IPS Julian Satran
Internet Draft Daniel Smith
Document: draft-ietf-ips-iscsi-09.txt Kalman Meth
Category: standards-track Ofer Biran
Jim Hafner
IBM
Costa Sapuntzakis
Mark Bakke
Cisco Systems
Matt Wakeley
Agilent Technologies
Luciano Dalle Ore
Quantum
Paul Von Stamwitz
Adaptec
Randy Haagens
Mallikarjun Chadalapaka
Hewlett-Packard Co.
Efri Zeidner
SANGate
Yaron Klein
SANRAD
iSCSI
Julian Satran Standards-Track, Expires July 2002 1
iSCSI 19-Nov-01
Status of this Memo
This document is an Internet-Draft and fully conforms to all
provisions of Section 10 of RFC2026 [1].
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other
groups may also distribute working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or made obsolete by other documents at
any time. It is inappropriate to use Internet- Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
The Small Computer Systems Interface (SCSI) is a popular family of
protocols for communicating with I/O devices, especially storage
devices. This memo describes a transport protocol for SCSI that
operates on top of TCP. The iSCSI protocol aims to be fully
compliant with the requirements laid out in the SCSI Architecture
Model - 2 [SAM2] document.
Acknowledgements
In addition to the authors, a large group of people contributed to
this work through their review, comments and valuable insights. We
are grateful to all of them. We are especially grateful to those who
found the time and patience to participate in our weekly phone
conferences and intermediate meetings in Almaden and Haifa, thus
helping to shape this document: John Hufferd, Prasenjit Sarkar, Meir
Toledano, John Dowdy, Steve Legg, Alain Azagury (IBM), Dave Nagle
(CMU), David Black (EMC), John Matze (Veritas), Steve DeGroote, Mark
Shrandt (NuSpeed), Gabi Hecht (Gadzoox), Robert Snively (Brocade),
Nelson Nachum (StorAge), Uri Elzur (Broadcom). Many more helped
clean up and improve this document within the IPS working group. We
are especially grateful to David Robinson and Raghavendra Rao (Sun),
Charles Monia, Joshua Tseng (Nishan), Somesh Gupta (Silverback
Systems), Michael Krause, Pierre Labat, Santosh Rao, Matthew
Burbridge (HP), Stephen Bailey (Sandburst), Robert Elliott (Compaq),
Steve Senum, Ayman Ghanem (CISCO), Barry Reinhold (Trebia Networks),
Satran, J. Standards-Track, Expires July 2002 2
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Bob Russell (UNH), Bill Lynn (Adaptec) and Doug Otis (Sanlight),
Robert Griswold and Bill Moody (Crossroads). The recovery chapter
was enhanced with help from Stephen Bailey (Sandburst), Somesh Gupta
(HP), Venkat Rangan (RhapsodyNetworks), Vince Cavanna, Pat Thaler
(Agilent), Eddy Quicksall (iVivity, Inc.) - Eddy also contributed
with some examples. Last, but not least, thanks to Ralph Weber for
keeping us in line with T10 (SCSI) standardization.
We would like to thank Steve Hetzler for his unwavering support and
for coming up with such a good name for the protocol, Micky Rodeh,
Jai Menon, Clod Barrera and Andy Bechtolsheim for helping this work
happen.
At the time of the writing, this document has to be considered in
conjunction with the "Naming & Discovery"[NDT], "Boot"[BOOT] and
"Securing iSCSI, iFCP and FCIP"[SEC-IPS] documents.
The "Naming & Discovery" is authored by:
Mark Bakke (Cisco), Joe Czap, Jim Hafner, John Hufferd,
Kaladhar Voruganti (IBM), Howard Hall (Pirus), Jack Harwood
(EMC), Yaron Klein (SANRAD), Lawrence Lamers (San Valley
Systems), Todd Sperry (Adaptec) and Joshua Tseng (Nishan).
The "Boot" is authored by:
Prasenjit Sarkar (IBM), Duncan Missimer (HP) and Costa
Sapuntzakis (CISCO).
The "Securing iSCSI, iFCP and FCIP" is authored by:
Bernard Aboba, William Dixon (Microsoft), David Black (EMC),
Joseph Tardo, Uri Elzur (Broadcom), Mark Bakke, Steve Senum
(Cisco Systems), Howard Herbert, Jesse Walker (Intel), Julian
Satran, Ofer Biran and Charles Kunzinger (IBM).
We are grateful to all of them for their good work and for helping us
correlate this document with the ones they produced.
Conventions used in this document
In examples, "I->" and "T->" indicate iSCSI PDUs sent by the
initiator and target respectively.
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iSCSI 19-Nov-01
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119.
Change Log
The following changes were made from draft-ietf-ips-iSCSI-08 to
draft-ietf-ips-iSCSI-09:
- Added Task management response "task management function not
supported"
- Negotiation (numeric) responder driven
- Added vendor specific data to reject
- Allow logout in discovery sessions
- Variable DataPDULength - renamed MaxRecvPDULength
- Key=value pairs can span PDU boundaries
- Uniform treatment of text exchange resets
- Reintroduced DataACK as a special form of SNACK
- Extended ISID in the Login Request
- Removed 0 as a "no limit value" (residue from mode pages)
- Reintroduced LogoutLoginMinTime
- Digests moved to Operational Keys
- Removed X bit in all commands and replaced it in Login and
added a cleaning rule to CmdSN numbering
- Added Task management response "task management function not
supported"
- Several simplifications in state transition section -
standard connection and session state diagrams are separately
described for initiators and targets
- Several minor technical and language changes in the error
recovery section
- Added irrelevant to negotiations
- Clarification to logout behavior
- Clarification to command ordering
- On SCSI timeout task abort instead of session failure
- Changed version to 0x03 - ALL VERSION NUMBERS are temporary
up to "RFC-time" (take them with a grain of salt)
The following changes were made from draft-ietf-ips-iSCSI-07 to
draft-ietf-ips-iSCSI-08:
- Clarified the use of initiator task tag with regard to the
SCSI tag in 3.2.1.7
- Added a clarification to 2.2.2.1 - response to a command
should not precede acknowledgment.
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- Added clarification to 3.7 - good status in Data-In must be
supported by initiators
- Clarified InitiatorName is required at login in 5.1
- Another clarification for SecurityContextComplete in 5.2
- Added "command not supported in this session type" to reject
reasons
- Discovery session implies MaxConnections = 1
- Second appearance of TargetAddress deleted
- Padding forbidden for non-end-of-sequence data PDUs
- Removed Boot and CopyManager Session types
- Changed explanation of ExpDataSN
- Removed/corrected response 05 in 3.4.3
- Brought 1.2.7 in line with NDT draft
- Fixed the syntax in accordance with [RFC2372] and [RFC2373]
- Removed forgotten references to the default iSCSI target
- Counters back to Reject Response
- Clarification - SendTargets admissible only in full feature
phase
- Changed name of DataOrder and DataDeliveryOrder to
DataSequenceOrder and DataPDUInOrder and clarified appendix
text
- Padding bytes SHOULD be sent as 0 (instead of MUST be 0)
- UA attention behavior for various resets deleted - replaced
with reference to SAM2
- Removed AccessID
- OpParmReset generalized
- Clarified the definition of full-feature phase in 1.2.5
- Added new Reject reason codes, tabular listing and a pointer
to 3.17.1
- Added additional Reject usage semantics on CmdSN and DataSN
to 3.17.1
- Added a new Logout Response code for failure
- Renamed BUSY as RECOVERY_START, removed RECOVERY_DONE, and
merged T11 and T14 transitions into T11-(1,2) in section 7.
- Corrected initiator handling of format errors
- Clarified usage of command replay
- Removed the delivery in same order as presented from Text
Response
- Clarified RefCmdSN function fro abort task
- Corrected length field for AHS of type Extended CDB
- Removed LUN from text management response
- Clarified F bit for Bidirectional commands
- Removed the Async iSCSI event "target reset"
- Removed wording in section 3.6 linking SCSI mode pages to
Async Messages
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- Changed the ASC/ASCQ values to better mean "not enough
unsolicited data"
- Names examples include date
- Removed references to S bit in 3.4
- Fixed NOP to simplify and avoid it consuming CmdSN
- Fixed CRC and examples
- Added the T, CSG & NSG fields to Login Command & Response,
rewrote chapter 1, changed all examples in Appendix A to fit
the above changes
- Key=value confined to one response
- Add command restart/replay to task management
- Removed cryptographic digests
- Removed "proxy required" status code
- Re-named and fixed descriptions of status codes
- Re-formatted login examples for clarity
- SCSI/iSCSI parameters - fixed chapter 4, out DataPDULength,
DataSequenceOrder
- Changed all sense keys to aborted command in the table in
3.4.2
- Rearranged requests to have all SCSI related grouped etc.
- Fixed Task Management Function Request ABORT TASK and removed
the part about it in chapter 9.
- Reintroduced aliases (the data format) in an Appendix F. The
aliasing mechanism once part of iSCSI is part of [SPC3]
- Login negotiations - using only login request response
(instead of former login and text)
- F bit in login changed name to T bit
- Stated defaults for mode parameters in chapter 3
- Updated chapter 10 to reflect the current consensus on
security
- Changed all sense keys to aborted command in the table in
2.4.2
- Minor language clarifications in sections 1.2.3, 1.2.5,
1.2.6, 1.2.8.
- Added a new Reject reason code "Task in progress" and
clarified language in the same section.
- Added more description to the session state transitions in
section 1.1.
- Several changes in section 8 corresponding to the new task
management function "reassign". Other language changes in
section 8 for better description. Format errors are mandated
to cause session failures.
- Renamed the erstwhile error recovery levels as error recovery
classes, and renamed "within-session" recovery to "connection
recovery" to better reflect the mechanics.
- Added section 8.12 to define the error recovery hierarchy.
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- Modifications to error recovery algorithms in Appendix F.
- Added a new Reject reason code "Invalid SNACK", added DataSN
to Reject PDU.
- Changed section 3.17 to use the "Invalid SNACK" reason code.
- Removed a Logout reason code in 3.14 to be consistent with
section 3.9.
- Collapsed the two event fields in Async Event and added
vendor specific event
- Immediate data can be negotiated anytime (consistency)
- Removed replay as a protocol notion and all references to it
- SNACK RunLength 0 means all
- Cleaning the bookmark mechanism for text
- New T10 approved ASC/ASQ codes
- Added a incipient definitions section - thanks to Eddy
Quicksall
- Change OpParmReset from yes/no to default/current
- Added Base64 to encode large strings
- The 255 limit for key values is now "unless specified
otherwise"
- Cleaned SNACK format
- Removed ExpR2TSN from SCSI command response it is too late
- MaxBurstSize/FirstBurstSize back as key=value
- Removed LogoutLoginMinTime (value provided in exchange)
- Clear language on component function in generating ISID/TSID
- Negotiation breaking is done through abort/reject
- Removed all iSCSI mode pages
The following changes were made from draft-ietf-ips-iSCSI-06 to
draft-ietf-ips-iSCSI-07:
- Clarified the "fate" of immediate commands and resources
mandated (1.2.2.1) and introduced a reject-code for rejected
immediate commands
- Clarify CmdSN handling and checking order for ITT and CmdSN
1.2.2.1
- Added a statement to the effect that a receiver must be able
to accept 0 length Data Segments to 2.7.6. Added also a
statement to 2.2.1 that a zero-length data segment implies a
zero-length digest
- SCSI MODE SELECT will not really set the parameters (will not
cause an error either). The parameters will be set exclusively
with text mode and can be retrieved with either text or Mode-
SENSE. This enables us to disable their change after the Login
negotiation. Also added to the negotiation (1.2.4) the value
"?" with special meaning of enquiry
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- Changed "task" to "command" wherever relevant
- EMDP usage in line with other SCSI protocols. EMDP governs
how a target may request data and deliver. Similar to FCP a
separate (protocol) parameter governs data PDU ordering within
Sequence (DataPDUInOrder). Cleaned wording of DataOrder. Fixed
final bit to define sequences in input stream.
- Added a "persistent state" part (1.2.8)
- Some Task Management commands may require authorization or
may not be implemented. If not authorized they will return as
if executed with a qualifier indicating "not authorized" or
"not implemented" (clear LU and the resets)
- Task management commands and responses are "generalized" to
all iSCSI tagged commands (they are named now Task Management
command and response). Their behavior with respect to their
CmdSN is clarified and mandated
- The logic to update ExpCmdSN etc. moved to 1.2.2.1
- Explicitly specified that a target can "initiate" negotiating
a parameter (offering)(1.2.4)
- Returned the "direction" bit and a set of codes similar to
version 05
- Introduced a "special" session type (CopyManagerSession) to
be used between a Copy Manager and all of its target; it may
help define authentication and limit the type f commands to be
executed in such a session
- Added 8.4 - How to Abort Safely a Command that Was Not
Received
- Fixed the Logout Text
- AHSLength is now the first field in the AHS
- Fixed wording in 2.35 indicating AHS is mandatory for Bi-
directional commands
- All key=value responses have to be explicit (none, not-
understood etc.); no more selection by hiatus
- Targets can also offer key=value pairs (i.e., initiate
negotiation) stated explicitly in 2.9.3
- Logout has a CmdSN field
- The Status SNACK can be discarded if the target has no such
recovery
- Some parameters have been removed and replaced by
"reasonable" defaults (read arbitrary defaults!); many others
can't be changed anymore while the session is in full-feature
phase
- NOP-Out specifies how LUN is generated when used (copied from
NOP-In)
- Initial Marker-Less Interval is not a parameter anymore
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- A response with F=1 during negotiation may not contain
key=value pairs that may require additional answers from the
initiator
- Clarified the meaning of the F bit on Write commands with
regard to immediate and unsolicited data; F bit 0 means that
unsolicited data will follow while F bit 1 means that this is
the last of them (if any)
- You can have both immediate and unsolicited Data-Out PDUs
- DataPDULength and FirstBurstSize of 0 are allowed and mean
unlimited length
- Task management command behavior relative to their own CmdSN
is now stated in no uncertain terms (they are mandated to
execute as if issued at CmdSN and, in case of aborts and
clear/reset no additional response/status is expected for those
commands after the task management command response
- DataSN field in R2T renamed as R2TSN (better reflects
semantics) and SNACK explicitly says that it requests Data or
R2T.
- A session can have only one outstanding text request (not
sequence)
- Text for Login Response 0301 changed (removed the maintenance
mention)
- Clarified when ExpDataSN is reserved in SCSI Response
- Clarified the text and parameter (timers) for iSCSI event
- Padding bytes should be 0 (2.1)
- TotalAHSLength in 2.1.1.1 includes padding
- DataSegmentLength in 2.1.1.2 excludes padding
- Clarified bits in AHS type
- Limit for key/value string lengths (63, 255) in 2.8.3
- Added an example of SCSI event to Asynchronous Message
- Changed "Who" to "Who can send" in appendix
- Clarified meaning of parameters on 2.18.1 - Asynchronous
Message - iSCSI Event
- Clarified the required initiator behavior at logout (not
sending other commands) and how one expects the TCP close to be
performed in 2.14
- Added a Login Response code indicating that a session can't
include a given connection (0208)
- Clarified transition to full feature phase (per session and
per connection and the role of the leading connection) in 1.2.5
- Corrected "one outstanding text request per connection"
instead of "per session"
- For the Login Response TSID must be valid only if Login is
accepted and the F bit is 1
- Added examples illustrating DataSN and R2TSN (from Eddy
Quicksall)
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- Added more text to the task management command 2.5
- Removed EnableACA and its dependents (in task management) and
stated the requirement for a Unit Attention conform to SAM2
- iSCSI Target Name if used on a connection other than the
first must be the same as on the first (4.1)
- Fixed the examples in the Login appendix to correspond to the
new keys
- Fixed SCSI Response Flags and made them consistent with the
Data-In PDU
- All specified keys except X-* MUST be accepted (2.8.3)
- Hexadecimal notation is 0xab123cd (not 0x'ab123cd')
- Clarified CmdSN usage in immediate commands and the meaning
of "execution engine" in 1.2.2.1
- Reject response that prevent the creation of a SCSI task or
result in a SCSI task being terminated must be followed by a
SCSI Response with a Check Condition status 2.19.1
- Additional Runs (AddRuns) dropped from the SNACK request (too
complex). With it disappeared also the implicit acknowledgement
of sequences "between runs"
- PDUs delivered because of SNACK will be exact replicas of the
original PDUs (including all flags) 2.16
- Added CommandReplaySupport key to negotiate support for full
command replay (a command can be replayed after the status has
been issued but has not been acknowledged) and a reject cause
of unsupported command reply
- Added CommandFailoverSupport key to negotiate support for
command allegiance change (command retry on another connection)
- Status SNACK for an acknowledged status is a protocol error
(cause for reject)
- Reject cause "Command In Progress" when requesting replay
before status is issued and while command is running
- Premature SNACKs are silently discarded (2.16)
- Status SNACK has to supported only if within command or
within connection recovery is supported. If within session
recovery is supported SNACK can be discarded and followed by an
Async. Message requesting logout
- StatSN added to Logout Response
- Added "CID not found" to Logout Response reason codes
- Async Message - iSCSI event 2 (request logout) has to be sent
on the connection to be dropped. Wording fixed.
