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Versions: 00 01

Internet-Draft                                                 J. Satran
<draft-satran-iscsi-00.txt>                                     D. Smith
Expires 14 August 2000                                           K. Meth
                                                                     IBM
                                                          C. Sapuntzakis
                                                           Cisco Systems
                                                             M. Toledano
                                                               P. Sarkar
                                                               C. Fuente
                                                                     IBM
                                                              E. Zeidner
                                                                 SanGate
                                                           February 2000


                        SCSI/TCP (SCSI over TCP)


Status of this Memo

     This document is an Internet-Draft and is in full conformance with
     all provisions of Section 10 of RFC2026.

     Internet-Drafts are working documents of the Internet Engineering
     Task Force (IETF), its areas, and its working groups. Note that
     other groups may also distribute working documents as Internet-
     Drafts.

     Internet-Drafts are draft documents valid for a maximum of six
     months and may be updated, replaced, or obsoleted by other docu-
     ments at any time. It is inappropriate to use Internet-Drafts as
     reference material or to cite them other than as "work in pro-
     gress."

     The list of current Internet-Drafts can be accessed at
     http://www.ietf.org/ietf/1id-abstracts.txt

     The list of Internat-Draft Shadow Directories can be accessed at
     http://www.ietf.org/shadow.html.












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Table of Contents

        1.  Abstract
        2.  Overview
        2.1.  SCSI Concepts
        2.2.  SCSI/TCP Functional Overview
        2.3.  SCSI/TCP Login
        2.4.  SCSI/TCP Full Feature Phase
        2.5.  SCSI/TCP Connection Termination
        2.6.  Naming
        3.  Message Formats
        3.1.  Template Header
        3.2.  SCSI Command
        3.3.  SCSI Response
        3.4.  Asynchronous Event
        3.5.  SCSI Task Management Message
        3.6.  SCSI Task Management Response
        3.7.  Ready To Transfer (RTT)
        3.8.  SCSI Data
        3.9.  Text Command
        3.10.  Text Response
        3.11.  Login Command
        3.12.  Login Response
        3.13.  Open Data Connections Command
        3.14.  Open Data Connections Response
        3.15.  Ping Command
        3.16.  Ping Response
        3.17.  Third Party Commands
        3.18.  Opcode Not Understood
        4.  Error Handling SCSI/TCP
        5.  Notes to Implementors
        5.1.  Small TCP Segments
        5.2.  Multiple Network Adapters
        5.3.  Autosense
        5.4.  TCP RDMA option
        5.5.  Data Connections Options
        6.  Security Considerations
        6.1.  Data Integrity
        6.2.  Login Process
        6.3.  IANA Considerations
        7.  Authors' Addresses
        8.  References and Bibliography
        9.  Appendix A - Examples
        9.1.  Read operation example
        9.2.  Write operation example
        10.  Appendix B - Login/Text keys





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1.  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 SCSI/TCP protocol aims to be fully compliant with the require-
     ments laid out in the SCSI Architecture Model - 2 [SAM2] document.

2.  Overview

2.1.  SCSI Concepts

     The endpoint of most SCSI commands is a "logical unit" (LUN). Exam-
     ples of logical units include hard drives, tape drives, CD and DVD
     drives, even printers and processors.

     A "target" is a collection of logical units and is directly
     addressable on the network. The target corresponds to the server in
     the client-server model.

     An "initiator" creates and sends SCSI commands to the target. The
     initiator corresponds to the client in the client-server model.

     A "task" is a linked set of SCSI commands. Some LUNs support multi-
     ple simultaneous tasks. The target uses a "task tag" to distinguish
     between simultaneous tasks. Only one command in a task can be out-
     standing at any given time.

     A SCSI command results in a data phase and a response phase. In the
     data phase, information travels either from the initiator to the
     target, as in a WRITE command, or from target to initiator, as in a
     READ command. In the response phase, the target returns the final
     status of the operation, including any errors. A response ter-
     minates a SCSI command.


2.2.  SCSI/TCP Functional Overview

     Communication between initiator and target occurs over one or more
     TCP connections. The first TCP connection opened is designated a
     control connection and used for sending control messages, SCSI com-
     mands, and parameters. Additional connections may be opened for
     sending data from the SCSI data phases.




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2.3.  SCSI/TCP Login

     The purpose of SCSI/TCP login is to create a connection, authenti-
     cate the parties, and authorize the initiator to send SCSI com-
     mands.

     The targets listen on a well-known TCP port for incoming connec-
     tions.  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. This can occur in many different ways. For
     example, the endpoints may wish to check the IP address of the
     other party. If the TCP connection uses transport layer security
     [TLS], certificates may be used to identify the endpoints. Also,
     SCSI/TCP includes commands for identifying the initiator and pass-
     ing an authenticator to the target (see Appendix B).

     Once suitable authentication has occured, 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 succesful authentication and authorization
     by sending a login response with "accept login".

     After authentication and authorization, other parameters may be
     negotiated using the highly extensible Text Command message that
     allows arbitrary key:value pairs to be passed.

     Finally, if any other TCP control or data connections between the
     initiator and target are currently open, they will be forced closed
     (TCP RST), flushing unacknowledged data.

2.4.  SCSI/TCP Full Feature Phase

     Once the initiator is authorized to do so, the connection is in
     SCSI/TCP full feature phase. The initiator may send SCSI commands
     to the various LUNs on the target.

     SCSI commands are encapsulated in messages that go over the control
     connection.

     Data phases associated with SCSI commands go over separate data
     connections. Initiators may explicitly request the establishment of
     data connections to targets using the "Open Data Connections" mes-
     sage.  A Target responds by granting some number of data connec-
     tions, (to be established using the well known SCSI/TCP data port),
     and by providing a cookie for the initiator to produce upon



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     establishment of its data connections.

