to be present to enable
   setting some mandatory parameters.

   If present, the security negotiation stage precedes the operational
   parameter negotiation stage.

   Progression from stage to stage is controlled by the T (Transition)
   bit in the Login Request/Response PDU header. Through the T bit set
   to 1, the initiator indicates that it would like to transition. The
   target agrees to the transition (and selects the next stage) when
   ready. A field in the Login PDU header indicates the current stage
   (CSG) and during transition, another field indicates the next stage
   (NSG) proposed (initiator) and selected (target).

   The Text negotiation process is used to negotiate or declare
   operational parameters. The negotiation process is controlled by the
   F (final) bit in the PDU header. During text negotiations, the F bit
   is used by the initiator to indicate that it is ready to finish the
   negotiation and by the Target to acquiesce the end of negotiation.

   Since some key=value pairs may not fit entirely in a single PDU, the
   C (continuation) bit is used (both in Login and Text) to indicate
   that "more follows".

   The text negotiation uses an additional mechanism by which a target
   may deliver larger amounts of data to an enquiring initiator. The
   target sets a Target Task Tag to be used as a bookmark which when


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   returned by the initiator, means "go on". If reset to a "neutral
   value", it means "forget about the rest".

   This chapter details types of keys and values used, the syntax rules
   for parameter formation, and the negotiation schemes to be used with
   different types of parameters.

5.1  Text Format

   The initiator and target send a set of key=value pairs encoded in
   UTF-8 Unicode. All the text keys and text values specified in this
   document are to be presented and interpreted in the case in which
   they appear in this document. They are case sensitive.

   The following character symbols are used in this document for text
   items (the hexadecimal values represent Unicode code points):

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

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

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

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

   A value is whatever follows the first = in the key=value pair up to
   the end of the key=value pair, but not including the null delimiter.

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

     standard-label: A string of one or more characters that consist
       of letters, digits, dot, minus, plus, commercial at, or


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       underscore. A standard-label MUST begin with a capital letter
       and must not exceed 63 characters.

     key-name: A standard-label.

     text-value: A string of zero or more characters that consist of
       letters, digits, dot, minus, plus, commercial at, underscore,
       slash, left bracket, right bracket, or colon.

     iSCSI-name-value: A string of one or more characters that
       consist of minus, dot, colon, or any character allowed by the
       output of the iSCSI string-prep template as specified in
       [STPREP-iSCSI] (see also Section 3.2.6.2 iSCSI Name Encoding).

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

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

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

     decimal-constant: An unsigned decimal number with the digit 0 or
       a string of one or more digits that start with a non-zero
       digit.  Decimal-constants are used to encode numerical values
       or binary strings. Decimal constants can only be used to
       encode binary strings if the stringlength is explicitly
       specified. There is no implicit length for decimal strings.
       Decimal-constant MUST NOT be used for parameter values if the
       values can be equal or greater than 2**64 (numerical) or for
       binary strings that can be longer than 64 bits.

     base64-constant: base64 constant encoded as a string that starts
       with "0b" or "0B" followed by 1 or more digits or letters or
       plus or slash or equal. The encoding is done according to
       [RFC2045] and each character, except equal, represents a
       base64 digit or a 6-bit binary string. Base64-constants are
       used to encode numerical-values or binary strings. When used
       to encode numerical values, the excessive use of leading 0
       digits (encoded as A) is discouraged. The string following 0B
       (or 0b) represents a base64 number that starts with the most
       significant base64 digit, followed by all other digits in


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       decreasing order of significance and ending with the least-
       significant base64 digit; the least significant base64 digit
       may be optionally followed by pad digits (encoded as equal)
       that are not considered as part of the number. When used to
       encode binary strings, base64-constants have an implicit byte-
       length that includes six bits for every character of the
       constant, excluding trailing equals (i.e., a base64-constant
       of n base64 characters excluding the trailing equals has a
       byte-length of ((the integer part of) (n*3/4)). Correctly
       encoded base64 strings cannot have n values of 1, 5 ... k*4+1.

     numerical-value: An unsigned integer always less than 2**64
       encoded as a decimal-constant or a hex-constant. Unsigned
       integer arithmetic applies to numerical-values.


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

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

     regular-binary-value: A binary string not longer than 64 bits
       encoded as a decimal constant, hex constant, or base64-
       constant. The length of the string is either specified by the
       key definition or is the implicit byte-length of the encoded
       string.

     large-binary-value: A binary string longer than 64 bits encoded
       as a hex-constant or base64-constant. The length of the string
       is either specified by the key definition or is the implicit
       byte-length of the encoded string.

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

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

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


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

   Any iSCSI target or initiator MUST support receiving at least 8192
   bytes of key=value data in a negotiation sequence. When proposing or
   accepting authentication methods that explicitly require support for
   very long authentication items, the initiator and target MUST
   support receiving of at least 64 kilobytes of key=value data (see
   Appendix 11.1.2 - Simple Public-Key Mechanism (SPKM) - that require
   support for public key certificates).


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5.2  Text Mode Negotiation

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

   The initiator starts the negotiation and/or declaration through a
   Text or Login request and indicates when it is ready for completion
   (by setting the F bit to 1 and keeping it to 1 in a Text Request or
   the T bit in the Login Request). As negotiation text may span PDU
   boundaries, a Text or Login Request or Text or Login Response PDU
   that have the C bit set to 1 MUST NOT have the F/T bit set to 1.

   A target receiving a Text or Login Request with the C bit set to 1
   MUST answer with a Text or Login Response with no data segment
   (DataSegmentLength 0). An initiator receiving a Text or Login
   Response with the C bit set to 1 MUST answer with a Text or Login
   Request with no data segment (DataSegmentLength 0).

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

   The format of a declaration is:

     Declarer-> <key>=<valuex>

   The general format of text negotiation is:

     Proposer-> <key>=<valuex>
     Acceptor-> <key>={<valuey>|NotUnderstood|Irrelevant|Reject}

   Thus a declaration is a one-way textual exchange while a negotiation
   is a two-way exchange.

   The proposer or declarer can either be the initiator or the target,
   and the acceptor can either be the target or initiator,
   respectively. Targets are not limited to respond to key=value pairs
   as proposed by the initiator. The target may propose key=value pairs
   of its own.

   All negotiations are explicit (i.e., the result MUST only be based
   on newly exchanged or declared values). There are no implicit
   proposals. If a proposal is not made, then a reply cannot be
   expected. Conservative design also requires that default values
   should not be relied upon when use of some other value has serious
   consequences.

   The value proposed or declared can be a numerical-value, a
   numerical-range defined by lower and upper value with both integers
   separated by tilde, a binary value, a text-value, an iSCSI-name-
   value, an iSCSI-local-name-value, a boolean-value (Yes or No), or a
   list of comma separated text-values. A range, a large-numerical-
   value, an iSCSI-name-value and an iSCSI-local-name-value MAY ONLY be


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   used if it is explicitly allowed.  An accepted value can be a
   numerical-value, a large-numerical-value, a text-value, or a
   boolean-value.

   If a specific key is not relevant for the current negotiation, the
   acceptor may answer with the constant "Irrelevant" for all types of
   negotiation. However the negotiation is not considered as failed if
   the answer is "Irrelevant". The "Irrelevant" answer is meant for
   those cases in which several keys are presented by a proposing party
   but the selection made by the acceptor for one of the keys makes
   other keys irrelevant. The following example illustrates the use of
   "Irrelevant":

   I->T OFMarker=Yes,OFMarkInt=2048~8192
   T->I OFMarker=No,OFMarkInt=Irrelevant

   I->T X#vkey1=(bla,alb,None),X#vkey2=(bla,alb)
   T->I X#vkey1=None,X#vkey2=Irrelevant


   Any key not understood by the acceptor may be ignored by the
   acceptor without affecting the basic function. However, the answer
   for a key not understood MUST be key=NotUnderstood.

   The constants "None", "Reject", "Irrelevant", and "NotUnderstood"
   are reserved and MUST ONLY be used as described here. Violation of
   this rule is a protocol error (in particular the use of "Reject",
   "Irrelevant", and "NotUnderstood" as proposed values).

   Reject or Irrelevant are legitimate negotiation options where
   allowed but their excessive use is discouraged. A negotiation is
   considered complete when the acceptor has sent the key value pair
   even if the value is "Reject", "Irrelevant", or "NotUnderstood.
   Sending the key again would be a re-negotiation and is forbidden for
   many keys.

   If the acceptor sends "Reject" as an answer the negotiated key is
   left at its current value (or default if no value was set). If the
   current value is not acceptable to the proposer on the connection or
   to the session it is sent, the proposer MAY choose to terminate the
   connection or session.

   All keys in this document, except for the X extension formats, MUST
   be supported by iSCSI initiators and targets when used as specified
   here. If used as specified, these keys MUST NOT be answered with
   NotUnderstood.

   Implementers may introduce new keys by prefixing them with X-
   followed by their (reversed) domain name, or with new keys
   registered with IANA prefixing them with X#. For example, the entity
   owning the domain example.com can issue:

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

   or a new registered key may be used as in:



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   X#SuperCalyPhraGilistic=Yes

   Implementers MAY also introduce new values, but ONLY for new keys or
   authentication methods (see Section 11 iSCSI Security Text Keys and
   Authentication Methods), or digests (see Section 12.1 HeaderDigest
   and DataDigest).

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

   In the Login Phase (see Section 5.3 Login Phase), every stage is a
   separate negotiation. In the FullFeaturePhase, a Text Request
   Response sequence is a negotiation. Negotiations MUST be handled as
   atomic operations. For example, all negotiated values go into effect
   after the negotiation concludes in agreement or are ignored if the
   negotiation fails.

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

   An iSCSI initiator or target MAY terminate a negotiation that does
   not end within a reasonable time or number of exchanges.

5.2.1  List negotiations

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

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

   The constant "None" MUST always be used to indicate a missing
   function. However, "None" is only a valid selection if it is
   explicitly proposed.

   If an acceptor does not understand any particular value in a list,
   it MUST ignore it. If an acceptor does not support, does not
   understand, or is not allowed to use any of the proposed options
   with a specific originator, it may use the constant "Reject" or
   terminate the negotiation. The selection of a value not proposed
   MUST be handled as a protocol error.

5.2.2  Simple-value Negotiations

   For simple-value negotiations, the accepting party MUST answer with
   the same key. The value it selects becomes the negotiation result.




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   Proposing a value not admissible (e.g., not within the specified
   bounds) MAY be answered with the constant "Reject" or the acceptor
   MAY select an admissible value.

   The selection, by the acceptor, of a value not admissible under the
   selection rules is considered a protocol error. The selection rules
   are key-specific.

   For a numerical range the value selected must be an integer within
   the proposed range or "Reject" (if the range is unacceptable).

   For Boolean negotiations (i.e., keys taking the values Yes or No),
   the accepting party MUST answer with the same key and the result of
   the negotiation when the received value does not determine that
   result by itself. The last value transmitted becomes the negotiation
   result. The rules for selecting the value to answer with are
   expressed as Boolean functions of the value received, and the value
   that the accepting party would have selected if given a choice.

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

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

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

5.3  Login Phase

   The Login Phase establishes an iSCSI connection between an initiator
   and a target; it creates also a new session or associates the
   connection to an existing session. The Login Phase sets the iSCSI
   protocol parameters, security parameters, and authenticates the
   initiator and target to each other.

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

   The default MaxRecvDataSegmentLength is used during Login.

   The Login Phase sequence of requests 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 of any connection MUST include the
   InitiatorName key=value pair. The initial login request of the first
   connection of a session MAY also include the SessionType key=value
   pair. For any connection within a session whose type is not



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   "Discovery", the first login request MUST also include the
   TargetName key=value pair.

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

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

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

   Some operational parameters can be negotiated outside the login
   through Text requests and responses.

   Security MUST be completely negotiated within the Login Phase. The
   use of underlying IPsec security is specified in Chapter 8 and in
   [SEC-IPS]. iSCSI support for security within the protocol only
   consists of authentication in the Login Phase.

   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 iSCSI authentication
   parameters. Once this negotiation is completed, the channel is
   considered secure.

   Most of the negotiation keys are only allowed in a specific stage.
   The SecurityNegotiation keys appear in Chapter 11 and the
   LoginOperationalNegotiation keys appear in Chapter 12. Only a
   limited set of keys (marked as Any-Stage in Chapter 12) may be used
   in any of the two stages.

   Any given Login request or response belongs to a specific stage;
   this determines the negotiation keys allowed with the request or
   response. It is considered to be a protocol error to send a key not
   allowed in the current stage.

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

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



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

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

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

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

   The Login Final-Response that accepts a Login Request can only come
   as a response to a Login request with the T bit set to 1, and both
   the request and response MUST indicate FullFeaturePhase as the next
   phase via the NSG field.

   Neither the initiator nor the target should attempt to declare or
   negotiate a parameter more than once during login except for
   responses to specific keys that explicitly allow repeated key
   declarations (e.g., TargetAddress). An attempt to renegotiate/
   redeclare parameters not specifically allowed MUST be detected by
   the initiator and target. If such an attempt is detected by the
   target, the target MUST respond with Login reject (initiator error);
   if detected by the initiator, the initiator MUST drop the
   connection.

5.3.1  Login Phase Start

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

        -Protocol version supported by the initiator.
        -iSCSI Initiator Name and iSCSI Target Name
        -ISID, TSIH, and connection Ids
        -Negotiation stage that the initiator is ready to enter.

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







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   +------------------------------------------------------------------+
   |ISID      | TSIH        | CID    |     Target action              |
   +------------------------------------------------------------------+
   |new       | non-zero    | any    |     fail the login             |
   |          |             |        |     ("session does not exist") |
   +------------------------------------------------------------------+
   |new       | zero        | any    |     instantiate a new session  |
   +------------------------------------------------------------------+
   |existing  | zero        | any    |     do session reinstatement   |
   |          |             |         |    (see section 5.3.5)        |
   +------------------------------------------------------------------+
   |existing  | non-zero    | new    |     add a new connection to    |
   |          | existing    |        |     the session                |
   +------------------------------------------------------------------+
   |existing  | non-zero    |existing|     do connection reinstatement|
   |          | existing    |        |    (see section 5.3.4)         |
   +------------------------------------------------------------------+
   |existing  | non-zero    | any    |         fail the login         |
   |          | new         |        |     ("session does not exist") |
   +------------------------------------------------------------------+


   Determination of "existing" or "new" are made by the target.

   Optionally, the login request may include:

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

   The target can answer the login in the following ways:

     -Login Response with Login reject. This is an immediate
       rejection from the target that causes the connection to
       terminate and the session to terminate if this is the first
       (or only) connection of a new session. The T bit and the CSG
       and NSG fields are reserved.
     -Login Response with Login accept as a final response (T bit set
       to 1 and the NSG in both request and response are set to
       FullFeaturePhase). The response includes the protocol version
       supported by the target and the session ID, and may include
       iSCSI operational or security parameters (that depend on the
       current stage).
     -Login Response with Login Accept as a partial response (NSG not
       set to FullFeaturePhase in both request and response) that
       indicates the start of a negotiation sequence. The response
       includes the protocol version supported by the target and
       either security or iSCSI parameters (when no security
       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


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   the target may reply with a Login Response that indicates that it is
   unwilling to accept the connection (see Section 10.13 Login
   Response) without SecurityNegotiation and will terminate the
   connection with a response of Authentication failure (see Section
   10.13.5 Status-Class and Status-Detail).

   If the initiator is willing to negotiate iSCSI security, but is
   unwilling to make the initial parameter proposal and may accept a
   connection without iSCSI 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 skip
   security, the login response only contains the TargetPortalGroupTag
   key (see Section 12.9 TargetPortalGroupTag), the T bit set to 1, the
   CSG set to SecurityNegotiation, and NSG set to
   LoginOperationalNegotiation.

   An initiator that chooses to operate without iSCSI 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 can finish its
   LoginOperationalNegotiation, the Login response has T bit set to 1,
   the CSG set to LoginOperationalNegotiation, and NSG set to
   FullFeaturePhase in the next stage.

   During the Login Phase the iSCSI target MUST return the
   TargetPortalGroupTag key with the first Login Response PDU with
   which it is allowed to do so (i.e., the first Login Response issued
   after the first Login Request with the C bit set to 0) for all
   session types. The TargetPortalGroupTag key value indicates the
   iSCSI portal group servicing the Login Request PDU. If the
   reconfiguration of iSCSI portal groups is a concern in a given
   environment, the iSCSI initiator should use this key to ascertain
   that it had indeed initiated the Login Phase with the intended
   target portal group.

5.3.2  iSCSI Security Negotiation

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

   An initiator directed negotiation proceeds as follows:

     -The initiator sends a login request with an ordered list of the
       options it supports (authentication algorithm). The options
       are listed in the initiator's order of preference. The
       initiator MAY also send private or public extension options.

     -The target MUST reply with the first option in the list it
       supports and is allowed to use for the specific initiator
       unless it does not support any in which case it MUST answer
       with "Reject" (see Section 5.2 Text Mode Negotiation). The



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       parameters are encoded in UTF8 as key=value. For security
       parameters, see Chapter 11.

     -When the initiator considers that it is ready to conclude the
       SecurityNegotiation stage, it sets the T bit to 1 and the NSG
       to what it would like the next stage to be. The target will
       then set the T bit to 1 and set NSG to the next stage in the
       Login response when it finishes sending its security keys. The
       next stage selected will be the one the target selected. If
       the next stage is FullFeaturePhase, the target MUST respond
       with a Login Response with the TSIH value.

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

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


5.3.3  Operational Parameter Negotiation During the Login Phase

   Operational parameter negotiation during the login MAY be done:

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

   Operational parameter negotiation MAY involve several Login request-
   response exchanges started and terminated by the initiator. The
   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 that has the T bit set to
   1 with a Login response that has the T bit set to 0, the initiator
   should keep sending the Login request (even empty) with the T bit
   set to 1, while it still wants to switch stage, until it receives
   the Login Response that has the T bit set to 1 or it receives a key
   that requires it to set the T bit to 0.

   Some session specific parameters can only be specified during the
   Login Phase of the first connection of a session (i.e., begun by a
   login request that contains a zero-valued TSIH) - the leading Login
   Phase (e.g., the maximum number of connections that can be used for
   this session).

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

   For operational parameters, see Chapter 12.



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5.3.4  Connection Reinstatement

   Connection reinstatement is the process of an initiator logging in
   with a ISID-TSIH-CID combination that is possibly active from the
   target's perspective, which causes the implicit logging out of the
   connection corresponding to the CID and reinstating a new Full
   Feature Phase iSCSI connection in its place (with the same CID).
   Thus, the TSIH in the Login PDU MUST be non-zero and CID does not
   change during a connection reinstatement. The Login request performs
   the logout function of the old connection if an explicit logout was
   not performed earlier. In sessions with a single connection, this
   may imply the opening of a second connection with the sole purpose
   of cleaning up the first. Targets MUST support opening a second
   connection even when they do not support multiple connections in
   Full Feature Phase if ErrorRecoveryLevel is 2 and SHOULD support
   opening a second connection if ErrorRecoveryLevel is less than 2.

   If the operational ErrorRecoveryLevel is 2, connection reinstatement
   enables future task reassignment. If the operational
   ErrorRecoveryLevel is less than 2, connection reinstatement is the
   replacement of the old CID without enabling task reassignment. In
   this case, all the tasks that were active on the old CID must be
   immediately terminated without further notice to the initiator.

   The initiator connection state MUST be CLEANUP_WAIT (section 7.1.3)
   when the initiator attempts a connection reinstatement.

   In practical terms, in addition to the implicit logout of the old
   connection, reinstatement is equivalent to a new connection login.

5.3.5  Session Reinstatement, Closure, and Timeout

   Session reinstatement is the process of the initiator logging in
   with an ISID that is possibly active from the target's perspective.
   Thus implicitly logging out the session that corresponds to the ISID
   and reinstating a new iSCSI session in its place (with the same
   ISID). Therefore, the TSIH in the Login PDU MUST be zero to signal
   session reinstatement.  Session reinstatement causes all the tasks
   that were active on the old session to be immediately terminated by
   the target without further notice to the initiator.

   The initiator session state MUST be FAILED (Section 7.3 Session
   State Diagrams) when the initiator attempts a session reinstatement.

   Session closure is an event defined to be one of the following:

     - A successful "session close" logout.
     - A successful "connection close" logout for the last Full
       Feature Phase connection when no other connection in the
       session is waiting for cleanup (Section 7.2 Connection Cleanup
       State Diagram for Initiators and Targets) and no tasks in the
       session are waiting for reassignment.

   Session timeout is an event defined to occur when the last
   connection state timeout expires and no tasks are waiting for



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   reassignment. This takes the session to the FREE state (N6
   transition in the session state diagram).

5.3.5.1  Loss of Nexus Notification

   The iSCSI layer provides the SCSI layer with the "I_T nexus loss"
   notification when any one of the following events happens:

      a)  Successful completion of session reinstatement.
      b)  Session closure event.
      c)  Session timeout event.

   Certain SCSI object clearing actions may result due to the
   notification in the SCSI end nodes, as documented in Appendix F. -
   Clearing Effects of Various Events on Targets -.


5.3.6  Session Continuation and Failure

   Session continuation is the process by which the state of a
   preexisting session continues to be used by connection reinstatement
   (Section 5.3.4 Connection Reinstatement), or by adding a connection
   with a new CID. Either of these actions associates the new transport
   connection with the session state.

   Session failure is an event where the last Full Feature Phase
   connection reaches the CLEANUP_WAIT state (Section 7.2 Connection
   Cleanup State Diagram for Initiators and Targets), or completes a
   successful recovery logout thus causing all active tasks (that are
   formerly allegiant to the connection) to start waiting for task
   reassignment.

5.4  Operational Parameter Negotiation Outside the Login Phase

   Some operational parameters MAY be negotiated outside (after) the
   Login Phase.

   Parameter negotiation in Full Feature Phase is done through Text
   requests and responses. Operational parameter negotiation MAY
   involve several Text request-response exchanges, which the initiator
   always starts, terminates, and uses the same Initiator Task Tag. 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 should
   keep sending the Text request (even empty) with the F bit set to 1,
   while it still wants to finish the negotiation, until it receives
   the Text response with the F bit set to 1. Responding to a Text
   request with the F bit set to 1 with an empty (no key=value pairs)
   response with the F bit set to 0 is discouraged.

   Targets MUST NOT submit parameters that require an additional
   initiator Text request in a Text response with the F bit set to 1.




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

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

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

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

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























































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6. iSCSI Error Handling and Recovery

6.1  Overview

6.1.1  Background

   The following two considerations prompted the design of much of the
   error recovery functionality in iSCSI:

          i)  An iSCSI PDU may fail the digest check and be dropped,
                 despite being received by the TCP layer.  The iSCSI
                 layer must optionally be allowed to recover such
                 dropped PDUs.
          ii)  A TCP connection may fail at any time during the data
                 transfer. All the active tasks must  optionally be
                 allowed to be continued on a different TCP connection
                 within the same session.

   Implementations have considerable flexibility in deciding what
   degree of error recovery to support, when to use it and by which
   mechanisms to achieve the required behavior. Only the externally
   visible actions of the error recovery mechanisms must be
   standardized to ensure interoperability.

   This chapter describes a general model for recovery in support of
   interoperability. See Appendix E. - Algorithmic Presentation of
   Error Recovery Classes - for further detail on how the described
   model may be implemented. Compliant implementations do not have to
   match the implementation details of this model as presented, but the
   external behavior of such implementations must correspond to the
   externally observable characteristics of the presented model.

6.1.2  Goals

   The major design goals of the iSCSI error recovery scheme are as
   follows:

      a)  Allow iSCSI implementations to meet different requirements
      by defining a collection of error recovery mechanisms that
      implementations may choose from.
      b)  Ensure interoperability between any two implementations
      supporting different sets of error recovery capabilities.
      c)  Define the error recovery mechanisms to ensure command
      ordering even in the face of errors, for initiators that demand
      ordering.
      d)  Do not make additions in the fast path, but allow moderate
      complexity in the error recovery path.
      e)  Prevent both the initiator and target from attempting to
      recover the same set of PDUs at the same time. For example,
      there must be a clear "error recovery functionality
      distribution" between the initiator and target.











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6.1.3  Protocol Features and State Expectations

   The initiator mechanisms defined in connection with error recovery
   are:

      a)  NOP-OUT to probe sequence numbers of the target (section
      10.18)
      b)  Command retry (section 6.2.1)
      c)  Recovery R2T support (section 6.7)
      d)  Requesting retransmission of status/data/R2T using the
      SNACK facility (section 10.16)
      e)  Acknowledging the receipt of the data (section 10.16)
      f)  Reassigning the connection allegiance of a task to a
      different TCP connection (section 6.2.2)
      g)  Terminating the entire iSCSI session to start afresh
      (section 6.1.4.4)

   The target mechanisms defined in connection with error recovery are:

      a)  NOP-IN to probe sequence numbers of the initiator (section
      10.19)
      b)  Requesting retransmission of data using the recovery R2T
      feature (section 6.7)
      c)  SNACK support (section 10.16)
      d)  Requesting that parts of read data be acknowledged (section
      10.7.2)
      e)  Allegiance reassignment support (section 6.2.2)
      f)  Terminating the entire iSCSI session to force the initiator
      to start over (section 6.1.4.4)

   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 the target,
   incoming data (read data) MAY be kept for recovery or it can be
   reread 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.
   A target that agrees to support data retransmission is expected to
   be prepared to retransmit the outgoing data (i.e., Data-In) on
   request until either the status for the completed command is
   acknowledged, or the data in question has been separately
   acknowledged.

6.1.4  Recovery Classes

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











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     - 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, which impacts a larger number of iSCSI tasks in any
   of the cases identified in the following discussion.

   In all classes, the implementer has the choice of deferring errors
   to the SCSI initiator (with an appropriate response code), in which
   case the task, if any, has to be removed from the target and all the
   side-effects, such as ACA, must be considered.

   Use of within-connection and within-command recovery classes MUST
   NOT be attempted before the connection is in Full Feature Phase.

   In the detailed description of the recover classes the mandating
   terms (MUST, SHOULD, MAY, etc.) indicate normative actions to be
   executed if the recovery class is supported and used.

6.1.4.1  Recovery Within-command

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

     - Lost data PDU - realized through one of the following:
      a)  Data digest error - dealt with as specified in Section 6.7
      Digest Errors, using the option of a recovery R2T.
      b)  Sequence reception timeout (no data or partial-data-and-no-
      F-bit) - considered an implicit sequence error and dealt with
      as specified in Section 6.8 Sequence Errors, using the option
      of a recovery R2T.
      c)  Header digest error, which manifests as a sequence
      reception timeout or a sequence error - dealt with as specified
      in Section 6.8 Sequence Errors, using the option of a recovery
      R2T.

   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)  Data digest error - dealt with as specified in Section 6.7
      Digest Errors, using the option of a SNACK.