- Naming changes - iqn (stands for iSCSI qualified name)
introduced as a replacement to fqn. Iqn prefixes also reversed
names
- text in 8.3 revised (task management implementation
mechanism)
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- Fixed bit 7 byte 1 in Task Management response to 1
(consistency)
- Clarified in 1.2.2 behavior when "command window" is 0
(MaxCmdSN = ExpCmdSN -1)
- Added state transitions part (new part 6)
- Refreshed recovery chapter (new part 7)
- Added an appendix with detailed recovery mechanisms (Appendix
E)
- Added session types a brief explanation in part 1
- Added DiscoverySession key and SendTargets appendix
- SCSI response made to fit having both a Status and a Response
field. Needed for target errors that result in a check
condition and ACA. In line with SAM2 that requires both fields
(former versions where modeled on FCP).
- The security appendix list SRP as mandatory to implement
- Clarified initial CmdSN and the role of TSID as a serializer
- Long Text Responses - additional fields added to the text
request and text response
- Added a SCSI to iSCSI concept mapping section 1.5
- Clarified SNACK wording to indicate that in general command.
Request, iSCSI command and iSCSI command have the same meaning.
Also status, response or numbered response.
- Changed InitStatSN and clarified how it increases
- Added requirement for a 0x00 delimiter after each key=value
- Added binary negotiations (yes|no) explicitly to 1.2.4
- All keys and values in the spec are case sensitive (stated in
the text request)
- Changed the "operational parameters sent before the
security.. MAY be discarded" into MUST be discarded
- Changed the login reject 0201 to read - Security Negotiation
Failed
- Added to 2.3.1 a paragraph about mandatory consistencies
- Stated clearly that F bit pairing is "local" (per/pair) and
not per negotiation
- Clarified dependent parameter status
- Added CRC Example
- Added OpParmReset=yes
- SecurityContextComplete is mandatory if any option offered
- Added a warning about the implications of not sending all
unsolicited data to part 8
- Added a recommendation to send unsolicited data at
FirstBurstSize and a response (error) for targets not
supporting less
- Many more minor editorial changes, clarifications, typos etc.
- Responses in same position in SCSI response, logout, task
etc.
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Table of Contents
Status of this Memo...................................................2
Abstract..............................................................2
Acknowledgements......................................................2
Conventions used in this document.....................................3
Change Log............................................................4
1. Definitions.......................................................19
2. Overview..........................................................23
2.1 SCSI Concepts..................................................23
2.2 iSCSI Concepts and Functional Overview.........................23
2.2.1 Layers and Sessions.........................................24
2.2.2 Ordering and iSCSI Numbering................................25
2.2.2.1 Command Numbering and Acknowledging......................25
2.2.2.2 Response/Status Numbering and Acknowledging..............28
2.2.2.3 Data Sequencing..........................................29
2.2.3 iSCSI Login.................................................29
2.2.4 Text Mode Negotiation.......................................30
2.2.5 iSCSI Full Feature Phase....................................32
2.2.6 iSCSI Connection Termination................................35
2.2.7 Naming and Addressing.......................................35
2.2.8 Persistent State............................................37
2.2.9 Message Synchronization and Steering........................38
2.2.9.1 Rationale................................................38
2.2.9.2 Synchronization (sync) and Steering Functional Model.....38
2.2.9.3 Sync and Steering and Other Encapsulation Layers.........42
2.2.9.4 Sync/Steering and iSCSI PDU Size.........................42
2.3 Third Party Commands...........................................43
2.4 iSCSI session types............................................43
2.5 SCSI to iSCSI concepts mapping model...........................43
2.5.1 iSCSI Architecture Model....................................44
2.5.2 SCSI Architecture Model.....................................47
2.5.3 Consequences of the model...................................49
2.5.3.1 I_T nexus state..........................................50
2.5.3.2 SCSI Mode Pages..........................................50
3. iSCSI PDU Formats.................................................52
3.1 iSCSI PDU Length and Padding...................................52
3.2 PDU Template, Header and Opcodes...............................52
3.2.1 Basic Header Segment (BHS)..................................53
3.2.1.1 I........................................................54
3.2.1.2 Opcode...................................................54
3.2.1.3 Opcode-specific Fields...................................55
3.2.1.4 TotalAHSLength...........................................55
3.2.1.5 DataSegmentLength........................................55
3.2.1.6 LUN......................................................55
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3.2.1.7 Initiator Task Tag.......................................55
3.2.2 Additional Header Segment (AHS).............................56
3.2.2.1 AHSType..................................................56
3.2.2.2 AHSLength................................................56
3.2.2.3 Extended CDB AHS.........................................56
3.2.2.4 Bidirectional Expected Read-Data Length AHS..............57
3.2.3 Header Digest and Data Digest...............................57
3.2.4 Data Segment................................................58
3.3 SCSI Command...................................................59
3.3.1 Flags and Task Attributes (byte 1)..........................59
3.3.2 CRN.........................................................60
3.3.3 CmdSN - Command Sequence Number.............................60
3.3.4 ExpStatSN...................................................60
3.3.5 Expected Data Transfer Length...............................60
3.3.6 CDB - SCSI Command Descriptor Block.........................61
3.3.7 Data Segment - Command Data.................................61
3.4 SCSI Response..................................................62
3.4.1 Flags (byte 1)..............................................62
3.4.2 Status......................................................63
3.4.3 Response....................................................64
3.4.4 Residual Count..............................................65
3.4.5 Bidirectional Read Residual Count...........................65
3.4.6 Data Segment - Sense and Response Data Segment..............66
3.4.6.1 SenseLength..............................................66
3.4.7 ExpDataSN...................................................66
3.4.8 StatSN - Status Sequence Number.............................66
3.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator..........67
3.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator....67
3.5 Task Management Function Request...............................68
3.5.1 Function....................................................68
3.5.2 LUN.........................................................70
3.5.3 Referenced Task Tag.........................................70
3.5.4 RefCmdSN or ExpDataSN.......................................70
3.6 Task Management Function Response..............................72
3.6.1 Response and Qualifier......................................72
3.6.2 Referenced Task Tag.........................................73
3.7 SCSI Data-out & SCSI Data-in...................................74
3.7.1 F (Final) Bit...............................................75
3.7.2 A (Acknowledge) bit.........................................76
3.7.3 Target Transfer Tag.........................................76
3.7.4 StatSN......................................................76
3.7.5 DataSN......................................................76
3.7.6 Buffer Offset...............................................77
3.7.7 DataSegmentLength...........................................77
3.7.8 Flags (byte 1)..............................................77
3.8 Ready To Transfer (R2T)........................................79
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3.8.1 R2TSN.......................................................80
3.8.2 StatSN......................................................80
3.8.3 Desired Data Transfer Length and Buffer Offset..............80
3.8.4 Target Transfer Tag.........................................81
3.9 Asynchronous Message...........................................82
3.9.1 AsyncEvent..................................................83
3.9.2 AsyncVCode..................................................84
3.9.3 Sense Data or iSCSI Event Data..............................84
3.10 Text Request..................................................85
3.10.1 F (Final) Bit..............................................85
3.10.2 Initiator Task Tag.........................................86
3.10.3 Target Transfer Tag........................................86
3.10.4 Text.......................................................86
3.11 Text Response.................................................88
3.11.1 F (Final) Bit..............................................88
3.11.2 Initiator Task Tag.........................................89
3.11.3 Target Transfer Tag........................................89
3.11.4 Text Response Data.........................................89
3.12 Login Request.................................................91
3.12.1 T (Transit) Bit............................................91
3.12.2 X - Restart Connection.....................................92
3.12.3 CSG and NSG................................................92
3.12.4 Version-max................................................93
3.12.5 Version-min................................................93
3.12.6 ISID.......................................................93
3.12.7 TSID.......................................................94
3.12.8 Connection ID - CID........................................94
3.12.9 CmdSN......................................................94
3.12.10 ExpStatSN.................................................95
3.12.11 Login Parameters..........................................95
3.13 Login Response................................................95
3.13.1 Version-max................................................96
3.13.2 Version-active.............................................96
3.13.3 TSID.......................................................96
3.13.4 StatSN.....................................................97
3.13.5 Status-Class and Status-Detail.............................97
3.13.6 T (Transit) bit............................................99
3.14 Logout Request...............................................100
3.14.1 CID.......................................................101
3.14.2 ExpStatSN.................................................101
3.14.3 Reason Code...............................................101
3.15 Logout Response..............................................103
3.15.1 Response..................................................103
3.15.2 Time2Wait.................................................104
3.15.3 Time2Retain...............................................104
3.16 SNACK Request................................................105
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3.16.1 Type......................................................106
3.16.2 BegRun....................................................107
3.16.3 RunLength.................................................107
3.17 Reject.......................................................108
3.17.1 Reason....................................................108
3.17.2 DataSN....................................................110
3.17.3 Complete Header of Bad PDU................................110
3.18 NOP-Out......................................................111
3.18.1 Initiator Task Tag........................................112
3.18.2 Target Transfer Tag.......................................112
3.18.3 Ping Data.................................................112
3.19 NOP-In.......................................................113
3.19.1 Target Transfer Tag.......................................114
3.19.2 LUN.......................................................114
4. SCSI Mode Parameters for iSCSI...................................115
5. Login Phase......................................................116
5.1 Login Phase Start.............................................118
5.2 iSCSI Security and Integrity Negotiation......................119
5.3 Operational Parameter Negotiation During the Login Phase......120
6. Operational Parameter Negotiation Outside the Login Phase........122
7. State transitions................................................124
7.1 Standard connection state diagrams............................124
7.1.1 Standard connection state diagram for an initiator.........124
7.1.2 Standard connection state diagram for a target.............126
7.1.3 State descriptions for initiators and targets..............128
7.1.4 State transition descriptions for initiators and targets...129
7.2 Connection cleanup state diagram for initiators and targets...131
7.2.1 State descriptions for initiators and targets..............133
7.2.2 State transition descriptions for initiators and targets...134
7.3 Session state diagram.........................................135
7.3.1 Session state diagram for an initiator.....................135
7.3.2 Session state diagram for a target.........................136
7.3.3 State descriptions for initiators and targets..............137
7.3.4 State transition descriptions for initiators and targets...138
8. iSCSI Error Handling and Recovery................................140
8.1 Retry and Reassign in Recovery................................140
8.1.1 Usage of Retry.............................................140
8.1.2 Allegiance Reassignment....................................141
8.2 Usage Of Reject PDU in Recovery...............................141
8.3 Format Errors.................................................142
8.4 Digest Errors.................................................142
8.5 Sequence Errors...............................................143
8.6 SCSI Timeouts.................................................144
8.7 Negotiation failures..........................................145
8.8 Protocol Errors...............................................145
8.9 Connection Failures...........................................145
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8.10 Session Errors...............................................146
8.11 Recovery Classes.............................................147
8.11.1 Recovery Within-command...................................147
8.11.2 Recovery Within-connection................................148
8.11.3 Connection Recovery.......................................149
8.11.4 Session Recovery..........................................149
8.12 Error Recovery Hierarchy.....................................150
9. Notes to Implementers............................................152
9.1 Multiple Network Adapters.....................................152
9.1.1 Conservative reuse of ISIDs................................152
9.1.2 iSCSI Name and ISID/TSID use...............................153
9.2 Autosense and Auto Contingent Allegiance (ACA)................154
9.3 Command retry and cleaning old command instances..............154
9.4 Task Management Commands and Immediate Delivery...............155
9.5 Synch and steering layer and performance......................157
9.6 Unsolicited data and performance..............................157
10. Security Considerations.........................................158
10.1 iSCSI Security mechanisms....................................158
10.2 In-band Initiator-Target Authentication......................158
10.3 IPsec........................................................159
10.3.1 Data Integrity and Authentication.........................160
10.3.2 Confidentiality...........................................160
10.3.3 Security Associations and Key Management..................161
11. IANA Considerations.............................................162
12. References and Bibliography.....................................163
13. Author's Addresses..............................................166
Appendix A. iSCSI Security and Integrity...........................169
01 Security Keys and Values.......................................169
02 Authentication.................................................170
03 Login Phase Examples...........................................174
Appendix B. Examples...............................................184
04 Read Operation Example.........................................184
05 Write Operation Example........................................185
06 R2TSN/DataSN use examples......................................185
07 CRC Examples...................................................189
Appendix C. Sync and Steering with Fixed Interval Markers..........191
08 Markers At Fixed Intervals.....................................191
09 Initial Marker-less Interval...................................192
Appendix D. Login/Text Operational Keys............................193
10 HeaderDigest and DataDigest....................................193
11 MaxConnections.................................................194
12 SendTargets....................................................195
13 TargetName.....................................................195
14 InitiatorName..................................................195
15 TargetAlias....................................................196
16 InitiatorAlias.................................................196
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17 TargetAddress..................................................196
18 FMarker........................................................197
19 RFMarkInt......................................................198
20 SFMarkInt......................................................198
21 InitialR2T.....................................................198
22 BidiInitialR2T.................................................199
23 ImmediateData..................................................200
24 MaxRecvPDULength...............................................201
25 MaxBurstSize...................................................201
26 FirstBurstSize.................................................201
27 LogoutLoginMaxTime.............................................202
28 LogoutLoginMinTime.............................................202
29 MaxOutstandingR2T..............................................203
30 DataPDUInOrder.................................................203
31 DataSequenceInOrder............................................203
32 ErrorRecoveryLevel.............................................204
33 SessionType....................................................204
34 The Vendor Specific Key Format.................................205
Appendix E. SendTargets operation..................................206
Appendix F. SCSI Alias designation formats.........................210
35 Format codes...................................................210
36 iSCSI Name designation format..................................211
37 iSCSI Name with binary IPv4 address designation format.........212
38 iSCSI Name with IPname designation format......................213
39 iSCSI Name with binary IPv6 address designation format.........214
Appendix G. Algorithmic presentation of error recovery classes.....216
40 General Data structure and procedure description...............216
41 Within-command error recovery algorithms.......................217
1 Procedure descriptions........................................217
2 Initiator algorithms..........................................218
3 Target algorithms.............................................220
42 Within-connection recovery algorithms..........................222
4 Procedure descriptions........................................222
1. Initiator algorithms.........................................223
2. Target algorithms............................................225
5 Connection recovery algorithms................................225
3. Procedure descriptions.......................................225
4. Initiator algorithms.........................................226
5. Target algorithms............................................228
Full Copyright Statement............................................230
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1. Definitions
- SCSI Layer: This builds/receives SCSI CDBs (Command Descriptor
Blocks) and relays/receives them with the remaining command execute
parameters to/from the iSCSI Layer.
- iSCSI Layer: This builds/receives iSCSI PDUs and relays/receives
them to/from one or more TCP connections that form an initiator-
target "session".
- PDU (Protocol Data Unit): The initiator and target divide their
communications into messages. The term "iSCSI protocol data unit"
(iSCSI PDU) is used for these messages.
- Connection: Communication between the initiator and target occurs
over one or more TCP connections. The TCP connections carry control
messages, SCSI commands, parameters and data within iSCSI Protocol
Data Units (iSCSI PDUs).