     The targets listen on another well-known TCP port for incoming
     SCSI/TCP data connections. The initiator connects to the well-known
     SCSI/TCP data connection port and provides the cookie it received
     in the "Open Data Connections" response. The cookie occupies the
     first 8 bytes of data sent by the initiator through the data con-
     nection.  The target uses the cookie to match a newly established
     data channel with its corresponding control channel.

2.5.  SCSI/TCP Connection Termination

     Graceful connection shutdowns are done by sending TCP FINs. Grace-
     ful connection shutdowns MUST only occur when there are no out-
     standing tasks on the connection. A target SHOULD respond rapidly
     to a FIN from the initiator by closing its half of the connection.

     Usually, the initiator will initiate the closing of data channels
     when it no longer needs them for its data transfer operations.
     Similarly, an initiator may initiate the closing of its control
     channel when it has finished all operations with the target device.

     The closing of one data channel has no effect on other data chan-
     nels connecting the initiator and the target.

     A target may wish to close a TCP data connection. Once an initiator
     has received the FIN, it SHOULD not add any more data to be sent
     onto that connection and should close its half of the connection
     when it is done sending the pending data.

     In the case where a control channel is closed, the target should
     clean up all of its state associated with the corresponding initia-
     tor; all outstanding tasks are cancelled and all resources that
     were allocated for the initiator can be freed. Any open data con-
     nections should be forcibly closed (using TCP RST).

2.6.  Naming

     Domain names, not IPv4 addresses, identify initiator and target
     interfaces.

     In order to express an address that is to be resolved locally
     (without a DNS server), standard conventions are to be used.  For
     example, a domain name of the form d.c.b.a.in-addr.arpa. might
     represent the IPv4 address a.b.c.d.






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3.  Message Formats

     All multi-byte integers specified in formats defined in this docu-
     ment are to be represented in network byte order (i.e., big
     endian).


3.1.  Template Header

     All SCSI/TCP messages and responses have a header of the same
     length (consisting of 40 bytes). Additional data may be added, as
     necessary, beginning with byte 40. The fields of Opcode and Length
     appear in all message and response headers. The other most commonly
     used fields are Initiator Task Tag, Logical Unit Number, and Flags,
     which, when used, always appear in the same location of 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        | Reserved (0)  | Length of Data After Header   |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Flags                         | Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     20/ Opcode-specific data                                          /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40


3.1.1.  Opcode

     The Opcode indicates which SCSI/TCP type of message or response is
     encapsulated by the header.  Valid opcodes for messages (sent by
     initiator to target) are:
          0x00 Ping Command (from initiator to target)
          0x01 SCSI Command (encapsulates a SCSI Command Block)
          0x02 SCSI Task Management Message
          0x03 Login Command
          0x04 Open Data Connections Command
          0x05 Text Command




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     Valid opcodes for responses (sent by target to initiator) are:
          0x80 Ping Response (from target to initiator)
          0x81 SCSI Response (contains SCSI status and possibly sense
               informaton or other response information)
          0x82 SCSI Task Management Response
          0x83 Login Response
          0x84 Open Data Connections Response
          0x85 Text Response
          0x86 Ready To Transfer (RTT - sent by target to initiator when
               it is ready to receive data from initiator)
          0x87 Asynchronous Event (sent by target to initiator to indi-
               cate certain special conditions)
          0x88 Opcode Not Understood

3.1.2.  Length

     The Length field indicates the number of bytes, beyond the 40 byte
     header, that are being sent together with this message header. It
     is anticipated that most SCSI/TCP messages and responses (not
     counting data transfer messages) will not need more than the 40
     byte header, and hence the Length field will contain the value 0.
     All messages using this header are sent over the control channel.
     Bulk data transfers are performed over the data channels, and have
     a different header format.

     Large amounts of data accompanying a SCSI command should not be
     sent over the control channel. If too much data is sent over the
     control channel, there is the possibility that it would fill the
     TCP window, thus preventing other critical control commands from
     passing through the control channel. The control channel should be
     kept open at all times so that important messages can always pass
     through. (These may include a message to cancel a data transfer or
     to reset a device that has somehow entered a bad state). The Length
     field is, therefore, intentionally limited to 16 bits, allowing
     only up to 64KB of data to be passed with any particular control
     message. Any large data transfers for READ and WRITE operations
     (including unsolicited WRITE operations) should be sent over the
     data channels.

3.1.3.  LUN

     The LUN specifies the Logical Unit for which the command is tar-
     geted.  If the command does not relate to a Logical Unit, this
     field is either ignored or may be used for some other purpose.
     According to [SAM2], a Logical Unit Number can take up to a 64-bit
     field that identifies the Logical Unit within a target device. The
     exact format of this field can be found in the [SAM2] document.




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3.1.4.  Initiator Task Tag

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

3.1.5.  Flags and additional information

     These field have different meanings for different messages.










































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3.2.  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| Opcode (0x01) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16|Rsrvd (0)|A|R|W|Rsrved(0)|ATTR | Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     20| Expected Data Transfer Length                                 |
       +---------------+---------------+---------------+---------------+
     24| SCSI Command Block (SCB)                                      |
       +                                                               +
     28|                                                               |
       +                                                               +
     32|                                                               |
       +                                                               +
     36|                                                               |
       +---------------+---------------+---------------+---------------+
     40/ Additional Data (Command Dependent)                           /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.2.1.  Flags

     The Flags field for a SCSI Command consists of two bytes.  (In gen-
     eral, one byte is used for data flow information while the other
     byte is used for Task Attributes information.)
               Byte 16
          b0   (W) set when data is expected to flow from initiator to
               target (write).
          b1   (R) set when data is expected to flow from target to ini-
               tiator (read).
          b2   (A) set to turn off Autosense for this command (see
               [SAM2]).
          b3-7 not used (should be set to 0).

