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IPS                                                       Julian Satran
Internet Draft                                             Daniel Smith
Document: draft-ietf-ips-iscsi-02.txt                       Kalman Meth
Category: standards-track                                           IBM

                                                 Constantin Sapuntzakis
                                                          Cisco Systems

                                                           Matt Wakeley
                                                   Agilent Technologies

                                                      Paul Von Stamwitz
                                                                Adaptec

                                                          Randy Haagens
                                                    Hewlett-Packard Co.

                                                           Efri Zeidner
                                                                SANGate

                                                      Luciano Dalle Ore
                                                                Quantum

                                                            Yaron Klein
                                                                 SANRAD


                                 iSCSI



























Julian Satran     Standards-Track, Expire June 2001                 1

                                iSCSI               December 30, 2000



Status of this Memo


   This document is an Internet-Draft and is in full conformance with
   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

   Besides the authors a large group of people contributed through their
   review, comments and valuable insights to the creation of this
   document - too many to mention them all. Nevertheless, we are
   grateful to all of them.  We are especially grateful to those that
   found the time and patience to participate in our weekly phone
   conferences and intermediate meetings in Almaden and Haifa and thus
   helped 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).  Many more helped
   clean and improve this document within the IPS working group. We are
   especially grateful to David Robinson (Sun), Charles Monia, Joshua
   Tseng (Nishan), Somesh Gupta, Mallikarjun C., Michael Krause (HP),
   Stephen Byan (Genroco), Yaron Klein (SANRAD). And last but not least


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   thanks Ralph Weber for keeping us in-line with T10 (SCSI)
   standardization.

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...........................................................8
 1.1 SCSI Concepts...................................................8
 1.2 iSCSI Concepts &  Functional Overview...........................9
  1.2.1 Layers & Sessions............................................9
  1.2.2 Ordering and iSCSI numbering.................................9
   1.2.2.1 Command numbering........................................10
   1.2.2.2 Response/Status numbering................................11
   1.2.2.3 Data PDU numbering.......................................12
  1.2.3 iSCSI Login.................................................12
  1.2.4 Text mode negotiation.......................................13
  1.2.5 iSCSI Full Feature Phase....................................14
  1.2.6 iSCSI Connection Termination................................16
  1.2.7 Naming & mapping............................................16
  1.2.8 Message Framing.............................................18
   1.2.8.1 Framing Justification....................................18
   1.2.8.2 Markers At Fixed Intervals...............................20
   1.2.8.3 iSCSI PDU Size...........................................20
   1.2.8.4 Initial marker-less interval.............................20
2. iSCSI PDU Formats.................................................21
 2.1 Template Header and Opcodes....................................21
  2.1.1 Opcode......................................................22
  2.1.2 Opcode-specific fields......................................23
  2.1.3 Length......................................................23
  2.1.4 LUN.........................................................23
  2.1.5 Initiator Task Tag..........................................23
  2.1.6 Header Digest and Data Digest...............................23
 2.2 SCSI Command...................................................25
  2.2.1 Flags & Task Attributes.....................................25
  2.2.2 AddCDB......................................................26
  2.2.3 CmdRN - Command Reference Number............................26
  2.2.4 ExpStatRN - Expected Status Reference Number................26
  2.2.5 Expected Data Transfer Length...............................26
  2.2.6 CDB - SCSI Command Descriptor Block.........................27
  2.2.7 Command-Data................................................27
 2.3 SCSI Response..................................................28
  2.3.1 Byte 1 - Flags..............................................28
  2.3.2 Basic Residual Count........................................29
  2.3.3 Bidi-Read Residual Count....................................29
  2.3.4 Command Status..............................................29


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  2.3.5 Resp_length - Response length...............................29
  2.3.6 Sense_length - Length of sense data.........................29
  2.3.7 Response and/or Sense Data..................................29
  2.3.8 StatRN - Status Reference Number............................30
  2.3.9 ExpCmdRN - next expected CmdRN from this initiator..........30
  2.3.10 MaxCmdRN - maximum CmdRN acceptable from this initiator....30
 2.4 SCSI Task Management Command...................................31
  2.4.1 Function....................................................31
  2.4.2 Referenced Task Tag.........................................32
 2.5 SCSI Task Management Response..................................33
  2.5.1 Referenced Task Tag.........................................34
 2.6 SCSI Data......................................................35
  2.6.1 F (Final) bit...............................................36
  2.6.2 Length......................................................36
  2.6.3 Target Task Tag.............................................37
  2.6.4 Buffer Offset...............................................37
  2.6.5 Flags.......................................................37
  2.6.6 Data numbering (DataRN).....................................37
 2.7 Text Command...................................................39
  2.7.1 Length......................................................39
  2.7.2 Initiator Task Tag..........................................39
  2.7.3 Text........................................................39
 2.8 Text Response..................................................41
  2.8.1 Length......................................................41
  2.8.2 Initiator Task Tag..........................................41
  2.8.3 Text Response...............................................41
 2.9 Login Command..................................................43
  2.9.1 Version-major and Version-minor.............................43
  2.9.2 CID.........................................................43
  2.9.3 InitCmdRN...................................................43
  2.9.4 Login Parameters............................................44
 2.10 Login Response................................................45
  2.10.1 Version-major minor........................................45
  2.10.2 InitStatRN.................................................45
  2.10.3 Status.....................................................46
  2.10.4 TSID.......................................................46
  2.10.5 Final bit..................................................46
 2.11 NOP-Out.......................................................47
  2.11.1 P - Ping bit...............................................48
  2.11.2 Length.....................................................48
  2.11.3 Initiator Task Tag.........................................48
  2.11.4 Target Task Tag............................................48
  2.11.5 Ping Data..................................................48
 2.12 NOP-In........................................................49
  2.12.1 Target Task Tag............................................49
 2.13 Logout Command................................................50


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  2.13.1 CID........................................................50
  2.13.2 Reason Code................................................50
 2.14 Logout Response...............................................51
  2.14.1 Status.....................................................51
 2.15 Ready To Transfer (R2T).......................................52
  2.15.1 Desired Data Transfer Length and Buffer Offset.............53
  2.15.2 Target Transfer Tag........................................53
 2.16 Asynchronous Event............................................54
  2.16.1 iSCSI Event................................................54
  2.16.2 SCSI Event Indicator.......................................55
 2.17 Third Party Commands..........................................56
 2.18 Reject........................................................57
 2.19 Reason........................................................57
3. Login phase.......................................................58
 3.1 Login phase start..............................................58
 3.2 Security negotiation...........................................59
 3.3 iSCSI Security.................................................59
4. iSCSI Error Handling and Recovery.................................61
 4.1 Connection failure.............................................61
 4.2 Protocol Errors................................................62
 4.3 Session Errors.................................................62
 4.4 Format errors..................................................62
 4.5 Digest errors..................................................63
5. Notes to Implementers.............................................64
 5.1 Multiple Network Adapters......................................64
 5.2 Autosense......................................................64
6. Security Considerations...........................................65
 6.1 Data Integrity.................................................65
 6.2 Network operations and the Threat Model........................65
  6.2.1 Threat Model................................................65
   6.2.1.1 Passive Attacks..........................................65
   6.2.1.2 Active Attacks...........................................66
  6.2.2 Security Model..............................................66
   6.2.2.1 No Security..............................................66
   6.2.2.2 End-to-End Authentication................................66
   6.2.2.3 iSCSI integrity and authentication.......................66
   6.2.2.4 Encryption...............................................67
  6.2.3 Other Considerations........................................67
 6.3 Login Process..................................................67
 6.4 Feasibility....................................................67
7. IANA Considerations...............................................69
8. References and Bibliography.......................................70
9. Author's Addresses................................................72
Apendix A. iSCSI Security............................................75
01 Security keys and values..........................................75
02 Authentication....................................................77


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03 Salt..............................................................78
04 Challenge.........................................................78
05 Login Phase examples:.............................................78
Apendix B. Examples..................................................82
06 Read operation example............................................82
07 Write operation example...........................................83
Apendix C. Login/Text keys (not security related)....................84
08 MaxConnections....................................................84
09 Target............................................................84
10 Initiator.........................................................84
11 AccessID..........................................................84
12 UPFrame.................................Error! Bookmark not defined.
13 UseR2T............................................................86
14 BidiUseR2T........................................................86
15 DataNumber........................................................86
16 ImmediateDataLength...............................................87
17 ITagLength........................................................87
18 PingMaxReplyLength................................................87
19 StartSecure.......................................................87
20 TotalText.........................................................87
21 KeyValueText......................................................87
22 MaxOutstandingR2T.................................................88
Full Copyright Statement.............................................89




























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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 situate readers in the vocabulary 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 a client-server architecture. Clients of a SCSI interface are
   called "initiators". Initiators issue SCSI "commands" to request
   service from a logical unit. The "device server" on the logical unit
   accepts SCSI commands and 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. The queue
   of tasks is managed by the target, though. 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
   "phase-binding" - 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 Data Blocks (CDB) are the data structures used to contain the
   command parameters 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 &  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 will use the term
   "iSCSI protocol data unit" (iSCSI PDU) for these messages.