- Session: The group of TCP connections that link an initiator with a
target, form a session (loosely equivalent to a SCSI I-T nexus). TCP
connections can be added and removed from a session. Across all
connections within a session, an initiator sees one "target image".
- CID (Connection ID): Connections within a session are identified by
a connection ID. It is a unique ID for this connection within the
session for the initiator. It is generated by the initiator and
presented to the target during login requests and during logouts that
close connections.
- ISID (Initiator Session ID): An ID generated by the initiator
during leading login for a session. It is used for all additional
logins for the same session. Between a given iSCSI Initiator and
iSCSI Target Portal Group (SCSI target port), there can be only one
session with a given ISID (identifying the SCSI Initiator Port). The
ISID is a structured field containing a naming authority component.
See 3.12.6 and [NDT].
- SSID (Session ID): A session is defined by a session ID that is
composed of an initiator part (ISID) and a target part (TSID).
- TSID (Target Session ID): The TSID is the target assigned tag for a
session with a specific named initiator that, together with the ISID
uniquely identifies a session with that initiator.
It is given to the target during additional connections for the same
session to identify the associated session.
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- iSCSI Name: The name of an iSCSI initiator or iSCSI target.
- iSCSI Target Name: The iSCSI Target Name specifies the worldwide
unique name of the target.
- iSCSI Initiator Name: The iSCSI Initiator Name specifies the
worldwide unique name of the initiator.
- Network Entity: The Network Entity represents a device or gateway
that is accessible from the IP network. A Network Entity must have
one or more Network Portals, each of which is usable by some iSCSI
Nodes contained in that Network Entity to gain access to the IP
network.
- Network Portal: The Network Portal is a component of a Network
Entity that has a TCP/IP network address and that may be used by an
iSCSI Node within that Network Entity for the connection(s) within
one of its iSCSI sessions. A Network Portal in an initiator is
identified by its IP address. A Network Portal in a target is
identified by its IP address and its listening TCP port.
- Portal Groups: iSCSI supports multiple connections within the same
session; some implementations will have the ability to combine
connections in a session across multiple Network Portals. A Portal
Group defines a set of Network Portals within an iSCSI Node that
collectively supports the capability of coordinating a session with
connections spanning these portals. Not all Network Portals within a
Portal Group need participate in every session connected through that
Portal Group. One or more Portal Groups may provide access to an
iSCSI Node. Each Network Portal as utilized by a given iSCSI Node
belongs to exactly one portal group within that node.
- Portal Group Tag: This simple integer value between 1 and 65535
identifies the Portal Group within an iSCSI Node. All Network Portals
with the same portal group tag in the context of a given iSCSI Node
are in the same Portal Group.
- iSCSI Node: The iSCSI Node represents a single iSCSI initiator or
iSCSI target. There are one or more iSCSI Nodes within a Network
Entity. The iSCSI Node is accessible via one or more Network Portals.
An iSCSI Node is identified by its iSCSI Name. The separation of the
iSCSI Name from the addresses used by and for the iSCSI node allows
multiple iSCSI nodes to use the same addresses, and the same iSCSI
node to use multiple addresses. iSCSI nodes also have addresses. An
iSCSI address specifies a single path to an iSCSI node.
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- iSCSI Initiator Node: The "initiator".
- iSCSI Target Node: The "target".
- Alias: An alias string could also be associated with an iSCSI Node.
The alias allows an organization to associate a user-friendly string
with the iSCSI Name. However, the alias string is not a substitute
for the iSCSI Name.
- I_T nexus: According to [SAM2], the I_T nexus is a relationship
between a SCSI Initiator Port and a SCSI Target Port. For iSCSI, this
relationship is a session, defined as a relationship between an iSCSI
Initiator's end of the session (SCSI Initiator Port) and the iSCSI
Target's Portal Group. The I_T nexus can be identified by the
conjunction of the SCSI port names; that is, the I_T nexus identifier
is the tuple (iSCSI Initiator Name + 'i'+ ISID, iSCSI Target Name +
't'+ Portal Group Tag). NOTE: The I_T nexus identifier is not equal
to the session identifier (SSID).
- SCSI Device: This is the SAM2 term for an entity that contains
other SCSI entities. For example, a SCSI Initiator Device contains
one or more SCSI Initiator Ports and zero or more application
clients; a SCSI Target Device contains one or more SCSI Target Ports
and one or more logical units. For iSCSI, the SCSI Device is the
component within an iSCSI Node that provides the SCSI functionality.
As such, there can be at most one SCSI Device within a given iSCSI
Node. Access to the SCSI Device can only be achieved in an iSCSI
normal operational session. The SCSI Device Name is defined to be the
iSCSI Name of the node and its use is mandatory in the iSCSI
protocol.
- SCSI Port: This is the SAM2 term for an entity in a SCSI Device
that provides the SCSI functionality to interface with a service
delivery subsystem or transport. For iSCSI, the definition of SCSI
Initiator Port and SCSI Target Port are different.
- SCSI Initiator Port: This maps to the endpoint of an iSCSI normal
operational session. An iSCSI normal operational session is
negotiated through the login process between an iSCSI initiator node
and an iSCSI target node. At successful completion of this process, a
SCSI Initiator Port is created within the SCSI Initiator Device. The
SCSI Initiator Port Name and SCSI Initiator Port Identifier are both
defined to be the iSCSI Initiator Name together with (a) a label that
identifies it as an initiator port name/identifier and (b) the ISID
portion of the session identifier.
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- SCSI Target Port: This maps to an iSCSI Target Portal Group.
- SCSI Port Name: A name made up as UTF-8 characters and is basically
the iSCSI Name + 'i' or 't' + ISID or Portal Group Tag.
- SCSI Target Port Name and SCSI Target Port Identifier: These are
both defined to be the iSCSI Target Name together with (a) a label
that identifies it as a target port name/identifier and (b) the
portal group tag.
- iSCSI Task: An iSCSI task is an iSCSI request for which a response
is expected.
- iSCSI Transfer Direction: The iSCSI transfer direction is defined
with regard to the initiator. Outbound or outgoing transfers are
transfers from initiator to target, while inbound or incoming
transfers are from target to initiator.
- Originator - in a negotiation or exchange the party that initiates
the negotiation or exchange
- Responder - in a negotiation or exchange the party that responds to
the originator of the negotiation or exchange
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2. Overview
2.1 SCSI Concepts
The SCSI Architecture Model-2 [SAM2] describes in detail the
architecture of the SCSI family of I/O protocols. This section
provides a brief background to familiarize readers with the
terminology of the SCSI architecture.
At the highest level, SCSI is a family of interfaces for requesting
services from I/O devices, including hard drives, tape drives, CD and
DVD drives, printers, and scanners. In SCSI terminology, an
individual I/O device is called a "logical unit" (LU).
SCSI is a client-server architecture. Clients of a SCSI interface are
called "initiators". Initiators issue SCSI "commands" to request
service from a logical unit. The "device server" on the logical unit
accepts SCSI commands and processed them.
A "SCSI transport" maps the client-server SCSI protocol to a specific
interconnect. Initiators are one endpoint of a SCSI transport. The
"target" is the other endpoint. A target can contain multiple Logical
Units (LUs). Each Logical Unit has an address within a target called
a Logical Unit Number (LUN).
A SCSI task is a SCSI command or possibly a linked set of SCSI
commands. Some LUs support multiple pending (queued) tasks but the
queue of tasks is managed by the target. The target uses an initiator
provided "task tag" to distinguish between tasks. Only one command in
a task can be outstanding at any given time.
Each SCSI command results in an optional data phase and a required
response phase. In the data phase, information can travel from the
initiator to target (e.g., WRITE), target to initiator (e.g., READ),
or in both directions. In the response phase, the target returns the
final status of the operation, including any errors. A response
terminates a SCSI command.
Command Descriptor Blocks (CDB) is the data structure used to contain
the command parameters that are to be handed by an initiator to a
target. The CDB content and structure is defined by [SAM] and device-
type specific SCSI standards.
2.2 iSCSI Concepts and Functional Overview
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The iSCSI protocol is a mapping of the SCSI remote procedure
invocation model (see [SAM]) over the TCP protocol.
In the rest of this document, the terms "initiator" and "target"
refer to "iSCSI initiator node" and "iSCSI target node", respectively
(see 2.5.1) unless otherwise qualified.
In keeping with similar protocols, the initiator and target divide
their communications into messages. This document uses the term
"iSCSI protocol data unit" (iSCSI PDU) for these messages.
For performance reasons, iSCSI allows a "phase-collapse". A command
and its associated data may be shipped together from initiator to
target and data and responses may be shipped together from targets.
The iSCSI transfer direction is defined with regard to the initiator.
Outbound or outgoing transfers are transfers from initiator to
target, while inbound or incoming transfers are from target to
initiator.
An iSCSI task is an iSCSI request for which a response is expected.
In this document "iSCSI request", "iSCSI command", request or
(unqualified) command have the same meaning. Also, unless specified
otherwise, status, response or numbered response have the same
meaning.
2.2.1 Layers and Sessions
To specify initiator and target actions and how they relate to
transmitted and received Protocol Data Units the following conceptual
layering model is used:
-the SCSI layer builds/receives SCSI CDBs (Command Descriptor
Blocks) and relays/receives them with the remaining command
execute parameters (cf. SAM2) to/from ->
-the iSCSI layer that builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections that
form an initiator-target "session".
Communication between the initiator and target occurs over one or
more TCP connections. The TCP connections carry control messages,
SCSI commands, parameters and data within iSCSI Protocol Data Units
(iSCSI PDUs). The group of TCP connections that link an initiator
with a target, form a session (loosely equivalent to a SCSI I-T nexus
- see 2.5.2). A session is defined by a session ID that is composed
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of an initiator part and a target part. TCP connections can be added
and removed from a session. Connections within a session are
identified by a connection ID (CID).
Across all connections within a session, an initiator sees one
"target image". All target identifying elements, like LUN, are the
same. In addition, across all connections within a session, a target
sees one "initiator image". Initiator identifying elements like the
Initiator Task Tag, can be used to identify the same entity
regardless of the connection on which they are sent or received.
iSCSI targets and initiators MUST support at least one TCP connection
and MAY support several connections in a session. For error recovery
purposes even targets and initiators supporting a single active
connection in a session may have to support two connections during
recovery.
2.2.2 Ordering and iSCSI Numbering
iSCSI uses Command and Status numbering schemes and a Data sequencing
scheme.
Command numbering is session-wide and is used for ordered command
delivery over multiple connections. It can also be used as a
mechanism for command flow control over a session.
Status numbering is per connection and is used to enable missing
status detection and recovery in the presence of transient or
permanent communication errors.
Data sequencing is per command or part of a command (R2T triggered
sequence) and is used to detect missing data and/or R2T PDUs due to
header digest errors.
Normally, fields in the iSCSI PDUs communicate the Sequence Numbers
between the initiator and target. During periods when traffic on a
connection is unidirectional, iSCSI NOP-Out/In PDUs may be utilized
to synchronize the command and status ordering counters of the target
and initiator.
2.2.2.1 Command Numbering and Acknowledging
iSCSI supports ordered command delivery within a session. All
commands (initiator-to-target PDUs) are numbered.
Many SCSI activities are related to a task (SAM2). The task is
identified by the Initiator Task Tag for the life of the task.
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Commands in transit from the initiator to the target layer are
numbered by iSCSI; the number is carried by the iSCSI PDU as CmdSN
(Command-Sequence-Number). The numbering is session-wide. Outgoing
iSCSI request PDUs carry this number. The iSCSI initiator allocates
CmdSNs with a 32-bit unsigned counter (modulo 2**32). Comparisons and
arithmetic on CmdSN SHOULD use Serial Number Arithmetic as defined in
[RFC1982] where SERIAL_BITS = 32.
Commands meant for immediate delivery are marked as such through an
immediate delivery flag. They too carry CmdSN, but CmdSN does not
advance for commands marked for immediate delivery.
Command numbering starts with the first login request on the first
connection of a session (the leading login on the leading connection)
and includes every non-immediate command issued afterwards.
If immediate delivery is used with task management commands, these
commands may reach the target task management before the tasks they
are supposed to act upon. However, their CmdSN is a marker of their
position in the stream of commands. The task management command MUST
carry the CmdSN that would be given to the next non-immediate
command. The initiator and target must ensure that the task
management commands act as specified by SAM2 - i.e., both commands
and responses appear as if delivered in order.
Not covered in this document are the means by which one may request
immediate delivery for a command or by which iSCSI will decide by
itself to mark a PDU for immediate delivery.
Please note that the number of commands used for immediate delivery
is not limited and their delivery to execution is not acknowledged
through the numbering scheme. Immediate commands can be rejected by
the iSCSI target due to lack of resources. An iSCSI target MUST be
able to handle at least one immediate task management command and one
immediate non-task-management iSCSI request per connection at any
time.
Except for the commands marked for immediate delivery the iSCSI
target layer MUST deliver the commands for execution in the order
specified by CmdSN. Commands marked for immediate delivery may be
handed over by the iSCSI target layer for execution as soon as
detected. iSCSI may avoid delivering some command for execution if so
required by some prior SCSI or iSCSI action (e.g., clear task set
Task Management request received before all the commands it was
supposed to act on). Delivery for execution means delivery to the
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SCSI execution engine or an iSCSI-SCSI protocol specific execution
engine (e.g., for text requests).
On any given connection, the iSCSI initiator MUST send the commands
in increasing order of CmdSN except for retransmitted commands due to
digest error recovery and connection recovery.
The initiator and target are assumed to have three registers, unique
session wide, that define the numbering mechanism:
- CmdSN - the current command Sequence Number advanced by 1 on
each command shipped except for commands marked for immediate
delivery contains always the number to be assigned next.
- ExpCmdSN - the next expected command by the target. The
target acknowledges all commands up to but not including this
number and the initiator has to mark the acknowledged commands
as such as soon as a PDU with the corresponding ExpCmdSN is
received. The target iSCSI layer sets the ExpCmdSN to the
largest non-immediate CmdSN that it is able to deliver for
execution plus 1 (no holes in the CmdSN sequence).
- MaxCmdSN - the maximum number to be shipped. The queuing
capacity of the receiving iSCSI layer is MaxCmdSN - ExpCmdSN +
1.
ExpCmdSN and MaxCmdSN are derived from target-to-initiator PDU
fields.
MaxCmdSN and ExpCmdSN fields are processed as follows:
-if the PDU MaxCmdSN is less than the PDU ExpCmdSN-1 (in Serial
Arithmetic Sense), they are both ignored
-if the PDU MaxCmdSN is less than the local MaxCmdSN (in Serial
Arithmetic Sense), it is ignored; else it updates the local
MaxCmdSN
-if the PDU ExpCmdSN is less than the local ExpCmdSN (in Serial
Arithmetic Sense), it is ignored; else it updates the local
ExpCmdSN
This sequence is required as updates may arrive out of order because
they travel on different TCP connections.
The target MUST NOT transmit a MaxCmdSN that is less than the last
ExpCmdSN. For non-immediate commands, the CmdSN field can take any
value from ExpCmdSN to MaxCmdSN. The target MUST silently ignore any
non-immediate command outside this range or non-immediate duplicates
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within the range that appear without a preceding logout operation on
the connection on which the commands where active.
iSCSI initiators and targets MUST support the command numbering
scheme.
A numbered iSCSI request will not change its allocated CmdSN
regardless of the number of times and circumstances in which it is
reissued. At the target, it is assumed that CmdSN is relevant only
while the command has not created any execution state (can't find the
Initiator Task Tag). Afterwards CmdSN becomes irrelevant. Testing
for execution state is assumed to precede any other action at the
target and is followed by ordering and delivery if no execution state
is found or delivery if execution state is found.
After reissuing a command with CmdSN R on a connection when the
current value of the CmdSN register is Q, while this connection is
operational, an initiator MUST not advance CmdSN past R + 2**31 - 1
unless a new non-immediate command with CmdSN equal or greater than Q
was issued on the given connection and its reception acknowledged by
the target (see also 9.3); the non-immediate command MUST be sent in-
order after the retried command.
A target MUST NOT issue a command response or DATA-In PDU with status
before acknowledging the command. However, the acknowledgement can be
included in the response or Data-in PDU itself.
