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.
`
`Satran, Smith, Sapuntzakis, Meth [Page 16]
`
`Ex.1056.016
`
`DELL
`
`

`

`
`SCSI/TCP February 2000
`
`3.6. SCSI Task Management Response
`
` Byte /