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      b)  Sequence reception timeout (no status) or response
      reception timeout - dealt with as specified in Section 6.8
      Sequence Errors, using the option of a SNACK.
      c)  Header digest error, which manifests as a sequence
      reception timeout or a sequence error - dealt with as specified
      in Section 6.8 Sequence Errors, using the option of a SNACK.

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

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

6.1.4.2  Recovery Within-connection

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

     - Requests not acknowledged for a long time. Requests are
       acknowledged explicitly through ExpCmdSN or implicitly by
       receiving data and/or status. The initiator MAY retry non-
       acknowledged commands as specified in Section 6.2 Retry and
       Reassign in Recovery.

     - Lost iSCSI numbered Response. It is recognized by either
       identifying a data digest error on a Response PDU or a Data-In
       PDU carrying the status, or by receiving a Response PDU with a
       higher StatSN than expected. In the first case, digest error
       handling is done as specified in Section 6.7 Digest Errors
       using the option of a SNACK. In the second case, sequence
       error handling is done as specified in Section 6.8 Sequence
       Errors, using the option of a SNACK.

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

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

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

6.1.4.3  Connection Recovery

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






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     - TCP connection failure: The initiator MUST close the
       connection. It then MUST either implicitly or explicitly
       logout the failed connection with the reason code "remove the
       connection for recovery" and reassign connection allegiance
       for all commands still in progress associated with the failed
       connection on one or more connections (some or all of which
       MAY be newly established connections) using the "Task
       reassign" task management function (see Section 10.5.1
       Function). For an initiator, a command is in progress as long
       as it has not received a response or a Data-In PDU including
       status.

       Note: The logout function is mandatory. However, a new
       connection establishment is only mandatory if the failed
       connection was the last or only connection in the session.

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

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

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

6.1.4.4  Session Recovery

   Session recovery should be performed when all other recovery
   attempts have failed.  Very simple initiators and targets MAY
   perform session recovery on all iSCSI errors and rely on recovery on
   the SCSI layer and above.

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

   For possible clearing effects of session recovery on SCSI and iSCSI
   objects, refer to Appendix F. - Clearing Effects of Various Events
   on Targets -.

6.1.5  Error Recovery Hierarchy

   The error recovery classes described so far are organized into a
   hierarchy for ease in understanding and to limit the implementation
   complexity. With few and well defined recovery levels
   interoperability is easier to achieve.  The attributes of this
   hierarchy are as follows:



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      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 requirements.
      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.

   The following diagram represents the error recovery hierarchy.

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

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

   +-------------------+--------------------------------------------+
   |ErrorRecoveryLevel |  Associated Error recovery capabilities    |
   +-------------------+--------------------------------------------+
   |        0          |  Session recovery class                    |
   |                   |  (Section 6.1.4.4 Session Recovery)        |
   +-------------------+--------------------------------------------+
   |        1          |  Digest failure recovery (See Note below.) |
   |                   |  plus the capabilities of ER Level 0       |
   +-------------------+--------------------------------------------+
   |        2          |  Connection recovery class                 |
   |                   |  (Section 6.1.4.3 Connection Recovery)     |
   |                   |  plus the capabilities of ER Level 1       |
   +-------------------+--------------------------------------------+

   Note: Digest failure recovery is comprised of two recovery classes:
   Within-Connection recovery class (Section 6.1.4.2 Recovery Within-
   connection) and Within-Command recovery class (Section 6.1.4.1
   Recovery Within-command).

   When a defined value of ErrorRecoveryLevel is proposed by an
   originator in a text negotiation, the originator MUST support the
   functionality defined for the proposed value and additionally,
   functionality corresponding to any defined value numerically less
   than the proposed. When a defined value of ErrorRecoveryLevel is
   returned by a responder in a text negotiation, the responder MUST
   support the functionality corresponding to the ErrorRecoveryLevel it
   is accepting.








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   When either party attempts to use error recovery functionality
   beyond what is negotiated, the recovery attempts MAY fail unless an
   apriori agreement outside the scope of this document exists between
   the two parties to provide such support.

   Implementations MUST support error recovery level "0", 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                    |
   +-------------------+---------------------------------------------+

6.2  Retry and Reassign in Recovery

   This section summarizes two important and somewhat related iSCSI
   protocol features used in error recovery.

6.2.1  Usage of Retry

   By resending the same iSCSI command PDU ("retry") in the absence of
   a command acknowledgement (by way of an ExpCmdSN update) or a
   response, an initiator attempts to "plug" (what it thinks are) the
   discontinuities in CmdSN ordering on the target end.  Discarded
   command PDUs, due to digest errors, may have created these
   discontinuities.

   Retry MUST NOT be used for reasons other than plugging command
   sequence gaps, and in particular, cannot be used for requesting PDU
   retransmissions from a target. Any such PDU retransmission requests
   for a currently allegiant command in progress may be made using the
   SNACK mechanism described in section 10.16, although the usage of
   SNACK is OPTIONAL.

   If initiators, as part of plugging command sequence gaps as
   described above, inadvertently issue retries for allegiant commands
   already in progress (i.e., targets did not see the discontinuities
   in CmdSN ordering), the duplicate commands are silently ignored by
   targets as specified in section 3.2.2.1.

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







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6.2.2  Allegiance Reassignment

   By issuing a "task reassign" task management request (Section 10.5.1
   Function), the initiator signals its intent to continue an already
   active command (but with no current connection allegiance) as part
   of connection recovery. This means that a new connection allegiance
   is requested for the command, which seeks to associate it to the
   connection on which the task management request is being issued.
   Before the allegiance reassignment is attempted for a task, an
   implicit or explicit Logout with the reason code "remove the
   connection for recovery" ( see section 10.14) MUST be successfully
   completed for the previous connection to which the task was
   allegiant.

   In reassigning connection allegiance for a command, the targets
   SHOULD continue the command from its current state. For example,
   when reassigning read commands, the target SHOULD take advantage of
   the ExpDataSN field provided by the Task Management function request
   (which must be set to zero if there was no data transfer) and bring
   the read command to completion by sending the remaining data and
   sending (or resending) the status.  ExpDataSN acknowledges all data
   sent up to, but not including, the Data-In PDU and or R2T with
   DataSN (or R2TSN) equal to ExpDataSN. However, targets may choose to
   send/receive all unacknowledged data or all of the data on a
   reassignment of connection allegiance if unable to recover or
   maintain accurate an state.  Initiators MUST not subsequently
   request data retransmission through Data SNACK for PDUs numbered
   less than ExpDataSN (i.e., prior to the acknowledged sequence
   number). For all types of commands, a reassignment request implies
   that the task is still considered in progress by the initiator and
   the target must conclude the task appropriately if the target
   returns the "Function Complete" response to the reassignment
   request.  This might possibly involve retransmission of data/R2T/
   status PDUs as necessary, but MUST involve the (re)transmission of
   the status PDU.

   It is OPTIONAL for targets to support the allegiance reassignment.
   This capability is negotiated via the ErrorRecoveryLevel text key
   during the login time.  When a target does not support allegiance
   reassignment, it MUST respond with a Task Management response code
   of "Allegiance reassignment not supported". If allegiance
   reassignment is supported by the target, but the task is still
   allegiant to a different connection, or a successful recovery Logout
   of the previously allegiant connection was not performed, the target
   MUST respond with a Task Management response code of "Task still
   allegiant".

   If allegiance reassignment is supported by the target, the Task
   Management response to the reassignment request MUST be issued
   before the reassignment becomes effective.

   If a SCSI Command that involves data input is reassigned, any SNACK
   Tag it holds for a final response from the original connection is
   deleted and the default value of 0 MUST be used instead.




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6.3  Usage Of Reject PDU in Recovery

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

   The above rule means that the initiator can eventually expect a
   response on receiving Rejects, if the received Reject is for a PDU
   other than the command PDU itself. The non-command Rejects only have
   diagnostic value in logging the errors, and they can be used for
   retransmission decisions by the initiators.

   The CmdSN of the rejected command PDU (if it is a non-immediate
   command) MUST NOT be considered received by the target (i.e., a
   command sequence gap must be assumed for the CmdSN), even though the
   CmdSN of the rejected command PDU may be reliably ascertained. Upon
   receiving the Reject, the initiator MUST plug the CmdSN gap in order
   to continue to use the session. The gap may be plugged either by
   transmitting a command PDU with the same CmdSN, or by aborting the
   task (see section 6.9 on how an abort may plug a CmdSN gap).

   When a data PDU is rejected and its DataSN can be ascertained, a
   target MUST advance ExpDataSN for the current data burst if a
   recovery R2T is being generated. The target MAY advance its
   ExpDataSN if it does not attempt to recover the lost data PDU.

6.4  Connection Timeout Management

   iSCSI defines two session-global timeout values (in seconds) -
   Time2Wait and Time2Retain - that are applicable when an iSCSI Full
   Feature Phase connection is taken out of service either
   intentionally or by an exception. Time2Wait is the initial "respite
   time" before attempting an explicit/implicit Logout for the CID in
   question or task reassignment for the affected tasks (if any).
   Time2Retain is the maximum time after the initial respite interval
   that the task and/or connection state(s) is/are guaranteed to be
   maintained on the target to cater to a possible recovery attempt.
   Recovery attempts for the connection and/or task(s) SHOULD NOT be
   made before Time2Wait seconds, but MUST be completed within
   Time2Retain seconds after that initial Time2Wait waiting period.

6.4.1  Timeouts on Transport Exception Events

   A transport connection shutdown or a transport reset without any
   preceding iSCSI protocol interactions informing the end-points of
   the fact causes a Full Feature Phase iSCSI connection to be abruptly
   terminated. The timeout values to be used in this case are the
   negotiated values of defaultTime2Wait (Section 12.15
   DefaultTime2Wait) and DefaultTime2Retain (Section 12.16
   DefaultTime2Retain) text keys for the session.




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6.4.2  Timeouts on Planned Decommissioning

   Any planned decommissioning of a Full Feature Phase iSCSI connection
   is preceded by either a Logout Response PDU, or an Async Message
   PDU. The Time2Wait and Time2Retain field values (section 10.15) in a
   Logout Response PDU, and the Parameter2 and Parameter3 fields of an
   Async Message (AsyncEvent types "drop the connection" or "drop all
   the connections"; section 10.9.1) specify the timeout values to be
   used in each of these cases.

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

6.5  Implicit Termination of Tasks

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

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

      b)  When a connection fails and eventually the connection state
      times out (state transition M1 in Section 7.2.2 State
      Transition Descriptions for Initiators and Targets) and there
      are active tasks allegiant to that connection.

      c)  When a successful Logout with the reason code of "remove
      the connection for recovery" is performed while there are
      active tasks allegiant to that connection, and those tasks
      eventually time out after the Time2Wait and Time2Retain periods
      without allegiance reassignment.

      d)  When a connection is implicitly or explicitly logged out
      with the reason code of "Close the session" and there are
      active tasks in that session.


   If the tasks terminated in the above cases a), b, c) and d)are SCSI
   tasks, they must be internally terminated as if with CHECK CONDITION
   status. This status is only meaningful for appropriately handling
   the internal SCSI state and SCSI side effects with respect to
   ordering because this status is never communicated back as a
   terminating status to the initiator. However additional actions may
   have to be taken at SCSI level depending on the SCSI context as
   defined by the SCSI standards (e.g., queued commands and ACA, UA for
   the next command on the I_T nexus in cases a), b), and c) etc. - see
   [SAM] and [SPC3]).












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6.6  Format Errors

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

         a)  Illegal contents of any PDU header field except the Opcode
         (legal values are specified in Section 10 iSCSI PDU Formats).
         b)  Inconsistent field contents (consistent field contents are
         specified in Section 10 iSCSI PDU Formats).

   Format errors indicate a major implementation flaw in one of the
   parties.

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

6.7  Digest Errors

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

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

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

        - If the discarded PDU is a solicited or unsolicited iSCSI data
          PDU (for immediate data in a command PDU, non-data PDU rule
          below applies), the target MUST do one of the following:
            a)  Request retransmission with a recovery R2T.
            b)  Terminate the task with a response PDU with a CHECK
                 CONDITION Status and an iSCSI Condition of "protocol
                service CRC error" (Section 10.4.7.2 Sense Data). If the
                target chooses to implement this option, it MUST wait to
                 receive all the data (signaled by a Data PDU with the
                 final bit set for all outstanding R2Ts) before sending
                 the response PDU. A task management command (such as an
                abort task) from the initiator during this wait may also
                 conclude the task.
        - No further action is necessary for targets if the discarded
          PDU is a non-data PDU.  In case of immediate data being








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       present on a discarded command, the immediate data is
       implicitly recovered when the task is retried (see section
       6.2.1) followed by the entire data transfer for the task.

   When an initiator receives any iSCSI PDU with a payload digest
   error, it MUST discard the PDU.
     - If the discarded PDU is an iSCSI data PDU, the initiator MUST
       do one of the following:

         a)  Request the desired data PDU through SNACK. In response
                to the SNACK, the target MUST either resend the data PDU
                or reject the SNACK with a Reject PDU with a reason code
                 of "SNACK reject" in which case:
                    i)If the status has not already been sent for the
                     command, the target MUST terminate the command with
                      a CHECK CONDITION Status and an iSCSI Condition of
                      "SNACK rejected" (Section 10.4.7.2 Sense Data).
                    ii)If the status was already sent, no further action
                      is necessary for the target. The initiator in this
                      case MUST wait for the status to be received and
                      then discard it, so as to internally signal the
                     completion with CHECK CONDITION Status and an iSCSI
                      Condition of "protocol service CRC error" (Section
                      10.4.7.2 Sense Data).
         b)  Abort the task and terminate the command with an error.

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

         a)  Request PDU retransmission with a status SNACK.
         b)  Logout the connection for recovery and continue the
                tasks on a different connection instance as described in
                 Section 6.2 Retry and Reassign in Recovery.
         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 (e.g., Async, Reject).  Task
       timeouts as in the initiator waiting for a command completion,
       or process timeouts as in the target waiting for a Logout will
       ensure that the correct operational behavior will result in
       these cases despite the discarded PDU.

6.8  Sequence Errors

   When an initiator receives an iSCSI R2T/data PDU with an out of
   order R2TSN/DataSN or a SCSI response PDU with an ExpDataSN that
   implies missing data PDU(s), it means that the initiator must have
   detected a header or payload digest error on one or more earlier
   R2T/data PDUs. The initiator MUST address these implied digest












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   errors as described in Section 6.7 Digest Errors. When a target
   receives a data PDU with an out of order DataSN, it means that the
   target must have hit a header or payload digest error on at least
   one of the earlier data PDUs. The target MUST address these implied
   digest errors as described in Section 6.7 Digest Errors.

   When an initiator receives an iSCSI status PDU with an out of order
   StatSN that implies missing responses, it MUST address the one or
   more missing status PDUs as described in Section 6.7 Digest Errors.
   As a side effect of receiving the missing responses, the initiator
   may discover missing data PDUs. If the initiator wants to recover
   the missing data for a command, it MUST NOT acknowledge the received
   responses that start from the StatSN of the relevant command, until
   it has completed receiving all the data PDUs of the command.

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

6.9  SCSI Timeouts

   An iSCSI initiator MAY attempt to plug a command sequence gap on the
   target end (in the absence of an acknowledgement of the command by
   way of ExpCmdSN) before the ULP timeout by retrying the
   unacknowledged command, as described in Section 6.2 Retry and
   Reassign in Recovery.

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

     -  Original command was dropped due to digest error.
     -  Connection on which the original command was sent was
       successfully logged out. On logout, the unacknowledged
       commands issued on the connection being logged out are
       discarded.

   If the abort request is received and the original command is
   missing, targets MUST consider the original command with that
   RefCmdSN to be received and issue a Task Management response with
   the response code: "Function Complete". This response concludes the
   task on both ends.

6.10  Negotiation Failures

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

     - None of the choices, or the stated value, is acceptable to one
       of the sides in the negotiation.


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     - The text request timed out and possibly terminated.
     - The text request was answered with a Reject PDU.


   The following two rules should be used to address negotiation
   failures:

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

     - A failure in negotiation, while in the Full Feature Phase,
       will terminate the entire negotiation sequence that may
       consist of a series of text requests that use the same
       Initiator Task Tag.  The operational parameters of the session
       or the connection MUST continue to be the values agreed upon
       during an earlier successful negotiation (i.e., any partial
       results of this unsuccessful negotiation MUST NOT take effect
       and MUST be discarded).

6.11  Protocol Errors

   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 of framing mechanisms to
   limit the effects of these errors may be onerous on performance for
   simple implementations.  Command Sequence Numbers and the above
   mechanisms for connection drop and 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 only be
   addressed by fixing the implementations; iSCSI defines Reject and
   response codes to enable this.

6.12  Connection Failures

   iSCSI can keep a session in operation if it is able to keep/
   establish at least one TCP connection between the initiator and the
   target in a timely fashion.  Targets and/or initiators may recognize
   a failing connection by either transport level means (TCP), a gap in
   the command sequence number, a response stream that is not filled
   for a long time, or by a failing iSCSI NOP (acting as a ping). The
   latter MAY be used periodically to increase the speed and likelihood
   of detecting connection failures.  Initiators and targets MAY also
   use the keep-alive option on the TCP connection to enable early link
   failure detection on otherwise idle links.

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

     - Attempt connection recovery within the session (Section
       6.1.4.3 Connection Recovery).



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     - Logout the connection with the reason code "closes the
       connection" (Section 10.14.5 Implicit termination of tasks),
       re-issue missing commands, and implicitly terminate all active
       commands. This option requires support for the within-
       connection recovery class (Section 6.1.4.2 Recovery Within-
       connection).
     - Perform session recovery (Section 6.1.4.4 Session Recovery).

   Either side may choose to escalate to session recovery (via the
   initiator dropping all the connections, or via an Async Message that
   announces the similar intent from a target), and the other side MUST
   give it precedence.  On a connection failure, a target MUST
   terminate and/or discard all of the active immediate commands
   regardless of which of the above options is used (i.e., immediate
   commands are not recoverable across connection failures).

6.13  Session Errors

   If all of 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.

   In this case, the initiator takes the following actions:

     - Resets or closes all the transport connections.
     - Terminates all outstanding requests with an appropriate
       response before initiating a new session. If the same I_T
       nexus is intended to be reestablished, the initiator MUST
       employ session reinstatement (see section 5.3.5).

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

     - Resets or closes the TCP connections (closes the session).
     - Terminates all active tasks that were allegiant to the
       connection(s) that constituted the session.

   A target MUST also be prepared to handle a session reinstatement
   request from the initiator, that may be addressing session errors.





























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7. State Transitions

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

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

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

   States and transitions are described in text, tables and diagrams.
   The diagrams are used for illustration. The text and the tables are
   the governing specification

7.1  Standard Connection State Diagrams

7.1.1  State Descriptions for Initiators and Targets

   State descriptions for the standard connection state diagram are as
   follows:
   -S1: FREE
       -initiator: State on instantiation, or after successful
        connection closure.
       -target: State on instantiation, or after successful
        connection closure.
   -S2: XPT_WAIT
       -initiator: Waiting for a response to its transport connection
        establishment request.
       -target: Illegal
   -S3: XPT_UP
       -initiator: Illegal
       -target: Waiting for the Login process to commence.

   -S4: IN_LOGIN
       -initiator: Waiting for the Login process to conclude,
        possibly involving several PDU exchanges.
       -target: Waiting for the Login process to conclude, possibly
        involving several PDU exchanges.
   -S5: LOGGED_IN
       -initiator: In Full Feature Phase, waiting for all internal,
        iSCSI, and transport events.
       -target: In Full Feature Phase, waiting for all internal,
        iSCSI, and transport events.










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   -S6: IN_LOGOUT
       -initiator: Waiting for a Logout response.
       -target: Waiting for an internal event signaling completion of
            logout processing.
   -S7: LOGOUT_REQUESTED
       -initiator: Waiting for an internal event signaling readiness
            to proceed with Logout.
       -target: Waiting for the Logout process to start after having
            requested a Logout via an Async Message.
   -S8: CLEANUP_WAIT
       -initiator: Waiting for the context and/or resources to
            initiate the cleanup processing for this CSM.
       -target: Waiting for the cleanup process to start for this
            CSM.
7.1.2  State Transition Descriptions for Initiators and Targets

   -T1:
       -initiator: Transport connect request was made (e.g., TCP SYN
            sent).
       -target: Illegal
   -T2:
       -initiator: Transport connection request timed out, a
            transport reset was received, or an internal event of
            receiving a Logout response (success) on another connection
            for a  "close the session"  Logout request was received.
       -target:Illegal
   -T3:
       -initiator: Illegal
       -target: Received a valid transport connection request that
            establishes the transport connection.
   -T4:
       -initiator: Transport connection established, thus prompting
            the initiator to start the iSCSI Login.
       -target: Initial iSCSI Login request was received.
   -T5:
       -initiator: The final iSCSI Login response with a Status-Class
            of zero was received.
       -target: The final iSCSI Login request to conclude the Login
            Phase was received, thus prompting the target to send the
            final iSCSI Login response with a Status-Class of zero.
   -T6:
       -initiator: Illegal
       -target: Timed out waiting for an iSCSI Login, transport
            disconnect indication was received, transport reset was
           received, or an internal event indicating a transport timeout
            was received. In all these cases, the connection is to be
            closed.




















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   -T7:
       -initiator - one of the following events caused the
            transition:
           - The final iSCSI Login response was received with a non-
                zero Status-Class.
           - Login timed out.
           - A transport disconnect indication was received.
           - A transport reset was received.
           - An internal event indicating a transport timeout was
                received.
           - An internal event of receiving a Logout response
                (success) on another connection for a  "close the
                session"  Logout request was received.

       In all these cases, the transport connection is closed.

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

       In all these cases, the connection is to be closed.
   -T8:
       -initiator: An internal event of receiving a Logout response
            (success) on another connection for a  "close the session"
            Logout request was received, thus closing this connection
            requiring no further cleanup.
       -target: An internal event of sending a Logout response
            (success) on another connection for a "close the session"
            Logout request was received, or an internal event of a
           successful connection/session reinstatement is received, thus
            prompting the target to close this connection cleanly.
   -T9, T10:
       -initiator: An internal event that indicates the readiness to
            start the Logout process was received, thus prompting an
            iSCSI Logout to be sent by the initiator.
       -target: An iSCSI Logout request was received.
   -T11, T12:
       -initiator: Async PDU with AsyncEvent "Request Logout" was
            received.



















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

   -T14:
       -initiator: Async PDU with AsyncEvent "Request Logout" was
           received again.
       -target: Illegal
   -T15, T16:
       -initiator: One or more of the following events caused this
           transition:
           -Internal event that indicates a transport connection
               timeout was received thus prompting transport RESET or
               transport connection closure.
           -A transport RESET.
           -A transport disconnect indication.
           -Async PDU with AsyncEvent "Drop connection" (for this
               CID).
           -Async PDU with AsyncEvent "Drop all connections".
       -target: One or more of the following events caused this
           transition:
           -Internal event that indicates a transport connection
               timeout was received, thus prompting transport RESET or
               transport connection closure.
           -An internal event of a failed connection/session
               reinstatement is received.
           -A transport RESET.
           -A transport disconnect indication.
           -Internal emergency cleanup event was received which
               prompts an Async PDU with AsyncEvent "Drop connection"
               (for this CID), or event "Drop all connections".

   -T17:
       -initiator: One or more of the following events caused this
           transition:


















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

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



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

7.1.3  Standard Connection State Diagram for an Initiator

   Symbolic names for States:

         S1: FREE
         S2: XPT_WAIT
         S4: IN_LOGIN
         S5: LOGGED_IN
         S6: IN_LOGOUT
         S7: LOGOUT_REQUESTED
         S8: CLEANUP_WAIT

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

   The state diagram is as follows:



























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

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





























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

7.1.4  Standard Connection State Diagram for a Target

   Symbolic names for States:
         S1: FREE
         S3: XPT_UP
         S4: IN_LOGIN
         S5: LOGGED_IN
         S6: IN_LOGOUT
         S7: LOGOUT_REQUESTED
         S8: CLEANUP_WAIT

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

   The state diagram is as follows:













































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



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



































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

7.2  Connection Cleanup State Diagram for Initiators and Targets

   Symbolic names for states:

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

   Whenever a connection state machine (e.g., CSM-C) enters the
   CLEANUP_WAIT state (S8), it must go through the state transitions
   described in the connection cleanup state diagram either a) using a
   separate full-feature phase connection (let's call it CSM-E) in the
   LOGGED_IN state in the same session, or b) using a new transport
   connection (let's call it CSM-I) in the FREE state that is to be
   added to the same session. In the CSM-E case, an explicit logout for
   the CID that corresponds to CSM-C (either as a connection or session
   logout) needs to be performed to complete the cleanup. In the CSM-I
   case, an implicit logout for the CID that corresponds to CSM-C needs
   to be performed by way of connection reinstatement (section 5.3.4)
   for that CID. In either case, the protocol exchanges on CSM-E or
   CSM-I determine the state transitions for CSM-C. Therefore, this
   cleanup state diagram is only applicable to the instance of the
   connection in cleanup (i.e., CSM-C). In the case of an implicit
   logout for example, CSM-C reaches FREE (R3) at the time CSM-I
   reaches LOGGED_IN. In the case of an explicit logout, CSM-C reaches
   FREE (R3) when CSM-E receives a successful logout response while
   continuing to be in the LOGGED_IN state.

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

   The following state diagram applies to both initiators and targets.









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

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

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

7.2.1  State Descriptions for Initiators and Targets

   -R1: CLEANUP_WAIT (Same as S8)
       -initiator: Waiting for the internal event to initiate the
           cleanup processing for CSM-C.
       -target: Waiting for the cleanup process to start for CSM-C.
   -R2: IN_CLEANUP
       -initiator: Waiting for the connection cleanup process to
           conclude for CSM-C.
       -target: Waiting for the connection cleanup process to
           conclude for CSM-C.
   -R3: FREE (Same as S1)
       -initiator: End state for CSM-C.
       -target: End state for CSM-C.









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7.2.2  State Transition Descriptions for Initiators and Targets

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


   -M2:  An implicit/explicit logout process was initiated by the
   initiator.
       -In CSM-I usage:
           -initiator: An internal event requesting the connection
               (or session) reinstatement was received, thus prompting a
               connection (or session) reinstatement Login to be sent
               transitioning CSM-I to state IN_LOGIN.
           -target: A connection/session reinstatement Login was
               received while in state XPT_UP.
       -In CSM-E usage:
           -initiator: An internal event that indicates that an
               explicit logout was sent for this CID in state LOGGED_IN.
           -target: An explicit logout was received for this CID in
               state LOGGED_IN.
   -M3: Logout failure detected
       -In CSM-I usage:
           -initiator: CSM-I failed to reach LOGGED_IN and arrived
               into FREE instead.
           -target: CSM-I failed to reach LOGGED_IN and arrived into
               FREE instead.
       -In CSM-E usage:
           -initiator: CSM-E either moved out of LOGGED_IN, or Logout
               timed out and/or aborted, or Logout response (failure)
               was received.
           -target: CSM-E either moved out of LOGGED_IN,  Logout
               timed out and/or aborted, or an internal event that
               indicates a failed Logout processing was received.  A
               Logout response (failure) was sent in the last case.