     Autosense refers to the automatic return of sense data to the ini-
     tiator in case a command did not complete successfully. If



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     autosense is turned off, the initiator must explicitly request that
     sense data be sent to it after some command has completed with a
     CHECK CONDITION status.
               Byte 17
          b0-2 used to indicate Task Attributes.
          b3-7 not used (should be set to 0).


3.2.2.  Task Attributes

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

             0    Untagged
             1    Simple
             2    Ordered
             3    Head of Queue
             4    ACA



3.2.3.  Expected Data Transfer Length

     The Expected Data Transfer Length field states the number of bytes
     expected to be sent over the data channel for this SCSI operation.
     (The SCSI command itself is sent over the control channel.)

     For a WRITE operation, the initiator uses this field to specify the
     number of bytes of data it expects to transfer for this operation
     over the data channel(s) (not counting data headers).

     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 over the data channel(s).

     If no data will be transferred over the data channels for this SCSI
     operation, this field should be set to 0.

     If data is sent together with the SCSI command over the control
     channel, the byte count should be included in the Length field
     (bytes 2-3).

     The target knows to expect data for this SCSI command over the data
     channel by receiving a non-zero value in the Expected Data Transfer
     Length field.

     Note that large amounts of data should be sent exclusively over the
     data channels so as not to clog the control channel. It is desired



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     that the control channel be available at all times in order to be
     able to send critical messages (such as to interrupt the current
     data transfer). 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.

3.2.4.  SCSI Command Block (SCB)

     There are 16 bytes in the SCB field, designed to accomodate the
     largest currently defined SCB.

     If, in the future, larger SCB's are allowed, the spill-over of the
     SCB may extend beyond the 40-byte boundary, followed by the data or
     parameters for the SCB. The target will use the SCSI/TCP Length
     field plus the information in the SCB to figure out how many addi-
     tional bytes are part of the SCB, with the remaining bytes serving
     as the data and parameters of the SCB.

3.2.5.  Command Data

     Some SCSI commands require additional parameters or data to accom-
     pany the SCSI command. This data may be placed beyond the 40-byte
     boundary of the SCSI/TCP header. The Length field is set to the
     length of this data beyond the 40-byte header. Note that the Length
     field is intentionally limited to 2 bytes, thus limiting the amount
     of data to 64K.

     Any SCSI command whose data/parameters require more than 64K beyond
     the 16 byte SCB must utilize one of the data connections to perform
     the data transfer.





















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3.3.  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| Opcode (0x81) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Rsrved(0) |O|U| Reserved (0)  | Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     20| Residual Count                                                |
       +---------------+---------------+---------------+---------------+
     24| Command Status|SCSI/TCP Status| Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     28/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Response or Sense Data (optional)                             /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.3.1.  Flags

     The SCSI Response has its own set of flags, that differs from the
     flags for a SCSI Command.
               Byte 16
          b0   (U) set for Residual Underflow. In this case, the Resi-
               dual 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 Residual
               Count indicates how many bytes could not be transferred
               because the initiator's Expected Data Transfer Length was
               too small.
          b2-7 not used (should be set to 0).
     Bits 0 and 1 are mutually exclusive.

3.3.2.  Residual Count

     The Residual Count field is valid only in case either the Residual
     Underflow bit or Residual Overflow bit is set. If neither bit is



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     set, the Residual Count field will be 0.

     If the Residual Underflow bit is set, the Residual Count indicates
     how many bytes were not transferred out of those expected to be
     transferred.

     If the Residual Overflow bit is set, the Residual Count indicates
     how many bytes could not be transferred because the initiator's
     Expected Data Transfer Length was too small.

3.3.3.  Command Status

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

3.3.4.  SCSI/TCP Status

     The SCSI/TCP Status field is used to report the status of the com-
     mand before it was sent to the LUN. The values are given below.

             1 Non-existant LUN


3.3.5.  Response or Sense Data

     If Autosense was not disabled in the originating SCB and the Com-
     mand Status was CHECK CONDITION (0x02), then the response field
     will contain sense data for the failed command.

     If the Command Status is Good (0x00) and there are no data streams
     opened, then the Response Data field will contain data from the
     data phase of the SCB.

     The Length parameter specifies the number of bytes in this field.
     If no error occured, and no data is needed for the response to the
     SCSI Command the Length field is 0.

     Note that if the Command Status was CHECK CONDITION but Autosense
     was disabled, then sense data must be explicitly requested by the
     initiator with a new SCSI command.











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3.4.  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| Opcode (0x87) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Reserved (0)                                                  |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Reserved (0)                                                  |
       +                                                               +
     20|                                                               |
       +---------------+---------------+---------------+---------------+
     24| Command Status|SCSI/TCP Status| Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     28|Event Indicator| Reserved (0)                                  |
       +---------------+---------------+---------------+---------------+
     32| Reserved (0)                                                  |
       +                                                               +
     36|                                                               |
       +---------------+---------------+---------------+---------------+
     40/ Sense Data                                                    /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.4.1.  SCSI/TCP Status

     Some Asynchronous Events are strictly related to SCSI/TCP while
     others are related to SAM-2.  The codes returned for SCSI/TCP Asyn-
     chronous Events are:

             2 Target is being reset.
             3 Expired cookie was used to establish a data connection.


3.4.2.  Event Indicator

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



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          1    An error condition was encountered after command comple-
               tion.
          2    A newly initialized device is available.
          3    Some other type of unit attention condition has occured.
          4    An asynchronous event has occured.

     Sense Data accompanying the report identifies the condition.  The
     Length parameter is set to the length of the Sense Data.











































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3.5.  SCSI Task Management Message


     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 (0x02) |  Reserved (0) |          Length               |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Msg indicator | Reserved (0)                                  |
       +---------------+---------------+---------------+---------------+
     20/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40


3.5.1.  Msg Indicator

     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 Task Tag
               field.
          2    Abort Task Set---aborts all Tasks issued by this initia-
               tor on the Logical Unit.
          3    Clear ACA---clears the Auto Contingent Allegiance condi-
               tion.
          4    Clear Task Set---Aborts all Tasks (from all initiators)
               for the Logical Unit.
          5    Logical Unit Reset.
          6    Target Reset.