2.2.2.2 Response/Status Numbering and Acknowledging
Responses in transit from the target to the initiator are numbered.
The StatSN (Status Sequence Number) is used for this purpose. StatSN
is a counter maintained per connection. ExpStatSN is used by the
initiator to acknowledge status. The status sequence number space is
that of 32bit integers and the arithmetic operations are the regular
mod(2**32) arithmetic.
Status numbering starts with the Login response to the first Login
request of the connection. The Login response includes an initial
value for status numbering.
To enable command recovery the target MAY maintain enough state
information to enable data and status recovery after a connection
failure. A target can discard all the state information maintained
for recovery after the status delivery is acknowledged through
ExpStatSN.
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A large absolute difference between StatSN and ExpStatSN may indicate
a failed connection. Initiators undertake recovery actions if the
difference is greater than an implementation defined constant that
SHALL NOT exceed 2**31-1.
Initiators and Targets MUST support the response-numbering scheme.
2.2.2.3 Data Sequencing
Data and R2T PDUs, transferred as part of some command execution,
MUST be sequenced. The DataSN field is used for data sequencing. For
input (read) data PDUs DataSN starts with 0 for the first data PDU of
an input command and advances by 1 for each subsequent data PDU. For
output data PDUs, DataSN starts with 0 for the first data PDU of a
sequence (the initial unsolicited sequence or any data PDU sequence
issued to satisfy an R2T) and advances by 1 for each subsequent data
PDU. R2Ts are also sequenced per command - i.e. the first R2T has an
R2TSN of 0 and advances by 1 for each subsequent R2T. For
bidirectional commands, the target uses the DataSN/R2TSN to sequence
Data-In and R2T PDUs in one continuous sequence (undifferentiated).
Unlike command and status, the data PDUs and R2Ts are not
acknowledged except as implied by status. The DataSN/R2TSN field is
meant to enable the initiator to detect missing data PDUs and
simplify this operation at the target.
For any given write command a target must have issued less than
2**32-1 R2Ts. Any input or output data sequence MUST contain less
than 2**32-1 numbered PDUs.
2.2.3 iSCSI Login
The purpose of the iSCSI login is to enable a TCP connection for
iSCSI use, authenticate the parties, negotiate the session's
parameters, open a security association protocol, and mark the
connection as belonging to an iSCSI session.
A session is used to identify to a target all the connections with a
given initiator that belong to the same I_T nexus (See 2.5.2 for more
details on how a session relates to an I_T nexus).
The targets listen on a well-known TCP port or other TCP port for
incoming connections. The initiator begins the login process by
connecting to one of these TCP ports.
As part of the login process, the initiator and target MAY wish to
authenticate each other and set a security association protocol for
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the session. This can occur in many different ways and is subject to
negotiation.
In order to protect the TCP connection, an IPsec security association
MAY be established before the Login request. Using IPsec security for
iSCSI is specified in chapter 10 and in [SEC-IPS].
The iSCSI Login Phase is carried through Login requests and
responses. Once suitable authentication has occurred and operational
parameters have been set, the initiator may start to send SCSI
commands. How the target chooses to authorize an initiator is beyond
the scope of this document. A more detailed description of the Login
Phase can be found in chapter 1.
The login PDU includes a session ID that is composed of an initiator
part ISID and a target part TSID. For a new session, the TSID is
null. As part of the response, the target generates a TSID.
During session establishment, the target identifies the SCSI
initiator port (the "I" in the "I_T nexus") through the value pair
(InitiatorName, ISID) (InitiatorName is described later in this
part). Any persistent state (e.g., persistent reservations) on the
target associated with a SCSI initiator port is identified based on
this value pair. Any state associated with the SCSI target port (the
"T" in the "I_T nexus") is identified externally by the TargetName
and portal group tag (see 2.5.1) and internally in an implementation
dependent way. As ISID is used to identify persistent state, it is
subject to reuse restrictions (see 2.5.3).
Before full feature phase is established, only Login Request and
Login Response PDUs are allowed. Any other PDU, when received at
initiator or target, is a protocol error and MUST result in the
connection being terminated.
2.2.4 Text Mode Negotiation
During login and thereafter some session or connection parameters are
negotiated through an exchange of textual information.
The initiator starts the negotiation through a Text/Login request and
indicates when it is ready for completion (by setting to 1 and
keeping to 1 the F bit in a Text Request or the T bit in the Login
Request).
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The general format of text negotiation is:
Originator-> <key>=<valuex>
Responder-> <key>=<valuey>|NotUnderstood|irrelevant
The originator can be either the initiator or the target and the
responder the target or initiator respectively. Target requests are
not limited to respond to key=value pairs as offered by the
initiator. The target may offer key=value pairs of its own.
All negotiations are stateless - i.e. the result MUST be based only
on newly exchanged values. Not offering a key for negotiation is not
equivalent to offering the current (or default) value.
The value can be a number, a single literal constant a Boolean value
(yes or no) or a list of comma separated literal constant values.
In literal list negotiation, the originator sends for each key a list
of options (literal constants which may include "none") in its order
of preference.
The responding party answers with the first value from the list it
supports and is allowed to use for the specific originator.
The constant "none" MUST always be used to indicate a missing
function. However, none is a valid selection only if it is explicitly
offered.
If a responder is not supporting, or not allowed to use with a
specific originator, any of the offered options, it may use the
constant "reject".
For numerical and single literal negotiations, the responding party
MUST respond with the required key and the value it selects, based on
the selection rule specific to the key, becomes the negotiation
result. Selection of a value not admissible under the selection
rules is considered a protocol error and handled accordingly.
For numerical negotiations, the value 0 MAY be specified by the
offering party as a "don't care"/"unlimited" value for parameters
that explicitly allow it; in this case, the responder may choose any
legal value for the parameter.
For Boolean negotiations (keys taking the values yes or no), the
responding party MUST respond with the required key and the result of
the negotiation when the received value does not determine that
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result by itself. The last value transmitted becomes the negotiation
result. The rules for selecting the value to respond with are
expressed as Boolean functions of the value received and the value
that the responding party would select in the absence of knowledge of
the received value.
Specifically, the two cases in which responses are OPTIONAL are:
- The Boolean function is "AND" and the value "no" is received.
The outcome of the negotiation is "no".
- The Boolean function is "OR" and the value "yes" is received.
The outcome of the negotiation is "yes".
Responses are REQUIRED in all other cases, and the value chosen and
sent by the responder becomes the outcome of the negotiation.
If a specific key is not relevant for the current negotiation the
responder may answer with the constant "irrelevant" for all types of
negotiation.
Any other key not understood by the target may be ignored by the
target without affecting basic function. However the Text Response
for a key that was not understood MUST be key=NotUnderstood.
The value "?" with any key has the meaning of enquiry and should be
answered with the current value or "NotUnderstood".
The constants "none", "reject", "irrelevant" and "NotUnderstood" are
reserved and must be used only as described here.
Some basic key=value pairs are described in Appendix D. All keys in
Appendix D, except for the X- extension format, MUST be supported by
iSCSI initiators and targets.
Manufacturers may introduce new keys by prefixing them with X-
followed by their (reversed) domain name, for example the company
owning the domain acme.com can issue:
X-com.acme.bar.foo.do_something=3
2.2.5 iSCSI Full Feature Phase
Once the initiator is authorized to do so, the iSCSI session is in
iSCSI full feature phase. A session is in full feature phase after
successfully finishing the login phase on the first (leading)
connection of a session. A connection is in full feature phase if the
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session is in full feature phase and the connection login has
completed successfully. An iSCSI connection is not in full feature
phase a) either when it does not have an established transport
connection, or b) when it has a valid transport connection but a
successful login was not performed on it or the connection is
currently logged out. In normal full feature phase the initiator may
send SCSI commands and data to the various LUs on the target by
wrapping them in iSCSI PDUs that go over the established iSCSI
session.
For an iSCSI request issued over a TCP connection, the corresponding
response and/or requested PDU(s) MUST be sent over the same
connection by default. We call this "connection allegiance". If the
original connection fails before the command is completed, the
connection allegiance of the command may be explicitly reassigned to
a different transport connection as described in detail in section
8.1.
As an illustration of the above rule, SCSI commands that require data
and/or parameter transfer, the (optional) data and the status for a
command MUST be sent over the same TCP connection to which the SCSI
command is currently allegiant.
Thus, if an initiator issues a READ command, the target MUST send the
requested data, if any, followed by the status to the initiator over
the same TCP connection that was used to deliver the SCSI command.
If an initiator issues a WRITE command, the initiator MUST send the
data, if any, for that command and the target MUST return Ready To
Transfer (R2T), if any and the status over the same TCP connection
that was used to deliver the SCSI command. Retransmission requests
(SNACK PDUs) as well as the data and status that they generate MUST
also use the same connection.
However, consecutive commands that are part of a SCSI linked command-
chain task MAY use different connections. Connection allegiance is
strictly per-command and not per-task. During the iSCSI Full Feature
Phase, the initiator and target MAY interleave unrelated SCSI
commands, their SCSI Data and responses, over the session.
Outgoing SCSI data (initiator to target user data or command
parameters) is sent as either solicited data or unsolicited data.
Solicited data is sent in response to R2T PDUs. Unsolicited data can
be sent as part of an iSCSI command PDU ("immediate data") or in
separate iSCSI data PDUs. An initiator may send unsolicited data as
immediate up to the negotiated maximum PDU size or in a separate PDU
sequence (up to the mode page limit). All subsequent data MUST be
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solicited. The maximum size of an individual data PDU or the
immediate-part of the first unsolicited burst MAY be negotiated at
login.
Targets operate in either solicited (R2T) data mode or unsolicited
(non R2T) data mode. In unsolicited mode, an initial R2T allowing
transfer up to the FirstBurstSize is implied. A target MAY separately
enable immediate data without enabling the more general (separate
data PDUs) form of unsolicited data.
An initiator SHOULD honor an R2T data request for a valid outstanding
command (i.e., carrying a valid Initiator Task Tag) provided the
command is supposed to deliver outgoing data and the R2T specifies
data within the command bounds.
It is considered an error for an initiator to send unsolicited data
PDUs to a target operating in R2T mode (only solicited data is
allowed). It is also an error for an initiator to send more data,
whether immediate or as separate PDUs, than the SCSI limit for first
burst. At login, an initiator MAY request to send data blocks and a
first burst of any size; in this case, the target MUST indicate the
size of the first burst and of the immediate and data blocks that it
is ready to accept. The agreed upon limits for the first burst as
well as the maximum data PDU are recorded in (and are retrievable
from) the disconnect-reconnect mode page.
A target SHOULD NOT silently discard data and request retransmission
through R2T. Initiators SHOULD NOT do any scoreboarding for data -
targets perform residual count calculation. Incoming data for
initiators is always implicitly solicited. SCSI data packets are
matched to their corresponding SCSI commands by using Tags that are
specified in the protocol.
Initiator tags for pending commands are unique initiator-wide for a
session. Target tags are not strictly specified by the protocol. It
is assumed that these tags are used by the target to tag (alone or in
combination with the LUN) the solicited data. Target tags are
generated by the target and "echoed" by the initiator. The above
mechanisms are designed to accomplish efficient data delivery and a
large degree of control over the data flow.
iSCSI initiators and targets MUST also enforce some ordering rules to
achieve deadlock-free operation. Unsolicited data MUST be sent on
every connection in the same order in which commands were sent. A
target receiving data out of order SHOULD terminate the session.
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2.2.6 iSCSI Connection Termination
Connection termination is assumed to be an exceptional event.
Graceful TCP connection shutdowns are done by sending TCP FINs.
Graceful connection shutdowns MUST only occur when there are no
outstanding tasks that have allegiance to the connection and when the
connection is not in full-feature phase. A target SHOULD respond
rapidly to a FIN from the initiator by closing its half of the
connection after waiting for all outstanding commands that have
allegiance to the connection to conclude and send their status.
Connection termination with outstanding commands may require recovery
actions.
Connection termination is also required as a prelude to recovery. By
terminating a connection before starting recovery, the initiator and
target can avoid having stale PDUs being received after recovery. In
this case, the initiator sends a Logout request on any of the
operational connections of a session indicating what connection
should be terminated.
Logout can also be issued by an initiator at the explicit request of
a target (through an Asynchronous Message PDU) or the connection can
be autonomously terminated by the target after announcing it to the
initiator (through an Asynchronous Message PDU).
2.2.7 Naming and Addressing
All iSCSI initiators and targets are named. Each target or initiator
is known by an iSCSI Name. The iSCSI Name is independent of the
location of the initiator and target; two formats are provided that
allow the use of existing naming authorities when generating them.
One of these formats allows the use of a registered domain name as a
naming authority; it is important not to confuse this with an
address. The iSCSI Name is a UTF-8 text string, and is defined in
[NDT].
iSCSI Names are used to provide:
- an initiator identifier for configurations that provide
multiple initiators behind a single IP address
- a target identifier for configurations that present multiple
targets behind a single IP address and port.
- a method to recognize multiple paths to the same device on
different IP addresses and ports.
- an identifier for source and destination targets for use in
third party commands.
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- an identifier for initiators and targets to enable them to
recognize each other regardless of IP address and port mapping
on intermediary firewalls.
The initiator MUST present both its iSCSI Initiator Name and the
iSCSI Target Name to which it wishes to connect in the first login
request of a new session. The only exception is if a discovery
session (see 2.4) is to be established; the iSCSI Initiator Name is
still required, but the iSCSI Target Name may be ignored. The key
"SessionType=discovery" is sent by the initiator at login to indicate
a discovery session.
The default name "iSCSI" is reserved, and is not used as an
individual initiator or target name.
iSCSI Names do not require special handling within iSCSI layer; they
are opaque and case-sensitive for the purposes of comparison.
Examples of iSCSI Names:
iqn.1998-03.com.disk-vendor.diskarrays.sn.45678
iqn.2000-01.com.gateways.yourtargets.24
iqn.1987-06.com.os-vendor.plan9.cdrom.12345
iqn.2001-03.com.service-provider.users.customer235.host90
eui.02004567A425678D
iSCSI nodes also have addresses. An iSCSI address specifies a single
path to an iSCSI node.
<domain-name>[:<port>]
Where <domain-name> is one of:
- IPv4 address, in dotted decimal notation. Assumed if the
name contains exactly four numbers, separated by dots (.),
where each number is in the range 0..255.
- IPv6 address, in colon-separated hexadecimal notation, as
specified in [RFC2373] and enclosed in "[" and "]" characters,
as specified in [RFC2732].
- Fully Qualified Domain Name (host name). Assumed if the
<domain-name> is neither an IPv4 nor an IPv6 address.
For iSCSI targets, the <port> in the address is optional; if
specified it is the TCP port on which the target is listening for
connections. If the <port> is not specified, a default port, to be
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assigned by IANA, will be assumed. For iSCSI initiators, the <port>
is omitted.
Examples of addresses:
10.40.1.2
[FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
[FEDC:BA98:7654:3210:FEDC:BA98:7654:3210]
[1080:0:0:0:8:800:200C:417A]
[3ffe:2a00:100:7031::1]
[1080::8:800:200C:417A]
[::192.9.5.5]
mydisks.example.com
To assist in providing a more human-readable user interface for
devices containing iSCSI targets and initiators, a target or
initiator may also provide an alias. This alias is a simple UTF-8
string, is not globally unique, and is never interpreted or used to
identify an initiator or device within the iSCSI protocol. Its use
is described in [NDT].
Third party commands require that protocol-specific addresses be
communicated within SCSI CDBs. The iSCSI protocol-specific address
consists of an iSCSI name, or an iSCSI name + TCP address.
An initiator may discover the iSCSI Target Names to which it has
access, along with their addresses, using the SendTargets text
request, or by other techniques discussed in [NDT].
2.2.8 Persistent State
iSCSI does not require any persistent state maintenance across
sessions. However, SCSI requires, in some cases, persistent
identification of the SCSI initiator port name (for iSCSI, the
InitiatorName plus the ISID portion of the session identifier) (See
2.5.2 and 2.5.3).
iSCSI sessions do not persist through power cycles and boot
operations.
All iSCSI session and connection parameters are reinitialized on
session and connection creation.