   -M4: Successful implicit/explicit logout was performed.
       - In CSM-I usage:














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


7.3  Session State Diagrams

7.3.1  Session State Diagram for an Initiator


   Symbolic Names for States:

     Q1: FREE
     Q3: LOGGED_IN
     Q4: FAILED
   State Q3 represents the Full Feature Phase operation of the session.

   The state diagram is as follows:

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

   The state transition table is as follows:








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

7.3.2  Session State Diagram for a Target

   Symbolic Names for States:

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

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


   The state diagram is as follows:

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

   The state transition table is as follows:















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


7.3.3  State Descriptions for Initiators and Targets

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

   -Q2: ACTIVE
       -initiator: Illegal.
       -target: The first iSCSI connection in the session
            transitioned to IN_LOGIN, waiting for it to complete the
            login process.
   -Q3: LOGGED_IN
       -initiator: Waiting for all session events.
       -target: Waiting for all session events.

   -Q4: FAILED
       -initiator: Waiting for session recovery or session
            continuation.
       -target: Waiting for session recovery or session continuation.
   -Q5: IN_CONTINUE
       -initiator: Illegal.
       -target: Waiting for session continuation attempt to reach a
            conclusion.


7.3.4  State Transition Descriptions for Initiators and Targets

   -N1:
       -initiator: At least one transport connection reached the
            LOGGED_IN state.
       -target: The first iSCSI connection in the session had reached
            the IN_LOGIN state.
   -N2:
       -initiator: Illegal.
       -target: At least one iSCSI connection reached the LOGGED_IN
            state.












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   -N3:
       -initiator: Graceful closing of the session via session
            closure (Section 5.3.6 Session Continuation and Failure).
       -target: Graceful closing of the session via session closure
            (Section 5.3.6 Session Continuation and Failure) or a
            successful session reinstatement cleanly closed the session.
   -N4:
       -initiator: A session continuation attempt succeeded.
       -target: Illegal.

   -N5:
       -initiator: Session failure (Section 5.3.6 Session
            Continuation and Failure) occurred.
       -target: Session failure (Section 5.3.6 Session Continuation
            and Failure) occurred.
   -N6:
       -initiator: Session state timeout occurred, or a session
           reinstatement cleared this session instance.  This results in
           the freeing of all associated resources and the session state
            is discarded.
       -target: Session state timeout occurred, or a session
           reinstatement cleared this session instance.  This results in
           the freeing of all associated resources and the session state
            is discarded.

   -N7:
       -initiator: Illegal.
       -target: A session continuation attempt is initiated.

   -N8:
       -initiator: Illegal.
       -target: The last session continuation attempt failed.

   -N9:
       -initiator: Illegal.
       -target: Login attempt on the leading connection failed.

   -N10:
       -initiator: Illegal.
       -target: A session continuation attempt succeeded.

   -N11:
       -initiator: Illegal.
       -target: A successful session reinstatement cleanly closed the
            session.



















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8. 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 Storage Area Network
   (SAN) distinctly separate from the communications network. The use
   of storage protocols, such as SCSI, over IP-networks requires that
   security concerns be addressed. iSCSI implementations MUST provide
   means of protection against active attacks (e.g., pretending to be
   another identity, message insertion, deletion, modification, and
   replaying) and passive attacks (e.g.,eavesdropping, gaining
   advantage by analyzing the data sent over the line).

   Although technically possible, iSCSI SHOULD NOT be configured
   without security. iSCSI configured without security should be
   confined, in extreme cases, to closed environments without any
   security risk. [SEC-IPS] specifies the mechanisms that must be used
   in order to mitigate risks fully described in that document.

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

8.1  iSCSI Security Mechanisms

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


8.2  In-band Initiator-Target Authentication

   During login, the target MUST authenticate the initiator and the
   initiator MAY authenticate the target. The authentication is
   performed on every new iSCSI connection by an exchange of iSCSI
   Login PDUs using a negotiated authentication method.

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


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

   Section 11 iSCSI Security Text Keys and Authentication Methods
   defines several authentication methods and the exact steps that must
   be followed in each of them, including the iSCSI-text-keys and their
   allowed values in each step. Whenever an iSCSI initiator gets a
   response whose keys, or their values, are not according to the step
   definition, it MUST abort the connection. Whenever an iSCSI target
   gets a response whose keys, or their values, are not according to
   the step definition, it MUST answer with a Login reject with the
   "Initiator Error" or "Missing Parameter" status. These statuses are
   not intended for cryptographically incorrect values such as the CHAP
   response, for which "Authentication Failure" status MUST be
   specified. The importance of this rule can be illustrated in CHAP
   with target authentication (see Section 11.1.4 Challenge Handshake
   Authentication Protocol (CHAP)) where the initiator would have been
   able to conduct a reflection attack by omitting his response key
   (CHAP_R) using the same CHAP challenge as the target and reflecting
   the target's response back to the target. In CHAP, this is prevented
   because the target must answer the missing CHAP_R key with a Login
   reject with the "Missing Parameter" status.

   For some of the authentication methods, a key specifies the identity
   of the iSCSI initiator or target for authentication purposes. The
   value associated with that key MAY be different from the iSCSI name
   and SHOULD be configurable. (CHAP_N, see Section 11.1.4 Challenge
   Handshake Authentication Protocol (CHAP) and SRP_U,  see Section
   11.1.3 Secure Remote Password (SRP)).

8.2.1  CHAP Considerations

   Compliant iSCSI initiators and targets MUST implement the CHAP
   authentication method [RFC1994] (according to Section 11.1.4
   Challenge Handshake Authentication Protocol (CHAP) including the
   target authentication option).

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

   An administrative entity of an environment in which CHAP is used
   with a secret that has less than 96 random bits MUST enforce IPsec
   encryption (according to the implementation requirements in Section
   8.3.2 Confidentiality) to protect the connection. Moreover, in this
   case IKE authentication with group pre-shared cryptographic keys



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   SHOULD NOT be used unless it is not essential to protect group
   members against off-line dictionary attacks by other members.

   A compliant implementation SHOULD NOT continue with the login step
   in which it should send a CHAP response (CHAP_R, Section 11.1.4
   Challenge Handshake Authentication Protocol (CHAP)) unless it can
   verify that the CHAP secret is at least 96 bits, or that IPsec
   encryption is being used to protect the connection.

   Any CHAP secret used for initiator authentication MUST NOT be
   configured for authentication of any target, and any CHAP secret
   used for target authentication MUST NOT be configured for
   authentication of any initiator.  If the CHAP response received by
   one end of an iSCSI connection is the same as the CHAP response that
   the receiving endpoint would have generated for the same CHAP
   challenge, the response MUST be treated as an authentication failure
   and cause the connection to close (this ensures that the same CHAP
   secret is not used for authentication in both directions).  Also, if
   an iSCSI implementation can function as both initiator and target,
   different CHAP secrets and identities MUST be configured for these
   two roles. The following is an example of the attacks prevented by
   the above requirements:

     Rogue wants to impersonate Storage to Alice, and knows that a
       single secret is used for both directions of Storage-Alice
       authentication.

     Rogue convinces Alice to open two connections to Rogue, and
       Rogue identifies itself as Storage on both connections.

     Rogue issues a CHAP challenge on connection 1, waits for Alice
       to respond, and then reflects Alice's challenge as the initial
       challenge to Alice on connection 2.

     If Alice doesn't check for the reflection across connections,
       Alice's response on connection 2 enables Rogue to impersonate
       Storage on connection 1, even though Rogue does not know the
       Alice-Storage CHAP secret.

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

   The same CHAP secret SHOULD NOT be configured for authentication of
   multiple initiators or multiple targets, as this enables any of them
   to impersonate any other one of them, and compromising one of them
   enables the attacker to impersonate any of them. It is recommended
   that iSCSI implementations check for use of identical CHAP secrets
   by different peers when this check is feasible, and take appropriate
   measures to warn users and/or administrators when this is detected.
   A single CHAP secret MAY be used for authentication of an individual
   initiator to multiple targets. Likewise, a single CHAP secret MAY be
   used for authentication of an individual target to multiple
   initiators.



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8.2.2  SRP Considerations

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

   The list of allowed SRP groups is provided in [SEC-IPS].

8.3  IPsec

   iSCSI uses the IPsec mechanism 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 cryptographic key
   management.

   An iSCSI initiator or target may provide the required IPsec support
   fully integrated or in conjunction with an IPsec front-end device.
   In the latter case, the compliance requirements with regard to IPsec
   support apply to the "combined device". Only the "combined device"
   is to be considered an iSCSI device.

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

8.3.1  Data Integrity and Authentication

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

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

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

   The ESP anti-replay service MUST also be implemented.

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


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8.3.2  Confidentiality

   Confidentiality is provided by encrypting the data in every packet.
   When confidentiality is used it MUST be accompanied by 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] in tunnel mode
   and MAY provide confidentiality by implementing IPsec with ESP in
   transport mode, with the following iSCSI specific requirements:

     - 3DES in CBC mode MUST be implemented [RFC2451].
     - AES in Counter mode SHOULD be implemented [AESCTR].

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

8.3.3  Policy, Security Associations, and Cryptographic Key Management

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


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

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

     - Conformant iSCSI implementations MUST support IKE Main Mode
       and SHOULD support Aggressive Mode. IKE main mode with pre-
       shared key authentication method SHOULD NOT be used when
       either the initiator or the target uses dynamically assigned
       IP addresses. While in many cases pre-shared keys offer good
       security, situations in which dynamically assigned addresses
       are used force the use of a group pre-shared key, which
       creates vulnerability to a man-in-the-middle attack.

     - In the IKE Phase 2 Quick Mode, exchanges for creating the
       Phase 2 SA, the Identity Payload, fields MUST be present.
       ID_IPV4_ADDR, ID_IPV6_ADDR (if the protocol stack supports
       IPv6) and ID_FQDN Identity payloads MUST be supported;
       ID_USER_FQDN SHOULD be supported. The IP Subnet, IP Address


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       Range, ID_DER_ASN1_DN, and ID_DER_ASN1_GN formats SHOULD NOT
       be used. The ID_KEY_ID Identity Payload MUST NOT be used.

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


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


   The method used by the initiator to determine whether the target
   should be connected using IPsec is regarded as an issue of IPsec
   policy administration, and thus not defined in the iSCSI standard.

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

































































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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 task
   tag mechanism was designed to enable Direct Data Placement (DDP - a
   DMA form) at the iSCSI level or lower.

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

   Implementers are also advised to consider the implementation
   consequences of the iSCSI to SCSI mapping model as outlined in
   Section 3.4.3 Consequences of the Model.

9.1  Multiple Network Adapters

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

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

9.1.1  Conservative Reuse of ISIDs

   Historically, the SCSI model (and implementations and applications
   based on that model) has assumed that SCSI ports are static,
   physical entities. Recent extensions to the SCSI model have taken
   advantage of persistent worldwide unique names for these ports. In
   iSCSI however, the SCSI initiator ports are the endpoints of
   dynamically created sessions, so the presumptions of "static and
   physical" do not apply. In any case, the model clauses
   (particularly, Section 3.4.2 SCSI Architecture Model) provide for
   persistent, reusable names for the iSCSI-type SCSI initiator ports
   even though there does not need to be any physical entity bound to
   these names.

   To both minimize the disruption of legacy applications and to better
   facilitate the SCSI features that rely on persistent names for SCSI
   ports, iSCSI implementations SHOULD attempt to provide a stable
   presentation of SCSI Initiator Ports (both to the upper OS-layers
   and to the targets to which they connect). This can be achieved in
   an initiator implementation by conservatively reusing ISIDs. In
   other words, the same ISID should be used in the Login process to
   multiple target portal groups (of the same iSCSI Target or different
   iSCSI Targets). The ISID RULE (Section 3.4.3 Consequences of the
   Model) only prohibits reuse to the same target portal group. It does
   not "preclude" reuse to other target portal groups.
   The principle of conservative reuse "encourages" reuse to other
   target portal groups. When a SCSI target device sees the same
   (InitiatorName, ISID) pair in different sessions to different target
   portal groups, it can identify the underlying SCSI Initiator Port on


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   each session as the same SCSI port. In effect, it can recognize
   multiple paths from the same source.

9.1.2  iSCSI Name, ISID, and TPGT Use

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

   When there are multiple hardware or software components coordinated
   as a single iSCSI Node, there must be some (logical) entity that
   represents the iSCSI Node that makes the iSCSI Node Name available
   to all components involved in session creation and login. Similarly,
   this entity that represents the iSCSI Node must be able to
   coordinate session identifier resources (ISID for initiators) to
   enforce both the ISID and TSIH RULES (see Section 3.4.3 Consequences
   of the Model).

   For targets, because of the closed environment, implementation of
   this entity should be straightforward. However, vendors of iSCSI
   hardware (e.g., NICs or HBAs) intended for targets, SHOULD provide
   mechanisms for configuration of the iSCSI Node Name across the
   portal groups instantiated by multiple instances of these components
   within a target.

   However, complex targets making use of multiple Target Portal Group
   Tags may reconfigure them to achieve various quality goals. The
   initiators have two mechanisms at their disposal to discover and/or
   check reconfiguring targets - the discovery session type and a key
   returned by the target during login to confirm the TPGT. An
   initiator should attempt to "rediscover" the target configuration
   anytime a session is terminated unexpectedly.

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

   Recognizing that such initiator APIs are not available today, other
   implementations of the role of this entity are possible. For
   example, a human may instantiate the (common) Node name as part of
   the installation process of each iSCSI component involved in session
   creation and login. This may be done either by pointing the
   component to a vendor-specific location for this datum or to a
   system-wide location. The structure of the ISID namespace (see
   Section 10.12.5 ISID and [NDT]) facilitates implementation of the
   ISID coordination by allowing each component vendor to independently
   (of other vendor's components) coordinate allocation, use, and reuse
   of its own partition of the ISID namespace in a vendor-specific
   manner. Partitioning of the ISID namespace within initiator portal
   groups managed by that vendor allows each such initiator portal
   group to act independently of all other portal groups when selecting



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   an ISID for a login; this facilitates enforcement of the ISID RULE
   (see Section 3.4.3 Consequences of the Model) at the initiator.

   A vendor of iSCSI hardware (e.g., NICs or HBAs) intended for use in
   initiators MUST implement a mechanism for configuring the iSCSI Node
   Name. Vendors, and administrators must ensure that iSCSI Node Names
   are unique worldwide. It is therefore important that when one
   chooses to reuse the iSCSI Node Name of a disabled unit, not to re-
   assign that name to the original unit unless its worldwide
   uniqueness can be ascertained again.

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

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
   initiators and targets MUST support and use autosense.

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

9.3  iSCSI Timeouts

   iSCSI recovery actions are often dependent on iSCSI time-outs being
   recognized and acted upon before SCSI time-outs. Determining the
   right time-outs to use for various iSCSI actions (command
   acknowledgements expected, status acknowledgements, etc.) is very
   much dependent on infrastructure (hardware, links, TCP/IP stack,
   iSCSI driver). As a guide, the implementer may use an average Nop-
   Out/Nop-In turnaround delay multiplied by a "safety factor" (e.g.,
   4) as a good estimate for the basic delay of the iSCSI stack for a
   given connection. The safety factor should account for the network
   load variability.  For connection teardown the implementer may want
   to consider also TCP common practice for the given infrastructure.

   Text negotiations MAY also be subject to either time-limits or
   limits in the number of exchanges. Those SHOULD be generous enough
   to avoid affecting interoperability (e.g., allowing each key to be
   negotiated on a separate exchange).

   The relation between iSCSI timeouts and SCSI timeouts should also be
   considered. SCSI timeouts should be longer than iSCSI timeouts plus
   the time required for iSCSI recovery whenever iSCSI recovery is
   planned. Alternatively, an implementer may choose to interlock iSCSI


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   timeouts and recovery with SCSI timeouts so that SCSI recovery will
   become active only where iSCSI is not planned to, or failed to,
   recover.

   The implementer may also want to consider the interaction between
   various iSCSI exception events - such as a digest failure - and
   subsequent timeouts. When iSCSI error recovery is active, a digest
   failure is likely to result in discovering a missing command or data
   PDU. In these cases, an implementer may want to lower the timeout
   values to enable faster initiation for recovery procedures.

9.4  Command Retry and Cleaning Old Command Instances

   To avoid having old, retried command instances appear in a valid
   command window after a command sequence number wrap around, the
   protocol requires (see Section 3.2.2.1 Command Numbering and
   Acknowledging) that on every connection on which a retry has been
   issued, a non-immediate command be issued and acknowledged within a
   2**31-1 commands interval from the CmdSN of the retried command.
   This requirement can be fulfilled by an implementation in several
   ways.

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

9.5  Synch and Steering Layer and Performance

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

9.6  Considerations for State-dependent Devices and Long-lasting SCSI
   Operations

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

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



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

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

   For many of those state changing commands, the execution model also
   assumes that the command is executed exactly once. Devices
   implementing READ POSITION and LOCATE provide a means for SCSI level
   command recovery and new tape-class  devices should support those
   commands. In their absence a retry at SCSI level is difficult and
   error recovery at iSCSI level is advisable.

   Devices operating on long latency delivery subsystems and performing
   long lasting SCSI operations may need mechanisms that enable
   connection replacement while commands are running (e.g., during an
   extended copy operation).

9.6.1  Determining the Proper ErrorRecoveryLevel


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

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

   A consideration of the above factors for SCSI tape devices as an
   example suggests that implementations SHOULD use
   ErrorRecoveryLevel=1 when transport connection failure is not a
   concern and SCSI level recovery is unavailable, and
   ErrorRecoveryLevel=2 when the connection failure is also of high
   likelihood during a backup/retrieval.

   For extended copy operations, implementations SHOULD use
   ErrorRecoveryLevel=2 whenever there is a relatively high likelihood
   of connection failure.








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10. iSCSI PDU Formats

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

   Any compliant sender MUST set all bits not defined and all reserved
   fields to zero unless specified otherwise. Any compliant receiver
   MUST ignore any bit not defined and all reserved fields unless
   specified otherwise. Receipt of reserved code values in defined
   fields MUST be reported as a protocol error.

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

10.1  iSCSI PDU Length and Padding

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

10.2  PDU Template, Header, and Opcodes

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

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

   The overall structure of an iSCSI  PDU is as follows:


   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0/ Basic Header Segment (BHS)                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Additional Header Segment 1 (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     / Additional Header Segment 2 (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   ----
     +---------------+---------------+---------------+---------------+
     / Additional Header Segment n (AHS)  (optional)                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


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   ----
     +---------------+---------------+---------------+---------------+
    k/ Header-Digest (optional)                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    l/ Data Segment(optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    m/ Data-Digest (optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

   All PDU segments and digests are padded to the closest integer
   number of four byte words. For example, all PDU segments and digests
   start at a four byte word boundary and the padding ranges from 0 to
   3 bytes. The padding bytes SHOULD be sent as 0.

   iSCSI response PDUs do not have AH Segments.

10.2.1  Basic Header Segment (BHS)

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

   The format of the BHS is:


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

10.2.1.1  I

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

10.2.1.2  Opcode

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


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   The Opcodes are divided into two categories: initiator opcodes and
   target opcodes. Initiator opcodes are in PDUs sent by the initiator
   (request PDUs). 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 Request
     0x04 Text Request
     0x05 SCSI Data-out (for WRITE operations)
     0x06 Logout Request
     0x10 SNACK Request
     0x1c-0x1e Vendor specific codes

   Target opcodes are:


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

   All other opcodes are reserved.

10.2.1.3  Final (F) bit

   When set to 1 it indicates the final (or only) PDU of a sequence.

10.2.1.4  Opcode-specific Fields

   These fields have different meanings for different opcode types.

10.2.1.5  TotalAHSLength

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




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

10.2.1.6  DataSegmentLength

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

10.2.1.7  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 is either ignored or may be
   used in an opcode specific way. The LUN field is 64-bits and should
   be formatted in accordance with [SAM2]. For example, LUN[0] from
   [SAM2] is BHS byte 8 and so on up to LUN[7] from [SAM2], which is
   BHS byte 15.

10.2.1.8  Initiator Task Tag

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

10.2.2  Additional Header Segment (AHS)

   The general format of an AHS is:

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

10.2.2.1  AHSType

   The AHSType field is coded as follows:

         bit 0-1 - Reserved

         bit 2-7 - AHS code

          0 - Reserved
          1 - Extended CDB
          2 - Expected Bidirectional Read Data Length


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          3 - 63 Reserved


10.2.2.2  AHSLength

   This field contains the effective length in bytes of the AHS
   excluding AHSType and AHSLength and padding, if any. The AHS is
   padded to the smallest integer number of 4 byte words (i.e., from 0
   up to 3 padding bytes).

10.2.2.3  Extended CDB AHS

   The format of the Extended CDB AHS is:

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

   This type of AHS MUST NOT be used if the CDBLength is less than 17.
   The length includes the reserved byte 3.

10.2.2.4  Bidirectional Expected Read-Data Length AHS

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

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

10.2.3  Header Digest and Data Digest

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

   The existence and type of digests are negotiated during the Login
   Phase.

   The separation of the header and data digests is useful in iSCSI
   routing applications, in which only the header changes when a



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   message is forwarded. In this case, only the header digest should be
   recalculated.

   Digests are not included in data or header length fields.

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

10.2.4  Data Segment

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





















































































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10.3  SCSI Command

   The format of the SCSI Command PDU is:

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

10.3.1  Flags and Task Attributes (byte 1)

     The flags for a SCSI Command are:

     bit 0   (F) is set to 1 when no unsolicited SCSI Data-Out PDUs
           follow this PDU.  When F=1 for a write and if Expected Data
           Transfer Length is larger than the DataSegmentLength, the
           target may solicit additional data through R2T.

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

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

     bit 3-4 Reserved.

     bit 5-7 contains Task Attributes.



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

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

   Setting both the W and the F bit to 0 is an error.
   Either or both of R and W MAY be 1 when either the Expected Data
   Transfer Length and/or Bidirectional Read Expected Data Transfer
   Length are 0, but they MUST NOT both be 0 when the Expected Data
   Transfer Length and/or Bidirectional Read Expected Data Transfer
   Length are not 0 (i.e., when some data transfer is expected the
   transfer direction is indicated by the R and/or W bit).


10.3.2  CmdSN - Command Sequence Number

   Enables ordered delivery across multiple connections in a single
   session.

10.3.3  ExpStatSN

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

10.3.4  Expected Data Transfer Length

   For unidirectional operations, the Expected Data Transfer Length
   field contains the number of bytes of data involved in this SCSI
   operation. For a unidirectional write operation (W flag set to 1 and
   R flag set to 0), the initiator uses this field to specify the
   number of bytes of data it expects to transfer for this operation.
   For a unidirectional read operation (W flag set to 0 and R flag set
   to 1), the initiator uses this field to specify the number of bytes
   of data it expects the target to transfer to the initiator.  It
   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
   transfer. For bidirectional operations, an additional header segment
   MUST be present in the header sequence that indicates the
   Bidirectional Read Expected Data Transfer Length.  The Expected Data
   Transfer Length field and the Bidirectional Read Expected Data
   Transfer Length field correspond to the SAM2 byte count

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

   If the Expected Data Transfer Length is higher than the
   FirstBurstLength (the negotiated maximum amount of unsolicited data


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   the target will accept), the initiator MUST send the maximum amount
   of unsolicited data OR ONLY the immediate data, if any.

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

10.3.5  CDB - SCSI Command Descriptor Block

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

10.3.6  Data Segment - Command Data

   Some SCSI commands require additional parameter data to accompany
   the SCSI command. This data may be placed beyond the boundary of the
   iSCSI header in a data segment.  Alternatively, user data (e.g.,
   from a WRITE operation) can be placed in the data segment (both
   cases are referred to as immediate data). These data are governed by
   the rules for solicited vs. unsolicited data outlined in Section
   3.2.4.2 Data Transfer Overview.



































































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10.4  SCSI Response

   The format of the SCSI Response PDU is:

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

10.4.1  Flags (byte 1)

     bit 1-2 Reserved.

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

     bit 4 - (u) set for Bidirectional Read Residual Underflow. In
       this case, the Bidirectional Read Residual Count indicates the
       number of bytes that were not transferred to the initiator out
       of the number of bytes expected to be transferred.




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     bit 5 - (O) set for Residual Overflow. In this case, the
       Residual Count indicates the number of bytes that were not
       transferred because the initiator's Expected Data Transfer
       Length was not sufficient. For a bidirectional operation, the
       Residual Count contains the residual for the write operation.

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

     bit 7 - (0) Reserved.

   Bits O and U and bits o and u are mutually exclusive (i.e., having
   both o and u or O and U set to 1 is a protocol error).
   For a response other than "Command Completed at Target", bits 3-6
   MUST be 0.

10.4.2  Status

   The Status field is used to report the SCSI status of the command
   (as specified in [SAM2]) and is only valid 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.

10.4.3  Response

   This field contains the iSCSI service response.

   iSCSI service response codes defined in this specification are:

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

   All other response codes are reserved.




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   The Response is used to report a Service Response. The mapping of
   the response code into a SCSI service response code value, if
   needed, is outside the scope of this document. However, in symbolic
   terms response value 0x00 maps to the SCSI service response (see
   [SAM2] and [SPC3]) of TASK COMPLETE or LINKED COMMAND COMPLETE. All
   other Response values map to the SCSI service response of SERVICE
   DELIVERY OR TARGET FAILURE.

   If a SCSI Response PDU does not arrive before the session is
   terminated, the SCSI service response is SERVICE DELIVERY OR TARGET
   FAILURE.

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

10.4.4  SNACK Tag

   This field contains a copy of the SNACK Tag of the last SNACK Tag
   accepted by the target on the same connection and for the command
   for which the response is issued. Otherwise it is reserved and
   should be set to 0.

   After issuing a R-Data SNACK the initiator must discard any SCSI
   status unless contained in an SCSI Response PDU carrying the same
   SNACK Tag as the last issued R-Data SNACK for the SCSI command on
   the current connection.

   For a detailed discussion on R-Data SNACK see Section 10.16 SNACK
   Request.

10.4.5  Residual Count

   The Residual Count field MUST be valid in the case where either the
   U bit or the O bit is set. If neither bit is set, the Residual Count
   field is reserved. Targets may set the residual count and initiators
   may use it when the response code is "completed at target" (even if
   the status returned is not GOOD). If the O bit is set, the Residual
   Count indicates the number of bytes that were not transferred
   because the initiator's Expected Data Transfer Length was not
   sufficient. If the U bit is set, the Residual Count indicates the
   number of bytes that were not transferred out of the number of bytes
   expected to be transferred.

