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IPS                                                       Julian Satran
Internet Draft                                             Daniel Smith
Document: draft-ietf-ips-iscsi-05.txt                       Kalman Meth
Category: standards-track                                    Ofer Biran
                                                                    IBM

                                                      Costa Sapuntzakis
                                                          Cisco Systems

                                                           Matt Wakeley
                                                   Agilent Technologies

                                                      Luciano Dalle Ore
                                                                Quantum

                                                      Paul Von Stamwitz
                                                                Adaptec

                                                          Randy Haagens
                                                    Hewlett-Packard Co.

                                                           Efri Zeidner
                                                                SANGate

                                                            Yaron Klein
                                                                 SANRAD



                                 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 [1].

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


Abstract

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

Acknowledgements

   In addition to the authors, a large group of people contributed to
   this work through their review, comments and valuable insights.  We
   are grateful to all of them.  We are especially grateful to those who
   found the time and patience to participate in our weekly phone
   conferences and intermediate meetings in Almaden and Haifa, thus
   helping to shape this document: Jim Hafner, John Hufferd, Prasenjit
   Sarkar, Meir Toledano, John Dowdy, Steve Legg, Alain Azagury (IBM),
   Dave Nagle (CMU), David Black (EMC), John Matze (Veritas), Mark
   Bakke, Steve DeGroote, Mark Shrandt (NuSpeed), Gabi Hecht (Gadzoox),
   Robert Snively (Brocade), Nelson Nachum (StorAge), Uri Elzur (Intel).
   Many more helped clean up and improve this document within the IPS
   working group. We are especially grateful to David Robinson and
   Raghavendra Rao (Sun), Charles Monia, Joshua Tseng (Nishan), Somesh
   Gupta, Mallikarjun C., Michael Krause, Pierre Labat, Santosh Rao
   (HP), Stephen Byan (Genroco), Robert Elliott (Compaq), Steve Senum
   (CISCO), Barry Reinhold (Trebia Networks). Last, but not least,

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   thanks to Ralph Weber for keeping us in line with T10 (SCSI)
   standardization.  We would like to thank Steve Hetzler for his
   unwavering support and for coming up with such a good name for the
   protocol, Micky Rodeh, Jai Menon, Clod Barrera and Andy Bechtolsheim
   for helping this work happen.


   At the time of the writing, this document has to be considered in
   conjunction with the "Naming & Discovery" and the "Boot" documents.

   The "Naming & Discovery" is authored by:

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

   The "Boot" is authored by:

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


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

Conventions used in this document


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

   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 RFC-2119.














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                           Table of Contents
Status of this Memo...................................................2
Abstract..............................................................2
Acknowledgements......................................................2
Conventions used in this document.....................................3
1. Overview...........................................................9
 1.1 SCSI Concepts...................................................9
 1.2 iSCSI Concepts and Functional Overview.........................10
  1.2.1 Layers and Sessions.........................................10
  1.2.2 Ordering and iSCSI Numbering................................11
   1.2.2.1 Command Numbering and Acknowledging......................11
   1.2.2.2 Response/Status Numbering and Acknowledging..............12
   1.2.2.3 Data Sequencing..........................................13
  1.2.3 iSCSI Login.................................................13
  1.2.4 Text Mode Negotiation.......................................14
  1.2.5 iSCSI Full Feature Phase....................................15
  1.2.6 iSCSI Connection Termination................................17
  1.2.7 Naming and Addressing.......................................17
  1.2.8 Message Synchronization and Steering........................20
   1.2.8.1 Rationale................................................20
   1.2.8.2 Synch and Steering Functional Model......................21
   1.2.8.3 Synch and Steering and Other Encapsulation Layers........23
   1.2.8.4 Synch/Steering and iSCSI PDU Size........................23
2. iSCSI PDU Formats.................................................25
 2.1 iSCSI PDU Length and Padding...................................25
 2.2 PDU Template, Header and Opcodes...............................25
  2.2.1 What's Next (WN)............................................26
  2.2.2 WN Specific Fields..........................................27
   2.2.2.1 WN Specific Fields for a Next Extended CDB Header Segment 27
   2.2.2.2 WN Specific Fields for Next Bi-directional Read Data Header
   Segment and Long Data Transfer Header............................27
   2.2.2.3 WN Specific Fields for Next Data Header Segment..........27
  2.2.3 Header Digest and Data Digest...............................27
  2.2.4 Basic Header Segment (BHS)..................................28
   2.2.4.1 X........................................................28
   2.2.4.2 Opcode...................................................28
   2.2.4.3 Opcode-specific Fields...................................30
   2.2.4.4 LUN......................................................30
   2.2.4.5 Initiator Task Tag.......................................30
  2.2.5 Extended CDB Additional Header Segment......................30
  2.2.6 Bi-directional Read Additional Header Segment...............30
  2.2.7 Long Data Additional Header Segment.........................31
 2.3 SCSI Command...................................................32
  2.3.1 Flags and Task Attributes...................................32


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  2.3.2 CmdRN.......................................................33
  2.3.3 CmdSN - Command Sequence Number.............................33
  2.3.4 ExpStatSN/EndDataSN - Expected Status Sequence Number.......33
  2.3.5 Expected Data Transfer Length...............................33
  2.3.6 CDB - SCSI Command Descriptor Block.........................34
  2.3.7 Command-Data................................................34
 2.4 SCSI Response..................................................35
  2.4.1 Byte 1 - Flags..............................................35
  2.4.2 Status/Response.............................................36
  2.4.3 Basic Residual Count........................................36
  2.4.4 Bidi-Read Residual Count....................................36
  2.4.5 Sense or Response Data......................................37
  2.4.6 EndDataSN...................................................37
  2.4.7 R2TEndDataSN................................................37
  2.4.8 StatSN - Status Sequence Number.............................37
  2.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator..........37
  2.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator....37
 2.5 SCSI Task Management Command...................................39
  2.5.1 Function....................................................39
  2.5.2 Referenced Task Tag.........................................40
 2.6 SCSI Task Management Response..................................41
  2.6.1 Referenced Task Tag.........................................42
 2.7 SCSI Data......................................................43
  2.7.1 F (Final) Bit...............................................44
  2.7.2 Target Transfer Tag.........................................44
  2.7.3 StatSN......................................................45
  2.7.4 DataSN......................................................45
  2.7.5 Buffer Offset...............................................45
  2.7.6 Flags.......................................................46
 2.8 Text Command...................................................47
  2.8.1 F (Final) Bit...............................................47
  2.8.2 Initiator Task Tag..........................................47
  2.8.3 Text........................................................48
 2.9 Text Response..................................................49
  2.9.1 F (Final) Bit...............................................49
  2.9.2 Initiator Task Tag..........................................50
  2.9.3 Text Response...............................................50
 2.10 Login Command.................................................51
  2.10.1 X - Restart................................................51
  2.10.2 F (Final) Bit..............................................51
  2.10.3 Version-max................................................52
  2.10.4 Version-min................................................52
  2.10.5 CID........................................................52
  2.10.6 ISID.......................................................52
  2.10.7 InitCmdSN..................................................52
  2.10.8 ExpStatSN..................................................52


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  2.10.9 Login Parameters...........................................52
 2.11 Login Response................................................53
  2.11.1 Version-max................................................53
  2.11.2 Version-active/lowest......................................53
  2.11.3 InitStatSN.................................................54
  2.11.4 Status-Class and Status-Detail.............................54
  2.11.5 TSID.......................................................56
  2.11.6 F (Final) bit..............................................56
 2.12 NOP-Out.......................................................57
  2.12.1 P (Ping) Bit...............................................58
  2.12.2 Initiator Task Tag.........................................58
  2.12.3 Target Transfer Tag........................................58
  2.12.4 Ping Data..................................................58
 2.13 NOP-In........................................................59
  2.13.1 P bit......................................................59
  2.13.2 Target Transfer Tag........................................60
  2.13.3 LUN........................................................60
 2.14 Logout Command................................................61
  2.14.1 CID........................................................61
  2.14.2 ExpStatSN..................................................61
  2.14.3 Reason Code................................................62
 2.15 Logout Response...............................................63
  2.15.1 Response...................................................63
 2.16 SACK Request..................................................64
  2.16.1 D..........................................................64
  2.16.2 AddRun.....................................................64
  2.16.3 BegRun.....................................................65
  2.16.4 RunLength..................................................65
 2.17 Ready To Transfer (R2T).......................................66
  2.17.1 DataSN.....................................................67
  2.17.2 Desired Data Transfer Length and Buffer Offset.............67
  2.17.3 Target Transfer Tag........................................67
 2.18 Asynchronous Message..........................................68
  2.18.1 iSCSI Event................................................69
  2.18.2 SCSI Event.................................................69
 2.19 Third Party Commands..........................................70
 2.20 Reject........................................................71
  2.20.1 Reason.....................................................71
  2.20.2 First Bad Byte.............................................71
3. SCSI Mode Parameters for iSCSI....................................72
 3.1 iSCSI Disconnect-Reconnect Mode Page...........................72
  3.1.1 Enable Modify Data Pointers Bit.............................72
  3.1.2 Maximum Burst Size Field (16 bit)...........................72
  3.1.3 First Burst Size Field (16 bit).............................72
  3.1.4 Other Fields................................................72
 3.2 iSCSI Logical Unit Control Mode Page...........................72


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  3.2.1 Protocol Identifier.........................................72
  3.2.2 Enable CmdRN................................................72
 3.3 iSCSI Port Control Mode Page...................................73
4. Login Phase.......................................................74
 4.1 Login Phase Start..............................................75
 4.2 iSCSI Security and Integrity Negotiation.......................76
 4.3 Operational Parameter Negotiation During the Login Phase.......77
5. Operational Parameter Negotiation Outside the Login Phase.........79
6. iSCSI Error Handling and Recovery.................................80
 6.1 Format Errors..................................................80
 6.2 Digest Errors..................................................80
 6.3 Sequence Errors................................................81
 6.4 Protocol Errors................................................81
 6.5 Connection Failure.............................................81
 6.6 Session Errors.................................................82
 6.7 Recovery Levels................................................82
  6.7.1 Recovery Within-task........................................83
   6.7.1.1 Recovery Within-connection...............................84
   6.7.1.2 Recovery Within-session..................................84
   6.7.1.3 Session Recovery.........................................85
7. Notes to Implementers.............................................86
 7.1 Multiple Network Adapters......................................86
 7.2 Autosense and Auto Contingent Allegiance (ACA).................86
8. Security Considerations...........................................87
 8.1 iSCSI Security Protection Modes................................87
  8.1.1 No Security.................................................87
  8.1.2 Initiator-Target Authentication.............................87
  8.1.3 Data Integrity and Authentication...........................87
  8.1.4 Encryption..................................................88
9. IANA Considerations...............................................89
10. References and Bibliography......................................90
11. Author's Addresses...............................................92
Appendix A. iSCSI Security and Integrity.............................94
 01 Security Keys and Values........................................94
 02 Authentication..................................................96
 03 Login Phase Examples............................................97
Appendix B. Examples................................................102
 04 Read Operation Example.........................................102
 05 Write Operation Example........................................103
Appendix C. Synch and Steering with Fixed Interval Markers..........104
 06 Markers At Fixed Intervals.....................................105
 07 Initial Marker-less Interval...................................105
Appendix D. Login/Text Miscellaneous Keys...........................106
 08 MaxConnections - LO............................................106
 09 TargetWWUI - LO................................................106
 10 InitiatorWWUI - LO.............................................106


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 11 TargetAlias....................................................107
 12 InitiatorAlias.................................................107
 13 TargetAddress..................................................108
 14 SendTargets....................................................108
 15 AccessID.......................................................108
 16 FMarker........................................................108
 17 RFMarkInt......................................................109
 18 SFMarkInt......................................................109
 19 IFMarkInt......................................................109
 20 UseR2T.........................................................110
 21 BidiUseR2T.....................................................110
 22 ImmediateData..................................................111
 23 DataPDULength..................................................111
 24 FirstBurstSize.................................................111
 25 ITagLength.....................................................111
 26 EnableCmdRN....................................................112
 27 PingMaxReplyLength.............................................112
 28 TotalText......................................................112
 29 KeyValueText...................................................112
 30 MaxOutstandingR2T..............................................113
 31 InDataOrder....................................................113
 32 BootSession - LO...............................................113
 33 The Glen-Turner Vendor Specific Key Format.....................113
Full Copyright Statement............................................114



























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1. Overview

1.1 SCSI Concepts

   The SCSI Architecture Model-2 [SAM2] describes in detail the
   architecture of the SCSI family of I/O protocols. This section
   provides a brief background to familiarize readers with the
   terminology of the SCSI architecture.

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

   SCSI is client-server architecture. Clients of a SCSI interface are
   called "initiators". Initiators issue SCSI "commands" to request
   service from a logical unit. The "device server" on the logical unit
   accepts SCSI commands and executes 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 have multiple Logical
   Units (LUs) behind it. Each Logical Unit has an address within a
   target called a Logical Unit Number (LUN).

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

   Each SCSI command results in an optional data phase and a required
   response phase. In the data phase, information can travel from the
   initiator to target (e.g., WRITE), target to initiator (e.g., READ),
   or in both directions. In the response phase, the target returns the
   final status of the operation, including any errors. A response
   terminates a SCSI command.  For performance reasons, iSCSI allows a
   "phase-collapse" (e.g., command and its associated data may be
   shipped together from initiator to target and data and responses may
   be shipped together from targets).

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



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1.2 iSCSI Concepts and Functional Overview

   The iSCSI protocol is a mapping of the SCSI remote procedure
   invocation model on top of the TCP protocol.

   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.

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

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

1.2.1 Layers and Sessions

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

      -the SCSI layer builds/receives SCSI CDBs (Command Descriptor
      Blocks) and relays/receives them with the remaining command
      execute parameters (cf. SAM-2) to/from ->
      -the iSCSI layer that builds/receives iSCSI PDUs and
      relays/receives them to/from one or more TCP connections that
      form an initiator-target "session".

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

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



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   iSCSI targets and initiators MUST support at least one TCP connection
   and MAY support several connections in a session.

1.2.2 Ordering and iSCSI Numbering

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

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

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

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

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

1.2.2.1 Command Numbering and Acknowledging

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

   Any SCSI activity is related to a task (SAM-2). The task is
   identified by the Initiator Task Tag for the life of the task.

   Commands in transit from the initiator SCSI layer to the SCSI target
   layer are numbered by iSCSI; the number is carried by the iSCSI PDU
   as CmdSN (Command-Sequence-Number).  The numbering is session-wide.
   All iSCSI PDUs that have a task association carry this number. CmdSNs
   are allocated by the initiator iSCSI within a 32-bit unsigned counter
   (modulo 2**32).  The value 0 is reserved and used to mean immediate
   delivery. Comparisons and arithmetic on CmdSN SHOULD use Serial
   Number Arithmetic as defined in [RFC1982] where SERIAL_BITS = 32.

   Not covered in this document are he means by which the SCSI layer may
   request immediate delivery for a command or by which iSCSI will
   decide by itself to mark a PDU for immediate delivery.


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   If immediate delivery is used with task management commands, these
   commands may reach the SCSI target task management before the tasks
   they are supposed to act upon.  Whenever those effects are
   undesirable, connection allegiance or ordered delivery MAY be used.