   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.

1.2.1 Layers & Sessions

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

      -the SCSI layer builds/receives SCSI CDB (Command Data Blocks)
      and relays/receives them with the remaining command execute
      parameters (cf. SAM-2) to/from the
      -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 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 linking an initiator with a
   target form a session (loosely equivalent to a SCSI I-T nexus). A
   session is defined by a session ID (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 will see one
   "target image". All target identifying elements, like LUN are the
   same. In addition, across all connections within a session a target
   will see one "initiator image". Initiator identifying elements like
   Initiator Task Tag can be used to identify the same entity regardless
   of the connection on which they are sent or received.

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

1.2.2 Ordering and iSCSI numbering

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   iSCSI uses Command, Status and Data numbering schemes.

   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 recovery
   in case of connection failure.

   Data numbering is per command and is meant to reduce the amount of
   memory needed by a target sending unrecoverable data for command
   retry.

   Normally, fields in the iSCSI PDUs communicate the reference 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.

   iSCSI NOP-Out PDUs are used as acknowledgements for data numbering.


1.2.2.1 Command numbering

   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 target SCSI
   layer are numbered by iSCSI and the number is carried by the iSCSI
   PDU as CmdRN (Command-Reference-Number).  The numbering is session-
   wide.  All iSCSI PDUs that have a task association carry this number.
   CmdRNs 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 CmdRN SHOULD use
   Serial Number Arithmetic as defined in [RFC1982] where SERIAL_BITS =
   32.

   The target may choose to deliver some task management commands for
   immediate delivery.  The 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 are outside the scope of
   this document.


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

   The target iSCSI layer SHOULD deliver the commands to the target SCSI
   layer in the order specified by CmdRN.

   The initiator and target are assumed to have three counters that
   define the allocation mechanism
       - CmdRN - the current command reference number advanced by 1
      on each command shipped
       - ExpCmdRN - the next expected command by the target -
      acknowledges all commands up to it
       - MaxCmdRN - the maximum number to be shipped - MaxCmdRN -
      ExpCmdRN defines the queuing capacity of the receiving iSCSI
      layer.

   The target SHOULD NOT transmit a MaxCmdRN that is more than 2**31 - 1
   above the last ExpCmdRN.  CmdRN can take any value from ExpCmdRN to
   MaxCmdRN except 0. The target MUST silently ignore any command
   outside this range or duplicates within the range not flagged with
   the retry bit (the X bit in the opcode).  The target and initiator
   counters MUST uphold causal ordering.

   iSCSI initiators MUST implement the command numbering scheme if they
   support more than one connection per session (as even sessions with a
   single connection may be expanded beyond one connection).

   Command numbering for sessions that will only be made up of one
   connection is optional. iSCSI initiators utilizing a single
   connection for a session and not utilizing command numbering MUST
   indicate that they will not support command numbering by setting
   InitCmdRN to 0 in the Login command.

   Whenever an initiator indicates support for command numbering, by
   setting InitCmdRN to a non-zero value at Login, the target MUST
   provide ExpCmdRN and MaxCmdRN values that will enable the initiator
   to make progress.


1.2.2.2 Response/Status numbering

   Responses in transit from the target to the initiator are numbered.
   The StatRN (Status Reference Number) is used for this purpose. StatRN


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   is a counter maintained per connection.  ExpStatRN is used by the
   initiator to acknowledge status.

   To enable command recovery the target MAY maintain enough state 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 ExpStatRN.
   A large difference between StatRN and ExpStatRN may indicate a failed
   connection.

   Initiators and Targets MUST support the response-numbering scheme
   regardless of the support for command recovery.

1.2.2.3 Data PDU numbering

   Incoming Data PDUs MAY be numbered by a target to enable fast
   recovery of long running READ commands.

   Data PDUs are numbered with DataRN.  NOP-Out PDUs carrying the same
   Initiator Tag as the Data PDUs are used to acknowledge the incoming
   Data PDUs with ExpDataRN.  Support for Data PDU acknowledgement and
   the maximum number of unacknowledged data PDUs are negotiated at
   login.
   In a PDU carrying both data and status, the field is used for StatRN
   and the last set of data blocks is implicitly acknowledged when
   Status is acknowledged.

1.2.3 iSCSI Login

   The purpose of 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 each of the
   initiator and target perceives 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 might
   realize a related function (e.g., establish a IPsec or TLS session).

   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 "accept login". Otherwise, it sends a response
   with a "login reject", indicating 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 - composed with an initiator
   part ISID and a target part TSID. For a new session, the TSID is
   null. As part of the response, the target will generate 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 sent on a TCP connection before
   this connection gets into full feature phase at the initiator SHOULD
   be ignored by the initiator. Any message except login and text
   reaching a target on a TCP connection before the full feature phase
   MUST be silently ignored by the target.

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 will send a list of values
   for a key in its order of preference.



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   The responding party will answer 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 was explicitly offered
   and it MAY be selected by omission (i.e. <key>:none MAY be omitted).

   The general format 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).

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, an 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 commands
   task MAY use different connections - connection allegiance is
   strictly per-command and not per-task. During 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) will be sent as either solicited data or unsolicited
   data.  Solicited data are sent in response to Ready To Transfer (R2T)
   PDUs. Unsolicited data can be part of an iSCSI command PDU
   ("immediate data") or an iSCSI data PDU.  An initiator may send
   unsolicited data (immediate or in a separate PDU) up to the SCSI
   limit (initial burst size - mode page 02h). All subsequent data have
   to be solicited.

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   Targets operate in either solicited (R2T) data mode or unsolicited
   (non R2T) data mode.  An initiator MUST always honor an R2T data
   request for a valid outstanding command (i.e., carrying a valid
   Initiator Task Tag) and 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).  It is
   also an error for an initiator to send more data whether immediate or
   as a separate PDU) than the SCSI limit for initial burst.  An
   initiator MAY request, at login, to send immediate data blocks of any
   size. If the initiator requests a specific block size the target MUST
   indicate the size of immediate data blocks it is ready to accept in
   its response.  Beside iSCSI, SCSI also imposes a limit on the amount
   of unsolicited data a target is willing to accept. The iSCSI
   immediate data limit MUST not exceed the SCSI limit.

   A target SHOULD NOT silently discard data and request retransmission
   through R2T.  Initiators MUST NOT perform any score boarding for data
   and 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 those will 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. If
   the amount of data exceeds the amount allowed for unsolicited write
   data, the specific connection MUST be stalled - i.e., no more
   unsolicited data will not be on this connection until the specific
   command has finished sending all its data and has received a
   response.  However new commands can be sent on the connection.  A
   target receiving data out of order or observing a connection
   violating the above rules MUST terminate the session.

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


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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 prelude to recovery.  By
   terminating a connection before starting recovery, initiator and
   target can avoid having stale PDUs being received after recovery.  In
   this case, the initiator will send a LOGOUT request on any of the
   operational connections of a session indicating what connection
   should be terminated.


1.2.7 Naming & mapping

   Text string names are used in iSCSI to:

      - provide explicitly a transportID for the target to enable the
      latter to recognize the initiator because the conventional IP-
      address and port pair is inaccurate behind firewalls and NAT
      devices (key - initiator)
      - provide a targetID for simple configurations hiding several
      targets behind an IP-address and port (key - target)
      - provide a symbolic address for source and destination targets
      in third party commands; those will be mapped into SCSI
      addresses by a SCSI aliasing mechanism

   The targetID MUST be presented within the login phase.