10.4.6  Bidirectional Read Residual Count

   The Bidirectional Read Residual Count field MUST be valid in the
   case where either the u bit or the o bit is set. If neither bit is
   set, the Bidirectional Read Residual Count field is reserved.
   Targets may set the Bidirectional Read Residual Count and initiators
   may use it when the response code is "completed at target". If the o
   bit is set, the Bidirectional Read Residual Count indicates the
   number of bytes that were not transferred to the initiator because
   the initiator's Expected Bidirectional Read Transfer Length was not
   sufficient. If the u bit is set, the Bidirectional Read Residual
   Count indicates the number of bytes that were not transferred to the
   initiator out of the number of bytes expected to be transferred.


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10.4.7  Data Segment - Sense and Response Data Segment

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

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

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

10.4.7.1  SenseLength

   Length of Sense Data.

10.4.7.2  Sense Data

   The Sense Data contains detailed information about a check condition
   and [SPC3] specifies the format and content of the Sense Data.

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

   +--------------------------+----------+---------------------------+
   | iSCSI Condition          |Sense     | Additional Sense Code &   |
   |                          |Key       | Qualifier                 |
   +--------------------------+----------+---------------------------+
   | Unexpected unsolicited   |Aborted   | ASC = 0x0c ASCQ = 0x0c    |
   | data                     |Command-0B| Write Error               |
   +--------------------------+----------+---------------------------+
   | Incorrect amount of data |Aborted   | ASC = 0x0c ASCQ = 0x0d    |
   |                          |Command-0B| Write Error               |
   +--------------------------+----------+---------------------------+
   | Protocol Service CRC     |Aborted   | ASC = 0x47 ASCQ = 0x05    |
   | error                    |Command-0B| CRC Error Detected        |
   +--------------------------+----------+---------------------------+
   | SNACK rejected           |Aborted   | ASC = 0x11 ASCQ = 0x13    |
   |                          |Command-0B| Read Error                |
   +--------------------------+----------+---------------------------+



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   The target reports the "Incorrect amount of data" condition if
   during data output the total data length to output is greater than
   FirstBurstLength and the initiator sent unsolicited non-immediate
   data but the total amount of unsolicited data is different than
   FirstBurstLength. The target reports the same error when the amount
   of data sent as a reply to an R2T does not match the amount
   requested.

10.4.8  ExpDataSN

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

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

10.4.9  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
   result of a retry or SNACK. In the case of responses sent due to a
   retransmission request, the StatSN MUST be the same as the first
   time the PDU was sent unless the connection has since been
   restarted.
10.4.10  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 variable with the same name. An ExpCmdSN equal to MaxCmdSN+1
   indicates that the target cannot accept new commands.

10.4.11  MaxCmdSN - Maximum CmdSN from this Initiator

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

























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10.5  Task Management Function Request

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

10.5.1  Function

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

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

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

     3  -  CLEAR ACA - clears the Auto Contingent Allegiance
       condition.

     4  -  CLEAR TASK SET - aborts all Tasks in the appropriate task
       set as defined by the TST field in the Control mode page (see
       [SPC3]).

     5  -  LOGICAL UNIT RESET

     6  -  TARGET WARM RESET



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     7  -  TARGET COLD RESET

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

   For all these functions, the Task Management function response MUST
   be returned as detailed in Section 10.6 Task Management Function
   Response. All these functions apply to the referenced tasks
   regardless of whether they are proper SCSI tasks or tagged iSCSI
   operations.  Task management requests must act on all the commands
   from the same session having a CmdSN lower than the task management
   CmdSN. LOGICAL UNIT RESET, TARGET WARM RESET and TARGET COLD RESET
   may affect commands from other sessions or commands from the same
   session with CmdSN equal or exceeding CmdSN.

   If the task management request is marked for immediate delivery, it
   must be considered immediately for execution, but the operations
   involved (all or part of them) may be postponed to allow the target
   to receive all relevant tasks. According to [SAM2], for all the
   tasks covered by the Task Management response (i.e., with CmdSN
   lower than the task management command CmdSN) but except the Task
   Management response to a TASK REASSIGN, additional responses MUST
   NOT be delivered to the SCSI layer after the Task Management
   response. The iSCSI initiator MAY deliver to the SCSI layer all
   responses received before the Task Management response (i.e., it is
   a matter of implementation if the SCSI responses, received before
   the Task Management response but after the task management request
   was issued, are delivered to the SCSI layer by the iSCSI layer in
   the initiator). The iSCSI target MUST ensure that no responses for
   the tasks covered by a task management function are delivered to the
   iSCSI initiator after the Task Management response except for a task
   covered by a TASK REASSIGN.

   For ABORT TASK SET and CLEAR TASK SET, the issuing initiator MUST
   continue to respond to all valid target transfer tags (received via
   R2T, Text Response, NOP-In, or SCSI Data-in PDUs) related to the
   affected task set, even after issuing the task management request.
   The issuing initiator SHOULD however terminate (i.e., by setting the
   F-bit to 1) these response sequences as quickly as possible.  The
   target on its part MUST wait for responses on all affected target
   transfer tags before acting on either of these two task management
   requests.  In case all or part of the response sequence is not
   received (due to digest errors) for a valid TTT, the target MAY
   treat it as a case of within-command error recovery class (see
   Section 6.1.4.1 Recovery Within-command) if it is supporting
   ErrorRecoveryLevel >= 1, or alternatively may drop the connection to
   complete the requested task set function.

   If an ABORT TASK is issued for a task created by an immediate
   command then RefCmdSN MUST be that of the Task Management request
   itself (i.e. CmdSN and RefCmdSN are equal); otherwise RefCmdSN MUST
   be set to the CmdSN of the task to be aborted (lower than CmdSN).

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


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

   At the target an ABORT TASK function MUST NOT be executed on a Task
   Management request; such a request MUST result in Task Management
   response of "Function rejected".

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

   The implementation of the TARGET WARM RESET function and the TARGET
   COLD RESET function is OPTIONAL and when implemented, should act as
   described below. The TARGET WARM RESET is also subject to SCSI
   access controls on the requesting initiator as defined in [SPC3].
   When authorization fails at the target, the appropriate response as
   described in Section 10.6 Task Management Function Response MUST be
   returned by the target. The TARGET COLD RESET function is not
   subject to SCSI access controls, but its execution privileges may be
   managed by iSCSI mechanisms such as login authentication.

   When executing the TARGET WARM RESET and TARGET COLD RESET
   functions, the target cancels all pending operations on all Logical
   Units known by the issuing initiator. Both functions are equivalent
   to the Target Reset function specified by [SAM2]. They can affect
   many other initiators logged in with the servicing SCSI target port.

   The target MUST treat the TARGET COLD RESET function additionally as
   a power on event, thus terminating all of its TCP connections to all
   initiators (all sessions are terminated).  For this reason, the
   Service Response (defined by [SAM2]) for this SCSI task management
   function may not be reliably delivered to the issuing initiator
   port.

   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 ONLY be received by the
   target after the connection on which the command was previously
   executing has been successfully logged-out. The Task Management
   response MUST be issued before the reassignment becomes effective.
   For additional usage semantics see Section 6.2 Retry and Reassign in
   Recovery.

   At the target a TASK REASSIGN function request MUST NOT be executed
   to reassign the connection allegiance of a Task Management function
   request, an active text negotiation task, or a Logout task; such a
   request MUST result in Task Management response of "Function
   rejected".


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   TASK REASSIGN MUST be issued as an immediate command.

10.5.2  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.

10.5.3  LUN

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

10.5.4  Referenced Task Tag

   The Initiator Task Tag of the task to be aborted for the ABORT TASK
   function or reassigned for the TASK REASSIGN function.
   For all the other functions this field MUST be set to the reserved
   value 0xffffffff.

10.5.5  RefCmdSN

   If an ABORT TASK is issued for a task created by an immediate
   command then RefCmdSN MUST be that of the Task Management request
   itself (i.e. CmdSN and RefCmdSN are equal).

   For an ABORT TASK of a task created by non-immediate command
   RefCmdSN MUST be set to the CmdSN of the task identified by the
   Referenced Task Tag field. Targets must use this field as described
   in section 10.6.1 when the task identified by the Referenced Task
   Tag field is not with the target.

   Otherwise, this field is reserved.

10.5.6  ExpDataSN

   For recovery purposes, the iSCSI target and initiator maintain a
   data acknowledgement reference number - the first input DataSN
   number unacknowledged by the initiator. When issuing a new command,
   this number is set to 0. If the function is TASK REASSIGN, which
   establishes a new connection allegiance for a previously issued Read
   or Bidirectional command, ExpDataSN will contain  an updated data
   acknowledgement reference number or the value 0; the latter
   indicating that the data acknowledgement reference number is
   unchanged. The initiator MUST discard any data PDUs from the
   previous execution that it did not acknowledge and the target MUST
   transmit all Data-in PDUs (if any) starting with the data
   acknowledgement reference number.  The number of retransmitted PDUs
   may or may not be the same as the original transmission depending on
   if there was a change in MaxRecvDataSegmentLength in the
   reassignment. The target MAY also send no more Data-In PDUs if all
   data has been acknowledged.

   The value of ExpDataSN  MUST be 0 or higher than the DataSN of the
   last acknowledged Data-In PDU, but not larger than DataSN+1 of the



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   last Data-IN PDU sent by the target. Any other value MUST be ignored
   by the target.

   For other functions this field is reserved.







































































































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10.6  Task Management Function Response


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

   For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
   SET, LOGICAL UNIT RESET, TARGET COLD RESET, TARGET WARM RESET and
   TASK REASSIGN, the target performs the requested Task Management
   function and sends a Task Management response back to the initiator.
   For TASK REASSIGN, the new connection allegiance MUST ONLY become
   effective at the target after the target issues the Task Management
   Response.

10.6.1  Response

   The target provides a Response, which may take on the following
   values:

      a)    0 - Function complete.
      b)    1 - Task does not exist.
      c)    2 - LUN does not exist.
      d)    3 - Task still allegiant.
      e)    4 - Task allegiance reassignment not supported.
      f)    5 - Task management function not supported.
      g)    6 - Function authorization failed.
      h)  255 - Function rejected.


   All other values are reserved.





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

   For the TARGET COLD RESET and TARGET WARM RESET functions, the
   target cancels all pending operations across all Logical Units known
   to the issuing initiator.  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
   value, if needed, is outside the scope of this document. However, in
   symbolic terms Response values 0 and 1 map to the SCSI service
   response of FUNCTION COMPLETE.  All other Response values map to the
   SCSI service response of FUNCTION REJECTED. If a Task Management
   function response PDU does not arrive before the session is
   terminated, the SCSI service response is SERVICE DELIVERY OR TARGET
   FAILURE.

   The response to ABORT TASK SET and CLEAR TASK SET MUST only be
   issued by the target after all of the commands affected have been
   received by the target, the corresponding task management functions
   have been executed by the SCSI target, and the delivery of all
   responses delivered until the task management function completion
   have been confirmed (acknowledged through ExpStatSN) by the
   initiator on all connections of this session.  For the exact
   timeline of events, refer to Section 10.6.2 Task Management Actions
   on Task Sets.

   For the ABORT TASK function,

      a)  If the Referenced Task Tag identifies a valid task leading
      to a successful termination, then targets must return the
      "Function complete" response.
      b)  If the Referenced Task Tag does not identify an existing
      task, but if the CmdSN indicated by the RefCmdSN field in the
      Task Management function request is within the valid CmdSN
      window and less than the CmdSN of the Task Management function
      request itself, then targets must consider the CmdSN received
      and return the "Function complete" response.
      c)  If the Referenced Task Tag does not identify an existing
      task and if the CmdSN indicated by the RefCmdSN field in the
      Task Management function request is outside the valid CmdSN
      window, then targets must return the "Task does not exist"
      response.

10.6.2  Task Management Actions on Task Sets

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

   The initiator:









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         a)  Issues ABORT TASK SET/CLEAR TASK SET request.
         b)  Continues to respond to each target transfer tag
                 received for the affected task set.
         c)  Receives any responses for the tasks in the affected
                 task set (may process them as usual because they are
                 guaranteed to be valid).
         d)  Receives the task set management response, thus
                 concluding all the tasks in the affected task set.


   The target:

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

10.6.3  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.

























































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10.7  SCSI Data-out & SCSI Data-in

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


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

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



























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


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

10.7.1  F (Final) Bit

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

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


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

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

10.7.2  A (Acknowledge) bit

   For sessions with ErrorRecoveryLevel 1 or higher, the target sets
   this bit to 1 to indicate that it requests a positive
   acknowledgement from the initiator for the data received.  The
   target should use the A bit moderately; it MAY only set the A bit to
   1 once every MaxBurstLength bytes, or on the last Data-In PDU that
   concludes the entire requested read data transfer for the task from
   the target's perspective, and it MUST NOT do so more frequently. The
   target MUST NOT set to 1 the A bit for sessions with
   ErrorRecoveryLevel=0. The initiator MUST ignore the A bit set to 1
   for sessions with ErrorRecoveryLevel=0.

   On receiving a Data-In PDU with the A bit set to 1 on a session with
   ErrorRecoveryLevel greater than 0, if there are no holes in the read
   data until that Data-In PDU, the initiator MUST issue a SNACK of
   type DataACK except when it is able to acknowledge the status for
   the task immediately via ExpStatSN on other outbound PDUs if the
   status for the task is also received. In the latter case
   (acknowledgement through ExpStatSN), sending a SNACK of type DataACK
   in response to the A bit is OPTIONAL, but if it is done, it must not
   be sent after the status acknowledgement through ExpStatSN.  If the
   initiator has detected holes in the read data prior to that Data-In
   PDU, it MUST postpone issuing the SNACK of type DataACK until the
   holes are filled. An initiator also MUST NOT acknowledge the status
   for the task before those holes are filled.  A status
   acknowledgement for a task that generated the Data-In PDUs is
   considered by the target as an implicit acknowledgement of the Data-
   In PDUs if such an acknowledgement was requested by the target.

10.7.3  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.



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     bit 2-4 - Reserved.

     bit 5-6 - used the same as in a SCSI Response. These bits are
       only valid when S is set to 1. For details see Section 10.4.1
       Flags (byte 1).

     bit 7 S (status)- set to indicate that the Command Status field
       contains status. If this bit is set to 1, the F bit MUST also
       be set to 1.


   The fields StatSN, Status, and Residual Count only have meaningful
   content if the S bit is set to 1 and their values are defined in
   Section 10.4 SCSI Response.

10.7.4  Target Transfer Tag and LUN

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

   On incoming data, the Target Transfer Tag and LUN MUST be provided
   by the target if the A bit is set to 1; otherwise they are reserved.
   The Target Transfer Tag and LUN are copied by the initiator into the
   SNACK of type DataACK that it issues as a result of receiving a SCSI
   Data-in PDU with the A bit set to 1.

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

10.7.5  DataSN

   For input (read) or bidirectional Data-In PDUs, the DataSN is the
   input PDU number within the data transfer for the command identified
   by the Initiator Task Tag.

   R2T and Data-In PDUs, in the context of bidirectional commands,
   share the numbering sequence (see Section 3.2.2.3 Data Sequencing).

   For output (write) data PDUs, the DataSN is the Data-Out PDU number
   within the current output sequence. The current output sequence is
   either identified by the Initiator Task Tag (for unsolicited data)
   or is a data sequence generated for one R2T (for data solicited
   through R2T).

10.7.6  Buffer Offset

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


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   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.

10.7.7  DataSegmentLength

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

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









































































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10.8  Ready To Transfer (R2T)

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


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

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

   An R2T MAY be answered with one or more SCSI Data-out PDUs with a
   matching Target Transfer Tag. If an R2T is answered with a single
   Data-out PDU, the Buffer Offset in the Data PDU MUST be the same as
   the one specified by the R2T, and the data length of the Data PDU
   MUST be the same as the Desired Data Transfer Length specified in
   the R2T. If the R2T is answered with a sequence of Data PDUs, the
   Buffer Offset and Length MUST be within the range of those specified
   by R2T, and the last PDU MUST have the F bit set to 1. If the last
   PDU (marked with the F bit) is received before the Desired Data
   Transfer Length is transferred, a target MAY choose to Reject that


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   PDU with "Protocol error" reason code.  DataPDUInOrder governs the
   Data-Out PDU ordering. If DataPDUInOrder is set to Yes, the Buffer
   Offsets and Lengths for consecutive PDUs MUST form a continuous non-
   overlapping range and the PDUs MUST be sent in increasing offset
   order.

   The target may send several R2T PDUs. It, therefore, can have a
   number of pending data transfers.  The number of outstanding R2T
   PDUs are limited by the value of the negotiated key
   MaxOutstandingR2T.  Within a connection, outstanding R2Ts MUST be
   fulfilled by the initiator in the order in which they were received.

   R2T PDUs MAY also be used to recover Data Out PDUs. Such an R2T
   (Recovery-R2T) is generated by a target upon detecting the loss of
   one or more Data-Out PDUs due to:

     - Digest error
     - Sequence error
     - Sequence reception timeout

   A Recovery-R2T carries the next unused R2TSN, but requests part of
   or the entire data burst that an earlier R2T (with a lower R2TSN)
   had already requested.

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

10.8.1  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.

10.8.2  R2TSN

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

   For bidirectional commands R2T and Data-In PDUs share the input PDU
   numbering sequence (see Section 3.2.2.3 Data Sequencing).

10.8.3  StatSN

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

10.8.4  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 MUST NOT be 0 and MUST not exceed
   MaxBurstLength.


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10.8.5  Target Transfer Tag

   The target assigns its own tag to each R2T request that it sends to
   the initiator. This tag can be used by the target to easily identify
   the data it receives. The Target Transfer Tag and LUN are copied in
   the outgoing data PDUs and are only used by the target. There is no
   protocol rule about the Target Transfer Tag except that the value
   0xffffffff is reserved and MUST NOT be sent by a target in an R2T.





























































































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10.9  Asynchronous Message

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

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


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

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

10.9.1  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,


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       identifies the condition. The sending of a SCSI Event
       (Asynchronous Event Reporting in SCSI terminology) is
       dependent on the target support for SCSI asynchronous event
       reporting (see [SAM2]) as indicated in the standard INQUIRY
       data (see [SPC3]). Its use may be enabled by parameters in the
       SCSI Control mode page (see [SPC3]).

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

     2 - target indicates it will drop the connection.
       The Parameter1 field indicates the CID of the connection going
       to be dropped.
       The Parameter2 field (Time2Wait) indicates, in seconds, the
       minimum time to wait before attempting to reconnect or
       reassign.
       The Parameter3 field (Time2Retain) indicates the maximum time
       allowed to reassign commands after the initial wait (in
       Parameter2).
       If the initiator does not attempt to reconnect and/or reassign
       the outstanding commands within the time specified by
       Parameter3, or if Parameter3 is 0, the target will terminate
       all outstanding commands on this connection. In this case, 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.
       Parameter1 field is reserved.
       The Parameter2 field (Time2Wait) indicates, in seconds, the
       minimum time to wait before attempting to reconnect.
       The Parameter3 field (Time2Retain) indicates the maximum time
       allowed to reassign commands after the initial wait (in
       Parameter2).
       If the initiator does not attempt to reconnect and/or reassign
       the outstanding commands within the time specified by
       Parameter3, or if Parameter3 is 0, the session is terminated.
       In this case, the target will terminate all outstanding
       commands in this session; no other responses should be
       expected from the target for the outstanding commands in this



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          session. A value of 0 for Parameter2 indicates that reconnect
          can be attempted immediately.

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

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

   All other event codes are reserved.

10.9.2  AsyncVCode

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

10.9.3  LUN

   The LUN field MUST be valid if AsyncEvent is 0. Otherwise, this
   field is reserved.
10.9.4  Sense Data and iSCSI Event Data

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

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

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

10.9.4.1  SenseLength

   This is the length of Sense Data. When the Sense Data field is empty
   (e.g., the event is not a SCSI event) SenseLength is 0.



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10.10  Text Request

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


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


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

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

10.10.1  F (Final) Bit

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







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10.10.2  C (Continue) Bit

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

10.10.3  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). The
   I bit for all requests in a sequence also MUST be the same.

10.10.4  Target Transfer Tag

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

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

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

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

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

   Long text responses are handled as in the following example:

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






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10.10.5  Text

   The data lengths of a text request MUST NOT exceed the iSCSI target
   MaxRecvDataSegmentLength (a per connection and per direction
   negotiated parameter).  The text format is specified in Section 5.2
   Text Mode Negotiation.

   Chapter 11 and Chapter 12 list some basic Text key=value pairs, some
   of which can be used in Login Request/Response and some in Text
   Request/Response.

   A key=value pair can span Text request or response boundaries.  A
   key=value pair can start in one PDU and continue on the next. In
   other words the end of a PDU does not necessarily signal the end of
   a key=value pair.

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

   Chapter 5 details the rules for the Text Requests and Responses.

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

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



















































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10.11  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       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x24      |F|C| Reserved                                  |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or 0xffffffff                             |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment (Text)                                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

10.11.1  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.

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

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




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

10.11.2  C (Continue) Bit

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

10.11.3  Initiator Task Tag

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

10.11.4  Target Transfer Tag

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

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

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

   When the target receives a Text Request with the Target Transfer Tag
   set to the reserved value of 0xffffffff, it resets its internal
   information (resets state) associated with the given Initiator Task
   Tag (restarts the negotiation).

   When a target cannot finish the operation in a single Text Response,
   and does not have enough resources to continue, it rejects the Text
   Request with the appropriate Reject code.

   A target may reset its internal state associated with an Initiator
   Task Tag (the current negotiation state), state expressed through
   the Target Transfer Tag if the initiator fails to continue the
   exchange for some time. The target may reject subsequent Text
   Requests with the Target Transfer Tag set to the "stale" value.

10.11.5  StatSN

   The target StatSN variable is advanced by each Text Response sent.

10.11.6  Text Response Data

   The data lengths of a text response MUST NOT exceed the iSCSI
   initiator MaxRecvDataSegmentLength (a per connection and per
   direction negotiated parameter).



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   The text in the Text Response Data is governed by the same rules as
   the text in the Text Request Data (see Section 10.10.5 Text).

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

































































































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10.12  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.

   Login requests are always considered as immediate.

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

10.12.1  T (Transit) Bit

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

   If the T bit is set to 1 and NSG is FullFeaturePhase, then this also
   indicates that the initiator is ready for the Final Login Response
   (see Chapter 5).

10.12.2  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Login Request is not complete (it will be continued on
   subsequent Login Requests); otherwise, it indicates that this Login


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

10.12.3  CSG and NSG

   Through these fields, Current Stage (CSG) and Next Stage (NSG), the
   Login negotiation requests and responses are associated with a
   specific stage in the session (SecurityNegotiation,
   LoginOperationalNegotiation, FullFeaturePhase) and may indicate the
   next stage to which they want to move (see Chapter 5). The next
   stage value is only valid  when the T bit is 1; otherwise, it is
   reserved.

   The stage codes are:

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

   All other codes are reserved.

10.12.4  Version

   The version number of the current draft is 0x00.  As such, all
   devices MUST carry version 0x00 for both Version-min and Version-
   max.

10.12.4.1  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.

10.12.4.2  Version-min


   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.

10.12.5  ISID

   This is an initiator-defined component of the session identifier and
   is structured as follows (see [NDT] and Section 9.1.1 Conservative
   Reuse of ISIDs for details):












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

   The T field identifies the format and usage of A, B, C, and D as
   indicated below:

     T

     00b     OUI-Format
             A&B are a 22 bit OUI
             (the I/G & U/L bits are omitted)
             C&D 24 bit qualifier
     01b     EN - Format (IANA Enterprise Number)
             A - Reserved
             B&C EN (IANA Enterprise Number)
             D - Qualifier
     10b     "Random"
             A - Reserved
             B&C Random
             D - Qualifier
     11b     A,B,C&D Reserved

   For the T field values 00b and 01b, a combination of A and B (for
   00b) or B and C (for 01b) identifies the vendor or organization
   whose component (software or hardware) generates this ISID.  A
   vendor or organization with one or more OUIs, or one or more
   Enterprise Numbers, MUST use at least one of these numbers and
   select the appropriate value for the T field when its components
   generate ISIDs.  An OUI or EN MUST be set in the corresponding
   fields in network byte order (byte big-endian).

   If the T field is 10b, B and C are set to a random 24-bit unsigned
   integer value in network byte order (byte big-endian).  See [NDT]
   for how this affects the principle of "conservative reuse".

   The Qualifier field is a 16 or 24-bit unsigned integer value that
   provides a range of possible values for the ISID within the selected
   namespace. It may be set to any value within the constraints
   specified in the iSCSI protocol (see Section 3.4.3 Consequences of
   the Model and Section 9.1.1 Conservative Reuse of ISIDs).

   The T field value of 11b is reserved.

   If the ISID is derived from something assigned to a hardware adapter
   or interface by a vendor, as a preset default value, it MUST be
   configurable to a value assigned according to the SCSI port behavior
   desired by the system in which it is installed (see Section 9.1.1
   Conservative Reuse of ISIDs and Section 9.1.2 iSCSI Name, ISID, and
   TPGT Use). The resultant ISID MUST also be persistent over power
   cycles, reboot, card swap, etc.


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10.12.6  TSIH

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

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

   The target MUST check the value presented with the first login
   request and act as specified in Section 5.3.1 Login Phase Start.

10.12.7  Connection ID - CID

   A unique ID for this connection within the session.

   All Login requests within the Login Phase MUST carry the same CID.

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

   A Login request with a non-zero TSIH and a CID equal to that of an
   existing connection implies a logout of the connection followed by a
   Login (see Section 5.3.4 Connection Reinstatement). For the details
   of the implicit Logout Request, see Section 10.14 Logout Request.

10.12.8  CmdSN

   CmdSN is either the initial command sequence number of a session
   (for the first Login request of a session - the "leading" login), or
   the command sequence number in the command stream if the login is
   for a new connection in an existing session.

   Examples:

        - Login on a leading connection - if the leading login carries
          the CmdSN 123, all other login requests in the same login
          phase carry the CmdSN 123 and the first non-immediate command
          in FullFeaturePhase also carries the CmdSN 123.

        - Login on other than a leading connection - if the current
          CmdSN at the time the first login on the connection is issued
          is 500, then that PDU carries CmdSN=500. Subsequent login
          requests that are needed to complete this login phase may
          carry a CmdSN higher than 500 if non-immediate requests that
          were issued on other connections in the same session advance
          CmdSN.

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






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10.12.9  ExpStatSN

   For the first Login Request on a connection this is ExpStatSN for
   the old connection and this field is only valid if the Login request
   restarts a connection (see Section 5.3.4 Connection Reinstatement).