   CmdSNs are significant only during command delivery to the target.
   Once the device serving part of the target SCSI has received a
   command, CmdSN ceases to be significant.  During command delivery to
   the target, the allocated numbers are unique session wide.

   The iSCSI target layer MUST deliver the commands to the SCSI target
   layer in the order specified by CmdSN.

   The initiator and target are assumed to have three counters that
   define the numbering mechanism:

       - CmdSN - the current command Sequence Number advanced by 1 on
      each command shipped.
       - ExpCmdSN - the next expected command by the target. The
      target acknowledges all commands up to this one.
       - MaxCmdSN - the maximum number to be shipped. MaxCmdSN -
      ExpCmdSN defines the queuing capacity of the receiving iSCSI
      layer.

   The target MUST NOT transmit a MaxCmdSN that is more than 2**31 - 1
   above the last ExpCmdSN.  CmdSN can take any value from ExpCmdSN to
   MaxCmdSN, except 0. The target MUST silently ignore any command
   outside this range or duplicates within the range that have not been
   flagged with the retry bit (the X bit in the opcode).

   iSCSI initiators and target MUST support the command numbering
   scheme.


1.2.2.2 Response/Status Numbering and Acknowledging

   Responses in transit from the target to the initiator are numbered.
   The StatSN (Status Sequence Number) is used for this purpose. StatSN
   is a counter maintained per connection.  ExpStatSN is used by the
   initiator to acknowledge status.

   Status numbering starts after Login. During login, there is always
   only one outstanding command per connection and status numbering is
   not needed.
   The login response includes an initial value for status numbering.



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   To enable command recovery the target MAY maintain enough state
   information to enable data and status recovery after a connection
   failure.
   A target can discard all the state information maintained for
   recovery after the status delivery is acknowledged through ExpStatSN.
   A large difference between StatSN and ExpStatSN may indicate a failed
   connection.

   Initiators and Targets MUST support the response-numbering scheme.

1.2.2.3 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 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 a R2T) and advances by 1 for each subsequent data PDU. R2T
   are also sequenced per command - i.e. the first R2T has a DataSN of 0
   and advances by 1 for each subsequent R2T. Unlike command and status,
   the data PDUs and R2Ts are not acknowledged except as implied by
   status. The DataSN field is meant to enable the initiator to detect
   missing data PDUs and simplify this operation at the target.
   0x'ffffffff' is not a valid DataSN and MUST be skipped when counting
   (serial arithmetic).

1.2.3 iSCSI Login

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

   A session is used to identify to a target all the connections with a
   given initiator that belong to the same I_T nexus. If an initiator
   and target are connected through more than one session, both the
   initiator and target perceive the other as a different entity on each
   session (a different I_T nexus in SAM-2 parlance).

   The targets listen on a well-known TCP port for incoming connections.
   The initiator begins the login process by connecting to that well-
   known TCP port.

   As part of the login process, the initiator and target MAY wish to
   authenticate each other and set a security association protocol for


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   the session. This can occur in many different ways and is subject to
   negotiation.

   Negotiation and security associations executed before the Login
   Command are outside the scope of this document although they may
   realize a related function (e.g., establish a IPsec tunnel).

   The Login Command starts the iSCSI Login Phase. Within the Login
   Phase, negotiation is carried on through parameters of the Login
   Command and Response, and optionally through intervening Text
   Commands and Responses. The Login Response concludes the Login Phase.
   Once suitable authentication has occurred, the target MAY authorize
   the initiator to send SCSI commands. How the target chooses to
   authorize an initiator is beyond the scope of this document. The
   target indicates a successful authentication and authorization by
   sending a login response with "login accept". Otherwise, it sends a
   response with a "login reject", which indicates that a session is not
   established.

   It is expected that iSCSI parameters will be negotiated after the
   security association protocol is established, if there is a security
   association.

   The login message includes a session ID that is composed of an
   initiator part ISID and a target part TSID. For a new session, the
   TSID is null. As part of the response, the target generates a TSID.
   Session specific parameters can be specified only for the first login
   of a session (TSID null)(e.g., the maximum number of connections that
   can be used for this session). Connection specific parameters, if
   any, can be specified for any login. Thus, a session is operational
   once it has at least one connection.

   Any message except login and text, which is sent on a TCP connection
   before this connection gets into full feature phase at the initiator
   MUST be rejected and cause the connection to terminate. At target,
   closing the connection should be preceded by a Reject PDU sent to the
   initiator.

1.2.4 Text Mode Negotiation

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

   In "list" negotiation, the offering party sends a list of values for
   a key in its order of preference.



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   The responding party answers with a value from the list.

   The value "none" MUST always be used to indicate a missing function.
   However, none is a valid selection only if it is explicitly offered
   and MAY be selected by omission (i.e., <key>=none MAY be omitted).

   The general format of text negotiation is:

      Offer-> <key>=<value1>,<value2>,...,<valuen>
      Answer-> <key>=<valuex>

   In "numerical" negotiations, the offering and responding party state
   a numerical value. The result of the negotiation is key dependent;
   usually the lower or the higher of the two values is used.

1.2.5 iSCSI Full Feature Phase

   Once the initiator is authorized to do so, the iSCSI session is in
   iSCSI full feature phase. The initiator may send SCSI commands and
   data to the various LUs on the target by wrapping them in iSCSI
   messages that go over the established iSCSI session.

   For SCSI commands that require data and/or parameter transfer, the
   (optional) data and the status for a command must be sent over the
   same TCP connection that was used to deliver the SCSI command. We
   call this "connection allegiance".  Thus, if an initiator issues a
   READ command, the target must send the requested data, if any,
   followed by the status to the initiator over the same TCP connection
   that was used to deliver the SCSI command.  If an initiator issues a
   WRITE command, the initiator must send the data, if any, for that
   command and the target MUST return R2T, if any, and the status over
   the same TCP connection that was used to deliver the SCSI command.

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

   Outgoing SCSI data (initiator to target user data or command
   parameters) is sent as either solicited data or unsolicited data.
   Solicited data is sent in response to Ready To Transfer (R2T) PDUs.
   Unsolicited data can be sent as part of an iSCSI command PDU
   ("immediate data") or in separate iSCSI data PDUs.  An initiator may
   send unsolicited data either as immediate (up to the negotiated
   maximum PDU size - DataPDULength - disconnect-reconnect mode page) or
   in a separate PDU sequence (up to the negotiated limit -

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   FirstBurstSize - disconnect-reconnect mode page). All subsequent data
   has to be solicited.  The maximum size of an individual data PDU or
   the immediate-part of the initial unsolicited burst as well as the
   initial burst size MAY be negotiated at login.

   Targets operate in either solicited (R2T) data mode or unsolicited
   (non R2T) data mode.  A target MAY separately enable immediate data
   without enabling the more general (separate data PDUs) form of
   unsolicited data.

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

   It is considered an error for an initiator to send unsolicited data
   PDUs to a target operating in R2T mode (only solicited data is
   allowed).  It is also an error for an initiator to send more data,
   whether immediate or as separate PDUs, than the SCSI limit for
   initial burst.  At login, an initiator MAY request, to send data
   blocks and an initial burst of any size; in this case, the target
   MUST indicate the size of the initial burst and of the immediate and
   data blocks that it is ready to accept.  The agreed upon limits for
   the initial burst as well as the maximum data PDU are recorded (and
   are retrievable from) the disconnect-reconnect mode page.

   A target SHOULD NOT silently discard data and request retransmission
   through R2T.  Initiators SHOULD NOT perform any score boarding for
   data. The residual count calculation is to be performed by the
   targets.  Incoming data is always implicitly solicited. SCSI data
   packets are matched to their corresponding SCSI commands by using
   Tags that are specified in the protocol.

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

   iSCSI initiators and targets MUST also enforce some ordering rules to
   achieve deadlock-free operation.  Unsolicited data MUST be sent on
   every connection in the same order in which commands were sent. A
   target receiving data out of order SHOULD terminate the session.



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   Each iSCSI session to a target is treated as if it originated from a
   different and logically independent initiator.

1.2.6 iSCSI Connection Termination

   Connection termination is assumed an exceptional event.
   Graceful TCP connection shutdowns are done by sending TCP FINs.
   Graceful connection shutdowns MUST only occur when there are no
   outstanding tasks that have allegiance to the connection.  A target
   SHOULD respond rapidly to a FIN from the initiator by closing it's
   half of the connection after waiting for all outstanding tasks that
   have allegiance to the connection to conclude and send their status.
   Connection termination with outstanding tasks may require recovery
   actions.

   Connection termination is also required as a prelude to recovery.  By
   terminating a connection before starting recovery, the initiator and
   target can avoid having stale PDUs being received after recovery.  In
   this case, the initiator sends a Logout request on any of the
   operational connections of a session indicating what connection
   should be terminated.

   Logout can also be issued by an initiator at the explicit request of
   a target (through an Asynchronous Event PDU).


1.2.7 Naming and Addressing

   This section provides a summary of the naming and addressing
   mechanisms used in iSCSI.  More details are provided in a separate
   document [NDT].

   All iSCSI initiators and targets are named.  Each target or initiator
   is known by a World-Wide Unique Identifier (WWUI).  The WWUI is
   independent of the location of the initiator and target. Various
   formats are provided for naming authorities to use when generating
   WWUI.  A special format of the ubiquitous internet domain name can be
   used as a name; it is important not to confuse this with an address.
   The WWUI is a UTF-8 text string, and its structure is defined in
   [NDT].

   WWUIs are used in iSCSI to provide:

      - A target identifier for configurations that present multiple
      targets behind a single IP address and port.
      - A method to recognize multiple paths to the same device on
      different IP addresses and ports.

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      - A symbolic address for source and destination targets for use
      in third party commands.
      - An identifier for initiators and targets to enable them to
      recognize each other regardless of IP address and port mapping
      on intermediary firewalls.

   The initiator MUST present both its initiator WWUI and the target
   WWUI to which it wishes to connect during the login phase.

   A target MAY also provide a canonical WWUI called "iSCSI".  This is
   not a globally unique name.  An initiator can log into this canonical
   target WWUI and use a text command called "SendTargets" to retrieve a
   list of WWUIs that exist at that address.

   The WWUI is an opaque object to iSCSI.

   In addition to names, iSCSI targets also have addresses.  An iSCSI
   address specifies a single path to an iSCSI target.  The WWUI is part
   of the address.  An iSCSI address is presented in an URL-like form,
   such as:

      <domain-name>[:<port>]/<wwui>

   Where <domain-name> is one of:

      - IPv4 address, in dotted decimal notation.  Assumed if the
      name contains exactly four numbers, separated by dots (.),
      where each number is in the range 0..255.
      - IPv6 address, in dotted decimal notation.  Assumed if the
      name contains more than four, but at most 16 numbers, separated
      by dots (.), where each number is in the range 0..255.
      - Fully Qualified Domain Name (FQDN - host name).  Assumed if
      the <domain-name> is neither an IPv4 nor an IPv6 address.

   and <wwui> is the WWUI of the target being addressed.

   The <port> in the address is optional; it specifies the TCP port
   on which the target is listening for connections.  If <port> is not
   specified, the well-known iSCSI target port is assumed.

   The iSCSI address, or URL, is not generally used within normal
   connections between iSCSI initiators and targets; it is primarily
   used during discovery.  Details are specified in [NDT].

   Examples of Worldwide Unique Identifiers:



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      com.disk-vendor.diskarrays.sn.45678
      com.gateways.yourtargets.24
      com.os-vendor.plan9.cdrom.12345
      com.service-provider.users.customer235.host90

   Examples of IPv4 addresses/names:

      10.0.0.1/com.disk-vendor.diskarrays.sn.45678
      10.0.0.2/iscsi

   Examples of IPv6 addresses/names:

      12.5.7.10.0.0.1/com.gateways.yourtargets.24
      12.5.6.10.0.0.2/iscsi

   For management/support tools, as well as naming services, that use a
   text prefix to express the protocol intended (as in http:// or
   ftp://) the following form MAY be used:

      iSCSI://<domain-name>[:port][/wwui]

   Examples:

      iSCSI://diskfarm1.acme.com/iscsi
      iSCSI://computingcenter.acme.com/com.disk-
      vendor.diskarrays.sn.45678
      iSCSI://computingcenter.acme.com:4002/com.gateways.yourtargets.
      24

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

   When a target has to act as an initiator for a third party command,
   it MAY use the initiator WWUI it learned during login as required by
   the authentication mechanism to the third party.

   To address targets and logical units within a target, SCSI uses a
   fixed length (8 bytes) uniform addressing scheme; in this document,
   we call these addresses SCSI reference addresses (SRA).

   To provide the target with the protocol specific addresses iSCSI
   relies on the SCSI aliasing mechanism (work in progress in T10).  The



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   aliasing support enables an initiator to associate protocol specific
   addresses with SRAs; the later can be used in subsequent commands.

   For iSCSI, a protocol specific address is a TCP address and a WWUI.

   An initiator may use one of a few techniques to configure and/or
   discover the target WWUIs to which it has access, along with their
   addresses.  These techniques are discussed fully in [NDT].

1.2.8 Message Synchronization and Steering

1.2.8.1 Rationale

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

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

   Unfortunately, when relying solely on the "message length in the
   iSCSI message" scheme to delineate iSCSI messages, a missing TCP
   segment that contains an iSCSI message header (with the message
   length) makes it impossible to find message boundaries in subsequent
   TCP segments. The missing TCP segment(s) must be received before any
   of the following segments can be steered to the correct SCSI buffers
   (due to the inability to determine the iSCSI message boundaries).
   Since these segments cannot be steered to the correct location, they
   must be saved in temporary buffers that must then be copied to the
   SCSI buffers.

   Different schemes can be used to recover synchronization. One of
   these schemes is detailed in an Appendix C.  To make those schemes
   work iSCSI implementations have to make sure that the appropriate

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   protocol layers are provided with enough information to implement a
   synchronization and/or data steering mechanism.

1.2.8.2 Synch and Steering Functional Model

   We assume that iSCSI is implemented according to the following
   layering scheme:

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

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

   According to our model of layering, iSCSI considers the information
   it delivers (headers and payloads) as a contiguous stream of bytes
   mapped to the positive integers from 0 to infinity. For all practical
   purposes, iSCSI is not supposed to have to handle infinitely long
   streams. The stream addressing scheme will wraps around at 2**32-1.

   It is also assumed that iSCSI will deliver to the layers beneath any
   PDU through an indivisible (atomic) operation.  If a specific
   implementation does PDU delivery to the Synch and Steering layer
   through multiple operations it MUST bracket an operation set used to
   deliver a single PDU in a manner understandable to the Synch and
   Steering Layer.

   The Synch and Steering Layer (which itself is OPTIONAL) MUST retain
   the PDU end address within the stream for every delivered iSCSI PDU.


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   To enable the Synch and Steering operation to perform Steering,
   additional information including identifying tags and buffer offsets
   MUST also be retained for every sent PDU. The Synch and Steering
   Layer is required to add to every sent data item (IP packet, TCP
   packet or some other superstructure) enough information to enable the
   receiver to steer it to a memory location independent of any other
   piece.