     For the functions above except <Target Reset>, a SCSI Task Manage-
     ment Response is returned, using the Initiator Task Tag to identify
     the operation for which it is responding.

     For the <Target Reset> function, the target cancels all pending
     operations. The target may send an Asynchronous Event to all
     attached initiators notifying them that the target is being reset.
     The target then closes all of its TCP connections.



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3.6.  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| Opcode (0x82) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Msg indicator | Reserved (0)  | Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     20| Reserved (0)                                                  |
       +---------------+---------------+---------------+---------------+
     24| Response      | Reserved (0)                                  |
       +---------------+---------------+---------------+---------------+
     28/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40


     For the functions <Abort Task, Abort Task Set, Clear ACA, Clear
     Task Set, Logical Unit reset>, the target performs the requested
     Task Management function and sends a SCSI Task Management Response
     back to the initiator.  The target includes all of the information
     the initiator provided in the SCSI Task Management Message, so the
     initiator can know exactly which SCSI Task Management Message was
     serviced.  In addition, the target provides a Response indication
     which may take on the following values:
          0    Function Complete
          1    Function Rejected

     For the <Target Reset> function, the target cancels all pending
     operations. The target may send an Asynchronous Event to all
     attached initiators notifying them that the target is being reset.
     The target then closes all of its TCP connections.









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3.7.  Ready To Transfer (RTT)

     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 the data blocks be delivered in whatever order is con-
     venient for the target at that particular instant. This information
     is passed from the target to the initiator in the Ready To Transfer
     (RTT) message.

     In order to allow write operations without RTT, the initiator and
     target must have agreed to do so by both sending the AllowNoRTT:yes
     key-pair attribute to each other (either during Login or through
     the Text Command/Response mechanism).

     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 (0x86) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Reserved (0)                                                  |
       +                                                               +
     12|                                                               |
       +                                                               +
     16|                                                               |
       +---------------+---------------+---------------+---------------+
     20| Expected Data Transfer Length                                 |
       +---------------+---------------+---------------+---------------+
     24| Data Offset                                                   |
       +---------------+---------------+---------------+---------------+
     28| Target Transfer Tag                                           |
       +---------------+---------------+---------------+---------------+
     32| Reserved (0)                                                  |
       +                                                               +
     36|                                                               |
       +---------------+---------------+---------------+---------------+
     40


3.7.1.  Expected Data Transfer Length and Data Offset

     The target specifies how many bytes it wants the initiator to send
     as a result of this RTT message.  The target may request the data
     from the initiator in several chunks, not necessarily in the origi-
     nal order of the data.  The target, therefore, also specifies a



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     Data Offset indicating the point at which the data transfer should
     begin.

3.7.2.  Target Transfer Tag

     The target assigns its own tag to each RTT request that it sends to
     the initiator. This can be used by the target to identify data it
     receives, and can also be used as an RDMA tag [RDMA].











































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3.8.  SCSI Data

     The initiator and target send data in messages over data
     channel(s).  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.  After sending the data for a
     particular SCSI command through a data channel, an end-of-data
     indication must be sent in that data channel.  The end-of-data
     indication consists of a SCSI Data header specifying a zero length
     data payload.  Note that the end-of-data indication must be sent in
     each data channel over which data was sent for the particular SCSI
     command.  The end-of-data marker indicates that no more data for
     this command will pass through this data channel.  The end-of-data
     indication SCSI Data header sent from a target to an initiator may
     optionally also contain the Command Status for the data transfer.
     In this case Sense Data cannot be sent together with the Command
     Status.  The typical SCSI Data message 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| Length                                                        |
       +---------------+---------------+---------------+---------------+
      4| Transfer Tag                                                  |
       +---------------+---------------+---------------+---------------+
      8| Buffer Offset                                                 |
       +---------------+---------------+---------------+---------------+
     12. Payload                                                       .
      +.                                                               .
       .                                                               .
       +---------------+---------------+---------------+---------------+


     The end-of-data indication 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| Length (0)                                                    |
       +---------------+---------------+---------------+---------------+
      4| Transfer Tag                                                  |
       +---------------+---------------+---------------+---------------+
      8| Command Status| Reserved (0)  | Rsvrd (0) |D|C| Reserved (0)  |
       +---------------+---------------+---------------+---------------+



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3.8.1.  Length

     The length field specifies the total number of bytes in the follow-
     ing payload.

3.8.2.  Transfer Tag

     The Transfer Tag identifies the operation to which this data
     transfer belongs.

     When the transfer is from the target to the initiator, the Transfer
     Task Tag is the Initiator Task Tag that was sent with the SCSI com-
     mand.

     When the transfer is from the initiator to the target, the Transfer
     Task Tag is the Target Transfer Tag when RTT is enabled, or the
     Initiator Task Tag when RTT is disabled.


3.8.3.  Buffer Offset

     The Buffer Offset field contains the offset of the following data
     against the complete data transfer. If the data transfer is not
     split over multiple Data transmissions, then this field will be
     zero.


3.8.4.  Status Flags

     The Status Flags field indicates how to interpret the Command
     Status field, when the end-of-data indicator is sent from a target
     to an initiator.
               Byte 10
          b0   (C) set when status is sent over the control channel.  In
               this case, the Command Status field is gnored.
          b1   (D) set when status is sent over this data channel.
          b2-7 not used (should be set to 0).
     Bits b0 and b1 are mutually exclusive.  It is permissable to not
     set any flag, in which case the Command Status field is ignored.

     For an end-of-data indicator sent from an initiator to a target (as
     for a WRITE operation), the Status Flags and Command Status fields
     should be set to zero.