   For subsequent Login Requests it is used to acknowledge the Login
   Responses with their increasing StatSN values.

10.12.10  Login Parameters

   The initiator MUST provide some basic parameters in order to enable
   the target to determine if the initiator may use the target's
   resources and the initial text parameters for the security exchange.

   All the rules specified in Section 10.10.5 Text for text requests
   also hold for login requests.  Keys and their explanations are
   listed in Chapter 11 (security negotiation keys) and Chapter 12
   (operational parameter negotiation keys). All keys in Chapter 12,
   except for the X extension formats, MUST be supported by iSCSI
   initiators and targets. Keys in Chapter 11 only need to be supported
   when the function to which they refer is mandatory to implement.



































































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10.13  Login Response

   The Login Response indicates the progress and/or end of the Login
   Phase.

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x23      |T|C|.|.|CSG|NSG| Version-max   | Version-active|
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| ISID                                                          |
     +                               +---------------+---------------+
   12|                               | TSIH                          |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Status-Class  | Status-Detail | Reserved                      |
     +---------------+---------------+---------------+---------------+
   40/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ DataSegment - Login Parameters in Text request Format         /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

10.13.1  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.

   The initiator MUST use the value presented as a response to the
   first login request.

10.13.2  Version-active

   Indicates the highest version supported by the target and initiator.
   If the target does not support a version within the range specified
   by the initiator, the target rejects the login and this field
   indicates the lowest version supported by the target.

   All Login responses within the Login Phase MUST carry the same
   Version-active.



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   The initiator MUST use the value presented as a response to the
   first login request.

10.13.3  TSIH

   The TSIH is the target assigned session identifying handle. Its
   internal format and content are not defined by this protocol except
   for the value 0 that is reserved. With the exception of the Login
   Final-Response in a new session, this field should be set to the
   TSIH provided by the initiator in the Login Request.  For a new
   session, the target MUST generate a non-zero TSIH and ONLY return it
   in the Login Final-Response (see Section 5.3 Login Phase).

10.13.4  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, including the next login
   response, if any, in the same Login Phase, will carry this number +
   1. This field is only valid if the Status-Class is 0.

10.13.5  Status-Class and Status-Detail

   The Status returned in a Login Response indicates the execution
   status of the Login Phase. The status includes:

     Status-Class
     Status-Detail

   0 Status-Class indicates success.

   A non-zero Status-Class indicates an exception. In this case,
   Status-Class is sufficient for a simple initiator to use when
   handling exceptions, without having to look at the Status-Detail.
   The Status-Detail allows finer-grained exception handling for more
   sophisticated initiators and for better information for logging.

   The status classes are as follows:

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

     1 - Redirection - indicates that the initiator must take further
          action to complete the request. This is usually due to the
          target moving to a different address. All of the redirection
          status class responses MUST return one or more text key
          parameters of the type "TargetAddress", which indicates the
          target's new address. A redirection response MAY be issued by
          a target prior or after completing a security negotiation if a
          security negotiation is required. A redirection SHOULD be
          accepted by an initiator even without having the target
          complete a security negotiation if any security negotiation is
          required, and MUST be accepted by the initiator after the



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       completion of the security negotiation if any security
       negotiation is required.

     2 - Initiator Error (not a format error) - indicates that the
       initiator most likely caused the error. This MAY be due to a
       request for a resource for which the initiator does not have
       permission.  The request should not be tried again.

     3 - Target Error - indicates that the target sees no errors in
       the initiator's login request, but is currently incapable of
       fulfilling the request.  The initiator may re-try the same
       login request later.

   The table below shows all of the currently allocated status codes.
   The codes are in hexadecimal; the first byte is the status class and
   the second byte is the status detail.















































































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   -----------------------------------------------------------------
   Status        | Code | Description
                 |(hex) |
   -----------------------------------------------------------------
   Success       | 0000 | Login is proceeding OK (*1).
   -----------------------------------------------------------------
   Target moved  | 0101 | The requested iSCSI Target Name (ITN)
   temporarily   |      |  has temporarily moved
                 |      |  to the address provided.
   -----------------------------------------------------------------
   Target moved  | 0102 | The requested ITN has permanently moved
   permanently   |      |  to the address provided.
   -----------------------------------------------------------------
   Initiator     | 0200 | Miscellaneous iSCSI initiator
   error         |      | errors.
   ----------------------------------------------------------------
   Authentication| 0201 | The initiator could not be
   failure       |      | successfully authenticated or target
                 |      | authentication is not supported.
   -----------------------------------------------------------------
   Authorization | 0202 | The initiator is not allowed access
   failure       |      | to the given target.
   -----------------------------------------------------------------
   Not found     | 0203 | The requested ITN does not
                 |      | exist at this address.
   -----------------------------------------------------------------
   Target removed| 0204 | The requested ITN has been removed and
                 |      |no forwarding address is provided.
   -----------------------------------------------------------------
   Unsupported   | 0205 | The requested iSCSI version range is
   version       |      | not supported by the target.
   -----------------------------------------------------------------
   Too many      | 0206 | Too many connections on this SSID.
   connections   |      |
   -----------------------------------------------------------------
   Missing       | 0207 | Missing parameters (e.g., iSCSI
   parameter     |      | Initiator and/or Target Name).
   -----------------------------------------------------------------
   Can't include | 0208 | Target does not support session
   in session    |      | spanning to this connection (address).
   -----------------------------------------------------------------
   Session type  | 0209 | Target does not support this type of
   not supported |      | of session or not from this Initiator.
   -----------------------------------------------------------------
   Session does  | 020a | Attempt to add a connection
   not exist     |      | to a non-existent session.
   -----------------------------------------------------------------
   Invalid during| 020b | Invalid Request type during Login.
   login         |      |
   -----------------------------------------------------------------
   Target error  | 0300 | Target hardware or software error.
   -----------------------------------------------------------------
   Service       | 0301 | The iSCSI service or target is not
   unavailable   |      | currently operational.
   -----------------------------------------------------------------
   Out of        | 0302 | The target has insufficient session,


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   resources     |      | connection, or other resources.
   -----------------------------------------------------------------

   (*1)If the response T bit is 1 in both the request and the matching
   response, and the NSG is FullFeaturePhase in both the request and
   the matching 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.

10.13.6  T (Transit) bit

   The T bit is set to 1 as an indicator of the end of the stage. If
   the T bit is set to 1 and NSG is FullFeaturePhase, then this is also
   the Final Login Response (see Chapter 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.

10.13.7  C (Continue) Bit

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

10.13.8  Login Parameters

   The target MUST provide some basic parameters in order to enable the
   initiator to determine if it is connected to the correct port and
   the initial text parameters for the security exchange.

   All the rules specified in Section 10.11.6 Text Response Data for
   text responses also hold for login responses.  Keys and their
   explanations are listed in Chapter 11 (security negotiation keys)
   and Chapter 12 (operational parameter negotiation keys). All keys in
   Chapter 12, except for the X extension formats, MUST be supported by
   iSCSI initiators and targets. Keys in Chapter 11, only need to be
   supported when the function to which they refer is mandatory to
   implement.











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10.14  Logout Request

   The Logout request is used to perform a controlled closing of a
   connection.

   An initiator MAY use a logout request to remove a connection from a
   session or to close an entire session.

   After sending the Logout request PDU, an initiator MUST NOT send any
   new iSCSI requests on the closing connection. If the Logout request
   is intended to close the session, new iSCSI requests MUST NOT be
   sent on any of the connections participating in the session.

   When receiving a Logout request with the reason code of "close the
   connection" or "close the session", the target MUST terminate all
   pending commands, whether acknowledged via ExpCmdSN or not, on that
   connection or session respectively.

   When receiving a Logout request with the reason code "remove
   connection for recovery", the target MUST discard all requests not
   yet acknowledged via ExpCmdSN that were issued on the specified
   connection, and suspend all data/status/R2T transfers on behalf of
   pending commands on the specified connection.

   The target then issues the Logout response and half-closes the TCP
   connection (sends FIN).  After receiving the Logout response and
   attempting to receive the FIN (if still possible), the initiator
   MUST completely close the logging-out connection. For the terminated
   commands, no additional responses should be expected.

   A Logout for a CID may be performed on a different transport
   connection when the TCP connection for the CID has already been
   terminated.  In such a case, only a logical "closing" of the iSCSI
   connection for the CID is implied with a Logout.

   All commands that were not terminated or not completed (with status)
   and acknowledged when the connection is closed completely can be
   reassigned to a new connection if the target supports connection
   recovery.

   If an initiator intends to start recovery for a failing connection,
   it MUST use the Logout request to "clean-up" the target end of a
   failing connection and enable recovery to start, or the Login
   request with a non-zero TSIH and the same CID on a new connection
   for the same effect (see Section 10.14.3 CID).  In sessions with a
   single connection, the connection can be closed and then a new
   connection reopened. A connection reinstatement login can be used
   for recovery (see Section 5.3.4 Connection Reinstatement).

   A successful completion of a logout request with the reason code of
   "close the connection" or "remove the connection for recovery"
   results at the target in the discarding of unacknowledged commands
   received on the connection being logged out. These are commands that
   have arrived on the connection being logged out, but have not been
   delivered to SCSI because one or more commands with a smaller CmdSN
   has not been received by iSCSI. See Section 3.2.2.1 Command


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   Numbering and Acknowledging.  The resulting holes the in command
   sequence numbers will have to be handled by appropriate recovery
   (see Chapter 6) unless the session is also closed.

   The entire logout discussion in this section is also applicable for
   an implicit Logout affected by way of a connection reinstatement or
   session reinstatement. When a Login Request performs an implicit
   Logout, the implicit Logout is performed as if having the reason
   codes specified below:

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



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

10.14.1  Reason Code

   Reason Code indicates the reason for Logout as follows:

     0 - close the session. All commands associated with the session
          (if any) are terminated.

     1 - close the connection. All commands associated with
          connection (if any) are terminated.




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     2 - remove the connection for recovery. Connection is closed and
       all commands associated with it, if any, are to be prepared
       for a new allegiance.

   All other values are reserved.

10.14.2  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.


10.14.3  CID

   This is the connection ID of the connection to be closed (including
   closing the TCP stream). This field is only valid if the reason code
   is not "close the session".

10.14.4  ExpStatSN

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

10.14.5  Implicit termination of tasks

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

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

      b)  When a connection fails and eventually the connection state
      times out (state transition M1 in Section 7.2.2 State
      Transition Descriptions for Initiators and Targets) and there
      are active tasks allegiant to that connection.

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

      d)  When a connection is implicitly or explicitly logged out
      with the reason code of "Close the session" and there are
      active tasks in that session.


   If the tasks terminated in any of the above cases are SCSI tasks,
   they must be internally terminated as if with CHECK CONDITION
   status.  This status is only meaningful for appropriately handling
   the internal SCSI state and SCSI side effects with respect to
   ordering because this status is never communicated back as a
   terminating status to the initiator. However additional actions may
   have to be taken at SCSI level depending on the SCSI context as
   defined by the SCSI standards (e.g., queued commands and ACA, UA for








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   the next command on the I_T nexus in cases a), b), and c) etc. - see
   [SAM] and [SPC3]).











































































































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10.15  Logout Response

   The logout response is used by the target to indicate if the cleanup
   operation for the connection(s) has completed.

   After Logout, the TCP connection referred by the CID MUST be closed
   at both ends (or all connections must be closed if the logout reason
   was session close).

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x26      |1| Reserved    | Response      | Reserved      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------------------------------------------------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Reserved                                                      |
     +---------------------------------------------------------------+
   40| Time2Wait                     | Time2Retain                   |
     +---------------+---------------+---------------+---------------+
   44| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

10.15.1  Response

   Logout response:

     0 - connection or session closed successfully.

     1 - CID not found.

     2 - connection recovery is 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.

10.15.2  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.


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10.15.3  Time2Wait

   If the Logout response code is 0 and if the operational
   ErrorRecoveryLevel is 2, this is the minimum amount of time, in
   seconds, to wait before attempting task reassignment. If the Logout
   response code is 0 and if the operational ErrorRecoveryLevel is less
   than 2, this field is to be ignored.

   This field is invalid if the Logout response code is 1.

   If the Logout response code is 2 or 3, this field specifies the
   minimum time to wait before attempting a new implicit or explicit
   logout.

   If Time2Wait is 0, the reassignment or a new Logout may be attempted
   immediately.

10.15.4  Time2Retain

   If the Logout response code is 0 and if the operational
   ErrorRecoveryLevel is 2, this is the maximum amount of time, in
   seconds, after the initial wait (Time2Wait), the target waits for
   the allegiance reassignment for any active task after which the task
   state is discarded.  If the Logout response code is 0 and if the
   operational ErrorRecoveryLevel is less than 2, this field is to be
   ignored.

   This field is invalid if the Logout response code is 1.

   If the Logout response code is 2 or 3, this field specifies the
   maximum amount of time, in seconds, after the initial wait
   (Time2Wait), the target waits for a new implicit or explicit logout.

   If it is the last connection of a session, the whole session state
   is discarded after Time2Retain.

   If Time2Retain is 0, the target has already discarded the connection
   (and possibly the session) state along with the task states.  No
   reassignment or Logout is required in this case.































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10.16   SNACK Request

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x10      |1|.|.|.| Type  | Reserved                      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or SNACK Tag or 0xffffffff                |
     +---------------+---------------+---------------+---------------+
   24| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   28| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   40| BegRun                                                        |
     +---------------------------------------------------------------+
   44| RunLength                                                     |
     +---------------------------------------------------------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

   If the implementation supports ErrorRecoveryLevel greater than zero,
   it MUST support all SNACK types.

   The SNACK is used by the initiator to request the retransmission of
   numbered-responses, data, or R2T PDUs from the target. The SNACK
   request indicates the numbered-responses or data "runs" whose
   retransmission is requested by the target, where the run starts with
   the first StatSN, DataSN, or R2TSN whose retransmission is requested
   and indicates the number of Status, Data, or R2T PDUs requested
   including the first. 0 has special meaning when used as a starting
   number and length:

     - When used in RunLength, it means all PDUs starting with the
       initial.
     - When used in both BegRun and RunLength, it means all
       unacknowledged PDUs.

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




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   The numbered Data-In PDUs, requested by a Data SNACK MUST be
   delivered as exact replicas of the ones that the target transmitted
   originally except for the fields ExpCmdSN and MaxCmdSN, which MUST
   carry the current values and except for resegmentation (see Section
   10.16.3 Resegmentation).

   Any SNACK that requests a numbered-response, Data, or R2T that was
   not sent by the target or was already acknowledged by the initiator,
   MUST be rejected with a reason code of "Protocol error".

10.16.1  Type

   This field encodes the SNACK function as follows:

     0-Data/R2T SNACK - requesting retransmission of one or more
       Data-In or R2T PDUs.

     1-Status SNACK - requesting retransmission of one or more
       numbered responses.

     2-DataACK - positively acknowledges Data-In PDUs.

     3-R-Data SNACK - requesting retransmission of Data-In PDUs with
       possible resegmentation and status tagging.


   All other values are reserved.

   Data/R2T SNACK, Status SNACK, or R-Data SNACK for a command MUST
   precede status acknowledgement for the given command.

10.16.2  Data Acknowledgement

   If an initiator operates at ErrorRecoveryLevel 1 or higher, it MUST
   issue a SNACK of type DataACK after receiving a Data-In PDU with the
   A bit set to 1. However, if the initiator has detected holes in the
   input sequence, it MUST postpone issuing the SNACK of type DataACK
   until the holes are filled. An initiator MAY ignore the A bit if it
   deems that the bit is being set aggressively by the target (i.e.,
   before the MaxBurstLength limit is reached).

   The DataACK is used to free resources at the target and not to
   request or imply data retransmission.

   An initiator MUST NOT request retransmission for any data it had
   already acknowledged.

10.16.3  Resegmentation

   If the initiator MaxRecvDataSegmentLength changed between the
   original transmission and the time the initiator requests
   retransmission, the initiator MUST issue a R-Data SNACK (see Section
   10.16.1 Type). With R-Data SNACK, the initiator indicates that it
   discards all the unacknowledged data and expects the target to
   resend it. It also expects resegmentation. In this case, the
   retransmitted Data-In PDUs MAY be different from the ones originally


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   sent in order to reflect changes in MaxRecvDataSegmentLength. Their
   DataSN starts with the BegRun of the last DataACK received by the
   target if any was received; otherwise it starts with 0 and is
   increased by 1 for each resent Data-In PDU.

   A target that has received a R-Data SNACK MUST return a SCSI
   Response
   that contains a copy of the SNACK Tag field from the R-Data SNACK in
   the SCSI Response SNACK Tag field as its last or only Response. For
   example, if it has already sent a response containing another value
   in the SNACK Tag field or had the status included in the last Data-
   In PDU, it must send a new SCSI Response PDU. If a target sends more
   than one SCSI Response PDU due to this rule, all SCSI responses must
   carry the same StatSN (see Section 10.4.4 SNACK Tag). If an
   initiator attempts to recover a lost SCSI Response (with a Status-
   SNACK, see Section 10.16.1 Type) when more than one response has
   been sent, the target will send the SCSI Response with the latest
   content known to the target, including the last SNACK Tag for the
   command.

   For considerations in allegiance reassignment of a task to a
   connection with a different MaxRecvDataSegmentLength, refer to
   Section 6.2.2 Allegiance Reassignment.

10.16.4  Initiator Task Tag

   For Status SNACK and DataACK, the Initiator Task Tag MUST be set to
   the reserved value 0xffffffff. In all other cases, the Initiator
   Task Tag field MUST be set to the Initiator Task Tag of the
   referenced command.

10.16.5  Target Transfer Tag or SNACK Tag

   For an R-Data SNACK, this field MUST contain a value that is
   different from 0 or 0xffffffff and is unique for the task
   (identified by the Initiator Task Tag). This value MUST be copied by
   the iSCSI target in the last or only SCSI Response PDU it issues for
   the command.

   For DataACK, the Target Transfer Tag MUST contain a copy of the
   Target Transfer Tag and LUN provided with the SCSI Data-In PDU with
   the A bit set to 1.

   In all other cases, the Target Transfer Tag field MUST be set to the
   reserved value of 0xffffffff.


10.16.6  BegRun

   The DataSN, R2TSN, or StatSN of the first PDU whose retransmission
   is requested (Data/R2T and Status SNACK), or the next expected
   DataSN (DataACK SNACK).

   BegRun 0 when used in conjunction with RunLength 0 means resend all
   unacknowledged Data-In, R2T or Response PDUs.



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   BegRun MUST be 0 for a R-Data SNACK.

10.16.7  RunLength

   The number of PDUs whose retransmission is requested.

   RunLength 0 signals that all Data-In, R2T, or Response PDUs carrying
   the numbers equal to or greater than BegRun have to be resent.

   The RunLength MUST also be 0 for a DataACK SNACK in addition to R-
   Data SNACK.

























































































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10.17  Reject

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x3f      |1| Reserved    | Reason        | Reserved      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| 0xffffffff                                                    |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| DataSN/R2TSN or Reserved                                      |
     +---------------+---------------+---------------+---------------+
   40| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   44| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
   xx/ Complete Header of Bad PDU                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   yy/Vendor specific data (if any)                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   zz| Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+


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

10.17.1  Reason

   The reject Reason is coded as follows:

















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   +------+----------------------------------------+------------------+
   | Code | Explanation                            | Can the original |
   | (hex)|                                        | PDU be re-sent?  |
   +------+----------------------------------------+------------------+
   | 0x01 | Reserved                               | no               |
   |      |                                        |                  |
   | 0x02 | Data (payload) Digest Error            | yes  (Note 1)    |
   |      |                                        |                  |
   | 0x03 | SNACK Reject                           | yes              |
   |      |                                        |                  |
   | 0x04 | Protocol Error (e.g., SNACK request for| no               |
   |      | a status that was already acknowledged)|                  |
   |      |                                        |                  |
   | 0x05 | Command not supported                  | no               |
   |      |                                        |                  |
   | 0x06 | Immediate Command Reject - too many    | yes              |
   |      | immediate commands                     |                  |
   |      |                                        |                  |
   | 0x07 | Task in progress                       | no               |
   |      |                                        |                  |
   | 0x08 | Invalid Data ACK                       | no               |
   |      |                                        |                  |
   | 0x09 | Invalid PDU field                      | no   (Note 2)    |
   |      |                                        |                  |
   | 0x0a | Long Operation Reject - Can't generate | yes              |
   |      | Target Transfer Tag - out of resources |                  |
   |      |                                        |                  |
   | 0x0b | Negotiation Reset                      | no               |
   |      |                                        |                  |
   | 0x0c | Waiting for Logout                     | no               |
   +------+----------------------------------------+------------------+

   Note 1: For iSCSI, Data-Out PDU retransmission is only done if the
   target requests retransmission with a recovery R2T. However, if this
   is the data digest error on immediate data, the initiator may choose
   to retransmit the whole PDU including the immediate data.

   Note 2: A target should use this reason code for all invalid values
   of PDU fields that are meant to describe a task,  a response, or a
   data transfer.  Some examples are invalid TTT/ITT, buffer offset,
   LUN qualifying a TTT, and an invalid sequence number in a SNACK.

   All other values for Reason are reserved.

   In all the cases in which a pre-instantiated SCSI task is terminated
   because of the reject, the target MUST issue a proper SCSI command
   response with CHECK CONDITION as described in Section 10.4.3
   Response. In these cases in which a status for the SCSI task was
   already sent before the reject, no additional status is required. If
   the error is detected while data from the initiator is still
   expected (i.e., the command PDU did not contain all the data and the
   target has not received a Data-out PDU with the Final bit set to 1
   for the unsolicited data, if any, and all outstanding R2Ts, if any),
   the target MUST wait until it receives the last expected Data-out
   PDUs with the F bit set to 1 before sending the Response PDU.



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   For additional usage semantics of Reject PDU, see Section 6.3 Usage
   Of Reject PDU in Recovery.

10.17.2  DataSN/R2TSN

   This field is only valid if the rejected PDU is a Data/R2T SNACK and
   the Reject reason code is "Protocol error" (see Section 10.16 SNACK
   Request).  The DataSN/R2TSN is the next Data/R2T sequence number
   that the target would send for the task, if any.

10.17.3  StatSN, ExpCmdSN and MaxCmdSN

   These fields carry their usual values and are not related to the
   rejected command

10.17.4  Complete Header of Bad PDU

   The target returns the header (not including digest) of the PDU in
   error as the data of the response.









































































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10.18  NOP-Out

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x00      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or 0xffffffff                             |
     +---------------+---------------+---------------+---------------+
   24| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Ping Data (optional)                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

   A NOP-Out may be used by an initiator as a "ping request" to verify
   that a connection/session is still active and all its components are
   operational.  The NOP-In response is the "ping echo".

   A NOP-Out is also sent by an initiator in response to a NOP-In.

   A NOP-Out may also be used to confirm a changed ExpStatSN if another
   PDU will not be available for a long time.

   Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
   value (not the reserved 0xffffffff), the initiator MUST respond with
   a NOP-Out. In this case, the NOP-Out Target Transfer Tag MUST
   contain a copy of the NOP-In Target Transfer Tag.

10.18.1  Initiator Task Tag

   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 (i.e., the
   NOP-Out is used as a ping request). Otherwise, the Initiator Task
   Tag MUST be set to 0xffffffff.

   When a target receives the NOP-Out with a valid Initiator Task Tag,
   it MUST respond with a Nop-In Response (see Section 10.19 NOP-In).


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   If the Initiator Task Tag contains 0xffffffff, the I bit MUST be set
   to 1 and the CmdSN is not advanced after this PDU is sent.

10.18.2  Target Transfer Tag

   A target assigned identifier for the operation.

   The NOP-Out MUST only have the Target Transfer Tag set if it is
   issued in response to a NOP-In with a valid Target Transfer Tag. In
   this case, it copies the Target Transfer Tag from the NOP-In PDU.
   Otherwise, the Target Transfer Tag MUST be set to 0xffffffff.

   When the Target Transfer Tag is set to a value other than
   0xffffffff, the LUN field MUST also be copied from the NOP-In.

10.18.3  Ping Data

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

































































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10.19  NOP-In

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x20      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or 0xffffffff                             |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Return Ping Data                                /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+


   NOP-In is either sent by a target as a response to a NOP-Out, as a
   "ping" to an initiator, or as a means to carry a changed ExpCmdSN
   and/or MaxCmdSN if another PDU will not be available for a long time
   (as determined by the target).

   When a target receives the NOP-Out with a valid Initiator Task Tag
   (not the reserved value 0xffffffff), it MUST respond with a NOP-In
   with the same Initiator Task Tag that was provided in the NOP-Out
   request. It MUST also duplicate up to the first
   MaxRecvDataSegmentLength bytes of the initiator provided Ping Data.
   For such a response, the Target Transfer Tag MUST be 0xffffffff.

   Otherwise, when a target sends a NOP-In that is not a response to a
   Nop-Out received from the initiator, the Initiator Task Tag MUST be
   set to 0xffffffff and the Data Segment MUST NOT contain any data
   (DataSegmentLength MUST be 0).







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10.19.1  Target Transfer Tag

   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.

10.19.2  StatSN

   The StatSN field will always contain the next StatSN. However, when
   the Initiator Task Tag is set to 0xffffffff StatSN for the
   connection is not advanced after this PDU is sent.

10.19.3  LUN

   A LUN MUST be set to a correct value when the Target Transfer Tag is
   valid (not the reserved value 0xffffffff).

































































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11. iSCSI Security Text Keys and Authentication Methods

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

     SessionType
     InitiatorName
     TargetName
     TargetAddress
     InitiatorAlias
     TargetAlias
     TargetPortalGroupTag
     AuthMethod and the keys used by the authentication methods
       specified under Section 11.1 AuthMethod along with all of
       their associated keys as well as Vendor Specific
       Authentication Methods.

   NO OTHER keys MAY be used.

   SessionType, InitiatorName, TargetName, InitiatorAlias, TargetAlias,
   and TargetPortalGroupTag are described in Chapter 12 as they can be
   used also in the OperationalNegotiation stage.

   All security keys have connection-wide applicability.

11.1  AuthMethod

   Use: During Login - Security Negotiation
   Senders: Initiator and Target
   Scope: connection

   AuthMethod = <list-of-values>

   The main item of security negotiation is the authentication method
   (AuthMethod).

   The authentication methods that can be used (appear in the list-of-
   values) are either those listed in the following table or are
   vendor-unique methods:

































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   +------------------------------------------------------------+
   | Name          | Description                                |
   +------------------------------------------------------------+
   | KRB5          | Kerberos V5 - defined in [RFC1510]         |
   +------------------------------------------------------------+
   | SPKM1         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SPKM2         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SRP           | Secure Remote Password                     |
   |               | defined in [RFC2945]                       |
   +------------------------------------------------------------+
   | CHAP          | Challenge Handshake Authentication Protocol|
   |               | defined in [RFC1994]                       |
   +------------------------------------------------------------+
   | None          | No authentication                          |
   +------------------------------------------------------------+


   The AuthMethod selection is followed by an "authentication exchange"
   specific to the authentication method selected.