   If the transmission stream is built dynamically, this information is
   used to insert Synch and Steering information in the transmission
   stream (at first transmission or at re-transmission) either through a
   globally accessible table or a call-back mechanism.  If the
   transmission stream is built statically, the Synch and Steering
   information is inserted in the transmission stream.

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

   On the outgoing path, the Synch and Steering layer MUST map the
   outgoing stream addresses from iSCSI stream addresses to TCP stream
   sequence numbers.

   On the incoming path, the Synch and Steering layer extracts the Synch
   & Steering information from the TCP stream. Then it helps deliver
   (steer) the data stream to its final location and/or recover iSCSI
   PDU boundaries when some TCP packets are lost or received out of
   order.  The data stream seen by the receiving iSCSI layer is
   identical to the data stream that left the sending iSCSI layer.




















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1.2.8.3 Synch and Steering and Other Encapsulation Layers


   We recognize that in many environments the following  isa more
   appropriate layering model:

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

   In this model, UFL can be TLS or some other transport conversion
   mechanism (a mechanism changing the TCP stream but transparent to
   iSCSI).

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

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

1.2.8.4 Synch/Steering and iSCSI PDU Size

   When a large iSCSI message is sent, the TCP segment(s) that contain
   the iSCSI header may be lost.  The remaining TCP segment(s) up to the
   next iSCSI message need to be buffered (in temporary buffers) since
   the iSCSI header that indicates what SCSI buffers the data is to be
   steered to was lost.  To minimize the amount of buffering, it is

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   recommended that the iSCSI PDU size be restricted to a small value
   (perhaps a few TCP segments in length). During login, each end of the
   iSCSI session specifies the maximum size of an iSCSI PDU it will
   accept.

















































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2. 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 bits not defined MUST be set to zero. Any reserved
   fields and values MUST be 0 unless specified otherwise.

2.1 iSCSI PDU Length and Padding

   iSCSI PDUs are padded to an integer number of 4 byte words.

2.2 PDU Template, Header and Opcodes

   All iSCSI PDUs begin with one or more header segments followed by 0
   or 1 data segments.  After the entire header segment group there MAY
   be a header-digest. The data segment MAY also be followed by a data-
   digest.

   The first segment, and in many cases the only segment, (Basic Header
   Segment or BHS) is a fixed-length 44-byte header segment.
   It may be followed by Additional Header Segments (AHS). Each header
   segment is preceded by a 4-byte Next-Qualifier.  Thus, when we have
   only a BHS (with no data or digests) the net size of the iSCSI PDU is
   48 bytes.


   The overall structure of a PDU is as follows:


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| WN            |WN specific fields                             |
     +---------------+---------------+---------------+---------------+
    4/ BHS                                                           /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| WN            |WN specific fields                             |
     +---------------+---------------+---------------+---------------+
   52/ AHS                                                           /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   ----
     +---------------+---------------+---------------+---------------+
    m/ Header-Digest (optional)                                      /
    +/                                                               /

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     +---------------+---------------+---------------+---------------+
    n/ Data Segment(optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
    m/ Data-Digest (optional)                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

   All PDU segments and digests are padded to an integer number of 4
   byte words.

2.2.1 What's Next (WN)

   This is an encoded field that indicates what the next segment is.

      bit 7  - 1  Next is another header segment.
         bit 6-4  Next header type code
               0  Extended CDB
               1  Bi-directional read-data transfer header
               2  Long Data Header
             3,4,5,6,7  Reserved
         bit 3-0  Reserved
      bit 7  - 0  Next is a data segment or no additional segment
      (empty data segment)
         bit 6 Header Digest Present (1) or Not (0)
         bit 5 Data Digest Present (1) or Not (0)
         bit 4-0  Reserved


   N.B. An empty data segment MUST NOT be followed by a digest.
   N.B. A digest MUST NOT follow a segment that is followed by another
   header segment in the same PDU (i.e., only the last header segment
   MAY be followed by a digest).

















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2.2.2 WN Specific Fields

   These fields carry information specific to the next segment type.

2.2.2.1 WN Specific Fields for a Next Extended CDB Header Segment

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

   Where AddCDB is the additional CDB length in units of 4 byte words
   beyond the first extension word (i.e., AddCDB 0 means a 20 byte CDB,
   1 a 24 byte etc.).

2.2.2.2 WN Specific Fields for Next Bi-directional Read Data Header
      Segment and Long Data Transfer Header

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


2.2.2.3 WN Specific Fields for Next Data Header Segment

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| WN            | Data Length or Reserved                       |
     +---------------+---------------+---------------+---------------+

   Whenever this Next-Qualifier is preceding a Long Data Header, or a
   Long Data Header appeared earlier in the sequence, the data length
   field is ignored and the data length is taken from within this long-
   data-header (a 32 bit field). Otherwise, the length field is the data
   length. Without a Long Data Header the maximum length of a data
   segment is 16 Mbytes.

2.2.3 Header Digest and Data Digest



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   Optional header and data digests protect the integrity and
   authenticity of header and data, respectively. The digests, if
   present, appear as trailers located, respectively, after the header
   and PDU-specific data.

   The digest types are negotiated during the login phase.

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



2.2.4 Basic Header Segment (BHS)

   The Basic Header Segment is 44 bytes long.
   The Opcode field appears in all iSCSI PDUs. In addition, the
   Initiator Task Tag, Logical Unit Number, and Flags fields, when used,
   always appear in the same location in the header.



   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|X| Opcode      |F| Opcode-specific fields                      |
     |               |P|                                             |
     +---------------+---------------+---------------+---------------+
    4| LUN or Opcode-specific fields                                 |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag or Opcode-specific fields                  |
     +---------------+---------------+---------------+---------------+
   16/ Opcode-specific fields                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44

2.2.4.1 X

   The first bit of the Opcode is used as a Retry/Restart indicator

2.2.4.2 Opcode


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   The Opcode indicates what type of iSCSI PDU the header encapsulates.
   The Opcode is further encoded as follows:

      b6   Response
      b5-0 Operation

   The Opcodes are divided into two categories: initiator opcodes and
   target opcodes. Initiator opcodes are in PDUs sent by the initiators,
   and target opcodes are in PDUs sent by the target. The initiator MUST
   NOT send target opcodes and the target MUST NOT send initiator
   opcodes.  Target opcodes are also called responses and are
   distinguished by having the Response bit (bit 6) set to 1.

   Valid initiator opcodes defined in this specification are:


      0x00 NOP-Out (from initiator to target)
      0x01 SCSI Command (encapsulates a SCSI Command Descriptor
      Block)
      0x02 SCSI Task Management Command
      0x03 Login Command
      0x04 Text Command
      0x05 SCSI Data (for WRITE operation)
      0x06 Logout Command
      0x10 SACK Request

   Valid target opcodes are:


      0x40 NOP-In (from target to initiator)
      0x41 SCSI Response (contains SCSI status and possibly sense
      information or other response information)
      0x42 SCSI Task Management Response
      0x43 Login Response
      0x44 Text Response
      0x45 SCSI Data (for READ operation)
      0x46 Logout Response
      0x50 Ready To Transfer (R2T - sent by target to initiator when
      it is ready to receive data from initiator)
      0x51 Asynchronous Message (sent by target to initiator to
      indicate certain special conditions)
      0x6f Reject

   Initiator opcodes 0x30-0x3f and target opcodes 0x70-0x7f are vendor
   specific codes.



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2.2.4.3 Opcode-specific Fields

   These fields have different meanings for different messages.
   Bit 7 of the second byte is used as a Poll/Final bit (P/F bit) for
   some iSCSI PDUs and must be 0 in all other iSCSI PDUs.  When used as
   a Poll bit it indicates that an answer is required.  When used as a
   Final bit it indicates a Final PDU in a logical sequence (e.g., the
   last Data PDU of unsolicited or solicited data PDU sequence or the
   perceived final Request/Response of the Login Phase).

2.2.4.4 LUN

   Some opcodes operate on a specific Logical Unit. The Logical Unit
   Number (LUN) field identifies which Logical Unit.  If the opcode does
   not relate to a Logical Unit, this field either is ignored or may be
   used for some other purpose.  The LUN field is 64-bits in accordance
   with [SAM2]. The exact format of this field can be found in the
   [SAM2] document.

2.2.4.5 Initiator Task Tag

   The initiator assigns a Task Tag to each iSCSI task that it issues.
   While a task exists this tag MUST uniquely identify it session-wide.


2.2.5 Extended CDB Additional Header Segment

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


2.2.6 Bi-directional Read Additional Header Segment

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| Bi-directional Read Expected Data Length                      |
     +---------------+---------------+---------------+---------------+


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2.2.7 Long Data Additional Header Segment

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











































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2.3 SCSI Command

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|X| 0x01        |F|R|W|0 0|ATTR | Reserved      | CmdRN or Rsvd |
     +---------------+---------------+---------------+---------------+
    4| Logical Unit Number (LUN)                                     |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Expected Data Transfer Length                                 |
     +---------------+---------------+---------------+---------------+
   20| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN or EndDataSN                                        |
     +---------------+---------------+---------------+---------------+
   28/ SCSI Command Descriptor Block (CDB)                           /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44


2.3.1 Flags and Task Attributes

      The flags for a SCSI Command are:

      b7   (F) set to 1 when the immediate data that accompany the
      command are all the data associated with this command. It is an
      error if the Length and Expected Length do not match and this
      bit is set to 1
      b6   (R) set to 1 when input data is expected
      b5   (W) set to 1 when output data is expected
      b3-4 Reserved (MUST be 0)
      b0-2 used to indicate Task Attributes

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

      0    Untagged
      1    Simple
      2    Ordered
      3    Head of Queue

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      4    ACA

2.3.2 CmdRN

   SCSI command reference number - if present in the SCSI execute
   command arguments

2.3.3 CmdSN - Command Sequence Number

   Enables ordered delivery across multiple connections in a single
   session.

2.3.4 ExpStatSN/EndDataSN - Expected Status Sequence Number

   Command responses up to ExpStatSN-1 (mod 2**32) have been received
   (acknowledges status) on the connection.  If the command is a retry
   (the X bit is 1) this field will contain the last consecutive input
   DataSN number seen by the initiator (no gaps) for this command in a
   previous execution or 0x'ffffffff'.

2.3.5 Expected Data Transfer Length

   For unidirectional operations, the Expected Data Transfer Length
   field states the number of bytes of data involved in this SCSI
   operation.  For a WRITE (W flag set to 1 and R flag set to 0)
   operation, the initiator uses this field to specify the number of
   bytes of data it expects to transfer for this operation.  For a READ
   (W flag set to 0 and R flag set to 1) operation, the initiator uses
   this field to specify the number of bytes of data it expects the
   target to transfer to the initiator.  It corresponds to the SAM-2
   byte count.

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

   For bi-directional operations (both R and W flags are set to 1), this
   field states the number of data bytes involved in the outbound
   transfer. For bi-directional operations, an additional header segment
   MUST be present in the header sequence indicating the Expected Bi-
   directional Read Data Length.  If this additional header segment is
   absent, the Expected Bi-directional Read Data Length is assumed 0.

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

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2.3.6 CDB - SCSI Command Descriptor Block

   There are 16 bytes in the CDB field to accommodate the commonly used
   CDB.  Whenever larger CDBs are used, the CDB spillover MAY extend
   beyond the 48-byte header.

2.3.7 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 (a data segment).  Alternatively, user data (as from a
   WRITE operation) can be placed in the same PDU (both cases referred
   to as immediate data). Those data are governed by the general rules
   for solicited vs. unsolicited data.





































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2.4 SCSI Response

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x41          |1|Rsv|S|o|u|O|U| Reserved (0)  |Status/Response|
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Basic Residual Count                                          |
     +---------------+---------------+---------------+---------------+
   20| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| EndDataSN or Reserved (0)                                     |
     +---------------+---------------+---------------+---------------+
   36| R2TEndDataSN or Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40| Bidi-Read Residual Count                                      |
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Sense Data (optional) or Response Data                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.4.1 Byte 1 - Flags

      b0   (U) set for Residual Underflow. In this case, the Basic
      Residual Count indicates how many bytes were not transferred
      out of those expected to be transferred.
      b1   (O) set for Residual Overflow. In this case, the Basic
      Residual Count indicates how many bytes could not be
      transferred because the initiator's Expected Data Transfer
      Length was too small.
      b2   (u) same as b0 but for the read-part of a bi-directional
      operation

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      b3   (o) same as b1 but for the read-part of a bi-directional
      operation
      b4   (S) Status-Response selector - if 1, the response contains
      a valid SCSI status otherwise it contains a valid iSCSI
      Response
      b5-7 Reserved

   Bits O and U are mutually exclusive and so are bits o and u.
   For a response (S=0) b0-b3 MUST be 0.

2.4.2 Status/Response

   The Status field is used to report the SCSI status of the command (as
   specified in [SAM2]).  The Response is used to report a Service
   Response. The exact mapping of the iSCSI response codes to SAM
   service response symbols is outside the scope of this document.

   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 the a Data PDU with the F bit set before
   sending the Response PDU.

   Valid iSCSI Response codes are:

      1 - Target Failure
      2 - Delivery Subsystem Failure
      3 - Unsolicited data rejected
      4 - SACK rejected

2.4.3 Basic Residual Count

   The Basic Residual Count field is valid only in the case where either
   the U bit or the O bit is set. If neither bit is set, the Basic
   Residual Count field SHOULD be zero.  If the U bit is set, the Basic
   Residual Count indicates how many bytes were not transferred out of
   those expected to be transferred.  If the O bit is set, the Basic
   Residual Count indicates how many bytes could not be transferred
   because the initiator's Expected Data Transfer Length was too small.

2.4.4 Bidi-Read Residual Count

   The Bidi-Read Residual Count field is valid only in the case case
   where either the u bit or the o bit is set. If neither bit is set,
   the Bidi-Read Residual Count field SHOULD be zero.  If the u bit is
   set, the Bidi-Read Residual Count indicates how many bytes were not
   transferred to the initiator out of those expected to be transferred.

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   If the o bit is set, the Bidi-Read Residual Count indicates how many
   bytes could not be transferred to the initiator because the
   initiator's Expected Bidi-Read Transfer Length was too small.



2.4.5 Sense or Response Data

   iSCSI targets MUST support and enable autosense.  If the Command
   Status was CHECK CONDITION (0x02), then the Sense Data field will
   contain sense data for the failed command.

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


2.4.6 EndDataSN

   One past the largest DataSN in an input (read) data PDU the target
   has sent for the command. 0 means no data PDUs where sent.

2.4.7 R2TEndDataSN

   One past the largest DataSN in an R2T PDU the target has sent for the
   command. 0 means no R2T PDUs where sent.

2.4.8 StatSN - Status Sequence Number

   StatSN is a Sequence Number that the target iSCSI layer generates per
   connection and that in turn enables the initiator to acknowledge
   status reception. StatSN is incremented by 1 for every
   response/status sent on a connection except for responses sent as a
   result of a retry or SACK. For responses sent because of retry the
   StatSN used MUST be the same as the first time the PDU was sent
   unless the connection was restarted since then.

2.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator

   ExpCmdSN is a Sequence Number that the target iSCSI returns to the
   initiator to acknowledge command reception. It is used to update a
   local counter with the same name.

2.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator





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   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 counter with the same name.