   The names do not require handling within iSCSI  - i.e. are opaque
   entities within this document.  In order to enable implementers to
   relate them to other names and name handling mechanisms the following
   syntax for names SHOULD be used

      <domain-name>[/modifier]

   Where domain-name follows DNS (or dotted IP) rules and the modifier
   is an alphanumeric string (N.B. the whole pattern follows the URL
   structure)

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   Some mapped names for third party command use might have to include a
   port number.  For those the following syntax SHOULD be used:

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

   The text to address transformation, wherever needed, will be
   performed through available name translation services (DNS servers,
   LDAP accessible directories etc.).

   To enable simple devices to operate without name-to-address
   conversion services the following conventions SHOULD be used:

      A domain name that contains exactly four numbers separated by
      dots (.), where each number is in the range 0 through 255, will
      be interpreted as an IPv4 address.
      A domain name that contains more than four, but at most 16
      numbers separated by dots (.), where each number is in the
      range 0 through 255, will be interpreted as an Ipv6 address.

   Examples of IPv4 addresses/names:

      10.0.0.1/diskfarm1
      10.0.0.2

   Examples of IPv6 addresses/names


      12.5.7.10.0.0.1/tapefarm1
      12.5.6.10.0.0.2


   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][/modifier]

   Examples:


      iSCSI://diskfarm1.acme.com
      iSCSI://computingcenter.acme.com/diskfarm1
      iSCSI://computingceneter.acme.com:4002/scanners




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   When a target has to act as an initiator for a third party command,
   it MAY use the initiator name 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 those 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
   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
   selector.

1.2.8 Message Framing

1.2.8.1 Framing Justification

   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).

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   Since these segments cannot be steered to the correct location, they
   must be save in temporary buffers that must then be copied to the
   SCSI buffers.

   To reduce the amount of temporary buffering and copying,
   synchronization information (markers) is placed at fixed intervals in
   the TCP stream to enable accelerated iSCSI/TCP implementations to
   find and delineate iSCSI messages in the presence of IP packet
   reordering.

   The use of markers is negotiable.  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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1.2.8.2 Markers At Fixed Intervals

   At fixed intervals in the TCP byte stream, a "Marker" is inserted.
   This 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 to find
   the next iSCSI message header.  There are two copies of the offset in
   the Marker to handle the case where the Marker straddles a TCP
   segment boundary. Each end of the iSCSI session specifies during
   login the interval of the Marker it will be receiving, or disables
   the Marker altogether. If a receiver indicates that it desires a
   Marker, the sender SHOULD provide the Marker at the desired interval.

   The marker interval (and the initial marker-less interval) are
   counted in terms of the TCP-sequence-number. Anything counted in the
   TCP sequence-number is counted for the interval and the initial
   marker-less interval.

   Markers MUST point to a 4 byte word boundary in the TCP stream - the
   last 2 bits of each marker word are reserved and will be considered 0
   for offset computation.

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

1.2.8.3 iSCSI PDU Size

   When a large iSCSI message is sent, the TCP segment(s) containing 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
   recommended that the iSCSI PDU size be restricted to a small value
   (perhaps a few TCP segments in length). Each end of the iSCSI session
   specifies during login the maximum size of an iSCSI PDU it will
   accept.


1.2.8.4 Initial marker-less interval

   To enable the connection setup including the login phase negotiation
   the negotiated marking will be started at negotiated boundary in the
   stream.  The marker-less interval will not be less than 64 kbytes and
   the default will be 64 kbytes.




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2. iSCSI PDU Formats

   All multi-byte integers specified in formats defined in this document
   are to be represented in network byte order (i.e., big endian).  Any
   bits not defined should be set to zero.

2.1 iSCSI PDU length and padding

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

2.2 Template Header and Opcodes

   All iSCSI PDUs begin with a 48-byte header. Additional data appears,
   as necessary, beginning with byte 48. The fields of Opcode and Length
   appear 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| Opcode        |X| Opcode-specific fields                      |
     |               |P|                                             |
     +---------------+---------------+---------------+---------------+
    4| Length of Data (after 48 byte Header)                         |
     +---------------+---------------+---------------+---------------+
    8| LUN or Opcode-specific fields                                 |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or Opcode-specific fields                  |
     +---------------+---------------+---------------+---------------+
   20/ Opcode-specific fields                                        /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header digest (optional-constant-length)                      |
     +---------------------------------------------------------------+
   +n/                                                               /
    +/ Data (optional)                                               /
     +---------------------------------------------------------------+
    m| Data digest (optional-variable-length)                        |
     +---------------------------------------------------------------+



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2.2.1 Opcode

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

      b7   Response
      b6-0 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


   Valid target opcodes are:


      0x80 NOP-In (from target to initiator)
      0x81 SCSI Response (contains SCSI status and possibly sense
      information or other response information)
      0x82 SCSI Task Management Response
      0x83 Login Response
      0x84 Text Response
      0x85 SCSI Data (for READ operation)
      0x86 Logout Response
      0x90 Ready To Transfer (R2T - sent by target to initiator when
      it is ready to receive data from initiator)
      0x91 Asynchronous Event (sent by target to initiator to
      indicate certain special conditions)
      0xef Reject


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   Initiator opcodes 0x70-0x7f and target opcodes 0xf0-0xff are vendor
   specific codes.



2.2.2 Opcode-specific fields

   These fields have different meanings for different messages.
   Bit 7 of the second byte is used as a retry indicator for commands (X
   bit) or Poll bit (P bit) and must be 0 in all other iSCSI PDUs

2.2.3 Length

   The Length field indicates the number of bytes, beyond the first 48
   bytes, that are being sent together with this message header. The
   length includes the header and data digests if any. It is anticipated
   that most iSCSI PDUs (not counting data transfer PDUs) will not need
   more than the 48 byte header.  The length field accounts for proper
   iSCSI PDU content; whatever padding is required to reach a 4 byte
   boundary in the TCP stream is implied by the protocol but not
   accounted for in the length field.


2.2.4 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.

2.2.5 Initiator Task Tag

   The initiator assigns a Task Tag to each SCSI task that it issues.
   This tag is a session-wide unique identifier that can be used to
   uniquely identify the Task.


2.2.6 Header Digest and Data Digest

   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.


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   The digest types are negotiated during the login phase.

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















































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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| 0x01          |X|R|W|0 0|ATTR | Reserved (0)  | AddCDB        |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Logical Unit Number (LUN)                                     |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Expected Data Transfer Length                                 |
     +---------------+---------------+---------------+---------------+
   24| CmdRN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatRN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ SCSI Command Descriptor Block (CDB)                           /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Command Data (Command Dependent)                              /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.3.1 Flags & Task Attributes

      The flags field for a SCSI Command is:


      b7   Retry (X)
      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

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      2    Ordered
      3    Head of Queue
      4    ACA

2.3.2 AddCDB

   Additional CDB length (over 16) in units of 4 bytes.

2.3.3 CmdRN - Command Reference Number

   Enables ordered delivery across multiple connections in a single
   session.

2.3.4 ExpStatRN - Expected Status Reference Number

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

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 operation, the initiator uses this field to
   specify the number of bytes of data it expects to transfer for this
   operation.  For a READ 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.

   For bi-directional operations, this field states the number of data
   bytes involved in the outbound transfer. For bi-directional
   operations, an additional field indicating the Expected Bidi-Read
   Data Transfer Length is following the (possibly extended) CDB as
   shown below:

     +---------------+---------------+---------------+---------------+
   48/ Additional CDB (if any)                                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   +n| Expected Bidi-Read Data Transfer Length                       |
     +---------------------------------------------------------------+
   +4/ Immediate data (optional)                                     /
     /                                                               /
     +---------------------------------------------------------------+





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   If no data will be transferred in SCSI Data packets for this SCSI
   operation, this field should be set to zero.