3.8.5.  Command Status





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3.9.  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| Opcode (0x05) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Text                                                          /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.9.1.  Length

     The length, in bytes, of the Text field.

3.9.2.  Initiator Task Tag

     The initiator assigned identifier for this Text Command.

3.9.3.  Text

     The initiator sends the target a set of key:value pairs in UTF-8
     unicode format. 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 nul '\0' (0x00) delimiters. Some basic
     key:value pairs are described in Appendix B.

     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 capabalities.

     Manufacturers may introduce new keys by prefixing them with their
     (reversed) domain name, for example,

             com.foo.bar.do_something:0000000000000003

     Any key that the target does not understand may be ignored without



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     affecting basic function. Once the target has processed all the
     key:value pairs, it reponds with the Text Response command, listing
     the parameters that it supports. It is recommended that Text opera-
     tions 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 tar-
     get.










































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3.10.  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| Opcode (0x85) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Text Response                                                 /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.10.1.  Length

     The length, in bytes, of the Text Response field.

3.10.2.  Initiator Task Tag

     The Initiator Task Tag matches the tag used in the initial Text
     Command and is used by the initiator to connect Text Commands with
     the appropriate Text Responses.

3.10.3.  Text Response

     The Text Response field contains responses in the same key:value
     format as the Text Command. Appendix B lists some basic Text Com-
     mands and their Responses.














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3.11.  Login Command

     After establishing a TCP connection between an initiator and a tar-
     get, the initiator should 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| Opcode (0x03) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      4/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Login Parameters in Text Command Format                       /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


     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.

     The format of the parameters is as specified for the Text Command.

     Targets may require keys to indicate the Domain Name of the initia-
     tor and the target, and perhaps also an Authenticator key.

     The initiator may also provide additional parameters to the target
     in Text Command format, if the initiator so desires.

     Keys and their explanations are listed in Appendix B. An example of
     the parameters passed is:

             Initiator:my.org/me
             Target:diskfarm.your.org
             Authenticator:open-sesame











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3.12.  Login Response

     The target responds to the Login Command with a Login Response.  It
     is sufficient for the target to respond with a Status indicating
     that the Login is accepted.

     In fact, the target may completely ignore the parameters that were
     sent to it and may provide service to any initiator that connects
     to it. The target may also send back parameters to the initiator in
     Text Command format, if the target so desires.

     In particular, the target may want to provide its Authenticator
     key, so that the initiator can be sure that it is in fact talking
     with the correct target.

     The initiator can request that the target provide the Authenticator
     parameter by specifying the SendAuthenticator:yes key:value pair.

     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 (0x83) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     24| Status        | Reserved (0)                                  |
       +---------------+---------------+---------------+---------------+
     28/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Login Parameters in Text Command Format                       /
      +/                                                               /
       +---------------+---------------+---------------+---------------+

     The format of the Login Response is the same as the Text Response,
     with the addition of one field.

3.12.1.  Status

     The Status returned in a Login Response is one of the following:
          0    accept login   (will now accept SCSI commands)
          1    reject login
          2    additional authentication required
     In the case that the Status is "accept login" the initiator may



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     proceed to issue SCSI commands.  In the case that the Status is
     "reject login" the target will immediately close down its end of
     the TCP conneciton.

     In the case that the Status is "additional authentication required"
     the initiator must provide additional authentication information by
     issuing the Text Command with the appropriate key:value pairs.
     (This may be required if the authentication method is based on a
     challenge/response algorithm.)  Upon receipt of the necessary
     authentication, the target will issue a Login Response with the
     "accept login" Status.  SCSI Commands will not be accepted until
     the target provides a Login Response with the "accept login"
     Status.






































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3.13.  Open Data Connections 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| Opcode (0x04) | Reserved (0)  | Length (0)                    |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     20| Number of Data Connections Requested                          |
       +---------------+---------------+---------------+---------------+
     24/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40

     The initiator requests that some number of data connections (TCP
     channels) be opened. These may be opened on any network address
     belonging to the initiator.


3.13.1.  Initiator Task Tag

     An initiator assigned identification number for this operation.






















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3.14.  Open Data Connections Response

     The target responds with the number of data connections it is wil-
     ling to grant in response to the Open Data Connections 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| Opcode (0x84) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     20| Number of Data Connections Granted                            |
       +---------------+---------------+---------------+---------------+
     24| Reserved (0)                                                  |
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40| Cookie                                                        |
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     72/ Target Address Names (and counts) for Data Connections        /
      +/                                                               /
       +---------------+---------------+---------------+---------------+


3.14.1.  Cookie

     The target provides the initiator with a 32 byte entity (referred
     to here as a "cookie"), which the initiator will later use to iden-
     tify itself to the target. The initiator will open data connections
     and will provide the cookie back to the target, so that the target
     can map a newly established data connection to an existing control
     connection.  Upon establishing the data connection, the initiator
     must send the cookie as the first bytes of data sent through the
     data connection.

     Cookies might be valid for only a short period of time (as deter-
     mined by the target). If a long time passes (as determined by the
     target) after the Open Data Connections Response and a data connec-
     tion has not been established, the target may invalidate the
     cookie.  If an initiator tries to use a cookie that has expired,
     the target immediately closes the data connection. The target may
     send an Asynchronous Event to the initiator (over the corresponding
     control connection) to inform it that an expired cookie was used.