   MaxCmdSN and ExpCmdSN are processed as follows:

      -if the PDU MaxCmdSN is less than the PDU ExpCmdSN (in Serial
      Arithmetic Sense and with a difference bounded by 2**31-1),
      they are both ignored
      -if the PDU MaxCmdSN is less than the current MaxCmdSN (in
      Serial Arithmetic Sense and with a difference bounded by 2**31-
      1), it is ignored; else it updates MaxCmdSN
      -if the PDU ExpCmdSN is less than the current ExpCmdSN (in
      Serial Arithmetic Sense and with a difference bounded by 2**31-
      1), it is ignored; else it updates ExpCmdSN

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

































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2.5 SCSI Task Management Command

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|X| 0x02        |0| Function    | Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
    4| Logical Unit Number (LUN) or Reserved (0)                     |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Referenced Task Tag or Reserved (0x'ffffffff')                |
     +---------------+---------------+---------------+---------------+
   20| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44

2.5.1 Function

   The Task Management functions provide an initiator with a way to
   explicitly control the execution of one or more Tasks. The Task
   Management functions are summarized as follows (for a more detailed
   description see the [SAM2] document):

      1    Abort Task - aborts the task identified by the Referenced
      Task Tag field.
      2    Abort Task Set - aborts all Tasks issued by this initiator
      on the Logical Unit.
      3    Clear ACA - clears the Auto Contingent Allegiance
      condition.
      4    Clear Task Set - Aborts all Tasks (from all initiators)
      for the Logical Unit.
      5    Logical Unit Reset
      6    Target Warm Reset
      7    Target Cold Reset




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   For all these functions, the SCSI Task Management Response MUST be
   returned using the Initiator Task Tag to identify the operation for
   which it is responding.

   For the <Clear Task Set>, if the SCSI control mode enables AE
   reporting, the target MUST send an Asynchronous Event to all other
   attached initiators to inform them that all pending tasks are
   cancelled. The target MUST then enter the ACA state for any initiator
   for which it had pending tasks.

   For the <Target Warm Reset> and <Target Cold Reset> functions, the
   target cancels all pending operations and are both equivalent to the
   Target Reset as specified by SAM-2.  Provided that SCSI control mode
   enables AE reporting, the target MUST send an Asynchronous Event to
   all attached initiators notifying them that the target is being
   reset.

   In addition, for the <Target Warm Reset> the target enters the ACA
   state on all sessions and all LUs on which an AE was sent.

   In addition, for the <Target Cold Reset> the target then MUST
   terminate all of its TCP connections to all initiators (all sessions
   are terminated). However, if the target finds that it cannot send the
   required response or AEN, it MUST continue the reset operation and it
   SHOULD log the condition for later retrieval. The logging operation
   MUST be reported through the target MIB.

   Further actions on reset functions are specified in the relevant SCSI
   documents for the specific class of devices.


2.5.2 Referenced Task Tag

   Initiator Task Tag of the task to be aborted - for abort task















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2.6 SCSI Task Management Response


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x42          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Logical Unit Number (LUN)                                     |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Referenced Task Tag or Reserved (0x'ffffffff')                |
     +---------------+---------------+---------------+---------------+
   20| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| Response      | Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44

   For the functions <Abort Task, Abort Task Set, Clear ACA, Clear Task
   Set, Logical Unit reset, Target Warm Reset>, the target performs the
   requested Task Management function and sends a SCSI Task Management
   Response back to the initiator. The target provides a Response, which
   may take on the following values:

       0    Function Complete
       1    Task was not in task set
      255   Function Rejected

   For the <Target Cold Reset> and <Target Warm Reset> functions, the
   target cancels all pending operations. If SCSI control mode enables
   AE reporting, the target MUST send an Asynchronous Event to all
   attached initiators notifying them that the target has been reset.



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   For the <Target Cold Reset> 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 is
   outside the scope of this document.

2.6.1 Referenced Task Tag

   Initiator Task Tag of the task not found











































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2.7 SCSI Data

   The typical data transfer specifies the length of the data payload,
   the Target Transfer Tag provided by the receiver for this data
   transfer, and a buffer offset.  The typical SCSI Data packet for
   WRITE (from initiator to target) has the following format:


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|0| 0x05        |F| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| LUN or Reserved (0)                                           |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Target Transfer Tag or (0x'ffffffff')                         |
     +---------------+---------------+---------------+---------------+
   20| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   28| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   32| DataSN                                                        |
     +---------------+---------------+---------------+---------------+
   36| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   40| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Payload                                                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+








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   The typical SCSI Data packet for READ (from target to initiator) has
   the following format:


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x45          |F|   (0) |S|O|U| Reserved (0)  |Status or Rsvd |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| StatSN or Reserved (0)                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| DataSN                                                        |
     +---------------+---------------+---------------+---------------+
   36| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   40| Residual Count                                                |
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Payload                                                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.7.1 F (Final) Bit

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

   For incoming data, this bit is 1 for the last input data PDU
   associated with the command (even if it includes the status).

2.7.2 Target Transfer Tag

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   On outgoing data, the Target Transfer Tag is provided to the target
   if the transfer is honoring a R2T. In this case, the Target Transfer
   Tag field is a replica of the Target Transfer Tag provided with the
   R2T.
   The Target Transfer Tag values are not specified by this protocol
   except that the all-bits-one value (0x'ffffffff') 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.


2.7.3 StatSN

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


2.7.4 DataSN

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

   For output (write) data PDUs, the DataSN is the data PDU number
   (starting with 0) within the current output sequence. The current
   output sequence is identified by the Initiator Task Tag (for
   unsolicited data) or by the Target Task Tag and LUN (for data
   solicited through R2T).

   0x'ffffffff' is not a valid DataSN and MUST be skipped when counting
   (serial arithmetic)

2.7.5 Buffer Offset

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

   Input data ordering is governed by a disconnect-reconnect mode page
   bit (EMDP). If this bit is 1 the target MUST deliver packets in
   increasing buffer offset order.

   Output data within a burst (initial or any data PDU sequence that
   fulfils a R2T) MUST be delivered in increasing buffer offset order.


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2.7.6 Flags

   The last SCSI Data packet sent from a target to an initiator for a
   particular SCSI command that completed successfully may also
   optionally contain the Command 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 packet and must not be sent in a
   SCSI Data packet.

      b0-1 as in an SCSI Response
      b2   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
      b3-6 not used (should be set to 0)


   If the S bit is set to 1, then there is meaning to the extra fields
   in the SCSI Data packet (StatSN, Command Status, Residual Count).
































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2.8 Text Command

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


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|0| 0x04        |F| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Text                                                          /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.8.1 F (Final) Bit

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

2.8.2 Initiator Task Tag

   The initiator assigned identifier for this Text Command.
   If the command is sent as part of a sequence of commands (e.g., the
   Login Phase or a sequence of Text commands) the Initiator Task Tag

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   MUST be the same for all the commands within the sequence (similar to
   linked SCSI commands).

2.8.3 Text

   The initiator sends the target a set of key=value or key=list pairs
   encoded in UTF-8 Unicode. The key and value are separated by a '='
   (0x3D) delimiter. Many key=value pairs can be included in the Text
   block by separating them with null (0x00) delimiters.  A list is a
   set of values separated by comma (0x2C). Large binary items can be
   encoded using their hexadecimal representation (e.g., 8190 is
   0x1FFE).

   Character strings are represented as plain text. Numeric and binary
   values are represented using either decimal numbers or the
   hexadecimal 0x'ffff' notation. The result is adjusted to the specific
   key.

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

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

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

      X-com.acme.bar.foo.do_something=0000000000000003

   Any other key not understood by the target may be ignored without
   affecting basic function.

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

   It is recommended that Text operations that will take a long time
   should be placed in their own Text command.  If the Text Response
   does not contain a key that was requested, the initiator must assume
   that the key was not understood by the target or, whenever
   appropriate, that the response was "none".

   Targets and initiators may limit the size of the text accepted in a
   text command and text response as well as the size of key=value
   pairs.  Such limits should be indicated at login.


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2.9 Text Response

   The Text Response message contains the target's responses to the
   initiator's Text Command. The format of the Text field matches that
   of the Text Command.


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x44          |F| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Text                                                          /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.9.1 F (Final) Bit

   When set to 1 in response to a text command with the Final bit set to
   1 the F bit indicates that the target has finished it's operation.
   Otherwise if set to 0 in response to a text command with the Final
   Bit set to 1 it indicates that the target has more work to do
   (invites a follow-on text command).  A text response with the F bit
   set to 1 in response to a text command with the F bit set to 0 is a
   protocol error.


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2.9.2 Initiator Task Tag

   The Initiator Task Tag matches the tag used in the initial Text
   Command or the Login Initiator Task Tag.

2.9.3 Text Response

   The Text Response field contains responses in the same key=value
   format as the Text Command. Appendix C lists some basic Text Commands
   and their Responses.  If the Text Response does not contain a key
   that was requested, the initiator must assume that the key was not
   understood by the target or that the answer is <key>=none.








































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2.10 Login Command

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

   A Login Command MUST NOT be issued more than once on an iSCSI TCP
   connection.


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|X| 0x03        |F| Reserved (0)| Version-max   | Version-min   |
     +---------------+---------------+---------------+---------------+
    4| CID                           | Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
    8| ISID                          |TSID                           |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| InitCmdSN   or   Reserved (0)                                 |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN   or   Reserved (0)                                 |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44/ Login Parameters in Text Command Format                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.10.1 X - Restart

   If this bit is set to 1 then this command is an attempt to reinstate
   a failed connection. CID does not change and this command is performs
   first the logout function of the old connection if an explicit logout
   is not performed earlier.

2.10.2 F (Final) Bit

   If set to 1 indicates that the initiator has no more parameters to
   set.

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2.10.3 Version-max

   Maximum Version number supported.

2.10.4 Version-min

   Minimum Version supported
   The version number of the current draft is 0x1.



2.10.5 CID

   This is a unique ID for this connection within the session.


2.10.6 ISID

   This an initiator defined session-identifier.  It MUST be the same
   for all connections within a session.

2.10.7 InitCmdSN

   Is significant only if TSID is zero and indicates the starting
   Command Sequence Number for this session; it SHOULD be zero for all
   other instances.

2.10.8 ExpStatSN

   This is ExpStatSN for the old connection.
   This field is valid only if the X bit is set to 1.


2.10.9 Login Parameters

   The initiator MAY provide some basic parameters in order to enable
   the target to determine if the initiator may use the target's
   resources and the initial text parameters for the security exchange.
   The format of the parameters is as specified for the Text Command.
   Keys and their explanations are listed in the Appendixes.








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2.11 Login Response

   The Login Response indicates the progress and/or end of the login
   phase.  Note that after security is established, the login response
   is authenticated.


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x43          |F| Reserved (0)| Version-max   | Version-active|
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
    8| ISID                          |TSID                           |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| InitStatSN                                                    |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| Status-Class  | Status-Detail |                                |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Login Parameters in Text Command Format                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.11.1 Version-max

   This is the highest version number supported by the target.


2.11.2 Version-active/lowest



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   Indicates the version supported (the highest version supported by the
   target and initiator). If the target is not supporting 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.

2.11.3 InitStatSN

   This is the starting status Sequence Number for this connection. The
   value is relevant for all subsequent responses. If the login phase
   involves two login responses then each of them will hold for the
   subsequent responses.

2.11.4 Status-Class and Status-Detail

   The Status returned in a Login Response indicates the status of the
   login request. The status includes:

      Status-Class
      Status-Detail

   The Status-Class is sufficient for a simple initiator to use when
   handling errors, without having to look at the Status-Detail.  The
   Status-Detail allows finer-grained error recovery for more
   sophisticated initiators, as well as better information for error
   logging.

   The status classes are as follows:

      0 - Success - indicates that the iSCSI target successfully
      received, understood, and accepted the request.

      1 - Redirection - indicates that further action must be taken
      by the initiator to complete the request. This is usually due
      to the target moving to a different address. All of the status
      class 3 responses MUST return one or more text key parameters
      of the type "TargetAddress", which indicates the target's new
      address.

      2 - Initiator Error - indicates that the initiator likely
      caused the error. This MAY be due to a request for a resource
      for which the initiator does not have permission.

      3 - Target Error - indicates that the target is incapable of
      fulfilling the request.



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   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.  The allowable state of the
   Final (F) bit in responses with each of the codes is also displayed.

   -----------------------------------------------------------------
   Status        | Code |  F  |   Description
                 |(hex) | bit |
   -----------------------------------------------------------------
   Accept Login  | 0000 | 1/0 | Login is OK, moving to Full Feature
                 |      |     | Phase (F=1) or Operational Parameter
                 |      |     | Negotiation (F=0).
   -----------------------------------------------------------------
   Authenticate  | 0001 | 0   | The target WWUI exists and
                 |      |     | authentication proceeds.
   -----------------------------------------------------------------
   Target WWUI   | 0002 | 0   | The target WWUI has to be provided
    required     |      |     | before authentication proceeds.
   -----------------------------------------------------------------
   Target Moved  | 0101 | 1   | The requested target WWUI has moved
   Temporarily   |      |     | temporarily to the address provided.
   -----------------------------------------------------------------
   Target Moved  | 0102 | 1   | The requested target WWUI has moved
   Permanently   |      |     | permanently to the address provided.
   -----------------------------------------------------------------
   Proxy Required| 0103 | 1   | The initiator must use an iSCSI
                 |      |     | proxy for this target.
                 |      |     | The address is provided.
   -----------------------------------------------------------------
   Authentication| 0201 | 1   | The initiator authentication failed.
   Failed        |      |     |
   -----------------------------------------------------------------
   Forbidden     | 0202 | 1   | The initiator is not allowed access
   Target        |      |     | to the given target.
   -----------------------------------------------------------------
   Not Found     | 0203 | 1   | The requested Target WWUI does not
                 |      |     | exist at this address.
   -----------------------------------------------------------------
   Target Removed| 0204 | 1   | The requested target WWUI has been
                 |      |     | removed. No forwarding address is
                 |      |     | provided.
   -----------------------------------------------------------------
   Target        | 0205 | 1   | Target is currently in use by
   Conflict      |      |     | another initiator and does
                 |      |     | not support multiple initiators.
   -----------------------------------------------------------------


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   Initiator     | 0206 | 1   | Invalid ISID or single connection
   SID error     |      |     |
                 |      |     |
   -----------------------------------------------------------------
   Target Error  | 0300 | 1   | An error occurred in the iSCSI
                 |      |     | target (out of resources, etc.).
   -----------------------------------------------------------------
   Service       | 0301 | 1   | The iSCSI service or target is not
   Unavailable   |      |     | currently operational. This is
                 |      |     | usually due to maintenance.
   -----------------------------------------------------------------
   Unsupported   | 0302 | 1   | The required version is not
   version       |      |     | supported by the target.
   -----------------------------------------------------------------

   If the Status is "accept login" (0x0000) and the F bit is 1, the
   initiator may proceed to issue SCSI commands. If the Status is
   "accept login" (0x0000) and the F bit is 0, the initiator may proceed
   to negote operational parameters. The target MUST not set the Status
   to 0x'0000' and the F bit to 1 if the Login Command had the F bit set
   to 0.

   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.