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

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 48-byte boundary of
   the iSCSI header.  Alternatively, user data (as from a WRITE
   operation) can be placed in the same PDU (both cases referred to as
   immediate 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| 0x81          |Rsvd   |o|u|O|U| Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Reserved (0)                                                  |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Basic Residual Count                                          |
     +---------------+---------------+---------------+---------------+
   24| StatRN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Command Status| Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40| Resp_length                   | Sense_length                  |
     +---------------+---------------+---------------+---------------+
   44| Bidi-Read Residual Count                                      |
     +---------------+---------------+---------------+---------------+
   48/ Response and/or sense Data (optional)                         /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

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
      b4-7 not used (SHOULD be set to 0)

   Bits O and U are mutually exclusive and so are bits o and u.

2.4.2 Basic Residual Count

   The Basic Residual Count field is valid only in case 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.

2.4.3 Bidi-Read Residual Count

   The Bidi-Read Residual Count field is valid only in case 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 in
   out of those expected to be transferred.  If the o bit is set, the
   Bidi-Read Residual Count indicates how many bytes could not be
   transferred in because the initiator's Expected Bidi-Read Transfer
   Length was too small.

2.4.4 Command Status

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

2.4.5 Resp_length - Response length

2.4.6 Sense_length - Length of sense data

2.4.7 Response and/or Sense Data

   iSCSI targets MUST support and enable autosense.  If the Command
   Status was CHECK CONDITION (0x02), then the Response and/or Sense
   Data field will contain sense data for the failed command after the
   response data.  Some sense codes will relate to iSCSI check
   conditions (e.g. excessive number of outstanding commands, immediate
   data blocks too large etc.).  The Length parameters specify the
   number of bytes in each section of this field.  If no error occurred,
   and no data is needed for the response to the SCSI Command the length


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   field is zero.  If both Response Data and Sense Data are present, the
   Response Data precedes the Sense Data.

2.4.8 StatRN - Status Reference Number

   StatRN is a reference number that the target iSCSI layer generates
   per connection and that in turn enables the initiator to acknowledge
   status reception. StatRN is incremented by 1 for every
   response/status sent on a connection.

2.4.9 ExpCmdRN - next expected CmdRN from this initiator

   ExpCmdRN is a reference 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 MaxCmdRN - maximum CmdRN acceptable from this initiator

   MaxCmdRN is a reference number that the target iSCSI returns to the
   initiator to indicate the maximum CmdRN the initiator can send. It is
   used to update a local counter with the same name.

   MaxCmdRN and ExpCmdRN are processed as follows:

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

   This sequence is required as updates may arrive out of order (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| 0x02          |0| Function    | Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Logical Unit Number (LUN)                                     |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Referenced Task Tag or Reserved (0)                           |
     +---------------+---------------+---------------+---------------+
   24| CmdRN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatRN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48

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 the functions above a 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 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 and
   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 will enter 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| 0x82          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Logical Unit Number (LUN)                                     |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Referenced Task Tag or Reserved (0)                           |
     +---------------+---------------+---------------+---------------+
   24| StatRN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Response      | Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48

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

       0    Function Complete
       1    No Task Found
      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


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   attached initiators notifying them that the target has been reset.
   For the <Target Cold Reset> the target MUST then close all of its TCP
   connections to all initiators (terminates all sessions).

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 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| 0x05          |F| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved (0)                                           |
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Target Task Tag (solicited) or Reserved (0) (unsolicited)     |
     +---------------+---------------+---------------+---------------+
   24| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   28| ExpStatRN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved (0)                                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   40| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   44| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   48/ 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| 0x85          |P|   (0) |S|O|U| Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   12| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Residual Count                                                |
     +---------------+---------------+---------------+---------------+
   24| DataRN /StatRN                                                |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Command Status| Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   44| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   48/ Payload                                                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.7.1 F (Final) bit

   This bit is 1 for the last PDU of immediate data or the last PDU of a
   sequence answering a R2T.

2.7.2 Length

   The length field specifies the total number of bytes in the following
   payload.

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2.7.3 Target Task Tag

   The Target Task Tag is provided to the target if the transfer is
   honoring a R2T. In this case, the Target Task Tag field is a replica
   of the Target Task Tag provided with the R2T.
   The Target Task Tag values are not specified by this protocol except
   that the all-bits-one value (0x'ffffffff') is reserved and means that
   the Target Task Tag is not supplied.  If the Target Task Tag is
   provided then the LUN field MUST hold a valid value and consistent
   with whatever was specified with the command, else the LUN field is
   reserved.

2.7.4 Buffer Offset

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

2.7.5 Flags

   The last SCSI Data packet sent from a target to an initiator for a
   particular SCSI command that completed successfully may optionally
   also contain the Command Status for the data transfer.  In this case
   Sense Data cannot be sent together with the Command Status.  If the
   command 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 ordinary SCSI Response
      b2   S (status)- set to indicate that the Command Status field
      contains status
      b3-6 not used (should be set to 0)
      b7   P (poll) - set to indicate data acknowledgement is
      requested; b7 and b2 are mutually exclusive - if S bit is set P
      bit MUST be ignored

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

2.7.6 Data numbering (DataRN)

   On inbound data, the target MAY number (sequence) the data packets to
   enable shorter recovery on connection failure.  In case the target
   numbers data packets, the initiator MUST acknowledge them by
   specifying the next expected packet in a NOP-Out with the same

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   Initiator Tag. Acknowledging NOP PDUs MAY be postponed for up to the
   number of incoming data PDUs negotiated at login.  An explicit
   request for acknowledgement made by setting the P bit MUST be
   honored.

















































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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| 0x04          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| CmdRN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatRN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Text                                                          /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.8.1 Length

   This is the length, in bytes, of the Text field.


2.8.2 Initiator Task Tag

   The initiator assigned identifier for this Text Command.
   If the command is sent as part of the Login Phase the Initiator Task
   Tag MUST be the same as the one sent with the Login Command.

2.8.3 Text

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   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 ':'
   (0x3A) delimiter. Many key:value pairs can be included in the Text
   block by separating them with null ' ' (0x00) delimiters.

   Character strings are represented following the C-language syntax.
   Numeric and binary values are represented using either using decimal
   numbers or the hexadecimal 0x'ffff' notation. The result is adjusted
   to the specific key.

   Some basic key:value pairs are described in Appendix A & C.  The
   target responds by sending its response back to the initiator. The
   target and initiator can then perform some advanced operations based
   on their common capabilities.

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

      com.acme.bar.foo.do_something:0000000000000003

   Any key that the target does not understand may be ignored without
   affecting basic function. Once the target has processed all the
   key:value or key:(list) pairs, it responds with the Text Response
   command, listing the parameters that it supports. 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.
   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.
   The default limit is 16384 UTF8 characters.















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2.9 Text Response

   The Text Response message contains the responses of the target 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| 0x84          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| StatRN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Text Response                                                 /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.9.1 Length

   This is the length, in bytes, of the Text Response field.

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


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   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 and the two
   MUST be equivalent where applicable.















































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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.


   Byte /    0       |       1       |       2       |       3       |
      /              |               |               |               |
     |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
     +---------------+---------------+---------------+---------------+
    0| 0x03          |0| Reserved (0)| Version-major | Version-minor |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| CID                           | Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
   12| ISID                          |TSID                           |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| InitCmdRN   or   0                                            |
     +---------------+---------------+---------------+---------------+
   28/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Login Parameters in Text Command Format                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

2.10.1 Version-major and Version-minor

   Currently 0.3

2.10.2 CID

   A unique id for this connection within the session

2.10.3 InitCmdRN

   Is significant only if TSID is zero and indicates the starting
   Command reference number for this session; it SHOULD be zero for all
   other instances. If it is significant (TSID is 0) and the value is


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   zero then this is a single connection session with no support for
   command numbering.

2.10.4 Login Parameters

   The initiator MAY provide some basic parameters in order to enable
   the target to determine if the initiator may in fact 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 Appendixes.










































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2.11 Login Response

   The Login Response indicates the end of the login phase.  Note, if
   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| 0x83          |F| Reserved (0)| Version-major | Version-minor |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   12| ISID                          |TSID                           |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   24| InitStatRN                                                    |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Status        | Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Login Parameters in Text Command Format                       /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.11.1 Version-major minor

   Indicates the version supported. Assuming versions are backward
   compatible, it indicates the highest (compatible) version supported
   by the target.