   The authentication method proposal may be made by either the
   initiator or the target. However the initiator MUST make the first
   step specific to the selected authentication method as soon as it is
   selected. It follows that if the target makes the authentication
   method proposal the initiator sends the first keys(s) of the
   exchange together with its authentication method selection.

   The authentication exchange authenticates the initiator to the
   target, and optionally, the target to the initiator.  Authentication
   is OPTIONAL to use but MUST be supported by the target and
   initiator.

   The initiator and target MUST implement CHAP. All other
   authentication methods are OPTIONAL.

   Private or public extension algorithms MAY also be negotiated for
   authentication methods. Whenever a private or public extension
   algorithm is part of the default offer (the offer made in absence of
   explicit administrative action) the implementer MUST ensure that
   CHAP is listed as an alternative  in the default offer and "None" is
   not part of the default offer.


   Extension authentication methods MUST be named using one of the
   following two formats:

         a)  Z-reversed.vendor.dns_name.do_something=
         b)  Z<#><IANA-registered-string>=


   Authentication methods named using the Z- format are used as private
   extensions. Authentication methods named using the Z# format are


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   used as public extensions that must be registered with IANA and MUST
   be described by an informational RFC.

   For all of the public or private extension authentication methods,
   the method specific keys MUST conform to the format specified in
   Section 5.1 Text Format for standard-label.

   To identify the vendor for private extension authentication methods,
   we suggest you use the reversed DNS-name as a prefix to the proper
   digest names.

   The part of digest-name following Z- and Z# MUST conform to the
   format for standard-label specified in Section 5.1 Text Format.

   Support for public or private extension authentication methods is
   OPTIONAL.

   The following subsections define the specific exchanges for each of
   the standardized authentication methods. As mentioned earlier the
   first step is always done by the initiator.

11.1.1  Kerberos

   For KRB5 (Kerberos V5) [RFC1510], the initiator MUST use:

       KRB_AP_REQ=<KRB_AP_REQ>

   where KRB_AP_REQ is the client message as defined in [RFC1510].

   The default principal name assumed by an iSCSI initiator or target
   (prior to any administrative configuration action) MUST be the iSCSI
   Initiator Name or iSCSI Target Name respectively, prefixed by the
   string "iscsi/".

   If the initiator authentication fails, the target MUST respond with
   a Login reject with "Authentication Failure" status. Otherwise, if
   the initiator has selected the mutual authentication option (by
   setting 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
   [RFC1510].

   If mutual authentication was selected and target authentication
   fails, the initiator MUST close the connection.

   KRB_AP_REQ and KRB_AP_REP are binary-values and their binary length
   (not the length of the character string that represents them in
   encoded form) MUST not exceed 65536 bytes.

11.1.2  Simple Public-Key Mechanism (SPKM)


   For SPKM1 and SPKM2 [RFC2025], the initiator MUST use:


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       SPKM_REQ=<SPKM-REQ>

   where SPKM-REQ is the first initiator token as defined in [RFC2025].

   [RFC2025] defines situations where each side may send an error token
   that may cause the peer to re-generate and resend its last token.
   This scheme is followed in iSCSI, and the error token syntax is:

       SPKM_ERROR=<SPKM-ERROR>

   However, SPKM-DEL tokens that are defined by [RFC2025] for fatal
   errors will not be used by iSCSI. If the target needs to send a
   SPKM-DEL token, it will, instead, send a Login "login reject"
   message with the "Authentication Failure" status and terminate the
   connection. If the initiator needs to send a SPKM-DEL token, it will
   close the connection.

   In the following sections, we assume that no SPKM-ERROR tokens are
   required.

   If the initiator authentication fails, the target MUST return an
   error. Otherwise, if the AuthMethod is SPKM1 or if the initiator has
   selected the mutual authentication option (by setting mutual-state
   bit in the options field of the REQ-TOKEN in the SPKM-REQ), the
   target MUST reply with:

       SPKM_REP_TI=<SPKM-REP-TI>

   where SPKM-REP-TI is the target token as defined in [RFC2025].

   If mutual authentication was selected and target authentication
   fails, the initiator MUST close the connection. Otherwise, if the
   AuthMethod is SPKM1, the initiator MUST continue with:

       SPKM_REP_IT=<SPKM-REP-IT>

   where SPKM-REP-IT is the second initiator token as defined in
   [RFC2025]. If the initiator authentication fails, the target MUST
   answer with a Login reject with "Authentication Failure" status.

   SPKM requires support for very long authentication items.

   All the SPKM-* tokens are binary-values and their binary length (not
   the length of the character string that represents them in encoded
   form) MUST not exceed 65536 bytes.

11.1.3  Secure Remote Password (SRP)


   For SRP [RFC2945], the initiator MUST use:

      SRP_U=<U> TargetAuth=Yes   /* or TargetAuth=No */

   The target MUST answer with a Login reject with the "Authorization
   Failure" status or reply with:


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   SRP_GROUP=<G1,G2...> SRP_s=<s>

   Where G1,G2... are proposed groups, in order of preference.

   The initiator MUST either close the connection or continue with:

   SRP_A=<A> SRP_GROUP=<G>

   Where G is one of G1,G2... that were proposed by the target.

   The target MUST answer with a Login reject with the "Authentication
   Failure" status or reply with:

      SRP_B=<B>

   The initiator MUST close the connection or continue with:

      SRP_M=<M>

   If the initiator authentication fails, the target MUST answer with a
   Login reject with "Authentication Failure" status. Otherwise, if the
   initiator sent TargetAuth=Yes in the first message (requiring target
   authentication), the target MUST reply with:

     SRP_HM=<H(A | M | K)>

   If the target authentication fails, the initiator MUST close the
   connection.

   Where U, s, A, B, M, and H(A | M | K) are defined in [RFC2945]
   (using the SHA1 hash function, such as SRP-SHA1) and G,Gn (Gn stands
   for G1,G2...) are identifiers of SRP groups specified in [SEC-IPS].
   G, Gn, and U are text strings, s,A,B,M, and H(A | M | K) are binary-
   values. The length of s,A,B,M and H(A | M | K) in binary form (not
   the length of the character string that represents them in encoded
   form) MUST not exceed 1024 bytes.

   For the SRP_GROUP, all the groups specified in [SEC-IPS] up to 1536
   bits (i.e., SRP-768, SRP-1024, SRP-1280, SRP-1536) must be supported
   by initiators and targets. To guarantee interoperability, targets
   MUST always offer "SRP-1536" as one of the proposed groups.

11.1.4  Challenge Handshake Authentication Protocol (CHAP)

   For CHAP [RFC1994], the initiator MUST use:

      CHAP_A=<A1,A2...>

   Where A1,A2... are proposed algorithms, in order of preference.

   The target MUST answer with a Login reject with the "Authentication
   Failure" status or reply with:

      CHAP_A=<A> CHAP_I=<I> CHAP_C=<C>



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   Where A is one of A1,A2... that were proposed by the initiator.

   The initiator MUST continue with:

      CHAP_N=<N> CHAP_R=<R>

   or, if it requires target authentication, with:

      CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>

   If the initiator authentication fails, the target MUST answer with a
   Login reject with "Authentication Failure" status. Otherwise, if the
   initiator required target authentication, the target MUST either
   answer with a Login reject with "Authentication Failure" or reply
   with:

      CHAP_N=<N> CHAP_R=<R>

   If target authentication fails, the initiator MUST close the
   connection.

   Where N, (A,A1,A2), I, C, and R are (correspondingly) the Name,
   Algorithm, Identifier, Challenge, and Response as defined in
   [RFC1994], N is a text string, A,A1,A2, and I are numbers, and C and
   R are binary-values and their binary length (not the length of the
   character string that represents them in encoded form) MUST not
   exceed 1024 bytes.

   For the Algorithm, as stated in [RFC1994], one value is required
   to be implemented:

       5       (CHAP with MD5)

   To guarantee interoperability, initiators MUST always offer it as
   one of the proposed algorithms.









































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12. Login/Text Operational Text Keys

   Some session specific parameters MUST only be carried on the leading
   connection and cannot be changed after the leading connection login
   (e.g., MaxConnections, the maximum number of connections). This
   holds for a single connection session with regard to connection
   restart. The keys that fall into this category have the use: LO
   (Leading Only).

   Keys that can only be used during login have the use: IO (initialize
   only), while those that can be used in both the Login Phase and Full
   Feature Phase have the use: ALL.

   Keys that can only be used during Full Feature Phase use FFPO (Full
   Feature Phase only).

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

   Keys that do not require an answer are marked as Declarative

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

   Result function, wherever mentioned, states the function that can be
   applied to check the validity of the responder selection. Minimum
   means that the selected value cannot exceed the offered value.
   Maximum means that the selected value cannot be lower than the
   offered value. AND means that the selected value must be a possible
   result of a Boolean "and" function with an arbitrary Boolean value
   (e.g., if the offered value is No the selected value must be No). OR
   means that the selected value must be a possible result of a Boolean
   "or" function with an arbitrary Boolean value (e.g., if the offered
   value is Yes the selected value must be Yes).

12.1  HeaderDigest and DataDigest

   Use: IO
   Senders: Initiator and Target
   Scope: CO

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

   Default is None for both HeaderDigest and DataDigest.

   Digests enable the checking of end-to-end, non-cryptographic data
   integrity beyond the integrity checks provided by the link layers
   and the covering of the whole communication path including all
   elements that may change the network level PDUs such as routers,
   switches, and proxies.

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


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

   The generator polynomial for this digest is given in hex-
   notation(e.g., 0x3b stands for 0011 1011 and the polynomial is
   x**5+X**4+x**3+x+1).

   When the Initiator and Target agree on a digest, this digest MUST be
   used for every PDU in Full Feature Phase.

   Padding bytes, when present in a segment covered by a CRC, SHOULD be
   set to 0 and are included in the CRC.

   The CRC MUST be calculated by a method that produces the same
   results as the following process:

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

     - The most significant 32 bits are complemented.

     - The polynomial is multiplied by x^32 then divided by G(x). The
       generator polynomial produces a remainder R(x) of degree <=
       31.

     - The coefficients of R(x) are considered a 32 bit sequence.

     - The bit sequence is complemented and the result is the CRC.

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

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

   For a discussion about selection criteria for the CRC, see [iSCSI-
   CRC]. For a detailed analysis of the iSCSI polynomial, see
   [Castagnoli93].




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   Private or public extension algorithms MAY also be negotiated for
   digests. Whenever a private or public digest extension algorithm is
   part of the default offer (the offer made in absence of explicit
   administrative action) the implementer MUST ensure that CRC32C is
   listed as an alternative  in the default offer and "None" is not
   part of the default offer.

   Extension digest algorithms MUST be named using one of the following
   two formats:

             a)  Y-reversed.vendor.dns_name.do_something=
             b)  Y<#><IANA-registered-string>=


   Digests named using the Y- format are used for private purposes
   (unregistered). Digests named using the Y# format (public extension)
   must be registered with IANA and MUST be described by an
   informational RFC.

   For private extension digests, to identify the vendor, we suggest
   you use the reversed DNS-name as a prefix to the proper digest
   names.

   The part of digest-name following Y- and Y# MUST conform to the
   format for standard-label specified in Section 5.1 Text Format.

   Support for public or private extension digests is OPTIONAL.

12.2  MaxConnections

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

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

   Default is 1.
   Result function is Minimum.

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

12.3  SendTargets

   Use: FFPO
   Senders: Initiator
   Scope: SW

   For a complete description, see Appendix D. - SendTargets Operation
   -.

12.4  TargetName

   Use: IO by initiator, FFPO by target - only as response to a
   SendTargets, Declarative, Any-Stage


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   Senders: Initiator and Target
   Scope: SW

   TargetName=<iSCSI-name-value>

   Examples:

        TargetName=iqn.1993-11.com.disk-vendor:diskarrays.sn.45678
        TargetName=eui.020000023B040506

   The initiator of the TCP connection MUST provide this key to the
   remote endpoint in the first login request if the initiator is not
   establishing a discovery session. The iSCSI Target Name specifies
   the worldwide unique name of the target.

   The TargetName key may also be returned by the "SendTargets" text
   request (which is its only use when issued by a target).

   TargetName MUST not be redeclared within the login phase.

12.5  InitiatorName

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

   InitiatorName=<iSCSI-name-value>

   Examples:

        InitiatorName=iqn.1992-04.com.os-vendor.plan9:cdrom.12345
        InitiatorName=iqn.2001-02.com.ssp.users:customer235.host90

   The initiator of the TCP connection MUST provide this key to the
   remote endpoint at the first Login of the Login Phase for every
   connection. The InitiatorName key enables the initiator to identify
   itself to the remote endpoint.

   InitiatorName MUST not be redeclared within the login phase.

12.6  TargetAlias

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

   TargetAlias=<iSCSI-local-name-value>

   Examples:

        TargetAlias=Bob-s Disk
        TargetAlias=Database Server 1 Log Disk
        TargetAlias=Web Server 3 Disk 20

   If a target has been configured with a human-readable name or
   description, this name SHOULD be communicated to the initiator


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   during a Login Response PDU if SessionType=Normal (see Section 12.21
   SessionType). This string is not used as an identifier, nor is it
   meant to be used for authentication or authorization decisions. It
   can be displayed by the initiator's user interface in a list of
   targets to which it is connected.

12.7  InitiatorAlias

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

   InitiatorAlias=<iSCSI-local-name-value>

   Examples:

     InitiatorAlias=Web Server 4
     InitiatorAlias=spyalley.nsa.gov
     InitiatorAlias=Exchange Server

   If an initiator has been configured with a human-readable name or
   description, it SHOULD 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, nor is meant to be used for
   authentication or authorization decisions. It can be displayed by
   the target's user interface in a list of initiators to which it is
   connected.

12.8  TargetAddress

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

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

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

   If the TCP port is not specified, it is assumed to be the IANA-
   assigned default port for iSCSI (see Section 13 IANA
   Considerations).

   If the TargetAddress is returned as the result of a redirect status
   in a login response, the comma and portal group tag MUST be omitted.

   If the TargetAddress is returned within a SendTargets response, the
   portal group tag MUST be included.

   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.example.com,23


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   Use of the portal-group-tag is described in Appendix D. -
   SendTargets Operation -. The formats for the port and portal-group-
   tag are the same as the one specified in Section 12.9
   TargetPortalGroupTag.

12.9  TargetPortalGroupTag

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

   TargetPortalGroupTag=<16-bit-binary-value>

   Examples:
   TargetPortalGroupTag=1

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

   For the complete usage expectations of this key see Section 5.3
   Login Phase.


12.10  InitialR2T

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

   InitialR2T=<boolean-value>

   Examples:

     I->InitialR2T=No
     T->InitialR2T=No

   Default is Yes.
   Result function is OR.

   The InitialR2T key is used to turn off the default use of R2T for
   unidirectional and the output part of bidirectional commands, thus
   allowing an initiator to start sending data to a target as if it has
   received an initial R2T with Buffer Offset=Immediate Data Length and
   Desired Data Transfer Length=(min(FirstBurstLength, Expected Data
   Transfer Length) - Received Immediate Data Length).

   The default action is that R2T is required, unless both the
   initiator and the target send this key-pair attribute specifying
   InitialR2T=No. Only the first outgoing data burst (immediate data



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   and/or separate PDUs) can be sent unsolicited (i.e., not requiring
   an explicit R2T).

12.11  ImmediateData

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

   ImmediateData=<boolean-value>

   Default is Yes.
   Result function is AND.

   The initiator and target negotiate support for immediate data. To
   turn immediate data off, the initiator or target must state its
   desire to do so. ImmediateData can be turned on if both the
   initiator and target have ImmediateData=Yes.

   If ImmediateData is set to Yes and InitialR2T is set to Yes
   (default), then only immediate data are accepted in the first burst.

   If ImmediateData is set to No and InitialR2T is set to Yes, then the
   initiator MUST NOT send unsolicited data and the target MUST reject
   unsolicited data with the corresponding response code.

   If ImmediateData is set to No and InitialR2T is set to No, then the
   initiator MUST NOT send unsolicited immediate data, but MAY send one
   unsolicited burst of Data-OUT PDUs.

   If ImmediateData is set to Yes and InitialR2T is set to No, then the
   initiator MAY send unsolicited immediate data and/or one unsolicited
   burst of Data-OUT PDUs.

   The following table is a summary of unsolicited data options:

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


12.12  MaxRecvDataSegmentLength

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


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

   Default is 8192 bytes.

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

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

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

12.13  MaxBurstLength

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

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

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

   The initiator and target negotiate maximum SCSI data payload in
   bytes in a Data-In or a solicited Data-Out iSCSI sequence. A
   sequence consists of one or more consecutive Data-In or Data-Out
   PDUs that end with a Data-In or Data-Out PDU with the F bit set to
   one.

12.14  FirstBurstLength

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery
   Irrelevant when: ( InitialR2T=Yes and ImmediateData=No )

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

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

   The initiator and target negotiate the maximum amount in bytes of
   unsolicited data an iSCSI initiator may send to the target during
   the execution of a single SCSI command. This covers the immediate
   data (if any) and the sequence of unsolicited Data-Out PDUs (if any)
   that follow the command.

   FirstBurstLength MUST NOT exceed MaxBurstLength.


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12.15  DefaultTime2Wait

   Use: LO
   Senders: Initiator and Target
   Scope: SW

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

   Default is 2.
   Result function is Maximum.

   The initiator and target negotiate the minimum time, in seconds, to
   wait before attempting an explicit/implicit logout or an active task
   reassignment after an unexpected connection termination or a
   connection reset.

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

12.16  DefaultTime2Retain

   Use: LO
   Senders: Initiator and Target
   Scope: SW

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

   Default is 20.
   Result function is Minimum.

   The initiator and target negotiate the maximum time, in seconds
   after an initial wait (Time2Wait), before which an active task
   reassignment is still possible after an unexpected connection
   termination or a connection reset.

   This value is also the session state timeout if the connection in
   question is the last LOGGED_IN connection in the session.

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

12.17  MaxOutstandingR2T

   Use: LO
   Senders: Initiator and Target
   Scope: SW

   MaxOutstandingR2T=<numerical-value-from-1-to-65535>
   Irrelevant when: SessionType=Discovery

   Default is 1.
   Result function is Minimum.

   Initiator and target negotiate the maximum number of outstanding
   R2Ts per task, excluding any implied initial R2T that might be part


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   of that task. An R2T is considered outstanding until the last data
   PDU (with the F bit set to 1) is transferred, or a sequence
   reception timeout (Section 6.1.4.1 Recovery Within-command) is
   encountered for that data sequence.

12.18  DataPDUInOrder

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

   DataPDUInOrder=<boolean-value>

   Default is Yes.
   Result function is OR.

   No is used by iSCSI to indicate that the data PDUs within sequences
   can be in any order. Yes is used to indicate that data PDUs within
   sequences have to be at continuously increasing addresses and
   overlays are forbidden.

12.19  DataSequenceInOrder

   Use: LO
   Senders: Initiator and Target
   Scope: SW
   Irrelevant when: SessionType=Discovery

   DataSequenceInOrder=<boolean-value>

   Default is Yes.
   Result function is OR.

   A Data Sequence is a sequence of Data-In or Data-Out PDUs that end
   with a Data-In or Data-Out PDU with the F bit set to one. A Data-out
   sequence is sent either unsolicited or in response to an R2T.
   Sequences cover an offset-range.

   If DataSequenceInOrder is set to No, Data PDU sequences may be
   transferred in any order.

   If DataSequenceInOrder is set to Yes, Data Sequences MUST be
   transferred using continuously non-decreasing sequence offsets (R2T
   buffer offset for writes, or the smallest SCSI Data-In buffer offset
   within a read data sequence).

   If DataSequenceInOrder is set to Yes, a target may retry at most the
   last R2T, and an initiator may at most request retransmission for
   the last read data sequence. For this reason, if ErrorRecoveryLevel
   is not 0 and DataSequenceInOrder is set to Yes then MaxOustandingR2T
   MUST be set to 1.

12.20  ErrorRecoveryLevel

   Use: LO


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   Senders: Initiator and Target
   Scope: SW

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

   Default is 0.
   Result function is Minimum.

   The initiator and target negotiate the recovery level supported.

   Recovery levels represent a combination of recovery capabilities.
   Each recovery level includes all the capabilities of the lower
   recovery levels and adds some new ones to them.

   In the description of recovery mechanisms, certain recovery classes
   are specified. Section 6.1.5 Error Recovery Hierarchy describes the
   mapping between the classes and the levels.

12.21  SessionType

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

   SessionType= <Discovery|Normal>

   Default is Normal.

   The Initiator indicates the type of session it wants to create. The
   target can either accept it or reject it.

   A discovery session indicates to the Target that the only purpose of
   this Session is discovery. The only requests a target accepts in
   this type of session are a text request with a SendTargets key and a
   logout request with reason "close the session".

   The discovery session implies MaxConnections = 1 and overrides both
   the default and an explicit setting.

12.22  The Private or Public Extension Key Format

   Use: ALL
   Senders: Initiator and Target
   Scope: specific key dependent

   X-reversed.vendor.dns_name.do_something=

   or

   X<#><IANA-registered-string>=

   Keys with this format are used for public or private extension
   purposes. These keys always start with X- if unregistered with IANA
   (private) or X# if registered with IANA (public).




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   For unregistered keys, to identify the vendor, we suggest you use
   the reversed DNS-name as a prefix to the key-proper.

   The part of key-name following X- and X# MUST conform to the format
   for key-name specified in Section 5.1 Text Format.

   For IANA registered keys the string following X# must be registered
   with IANA and the use of the key MUST be described by an
   informational RFC.

   Vendor specific keys MUST ONLY be used in normal sessions.

   Support for public or private extension keys is OPTIONAL.





















































































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13. IANA Considerations


   The well-known TCP port number for iSCSI connections assigned by
   IANA is 3260. A system port must be assigned by IANA when this draft
   is approved to become a RFC.

   Extension keys, authentication methods, or digest types for which a
   vendor or group of vendors intend to provide publicly available
   descriptions MUST be described by an RFC and MUST be registered with
   IANA.

   IANA must maintain three registries:

            a)  iSCSI extended key registry
            b)  iSCSI authentication methods registry
            c)  iSCSI digests registry

   [SEC-IPS] also instructs IANA to maintain a registry for the values
   of the SRP_GROUP key. The format of these values must conform to the
   one specified for iSCSI extension item-label in Section 13.5.4
   Standard iSCSI extension item-label format.

   For the iSCSI authentication methods registry and the iSCSI digests
   registry, IANA MUST also assign a 16-bit unsigned integer number
   (the method number for the authentication method and the digest
   number for the digest).

   The following initial values for the registry for authentication
   methods are specified by the standards action of this document:

    Authentication Method                   | Number |
   +----------------------------------------+--------+
   | CHAP                                   |     1  |
   +----------------------------------------+--------+
   | SRP                                    |     2  |
   +----------------------------------------+--------+
   | KRB5                                   |     3  |
   +----------------------------------------+--------+
   | SPKM1                                  |     4  |
   +----------------------------------------+--------+
   | SPKM2                                  |     5  |
   +----------------------------------------+--------+

   All other record numbers from 0 to 255 are reserved. IANA will
   register numbers above 255.

   Authentication methods with numbers above 255 MUST be unique within
   the registry and MUST be used with the prefix Y#.

   The following initial values for the registry for digests are
   specified by the standards action of this document:








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    Digest                                  | Number |
   +----------------------------------------+--------+
   | CRC32C                                 |     1  |
   +----------------------------------------+--------+

   All other record numbers from 0 to 255 are reserved. IANA will
   register numbers above 255.

   Digests with numbers above 255 MUST be unique within the registry
   and MUST be used with the prefix Z#.

   The RFC that describes the item to be registered MUST indicate in
   the IANA consideration section the string and iSCSI registry to
   which it should be recorded.

   Extension Keys, Authentication Methods, and digests (iSCSI extension
   items) must conform to a number of requirements as described below.

13.1  Naming Requirements

   Each iSCSI extension item must have a unique name in its category.
   This name will be used as a standard-label for the key, access
   method, or digest and must conform to the syntax specified in
   Section 13.5.4 Standard iSCSI extension item-label format for iSCSI
   extension item-labels.

13.2  Mechanism Specification Requirements

   For iSCSI extension items all of the protocols and procedures used
   by a given iSCSI extension item must be described, either in the
   specification of the iSCSI extension item itself or in some other
   publicly available specification, in sufficient detail for the iSCSI
   extension item to be implemented by any competent implementor.  Use
   of secret and/or proprietary methods in iSCSI extension items are
   expressly prohibited. In addition, the restrictions imposed by RFC
   1602 on the standardization of patented algorithms must be
   respected.

13.3  Publication Requirements

   All iSCSI extension items must be described by an RFC. The RFC may
   be informational rather than standards-track, although standard-
   track review and approval are encouraged for all iSCSI extension
   items.

13.4  Security Requirements

   Any known security issues that arise from the use of the iSCSI
   extension item must be completely and fully described. It is not
   required that the iSCSI extension item be secure or that it be free
   from risks, but that the known risks be identified.  Publication of
   a new iSCSI extension item does not require an exhaustive security
   review, and the security considerations section is subject to
   continuing evaluation.

   Additional security considerations should be addressed by publishing


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   revised versions of the iSCSI extension item specification.

   For each of these registries, IANA must record the registered
   string, which MUST conform to the format rules described in Section
   13.5.4 Standard iSCSI extension item-label format for iSCSI
   extension item-labels, and the RFC number that describes it. The key
   prefix (X#, Y# or Z#) is not part of the recorded string.

13.5  Registration Procedure


   Registration of a new iSCSI extension item starts with the
   construction of a draft of an RFC.

13.5.1  Present the iSCSI extension item to the Community

   Send a proposed access type specification to the IPS WG mailing list
   or if the IPS WG is disbanded at the registration time to a mailing
   list designated by the IETF Transport Area Director for a review
   period of a month.  The intent of the public posting is to solicit
   comments and feedback on the iSCSI extension item specification and
   a review of any security considerations.

13.5.2  iSCSI extension item review and IESG approval

   When the one month period has passed, the IPS WG chair or a person
   nominated by the IETF Transport Area Director  (the iSCSI extension
   item reviewer)  forwards the draft to the IESG for publication as an
   informational RFC or rejects it. If the specification is a standards
   track draft the usual IETF procedures for such documents are
   followed.

   Decisions made by the iSCSI extension item reviewer must be
   published within two weeks after the month-long review period.
   Decisions made by the iSCSI extension item reviewer can be appealed
   through the IESG appeal process.