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3.14.2.  Target Address Names

     The target may have several addresses through which it allows data
     connections. The target may also allow a different number of conne-
     tions to each of those addresses, based, perhaps, on the bandwidth
     of the connections that those addresses represent.  These are
     specified in the Target Address Names field in Text Command format.
     For each target address to be used for data connections, the target
     specifies the Name of the address and number of connections allowed
     on that address with a colon ':' separating Address Name from the
     number of connetions.  The target may also specify the number of
     connections without specifying the address, thereby implying use of
     the same Domain Name that was used for the control connection over
     which the Open Data Connections Command arrived.  In this case, no
     Address Name preceeds the colon; only the number of connections
     follows the colon in Text format.  Entries are separated by nul
     '\0' (0x00). For example:

             name1.trg.org:3
             :2
             name3.trg.org/disk3:4

     This example indicates that 3 data channels may be opened at the
     address named "name1.trg.org" and 4 data channels may be opened at
     the address named "name3.trg.org/disk3."  In addition, 2 data con-
     nections may be made at the address that was used for the control
     connection.

     Note that the sum of the individually specified numbers (per-target
     address) for data connections as they appear in the Text format may
     be more than the number specified in the "Number of Data Connec-
     tions Granted" field. The target simply specifies where it it con-
     venient for the target to receive data connections. Upon establish-
     ing the granted number of data connections, the target may disallow
     any further data connections from the initiator.

3.14.3.  Length

     The Length parameter contains the length of the cookie plus the
     total length of the Text containing address and connection informa-
     tion.










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3.15.  Ping 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| Opcode (0x0)  | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Ping Data (optional)                                          /
      +/                                                               /
       +---------------+---------------+---------------+---------------+

     The Ping Command can be used to verify that a control connection is
     still active. This command may be useful in the case where an ini-
     tiator has been waiting a long time for the response to some com-
     mand, and the initiator suspects that there is some problem with
     the connection.

     When a target receives the Ping Command, it should respond with a
     Ping Response, duplicating the data that was provided in the Ping
     Command, if present.

     If the initiator does not receive the Ping Response within some
     period of time (determined by the initiator), or if the data
     returned by the Ping Response is different from the data that was
     in the Ping Command, the initiator may conclude that there is a
     problem with the control connection. The initiator will then close
     the control connection and may try to establish a new control con-
     nection.

3.15.1.  Length

     The length of the optional Ping Data.

3.15.2.  Initiator Task Tag

     An initiator assigned identifier for the operation.

3.15.3.  Ping Data

     Binary data that will be reflected in the Ping Response.




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3.16.  Ping 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| Opcode (0x80) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Return Ping Data                                              /
      +/                                                               /
       +---------------+---------------+---------------+---------------+

     When a target receives the Ping Command, it should respond with a
     Ping Response, duplicating the data and Initiator Task Tag that was
     provided in the Ping Command, if present.






























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3.17.  Third Party Commands

     There are some third-party SCSI commands, such as COPY and EXTENDED
     COPY, that require one target (Target A) to act as an initiator to
     other targets (e.g., Target B).  Some such commands can be extended
     in a straightforward way to accommodate new forms of addressing,
     and this should be done to address targets using SCSI/TCP. These
     extensions are not straightforward for all commands, and they may
     not be able to encompass the full name space and authentication
     information needed for SCSI/TCP in some contexts. Thus SCSI/TCP
     also provides a facility for assigning local short-form aliases to
     full addressing/authorization information for targets, and the
     aliases can be used in the SCSI commands and parameter data.  The
     alias information is specified as Text following the header of the
     SCSI command specifying the third-party command.  The header will
     thus appear as follows:

     Byte /    0       |       1       |       2       |       3       |
        /              |               |               |               |
       |7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
       +---------------+---------------+---------------+---------------+
      0| Opcode (0x01) | Reserved (0)  | Length (!= 0)                 |
       +---------------+---------------+---------------+---------------+
      4| Initiator Task Tag                                            |
       +---------------+---------------+---------------+---------------+
      8| Logical Unit Number (LUN)                                     |
       +                                                               +
     12|                                                               |
       +---------------+---------------+---------------+---------------+
     16| Flags         |Task Attributes| Reserved (0)                  |
       +---------------+---------------+---------------+---------------+
     20| Expected Data Transfer Length                                 |
       +---------------+---------------+---------------+---------------+
     24| SCSI Command Block (SCB)                                      |
       +                                                               +
     28|                                                               |
       +                                                               +
     32|                                                               |
       +                                                               +
     36|                                                               |
       +---------------+---------------+---------------+---------------+
     40/ Data/Parameters for SCB                                       /
      +/ Parameters needed for Target B                                /
       /                                                               /
       +---------------+---------------+---------------+---------------+

     The Length field will not be zero. Rather, it will contain the
     length of the alias information which may include the name of



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     Target B and an Authentication key in Text Command format. An exam-
     ple of the data for this command might be:

               LocalName:TargetB
               FullName:disk2.sj.foo.com
               OriginalAuthenticator:open-sesame


     If the SCSI command requires data/parameters beyond the 16-byte
     SCB, the target can figure this out by examining the particular
     SCSI command and the other contents of the SCB.  Any data (as
     specified by the Length parameter) beyond what is needed for the
     specific SCSI command are parameters in Text Command format needed
     to connect to Target B.

     Upon receiving a third-party command, Target A will perform login
     operations with the identified targets.  In effect, Target A will
     become an initiator to Target B.  Among the parameters provided to
     Target B, Target A may specify the authentication information from
     the initiator.  The Text provided by Target A when it performs the
     Login command to Target B may contain the keys Target (referring to
     Target B) and Initiator (referring to Target A), and it may also
     contain the keys Authenticator (of Target A), OriginalInitiator and
     OriginalAuthenticator (referring to authenticator of the original
     initiator).


























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3.18.  Opcode Not Understood


     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 (0x88) | Reserved (0)  | Length                        |
       +---------------+---------------+---------------+---------------+
      4/ Reserved (0)                                                  /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     40/ Header of Bad Message                                         /
      +/                                                               /
       +---------------+---------------+---------------+---------------+
     80

     It may happen that a target receives a message with an Opcode that
     it doesn't recognize. This may occur because of a new version of
     the protocol that defines a new Opcode, or because of some corrup-
     tion of a message header.