2.11.2 InitStatRN


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   This is the starting status reference number for this connection.

2.11.3 Status

   The Status returned in a Login Response is one of the following:

      0 accept login   (will now accept SCSI commands)
      1 reject login

   In the case that the Status is "accept login" the initiator may
   proceed to issue SCSI commands.  In the case that the Status is
   "reject login" the initiator should immediately close down its end of
   the TCP connection, thus freeing up the target's port for some other
   connection. The target also has the option of immediately closing
   down its end of the TCP connection.

2.11.4 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 is rejecting the login.

2.11.5 Final bit

   Final bit is set to one in the Final Login Response. A Final bit of 0
   indicates a "partial" response - 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| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or Reserved (0)                            |
     +---------------+---------------+---------------+---------------+
   20| Target Tag or Reserved (0x'ffffffff')                         |
     +---------------+---------------+---------------+---------------+
   24| CmdRN or (0)                                                  |
     +---------------+---------------+---------------+---------------+
   28| ExpStatRN or (0)                                              |
     +---------------+---------------+---------------+---------------+
   32| ExpDataRN or (0)                                              |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ 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 it's components are operational using in-order
   delivery or out-of-order delivery. It 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 as much as
   possible of the data that was provided in the NOP-Out.  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 will then
   close the connection and may try to establish a new connection.


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   The NOP-Out with the P bit not set MUST be used to acknowledge data
   received from a target (data-ack) whenever data numbering is used. In
   this case, the command caries the same Initiator Task Tag as the data
   it acknowledges and the CmdRN field MUST be zero.  Duplicate or
   obsolete data acknowledgements MUST be silently discarded by the
   target.

   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 will copy the NOP-In
   value.


2.12.1 P - Ping bit

   Request a NOP-In

2.12.2 Length

   This is the length of the optional Ping Data.

2.12.3 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
   one or the DataRN field is set.

2.12.4 Target Task 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 Tag from the NOP-In PDU.



2.12.5 Ping Data

   Binary data that will be reflected in the Ping Response.








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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| 0x80          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20 Target Tag or Reserved (0x'ffffffff')                          |
     +---------------+---------------+---------------+---------------+
   24| StatRN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ 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 Ping Command. It SHOULD also duplicate as much of the
   initiator provided Ping Data as allowed by a configurable target
   parameter.

   A target may issue a NOP-In by its own to test connection and the
   state of the initiator. In this case the Initiator Task Tag MUST be 0
   and the Target Tag MUST be set (not x'ffffffff') only if the P bit is
   1.

2.13.1 Target Task Tag

   A target assigned identifier for the operation.

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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.

   If an initiator intends to start recovery for a failing connection it
   MUST use the Logout command to "clean-up" the target end of a failing
   connection and enable recovery to start.  On sessions with a single
   connection, this might imply opening 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          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| CID                           | Reserved (0)  |Reason Code    |
     +---------------+---------------+---------------+---------------+
   12| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48

2.14.1 CID

   The connection ID of the connection to be closed (including closing
   the TCP stream)

2.14.2 Reason Code

   Indicate the reason for Logout:

      0 - Remove the connection session is closing
      1 - Remove the connection for recovery
      2 - Remove the connection at targets requests (requested
      through an AEN)

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2.15 Logout Response

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



   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| 0x86          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Status        | Reserved (0)                                  |
     +---------------------------------------------------------------+
   48

2.15.1 Status

   Logout ending status:

      0 - connection closed successfully
      1 - cleanup failed












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2.16 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 whatever 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 both sending the UseR2T:no key-
   pair attribute to each other (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 Task 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 and 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 Buffer Offsets and Lengths for
   consecutive PDUs SHOULD form a continuous non-overlapping range and
   the PDUs should be sent in increasing offset order.

   The target may send several R2T PDUs and thus have a number or data
   transfers pending.  The present document does not limit the number of
   outstanding data transfers. However, the target SHOULD NOT issue
   overlapping R2T request (i.e. referring to the same data area).  All
   outstanding R2T should have different Target Transfer Tags.


   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| 0x90          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Reserved (0)                                                  |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+


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   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Target Task Tag                                               |
     +---------------+---------------+---------------+---------------+
   24| Reserved (0)                                                  |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Desired Data Length                                           |
     +---------------+---------------+---------------+---------------+
   40| Buffer Offset                                                 |
     +---------------+---------------+---------------+---------------+
   44| Reserved (0)                                                  |
     |                                                               |
     +---------------+---------------+---------------+---------------+
   48

2.16.1 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 indicating the point at which the data transfer should begin,
   relative to the beginning of the total data transfer.


2.16.2 Target Transfer Tag

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











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2.17 Asynchronous Event

   An Asynchronous Event 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| 0x91          |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8| Logical Unit Number (LUN)                                     |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   24| StatRN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdRN                                                      |
     +---------------+---------------+---------------+---------------+
   36|SCSI Event Ind |iSCSI Event Ind| Reserved (0)                  |
     +---------------+---------------+---------------+---------------+
   40/ Reserved (0)                                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Sense Data                                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+


2.17.1 iSCSI Event

   Some Asynchronous Events are strictly related to iSCSI while others
   are related to SAM-2.  The codes returned for iSCSI Asynchronous
   Events are:

      1    Target is being reset.
      2    Target requests Logout on this connection

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2.17.2 SCSI Event Indicator

   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    All Task Sets are being Reset by another Initiator
      5    Some other type of unit attention condition has occurred.
      6    An asynchronous event has occurred.

   Sense Data accompanying 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.

   Please note that StatRN counts this PDU as a acknowledgeable event
   allowing the initiator and target state synchronization.































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2.18 Third Party Commands

   SCSI allows every addressable entity to be ether initiator or target.
   In host-to-host communication, each one of them 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 commands 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, called sources and
   destinations. Sources and destinations act as targets.  The whole
   operation is described by one "master CDB" delivered to the copy-
   manager and a series of descriptor blocks; each descriptor block
   addresses a source and destination target and 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.

   To address them an iSCSI copy-manager will use information provided
   to it through map commands and the SRAs and flags provided in the
   descriptors - allowing for iSCSI and FC sources and destinations.

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




















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2.19 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|0| 0xef        |0| Reserved (0)                                |
     +---------------+---------------+---------------+---------------+
    4| Length                                                        |
     +---------------+---------------+---------------+---------------+
    8/ Reserved (0)                                                  /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   36| Reason        | Reserved (0)                                  |
     +---------------+---------------+---------------+---------------+
   40| Reserved (0)                                                  |
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ Header of Bad Message                                         /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   96

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

2.20 Reason

   The reject Reason is coded as follows:

      1 - Format Error
      2 - Header Digest Error
      3 - Payload Digest Error












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3. Login phase

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

   The login phase is implemented via login and text commands and
   responses only. The login command is sent from the initiator to
   target in order to start the login phase and 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 (very much like 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)

3.1 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 0.3)
      -Session and connection Ids
      -Security Parameters (if security is requested) and
      -Protocol parameters

   The target can answer in the following ways:

      -Login Response with Login Reject (and Final bit 1).  This is
      an immediate rejection from the target causing the session to
      terminate. Causes for rejection are address rejection, local
      protection etc.. Login reject with Final bit 0 is a format
      error.
      -Login Response with Login Accept with session ID and iSCSI
      parameters and Final bit 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 Final bit 0 indicating the start of a
      authentication/negotiation sequence. The response includes the
      protocol version supported by the target and the security
      parameters (not iSCSI parameters, those will be returned only
      after security is established to protect them) supported by the
      target.

3.2 Security negotiation

   The negotiation proceeds as follows:

      -The initiator sends a text command with an ordered list of the
      options it supports for each subject (encryption algorithm,
      authentication algorithm, iSCSI parameters and so on). The
      options are listed from the most preferable (to the initiator)
      to the least.
      -The target MUST reply with the first option in the list it
      supports.  The parameters are encoded in Unicode - UTF8 as
      key:value (e.g., the encryption option of triple-DES will
      appear as encryption:3des-cbc).  The initiator MAY send
      proprietary options as well. The "none" option MUST be included
      in the list, indicating no algorithm 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 general parameters should be negotiated only after security
      is established at the desired level.  Any operational
      parameters sent before establishing a secure context MUST be
      reset by both the target and the initiator when establishing
      the security context. For a list of security parameters see
      Appendix A.