13.5.3  IANA Registration

   Provided that the iSCSI extension item has either passed review or
   has been successfully appealed to the IESG, and the specification is
   published as an RFC, then IANA will register the iSCSI extension
   item and make the registration available to the community.

13.5.4  Standard iSCSI extension item-label format

   The following character symbols are used iSCSI extension item-labels
   (the hexadecimal values represent Unicode code points):

   (a-z, A-Z) - letters
   (0-9) - digits
   "."  (0x2e) - dot
   "-"  (0x2d) - minus
   "+"  (0x2b) - plus
   "@"  (0x40) - commercial at
   "_"  (0x5f) - underscore


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   An iSCSI extension item-label is a string of one or more characters
   that consist of letters, digits, dot, minus, plus, commercial at, or
   underscore. An iSCSI extension item-label MUST begin with a capital
   letter and must not exceed 63 characters.


13.6  IANA Procedures for Registering iSCSI extension items


   The identity of the iSCSI extension item reviewer is communicated to
   the IANA by the IESG.  Then, the IANA only acts in response to iSCSI
   extension item definitions that  are approved by the iSCSI extension
   item reviewer and forwarded by the reviewer to the IANA for
   registration, or in response to a communication from the IESG that
   an iSCSI extension item definition appeal has overturned the iSCSI
   extension item reviewer's ruling.













































































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References and Bibliography

   Normative References

     [AESCBC] Frankel, S., Kelly, S., Glenn, R., "The AES Cipher
       Algorithm and Its Use with IPsec", draft-ietf-ipsec-ciph-aes-
       cbc-03.txt, November 2001 (Work In Progress).
     [AESCTR] draft-ietf-ipsec-ciph-aes-ctr-00.txt  R. Housley  23-
       Jul-02 (Work In Progress).
     [CAM] ANSI X3.232-199X, Common Access Method-3.
     [EUI] "Guidelines for 64-bit Global Identifier (EUI-64)", http:/
       /standards.ieee.org/regauth/oui/tutorials/EUI64.html
     [OUI] "IEEE OUI and Company_Id Assignments", http://
       standards.ieee.org/regauth/oui
     [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.
     [RFC1737] K. Sollins, L. Masinter "Functional Requirements for
       Uniform Resource Names".
     [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", August
       1996.
     [RFC1994] "W. Simpson, PPP Challenge Handshake Authentication
       Protocol (CHAP)", August 1996.
     [RFC2025] C. Adams, "The Simple Public-Key GSS-API Mechanism
       (SPKM)", October 1996.
     [RFC2026] Bradner, S., "The Internet Standards Process --
       Revision 3", 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, 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", July 1998.
     [RFC2396] T. Berners-Lee, R. Fielding, L. Masinter "Uniform
       Resource Identifiers".
     [RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
       Internet Protocol", November 1998.


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                              iSCSI                    19-January-03


     [RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96 within ESP
      and AH", November 1998.
      [RFC2406] S. Kent, R. Atkinson, "IP Encapsulating Security Payload
      (ESP)", November 1998.

     [RFC2407] D. Piper, "The Internet IP Security Domain of
       Interpretation of ISAKMP", November 1998.
     [RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange
       (IKE)", November 1998.
     [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing
       an IANA Considerations Section in RFCs.", October 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", December 1999.
     [RFC2945] Wu, T., "The SRP Authentication and Key Exchange
       System", September 2000.
     [SAM] ANSI X3.270-1998, SCSI-3 Architecture Model (SAM).
     [SAM2] T10/1157D, SCSI Architecture Model - 2 (SAM-2).
     [SBC] NCITS.306-1998, SCSI-3 Block Commands (SBC).
     [SEQ-EXT] Kent, S., "IP Encapsulating Security Payload (ESP)",
       Internet draft (work in progress), draft-ietf-ipsec-esp-v3-
       03.txt, July 2002.
     [SEC-IPS] B. Aboba & team "Securing Block Storage Protocols over
       IP", Internet draft (work in progress), draft-ietf-ips-
       security-16.txt, September 2002.
     [SPC3]T10/1416-D, SCSI Primary Commands-3.
     [STPREP] P. Hoffman, M. Blanchet, "Preparation of
       Internationalized Strings", draft-hoffman-stringprep-07.txt,
       October 2002 (Work In Progress).
     [STPREP-iSCSI] M. Bakke, "String Profile for iSCSI Names",
       draft-ietf-ips-iscsi-string-prep-03.txt, October 2002 (Work In
       Progress).
     [UNICODE] Unicode Standard Annex #15, "Unicode Normalization
       Forms", http://www.unicode.org/unicode/reports/tr15

   Informative References:

     [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-03.txt (Work
       In Progress).
     [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-07.txt
       (Work In Progress)
     [RFC3347] M. Krueger & team, Small Computer Systems Interface
       protocol over the Internet (iSCSI) Requirements and Design
       Considerations
     [RFC3385] D. Sheinwald & team, Internet Protocol Small Computer
       System Interface (iSCSI) Cyclic Redundancy Check (CRC)/
       Checksum Considerations






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     [Schneier] B. Schneier, "Applied Cryptography: Protocols,
           Algorithms, and Source Code in C", 2nd edition, John Wiley &
           Sons, New York, NY, 1996.


Authors' Addresses

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

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

     Costa Sapuntzakis
     Cisco Systems, Inc.
     170 W. Tasman Drive
     San Jose, CA 95134, USA
     Phone: +1.408.525.5497
     E-mail: csapuntz@cisco.com

     Efri Zeidner
     SANgate Systems, Inc.
     41 Hameyasdim Street
     P.O.B. 1486
     Even-Yehuda, Israel 40500
     Phone: +972.9.891.9555
     E-mail: efri@sangate.com

     Mallikarjun Chadalapaka
     Hewlett-Packard Company
     8000 Foothills Blvd.
     Roseville, CA 95747-5668, USA
     Phone: +1.916.785.5621
     E-mail: cbm@rose.hp.com



   Comments may be sent to Julian Satran



















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Appendix A. Sync and Steering with Fixed Interval Markers

   This appendix presents a simple scheme for synchronization (PDU
   boundary retrieval). It uses markers that include synchronization
   information placed at fixed intervals in the TCP stream.

   A Marker consists of:

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

   The Marker scheme uses payload byte stream counting that includes
   every byte placed by iSCSI in the TCP stream except for the markers
   themselves. It also excludes any bytes that TCP counts but are not
   originated by iSCSI.

   Markers MUST NOT be included in digest calculation.

   The Marker indicates the offset to the next iSCSI PDU header. The
   Marker is eight bytes in length and contains two 32-bit offset
   fields that indicate how many bytes to skip in the TCP stream in
   order to find the next iSCSI PDU header. The marker uses two copies
   of the pointer so that a marker that spans a TCP packet boundary
   should leave at least one valid copy in one of the packets.

   The inserted value is independent of the marker interval.

   The use of markers is negotiable. The initiator and target MAY
   indicate their readiness to receive and/or send markers during login
   separately for each connection. The default is No.

A.1  Markers At Fixed Intervals

   A marker is inserted at fixed intervals in the TCP byte stream.
   During login, each end of the iSCSI session specifies the interval
   at which it is willing to receive the marker, or it disables the
   marker altogether. If a receiver indicates that it desires a marker,
   the sender MAY agree (during negotiation) and provide the marker at
   the desired interval. However, in certain environments, a sender
   that does not provide markers to a receiver that wants markers may
   suffer an appreciable performance degradation.

   The marker interval and the initial marker-less interval are counted
   in terms of the bytes placed in the TCP stream data by iSCSI.

   When reduced to iSCSI terms, markers MUST indicate the offset to a
   4-byte word boundary in the stream. The least significant two bits
   of each marker word are reserved and are considered 0 for offset
   computation.



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   Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
   marker manipulation.

A.2  Initial Marker-less Interval

   To enable the connection setup including the Login Phase
   negotiation, marking (if any) is only started at the first marker
   interval after the end of the Login Phase. However, in order to
   enable the marker inclusion and exclusion mechanism to work without
   knowledge of the length of the Login Phase, the first marker will be
   placed in the TCP stream as if the Marker-less interval had included
   markers.

   Thus, all markers appear in the stream at locations conforming to
   the formula: [(MI + 8) * n - 8] where MI = Marker Interval, n =
   integer number.

   For example, if the marker interval is 512 bytes and the login ended
   at byte 1003 (first iSCSI placed byte is 0), the first marker will
   be inserted after byte 1031 in the stream.

A.3  Negotiation

   The following operational key=value pairs are used to negotiate the
   fixed interval markers. The direction (output or input) is relative
   to the initiator.

A.3.1   OFMarker, IFMarker

   Use: IO
   Senders: Initiator and Target
   Scope: CO

   OFMarker=<boolean-value>
   IFMarker=<boolean-value>

   Default is No.

   Result function is AND.

   OFMarker is used to turn on or off the initiator to target markers
   on the connection.  IFMarker is used to turn on or off the target to
   initiator markers on the connection.

   Examples:

     I->OFMarker=Yes,IFMarker=Yes
     T->OFMarker=Yes,IFMarker=Yes

   Results in the Marker being used in both directions while:

     I->OFMarker=Yes,IFMarker=Yes
     T->OFMarker=Yes,IFMarker=No

   Results in Marker being used from the initiator to the target, but
   not from the target to initiator.


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A.3.2   OFMarkInt, IFMarkInt

   Use: IO
   Senders: Initiator and Target
   Scope: CO
   OFMarkInt is Irrelevant when: OFMarker=No
   IFMarkInt is Irrelevant when: IFMarker=No

   Offering:

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

   Responding:

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

   OFMarkInt is used to set the interval for the initiator to target
   markers on the connection.  IFMarkInt is used to set the interval
   for the target to initiator markers on the connection.

   For the offering, the initiator or target indicates the minimum to
   maximum interval (in 4-byte words) it wants the markers for one or
   both directions. In case it only wants a specific value, only a
   single value has to be specified. The responder selects a value
   within the minimum and maximum offered or the only value offered or
   indicates through the xFMarker key=value its inability to set and/or
   receive markers. When the interval is unacceptable the responder
   answers with "Reject".  Reject is resetting the marker function in
   the specified direction (Output or Input) to No.

   The interval is measured from the end of a marker to the beginning
   of the next marker. For example, a value of 1024 means 1024 words
   (4096 bytes of iSCSI payload between markers).

   The default is 2048.



































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Appendix B. Examples

B.1  Read Operation Example

   +------------------+-----------------------+----------------------+
   |Initiator Function|    PDU Type           |  Target Function     |
   +------------------+-----------------------+----------------------+
   |  Command request |SCSI Command (READ)>>> |                      |
   |  (read)          |                       |                      |
   +------------------+-----------------------+----------------------+
   |                  |                       |Prepare Data Transfer |
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data-in    |   Send Data          |
   +------------------+-----------------------+----------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense |
   +------------------+-----------------------+----------------------+
   | Command Complete |                       |                      |
   +------------------+-----------------------+----------------------+

B.2  Write Operation Example

   +------------------+-----------------------+---------------------+
   |Initiator Function|    PDU Type           |  Target Function    |
   +------------------+-----------------------+---------------------+
   |  Command request |SCSI Command (WRITE)>>>| Receive command     |
   |  (write)         |                       | and queue it        |
   +------------------+-----------------------+---------------------+
   |                  |                       | Process old commands|
   +------------------+-----------------------+---------------------+
   |                  |                       | Ready to process    |
   |                  |   <<< R2T             | WRITE command       |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< R2T             | Ready for data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< R2T             | Ready for data      |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data-out >>>   |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense|
   +------------------+-----------------------+---------------------+
   | Command Complete |                       |                     |
   +------------------+-----------------------+---------------------+

B.3  R2TSN/DataSN Use Examples

   Output (write) data DataSN/R2TSN Example




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   +------------------+-----------------------+----------------------+
   |Initiator Function|    PDU Type & Content |  Target Function     |
   +------------------+-----------------------+----------------------+
   |  Command request |SCSI Command (WRITE)>>>| Receive command      |
   |  (write)         |                       | and queue it         |
   +------------------+-----------------------+----------------------+
   |                  |                       | Process old commands |
   +------------------+-----------------------+----------------------+
   |                  |   <<< R2T             | Ready for data       |
   |                  |   R2TSN = 0           |                      |
   +------------------+-----------------------+----------------------+
   |                  |   <<< R2T             | Ready for more data  |
   |                  |   R2TSN = 1           |                      |
   +------------------+-----------------------+----------------------+
   |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
   |  for R2TSN 0     |   DataSN = 0, F=0     |                      |
   +------------------+-----------------------+----------------------+
   |  Send Data       |   SCSI Data-out >>>   |   Receive Data       |
   |  for R2TSN 0     |   DataSN = 1, F=1     |                      |
   +------------------+-----------------------+----------------------+
   |  Send Data       |   SCSI Data >>>       |   Receive Data       |
   |  for R2TSN 1     |   DataSN = 0, F=1     |                      |
   +------------------+-----------------------+----------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense |
   |                  |   ExpDataSN = 0       |                      |
   +------------------+-----------------------+----------------------+
   | Command Complete |                       |                      |
   +------------------+-----------------------+----------------------+



    Input (read) data DataSN Example

   +------------------+-----------------------+----------------------+
   |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 sequentially as in an atomic
   Read-Update-Write (in the latter case the R2T may follow the
   received data).

   Unsolicited and immediate output (write) data with DataSN Example









































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   +------------------+-----------------------+----------------------+
   |Initiator Function|    PDU Type & Content |  Target Function     |
   +------------------+-----------------------+----------------------+
   |  Command request |SCSI Command (WRITE)>>>| Receive command      |
   |  (write)         |F=0                    | and data             |
   |+ immediate data  |                       | and queue it         |
   +------------------+-----------------------+----------------------+
   | Send Unsolicited |   SCSI Write Data >>> | Receive more Data    |
   |  Data            |   DataSN = 0, F=1     |                      |
   +------------------+-----------------------+----------------------+
   |                  |                       | Process old commands |
   +------------------+-----------------------+----------------------+
   |                  |   <<< R2T             | Ready for more data  |
   |                  |   R2TSN = 0           |                      |
   +------------------+-----------------------+----------------------+
   |  Send Data       |   SCSI Write Data >>> |   Receive Data       |
   |  for R2TSN 0     |   DataSN = 0, F=1     |                      |
   +------------------+-----------------------+----------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense |
   |                  |                       |                      |
   +------------------+-----------------------+----------------------+
   | Command Complete |                       |                      |
   +------------------+-----------------------+----------------------+

B.4  CRC Examples

   N.B. all Values are Hexadecimal

   32 bytes of zeroes:

     Byte:        0  1  2  3

        0:       00 00 00 00
      ...
       28:       00 00 00 00

      CRC:       aa 36 91 8a

   32 bytes of ones:

     Byte:        0  1  2  3

        0:       ff ff ff ff
      ...
       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



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      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

   An iSCSI - SCSI Read (10) Command PDU

    Byte:        0  1  2  3

       0:       01 c0 00 00
       4:       00 00 00 00
       8:       00 00 00 00
      12:       00 00 00 00
      16:       14 00 00 00
      20:       00 00 04 00
      24:       00 00 00 14
      28:       00 00 00 18
      32:       28 00 00 00
      36:       00 00 00 00
      40:       02 00 00 00
      44:       00 00 00 00

     CRC:       56 3a 96 d9



















































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Appendix C. Login Phase Examples

   In the first example, the initiator and target authenticate each
   other via Kerberos:

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login (CSG,NSG=0,0 T=0)
         AuthMethod=KRB5


     I-> Login (CSG,NSG=0,1 T=1)
         KRB_AP_REQ=<krb_ap_req>

     (krb_ap_req contains the Kerberos V5 ticket and authenticator
          with MUTUAL-REQUIRED set in the ap-options field)

     If the authentication is successful, the target proceeds with:

     T-> Login (CSG,NSG=0,1 T=1)
         KRB_AP_REP=<krb_ap_rep>

     (krb_ap_rep is the Kerberos V5 mutual authentication reply)

     If the authentication is successful, the initiator may proceed
          with:

     I-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=8192
     T-> Login (CSG,NSG=1,0 T=0) FirstBurstLength=4096
          MaxBurstLength=8192
     I-> Login (CSG,NSG=1,0 T=0) MaxBurstLength=8192
         ... more iSCSI Operational Parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... more iSCSI Operational Parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"

     If the initiator's authentication by the target is not
          successful, the target responds with:

     T-> Login "login reject"

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






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     If the target's 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)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=SRP,KRB5,None

     T-> Login-PR (CSG,NSG=0,0 T=0)
         AuthMethod=KRB5

     I-> Login (CSG,NSG=0,1 T=1)
         KRB_AP_REQ=krb_ap_req

     (MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)

     If the authentication is successful, the target proceeds with:

     T-> Login (CSG,NSG=0,1 T=1)

     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     . . .

     T-> Login (CSG,NSG=1,3 T=1)"login accept"


   In the next example, the initiator and target authenticate each
   other via SPKM1:

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=SPKM1,KRB5,None

     T-> Login (CSG,NSG=0,0 T=0)
         AuthMethod=SPKM1

     I-> Login (CSG,NSG=0,0 T=0)
         SPKM_REQ=<spkm-req>

     (spkm-req is the SPKM-REQ token with the mutual-state bit in the
       options field of the REQ-TOKEN set)

     T-> Login (CSG,NSG=0,0 T=0)
         SPKM_REP_TI=<spkm-rep-ti>

     If the authentication is successful, the initiator proceeds:


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     I-> Login (CSG,NSG=0,1 T=1)
         SPKM_REP_IT=<spkm-rep-it>

     If the authentication is successful, the target proceeds with:

     T-> Login (CSG,NSG=0,1 T=1)

     The initiator may proceed:

     I-> Login  (CSG,NSG=1,0 T=0) ... iSCSI parameters
     T-> Login  (CSG,NSG=1,0 T=0) ... iSCSI parameters

     And at the end:

     I-> Login  (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"


     If the target's authentication by the initiator is not
          successful, the initiator terminates the connection (without
          responding to the Login SPKM_REP_TI message).

     If the initiator's authentication by the target is not
          successful, the target responds with:

     T-> Login "login reject"

     instead of the Login "proceed and change stage" message, and
          terminates the connection.


   In the next example, the initiator and target authenticate each
   other via SPKM2:

     I-> Login (CSG,NSG=0,0 T=0)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
               AuthMethod=SPKM1,SPKM2

     T-> Login-PR (CSG,NSG=0,0 T=0)
         AuthMethod=SPKM2

     I-> Login (CSG,NSG=0,1 T=1)
         SPKM_REQ=<spkm-req>

     (spkm-req is the SPKM-REQ token with the mutual-state bit in the
          options field of the REQ-TOKEN not set)

     If the authentication is successful, the target proceeds with:

     T-> Login (CSG,NSG=0,1 T=1)

     The initiator may proceed:


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     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login  (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"


   In the next example, the initiator and target authenticate each
   other via SRP:

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR  (CSG,NSG=0,0 T=0)
         AuthMethod=SRP

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_U=<user>
         TargetAuth=Yes

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_N=<N>
         SRP_g=<g>
         SRP_s=<s>

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_A=<A>

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_B=<B>

     I-> Login (CSG,NSG=0,1 T=1)
         SRP_M=<M>

     If the initiator authentication is successful, the target
          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].

     If the target authentication is not successful, the initiator
          terminates the connection; otherwise, it proceeds.



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     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login  (CSG,NSG=1,3 T=1) "login accept"

     If the initiator authentication is not successful, the target
          responds with:

     T-> Login "login reject"

     Instead of the T-> Login SRP_HM=<H(A | M | K)>  message and
          terminates the connection.

   In the next example, only the initiator is authenticated by the
   target via SRP:

     I-> Login (CSG,NSG=0,1 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR (CSG,NSG=0,0 T=0)
         AuthMethod=SRP

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_U=<user>
         TargetAuth=No

      T-> Login (CSG,NSG=0,0 T=0)
          SRP_N=<N>
          SRP_g=<g>
          SRP_s=<s>

     I-> Login (CSG,NSG=0,0 T=0)
         SRP_A=<A>

     T-> Login (CSG,NSG=0,0 T=0)
         SRP_B=<B>

     I-> Login (CSG,NSG=0,1 T=1)
         SRP_M=<M>

     If the initiator authentication is successful, the target
          proceeds:

     T-> Login (CSG,NSG=0,1 T=1)

     I-> Login (CSG,NSG=1,0 T=0)


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         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"


   In the next example the initiator and target authenticate each other
   via CHAP:

     I-> Login (CSG,NSG=0,0 T=0)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         AuthMethod=KRB5,CHAP,None

     T-> Login-PR (CSG,NSG=0,0 T=0)
         AuthMethod=CHAP

     I-> Login (CSG,NSG=0,0 T=0)
         CHAP_A=<A1,A2>

      T-> Login (CSG,NSG=0,0 T=0)
          CHAP_A=<A1>
          CHAP_I=<I>
          CHAP_C=<C>

     I-> Login (CSG,NSG=0,1 T=1)
         CHAP_N=<N>
         CHAP_R=<R>
         CHAP_I=<I>
         CHAP_C=<C>

     If the initiator authentication is successful, the target
       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.

     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters
     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)


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         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"

     If the initiator authentication is not successful, the target
       responds with:

     T-> Login "login reject"

     Instead of the 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.example:diskarray.sn.88
         AuthMethod=KRB5,CHAP,None

     T-> Login-PR (CSG,NSG=0,0 T=0)
         AuthMethod=CHAP

     I-> Login (CSG,NSG=0,0 T=0)
         CHAP_A=<A1,A2>

      T-> Login (CSG,NSG=0,0 T=0)
          CHAP_A=<A1>
          CHAP_I=<I>
          CHAP_C=<C>

     I-> Login (CSG,NSG=0,1 T=1)
         CHAP_N=<N>
         CHAP_R=<R>

     If the initiator authentication is successful, the target
       proceeds:

     T-> Login (CSG,NSG=0,1 T=1)

     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"




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   In the next example, the initiator does not offer any security
   parameters. It therefore may offer iSCSI parameters on the Login PDU
   with the T bit set to 1, and the target may respond with a final
   Login Response PDU immediately:

     I-> Login (CSG,NSG=1,3 T=1)
         InitiatorName=iqn.1999-07.com.os:hostid.77
         TargetName=iqn.1999-07.com.example:diskarray.sn.88
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"
         ... ISCSI parameters

     In the next example, the initiator does offer security
       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.example:diskarray.sn.88
         AuthMethod=KRB5,SRP,None

     T-> Login-PR (CSG,NSG=0,1 T=1)
         AuthMethod=None

     I-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     T-> Login (CSG,NSG=1,0 T=0)
         ... iSCSI parameters

     And at the end:

     I-> Login (CSG,NSG=1,3 T=1)
         optional iSCSI parameters

     T-> Login (CSG,NSG=1,3 T=1) "login accept"





































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Appendix D. SendTargets Operation

   To reduce the amount of configuration required on an initiator,
   iSCSI provides the SendTargets text request.  The initiator uses the
   SendTargets request to get a list of targets to which it may have
   access, as well as the list of addresses (IP address and TCP port)
   on which these targets may be accessed.

   To make use of SendTargets, an initiator must first establish one of
   two types of sessions.  If the initiator establishes the session
   using the key "SessionType=Discovery", the session is a discovery
   session, and a target name does not need to be specified.
   Otherwise, the session is a normal, operational session.  The
   SendTargets command MUST only be sent during the Full Feature Phase
   of a normal or discovery session.

   A system that contains targets MUST support discovery sessions on
   each of its iSCSI IP address-port pairs, and MUST support the
   SendTargets command on the discovery session.  A target MUST return
   all path information (IP address-port pairs and portal group tags)
   for the targets for which the requesting initiator is authorized.

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

   An initiator MAY make use of the SendTargets as it sees fit.

   A SendTargets command consists of a single Text request PDU.
   This PDU contains exactly one text key and value.  The text key MUST
   be SendTargets.  The expected response depends upon the value, as
   well as whether the session is a discovery or operational session.

   The value must be one of:

     All

     The initiator is requesting that information on all relevant
       targets known to the implementation be returned.  This value
       MUST be supported on a discovery session, and MUST NOT be
       supported on an operational session.

     <iSCSI-target-name>

     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>




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     The session should only respond with addresses for the target to
       which the session is logged in.  This MUST be supported on
       operational sessions, and MUST NOT return targets other than
       the one to which the session is logged in.

   The response to this command is a text response that contains a list
   of zero or more targets and, optionally, their addresses.  Each
   target is returned as a target record.  A target record begins with
   the TargetName text key, followed by a list of TargetAddress text
   keys, and bounded by the end of the text response or the next
   TargetName key, which begins a new record.  No text keys other than
   TargetName and TargetAddress are permitted within a SendTargets
   response.

   For the format of the TargetName, see Section 12.4 TargetName.

   A discovery session MAY respond to a SendTargets request with its
   complete list of targets, or with a list of targets that is based on
   the name of the initiator logged in to the session.

   A SendTargets response MUST NOT contain target names if there are no
   targets for the requesting initiator to access.

   Each target record returned includes zero or more TargetAddress
   fields.

   Each target record starts with one text key of the form:

     TargetName=<target-name-goes-here>

   Followed by zero or more address keys of the form:

     TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],<portal-
       group-tag>

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

   Each TargetAddress belongs to a portal group, identified by its
   numeric portal group tag (as in Section 12.9 TargetPortalGroupTag).
   The iSCSI target name, together with this tag, constitutes the SCSI
   port identifier; the tag only needs to be unique within a given
   target's name list of addresses.

   Multiple-connection sessions can span iSCSI addresses that belong to
   the same portal group.

   Multiple-connection sessions cannot span iSCSI addresses that belong
   to different portal groups.

   If a SendTargets response reports an iSCSI address for a target, it
   SHOULD also report all other addresses in its portal group in the
   same response.

   A SendTargets text response can be longer than a single Text
   Response


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   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
   discovery session open, and MAY send subsequent SendTargets commands
   to
   discover new targets.

   Examples:


   This example is the SendTargets response from a single target that
   has no other interface ports.

   Initiator sends text request that contains:

         SendTargets=All

   Target sends a text response that contains:

         TargetName=iqn.1993-11.com.example:diskarray.sn.8675309

   All the target  had to return in the simple case was the target
   name.  It is assumed by the initiator that the IP address and TCP
   port for this target are the same as used on the current connection
   to the default iSCSI target.

   The next example has two internal iSCSI targets, each accessible via
   two different ports with different IP addresses.  The following is
   the text response:

         TargetName=iqn.1993-11.com.example:diskarray.sn.8675309
         TargetAddress=10.1.0.45:3000,1
         TargetAddress=10.1.1.45:3000,2
         TargetName=iqn.1993-11.com.example:diskarray.sn.1234567
         TargetAddress=10.1.0.45:3000,1
         TargetAddress=10.1.1.45:3000,2

   Both targets share both addresses; the multiple addresses are likely
   used to provide multi-path support. The initiator may connect to
   either target name on either address. Each of the addresses has its
   own portal group tag; they do not support spanning multiple-
   connection sessions with each other. Keep in mind 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 target.