Commands persist beyond connection termination if the session
persists and command recovery within session is supported. However
command execution as perceived by iSCSI (i.e., involving iSCSI
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protocol exchanges for the affected task) is suspended when a
connection is dropped until a new allegiance is established by the
'task reassign' task management function (section 3.5)
2.2.9 Message Synchronization and Steering
2.2.9.1 Rationale
iSCSI presents a mapping of the SCSI protocol onto TCP. This
encapsulation is accomplished by sending iSCSI PDUs that are of
varying length. Unfortunately, TCP does not have a built-in mechanism
for signaling message boundaries at the TCP layer. iSCSI overcomes
this obstacle by placing the message length in the iSCSI message
header. This serves to delineate the end of the current message as
well as the beginning of the next message.
In situations where IP packets are delivered in order from the
network, iSCSI message framing is not an issue; messages are
processed one after the other. In the presence of IP packet
reordering (e.g., frames being dropped), legacy TCP implementations
store the "out of order" TCP segments in temporary buffers until the
missing TCP segments arrive, upon which the data must be copied to
the application buffers. In iSCSI it is desirable to steer the SCSI
data within these out of order TCP segments into the pre-allocated
SCSI buffers rather than store them in temporary buffers. This
decreases the need for dedicated reassembly buffers as well as the
latency and bandwidth related to extra copies.
Relying solely on the "message length" information from the iSCSI
message header may make it impossible to find iSCSI message
boundaries in subsequent TCP segments due to the loss of a TCP
segment containing the iSCSI message length. The missing TCP
segment(s) must be received before any of the following segments can
be steered to the correct SCSI buffers (due to the inability to
determine the iSCSI message boundaries). Since these segments cannot
be steered to the correct location, they must be saved in temporary
buffers that must then be copied to the SCSI buffers.
Different schemes can be used to recover synchronization. One of
these schemes is detailed in an Appendix C. To make those schemes
work iSCSI implementations have to make sure that the appropriate
protocol layers are provided with enough information to implement a
synchronization and/or data steering mechanism.
2.2.9.2 Synchronization (sync) and Steering Functional Model
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We assume that iSCSI is implemented according to the following
layering scheme:
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+------------------------+
| SCSI |
+------------------------+
| iSCSI |
+------------------------+
| Sync and Steering |
| +-------------------+ |
| | TCP | |
| +-------------------+ |
+------------------------+
| Lower Functional Layers|
| (LFL) |
+------------------------+
| IP |
+------------------------+
| Link |
+------------------------+
In this model, LFL can be IPsec (a mechanism changing the IP stream
and invisible to TCP). We assume that Sync and Steering operates just
underneath iSCSI. Note that an implementation may choose to place
Sync and Steering somewhere else in the stack if it can translate the
information kept by iSCSI in terms valid for the chosen layer.
According to our model of layering, iSCSI considers the information
it delivers to the Sync and Steering layer (headers and payloads) as
a contiguous stream of bytes mapped to the positive integers from 0
to infinity. In practice, though, iSCSI is not expected to handle
infinitely long streams; stream addressing will wrap around at 2**32-
1.
This model assumes that the iSCSI layer will deliver complete PDUs to
underlying layers in single (atomic) operations. The underlying
layer doe not need to examine the stream content to discover the PDU
boundaries. If a specific implementation does PDU delivery to the
Sync and Steering layer through multiple operations it MUST bracket
an operation set used to deliver a single PDU in a manner
understandable to the Sync and Steering Layer.
The Sync and Steering Layer (which itself is OPTIONAL) MUST retain
the PDU end address within the stream for every delivered iSCSI PDU.
To enable the Sync and Steering operation to perform Steering,
additional information including identifying tags and buffer offsets
MUST also be retained for every sent PDU. The Sync and Steering Layer
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is required to add to every sent data item (IP packet, TCP packet or
some other superstructure) enough information to enable the receiver
to steer it to a memory location independent of any other piece.
If the transmission stream is built dynamically, this information is
used to insert Sync and Steering information in the transmission
stream (at first transmission or at re-transmission) either through a
globally accessible table or a call-back mechanism. If the
transmission stream is built statically, the Sync and Steering
information is inserted in the transmission stream.
The retained information can be released whenever the transmitted
data is acknowledged by the receiver (in case of dynamically built
streams by deletion from the global table or by an additional
callback).
On the outgoing path, the Sync and Steering layer MUST map the
outgoing stream addresses from iSCSI stream addresses to TCP stream
sequence numbers.
On the incoming path, the Sync and Steering layer extracts the Sync
and Steering information from the TCP stream. Then it helps steer
(place) the data stream to its final location and/or recover iSCSI
PDU boundaries when some TCP packets are lost or received out of
order. The data stream seen by the receiving iSCSI layer is
identical to the data stream that left the sending iSCSI layer. The
Sync and Steering information is kept until the PDUs it refers to are
completely processed by the iSCSI layer.
On the incoming path, the Sync and Steering layer does not change the
way TCP notifies iSCSI about in-order data arrival. All data
placements, in-order or out-of-order, performed by the Sync and
Steering layer are hidden from iSCSI while conventional, in order,
data arrival notifications generated by TCP are passed through to
iSCSI
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2.2.9.3 Sync and Steering and Other Encapsulation Layers
We recognize that in many environments the following is a more
appropriate layering model:
+----------------------------------+
| SCSI |
+----------------------------------+
| iSCSI |
+----------------------------------+
| Upper Functional Layers (UFL) |
+----------------------------------+
| Sync and Steering |
| +-----------------------------+ |
| | TCP | |
| +-----------------------------+ |
+----------------------------------+
| Lower Functional Layers (LFL) |
+----------------------------------+
| IP |
+----------------------------------+
| Link |
+----------------------------------+
In this model, UFL can be TLS (see[RFC2246]) or some other transport
conversion mechanism (a mechanism changing the TCP stream but
transparent to iSCSI).
To be effective and act on reception of TCP packets out of order,
Sync and Steering has to be underneath UFL and Sync and Steering data
has to be left out of any UFL transformation (encryption,
compression, padding etc.). However, Sync and Steering MUST take
into account the additional data inserted in the stream by UFL. Sync
and Steering MAY also restrict the type of transformations UFL may
perform on the stream.
This makes implementation of Sync and Steering in the presence of
otherwise opaque UFLs less attractive.
2.2.9.4 Sync/Steering and iSCSI PDU Size
When a large iSCSI message is sent, the TCP segment(s) that contain
the iSCSI header may be lost. The remaining TCP segment(s) up to the
next iSCSI message need to be buffered (in temporary buffers) since
the iSCSI header that indicates what SCSI buffers the data is to be
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steered to was lost. To minimize the amount of buffering, it is
recommended that the iSCSI PDU size be restricted to a small value
(perhaps a few TCP segments in length). During login, each end of the
iSCSI session specifies the maximum size of an iSCSI PDU it will
accept.
2.3 Third Party Commands
SCSI allows every addressable entity to be either an initiator or a
target. In host-to-host communication, each such entity can take on
the initiator role. In typical I/O operations between a host and a
peripheral subsystem, the host plays the initiator role and the
peripheral subsystem plays the target role.
For EXTENDED COPY and other third party SCSI commands, that involve
device-to-device communication, such as (EXTENDED) COPY and COMPARE,
SCSI defines a copy-manager. The copy-manager takes on the role of
initiator in the device-to-device communication. The copy-manager is
the "original-target" of the command and acts as initiator for a
(variable) number of the devices, which are called sources and
destinations. Sources and destinations act as targets.
The copy operation is described in one CDB to the copy-manager, along
with a series of descriptor blocks. Each descriptor block addresses
source and destination target, LU, and a description of the work to
be done in terms of blocks or bytes as required by the device types.
The relevant SCSI standards do not require full support of the
(EXTENDED) COPY or COMPARE, nor do they provide a detailed execution
model.
2.4 iSCSI session types
iSCSI defines two types of sessions:
normal operational session - an unrestricted session
discovery-session - a session opened only for target
discovery; the target MAY accept only text requests with
the SendTargets key and a close session type of logout
request
The session type is defined during login with key=value parameter in
the login command.
2.5 SCSI to iSCSI concepts mapping model
The following diagram shows an example of how multiple iSCSI Nodes
(targets in this case) can co-exist within the same Network Entity
and can share Network Portals (IP addresses and TCP ports). Other
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more complex configurations are also possible. Detailed descriptions
of the components of these diagrams are given in 2.5.1.
+-----------------------------------+
| Network Entity (iSCSI Client) |
| |
| +-------------+ |
| | iSCSI Node | |
| | (Initiator) | |
| +-------------+ |
| | | |
| +--------------+ +--------------+ |
| |Network Portal| |Network Portal| |
| | 10.1.30.4 | | 10.1.40.6 | |
+-+--------------+-+--------------+-+
| |
| IP Networks |
| |
+-+--------------+-+--------------+-+
| |Network Portal| |Network Portal| |
| | 10.1.30.21 | | 10.1.40.3 | |
| | TCP Port 4 | | TCP Port 4 | |
| +--------------+ +--------------+ |
| | | |
| ----------------- |
| | | |
| +-------------+ +--------------+ |
| | iSCSI Node | | iSCSI Node | |
| | (Target) | | (Target) | |
| +-------------+ +--------------+ |
| |
| Network Entity (iSCSI Server) |
+-----------------------------------+
2.5.1 iSCSI Architecture Model
This section describes that part of the iSCSI architecture model that
has the most bearing on the relationship between iSCSI and the SCSI
Architecture Model.
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a) Network Entity - The Network Entity represents a device
or gateway that is accessible from the IP network. A
Network Entity must have one or more Network Portals (see
item (c)), each of which is usable by some iSCSI Nodes
(see item (b)) contained in that Network Entity to gain
access to the IP network.
b) iSCSI Node - The iSCSI Node represents a single iSCSI
initiator or iSCSI target. There are one or more iSCSI
Nodes within a Network Entity. The iSCSI Node is
accessible via one or more Network Portals (see item (c)).
An iSCSI Node is identified by its iSCSI Name (see 2.2.7
and Appendix D). The separation of the iSCSI Name from
the addresses used by and for the iSCSI node allows
multiple iSCSI nodes to use the same addresses, and the
same iSCSI node to use multiple addresses.
An alias string could also be associated with an iSCSI
Node. The alias allows an organization to associate a user
friendly string with the iSCSI Name. However, the alias
string is not a substitute for the iSCSI Name.
c) Network Portal - The Network Portal is a component of a
Network Entity that has a TCP/IP network address and that
may be used by an iSCSI Node within that Network Entity
for the connection(s) within one of its iSCSI sessions. A
Network Portal in an initiator is identified by its IP
address. A Network Portal in a target is identified by
its IP address and its listening TCP port.
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d) Portal Groups - iSCSI supports multiple connections
within the same session; some implementations will have
the ability to combine connections in a session across
multiple Network Portals. A Portal Group defines a set of
Network Portals within an iSCSI Node that collectively
supports the capability of coordinating a session with
connections spanning these portals. Not all Network
Portals within a Portal Group need participate in every
session connected through that Portal Group. One or more
Portal Groups may provide access to an iSCSI Node. Each
Network Portal as utilized by a given iSCSI Node belongs
to exactly one portal group within that node. Portal
Groups are identified within an iSCSI Node by a portal
group tag, a simple integer value between 1 and 65535 (see
SendTargets in Appendix D, item 11). All Network Portals
with the same portal group tag in the context of a given
iSCSI Node are in the same Portal Group.
Both iSCSI Initiators and iSCSI Targets have portal
groups, though only the iSCSI Target Portal Groups are
used directly in the iSCSI protocol (e.g., in SendTargets,
see Appendix E). See 9.1.1 9.1.1 for references to the
Initiator Portal Groups.
Portals within a Portal Group are expected to have similar
hardware characteristics, as SCSI port specific mode pages
may affect all portals within a portal group. (See
2.5.3.2 SCSI Mode Pages)
The following diagram shows an example of one such configuration on a
target and how a session may be established that shares Network
Portals within a Portal Group.
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----------------------------IP Network---------------------
| | |
+--------|---------------|--------------------|---------------------+
| +----|---------------|-----+ +----|---------+ |
| | +---------+ +---------+ | | +---------+ | |
| | | Network | | Network | | | | Network | | |
| | | Portal | | Portal | | | | Portal | | |
| | +--|------+ +---------+ | | +---------+ | |
| | | | | | | | |
| | | Portal | | | | Portal | |
| | | Group 1 | | | | Group 2 | |
| +--------------------------+ +--------------+ |
| | | | |
| +----------------------------+ +-----------------------------+ |
| | iSCSI Session (Target side)| | iSCSI Session (Target side) | |
| | | | | |
| | (iSCSI Name + TSID=2) | | (iSCSI Name + TSID=1) | |
| +----------------------------+ +-----------------------------+ |
| |
| iSCSI Target Node |
| (within Network Entity, not shown) |
+-------------------------------------------------------------------+
2.5.2 SCSI Architecture Model
This part describes the relationship between the SCSI Architecture
Model [SAM2] constructs of SCSI device, SCSI port and I_T nexus and
the iSCSI constructs described above.
This relationship implies implementation requirements in order to
conform to the SAM2 model and other SCSI operational functions. These
requirements are detailed in 2.5.3.
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a) SCSI Device - This is the SAM2 term for an entity that
contains other SCSI entities. For example, a SCSI Initiator
Device contains one or more SCSI Initiator Ports and zero or
more application clients; a SCSI Target Device contains one or
more SCSI Target Ports and one or more logical units. For
iSCSI, the SCSI Device is the component within an iSCSI Node
that provides the SCSI functionality. As such, there can be at
most one SCSI Device within a given iSCSI Node. Access to the
SCSI Device can only be achieved in an iSCSI normal operational
session (see 2.4). The SCSI Device Name is defined to be the
iSCSI Name of the node and its use is mandatory in the iSCSI
protocol.
b) SCSI Port - This is the SAM2 term for an entity in a SCSI
Device that provides the SCSI functionality to interface with a
service delivery subsystem or transport. For iSCSI, the
definition of SCSI Initiator Port and SCSI Target Port are
different.
SCSI Initiator Port: this maps to the endpoint of an iSCSI
normal operational session (see 2.4). An iSCSI normal
operational session is negotiated through the login process
between an iSCSI initiator node and an iSCSI target node. At
successful completion of this process, a SCSI Initiator Port is
created within the SCSI Initiator Device. The SCSI Initiator
Port Name and SCSI Initiator Port Identifier are both defined
to be the iSCSI Initiator Name together with (a) a label that
identifies it as an initiator port name/identifier and (b) the
ISID portion of the session identifier.
SCSI Target Port: this maps to an iSCSI target Portal Group.
The SCSI Target Port Name and the SCSI Target Port Identifier
are both defined to be the iSCSI Target Name together with (a)
a label that identifies it as a target port name/identifier and
(b) the portal group tag.
The SCSI Port Name is mandatory in iSCSI. When used in SCSI
parameter data, the SCSI port name shall be formatted as
- the iSCSI Name in UTF-8 format, followed by
- a null terminator (1byte), followed by
- the ASCII character 'i' (for SCSI Initiator Port) or the
ASCII character 't' (for SCSI Target Port), followed by
- a null terminator (1byte), followed by
- zero to 3 null pad bytes so that the complete format is a
multiple of 4 bytes long, followed by
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- the 6byte value of the ISID (for SCSI initiator port) or the
2byte value of the portal group tag (for SCSI target port) in
network byte order (BigEndian).
SCSI port names have a maximum length of 264 bytes for
initiator ports and 260 bytes for target ports and must be a
multiple of 4 bytes long. The ASCII character 'i' or 't' is
the label that identifies this as either a SCSI Initiator
Port or SCSI Target Port, and so also provides the
interpretation and size of the remaining six bytes
(initiator) or two bytes (target).
c) I_T nexus - According to [SAM2], the I_T nexus is a
relationship between a SCSI Initiator Port and a SCSI Target
Port. For iSCSI, this relationship is a session, defined as a
relationship between an iSCSI Initiator's end of the session
(SCSI Initiator Port) and the iSCSI Target's Portal Group. The
I_T nexus can be identified by the conjunction of the SCSI port
names; that is, the I_T nexus identifier is the tuple (iSCSI
Initiator Name + 'i' + ISID, iSCSI Target Name + 't' + Portal
Group Tag).