3.3 iSCSI Security

   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 security mechanism includes the following elements:

      -Initial authentication - the host and the target authenticate
      themselves to each other. A negotiable algorithm, e.g.,
      user/password or public key, provides this feature.
      -Message integrity - an integrity and authentication digest is
      attached to each packet and authenticates it. The algorithm is
      negotiable.



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      -Encryption - data from host to target and from target to host
      is encrypted. The user MAY choose to encrypt only part of the
      data, e.g., headers only (for complexity reasons). Encryption
      MAY use IPsec. The algorithm and its parameters are negotiable.

   Using IPsec for encryption or authentication may eliminate the need
   for parameter negotiation at the iSCSI level (for example, ISAKMP for
   IPsec). However, there is still a need to negotiate for the algorithm
   itself.

   If security is established in the login phase note that:

      -After setting message integrity, each iSCSI message MUST
      include the appropriate digest field (i.e., each message after
      the one through which the target choose the algorithm.
      -If encryption is to be set (e.g., IPsec), it should be set
      prior to the login phase.
      -The iSCSI parameter negotiation (non-security parameters)
      SHOULD start only after security is established. This should be
      carried on text commands.































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4. iSCSI Error Handling and Recovery

4.1 Connection failure

   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, that outgoing data
   is available (in host memory) for retransmission while the command is
   outstanding. It is also assumed that, at a target, iSCSI and
   specialized TCP implementations are able to recover unacknowledged
   data packets from a closing connection or, alternatively, the target
   has means to re-read data 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. A target will
   sequentially number the delivered responses and thus enable
   initiators to tell when a response is missing and which response is
   missing.

   Under those conditions, iSCSI will be able to 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.  Unfortunately,
   the maximum admissible recovery time is a function of the target and
   for some devices and communications networks recovery may be complex
   and may percolate to upper software layers.  It is assumed that
   targets and/or initiators will recognize a failing connection by
   either transport level means (TCP) or by 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 idle links.

   The iSCSI recovery involves the following steps:

      -abort offending TCP connection(s) (target & initiator) and
      recover at target all unacknowledged read-data
      -issue a Logout command on a remaining connection or create a
      new connection and issue the Logout command
      -wait for the Logout response
      -if needed, create one or more new TCP connections (within the
      same session) and associate all outstanding commands from the
      failed connection to the new connection at both initiator and
      target.




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      -the initiator will reissue all outstanding commands with their
      original Initiator Task Tag and their original CmdRN if they
      are not acknowledged yet or a CmdRN of 0 (not-numbered) if they
      were acknowledged; the retry (X) flag in the command PDU will
      be set
      -upon receiving the new/retry commands the target will resume
      command execution; for write commands it means requesting data
      retransmission through R2T, for reads retransmitting recovered
      data and for "terminated" commands retransmitting the Status &
      Sense while retaining the original StatRN. If data recovery is
      not possible, the target will either provide data from the
      media or redo the operation (if the operation is not idempotent
      the device server may fail the operation).


4.2 Protocol Errors

   The authors recognize that mapping framed messages over a "stream"
   connection (like TCP) makes the proposed mechanisms vulnerable to
   simple software framing errors and introducing framing mechanisms may
   be onerous for performance and bandwidth.  Command reference numbers
   and the above mechanisms for connection drop and reestablishment will
   help handle this type of mapping errors.

4.3 Session Errors

   If all the connections of a session fail and can't 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 will terminate all outstanding requests with an iSCSI
   error indication before initiating a new session.  A target that
   detects one of the above errors will take the following actions:

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

4.4 Format errors

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

   While a session is active whenever a target receives an iSCSI PDU
   with a format error is MUST answer with a Reject iSCSI PDU with
   a Reason-code of Format-error.



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   When a session is active whenever 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 as a SCSI check condition
   status with a sense key of 4h (hardware error).

4.5 Digest errors

   When a target receives an iSCSI data PDU with a data payload digest
   error, it MUST discard it and request retransmission with a R2T.
   When a target receives an iSCSI PDU with a header digest error or a
   payload digest error in anything but a data iSCSI PDU it MUST answer
   with a Reject iSCSI PDU with a Reject iSCSI PDU with a Reason-code of
   Digest-error.

   When an initiator receives an iSCSI data PDU with a data payload
   digest error or any other iSCSI PDU with a header or payload digest
   error it MUST discard it, and restart the task - the later provided
   it could recognize the Initiator Task Tag.  If the initiator can't
   recognize the Initiator Task Tag, (e.g., a header digest error) the
   initiators MUST logout the connection and restart it (including
   restarting all outstanding tasks).






























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5. 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.

5.1 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.

5.2 Autosense

   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.






























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6. Security Considerations

6.1 Data Integrity

   We assume that basic level end-to-end data integrity can be
   reasonably handled by TCP, by using the standard checksum.  For those
   applications for which data integrity is of utmost importance iSCSI
   will provide an integrity option.

6.2 Network operations and the Threat Model

   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.

6.2.1 Threat Model

   Attacks fall into three main areas; passive, active, and denial of
   service.

6.2.1.1 Passive Attacks

   Often, data transfers will be made through a switched fabric, making
   sniffing difficult. In addition, the nature of the data (block
   transfers), even if sniffed, would not necessarily be readily
   understandable to the attacker.  That being said, a determined
   attacker, by capturing of content and analyzing traffic over time,
   could replicate enough of a storage device to make the captured data
   meaningful. Certain storage operations which are mostly
   unidirectional, such as writing to a tape or reading from a CD-ROM,
   are more susceptible to passive attacks since the listener will be
   able to replicate most if not all of the operation.

   Passive attacks by traffic analysis alone is deemed out of scope
   since it is unlikely that the listener will be able to guess any
   pertinent information without knowing the content of the messages.
   It is also out of scope to detect passive attacks. The protocol must
   be able to prevent passive attacks by masking the contents of
   messages through some form of encryption.

   Finally, it is assumed that a strong authentication mechanism will be
   necessary. Therefore, any long-lived passwords or private keys SHOULD
   never be sent in the clear.

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6.2.1.2 Active Attacks

   Whereas passive attacks involve SNIFFING, active attacks will
   generally involve SPOOFING. If an attacker can successfully
   masquerade as a client, he will have total read/write access to those
   storage resources assigned to that client. Spoofing as a server is
   sometimes more difficult, since many operations involve client reads
   of some expected or otherwise understandable data.

   Most likely, many of the sessions will be long-lived. This feature
   has a dual effect of making these sessions more vulnerable to attack
   (hijacking TCP connections, cryptographic attacks), while at the same
   time providing mechanisms to detect attacks. An attempt to open a
   session while one is already active can be treated as a possible
   attack. Both the transport and session layer protocols will have
   sequencing that would need to be adhered to by the attacker to avoid
   generating errors that could also be treated as a possible attack.

   Message modification can be a significant threat to an environment
   reliant on the integrity of the data. Message replay, insertion, or
   deletion will generally produce errors (such as data
   overruns/underruns) that can be recovered successfully, they can have
   the effect of reducing performance, and as such can act as a denial
   of service. It is possible that an attacker can modify a message in
   such a way the session becomes uncoordinated, resulting in a tear
   down of the session.

6.2.2 Security Model

6.2.2.1 No Security

   This mode does not authenticate nor does it encrypt data. This mode
   should only be used in environments where there is minimal security
   risk and little chance for configuration errors.

6.2.2.2 End-to-End Authentication

   This mode protects against an unauthorized access to storage
   resources either through an active attack (SPOOFING) or configuration
   errors. Once the client is authenticated, all messages are sent and
   received in the clear.  This mode should only be used when there is
   minimal risk to man-in-the-middle attacks, eavesdropping, message
   insertion, deletion, and modification. For example, this mode can be
   used when IPsec is used in security gateways.

6.2.2.3 iSCSI integrity and authentication

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   The iSCSI protocol provides an authentication mechanism for initiator
   and target. This includes login authentication and authentication
   trailers for headers and data. No encryption is provided at the iSCSI
   protocol level. The implementers may use other protocols (e.g.,
   IPsec) for this purpose.