   In the above example, a DNS host name or an IPv6 address could have
   been returned instead of an IPv4 address.

   The next text response shows a target that supports spanning
   sessions across multiple addresses, and further illustrates the use
   of the portal group tags:

         TargetName=iqn.1993-11.com.example:diskarray.sn.8675309


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     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.

   This SendTargets response does not indicate whether .49 supports
   multiple connections per session; it is communicated via the
   MaxConnections text key upon login to the target.















































































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Appendix E. Algorithmic Presentation of Error Recovery Classes

   This appendix illustrates the error recovery classes using a pseudo-
   programming-language.  The procedure names are chosen to be obvious
   to most implementers. Each of the recovery classes described has
   initiator procedures as well as target procedures. These algorithms
   focus on outlining the mechanics of error recovery classes, and do
   not exhaustively describe all other aspects/cases. Examples of this
   approach are:

         - Handling for only certain Opcode types is shown.

         - Only certain reason codes (e.g., Recovery in Logout command)
           are outlined.

         - Resultant cases, such as recovery of Synchronization on a
           header digest error are considered out-of-scope in these
          algorithms.  In this particular example, a header digest error
           may lead to connection recovery if some type of sync and
           steering layer is not implemented.

   These algorithms strive to convey the iSCSI error recovery concepts
   in the simplest terms, and are not designed to be optimal.

E.1  General Data Structure and Procedure Description

   This section defines the procedures and data structures that are
   commonly used by all the error recovery algorithms. 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 {              /* task control block */
           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
                       TransferContextList[MaxOutStandingR2T];
           int InitiatorTaskTag;
           int CmdSN;

           int SNACK_Tag;








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   };

   struct Connection {
           struct Session SessionReference;
           Boolean SoFarInOrder;
           int CID;
           int State;

           int CurrentTimeout;
           int ExpectedStatSN;
           int MissingStatSNList[MaxMissingSPDU];
           Boolean PerformConnectionCleanup;
   };

   struct Session {
           int NumConnections;
           int CmdSN;
           int Maxconnections;
           int ErrorRecoveryLevel;
           struct iSCSIEndpoint OtherEndInfo;
           struct Connection ConnectionList[MaxSupportedConns];
   };

   Procedure descriptions -
   Receive-a-In-PDU(transport connection, inbound PDU);
   check-basic-validity(inbound PDU);
   Start-Timer(timeout handler, argument, timeout value);
   Build-And-Send-Reject(transport connection, bad PDU, reason code);


E.2  Within-command Error Recovery Algorithms

E.2.1   Procedure Descriptions

   Recover-Data-if-Possible(last required DataSN, task control
   block);
   Build-And-Send-DSnack(task control block);
   Build-And-Send-RDSnack(task control block);
   Build-And-Send-Abort(task control block);
   SCSI-Task-Completion(task control block);
   Build-And-Send-A-Data-Burst(transport connection, data-descriptor,
                                                 task control block);
   Build-And-Send-R2T(transport connection, data-descriptor,
                                                task control block);
   Build-And-Send-Status(transport connection, task control block);
   Transfer-Context-Timeout-Handler(transfer context);


   Notes:















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        - One procedure used in this section: Handle-Status-SNACK-
          request is defined in Within-connection recovery algorithms.

        - The Response processing pseudo-code, shown in the target
          algorithms, applies to all solicited PDUs that carry StatSN -
          SCSI Response, Text Response etc.

E.2.2   Initiator Algorithms

   Recover-Data-if-Possible(LastRequiredDataSN, TCB)
   {
       if (operational ErrorRecoveryLevel > 0) {
            if (# of missing PDUs is trackable) {
                  Note the missing DataSNs in TCB.
                  if (the task spanned a change in
                            MaxRecvDataSegmentLength) {
                       if (TCB.StatusXferd is TRUE)
                          drop the status PDU;
                       Build-And-Send-RDSnack(TCB);
                  } else {
                       Build-And-Send-DSnack(TCB);
                  }
            } else {
                TCB.Reason = "Protocol service CRC error";
                }
       } else {
             TCB.Reason = "Protocol service CRC error";
       }
       if (TCB.Reason == "Protocol service CRC error") {
             Clear the missing PDU list in the TCB.
             if (TCB.StatusXferd is not TRUE)
                Build-And-Send-Abort(TCB);
       }
   }

   Receive-a-In-PDU(Connection, CurrentPDU)
   {
      check-basic-validity(CurrentPDU);
      if (Header-Digest-Bad) discard, return;
      Retrieve TCB for CurrentPDU.InitiatorTaskTag.
      if ((CurrentPDU.type == Data)
                  or (CurrentPDU.type = R2T)) {
         if (Data-Digest-Bad for Data) {
               send-data-SNACK = TRUE;
           LastRequiredDataSN = CurrentPDU.DataSN;
             } else {
               if (TCB.SoFarInOrder = TRUE) {
                   if (current DataSN is expected) {
                        Increment TCB.ExpectedDataSN.
                   } else {














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                        TCB.SoFarInOrder = FALSE;
                        send-data-SNACK = TRUE;
                       }
               } else {
                      if (current DataSN was considered missing) {
                          remove current DataSN from missing PDU list.
                      } else if (current DataSN is higher than expected)
   {
                            send-data-SNACK = TRUE;
                       } else {
                             discard, return;
                       }
                       Adjust TCB.ExpectedDataSN if appropriate.
               }
               LastRequiredDataSN = CurrentPDU.DataSN - 1;
            }
            if (send-data-SNACK is TRUE and
                   task is not already considered failed) {
               Recover-Data-if-Possible(LastRequiredDataSN, TCB);
         }
            if (missing data PDU list is empty) {
               TCB.SoFarInOrder = TRUE;
            }
         if (CurrentPDU.type == R2T) {
            Increment ActiveR2Ts for this task.

            Create a data-descriptor for the data burst.
            Build-And-Send-A-Data-Burst(Connection, data-descriptor,

                                                    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;
               }
         }
      } else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT
   SHOWN */
      }
      if ((TCB.SoFarInOrder == TRUE) and
















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                            (TCB.StatusXferd == TRUE)) {
         SCSI-Task-Completion(TCB);
      }
   }

E.2.3   Target Algorithms

   Receive-a-In-PDU(Connection, CurrentPDU)
   {
     check-basic-validity(CurrentPDU);
     if (Header-Digest-Bad) discard, return;
     Retrieve TCB for CurrentPDU.InitiatorTaskTag.
     if (CurrentPDU.type == Data) {
         Retrieve TContext from CurrentPDU.TargetTransferTag;
         if (Data-Digest-Bad) {
               Build-And-Send-Reject(Connection, CurrentPDU,
                                 Payload-Digest-Error);
            Note the missing data PDUs in MissingDataRange[].
               send-recovery-R2T = TRUE;
            } else {
            if (current DataSN is not expected) {
                Note the missing data PDUs in MissingDataRange[].
                   send-recovery-R2T = TRUE;
               }
            if (CurrentPDU.Fbit == TRUE) {
                if (current PDU is solicited) {
                       Decrement TCB.ActiveR2Ts.
                }
                if ((current PDU is unsolicited and
                       data received is less than I/O length and
                         data received is less than FirstBurstLength)
                    or (current PDU is solicited and the length of
                         this burst is less than expected)) {
                    send-recovery-R2T = TRUE;
                    Note the missing data in MissingDataRange[].
                }
               }
            }
            Increment TContext.ExpectedDataSN.
         if (send-recovery-R2T is TRUE  and
                   task is not already considered failed) {
            if (operational ErrorRecoveryLevel > 0) {
                Increment TCB.ActiveR2Ts.
                Create a data-descriptor for the data burst
                           from MissingDataRange.
                Build-And-Send-R2T(Connection, data-descriptor, TCB);
            } else {
                 if (current PDU is the last unsolicited)


















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                     TCB.Reason = "Not enough unsolicited data";
                 else
                     TCB.Reason = "Protocol service CRC error";
            }
         }
         if (TCB.ActiveR2Ts == 0) {
            Build-And-Send-Status(Connection, TCB);
         }
     } else if (CurrentPDU.type == SNACK) {
         snack-failure = FALSE;
         if (operational ErrorRecoveryLevel > 0) {
            if (CurrentPDU.type == Data/R2T) {
                 if (the request is satisfiable) {

                    if (request for Data) {
                       Create a data-descriptor for the data burst
                           from BegRun and RunLength.
                       Build-And-Send-A-Data-Burst(Connection,

                                     data-descriptor, TCB);
                    } else { /* R2T */
                       Create a data-descriptor for the data burst
                           from BegRun and RunLength.
                       Build-And-Send-R2T(Connection, data-
   descriptor,

                                      TCB);
                     }
                 } else {
                       snack-failure = TRUE;
                 }
            } else if (CurrentPDU.type == status) {
                 Handle-Status-SNACK-request(Connection, CurrentPDU);
            } else if (CurrentPDU.type == DataACK) {
                 Consider all data upto CurrentPDU.BegRun as
                 acknowledged.
                 Free up the retransmission resources for that data.
            } else if (CurrentPDU.type == R-Data SNACK) {
                    Create a data descriptor for a data burst covering
                    all unacknowledged data.
                 Build-And-Send-A-Data-Burst(Connection,

                                     data-descriptor, TCB);
                 TCB.SNACK_Tag = CurrentPDU.SNACK_Tag;
                 if (there's no more data to send) {
                    Build-And-Send-Status(Connection, TCB);
                 }
            }
         } else { /* operational ErrorRecoveryLevel = 0 */
                 snack-failure = TRUE;

         }
         if (snack-failure == TRUE) {








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             Build-And-Send-Reject(Connection, CurrentPDU,
                                                     SNACK-Reject);
             if (TCB.StatusXferd != TRUE) {
                 TCB.Reason = "SNACK Rejected";
                 Build-And-Send-Status(Connection, TCB);
             }
         }


     } else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN
   */
     }
   }

   Transfer-Context-Timeout-Handler(TContext)
   {
     Retrieve TCB and Connection from TContext.
     Decrement TCB.ActiveR2Ts.
     if (operational ErrorRecoveryLevel > 0 and
                   task is not already considered failed) {
         Note the missing data PDUs in MissingDataRange[].
         Create a data-descriptor for the data burst
                           from MissingDataRange[].
         Build-And-Send-R2T(Connection, data-descriptor, TCB);
     } else {
         TCB.Reason = "Protocol service CRC error";
         if (TCB.ActiveR2Ts = 0) {
            Build-And-Send-Status(Connection, TCB);
         }
     }
   }

E.3  Within-connection Recovery Algorithms

E.3.1   Procedure Descriptions

   Procedure descriptions:
   Recover-Status-if-Possible(transport connection,
                                       currently received PDU);
   Evaluate-a-StatSN(transport connection, currently received PDU);
   Retransmit-Command-if-Possible(transport connection, CmdSN);
   Build-And-Send-SSnack(transport connection);
   Build-And-Send-Command(transport connection, task control block);
   Command-Acknowledge-Timeout-Handler(task control block);
   Status-Expect-Timeout-Handler(transport connection);
   Build-And-Send-Nop-Out(transport connection);
   Handle-Status-SNACK-request(transport connection, status SNACK
   PDU);
   Retransmit-Status-Burst(status SNACK, task control block);
















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   Is-Acknowledged(beginning StatSN, run length);


   Implementation-specific tunables:
   InitiatorProactiveSNACKEnabled

   Notes:
         - The initiator algorithms only deal with unsolicited Nop-In
          PDUs for generating status SNACKs.  A 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 the retransmission of
           unacknowledged commands in more cases than necessary.  This
           will not, however, affect the correctness of the operation
           because the target is required to discard the duplicate
           CmdSNs.

         - The procedure Build-And-Send-Async is defined in the
           Connection recovery algorithms.

         - The procedure Status-Expect-Timeout-Handler describes how
           initiators may proactively attempt to retrieve the Status if
          they so choose. This procedure is assumed to be triggered much
           before the standard ULP timeout.

E.3.2   Initiator Algorithms

   Recover-Status-if-Possible(Connection, CurrentPDU)
   {
       if ((Connection.state == LOGGED_IN) and
                      connection is not already considered failed) {
          if (operational ErrorRecoveryLevel > 0) {
             if (# of missing PDUs is trackable) {
                   Note the missing StatSNs in Connection

                  that were not already requested with SNACK;
               Build-And-Send-SSnack(Connection);
                 } else {
                   Connection.PerformConnectionCleanup = TRUE;
             }
          } else {
                 Connection.PerformConnectionCleanup = TRUE;
          }
          if (Connection.PerformConnectionCleanup == TRUE) {
             Start-Timer(Connection-Cleanup-Handler, Connection, 0);
              }
       }
   }

   Retransmit-Command-if-Possible(Connection, CmdSN)
   {








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       if (operational ErrorRecoveryLevel > 0) {
          Retrieve the InitiatorTaskTag, and thus TCB for the CmdSN.
          Build-And-Send-Command(Connection, TCB);
       }
   }

   Evaluate-a-StatSN(Connection, CurrentPDU)
   {
       send-status-SNACK = FALSE;
       if (Connection.SoFarInOrder == TRUE) {
          if (current StatSN is the expected) {
               Increment Connection.ExpectedStatSN.
          } else {
                   Connection.SoFarInOrder = FALSE;
                   send-status-SNACK = TRUE;
              }
       } else {
          if (current StatSN was considered missing) {
               remove current StatSN from the missing list.
          } else {
                   if (current StatSN is higher than expected){
                       send-status-SNACK = TRUE;
                   } else {
                       send-status-SNACK = FALSE;
                   discard the PDU;
               }
          }
          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 Session.CmdSN) {
                       Retransmit-Command-if-Possible(Connection,


















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                                      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);
            if (send-status-SNACK == TRUE)
                Recover-Status-if-Possible(Connection, CurrentPDU);
       } else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOVERY,
                 * NOT SHOWN */
       }
   }

   Command-Acknowledge-Timeout-Handler(TCB)
   {
       Retrieve the Connection for TCB.
       Retransmit-Command-if-Possible(Connection, TCB.CmdSN);
   }

   Status-Expect-Timeout-Handler(Connection)
   {
       if (operational ErrorRecoveryLevel > 0) {
           Build-And-Send-Nop-Out(Connection);
       } else if (InitiatorProactiveSNACKEnabled){
           if ((Connection.state == LOGGED_IN) and
                  connection is not already considered failed) {
                Build-And-Send-SSnack(Connection);
           }
       }
   }

E.3.3   Target Algorithms

   Handle-Status-SNACK-request(Connection, CurrentPDU)
   {
       if (operational ErrorRecoveryLevel > 0) {
          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);


















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          }
       } else {
          Build-And-Send-Async(Connection, DroppedConnection,
                                  DefaultTime2Wait,
   DefaultTime2Retain);
       }
   }


E.4  Connection Recovery Algorithms

E.4.1   Procedure Descriptions

   Build-And-Send-Async(transport connection, reason code,
                                      minimum time, maximum time);
   Pick-A-Logged-In-Connection(session);
   Build-And-Send-Logout(transport connection, logout connection
                     identifier, reason code);
   PerformImplicitLogout(transport connection, logout connection
                     identifier, target information);
   PerformLogin(transport connection, target information);
   CreateNewTransportConnection(target information);
   Build-And-Send-Command(transport connection, task control block);
   Connection-Cleanup-Handler(transport connection);
   Connection-Resource-Timeout-Handler(transport connection);
   Quiesce-And-Prepare-for-New-Allegiance(session, task control
   block);
   Build-And-Send-Logout-Response(transport connection,
                            CID of connection in recovery, reason
   code);
   Build-And-Send-TaskMgmt-Response(transport connection,
                          task mgmt command PDU, response code);
   Establish-New-Allegiance(task control block, transport
   connection);
   Schedule-Command-To-Continue(task control block);

   Notes:
        - Transport exception conditions, such as unexpected connection
          termination, connection reset, and hung connection while the
          connection is in the full-feature phase, are all assumed to be
          asynchronously signaled to the iSCSI layer using the
          Transport_Exception_Handler procedure.

E.4.2   Initiator Algorithms


   Receive-a-In-PDU(Connection, CurrentPDU)
   {
       check-basic-validity(CurrentPDU);
       if (Header-Digest-Bad) discard, return;














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       Retrieve TCB from CurrentPDU.InitiatorTaskTag.
       if (CurrentPDU.type == Async) {
           if (CurrentPDU.AsyncEvent == ConnectionDropped) {
              Retrieve the AffectedConnection for
   CurrentPDU.Parameter1.
              AffectedConnection.CurrentTimeout = CurrentPDU.Parameter3;
             AffectedConnection.State = CLEANUP_WAIT;
             Start-Timer(Connection-Cleanup-Handler,
                           AffectedConnection,
   CurrentPDU.Parameter2);
           } else if (CurrentPDU.AsyncEvent == LogoutRequest)) {
             AffectedConnection = Connection;
             AffectedConnection.State = LOGOUT_REQUESTED;
             AffectedConnection.PerformConnectionCleanup = TRUE;

              AffectedConnection.CurrentTimeout =
   CurrentPDU.Parameter3;
             Start-Timer(Connection-Cleanup-Handler,
                           AffectedConnection, 0);
           } else if (CurrentPDU.AsyncEvent == SessionDropped)) {
             for (each Connection) {
                 Connection.State = CLEANUP_WAIT;
                 Connection.CurrentTimeout = CurrentPDU.Parameter3;
                 Start-Timer(Connection-Cleanup-Handler,

                           Connection, CurrentPDU.Parameter2);
             }
             Session.state = FAILED;
           }

       } else if (CurrentPDU.type == LogoutResponse) {
           Retrieve the CleanupConnection for CurrentPDU.CID.
           if (CurrentPDU.Response = failure) {
              CleanupConnection.State = CLEANUP_WAIT;
           } else {
               CleanupConnection.State = FREE;
           }
       } else if (CurrentPDU.type == LoginResponse) {
            if (this is a response to an implicit Logout) {
               Retrieve the CleanupConnection.
               if (successful) {
                   CleanupConnection.State = FREE;
                   Connection.State = LOGGED_IN;
               } else {
                    CleanupConnection.State = CLEANUP_WAIT;
                    DestroyTransportConnection(Connection);
               }
            }
       } else { /* REST UNRELATED TO CONNECTION-RECOVERY,
















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                 * NOT SHOWN */
       }
       if (CleanupConnection.State == FREE) {
          for (each command that was active on CleanupConnection) {
          /* Establish new connection allegiance */
               NewConnection = Pick-A-Logged-In-Connection(Session);
               Build-And-Send-Command(NewConnection, TCB);
           }
       }
   }

   Connection-Cleanup-Handler(Connection)
   {
       Retrieve Session from Connection.
       if (Connection can still exchange iSCSI PDUs) {
           NewConnection = Connection;
       } else {
           Start-Timer(Connection-Resource-Timeout-Handler,
                 Connection, Connection.CurrentTimeout);
           if (there are other logged-in connections) {
                NewConnection = Pick-A-Logged-In-Connection(Session);
           } else {
                NewConnection =
                     CreateTransportConnection(Session.OtherEndInfo);
                Initiate an implicit Logout on NewConnection for
                                                  Connection.CID.
                return;
           }
       }
       Build-And-Send-Logout(NewConnection, Connection.CID,
                                           RecoveryRemove);
   }

   Transport_Exception_Handler(Connection)
   {
       Connection.PerformConnectionCleanup = TRUE;
       if (the event is an unexpected transport disconnect) {
           Connection.State = CLEANUP_WAIT;

           Connection.CurrentTimeout = DefaultTime2Retain;
           Start-Timer(Connection-Cleanup-Handler, Connection,
                                             DefaultTime2Wait);

       } else {
           Connection.State = FREE;
       }
   }


















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E.4.3   Target Algorithms

   Receive-a-In-PDU(Connection, CurrentPDU)
   {
       check-basic-validity(CurrentPDU);
       if (Header-Digest-Bad) discard, return;
       else if (Data-Digest-Bad) {
             Build-And-Send-Reject(Connection, CurrentPDU,
                                         Payload-Digest-Error);
             discard, return;
       }
       Retrieve TCB and Session.
       if (CurrentPDU.type == Logout) {
          if (CurrentPDU.ReasonCode = RecoveryRemove) {
              Retrieve the CleanupConnection from CurrentPDU.CID).
              for (each command active on CleanupConnection) {
                   Quiesce-And-Prepare-for-New-Allegiance(Session,
   TCB);
                   TCB.CurrentlyAllegiant = FALSE;
              }
              Cleanup-Connection-State(CleanupConnection);
              if ((quiescing successful) and (cleanup successful)) {
                   Build-And-Send-Logout-Response(Connection,
                                       CleanupConnection.CID,
   Success);
              } else {
                   Build-And-Send-Logout-Response(Connection,
                                       CleanupConnection.CID,
   Failure);
              }
          }
       } else if ((CurrentPDU.type == Login) and
                          operational ErrorRecoveryLevel == 2) {
              Retrieve the CleanupConnection from CurrentPDU.CID).
              for (each command active on CleanupConnection) {
                   Quiesce-And-Prepare-for-New-Allegiance(Session,
   TCB);
                   TCB.CurrentlyAllegiant = FALSE;
              }
              Cleanup-Connection-State(CleanupConnection);
              if ((quiescing successful) and (cleanup successful)) {
                   Continue with the rest of the Login processing;
              } else {
                   Build-And-Send-Login-Response(Connection,
                                 CleanupConnection.CID, Target
   Error);
              }
          }


















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       } else if (CurrentPDU.type == TaskManagement) {
            if (CurrentPDU.function == "TaskReassign") {
                  if (Session.ErrorRecoveryLevel < 2) {
                     Build-And-Send-TaskMgmt-Response(Connection,
                          CurrentPDU, "Allegiance reassignment
                                                 not supported");
                  } else if (task is not found) {
                     Build-And-Send-TaskMgmt-Response(Connection,
                          CurrentPDU, "Task not in task set");
                  } else if (task is currently allegiant) {
                     Build-And-Send-TaskMgmt-Response(Connection,
                               CurrentPDU, "Task still allegiant");
                  } else {
                     Establish-New-Allegiance(TCB, Connection);
                     TCB.CurrentlyAllegiant = TRUE;
                     Schedule-Command-To-Continue(TCB);
                  }
            }
       } else { /* REST UNRELATED TO CONNECTION-RECOVERY,
                 * NOT SHOWN */
       }
   }

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

   (DefaultTime2Wait+DefaultTime2Retain));
           if (this Session has full-feature phase connections left)
   {
               DifferentConnection =
                  Pick-A-Logged-In-Connection(Session);
                Build-And-Send-Async(DifferentConnection,
                      DroppedConnection, DefaultTime2Wait,
                        DefaultTime2Retain);
          }
       } else {
           Connection.State = FREE;
       }
   }























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Appendix F. Clearing Effects of Various Events on Targets

F.1  Clearing Effects on iSCSI Objects

   The following tables describe the target behavior on receiving the
   events specified in the rows of the table.  The second table is  an
   extension of the first table and defines clearing actions for more
   objects on the same events.  The legend is:

     Y   = Yes (cleared/discarded/reset on the event specified in the
       row).  Unless otherwise noted, the clearing action is only
       applicable for the issuing initiator port.
     N   = No  (not affected on the event specified in the row, i.e.,
       stays at previous value).
     NA  = Not Applicable or Not Defined.

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



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   1.Incomplete TTTs - Target Transfer Tags on which the target is
   still expecting PDUs to be received. Examples include TTTs received
   via R2T, NOP-IN, etc.

   2.Immediate Commands - immediate commands, but waiting for execution
   on a target. For example, Abort Task Set.

   5.Connection Tasks - tasks that are active on the iSCSI connection
   in question.

   6.Session Tasks - tasks that are active on the entire iSCSI session.
   A union of "connection tasks" on all participating connections.

   7.Partial PDUs (if any) - PDUs that are partially sent and waiting
   for transport window credit to complete the transmission.

   8.Connection failure is a connection exception condition - one of
   the transport connections shutdown, transport connections reset, or
   transport connections timed out, which abruptly terminated the iSCSI
   full-feature phase connection. A connection failure always takes the
   connection state machine to the CLEANUP_WAIT state.

   9.Connection state timeout happens if a connection spends more time
   than agreed upon during Login negotiation in the CLEANUP_WAIT state,
   and this takes the connection to the FREE state (M1 transition in
   connection cleanup state diagram).

   10.These are defined in Section 5.3.5 Session Reinstatement,
   Closure, and Timeout.

   11.This clearing effect is "Y" only if it is a connection
   reinstatement and the operational ErrorRecoveryLevel is less than 2.

   12.Session continuation is defined in Section 5.3.6 Session
   Continuation and Failure.

   13.This clearing effect is only valid if the connection is being
   logged out on a different connection and when the connection being
   logged out on the target may have some partial PDUs pending to be
   sent. In all other cases, the effect is "NA".

   14.This clearing effect is only valid for a "close the session"
   logout in a multi-connection session.  In all other cases, the
   effect is "NA".

   15.Only applicable if this leading connection login is a session
   reinstatement. If this is not the case, it is "NA".

   16.This operation affects all logged-in initiators.

   18.Session failure is defined in Section 5.3.6 Session Continuation
   and Failure.

   19.This operation affects all logged-in initiators and the clearing
   effects are only applicable to the LU being reset.



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

   1.Discontiguous Commands - commands allegiant to the connection in
   question and waiting to be reordered in the iSCSI layer. All "Y"s in
   this column assume that the task causing the event (if indeed the
   event is the result of a task) is issued as an immediate command,
   because the discontiguities can be ahead of the task.

   2.Discontiguous Data - data PDUs received for the task in question
   and waiting to be reordered due to prior discontiguities in DataSN.

   3.StatSN

   4.CmdSN

   5.DataSN

   7.It clears the StatSN on all the connections.

   8.This sequence number is instantiated on this event.


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   9.A logout failure drives the connection state machine to the
   CLEANUP_WAIT state, similar to the connection failure event. Hence,
   it has a similar effect on this and several other protocol aspects.

   10.This is cleared by virtue of the fact that all sessions with all
   initiators are terminated.

   11.This clearing effect is "Y" if it is a connection reinstatement.

   12.This clearing effect is "Y" only if it is a connection
   reinstatement and the operational ErrorRecoveryLevel is 2.

   13.This clearing effect is "N" only if it is a connection
   reinstatement and the operational ErrorRecoveryLevel is 2.

F.2  Clearing Effects on SCSI Objects

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

   Since iSCSI defines a target cold reset as a protocol-equivalent to
   a target power-cycle, the iSCSI target cold reset must also be
   considered as the power-on reset event in interpreting the actions
   defined in the SCSI standards.

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







































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