     The target returns the header of the message with the unrecognized
     opcode as the data of the response.



























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4.  Error Handling SCSI/TCP

     The following errors might be detected by the initiator and tar-
     gets:
        - TCP connection termination with outstanding operations pending
        - Operation timed out
        - Illegal field format---could be an implementation error or a
          data stream synchronization error.

     Initiators that detect one of the above errors will take the fol-
     lowing actions:
        - Reset the TCP connection.
        - Terminate all outstanding requests on behalf of the LUNs on
          the target with the error.
        - Reestablish the session by:
               - Opening a new TCP connection.
               - Performing the login process.

     Note: After the initiator resets its TCP connection, the target
     connection may remain active.  If a new TCP connection is opened by
     the initiator, it can lead to two active connections at the target
     side for the same initiator. The target is not aware of the cleanup
     actions taken by the initiator. To avoid this situation, the target
     has to check on every Login to see whether or not it established an
     already existing session.  If the session already exists, the tar-
     get performs cleanup actions (described in the following paragraph)
     for the old session before performing the new Login.

     A target that detects one of the above errors will take the follow-
     ing actions:

        - Reset the TCP connection.
        - Abort all Tasks in the task set for the corresponding initia-
          tor.

















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5.  Notes to Implementors

     This protocol was designed to take advantage of the Remote DMA TCP
     options [RDMA], although it can still operate effectively without
     this TCP extension. This section notes some of the performance con-
     siderations of the SCSI/TCP protocol.

5.1.  Small TCP Segments

     It is recommended that TCP segments be limited in size to no more
     than 8K bytes. One reason is to ensure that segments won't get bro-
     ken into smaller packets, thereby possibly breaking the assumptions
     for RDMA and the information in the RDMA header. Another reason we
     recommend small segments is to allow a stronger type of checksum,
     possibly utilizing CRC, which is practical only for smaller seg-
     ments.

5.2.  Multiple Network Adapters

     The SCSI/TCP protocol assumes that the Task Tags will also serve as
     RDMA tags. The SCSI/TCP protocol allows multiple data connections,
     not all of which need go over the same network adapter. If multiple
     network connections are to be utilized with RDMA, the SCSI/TCP pro-
     tocol requires that the Task Tag (RDMA Tag) contain sufficient
     information (and sufficient support from the various network
     adapters) to allow data to arrive on any of the data connections,
     even if they are not all through the same network adapter.

5.3.  Autosense

     Autosense refers to the automatic return of sense data to the ini-
     tiator in case a command did not complete successfully. If
     autosense is turned off, the initiator must explicitly request that
     sense data be sent to it after some command has completed with a
     CHECK CONDITION status.  The default for SCSI/TCP is to work with
     Autosense enabled.

     Note that even if a SCSI target/LUN does not support Autosense, it
     may still be possible for SCSI/TCP to work with Autosense.  This
     can be accomplished as follows. Whenever a CHECK CONDITION status
     is about to be returned, the SCSI/TCP component on the target
     immediately queries the target/LUN for the sense data. SCSI/TCP can
     then return the sense data to the initiator together with the CHECK
     CONDITION status.  It is not necessary for SCSI/TCP to wait for the
     initiator to explicitly request the sense data; the target SCSI/TCP
     code can perform this operation automatically, even for
     devices/LUNs that do not ordinarily provide automatic sense data.




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5.4.  TCP RDMA option

     The TCP RDMA option [RDMA] is an annotation on individual TCP seg-
     ments that can reduce the number of copies necessary at the
     receiver. The RDMA option succinctly describes the portion of a TCP
     payload that holds bulk data.

     In SCSI/TCP, all bulk data transfers occur over the data connec-
     tions.  Thus, RDMA options will only appear on the data connection.

     To disambiguate between multiple transfers on a TCP connection, a
     48-bit RDMA ID (RID) appears in the TCP option. In the case of
     SCSI/TCP, the upper 16 bits of the RID are zero and the lower bits
     are the same as the Transfer Tag on the data message.

     In the case of an initiator to target data phase without ready-to-
     transfer (RTT), the unsolicited bit should be set in the RDMA
     option.


5.5.  Data Connection Options

     Some targets may want to inform (or negotiate with) an initiator
     concerning some parameters related to bandwidth, Quality of Ser-
     vice, or some other available features on its various network con-
     nections.  These are exchanged between the initiator and the target
     using Text Commands and Responses. These should be exchanged after
     a successful login, but before any data connections are esta-
     blished.






















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6.  Security Considerations


6.1.  Data Integrity


     We assume that end-to-end data integrity can be assured by TCP, by
     adding a more powerful checksum option whenever this is considered
     important, or replacing the checksum by a weaker one (or even "nul-
     lifying it") for applications in which data integrity is not impor-
     tant and recovery from data errors could be harmful (e.g., audio or
     video distribution streams).

6.2.  Login Process

     In some environments, a target will not be interested in authenti-
     cating the initiator. In this case, the target can simply ignore
     some or all of the parameters sent in a Login Command, and the tar-
     get can simply reply with a basic Login Response indicating a suc-
     cessful login.

     Some targets may want to perform some kind of authentication.  The
     Authenticator key is defined for this purpose.  Various authentica-
     tion 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 control channel is considered
     secure.  The initiator then proceeds to request (over the secure
     control channel) the allocation of data channels.  The target pro-
     vides the initiator with a cookie that must be used when establish-
     ing a data channel.  This enables the target to match a data chan-
     nel to its corresponding control channel.  The target may set a
     time limit to the validity of a cookie that it has provided for
     data connections.

     It is anticipated that most target devices will not bother with all
     of the possible checks, but the protocol provides sufficient means
     to perform the checks, if required by the target.

6.3.  IANA Considerations

     There will be a well known port for SCSI/TCP control connections
     and a well known port for SCSI/TCP data connections.  These well
     known ports will have to be registered with IANA.