6.2.2.4 Encryption

   This mode provides for the end-to-end encryption (e.g. IPsec). In
   addition to authenticating the client, it provides end-to-end data
   integrity and protects against man-in-the-middle attacks,
   eavesdropping, message insertion, deletion, and modification.

   A connection or multiple connections can be protected end-to-end by
   using IPSec.  In this case, the initiator must use the "Implicit
   Authentication" parameter to indicate that IPSec should be used to
   specify the Access ID and perform authentication.

6.2.3 Other Considerations

   Due to long-lived sessions, is there a need for periodic
   authentication after the session is established? For example, should
   the client be challenged during key-alive exchanges in addition to
   login?

   Due to long-lived sessions with encryption, is there a higher level
   of vulnerability to cryptographic attacks?

6.3 Login Process

   In some environments, a target will not be interested in
   authenticating the initiator. In this case, the target can simply
   ignore some or all of the parameters sent in a Login Command, and the
   target can simply reply with a basic Login Response indicating a
   successful login.  Some targets MAY want to perform some kind of
   authentication. Various authentication schemes can be used, including
   encrypted passwords and trusted certificate authorities.  Once the
   initiator and target are confident of the identity of the attached
   party, the established channel is considered secure.


6.4 Feasibility

   The encryption algorithms are computationally complex. Therefore, the
   real time constraints on the transmission and reception may render

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   difficult the implementation of completely encrypted streams. Working
   with fast networks will force the implementers to use one of the
   following alternatives:

      -Hardware implementation
      -Partial encryption

   The first alternative enables the use of completely encrypted
   streams. Although robust, this may be (at least at top speeds)
   expensive.

   The second alternative does not require specialized hardware, but
   will reduce the safety of the system.  In most cases, however, the
   safety tradeoff is acceptable (e.g., encryption of headers only by
   defining an IPsec policy).

   Data integrity/authentication through data and header digests can
   easily be performed.

































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7. 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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8. References and Bibliography

      [AC]  A detailed proposal for Access Control, Jim Hafner,
      T10/99-245
      [ALTC]    Internet Draft: Alternative checksums (work in
      progress)
      [CAM]     ANSI X3.232-199X, Common Access Method-3 (Cam-3)
      [CRC]     ISO 3309, High-Level Data Link Control (CRC 32)
      [FIPS-180-1] FIPS-Secure Hash Standard
      [FIPS-186-2] FIPS-Digital Signature Standard
      [Orm96] Orman, H., "The Oakley Key Determination Protocol",
      version 1, TR97-92, Department of Computer Science Technical
      Report, University of Arizona.
      [PKIX-Part1] Housley, R., et al, "Internet X.509 Public Key
      Infrastructure, Certificate and CRL Profile", Internet Draft,
      draft-ietf-pkix-ipki-part1-11.txt
      [RFC793]  Transmission Control Protocol, RFC 793
      [RFC1122] Requirements for Internet Hosts-Communication Layer,
      RFC1122, R. Braden (editor)
      [RFC-1766] Alvestrand, H., "Tags for the Identification of
      Languages", March 1995.
      [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.
      [RFC-2104] Krawczyk, H., Bellare, M., and Canetti, R., "HMAC:
      Keyed-Hashing for Message Authentication", February 1997
      [RFC-2119] Bradner, S. "Key words for use in RFCs to Indicate
      Requirement Levels", BCP 14, RFC 2119, March 1997.
      [RFC-2144] Adams, C., "The CAST-128 Encryption Algorithm", May
      1997.
      [RFC-2234] D. Crocker, P. Overell Augmented BNF for Syntax
      Specifications: ABNF
      [RFC-2313] B. Kaliski, PKCS #1: RSA Encryption, Version 1.5
      [RFC-2434] T. Narten, and H. Avestrand, "Guidelines for Writing
      an IANA Considerations Section in RFCs.", RFC2434,  October
      1998.
      [RFC-2440] Callas, J., et al, "OpenPGP Message Format",
      November 1998.
      [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 Second Edition:
      protocols, algorithms, and source code in C", 2nd edition, John
      Wiley & Sons, New York, NY, 1996.

Satran, J.            Standards-Track, June 2001                    70

                                iSCSI               December 30, 2000


      [SPC]     ANSI X3.301-199X, SCSI-3 Primary Commands (SPC)
      [TLS]     The TLS Protocol, RFC 2246, T. Dierks et al.



















































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9. Author's Addresses

        Julian Satran
        Kalman Meth
        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



        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


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        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:  lldalleore@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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Apendix A. iSCSI Security

01 Security keys and values

   The parameters (keys) negotiated for security are:

      - digests (header_digest:, data_digest:)
      - authentication methods (init_auth:, target_auth:)
      - public key algorithm (public_key)

   The following table lists cyclic integrity checksums that can be
   negotiated for the digests.

   +---------------------------------------------+
   | Name          | Description                 |
   +---------------------------------------------+
   | crc-16        | 16 bit CRC                  |
   +---------------------------------------------+
   | crc-CCITT     | 16 bit CRC                  |
   +---------------------------------------------+
   | crc-32        | 32 bit CRC                  |
   +---------------------------------------------+
   | crc-64        | 64 bit CRC                  |
   +---------------------------------------------+
   | none          | no digest                   |
   +---------------------------------------------+

   The generator polynomials for those digests are:

      crc-16    - x**16+x**15+x**2+1
      crc-CCITT - x**16+x**12+x**5+1
      crc-32    - x**32+x**26+x**x23+x**22+x**16+x**12+x**11+x**10+
                  x**8+x**7+x**5+x**4+x**2+x+1
      crc-64    -


   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.).

   crc-16 and crc-CCITT are considered adequate for very short blocks
   (like PDU headers or very short payloads).

   crc-32 and crc-64 are considered adequate for longer blocks.



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   Cyclic codes are particularly well suited for hardware
   implementations.

   Implementations MAY also negotiate some hash functions that may
   provide data authentication in addition to integrity as detailed in
   the following table:


   +-----------------------------------------------------------+
   | Name          | Description                 | Definition  |
   +-----------------------------------------------------------+
   | hmac-sha1     | HMAC-SHA1 length=20         | RFC-2104    |
   +-----------------------------------------------------------+
   | hmac-sha-96   | first 96 bits of HMAC-SHA 1 | RFC-2104    |
   +-----------------------------------------------------------+
   | hmac-md5      | HMAC-MD5 length 16          | RFC-2104    |
   +-----------------------------------------------------------+
   | hmac-md5-96   | first 96 bits of HMAC-MD5   | RFC-2104    |
   +-----------------------------------------------------------+


   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                               |
   +-----------------------------------------------------------+
   | publickey     | Public key authentication                 |
   +-----------------------------------------------------------+
   | password      | Plain text user-password                  |
   +-----------------------------------------------------------+
   | challenge     | Challenge and response                    |
   +-----------------------------------------------------------+
   | none          | No authentication                         |
   +-----------------------------------------------------------+

   The following table details public key algorithms for authentication:








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   +-----------------------------------------------------------+
   | Name          | Description                 | Definition  |
   +-----------------------------------------------------------+
   | ssh-dss       | Simple DSS                  | [FIPS-186]  |
   +-----------------------------------------------------------+
   | rsa           | RSA public key              | [RFC2313]   |
   +-----------------------------------------------------------+
   | none          | No Public Key               | -           |
   +-----------------------------------------------------------+

   Where the public key information is encoded as:

      public_key:<name>,<parameters>

   For example, if ssh-dss is selected:

      public_key:ssh-dss,p,q,g,y

   Here the "p", "q", "g", and "y" parameters (encoded as numbers in
   Unicode UTF8) form the signature key blob.

   Signing and verifying using this key format are done according to the
   Digital Signature Standard [FIPS-186] using the SHA-1 hash. A
   description can also be found in [Schneier].

   The dss signature blob is encoded as a string containing "r" followed
   by "s" (which are 160 bits long integers, without lengths or padding,
   unsigned and in network byte order).



02 Authentication

   The authentication exchange SHOULD authenticate 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 public key, user/password
   or challenge/response.