NOTE: The I_T nexus identifier is not equal to the session
identifier (SSID).
2.5.3 Consequences of the model
This section describes implementation and behavioral requirements
that result from the mapping of SCSI constructs to iSCSI constructs
defined above. Two assumptions are at the basis of the requirements
stated here.
a) Between a given iSCSI Initiator and iSCSI Target, at
any given time there can exist only one session with a
given session identifier (SSID).
b) Between a given SCSI initiator port and SCSI target
port, there can be only one I_T nexus (session); that is,
no more than one nexus relationship (parallel nexus) is
allowed.
These assumptions lead to the following conclusions and requirements.
ISID RULE: Between a given iSCSI Initiator and iSCSI Target Portal
Group (SCSI target port), there can be only one session with a given
value for ISID that identifies the SCSI initiator port. See 3.12.6.
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The structure of the ISID containing a naming authority component
(see 3.12.6 and [NDT]) provides a mechanism to facilitate compliance
with the ISID rule. (See also 9.1.1.)
The iSCSI Initiator Node is expected to manage the assignment of
ISIDs prior to session initiation. The "ISID RULE" does not preclude
the use of the same ISID from the same iSCSI Initiator with different
Target Portal Groups on the same iSCSI target or on other iSCSI
targets (see 9.1.1). Allowing this would be analogous to a single
SCSI Initiator Port having relationships (nexus) with multiple SCSI
target ports on the same SCSI target device or SCSI target ports on
other SCSI target devices. It is also possible to have multiple
sessions with different ISIDs to the same Target Portal Group. The
same ISID may be used by a different iSCSI initiator because it is
the iSCSI Name together with the ISID that identifies the SCSI
Initiator Port.
NOTE: A consequence of the ISID RULE and the specification for the
I_T nexus identifier, two nexus with the same identifier should never
occur.
TSID RULE: The iSCSI Target SHALL NOT select a TSID for a given login
request if the resulting SSID is already in use by an existing
session between that the target and the requesting iSCSI Initiator.
See 9.1.1.
2.5.3.1 I_T nexus state
Certain nexus relationships contain explicit state (e.g., initiator-
specific mode pages or reservation state) that may need to be
preserved by the target (actually, the device server in a logical
unit) through changes or failures in the iSCSI layer (e.g., session
failures). In order for that state to be restored, the iSCSI
initiator should re-establish its session (re-login) to the same
Target Portal Group using the previous ISID. That is, it should do
session recovery as described in section 8. This is because the SCSI
initiator port identifier and the SCSI target port identifier (or
relative target port) form the datum that the SCSI logical unit
device server uses to identify the I_T nexus.
2.5.3.2 SCSI Mode Pages
If the SCSI logical unit device server does not maintain initiator-
specific mode pages, and an initiator makes changes to port-specific
mode pages, the changes may affect all other initiators logged in to
that iSCSI Target through the same Target Portal Group.
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Changes via mode pages to the behavior of a portal group via one
iSCSI node should not affect the behavior of this portal group with
respect to other iSCSI Target Nodes, even if the underlying
implementation of a portal group serves multiple iSCSI Target Nodes
in the same Network Entity.
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3. iSCSI PDU Formats
All multi-byte integers that are specified in formats defined in this
document are to be represented in network byte order (i.e., big
endian). Any field appearing in this document assumes that the most
significant byte is the lowest numbered byte and the most significant
bit (within byte or field) is the highest numbered bit unless
specified otherwise.
Any compliant sender MUST set to zero all bits not defined and all
reserved fields unless specified otherwise. Any compliant receiver
MUST ignore any bit not defined and all reserved fields unless
specified otherwise.
3.1 iSCSI PDU Length and Padding
iSCSI PDUs are padded to the closest integer number of 4 byte words.
The padding bytes SHOULD be 0.
3.2 PDU Template, Header and Opcodes
All iSCSI PDUs have one or more header segments and, optionally, a
data segment. After the entire header segment group there MAY be a
header-digest. The data segment MAY also be followed by a data-
digest.
The Basic Header Segment (BHS) is the first segment in all iSCSI
PDUs. The BHS is a fixed-length 48-byte header segment. It may be
followed by Additional Header Segments (AHS), a Header-Digest, a Data
Segment, and/or a Data-Digest.
The overall structure of a PDU is as follows:
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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 / Basic Header Segment (BHS) /
+/ /
+---------------+---------------+---------------+---------------+
48/ Additional Header Segment (AHS) (optional) /
+/ /
+---------------+---------------+---------------+---------------+
----
+---------------+---------------+---------------+---------------+
k/ Header-Digest (optional) /
+/ /
+---------------+---------------+---------------+---------------+
l/ Data Segment(optional) /
+/ /
+---------------+---------------+---------------+---------------+
m/ Data-Digest (optional) /
+/ /
+---------------+---------------+---------------+---------------+
All PDU segments and digests are padded to an integer number of 4
byte words. The padding bytes SHOULD be sent as 0.
3.2.1 Basic Header Segment (BHS)
The BHS is 48 bytes long. The Opcode, TotalAHSLength and
DataSegmentLength fields appear in all iSCSI PDUs. In addition, the
Initiator Task Tag and Logical Unit Number when used, always appear
in the same location in the header.
The format of the BHS is:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| Opcode | Opcode-specific fields |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
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8| LUN or Opcode-specific fields |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or Opcode-specific fields |
+---------------+---------------+---------------+---------------+
20/ Opcode-specific fields /
+/ /
+---------------+---------------+---------------+---------------+
48
3.2.1.1 I
For request PDUs the I bit set to 1 is an immediate delivery marker.
This bit is always 1 for response PDUs (PDUs from target to
initiator).
3.2.1.2 Opcode
The Opcode indicates what type of iSCSI PDU the header encapsulates.
The Opcodes are divided into two categories: initiator opcodes and
target opcodes. Initiator opcodes are in PDUs sent by the initiators
(request PDUs), and target opcodes are in PDUs sent by the target
(response PDUs).
Initiators MUST NOT use target opcodes and targets MUST NOT use
initiator opcodes.
Initiator opcodes defined in this specification are:
0x00 NOP-Out
0x01 SCSI Command (encapsulates a SCSI Command Descriptor
Block)
0x02 SCSI Task Management Function Request
0x03 Login Command
0x04 Text request
0x05 SCSI Data-out (for WRITE operations)
0x06 Logout Command
0x10 SNACK Request
0x1c-0x1e Vendor specific codes
Target opcodes are:
0x20 NOP-In
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0x21 SCSI Response (contains SCSI status and possibly sense
information or other response information)
0x22 SCSI Task Management Function Response
0x23 Login Response
0x24 Text Response
0x25 SCSI Data-in (for READ operations)
0x26 Logout Response
0x31 Ready To Transfer (R2T - sent by target when it is ready
to receive data)
0x32 Asynchronous Message (sent by target to indicate certain
special conditions)
0x3c-0x3e Vendor specific codes
0x3f Reject
All other opcodes are reserved.
3.2.1.3 Opcode-specific Fields
These fields have different meanings for different opcode types.
3.2.1.4 TotalAHSLength
Total length of all AHS header segments in 4 byte words including
padding if any.
3.2.1.5 DataSegmentLength
This is the data segment payload length in bytes (excluding padding).
3.2.1.6 LUN
Some opcodes operate on a specific Logical Unit. The Logical Unit
Number (LUN) field identifies which Logical Unit. If the opcode does
not relate to a Logical Unit, this field either is ignored or may be
used in an opcode specific way. The LUN field is 64-bits and it is
to be formatted in accordance with [SAM2].
3.2.1.7 Initiator Task Tag
The initiator assigns a Task Tag to each iSCSI task that it issues.
While a task exists, this tag MUST uniquely identify it session-wide.
The initiator task tag may be used by SCSI too as part of the SCSI
task identifier as the time span during which an iSCSI initiator task
tag has to be unique extends over the time span during which a SCSI
task tag has to be unique. However, the iSCSI Initiator Task Tag has
to exist and be unique even for untagged SCSI commands.
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3.2.2 Additional Header Segment (AHS)
The general format of an AHS is:
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| AHSLength | AHSType | AHS-Specific |
+---------------+---------------+---------------+---------------+
4/ AHS-Specific /
+/ /
+---------------+---------------+---------------+---------------+
x
3.2.2.1 AHSType
The AHSType field is coded as follows:
bit 7 - Drop Bit - if set to 1 this AHS may be ignored if not
understood; if set to 0 this AHS must be rejected if not
understood.
bit 6 - Reserved
bit 5-0 - AHS code
0 - Reserved
1 - Extended CDB
2 - Expected Bidirectional Read Data Length
3-59 Reserved
60-63 Non-iSCSI extensions
3.2.2.2 AHSLength
This field contains the effective length in bytes of the AHS
excluding AHSType and AHSLength (not including padding). The AHS is
padded to an integer number of 4 byte words.
3.2.2.3 Extended CDB AHS
The format of the Extended CDB AHS is:
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| AHSLength (CDBLength-15) | 0x01 | Reserved |
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+---------------+---------------+---------------+---------------+
4/ ExtendedCDB...+padding /
+/ /
+---------------+---------------+---------------+---------------+
x
3.2.2.4 Bidirectional Expected Read-Data Length AHS
The format of the Bidirectional Read Expected Data Transfer Length
AHS is:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|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| AHSLength (0x0005) | 0x02 | Reserved |
+---------------+---------------+---------------+---------------+
4| Expected Read-Data Length |
+---------------+---------------+---------------+---------------+
8
3.2.3 Header Digest and Data Digest
Optional header and data digests protect the integrity of header and
data, respectively. The digests, if present, are located,
respectively, after the header and PDU-specific data and include the
padding bytes.
The digest types are negotiated during the login phase.
The separation of the header and data digests is useful in iSCSI
routing applications, where only the header changes when a message is
forwarded. In this case, only the header digest should be re-
calculated.
Digests are not included in data or header length fields.
A zero-length Data Segment implies also a zero-length data-digest.
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3.2.4 Data Segment
The (optional) Data Segment contains PDU associated data. Its payload
effective length is given in the BHS field - Data Segment Length and.
The Data Segment is also padded to an integer number of 4 byte words.
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3.3 SCSI Command
The format of the SCSI Command PDU is:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| 0x01 |F|R|W|0 0|ATTR | Reserved | CRN or Rsvd |
+---------------+---------------+---------------+---------------+
4|TotalAHSLength | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Logical Unit Number (LUN) |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Expected Data Transfer Length |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ SCSI Command Descriptor Block (CDB) /
+/ /
+---------------+---------------+---------------+---------------+
48| AHS (if any), Header Digest (if any) |
+---------------+---------------+---------------+---------------+
/ DataSegment - Command Data (optional) /
+/ /
+---------------+---------------+---------------+---------------+
3.3.1 Flags and Task Attributes (byte 1)
The flags for a SCSI Command are:
bit 7 (F) set to 1 when no unsolicited SCSI Data-Out PDUs
follow this PDU. For a write, if Expected Data Transfer Length
is larger than the DataSegmentLength the target may solicit
additional data through R2T.
bit 6 (R) set to 1 when input data is expected
bit 5 (W) set to 1 when output data is expected
bit 4-3 Reserved
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bit 2-0 contain Task Attributes
The Task Attributes (ATTR) has one of the following integer values
(see [SAM2] for details):
0 Untagged
1 Simple
2 Ordered
3 Head of Queue
4 ACA
5-7 Reserved
Having both the W and the F bit set to 0 is an error.
The R and W MAY both be 1 while the corresponding Expected Data
Transfer Lengths are 0 but they MUST NOT both be 0 when the
corresponding Expected Data Transfer Lengths are not 0.
3.3.2 CRN
SCSI command reference number - if present in the SCSI execute
command arguments (according to [SAM2]).
3.3.3 CmdSN - Command Sequence Number
Enables ordered delivery across multiple connections in a single
session.
3.3.4 ExpStatSN
Command responses up to ExpStatSN-1 (mod 2**32) have been received
(acknowledges status) on the connection.
3.3.5 Expected Data Transfer Length
For unidirectional operations, the Expected Data Transfer Length
field contains the number of bytes of data involved in this SCSI
operation. For a unidirectional write (W flag set to 1 and R flag
set to 0) operation, the initiator uses this field to specify the
number of bytes of data it expects to transfer for this operation.
For a unidirectional read (W flag set to 0 and R flag set to 1)
operation, the initiator uses this field to specify the number of
bytes of data it expects the target to transfer to the initiator. It
corresponds to the SAM2 byte count.
For bidirectional operations (both R and W flags are set to 1), this
field contains the number of data bytes involved in the write
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transfer. For bidirectional operations, an additional header segment
MUST be present in the header sequence indicating the Bidirectional
Read Expected Data Transfer Length. The Expected Data Transfer
Length field and the Bidirectional Read Expected Data Transfer Length
field correspond to the SAM2 byte count
If the Expected Data Transfer Length for a write and the length of
immediate data part that follows the command (if any) are the same
then no more data PDUs are expected to follow. In this case, the F
bit MUST be set to 1.
If the Expected Data Transfer Length is higher than the
FirstBurstSize (the negotiated maximum amount of unsolicited data the
target will accept) the initiator SHOULD send the maximum size of
unsolicited data. The target MAY terminate in error a command for
which the Expected Data Transfer Length is higher than the
FirstBurstSize and for which the initiator sent less than
FirstBurstSize unsolicited data.
Upon completion of a data transfer, the target informs the initiator
of how many bytes were actually processed (sent and/or received) by
the target. This is done through residual counts.
3.3.6 CDB - SCSI Command Descriptor Block
There are 16 bytes in the CDB field to accommodate the commonly used
CDBs. Whenever the CDB is larger than 16 bytes, an Extended CDB AHS
MUST be used to contain the CDB spillover.
3.3.7 Data Segment - Command Data
Some SCSI commands require additional parameter data to accompany the
SCSI command. This data may be placed beyond the boundary of the
iSCSI header in a data segment. Alternatively, user data (as from a
WRITE operation) can be placed in the same PDU (both cases referred
to as immediate data). Those data are governed by the general rules
for solicited vs. unsolicited data.
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3.4 SCSI Response
The format of the SCSI Response PDU is:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x21 |1 0 0|o|u|O|U|0| Response | Status |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Residual Count |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+---------------+
40| Reserved |
+---------------+---------------+---------------+---------------+
44| Bidirectional Read Residual Count |
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ Data Segment - see 3.4.6 (optional) /
+/ /
+---------------+---------------+---------------+---------------+
3.4.1 Flags (byte 1)
bit 7-5 Reserved
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bit 4 (o) set for Bidirectional Read Residual Overflow. In
this case, the b Bidirectional Read Residual Count indicates
the number of bytes that were not transferred to the initiator
because the initiator's Expected Bidirectional Read Data
Transfer Length was not sufficient.
bit 3 (u) set for Bidirectional Read Residual Underflow. In
his case, the Bidirectional Read Residual Count indicates the
number of bytes that were not transferred to the initiator out
of the number of bytes that expected to be transferred.
bit 2 (O) set for Residual Overflow. In this case, the
Residual Count indicates the number of bytes that were not
transferred because the initiator's Expected Data Transfer
length was not sufficient. For a bidirectional operation, the
Residual Count contains the residual for the write operation.
bit 1 (U) set for Residual Underflow. In this case, the
Residual Count indicates the number of bytes that were not
transferred out of the number of bytes that expected to be
transferred. For a bidirectional operation, the Residual Count
contains the residual for the write operation.
bit 0 (0) Reserved
Bits O and U are mutually exclusive and so are bits o and u.
For a response other than "Command Completed at Target" bit 4-1 MUST
be 0.
3.4.2 Status
The Status field is used to report the SCSI status of the command (as
specified in [SAM2]) and is valid only if the Response Code is
Command Completed at target.
Some of the status codes defined in [SAM2] are:
0x00 GOOD
0x02 CHECK CONDITION
0x08 BUSY
0x18 RESERVATION CONFLICT
0x28 TASK SET FULL
0x30 ACA ACTIVE
0x40 TASK ABORTED
See [SAM2] for the complete list and definitions.