2.11.5 TSID

   The TSID is an initiator identifying tag set by the target.  A 0 in
   the returned TSID indicates that either the target supports only a
   single connection or that the ISID has already been used as a leading
   ISID. In both cases, the target rejects the login.

2.11.6 F (Final) bit

   Final bit is set to one in the Final Login Response. A Final bit of 0
   indicates a "partial" response, which means "more negotiation
   needed".
   TSID must be returned in the partial response and the same value must
   be presented with the final response.




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2.12 NOP-Out


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x00          |P| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| LUN                                                           |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag or Reserved (0x'ffffffff')                 |
     +---------------+---------------+---------------+---------------+
   16| Target Transfer Tag or Reserved (0x'ffffffff')                |
     +---------------+---------------+---------------+---------------+
   20| CmdSN or (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN or (0)                                              |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Ping Data (optional)                                          /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

   The NOP-Out with the P bit set acts as a "ping command".
   This form of the NOP-Out can be used to verify that a connection is
   still active and all its components are operational. This command MAY
   use in-order delivery or immediate delivery. The NOP-Out may be
   useful in the case where an initiator has been waiting a long time
   for the response to some command, and the initiator suspects that
   there is some problem with the connection.  When a target receives
   the NOP-Out with the Ping bit set, it should respond with a Ping
   Response, duplicating the data that was provided in the NOP-Out as
   much as possible.  If the initiator does not receive the NOP-In
   within some time (determined by the initiator), or if the data
   returned by the NOP-In is different from the data that was in the
   NOP-Out, the initiator may conclude that there is a problem with the
   connection. The initiator then closes the connection and may try to
   establish a new connection.


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   The NOP-Out can be sent by an initiator because of a NOP-In with the
   poll bit set, in which case the Target Tag copies the NOP-In value
   and the P bit MUST be 0.


2.12.1 P (Ping) Bit

   Request a NOP-In


2.12.2 Initiator Task Tag

   An initiator assigned identifier for the operation.

   The NOP-Out MUST have the Initiator Task Tag set only if the P bit is
   1.

2.12.3 Target Transfer Tag

   A target assigned identifier for the operation.

   The NOP-Out MUST have the Target Tag set only if it issued in
   response to a NOP-In with the P bit one, in which case it copies the
   Target Transfer Tag from the NOP-In PDU.
   When the Target Transfer Tag is set the LUN field must have the
   correct value for the task.

2.12.4 Ping Data

   Ping data is reflected in the Ping Response. Note that the length of
   the reflected data is limited by a negotiated parameter and the
   initiator SHOULD avoid sending more than the negotiated limit.

















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2.13 NOP-In


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x40          |P| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| LUN or Reserved (0)                                           |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag or Reserved (0x'ffffffff')                 |
     +---------------+---------------+---------------+---------------+
   16| Target Transfer Tag or Reserved (0x'ffffffff')                |
     +---------------+---------------+---------------+---------------+
   20| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Return Ping Data                                              /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


   When a target receives the NOP-Out with the P bit set, it MUST
   respond with a NOP-In with the same Initiator Task Tag that was
   provided in the NOP-Out Command. It SHOULD also duplicate as much of
   the initiator provided Ping Data as allowed by a configurable target
   parameter. For such a response the P bit MUST be 0.

2.13.1 P bit

   A target may issue a NOP-In on its own to test the connection and the
   state of the initiator. If the target wants to test the initiator, it
   sets the P bit to 1 in order to ask for an answer from the initiator.
   In this case the Initiator Task Tag MUST be 0x'ffffffff' and the
   Target Tag MUST be set to a valid value (not 0x'ffffffff').  The LUN

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   field MUST also contain a valid LUN. If the target wants only to test
   the connection, the P bit is set to 0 and both tags MUST hold the
   reserved value 0x'ffffffff'.

   Whenever the NOP-In is not issued in response to a NOP-Out the StatSN
   field will contain as usual the next StatSN but StatSN for this
   connection is not advanced.

2.13.2 Target Transfer Tag

   A target assigned identifier for the operation.

2.13.3 LUN

   A LUN must be set to a correct value when the P bit is set to 1 and
   the Target Transfer Tag is set.




































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2.14 Logout Command

   The Logout command is used to perform a controlled closing of a
   connection.

   An initiator MAY use a logout command to remove a connection from a
   session or to close an entire session.

   If an initiator intends to start recovery for a failing connection it
   MUST use either the Logout command to "clean-up" the target end of a
   failing connection and enable recovery to start, or use the restart
   option of the Login command for the same effect.  In sessions with a
   single connection, this may imply the opening of a second connection
   with the sole purpose of cleaning-up the first.

   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x06          |1| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| CID                           | Reserved (0)  |Reason Code    |
     +---------------+---------------+---------------+---------------+
    8| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   24| ExpStatSN or (0)                                              |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44

2.14.1 CID

   This is the connection ID of the connection to be closed (including
   closing the TCP stream). This field is valid only if the reason code
   is not "close connection"

2.14.2 ExpStatSN

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

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2.14.3 Reason Code

   Indicate the reason for Logout:

      0 - closes the session
      1 - removes the connection for recovery
      2 - removes the connection at target's request (requested
      through an Asynchronous Message)












































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2.15 Logout Response

   The logout response is used by the target to indicate that the
   cleanup operation for the failed connection has completed.

   After Logout, the TCP connection referred by the CID MUST be closed
   at both ends (or all connections must be closed if the logout reason
   was session close).




   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x46          |1| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| Response      | Reserved (0)                                  |
     +---------------------------------------------------------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44



2.15.1 Response

   Logout response:

      0 - connection closed successfully
      1 - cleanup failed

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2.16 SACK Request


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x10          |1|Reserved(0)|D|               | AddRuns       |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag or Reserved (0x'ffffffff')                 |
     +---------------+---------------+---------------+---------------+
   16| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   20| BegRun                                                        |
     +---------------+---------------+---------------+---------------+
   24| RunLength                                                     |
     +---------------+---------------+---------------+---------------+
   28/ Additional Runs or Reserved (0)                               /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44

   SACK request is used to request retransmission of status or data PDUs
   from the target. It also implicitly acknowledges data or status PDUs.
   The SACK request indicates to the target the missed status or data
   runs, where a run is composed of an initial missed StatSN or DataSN
   and the number of additional missed Status or Data PDUs (0 means only
   the initial).

2.16.1 D

   If 1, indicates that this is a Data SACK; otherwise it is a status
   SACK.
   The data SACK for a command MUST precede implicit or explicit status
   acknowledgement for the given command.
   For a data SACK, the Initiator Task Tag has to be set to the
   Initiator Task Tag of the referenced Command.

2.16.2 AddRun

   Runs are gaps in sequence numbers as perceived by the receiver. Each
   run is characterized by a starting sequence and a length.

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   This field specifies the number of additional runs (0, 1, or 2 are
   the only valid values).


2.16.3 BegRun

   First missed DataSN or StatSN

2.16.4 RunLength

   Number of additional missed DataSN or StatSN. If BegRun is the only
   one missing RunLength MUST be 0.







































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2.17 Ready To Transfer (R2T)

   When an initiator has submitted a SCSI Command with data passing from
   the initiator to the target (WRITE), the target may specify which
   blocks of data it is ready to receive. In general, 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) message.

   In order to allow write operations without R2T, the initiator and
   target MUST have agreed to do so by sending the UseR2T=no key-pair to
   each other, which happens either during Login or through the Text
   Command/Response mechanism.

   An R2T MAY be answered with one or more iSCSI Data-out PDU with a
   matching Target Transfer Tag. If an R2T is answered with a single
   Data PDU, the Buffer Offset in the Data PDU MUST be the same as the
   one specified by the R2T. The data length of the Data PDU must not
   exceed the Desired Data Length specified in R2T. If the R2T is
   answered with a sequence of Data PDUs, the Buffer Offset and Length
   MUST be within the range of those specified by R2T. The last PDU
   should have the F bit set to 1.


   The target may send several R2T PDUs and thus have a number of data
   transfers pending.  All outstanding R2Ts should have different Target
   Transfer Tags. Within a connection, outstanding R2Ts MUST be
   fulfilled by the initiator in the order in which they where received.


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x50          |1| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Reserved (0)                                                  |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   16| Target Transfer Tag                                           |
     +---------------+---------------+---------------+---------------+


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   20| StatSN                                                  |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| DataSN                                           |
     +---------------+---------------+---------------+---------------+
   36| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   40| Desired Data Length                                           |
     +---------------------------------------------------------------+
     | Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   44

2.17.1 DataSN

   DataSN is the R2T PDU number (starting with 0) within the command
   identified by the Initiator Task Tag.

   0x'ffffffff' is not a valid DataSN and MUST be skipped when counting
   (serial arithmetic)

2.17.2 Desired Data Transfer Length and Buffer Offset

   The target specifies how many bytes it wants the initiator to send
   because of this R2T message.  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.


2.17.3 Target Transfer Tag

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





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2.18 Asynchronous Message

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


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x51          |1| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Logical Unit Number (LUN)                                     |
     +                                                               +
    8|                                                               |
     +---------------+---------------+---------------+---------------+
   12/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   20| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   24| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   28| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32|SCSI Event     |iSCSI Event    | Parameter1 or Reserved (0)    |
     +---------------+---------------+---------------+---------------+
   36| Parameter2 or Reserved (0)     | Reserved (0)                 |
     +---------------+---------------+---------------+---------------+
   40| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   44| Digests if any...                                             |
     +---------------+---------------+---------------+---------------+
     / Sense Data                                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


   Some Asynchronous Messages are strictly related to iSCSI while others
   are related to SCSI [SAM-2}. An Asynchronous Message may contain both
   types of events.

   Please note that StatSN counts this PDU as an acknowledgeable event,
   allowing initiator and target state synchronization.


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2.18.1 iSCSI Event

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

      1    Target is being reset.
      2    Target requests Logout - the Parameter1 field indicates on
      what CID.
      3    Target indicates it will/has dropped the connection - the
      Parameter1 field will indicate on what CID while the Parameter2
      field indicates, in seconds, the minimum time to reconnect.

2.18.2 SCSI Event

   The following values are defined.  (See [SAM2] for details):

      1    An error condition was encountered after command
      completion.
      2    A newly initialized device is available to this initiator.
      3    Some other type of unit attention condition has occurred.
      4    An asynchronous event has occurred.

   Event 4 also includes the case where all Task Sets are Reset by
   another Initiator.
   Sense Data that accompanies the report identifies the condition.  The
   Length parameter is set to the length of the Sense Data.

   For new device identification, an iSCSI target MUST support the
   Device Identification page.





















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2.19 Third Party Commands

   SCSI allows every addressable entity to be either an initiator or a
   target. In host-to-host communication, each such entity can take on
   the initiator role.  In typical I/O operations between a host and a
   peripheral subsystem, the host plays the initiator role and the
   peripheral subsystem plays the target role.

   For EXTENDED COPY and other third party SCSI commands, that involve
   device-to-device communication, such as (EXTENDED) COPY and COMPARE,
   SCSI defines a copy-manager. The copy-manager takes on the role of
   initiator in the device-to-device communication.  The copy-manager is
   the "original-target" of the command and acts as initiator for a
   (variable) number of the devices, which are called sources and
   destinations. Sources and destinations act as targets.  The whole
   operation is described by one "master CDB" that is delivered to the
   copy-manager and a series of descriptor blocks; each descriptor block
   addresses a source and destination target, LU and a description of
   the work to be done in terms of blocks or bytes as required by the
   device types. The relevant SCSI standards do not require full support
   of the (EXTENDED) COPY or COMPARE, nor do they provide a detailed
   execution model.

   Enabling a FC copy-manager to support iSCSI sources and destinations
   is subject to coordination with T10.
























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2.20 Reject


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0|   0x6f        |1| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   36| Reason        | Reserved (0)  | First Bad Byte or Rsvd(0)     |
     +---------------+---------------+---------------+---------------+
   40| Reserved (0)                                                  |
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   44/ Complete Header of Bad Message                                /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   xx


   It may happen that a target receives a message with a format error
   (e.g., inconsistent fields, reserved fields not 0, inexistent LUN
   etc.) or a digest error (e.g., invalid payload or header). The target
   returns the header of the message in error as the data of the
   response.

2.20.1 Reason

   The reject Reason is coded as follows:

      1 - Format Error
      2 - Header Digest Error
      3 - Payload Digest Error
      4 - Data-SACK Reject
      5 - Command Retry Reject
      15 - Full Feature Phase Command before login

2.20.2 First Bad Byte

   For a format error reject, this is the offset of the first offending
   byte in the header.



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3. SCSI Mode Parameters for iSCSI

   This chapter describes fields and mode pages that control and report
   the behavior of the iSCSI protocol. All fields not described here
   MUST control the behavior of iSCSI devices as defined by the
   corresponding command set standard.

3.1 iSCSI Disconnect-Reconnect Mode Page

3.1.1 Enable Modify Data Pointers Bit

   This field is used to control incoming data ordering. Incoming data
   PDUs can be in any order (EMDP = 1) or at continuously increasing
   addresses (EMDP = 0).
   EMDP can also be set by a text-mode key=value pair (InDataOrder).


3.1.2 Maximum Burst Size Field (16 bit)

   This field is used by iSCSI to define the maximum data payload in
   iSCSI data PDUs or as immediate data in command PDUs in units of 512
   bytes. This value can also be set by a text-mode key=value pair
   (DataPDULength).

3.1.3 First Burst Size Field (16 bit)

   This field is used by iSCSI to define the maximum  amount of
   unsolicited data an iSCSI initiator is allowed to send to the target
   in units of 512 bytes. This value can also be set by a text-mode
   key=value pair (FirstBurstSize).

3.1.4 Other Fields

   No other fields in this page are used by iSCSI.

3.2 iSCSI Logical Unit Control Mode Page

3.2.1 Protocol Identifier

   This field is set to the iSCSI code set by T10 (xx)

3.2.2 Enable CmdRN

   When this field is set to 1 the CmdRN field is valid.
   This field can also be set by a text-mode key=value pair
   (EnableCmdRN).



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3.3 iSCSI Port Control Mode Page

   No field in this page is used by iSCSI

















































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4. Login Phase

   In the rest of this chapter, whenever we mention security we mean
   security and/or data integrity.

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

   Operational parameters MAY be negotiated within or outside (after)
   the login phase.

   Security MUST be completely negotiated within the Login Phase or
   provided by external means (e.g., IPSec).

   In some environments, a target or an initiator is not interested in
   authenticating its counterpart. It is possible to bypass
   authentication through the Login Command and Response.

   The initiator and target MAY want to negotiate authentication and
   data integrity parameters. Once this negotiation is completed, the
   channel is considered secure.

   Authentication and a Secure Channel setup MAY be performed
   independent of iSCSI (as when using tunneling IPSec or some
   implementations of transport IPSec) in which case the Login phase can
   be reduced to operational parameter negotiations.

   The login phase is implemented via login and text commands and
   responses only. The login command is sent from the initiator to the
   target in order to start the login phase. The login response is sent
   from the target to the initiator to conclude the login phase. Text
   messages are used to implement negotiation, establish security, and
   set operational parameters.