   If public key is selected then each party MUST use:

      authenticate:<user-id>,<blob>


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   where user-id is an assigned id of the host-OS for the initiator or
   the World-Wide-Name for the target and blob is the public-key blob.

   For user/password each party must use:

      authenticate:<user-id>,<password>

   where user-id is as above and password is a plain-text password.

03 Salt

   salt:<number> can be used by different authentication schemes to
   prevent replay attacks (a random number - cookie - or a time stamp or
   both)

04 Challenge

   challenge:<string> and authenticate:<string> MUST be used for
   challenge answer schemes

05 Login Phase examples:

   The first example is a "user-password" authentication:

   In this example, the result of the negotiation is to use md5 for
   header digest, crc32-2k for data digest and user/password for
   initiator authentication. No target authentication required.

      I-> Login header_digest:(hmac-md5,hmac-md5-96,crc32,none)
      data_digest:(crc32-2k) init_auth:(public-key,password,none)
      target_auth:(none) public_key:((ssh-dss,parameters),none)
      T-> Text header_digest:hmac-md5 data_digest:crc32-2k
      init_auth:password
      I-> Text authenticate:alef,sesam
   If the authentication is successful:
      T->StartSecure:HERE
      ...
      T-> Login "login accept"
   If the authentication was not successful:
      T-> Login "login reject"


   Note - the Text command including SecureStart:HERE and each PDU after
   it will have the trailer consisting in a hmac-md5 digest for the
   header and a crc32 for each 2k of data (or fraction thereof).


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   The next example is a "public-key" authentication. The initiator
   authenticates itself to the target; no keys are exchanged:

       I-> Login header_digest:(hmac-md5,hmac-md5-
      96,crc32,none)data_digest:(crc32-2k,none)
      init_auth:(publickey,password,none) target_auth:(none)
      public_key:((rsa,parameters),(ssh-dss,parameters),none)
      T-> Text header_digest:hmac-md5 data_digest:crc32-2k
      init_auth:publickey public_key:(ssh-dss,parameters)
      I-> Text authenticate:user,blob salt:578913456

             NB - where the parameters stands for the hash of header
         and the salt, i.e., hash(heder || salt).  The initiator
         SHOULD add "salt" to the packet, e.g. add the pair
         salt:<random-number> (or timestamp or a mixture) to its
         packet to prevent record and replay.
         The key distribution may be done by a certificate authority
         or other server and is beyond the scope of this document

         If the user was not confirmed, the target sends a login
         response message with "login reject" to the initiator. Else,
         it can send a login response with "login accept" and MAY
         attach a secret:

      T->Text StartSecure:HERE secret:
      I->Text ... parameters ...EndLogin:HERE
      T->Login (accept) ... parameters ...

   The next example is another "public-key" authentication. The
   initiator authenticates itself to the target. The target
   authenticates itself to the initiator and key are exchanged:

       I-> Login header_digest:(hmac-md5,hmac-md5-
      96,crc32,none)data_digest:(crc32-2k,none)
      init_auth:(publickey,password,none) target_auth:
      (none) public_key:((ssh-dss,parameters),(rsa, parameters),none)
      T-> Text header_digest:hmac-md5 data_digest:crc32-2k
      init_auth:publickey public_key:(ssh-dss,parameters)
      target_auth:(publickey,password,none) public_key:(ssh-
      dss,parameters),none
      I-> Text authenticate:user,blob target_auth:publickey
      public_key:(ssh_dss,parameters) salt:20001103172433

      where blob stands for hash(header || salt).

         Note: the last packet should have the appropriate trailers.


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   If the initiator was not confirmed, the target sends a login response
   message with "login reject" to the initiator. Else, it can continue
   with the login process:

      T-> Text authenticate:user,blob salt:532678925

      where blob stands for hash(header || salt).

   In here, the target authenticates itself to the initiator. If the
   authentication was successful, the initiator responses with an empty
   text command, continuing the login phase. Else, it stops the login
   phase.

      I->Text
      T->Text secret:blob

   Where blob is a key encrypted with the initiator’s public key.

      I->Text StartSecure:HERE... parameters ...
      ...
      T->Login "login accept" ... parameters ...

   In the next example the target authenticates the initiator via
   challenge and response.


      I-> Login header_digest:(hmac-md5,hmac-md5-96,crc32,none)
      data_digest:(crc32-2k) init_auth:(public-
      key,password,challenge,none) target_auth:(none)
      public_key:(ssh-dss,parameters)
      T-> Text header_digest:hmac-md5 data_digest:crc32-2k
      init_auth:challenge challenge:question
      I-> Text authenticate:answer

   If authentication is successful, i.e., the answer to the question is
   correct, the target may proceeds:

      T->... parameter negotiation

   Or give another challenge:

      T-> Text challenge:question2
      I-> Text authenticate:answer2

   And at the end:


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      T-> Login "login accept"

   If the authentication was not successful:

      T-> Login "login reject"

   Note - the Text command after authentication and each PDU thereafter
   will have in the trailer an hmac-md5 digest for the header and a
   crc32 for each 2k of data (or fraction of it).










































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Apendix B. Examples

06 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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07 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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Apendix C. Login/Text keys (not security related)

   ISID and TSID form collectively the SSID (session id). A TSID of zero
   indicates a leading connection. Only a leading connection login can
   carry session specific parameters, e.g. MaxConnections, the maximum
   immediate data length requested, etc..

08 MaxConnections

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

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


09 Target

   Target:<domainname>[/modifier]

   Examples:

      Target:disk-array.sj-bldg-h.cisco.com
      Target:disk-array.sj-bldg-h.cisco.com/control7

   This key is provided by the initiator of the TCP connection to the
   remote endpoint. The Target key specifies the domain name of the
   target, since that information is not available from the TCP layer.
   The target is not required to support this key.  The initiator should
   send this key in the first login message. The Target key might be
   used by the target to select a unit within a multi-unit target.

10 Initiator

   Initiator:[domainname[/modifier]] Examples:

      Initiator:sample.foobar.org
      Initiator:cluster.foobar.org/machine1
      Initiator:

   The Initiator key enables the initiator to identify itself to the
   remote endpoint. The domain name should be that of the initiator.  A
   zero-length domain name is interpreted as "other side of TCP
   connection". The target may silently ignore this key if it does not
   support it.

11 AccessID


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   AccessID:<SCSI-AccessID-value>

   Deliver a SCSI AccessID to the target


12 FMarker

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

   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.


13 RFMarkInt

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

   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.


14 SFMarkInt

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

   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.

15 IFMarkInt

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

   Indicates that the initial marker-less interval required by the
   initiator in both directions.


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16 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 than only the first
   outgoing data item (either immediate data or a separate PDU) can be
   sent unsolicited by a R2T.

17 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
   BidiUseR2T:no.  Once BidiUseR2T has been set to 'no', it cannot be
   set back to 'yes'.  Note than only the first outgoing data item
   (either immediate data or a separate PDU) can be sent unsolicited by
   a R2T.

18 DataNumber

   DataNumber:<number-from-0-to-65535>

   Example:

   The DataNumber key is used by targets to turn on the use of input
   data packet numbering, thus allowing a target to discard input data

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   as soon as acknowledged without loosing recovery capabilities.  By
   default data numbering is off. A nonzero value for DataNumber
   indicates both that data numbering is requested and the maximum
   number of unacknowledged packets. An initiator MUST support data
   numbering if requested.

19 ImmediateDataLength

   ImmediateDataLength:<number>

   Initiator and target negotiate the maximum length supported for
   immediate data. Default is 2**32-1 bytes.


20 ITagLength

   ITagLength:<number-from16-to-32>

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


21 PingMaxReplyLength

   PingMaxReplyLength:<number>

   Initiator and target negotiate the maximum length of data contained
   in a ping reply. Default is 4096.

22 StartSecure

   StartSecure:HERE

   Initiator and target indicate the end-of-authentication/integrity
   exchange (start of parameter negotiation if any).

23 TotalText

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

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


24 KeyValueText

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

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   Initiator and target indicate the total text limit for any key:value
   pair.

25 MaxOutstandingR2T

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

   Initiator and target negotiate the maximum number of outstanding R2Ts
   per task. The default is 256.










































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Full Copyright Statement

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   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
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   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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