If a SCSI device error is detected while data from the initiator is
still expected (the command PDU did not contain all the data and the
target has not received a Data PDU with the final bit Set) the target
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MUST wait until it receives a Data PDU with the F bit set, in the
last expected sequence, before sending the Response PDU.
3.4.3 Response
This field contains the iSCSI service response.
iSCSI service response codes defined in this specification are:
0x00 - Command Completed at Target
0x01 - Target Failure
0x80-0xff - Vendor specific
The Response is used to report a Service Response. The exact mapping
of the iSCSI response codes to SAM service response symbols is
outside the scope of this document.
Certain iSCSI conditions result in the command being terminated at
the target (response Command Completed at Target) with a SCSI Check
Condition Status as outlined in the next table:
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+--------------------------+----------+---------------------------+
| Reason |Sense | Additional Sense Code & |
| |Key | Qualifier |
+--------------------------+----------+---------------------------+
| Unexpected unsolicited |Aborted | ASC = 0x0c ASCQ = 0x0c |
| data |Command-0B| Write Error |
+--------------------------+----------+---------------------------+
| Not enough unsolicited |Aborted | ASC = 0x0c ASCQ = 0x0d |
| data |Command-0B| Write Error |
+--------------------------+----------+---------------------------+
| Protocol Service CRC |Aborted | ASC = 0x47 ASCQ = 0x05 |
| error |Command-0B| CRC Error Detected |
+--------------------------+----------+---------------------------+
| SNACK rejected |Aborted | ASC = 0x11 ASCQ = 0x13 |
| |Command-0B| Read Error |
+--------------------------+----------+---------------------------+
"Not enough unsolicited data" condition is reported by the target
only if it does not support output (write) operations in which the
total data length is higher than FirstBurstSize but the initiator
sent less than FirstBurstSize amount of unsolicited data, and out-of-
order R2Ts can't be used.
3.4.4 Residual Count
The Residual Count field is valid only in the case where either the U
bit or the O bit is set. If neither bit is set, the Residual Count
field SHOULD be zero. If the O bit is set, the Residual Count
indicates the number of bytes that were not transferred because the
initiator's Expected Data Transfer Length was not sufficient. If the
U bit is set, the Residual Count indicates the number of bytes that
were not transferred out of the number of bytes expected to be
transferred.
3.4.5 Bidirectional Read Residual Count
The Bidirectional Read Residual Count field is valid only in the case
where either the u bit or the o bit is set. If neither bit is set,
the Bidirectional Read Residual Count field SHOULD be zero. If the o
bit is set, the Bidirectional Read Residual Count indicates the
number of bytes that were not transferred to the initiator because
the initiator's Expected Bidirectional Read Transfer Length was not
sufficient. If the u bit is set, the Bidirectional Read Residual
Count indicates the number of bytes that were not transferred to the
initiator out of the number of bytes expected to be transferred.
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3.4.6 Data Segment - Sense and Response Data Segment
iSCSI targets MUST support and enable autosense. If Status is CHECK
CONDITION (0x02), then the Data Segment contains sense data for the
failed command.
For some iSCSI responses, the response data segment MAY contain some
response related information, (e.g., for a target failure it may
contain a vendor specific detailed description of the failure).
If the DataSegmentLength is not 0 the format of the Data Segment is:
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|SenseLength | Sense Data |
+---------------+---------------+---------------+---------------+
x/ Sense Data /
+---------------+---------------+---------------+---------------+
y/ Response Data /
+ +
/ /
+---------------+---------------+---------------+---------------+
z|
3.4.6.1 SenseLength
Length of Sense Data.
3.4.7 ExpDataSN
The number of Data-In (read) PDUs the target has sent for the
command.
This field is reserved if the response code is not Command Completed
at Target.
3.4.8 StatSN - Status Sequence Number
StatSN is a Sequence Number that the target iSCSI layer generates per
connection and that in turn enables the initiator to acknowledge
status reception. StatSN is incremented by 1 for every
response/status sent on a connection except for responses sent as a
result of a retry or SNACK. In case of responses sent because of a
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retransmission request the StatSN used MUST be the same as the first
time the PDU was sent unless the connection was restarted since then.
3.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator
ExpCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to acknowledge command reception. It is used to update a
local register with the same name. An ExpCmdSN equal to MaxCmdSN+1
indicates that the target cannot accept new commands.
3.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initiator
MaxCmdSN is a Sequence Number that the target iSCSI returns to the
initiator to indicate the maximum CmdSN the initiator can send. It is
used to update a local register with the same name. If MaxCmdSN is
equal to ExpCmdSN-1 that indicates to the initiator that the target
can't receive any additional commands. When MaxCmdSN changes at the
target while the target has no pending PDUs to convey this
information to the initiator it MUST generate a NOP-IN to carry the
new MaxCmdSN.
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3.5 Task Management Function Request
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| x02 |0| Function | Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved |
+---------------+---------------+---------------+---------------+
8| Logical Unit Number (LUN) or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Referenced Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32| RefCmdSN or ExpDataSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48
3.5.1 Function
The Task Management functions provide an initiator with a way to
explicitly control the execution of one or more Tasks (SCSI and iSCSI
tasks). The Task Management functions are (for a more detailed
description of SCSI task management see [SAM2]):
1 ABORT TASK - aborts the task identified by the Referenced
Task Tag field.
2 ABORT TASK SET - aborts all Tasks issued by this initiator
on the Logical Unit.
3 CLEAR ACA - clears the Auto Contingent Allegiance
condition.
4 CLEAR TASK SET - Aborts all Tasks (from all initiators)
for the Logical Unit.
5 LOGICAL UNIT RESET
6 TARGET WARM RESET
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7 TARGET COLD RESET
8 TASK REASSIGN - reassign connection allegiance for the
task identified by the Initiator Task Tag field on this
connection, thus resuming the iSCSI exchanges for the task
For all these functions, if executed, the Task Management Function
Response MUST be returned using the Initiator Task Tag to identify
the operation for which it is responding. All those functions apply
to the referenced tasks regardless if they are proper SCSI tasks or
tagged iSCSI operations. Task management commands must be executed
as if all the commands having a CmdSN lower or equal to the task
management CmdSN have been received by the target (i.e., have to be
executed as if received for ordered delivery even when marked for
immediate delivery). For all the tasks covered by the task
management response (i.e., with CmdSN not higher than the task
management command CmdSN), additional responses MUST NOT be delivered
to the SCSI layer after the task management response. This
requirement implies that the initiator must keep around state until
the status is received from the target for all aborted tasks and the
target MUST deliver to the initiator good status for all aborted task
for which no status was delivered yet. The task management response
MAY be issued by the target immediately after marking all tasks to be
aborted.
ABORT TASK MUST be issued on the same connection to which the task to
be aborted is allegiant at the time the Task Management Request is
issued if the connection is still active (it is not undergoing an
implicit or explicit logout). If the connection is being implicitly
or explicitly logged out (i.e., no other request will be issued on
the failing connection and no other response will be received on the
failing connection) then an ABORT TASK function request may be issued
on another connection. This Task Management request will then both
establish a new allegiance for the command to be aborted, and abort
it as well (i.e., the task to be aborted will not have to be retried
or reassigned, and its status if issued but not acknowledged will be
reissued). For the ABORT TASK function, the target MUST NOT deliver
additional responses after sending the task management response. In
case both responses were delivered, whether the initiator should
deliver task responses before delivering the task management response
or not while an ABORT TASK is executing is a matter of
implementation. This requirement implies that the initiator must
keep around state until the status is received from the target for an
aborted task and the target MUST deliver to the initiator good status
for an aborted task if no status was delivered yet. The task
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management response MUST be issued after the command status (if any)
was issued.
For the LOGICAL UNIT RESET function, the target MUST behave as
dictated by the Logical Unit Reset function in [SAM2].
The TARGET RESET function (WARM and COLD) implementation is OPTIONAL
and when implemented should act as described below. Target Reset MAY
be also subject to SCSI access controls for the requesting initiator.
When not implemented or when authorization fails at target, Target
Reset functions should end as if the function was executed
successfully and the response qualifier will detail what was
executed.
For the TARGET WARM RESET and TARGET COLD RESET functions, the target
cancels all pending operations and are both equivalent to the Target
Reset function specified by [SAM2]. They can both affect many other
initiators.
In addition, for the TARGET COLD RESET the target then MUST terminate
all of its TCP connections to all initiators (all sessions are
terminated).
For the TASK REASSIGN function, the target should reassign the
connection allegiance to this new connection (and thus resume iSCSI
exchanges for the task). TASK REASSIGN MUST be received by the
target ONLY after the connection on which the command was previously
executing has been successfully logged-out. For additional usage
semantics, see section 8.1.
TASK REASSIGN MUST be issued as an immediate command.
3.5.2 LUN
This field is required for functions addressing a specific LU (ABORT
TASK, CLEAR TASK SET, ABORT TASK SET, CLEAR ACA, LOGICAL UNIT RESET)
and is reserved in all others.
3.5.3 Referenced Task Tag
Initiator Task Tag of the task to be aborted or reassigned.
3.5.4 RefCmdSN or ExpDataSN
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For ABORT TASK the task CmdSN to enable task removal. If RefCmdSN
does not match the CmdSN of the command to be aborted at the target,
the abort action MUST NOT be performed and the response MUST be
function rejected.
If the function is TASK REASSIGN establishing a new connection
allegiance for a previously issued Read or Bidirectional command,
this field will contain the next consecutive input DataSN number
expected by the initiator (no gaps) for the referenced command in a
previous execution.
Otherwise, this field is reserved.
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3.6 Task Management Function 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|0|1| 0x22 |1| Reserved | Response | Qualifier |
+---------------+---------------+---------------+---------------+
4/ Reserved /
/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Referenced Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------------------------------------------------------+
For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA, CLEAR TASK
SET, LOGICAL UNIT RESET, TARGET WARM RESET, the target performs the
requested Task Management function and sends a Task Management
Response back to the initiator.
3.6.1 Response and Qualifier
The target provides a Response, which may take on the following
values:
0 - Function Complete
1 - Task specified in the Referenced Task Tag field was
not in task set
2 - LUN does not exist
3 - Task still allegiant
4 - Task failover not supported
5 - Task management function not supported
255 Function Rejected
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All other values are reserved.
The Qualifier field provides additional information about the
Response.
For a Response of "Function Complete" the valid Qualifiers are:
0 - Function Executed
1 - Not Authorized
For a discussion on usage of response codes 3 and 4, see section
8.1.2.
For the TARGET COLD RESET and TARGET WARM RESET functions, the target
cancels all pending operations. For the TARGET COLD RESET function
the target MUST then close all of its TCP connections to all
initiators (terminates all sessions).
The mapping of the response code into a SCSI service response code,
if needed, is outside the scope of this document.
3.6.2 Referenced Task Tag
If the Request was ABORT TASK and the Response is "task not found"
Referenced Task Tag contains the Initiator Task Tag of the task that
had to be aborted. It MUST be set to 0xffffffff in other cases.
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3.7 SCSI Data-out & SCSI Data-in
The SCSI Data-out PDU for WRITE operations has the following format:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|0| 0x05 |F| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| Reserved |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32| Reserved |
+---------------+---------------+---------------+---------------+
36| DataSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment /
+/ /
+---------------+---------------+---------------+---------------+
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The SCSI Data-in PDU for READ operations has the following format:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x25 |F|A|0 0 0|O|U|S| Reserved |Status or Rsvd |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Residual Count |
+---------------+---------------+---------------+---------------+
24| StatSN or Reserved |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| DataSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Header Digest (if any) |
+---------------+---------------+---------------+---------------+
/ DataSegment (and digest if any) /
+/ /
+---------------+---------------+---------------+---------------+
Status can accompany the last Data-in PDU if the command did not end
with an exception. Presence of status (and of a residual count) is
signaled though the S flag bit. Although targets MAY choose to send
even non-exception status in separate responses initiators MUST
support non-exception status in Data-In PDUs.
3.7.1 F (Final) Bit
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For outgoing data, this bit is 1 for the last PDU of unsolicited data
or the last PDU of a sequence answering an R2T.
For incoming data, this bit is 1 for the last input (read) data PDU
of a sequence. Input can be split in several sequences each one
having it's own F bit. Splitting the data stream in sequences does
not affect DataSN counting on Data-In PDUs. It MAY be used as a
"change direction" indication for Bidirectional operations that need
such a change.
For Bidirectional operations, the F bit is 1 both for the end of the
input sequences as well as the end of the output sequences.
3.7.2 A (Acknowledge) bit
For sessions with ErrorRecoveryLevel 1 or higher the target sets this
bit to 1 to indicate that it requests from the initiator a positive
acknowledgement for the data received. The target should use the A
bit moderately; it MAY set the A-bit to 1 once at most every
MaxBurstSize bytes, and MUST NOT do so any more frequently than that.
On receiving a Data-In PDU with the A bit set to 1 the initiator MUST
issued a SNACK of type DataACK. If the initiator has detected holes
in the input sequence, it MUST postpone issuing the SNACK of type
ACKN until the holes are filled.
3.7.3 Target Transfer Tag
On outgoing data, the Target Transfer Tag is provided to the target
if the transfer is honoring an R2T. In this case, the Target Transfer
Tag field is a replica of the Target Transfer Tag provided with the
R2T.
The Target Transfer Tag values are not specified by this protocol
except that the value 0xffffffff is reserved and means that the
Target Transfer Tag is not supplied. If the Target Transfer Tag is
provided then the LUN field MUST hold a valid value and be consistent
with whatever was specified with the command, otherwise the LUN field
is reserved.
3.7.4 StatSN
This field MUST be set only if the S bit is set to 1.
3.7.5 DataSN
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For input (read) data PDUs, the DataSN is the data PDU number
(starting with 0) within the data transfer for the command identified
by the Initiator Task Tag.
For output (write) data PDUs, the DataSN is the data PDU number
(starting with 0) within the current output sequence. The current
output sequence is identified by the Initiator Task Tag (for
unsolicited data) or is a data sequence generated for one R2T (for
data solicited through R2T).
Any input or output data sequence MUST contain less than 2**32-1
numbered PDUs.
3.7.6 Buffer Offset
The Buffer Offset field contains the offset of this PDU payload data
within the complete data transfer. The sum of the buffer offset and
length should not exceed the expected transfer length for the
command.
The order of data PDUs within a sequence is determined by
DataPDUInOrder (when set to yes it means that PDUs have to be in
increasing Buffer Offset order and overlays are forbidden).
The ordering between sequences is determined by DataSequenceInOrder
(when set to yes it means that sequences have to be in increasing
Buffer Offset order and overlays are forbidden).
3.7.7 DataSegmentLength
This is the data payload length of a SCSI Data-In or SCSI Data-Out
PDU; sending of 0 length data segments should be avoided, but
initiators and targets MUST be able to properly receive 0 length data
segments.
The Data Segments of Data-in and Data-out PDUs SHOULD be filled to
integer number of 4 byte words (real payload) unless the F bit is set
to 1.
3.7.8 Flags (byte 1)
The last SCSI Data packet sent from a target to an initiator for a
SCSI command that completed successfully (with a status of GOOD,
CONDITION MET, INTERMEDIATE or INTERMEDIATE CONDITION MET) may also
optionally contain the Status for the data transfer. In this case,
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Sense Data cannot be sent together with the Command Status. If the
command is completed with an error, then the response and sense data
MUST be sent in a SCSI Response PDU (i.e., MUST NOT be sent in a SCSI
Data packet). For Bidirectional commands, the status MUST be sent in
a SCSI Response PDU.
bit 3-6 not used (should be set to 0)
bit 1-2 as in an SCSI Response
bit 0 S (status)- set to indicate that the Command Status
field contains status. If this bit is set to 1 the F bit MUST
also be set to 1
The fields StatSN, Status, Residual Count have meaningful content
only if the S bit is set to 1.
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3.8 Ready To Transfer (R2T)
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x31 |1| Reserved |
+---------------+---------------+---------------+---------------+
4/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| R2TSN |
+---------------+---------------+---------------+---------------+
40| Buffer Offset |
+---------------+---------------+---------------+---------------+
44| Desired Data Transfer Length |
+---------------------------------------------------------------+
48| Digest (if any) |
+---------------------------------------------------------------+
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. The target may request that
the data blocks be delivered in whichever order is convenient for the
target at that particular instant. This information is passed from
the target to the initiator in the Ready To Transfer (R2T) PDU.