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

   The login phase sequence of commands and responses proceeds as
   follows:

      - Login command (mandatory)
      - Login Partial-Response (optional)
      - Text Command(s) and Response(s) (optional)
      - Login Final-Response (mandatory)



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   The Login Final-Response can come only as a response to a Login
   command with the F bit set to 1 or a Text Command with the F bit set
   to 1.


4.1 Login Phase Start

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

      -Protocol version supported by the initiator (currently 0x'01')
      -Session and connection Ids
      -Security/Integrity Parameters OR
      -iSCSI operational parameters

   A target MAY use the Initiator WWUI as part of its access control
   mechanism; therefore, the Initiator WWUI must be sent before the
   target is required to disclose its LUs.

   If the target WWUI is going to be used in determining the security
   mode or it is implicit part of authentication, then the target WWUI
   MUST be sent in the login command of the first connection of a
   session to identify the storage endpoint of the session.  However, it
   is OPTIONAL for all the connections after the first. It is ignored by
   the target for new connections within an existing session.  If the
   target WWUI is going to be used only for access control, it can be
   sent after the Security Context Complete is achieved. A unknown
   target can be accessed by using "iSCSI" as a placeholder for the
   WWUI.

   The WWUIs MUST be in text command format.

   The target can answer in the following ways:

      -Login Response with Login Reject (and F bit 1).  This is an
      immediate rejection from the target, that causes the session to
      terminate.
      -Login Response with Login Accept with session ID and iSCSI
      parameters and F bit set to 1.  This is a valid response only
      if the Login Command also had the F bit set to 1.  In this
      case, the target does not support any security or
      authentication mechanism and starts with the session
      immediately (enters full feature phase).





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      -Login Response with F bit 0 indicating the start of a
      negotiation sequence.  The response includes the protocol
      version supported by the target and either security/integrity
      parameters or iSCSI parameters (when no security/integrity
      mechanism is chosen) supported by the target. It also indicates
      what sequence is expected next (security/integrity or iSCSI
      parameters negotiation).  The initiator MAY decide to drop the
      connection if the sequence is not what it expects (e.g., an
      initiator that expects a security/integrity sequence and gets a
      response indicating that iSCSI parameters negotiation is the
      next phase expected by the initiator).

4.2 iSCSI Security and Integrity Negotiation

   The security exchange sets the security mechanism and authenticates
   the user and the target to each other. The exchange proceeds
   according to the algorithms that were chosen in the negotiation phase
   and is conducted by the text commands key=value parameters.

   The negotiable security mechanisms include the following modes:

      -Initiator-target authentication - the host and the target
      authenticate themselves to each other. A negotiable algorithm
      such as Kerberos provides this feature.
      -Message integrity - an integrity/authentication digest is
      attached to each packet.  The algorithm is negotiable.

      Using IPsec for encryption or authentication may eliminate the
      need for security negotiation at the iSCSI level, e.g., ISAKMP
      for IPsec.

   If security is established in the login phase note that:

      -After the security context negotiation is complete, each iSCSI
      message MUST include the appropriate digest field if any.

      -The iSCSI parameter negotiation (non-security parameters)
      SHOULD start only after security is established. This should be
      performed using text commands.

   The negotiation proceeds as follows:

      -The initiator sends a text command with an ordered list of the
      options it supports for each subject (authentication algorithm,
      iSCSI parameters and so on). The options are listed in the
      initiator's reverse order of preference.


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      -The target MUST reply with the first option in the list it
      supports.  The parameters are encoded in UTF8 as key=value.
      The initiator MAY also send proprietary options. The "none"
      option, if allowed, MUST be included in the list, which
      indicates that no algorithm is supported by the target. If
      security is to be established, the initiator MUST NOT send
      parameters other than security parameters in the login command.
      The operational parameters should be negotiated only after
      security is established at the desired level.  When
      establishing the security context, any operational parameters
      sent before establishing a secure context MUST be reset by both
      the target and the initiator. For a list of security parameters
      see Appendix A.

      -Every party in the security negotiation indicates that it has
      completed building its security context (has all the required
      information) by sending the key=value pair:

         SecurityContextComplete=Yes

      The other party either offers some more parameters or answers
      with the same:

         SecurityContextComplete=Yes


      The party that is ready keeps sending the
      SecurityContextComplete=Yes pair (in addition to new security
      parameters if required) until the handshake is complete.

      If the initiator has been the last to complete the handshake it
      MUST NOT start sending operational parameters within the same
      text command; a text response including only
      SecurityContextComplete=Yes concludes the security sub-phase.

      If the target has been the last to complete the handshake, the
      initiator can start the operational parameter negotiation with
      the next text command; the security negotiation sub-phase
      endeds with the target text response.

      All PDUs sent after the security negotiation sub phase MUST be
      built using the agreed security.

4.3 Operational Parameter Negotiation During the Login Phase

   Operational parameter negotiation during the login MAY be done:


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      - starting with the Login command if the initiator does not
      offer  any security/ integrity option
      - starting immediately after the security/integrity negotiation
      if the initiator and target perform such a negotiation
      - starting immediately after the Login response with Final bit
      0 if the initiator does offer  security/integrity options but
      the target chose none.

   Operational parameter negotiation MAY involve several request-
   response exchanges (login and/or text) always driven by the
   initiator. The initiator MUST indicate its intent to terminate the
   negotiation by setting the F bit to 1; the target sets the F bit to 1
   on the last response. The last response must be the Login Response.
   If the target responds to a text or Login command with the F bit set
   to 1, with a text response with the F bit set to 0, or a login
   response with the text bit set to 0, the initiator must keep sending
   the text command (even empty) with the F bit set to 1 until it gets
   the Login Response with the F bit set to 1.

   A target MUST NOT send more than one Login Response with the F bit
   set to 0.

   An initiator MUST send a single Login command per connection, per
   session.

























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5. Operational Parameter Negotiation Outside the Login Phase

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

   Operational parameter negotiation MAY involve several text request-
   response exchanges always driven by the initiator. The initiator MUST
   indicate its intent to terminate the negotiation by setting the F bit
   to 1; the target sets the F bit to 1 on the last response.
   If the target responds to a text command with the F bit set to 1,
   with a text response with the F bit set to 0, the initiator must keep
   sending the text command (even empty) with the F bit set to 1 until
   it gets the text response with the F bit set to 1.







































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6. iSCSI Error Handling and Recovery

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

   It is further assumed that a target will keep the "status & sense"
   for a command it has executed while the total number of outstanding
   commands and executed commands does not exceed its limit and status
   has not been acknowledged.

6.1 Format Errors

   Explicit violations of the rules stated in this document are format
   errors.

   While a session is active, whenever a target receives an iSCSI PDU
   with a format error, it MUST answer with a Reject iSCSI PDU with a
   Reason-code of Format Error. It MUST also provide a 2-byte offset of
   the first offending byte in the rejected PDU.

   When an initiator receives an iSCSI PDU with a format error, for
   which it has an outstanding task, it MUST abort the target task and
   report the error through an appropriate service response (e.g.,
   Target Failure).  The exact coding of the service response is outside
   the scope of this document.

6.2 Digest Errors

   When a target receives an iSCSI PDU with a header digest error or a
   payload digest error in an iSCSI PDU, it MUST answer with a Reject
   iSCSI PDU with a Reason-code of Header-Digest-error or Data-Digest-
   Error and discard the offending PDU.  If the error is a Data-Digest-
   Error in a Data-PDU, the target MUST either request retransmission
   with a R2T or answer with a Reject iSCSI PDU and abort the task.
   However if the error is detected while data from the initiator is
   still expected (the command PDU did not contain all the data and the
   target has not received a Data PDU with the final bit Set) the target
   MUST wait until it receives the a Data PDU with the F bit set before
   sending the Reject PDU.

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

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   than a data PDU, with a Data-Digest-Error, and this PDU is part of a
   task (has an Initiator Task Tag set), it MUST discard the PDU. It MAY
   restart the task (reissue the command with the same Initiator Task
   Tag and the X-bit set to 1).  If the reissued command is a SCSI
   command and it implies Read Data (Expected Data Length is not 0), the
   reissued command also includes the sequence number of the Next Data
   Packet expected by the initiator (0 if there was no data packet yet).

   When an initiator receives an iSCSI data PDU with a Data-Digest
   error, it must discard the PDU and it MUST either request the missing
   data PDUs through SACK or abort the task and terminate the command
   with an error.

6.3 Sequence Errors

   When an initiator receives an iSCSI data PDU with an out-of-order
   DataSN or a SCSI command response PDU with an EndDataSN implying
   missing data PDUs it MAY request the missing data PDUs through a data
   SACK PDU or handle this case as a connection failure.  In its turn,
   the target MUST either reject the SACK with a Reject PDU with a
   reason-code of Data-SACK-Reject or resend the data PDU.

   When an initiator receives an iSCSI status PDU with an out-of-order
   StatSN implying missing responses, it MUST either request the missing
   response PDUs through a status SACK or handle this case as a
   connection failure.  The target MUST reissue the missing responses.
   As a side effect of receiving the missing responses, the initiator
   may discover missing data PDUs. The initiator MUST NOT acknowledge
   (either explicitly through ExpStatRN or implicitly through a status
   SACK) the received responses until it has completed receiving all the
   data PDUs of a SCSI command.

6.4 Protocol Errors

   The authors recognize that mapping framed messages over a "stream"
   connection, such as TCP, makes the proposed mechanisms vulnerable to
   simple software framing errors. The introduction of framing
   mechanisms may be onerous for performance and bandwidth.  Command
   Sequence Numbers and the above mechanisms for connection drop and
   reestablishment help handle this type of mapping errors.

6.5 Connection Failure

   iSCSI can keep a session in operation if it is able to keep/establish
   at least one TCP connection between the initiator and target in a
   timely fashion.  It is assumed that targets and/or initiators
   recognize a failing connection by either transport level means (TCP),

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   a gap in the command or response stream that is not filled for a long
   time, or by a failing iSCSI NOP-ping. The later MAY be used
   periodically by highly reliable implementations.  Initiators and
   targets MAY also use the keep-alive option on the TCP connection to
   enable early link failure detection on otherwise idle links.

   At connection failure, the initiator and target MUST either attempt
   connection recovery within the session or session recovery.



6.6 Session Errors

   If all the connections of a session fail and cannot be reestablished
   in a short time or if initiators detect protocol errors repeatedly,
   an initiator may choose to terminate a session and establish a new
   session. It terminates all outstanding requests with a appropriate
   response before initiating a new session.  The target takes the
   following actions:

      - Resets the TCP connections (close the session).
      - Aborts all Tasks in the task set for the corresponding
      initiator.

6.7 Recovery Levels

   iSCSI enables the following levels of recovery (in increasing
   coverage order):

      - within a task (i.e., without requiring command restart).
      - within a connection (i.e., without requiring the connection
      to be rebuilt but perhaps requiring command restart).
      - within a session (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 level recovery that MAY be attempted. The implementer is left
   to decide under which circumstances to raise the recovery level
   and/or what recovery levels to implement.

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


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6.7.1 Recovery Within-task

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

      (1)Lost data PDU - a data PDU may be lost due to a header
      digest error or a data digest error.  In case of a data digest
      error, the error is recognized immediately, and the target MAY
      request the missing data through R2T. In case of a header
      digest error, the target will recognize the missing data either
      when receiving a subsequent piece out of sequence or by a
      timeout in completing a sequence (no data or partial-data-and-
      no-F-bit).  In this case, too, the target MAY request the
      missing data through a R2T.

      The timeout value to be used by a target is outside the scope
      of this document.

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

      (1)Lost data PDU or lost R2T - a data PDU or R2T may be lost
      due to a header digest error or a data digest error.  In case
      of a data digest error, the error is recognized immediately and
      the initiator MAY request the missing data through SACK. In
      case of a header digest error, the initiator recognizes the
      missing data or R2T either when receiving a subsequent piece
      out of sequence or by a timeout in completing a sequence (no
      status).  In this case, the initiator MAY request the missing
      data or R2T through a SACK.  Note however that an initiator
      SHOULD not request a missing R2T by a SACK after a timeout to
      avoid a race; this action is better left to the target.

      The timeout value to be used by an initiator is outside the
      scope of this document.


   Both the iSCSI target and initiator MAY resort to a more drastic,
   not-within-task recovery procedure in any of these cases.

   An initiator MAY reissue a command when missing data or status.

   An iSCSI target MAY reject a data-SACK and terminate the command with
   an iSCSI error response of SACK rejected.



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   An iSCSI initiator MUST accept an R2T.

   An iSCSI target on detecting missing data MAY terminate the command
   with an iSCSI error response of Delivery Subsystem Failure.

6.7.1.1 Recovery Within-connection

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

      (1)Lost iSCSI numbered Response recognized by either receiving
      it with a data digest error or receiving a Response PDU with a
      higher StatSN than expected. The initiator MAY request the
      missing responses through SACK, in which case the target MUST
      reissue them.
      (2)Requests not acknowledged for a long time. Requests are
      acknowledged explicitly through ExpCmdSN or implicitly by
      receiving data and/or status. The initiator MAY reissue non-
      acknowledged commands. The reissued, non-acknowledged commands
      MUST carry their original CmdSN and the X (retry) flag set to
      1.  Note that this is the only case in which the reissued
      command carries the same CmdSN as the "original".
      N.B. While the original connection for a command is still
      "active" (i.e., has not been logged-out or restarted), any
      command MUST be retried only on the original connection. After
      logging out the original connection, commands can be retried on
      a different connection, but must still carry the original
      CmdSN.

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

      (1)Status/Response not acknowledged for a long time. The target
      MAY issue a NOP-IN, with the P bit set to 1 or 0, which
      indicates in the StatSN field the next status number it is
      going to issue.  This helps the initiator detect missing StatSN
      and issue a SACK-status.

   The time to timeout by both initiator and target are outside the
   scope of this document.

   Both the iSCSI target and initiator MAY resort to a more drastic,
   not-within-connection recovery procedure in any of those cases.

6.7.1.2 Recovery Within-session



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

      (1)TCP connection failure. The initiator MUST close the
      connection following which it MUST either Logout the failed
      connection, or Login with an implied Logout, and reissue all
      commands associated with the failed connection on another
      connection (that MAY be a newly established connection) with
      the X (retry) flag set to 1.

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

      N.B. As an alternative to Logout and reissue commands, the
      initiator MAY instead reset the target and terminate all
      outstanding commands with a service response indicating
      Delivery Subsystem Failure. The initiator MUST perform one of
      the two actions.

      (2)Receiving an Asynchronous Message requiring recovery Logout.
      The initiator MUST handle it as a TCP connection failure for
      the connection referred to in the message.

   At an iSCSI target, the following cases lend themselves to within-
   session recovery

      (1)TCP connection failure. The target MUST close the connection
      and then, if more than one connection is available, the target
      SHOULD send an Asynchronous Message indicating it has dropped
      the connection. Following that, the target will wait for the
      initiator to continue recovery.

6.7.1.3 Session Recovery

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

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


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7. Notes to Implementers

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

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

7.1 Multiple Network Adapters

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

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

7.2 Autosense and Auto Contingent Allegiance (ACA)

   Autosense refers to the automatic return of sense data to the
   initiator in case a command did not complete successfully. iSCSI
   mandates support for autosense.