     A checksum type will also have to be registered with IANA.




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7.  Authors' Addresses


     Julian Satran
     Kalman Meth
     Meir Toledano
     IBM, Haifa Research Lab
     MATAM - Advanced Technology Center
     Haifa 31905, Israel
     Phone +972 4 829 6211
     Email: satran@il.ibm.com meth@il.ibm.com
            toledano@il.ibm.com


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


     Efri Zeidner
     SanGate
     Israel


     Comments may be sent to Julian Satran, Daniel Smith, Costa
     Sapuntzakis, or Kalman Meth.











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8.  References and Bibliography

     [RDMA]    Internet Draft: TCP RDMA option (work in progress)
     [SAM2]    ANSI X3.270-1998, SCSI-3 Architecture Model (SAM-2)
     [TLS]     The TLS Protocol, RFC 2246, T. Dierks et al.

     [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)
     [RFC793]  Transmission Control Protocol, RFC 793
     [RFC1122] Requirements for Internet Hosts -- Communication Layer,
               RFC 1122, R. Braden (editor)
     [SBC]     ANSI X3.306-199X, SCSI-3 Block Commands (SBC)
     [SCSI2]   ANSI X3.131-1994, SCSI-2
     [SPC]     ANSI X3.301-199X, SCSI-3 Primary Commands (SPC)




































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9.  Appendix A - Examples


9.1.  Read operation example


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























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9.2.  Write operation example


     +------------------+-----------------------+---------------------+
     |Initiator Function|    Message Type       |  Target Function    |
     +------------------+-----------------------+---------------------+
     |  Command request |SCSI Command (WRITE)>>>| Receive command     |
     |  (write)         | (on control channel)  | and queue it        |
     +------------------+-----------------------+---------------------+
     |                  |                       | Process old commands|
     +------------------+-----------------------+---------------------+
     |                  |                       | Ready to process    |
     |                  |   <<< RTT             | WRITE command       |
     |                  | (on control channel)  |                     |
     +------------------+-----------------------+---------------------+
     |   Send Data      |   SCSI Data >>>       |   Receive Data      |
     |                  | (on data channel)     |                     |
     +------------------+-----------------------+---------------------+
     |   Send Data      |   SCSI Data >>>       |   Receive Data      |
     |                  | (on data channel)     |                     |
     +------------------+-----------------------+---------------------+
     |                  |   <<< RTT             |                     |
     |                  | (on control channel)  |                     |
     +------------------+-----------------------+---------------------+
     |   Send Data      |   SCSI Data >>>       |   Receive Data      |
     |                  | (on data channel)     |                     |
     +------------------+-----------------------+---------------------+
     |                  |   <<< SCSI Response   |Send Status and Sense|
     |                  | (on control channel)  |                     |
     +------------------+-----------------------+---------------------+
     | Command Complete |                       |                     |
     +------------------+-----------------------+---------------------+



















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10.  Appendix B - Login/Text keys


10.1.  Target

     Target:domainname[/modifier]

     Examples:

             Target:disk-array.sj-bldg-h.cisco.com
             Target:disk-array.sj-bldg-h.cisco.com/disk3


     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 application layer proxies to learn the
     intended endpoint of the conversation.


10.2.  Initiator

     Initiator:domainname/principal

     Examples:

             Initiator:sample.foobar.org/
             Initiator:sample.foobar.org/fred
             Initiator:/fred
             Initiator:/

     The Initiator key enables the initiator to identify itself to the
     remote endpoint. A zero-length principal is valid and indicates
     that the initiator has no specific principal to communicate to the
     target.  The domain name should be that of the initiator. A zero-
     length domain name is interpreted as "other side of TCP connec-
     tion". The target may silently ignore this call if it does not sup-
     port it.

     For more security, a certificate-based protocol [TLS] may be used
     on the channel and take precedence over this protocol.







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10.3.  Authenticator

     Authenticator:<UTF8-String>

     Examples:

             Authenticator:open-sesame

     The authenticator is a secret that the initiator uses to gain
     access to the target's LUNs.


10.4.  SendAuthenticator

     SendAuthenticator:yes Response: Authenticator:<UTF8-String>

     Examples:

             SendAuthenticator:yes
             -> Authenticator:alakazam

     The SendAuthenticator key is used to request from the party on the
     other side of the TCP connection to send its Authenticator.
     SCSI/TCP devices may refuse to grant access until proper authenti-
     cation has been performed by the parties involved.


10.5.  AllowNoRTT

     AllowNoRTT:<yes|no> Response: AllowNoRTT:<yes|no>

     Examples:

             AllowNoRTT:yes
             -> AllowNoRTT:yes

     The AllowNoRTT key is used to allow an initiator to send data to a
     target without the target having sent an RTT to the initiator.  The
     default action is that RTT is required, unless both the initiator
     and the target send this key-pair attribute specifying
     AllowNoRTT:yes.  Once AllowNoRTT has been set to 'yes', it cannot
     be set back to 'no'.


10.6.  OriginalInitiator

     OriginalInitiator:domainname/principal




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     Examples:

             OriginalInitiator:sample.foobar.org/fred

     The OriginalInitiator key is used to perform a proxy login from one
     target to another target in order to perform a third-party opera-
     tion (like COPY) for some initiator. The first target acts as the
     initiator for the second target, but it must provide the authoriza-
     tion information of the original initiator.


10.7.  Target2

     Target2:domainname[/modifier]

     Examples:

             Target2:sample.foobar.org
             Target2:sample.foobar.org/disk2

     The target2 key is used in a third-party SCSI command (like COPY)
     between targets that do not lie on the same SCSI fabric. The ini-
     tiator must specify the name of the distant target to the original
     target, so that the original target can Login to the distant target
     and then perform the third-party command.



     Expires 14 August 2000






















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