   ACA helps preserving ordered command execution in presence of errors.
   As iSCSI can have many commands in-flight between initiator and
   target iSCSI mandates support for ACA.



















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

   The following section describes the security protection modes that
   should be provided by an iSCSI implementation.

   Authentication and a Secure Channel setup MAY be performed
   independent of iSCSI (as when using tunneling IPSec or some
   implementations of transport IPSec).


8.1 iSCSI Security Protection Modes

8.1.1 No Security

   This mode does not authenticate nor does it encrypt data. This mode
   should only be used in environments where the security risk is
   minimal and configuration errors are improbable.

8.1.2 Initiator-Target Authentication

   In this mode, the target authenticates the initiator and the
   initiator optionally authenticates the target. An attacker should not
   gain any advantage by inspecting the authentication phase messages
   (i.e., sending "clear password" is out of the question). This mode
   protects against an unauthorized access to storage resources by using
   a false identity (spoofing). Once the authentication phase is
   completed, all messages are sent and received in clear.  This mode
   should only be used when there is minimal risk to man-in-the-middle
   attacks, eavesdropping, message insertion, deletion, and
   modification.

8.1.3 Data Integrity and Authentication

   This mode provides origin authentication and data integrity for every
   message that is sent after a security context is established. It

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   protects against man-in-the-middle attacks, message insertion,
   deletion, and modification.

   It is possible to use different authentication mechanisms for headers
   and data.

   Every compliant iSCSI initiator and target MUST be able to provide
   initiator-target authentication and data integrity and
   authentication.  This quality of protection MAY be achieved on every
   connection through properly configured IPSec involving only
   administrative (indirect) interaction with iSCSI implementations.


8.1.4 Encryption

   This mode provides data privacy in addition to data integrity and
   authentication, and protects against eavesdropping, man-in-the-middle
   attacks, message insertion, deletion, and modification.

   A connection or multiple connections MAY be protected end-to-end or
   partial-path (gateway tunneling) by using IPSec.






























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9. IANA Considerations

   There will be a well-known port for iSCSI connections.  This well-
   known port will be registered with IANA.

















































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10. References and Bibliography

      [AC]  A Detailed Proposal for Access Control, Jim Hafner,
      T10/99-245
      [BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-01.txt
      [CAM]  ANSI X3.232-199X, Common Access Method-3 (Cam-3)
      [CRC]  ISO 3309, High-Level Data Link Control (CRC 32)
      [NDT] M. Bakke & team,  draft-ietf-ips-iSCSI-
      NamingAndDiscovery-00.txt
      [RFC793]  Transmission Control Protocol, RFC 793
      [RFC1122] Requirements for Internet Hosts-Communication Layer
      RFC1122, R. Braden (editor)
      [RFC-1510] J. Kohl, C. Neuman, "The Kerberos Network
      Authentication Service (V5)", September 1993.
      [RFC1766] Alvestrand, H., "Tags for the Identification of
      Languages", March 1995.
      [RFC1964] J. Linn, "The Kerberos Version 5 GSS-API Mechanism",
      June 1996.
      [RFC1982] Elz, R., Bush, R., "Serial Number Arithmetic", RFC
      1982, August 1996.
      [RFC2026] Bradner, S., "The Internet Standards Process --
      Revision 3", RFC 2026, October 1996.
      [RFC-2044] Yergeau, F., "UTF-8, a Transformation Format of
      Unicode and ISO 10646", October 1996.
      [RFC2119] Bradner, S. "Key words for use in RFCs to Indicate
      Requirement Levels", BCP 14, RFC 2119, March 1997.
      [RFC2234] D. Crocker, P. Overell Augmented BNF for Syntax
      Specifications: ABNF
      [RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing
      an IANA Considerations Section in RFCs.", RFC2434,  October
      1998.
      [RFC2401] S. Kent, R. Atkinson, " Security Architecture for the
      Internet Protocol", RFC 2401, November 1998
      [RFC2945], Wu, T., "The SRP Authentication and Key Exchange
      System", September 2000.
      [SAM2]    ANSI X3.270-1998, SCSI-3 Architecture Model (SAM-2)
      [SBC]     ANSI X3.306-199X, SCSI-3 Block Commands (SBC)
      [SCSI2]   ANSI X3.131-1994, SCSI-2
      [Schneier] Schneier, B., "Applied Cryptography: Protocols,
      Algorithms, and Source Code in C", 2nd edition, John Wiley &
      Sons, New York, NY, 1996.
      [SPC]     ANSI X3.301-199X, SCSI-3 Primary Commands (SPC)
      [Wolf94]  J. K. Wolf et al. The Single Burst Error Detection
      Performance of Binary Cyclic Codes - IEEE Transactions on
      Communications, Vol. 42 No. 1



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      [Wolf88]  J. K. Wolf et al. The Exact Evaluation of the
      Probability of Undetected Error for Certain Shortened Binary
      CRC Codes - Proc. MILCOM 1988 pp 15.2.1-15.2.6


















































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11. Author's Addresses

        Julian Satran
        Kalman Meth
        Ofer Biran
        IBM, Haifa Research Lab
        MATAM - Advanced Technology Center
        Haifa 31905, Israel
        Phone +972 4 829 6211
        Email: Julian_Satran@vnet.ibm.com meth@il.ibm.com
               biran@il.ibm.com

        Daniel F. Smith
        IBM Almaden Research Center
        650 Harry Road
        San Jose, CA 95120-6099, USA
        Phone: +1 408 927 2072
        Email: dfsmith@almaden.ibm.com

        Costa Sapuntzakis
        Cisco Systems, Inc.
        170 W. Tasman Drive
        San Jose, CA 95134, USA
        Phone: +1 408 525 5497
        Email: csapuntz@cisco.com

        Randy Haagens
        Hewlett-Packard Company
        8000 Foothills Blvd.
        Roseville, CA 95747-5668, USA
        Phone: +1 (916) 785-4578
        E-mail: Randy_Haagens@hp.com

        Matt Wakeley
        Agilent Technologies
        1101 Creekside Ridge Drive
        Suite 100, M/S RH21
        Roseville, CA 95661
        Phone: +1 (916) 788-5670
        E-Mail: matt_wakeley@agilent.com

        Efri Zeidner
        SANGate
        Israel
        efri@sangate.com



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        Paul von Stamwitz
        Adaptec, Inc.
        691 South Milpitas Boulevard
        Milpitas, CA 95035
        Phone: +1(408) 957-5660
        E-mail:  paulv@corp.adaptec.com

        Luciano Dalle Ore
        Quantum Corp.
        Phone: +1(408) 232 6524
        E-mail:  ldalleore@snapserver.com

        Yaron Klein
        SANRAD
        24 Raul Valenberg St.
        Tel-Aviv, 69719 Israel
        Phone: +972-3-7659998
        E-mail:  klein@sanrad.com


   Comments may be sent to Julian Satran






























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Appendix A. iSCSI Security and Integrity

01 Security Keys and Values

   The parameters (keys) negotiated for security are:

      - Digests (HeaderDigest, DataDigest)
      - Authentication method (AuthMethod)

   Digests enable checking end-to-end data integrity beyond the
   integrity checks provided by the link layers and covering the whole
   communication path including all elements that may change the network
   level PDUs like routers, switches, proxies etc.


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

   +---------------------------------------------+
   | Name          | Description                 |
   +---------------------------------------------+
   | crc-32Q       | 32 bit CRC      | 1814141AB |
   +---------------------------------------------+
   | crc-64        | 64 bit CRC      | TBD       |
   +---------------------------------------------+
   | none          | no digest                   |
   +---------------------------------------------+

   The generator polynomials for those digests are given in hex-
   notation, for example 3a stands for 0011 1010 - the polynomial
   x**5+X**4+x**3+x+1.


   crc-64 MUST NOT be used for HeaderDigest.
   Cyclic codes are particularly well suited for hardware
   implementations.


   Implementations MAY also negotiate digests with security significance
   for data authentication and integrity as detailed in the following
   table:


   +-------------------------------------------------------------+
   | Name          | Description                   | Definition  |

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   +-------------------------------------------------------------+
   | KRB5_MD5      | the SGN_CKSUM field (8 bytes) | RFC-1964    |
   |               | of the GSS_GetMIC() token in  |             |
   |               | GSS_KRB5_INTEG_C_QOP_MD5 QOP  |             |
   |               | (partial MD5 ("MD2.5") )      |             |
   +-------------------------------------------------------------+
   | KRB5_DES_MD5  | the SGN_CKSUM field (8 bytes) | RFC-1964    |
   |               | of the GSS_GetMIC() token in  |             |
   |               | GSS_KRB5_INTEG_C_QOP_DES_MD5  |             |
   |               | QOP (DES MAC of MD5)          |             |
   +-------------------------------------------------------------+
   | KRB5_DES_MAC  | the SGN_CKSUM field (8 bytes) | RFC-1964    |
   |               | of the GSS_GetMIC() token in  |             |
   |               | GSS_KRB5_INTEG_C_QOP_ DES_MAC |             |
   |               | QOP (DES MAC)                 |             |
   +-------------------------------------------------------------+

   Note: the KRB5_* digests are allowed only when combined with KRB5
   authentication method (see below). For example, the initiator may
   offer one of these digests only if it also offers KRB5 as AuthMethod,
   and the target may respond with one of these digests only if it also
   responds with KRB5 as the AuthMethod.



   Other and proprietary algorithms MAY also be negotiated.
   The none value is the only one that MUST be supported.


   The following table details authentication methods:

   +-----------------------------------------------------------+
   | Name          | Description                               |
   +-----------------------------------------------------------+
   | KRB5          | Kerberos V5                               |
   +-----------------------------------------------------------+
   | SRP           | Secure Remote Password                    |
   +-----------------------------------------------------------+
   | none          | No authentication                         |
   +-----------------------------------------------------------+

   KRB5 is defined in [RFC-1510] and Secure Remote Password is defined
   in [RFC-2945].





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02 Authentication

   The authentication exchange authenticates the initiator and target to
   each other.  Authentication is not mandatory and is distinct from the
   data integrity exchange.

   Different levels of authentication can be applied such as initiator
   authentication, target authentication or both.

   The authentication methods to be used are KRB5, SRP or proprietary.

   For KRB5 (Kerberos V5) [RFC-1510], the initiator MUST use:

       KRB_AP_REQ=<blob>

   where blob contains the KRB_AP_REQ message encoded as a number.

   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 either return an error or use:

       KRB_AP_REP=<blob>

   where blob contains the KRB_AP_REP message encoded as a hexadecimal
   string.  The format of these messages is defined in [RFC1510].

   For SRP [RFC2945], the initiator MUST use:

      U=<user> TargetAuth=yes   /* or TargetAuth=no */

   The target MUST either return an error or reply with:

      N=<N> g=<g> s=<s>

   The initiator MUST continue with:

      A=<A>

   The target MUST either return an error or reply with:

      B=<B>

   The initiator MUST either abort or continue with:

      M=<M>



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   If the initiator sent TargetAuth=yes in the first message (requiring
   target authentication) the target MUST either return an error or
   reply with:

     HM=<H(A | M | K)>


   Where N, g, s, A, B, M and H(A | M | K) are defined in [RFC2945].


03 Login Phase Examples

   In the first example, the initiator and target authenticate each
   other via Kerberos:

      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88
      HeaderDigest=KRB5_MD5,KRB5_DES_MAC,crc-32Q,none
      DataDigest=crc-32Q,none AuthMethod=SRP,KRB5,none

      T-> Login-PR HeaderDigest=KRB5_MD5 DataDigest=crc-32Q
      AuthMethod=KRB5

        (Login-PR stands for Login-Partial-Response)

      I-> Text 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-> Text KRB_AP_REP=krb_ap_rep SecurityContextComplete=Yes
      (krb_ap_rep is the Kerberos V5 mutual authentication reply)

      If the authentication is successful, the initiator proceeds:

      I-> Text SecurityContextComplete=Yes
      T-> Text SecurityContextComplete=Yes

      From this point on, any Text command and each PDU thereafter
      has a KRB5_MD5 digest for the header and a crc-32Q for the
      data.

      The initiator may proceed:

      I-> Text ... iSCSI parameters


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      T-> Text ... iSCSI parameters

      And at the end:

      I-> Text optional iSCSI parameters F bit set to 1
      T-> Login "login accept" TargetWWUI=com.acme.diskarray.sn.88

      If the initiator authentication by the target is not
      successful, the target responds with:

      T-> Login "login reject"

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

      If the target authentication by the initiator is not
      successful, the initiator terminates the connection (without
      responding to the Text KRB_AP_REP message).

   In the next example only the initiator is authenticated by the target
   via Kerberos:

      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88
      HeaderDigest=KRB5_MD5,KRB5_DES_MAC,crc-32Q,none
      DataDigest=crc-32Q,none AuthMethod=SRP,KRB5,none
      T-> Login-PR HeaderDigest=KRB5_MD5 DataDigest=crc-32Q
      AuthMethod=KRB5

      I-> Text KRB_AP_REQ=krb_ap_req SecurityContextComplete=Yes
      (MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)

      T-> Text SecurityContextComplete=Yes

      From this point on, any Text command and each PDU thereafter
      must have a KRB5_MD5 digest for the header and a crc-32Q for
      the data.

      I-> Text ... iSCSI parameters
      T-> Text ... iSCSI parameters

      . . .

      T-> Login "login accept" TargetWWUI=com.acme.diskarray.sn.88




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   In the next example, the initiator and target authenticate each other
   via SRP:

      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88 HeaderDigest=crc-32Q,none
      DataDigest=crc-32Q,crc-64, none AuthMethod=KRB5,SRP,none
      T-> Login-PR HeaderDigest=crc-32Q DataDigest=crc-64
      AuthMethod=SRP

      I-> Text U=<user> TargetAuth=yes
      T-> Text N=<N> g=<g> s=<s>
      I-> Text A=<A>
      T-> Text B=<B>
      I-> Text M=<M>

      If the initiator authentication is successful, the target
      proceeds:

      T-> Text HM=<H(A | M | K)> SecurityContextComplete=Yes

      If the target authentication is successful, the initiator
      proceeds:

      I-> Text SecurityContextComplete=Yes
      T-> Text SecurityContextComplete=Yes

      Where N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945].

      From this point on, any Text command and each PDU thereafter
      has a crc-32Q digest for the header and a crc-64 for the data.

      I-> Text ... iSCSI parameters
      T-> Text ... iSCSI parameters

      And at the end:

      I-> Text optional iSCSI parameters and F bit set to 1
      T-> Login "login accept" TargetWWUI=com.acme.diskarray.sn.88

      If the initiator authentication is not successful, the target
      responds with:

      T-> Login "login reject"

      Instead of the T-> Text HM=<H(A | M | K)>  message and
      terminates the connection.


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   In the next example only the initiator is authenticated by the target
   via SRP:

      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88 HeaderDigest=crc-32Q,none
      DataDigest=crc-32Q,crc-64, none AuthMethod=KRB5,SRP,none
      T-> Login-PR HeaderDigest=crc-32Q DataDigest=crc-64
      AuthMethod=SRP

      I-> Text U=<user> TargetAuth=no
      T-> Text N=<N> g=<g> s=<s>
      I-> Text A=<A>
      T-> Text B=<B>
      I-> Text M=<M> SecurityContextComplete=Yes

      If the initiator authentication is successful, the target
      proceeds:

      T-> Text SecurityContextComplete=Yes

      From this point on, any Text command and each PDU thereafter
      has a crc-32Q digest for the header and a crc-64 for the data.

      I-> Text … iSCSI parameters
      T-> Text … iSCSI parameters

      And at the end:

      I-> Text optional iSCSI parameters and F bit set to 1
      T-> Login "login accept" TargetWWUI=com.acme.diskarray.sn.88


   In the next example, the initiator does not offer any
   security/integrity parameters, so it may offer iSCSI parameters on
   the Login message with the F bit set to 1, and the target may respond
   with a final Login message immediately:

      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88  ... iSCSI parameters
      T-> Login "login accept"
      TargetWWUI=com.acme.diskarray.sn.88  ... ISCSI parameters

   In the next example, the initiator does offer security/integrity
   parameters on the Login message, but the target does not choose
   any (i.e., chooses the "none" values):


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      I-> Login InitiatorWWUI=com.os.hostid.77
      TargetWWUI=com.acme.diskarray.sn.88 HeaderDigest=crc-32Q,none
      DataDigest=crc-32Q,crc-64,none AuthMethod:KRB5,SRP
      T-> Login-PR

      I-> Text ... iSCSI parameters
      T-> Text ... iSCSI parameters

      And at the end:

      I-> Text optional iSCSI parameters F bit set to 1
      T-> Login "login accept" TargetWWUI=com.acme.diskarray.sn.88

   Note that no SecurityContextComplete=Yes is required since no
   security mechanism was chosen.



































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Appendix B. Examples

04 Read Operation Example

   |Initiator Function|    Message Type       |  Target Function     |
   +------------------+-----------------------+----------------------+
   |  Command request |SCSI Command (READ)>>> |                      |
   |  (read)          |                       |                      |
   +------------------+-----------------------+----------------------+
   |                  |                       | Prepare Data Transfer|
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data       |   Send Data          |
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data       |   Send Data          |
   +------------------+-----------------------+----------------------+
   |   Receive Data   |   <<< SCSI Data       |   Send Data          |
   +------------------+-----------------------+----------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense |
   +------------------+-----------------------+----------------------+
   | Command Complete |                       |                      |
   +------------------+-----------------------+----------------------+






























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05 Write Operation Example


   +------------------+-----------------------+---------------------+
   |Initiator Function|    Message 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 >>>       |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< R2T             |                     |
   +------------------+-----------------------+---------------------+
   |                  |   <<< R2T             |                     |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data >>>       |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |   Send Data      |   SCSI Data >>>       |   Receive Data      |
   +------------------+-----------------------+---------------------+
   |                  |   <<< SCSI Response   |Send Status and Sense|
   +------------------+-----------------------+---------------------+
   | Command Complete |                       |                     |
   +------------------+-----------------------+---------------------+





















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Appendix C. Synch and Steering with Fixed Interval Markers

   This appendix presents a simple scheme for synchronization (PDU
   boundary retrieval).  It uses markers including synchronization
   information placed at fixed intervals in the TCP stream.

   A Marker consists of:

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

   The Marker indicates the offset to the next iSCSI message 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 message header.  The marker uses two
   copies of the pointer so that a marker spanning a TCP packet boundary
   will leave at least one valid copy in one of the packets.

   The use of markers is negotiable. The initiator and target MAY
   indicate their readiness to receive and/or send markers during login
   separately for each connection.  The default is NO. In certain
   environments a sender not willing to supply markers to a receiver
   willing to accept markers MAY suffer from a considerable performance
   degradation.




















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06 Markers At Fixed Intervals

   At fixed intervals in the TCP byte stream, a marker is inserted.
   Each end of the iSCSI session specifies during login the interval at
   which it is willing to receive the marker or disables the marker
   altogether. If a receiver indicates that it desires a marker, the
   sender SHOULD agree (during negotiation) and provide the marker at
   the desired interval.

   The marker interval and the initial marker-less interval are counted
   in terms of the TCP stream data. Anything counted in the TCP
   sequence-number is counted for the interval and the initial marker-
   less interval. Specifically this includes any bytes "inserted" in the
   TCP stream by an UFL.

   When reduced to iSCSI terms markers MUST point to a 4-byte word
   boundary in the stream.  The last 2 bits of each marker word are
   reserved and are considered 0 for offset computation.

   Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
   marker manipulation.



07 Initial Marker-less Interval

   To enable the connection setup including the login phase negotiation,
   the negotiated marking is started at a negotiated boundary in the
   stream.  The marker-less interval is not less than 4 kbytes and the
   default is 4 kbytes.




















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Appendix D. Login/Text Miscellaneous Keys

   ISID and TSID form collectively the SSID (session id). A TSID of zero
   indicates a leading connection. Some session specific parameters MUST
   be carried only on the leading connection and cannot be changed after
   the leading connection login(e.g., MaxConnections, the maximum
   immediate data length requested).  This holds even for a single
   connection session during connection restart. The keys that fall into
   this category are marked - LO (Leading Only).

   Unless explicitly stated otherwise, all the key=value pairs specified
   here are session specific.

08 MaxConnections - LO

   MaxConnections=<number-from-1-to-65535>

   Default is 8.

   Initiator and target negotiate the maximum number of connections
   requested/acceptable.  The lower of the 2 numbers is selected.


09 TargetWWUI - LO

   TargetWWUI=<wwui>

   Examples:

      TargetWWUI=com.disk-vendor.diskarrays.sn.45678
      TargetWWUI=eui.020000023B040506
      TargetWWUI=oui.00023B.target.45
      TargetWWUI=iSCSI

   This key MUST be provided by the initiator of the TCP connection to
   the remote endpoint before the end of the login phase. The Target
   WWUI specifies the worldwide unique name of the target.  The non-
   unique default name "iSCSI" may be used to indicate whatever default
   target exists at the address to which the connection was made. Some
   targets MAY require this key before authenticating.

   The TargetWWUI key may also be returned by the "SendTargets" text
   command, described in detail in [NDT].

10 InitiatorWWUI - LO

   InitiatorWWUI=<wwui>

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   Examples:

      InitiatorWWUI=com.os-vendor.plan9.cdrom.12345
      InitiatorWWUI=com.service-provider.users.customer235.host90
      InitiatorWWUI=iSCSI

   The Initiator key enables the initiator to identify itself to the
   remote endpoint.  The use of the default WWUI "iSCSI" is interpreted
   as "other side of TCP connection". The target may silently ignore
   this key if it does not support it, and does not need to track or
   verify which initiators use it.  A target that supports this field
   may use it to allow or deny access to an initiator.

11 TargetAlias

   TargetAlias=<UTF-8 string>

   Examples:

      TargetAlias=Bob's Disk
      TargetAlias=Database Server 1 Log Disk
      TargetAlias=Web Server 3 Disk 20

   If a target has been configured with a human-readable name or
   description, it may be communicated to the initiator during a Login
   Response message.  This string is not used as an identifier, but can
   be displayed by the initiator's user interface in a list of targets
   to which it is connected.

   This key is OPTIONAL, and MAY be returned by a target within a Login
   Response.  This field may also be returned in the response to the
   "SendTargets" text command.

12 InitiatorAlias

   InitiatorAlias=<UTF-8 string>

   Examples:

      InitiatorAlias=Web Server 4
      InitiatorAlias=spyalley.nsa.gov
      InitiatorAlias=Exchange Server

   If an initiator has been configured with a human-readable name or
   description, it may be communicated to the target during a Login
   Request message.  If not, the host name can be used instead.

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   This string is not used as an identifier, but can be displayed by the
   target's user interface in a list of initiators to which it is
   connected.

   This key is OPTIONAL, and MAY be sent by an initiator within a Login
   Request.

13 TargetAddress

   TargetAddress=domainname[:port]/wwui

   N.B. If the address contains a wwui part then this is a LO parameter.

   Examples:

      TargetAddress=10.0.0.1/com.disk-vendor.diskarrays.sn.45678
      TargetAddress=12.5.7.10.0.0.1/com.gateways.yourtargets.24
      TargetAddress=computingcenter.acme.com/com.disk-
      vendor.diskarrays.sn.45678

   The response to a SendTargets text command returns one or more target
   addresses for each target WWUI it returns.  This field is used to
   indicate one of the known addresses of the target.

14 SendTargets

   This key is used within a text command to request a list of targets
   be sent back to the initiator in a text response.

   The presence of this key is sufficient to do this; no value should be
   sent with this key.

      Example:

         SendTargets=

15 AccessID

   AccessID=<SCSI-AccessID-value>

   Deliver a SCSI AccessID to the target


16 FMarker

   FMarker=<send|receive|send-receive|no>


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   This is a connection specific parameter.

   Examples:

      I->FMarker=send-receive
      T->FMarker=send-receive

   results in Marker being used in both directions while

      I->FMarker=send-receive
      T->FMarker=receive

   results in Marker being used from the initiator to the target but not
   from the target to initiator.


17 RFMarkInt

   RFMarkInt=<number-from-1-to-65535>

   This is a connection specific parameter.

   Indicates at what interval (in 4-byte words) the receiver wants the
   markers. The larger of the numbers (wanted by receiver and offered by
   sender) is selected. The interval is measured from the beginning of a
   marker to the beginning of the next marker. For example, a value of
   1026 means 1026 words (4096 bytes of "pure" payload between markers).

   Default is 2050.

18 SFMarkInt

   SFMarkInt=<number-from-1-to-65535>

   This is a connection specific parameter.

   Indicates at what interval (in 4-byte words) the sender offers to
   send the markers. The larger of the numbers (wanted by receiver and
   offered by sender) is selected. The interval is measured from the
   beginning of a marker to the beginning of the next marker. For
   example, a value of 1026 means 1026 words (4096 bytes of "pure"
   payload between markers).

   Default is 2050.

19 IFMarkInt


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   IFMarkInt=<number-from-1-to-65535>

   This is a connection specific parameter.

   Indicates the initial marker-less interval required by the initiator
   in both directions in 4-byte words. The interval is measured from the
   beginning of the TCP stream to the beginning of the first marker. For
   example, a value of 1024 means 1024 words (4096 bytes of "pure"
   payload up to the first marker).

   Default is 4096.



20 UseR2T

   UseR2T=<yes|no>

   Examples:

      I->UseR2T=no
      T->UseR2T=no

   The UseR2T key is used to turn off the default use of R2T, thus
   allowing an initiator to send data to a target without the target
   having sent an R2T to the initiator.  The default action is that R2T
   is required, unless both the initiator and the target send this key-
   pair attribute specifying UseR2T:no.  Once UseR2T has been set to
   'no', it cannot be set back to 'yes'.  Note that only the first
   outgoing data item (either immediate data or a separate PDU) can be
   sent unsolicited by a R2T.

21 BidiUseR2T

   BidiUseR2T=<yes|no>

   Examples:

      I->BidiUseR2T=no
      T->BidiUseR2T=no

   The BidiUseR2T key is used to turn off the default use of BiDiR2T,
   thus allowing an initiator to send data to a target without the
   target having sent an R2T to the initiator for the output data (write
   part) of a Bi-directional command (having both the R and the W bits
   set).  The default action is that R2T is required, unless both the
   initiator and the target send this key-pair attribute specifying

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   BidiUseR2T=no.  Once BidiUseR2T has been set to 'no', it cannot be
   set back to 'yes'.  Note that only the first outgoing data burst
   (immediate data or separate PDUs) can be sent unsolicited by a R2T.

22 ImmediateData

   ImmediateData=<yes|no>

   Initiator and target negotiate support for immediate data. Default is
   yes.  If ImmediateData is set to yes and UseR2T is set to yes
   (default) then only immediate data are accepted in the first burst.

   If ImmediateData is set to no and UseR2T is set to yes then the
   initiator MUST NOT send unsolicited data and the target MUST reject
   them with the corresponding response code.


23 DataPDULength

   DataPDULength=<number-1-to-(2**23-1)>

   Initiator and target negotiate the maximum data payload supported for
   command or data PDUs in units of 512 bytes. Default is 16. This
   parameter sets the maximum-burst-size value stored in the SCSI
   disconnect-reconnect mode page. The value can subsequently be
   retrieved with the mode sense SCSI command.

24 FirstBurstSize

   FirstBurstSize=<number-from-1-to-(2**23-1)>

   Initiator and target negotiate the maximum length supported for
   unsolicited data in units of 512 bytes. Default is 128 units . This
   parameter sets the first-burst-size value stored in the SCSI
   disconnect-reconnect mode page. The value can subsequently be
   retrieved with the mode sense SCSI command.



25 ITagLength

   ITagLength=<number-from16-to-32>

   Initiator and target negotiate the significant length of the
   initiator tag to be used. Default is 32.



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26 EnableCmdRN

   EnableCmdRN=<no|yes>

   Default is no.

   Initiator and target negotiate support for CmdRN.

   If CmdRN is not supported by the target, the CmdRN field is ignored.
   This parameter sets the EnableCmdRN field stored in the SCSI Logical
   Unit Control mode page.


27 PingMaxReplyLength

   PingMaxReplyLength=<number>

   Initiator and target negotiate the maximum length of data contained
   in a ping reply. Default is DataPDULength*512. The lowest of the two
   numbers is selected.

   PingMaxReplyLength cannot be larger than DataPDULength*512 and the
   target MUST reset PingMaxReplyLength to DataPDULength*512 whenever it
   becomes lower than the current PingMaxReplyLength.

28 TotalText

   TotalText=<number-from-512-to-65535>

   Initiator and target indicate the total text limit for any Text or
   Login command.

   Default is DataPDULength*512.

   TotalText cannot be larger than DataPDULength*512 and the target MUST
   reset TotalText to DataPDULength*512 whenever it becomes lower than
   the current TotalText.

29 KeyValueText

   KeyValueText=<number-from-256-to-8192>

   Initiator and target indicate the total text limit for any key=value
   pair including delimiter.

   Default is 255.


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   KeyValueText MUST NOT be larger than TotalText

30 MaxOutstandingR2T

   MaxOutstandingR2T=<number-from-1-to-65535>

   Initiator and target negotiate the maximum number of outstanding R2Ts
   per task. The default is 8.

31 InDataOrder

   InDataOrder=<yes|no>

   No is used by iSCSI to indicate that the incoming data PDUs can be in
   any order (EMDP = 1). Yes is used to indicate that incoming data PDUs
   have to be at continuously increasing addresses (EMDP = 0).

   This also sets the Connect-Disconnect mode page EMDP bit.

   The default is yes but targets MAY support no.

32 BootSession - LO

   BootSession=<no|yes>

   Default is no.

   BootSession MAY be set to yes by the Login Command indicating to the
   Target that the only purpose of this Session is boot.  The target MAY
   restrict the type of iSCSI requests it accepts in such a Session to
   Logout, NOP-out, and SCSI read commands.  Accepting other commands in
   this type of session is vendor-dependent.  A target MAY reject a
   boot-session.

33 The Glen-Turner Vendor Specific Key Format

   X-reversed.vendor.dns_name.do_something=

   Keys with this format are used for vendor-specific purposes. These
   keys always start with X- .

   To identify the vendor it is suggested to use the reversed DNS-name
   as a prefix to the key-proper.





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