In order to allow write operations without an explicit initial R2T,
the initiator and target MUST have agreed to do so by sending the
InitialR2T=no key-pair to each other, which happens either during
Login or through the Text request/Response mechanism.
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An R2T MAY be answered with one or more SCSI Data-out PDUs with a
matching Target Transfer Tag. If an R2T is answered with a single
Data-out PDU, the Buffer Offset in the Data PDU MUST be the same as
the one specified by the R2T. The data length of the Data PDU MUST
not exceed the Desired Data Transfer Length specified in the R2T. If
the R2T is answered with a sequence of Data PDUs the Buffer Offset
and Length MUST be within the range of those specified by R2T, the
last PDU SHOULD have the F bit set to 1. The Data-Out PDU ordering is
governed by DataPDUInOrder. If DataPDUInOrder is set to yes the
Buffer Offsets and Lengths for consecutive PDUs MUST form a
continuous non-overlapping range and the PDUs MUST be sent in
increasing offset order.
The target may send several R2T PDUs (up to a negotiated number) and
thus have a number of data transfers pending. Within a connection,
outstanding R2Ts MUST be fulfilled by the initiator in the order in
which they were received.
Buffer offset ordering in consecutive R2Ts is governed by
DataSequenceInOrder. If DataSequenceInOrder is yes then consecutive
R2Ts SHOULD refer to continuous non-overlapping ranges. However,
even when DataSequenceInOrder is no, a target MAY send out-of-order
R2Ts (e.g., for recovery) and an initiator MAY choose to terminate a
command when receiving an out-of-order R2T that it can't fulfill,
with an appropriate response after aborting the command at the target
with the appropriate task management command.
3.8.1 R2TSN
R2TSN is the R2T PDU number (starting with 0) within the command
identified by the Initiator Task Tag.
The number of R2Ts in a command MUST be less than 0xffffffff.
3.8.2 StatSN
The StatSN field will contain as usual the next StatSN but StatSN for
this connection is not advanced.
3.8.3 Desired Data Transfer Length and Buffer Offset
The target specifies how many bytes it wants the initiator to send
because of this R2T PDU. The target may request the data from the
initiator in several chunks, not necessarily in the original order of
the data. The target, therefore, also specifies a Buffer Offset that
indicates the point at which the data transfer should begin, relative
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to the beginning of the total data transfer. The Desired Data
Transfer Length SHOULD not be 0 and MUST not exceed MaxBurstSize.
3.8.4 Target Transfer Tag
The target assigns its own tag to each R2T request that it sends to
the initiator. This tag can be used by the target to easily identify
the data it receives. The Target Transfer Tag is copied in the
outgoing data PDUs and is used by the target only. There is no
protocol rule about Target Transfer Tag, but it is assumed that it is
used to tag the response data to the target (alone or in combination
with the LUN).
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3.9 Asynchronous Message
An Asynchronous Message may be sent from the target to the initiator
without corresponding to a particular command. The target specifies
the reason 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|0|1| 0x32 |1| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN |
+ +
12| |
+---------------+---------------+---------------+---------------+
16/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| AsyncEvent | AsyncVCode | Parameter1 or Reserved |
+---------------+---------------+---------------+---------------+
40| Parameter2 or Reserved | Parameter3 or Reserved |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment - Sense Data or iSCSI Event Data /
+/ /
+---------------+---------------+---------------+---------------+
Some Asynchronous Messages are strictly related to iSCSI while others
are related to SCSI [SAM2].
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Please note that StatSN counts this PDU as an acknowledgeable event
(StatSN is advanced), allowing initiator and target state
synchronization.
3.9.1 AsyncEvent
The codes used for iSCSI Asynchronous Messages (Events) are:
0 A SCSI Asynchronous Event is reported in the sense data.
Sense Data that accompanies the report, in the data segment,
identifies the condition. Sending of a SCSI Event (Asynchronous
Event Notification in SCSI terminology) is controlled by a SCSI
Control Mode Page bit.
1 Target requests Logout. This Async Message MUST be sent on
the same connection as the one being requested to be logged
out. Initiator MUST honor this request by issuing a Logout as
early as possible, but no later than Parameter3 seconds.
Initiator MUST send a Logout with a reason code of "Close the
connection" to cleanly shutdown the connection. The initiator
MAY also issue a Logout with the reason code of "Close the
session", to completely close the session, but ONLY if it does
not support or use multiple connections in the specific
session. Once this message is received, initiator SHOULD NOT
issue new iSCSI commands. The target MAY reject any new I/O
requests that it receives after this Message with the reason
code "Waiting for Logout". If the initiator does not Logout in
Parameter3 seconds, the target should send an Async PDU with
iSCSI event code "Dropped the connection" if possible, or
simply terminate the transport connection. Parameter1 and
Parameter2 are reserved.
2 Target indicates it will drop the connection.
The Parameter1 field indicates on what CID the connection will
dropped.
The Parameter2 field indicates, in seconds, the minimum time to
wait before attempting to reconnect (Time2Wait).
Parameter3 indicates the maximum time to reconnect and/or
restart commands after the initial wait (Parameter2).
If the initiator does not attempt to reconnect and/or restart
the outstanding commands, within the time specified by
Parameter3 or, if Parameter3 is 0, the target will terminate
all outstanding commands on this connection, no other responses
should be expected from the target for the outstanding commands
on this connection (Time2Retain).
A value of 0 for Parameter2 indicates that reconnect can be
attempted immediately.
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3 Target indicates it will drop all the connections of this
session.
The Parameter2 field indicates, in seconds, the minimum time to
wait before attempting to reconnect (Time2Wait).
The Parameter3 field indicates the maximum time to reconnect
and restart commands after the initial wait (Parameter2).
If the initiator does not attempt to reconnect within the time
specified by Parameter 3 or, if Parameter 3 is 0, the session
is terminated (Time2Retain). In this case, the target will
terminate all outstanding commands in this session; no other
responses should be expected from the target for the
outstanding commands in this session. A value of 0 for
Parameter2 indicates that reconnect can be attempted
immediately.
255 Vendor specific iSCSI Event. The AsyncVCode details the
vendor code and data MAY accompany the report.
All other event codes are reserved.
3.9.2 AsyncVCode
AsyncVCode is a vendor specific detail code valid only if the
AsyncEvent field indicates a vendor specific event. Otherwise it is
reserved.
3.9.3 Sense Data or iSCSI Event Data
For a SCSI Event this data accompanies the report, in the data
segment, identifies the condition.
For an iSCSI Event additional data that MAY accompany the report
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3.10 Text Request
The Text Request 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.
An initiator MUST have only one outstanding Text Request on a
connection at any given time.
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| 0x04 |F| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+---------------+
3.10.1 F (Final) Bit
When set to 1 it indicates that this is the last or only text request
in a sequence of commands; otherwise it indicates that more commands
will follow.
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3.10.2 Initiator Task Tag
The initiator assigned identifier for this Text Request.
If the command is sent as part of a sequence of text requests and
responses, the Initiator Task Tag MUST be the same for all the
requests within the sequence (similar to linked SCSI commands).
3.10.3 Target Transfer Tag
When the Target Transfer Tag is set to the reserved value 0xffffffff,
it tells the target that this is a new request and the target should
reset any internal state associated with the Initiator Task Tag.
The target sets in a text response the Target Transfer Tag to a value
other than the reserved value 0xffffffff whenever it indicates that
it has more data to send or more operations to perform associated
with the specified Initiator Task Tag (it MUST do so whenever it sets
the F bit to 0 in the response). By copying the Target Transfer Tag
from the response to the next Text Request, the initiator tells the
target to continue the operation for the specific Initiator Task Tag.
This mechanism allows the initiator and target to transfer a large
amount of textual data over a sequence of text-command/text-response
exchange or to perform extended negotiation sequences
A target MAY reset its internal state if an exchange is stalled by
the initiator for a long time or if it is running out of resources.
Long text responses are handled as in the following example:
I->T Text SendTargets=all (F=1,TTT=0xffffffff)
T->I Text <part 1> (F=0,TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
T->I Text <part 2> (F=0, TTT=0x12345678)
I->T Text <empty> (F=1, TTT=0x12345678)
...
T->I Text <part n> (F=1, TTT=0xffffffff)
3.10.4 Text
The initiator sends the target a set of key=value or key=list pairs
encoded in UTF-8 Unicode. All the text keys and text values specified
in this document are to be presented and interpreted in the case they
appear in this document (they are case sensitive). Text keys and
values MUST contain ONLY letters (a-z, A-Z), digits (0-9), space
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(0x20), point (.), minus (-), plus (+) and underscore (_). The key
and value are separated by a '=' (0x3d) delimiter. Every key=value
pair (including the last or only pair) MUST be followed by at least
one null (0x00) delimiter. A list is a set of values separated by
comma (0x2c).
Character strings are represented as plain text. Binary items can be
encoded using their decimal representation (with or without leading
zeros) or hexadecimal representation (e.g., 8190 is 0x1ffe). Upper
and lower case letters may be used interchangeably in hexadecimal
notation (i.e., 0x1aBc, 0x1AbC, 0X1aBc and 0x1ABC are equivalent).
Binary items can also be encoded using the more compact Base64
encoding as specified by [RFC2045] preceded by the 0b. Key names
MUST NOT exceed 63 bytes.
If not specified otherwise the maximum length of an individual value
(not its encoded representation) is 255 bytes not including the
delimiter (comma or null).
The data lengths of a text request or response MUST NOT exceed
MaxRecvPDULength (a per connection negotiated parameter).
A Key=value pair can span Text request or response boundaries (i.e. a
key=value pair can start in one PDU and continue on the next).
The target responds by sending its response back to the initiator.
The response text format is similar to the request text format.
As text for text requests and responses can span several PDUs (e.g.,
if the PDU length does not allow the whole text to be contained in a
single PDU) the text response MAY refer to key=value pairs presented
in an earlier text request and the text in the request may refer to
earlier responses.
Text operations are usually meant for parameter setting/negotiations
but can be used also to perform some long lasting operations.
Text operations that will take a long time should be placed in their
own Text request.
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3.11 Text Response
The Text Response PDU contains the target's responses to the
initiator's Text request. The format of the Text field matches that
of the Text request.
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x24 |F| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment (Text) /
+/ /
+---------------+---------------+---------------+---------------+
3.11.1 F (Final) Bit
When set to 1 in response to a text request with the Final bit set to
1 the F bit indicates that the target has finished the whole
operation. Otherwise, if set to 0 in response to a text request with
the Final Bit set to 1 it indicates that the target has more work to
do (invites a follow-on text request). A text response with the F
bit set to 1 in response to a text request with the F bit set to 0 is
a protocol error.
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A text response with the F bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator.
A text response with the F bit set to 0 MUST have a Target Transfer
Tag field set to a value different than the reserved 0xffffffff.
3.11.2 Initiator Task Tag
The Initiator Task Tag matches the tag used in the initial Text
request.
3.11.3 Target Transfer Tag
When a target has more work to do (e.g., can't transfer all the
remaining text data in a single Text response or has to continue the
negotiation) and has enough resources to proceed it MUST set the
Target Transfer Tag to a value different from the reserved value of
0xffffffff.
The initiator MUST copy this Target Transfer Tag in its next request
to indicate that it wants the rest of the data.
If the target receives a Text Request with the Target Task Tag set to
the reserved value of 0xffffffff it resets its internal state
associated with the given Initiator Task Tag.
When a target can't finish the operation in single text response but
has not enough resources to continue it rejects the Text request with
an appropriate Reject code. A target may reset its internal state
associated with an Initiator Task Tag and expressed through the
Target Transfer Tag, if the initiator fails to continue the exchange
for some time, and reject subsequent Text requests with the Target
Transfer Tag set to the "stale" value.
3.11.4 Text Response Data
The Text Response Data Segment contains responses in the same
key=value format as the Text request and with the same length and
coding constraints. Appendix A and Appendix D lists some basic Text
requests and their Responses.
As text for text requests and responses can span several PDUs (e.g.,
if the PDU length does not allow the whole text to be contained in a
single PDU) the text response MAY refer to key=value pairs presented
in an earlier text request.
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Although the initiator is the requesting party and controls the
request-response initiation and termination the target can offer
key=value pairs of its own as part of a sequence and not only in
response to the initiator.
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3.12 Login Request
After establishing a TCP connection between an initiator and a
target, the initiator MUST start a Login phase to gain further access
to the target's resources.
The Login Phase (see chapter 1) consists of a sequence of Login
requests and responses that carry the same Initiator Task Tag.
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x03 |T|X|0 0|CSG|NSG| Version-max | Version-min |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| ISID |
+ +---------------+---------------+
12| |TSID |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| CID | Reserved |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN or Reserved |
+---------------+---------------+---------------+---------------+
32| Reserved |
+---------------+---------------+---------------+---------------+
36| Reserved |
+---------------+---------------+---------------+---------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------+---------------+---------------+---------------+
/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+---------------+
3.12.1 T (Transit) Bit
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If set to 1 indicates that the initiator is ready to transit to next
stage.
If the T bit is set to 1 and NSG is FullFeaturePhase then this is
also indicating that the initiator is ready for the Final Login
Response (see chapter 1).
The target MAY answer with a Login response with the T bit set to 1
ONLY if the T is set to 1 in the request.
3.12.2 X - Restart Connection
If this bit is set to 1 then this command is an attempt to reinstate
a failed connection or a failed session.
The TSID MUST be non-zero if the X bit is 1. CID does not change
and this command performs first the logout function of the old
connection if an explicit logout was not performed earlier. In
sessions with a single connection, this may imply the opening of a
second connection with the sole purpose of cleaning-up the first.
Targets should support opening a second connection even when not
supporting multiple connections in full feature phase.
If TSID is 0 then the X bit MUST be 0.
The X bit MAY be set to 1 ONLY on the first request of the Login
phase.
If the operational ErrorRecoveryLevel is 2, connection reinstatement
is a complete connection recovery which enables future task
reassignment. If the operational ErrorRecoveryLevel is less than 2,
connection reinstatement refers to a mere replacement of the old CID
without enabling task reassignment.
3.12.3 CSG and NSG
Through these fields, called Current Stage (CSG) and Next Stage
(NSG), the Login negotiation commands and responses are associated
with a specific stage in the session (SecurityNegotiation,
LoginOperationalNegotiation, FullFeaturePhase) and may indicate the
next stage they want to move to (see chapter 1).
The next stage value is valid only when the T bit is 1 and is
reserved otherwise.
The stage codes are:
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- 0 - SecurityNegotiation
- 1 - LoginOperationalNegotiation
- 3 - FullFeaturePhase
3.12.4 Version-max
Maximum Version number supported.
All Login requests within the Login phase MUST carry the same
Version-max.
The target MUST use the value presented with the first login request.
3.12.5 Version-min
Minimum Version supported.
The version number of the current draft is 0x3.
All Login requests within the Login phase MUST carry the same
Version-min.
The target MUST use the value presented with the first login request.
3.12.6 ISID
This is an initiator-defined component of the session identifier
(SSID). The ISID is structured as follows (see [NDT] for details and
also 9.1.1):
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| Type | Naming Authority |
+---------------+---------------+---------------+---------------+
4| Qualifier |
+---------------+---------------+
The Type field identifies the format of the Naming Authority field
and takes on three defined values with all other possible values
reserved as indicated in the following table:
Type naming authority format
0x00 IEEE OUI
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0x01 IANA Enterprise Number (EN)
0x02 "Random"
0x03-0xFF Reserved
The Naming Authority field identifies the vendor or organization
whose component (SW or HW) is generating this ISID. A vendor or
organization with one or more OUIs and/or one or more Enterprise
Numbers MUST use at least one of these numbers and select the
appropriate value for the Type field when its components generate
ISIDs. An OUI or EN MUST be set in the Naming Authority field in
network byte order (BigEndian).
If the Type field is 02h, the Naming Authority field SHOULD be set to
a random or pseudo-random 24bit unsigned integer value in network
byte order (BigEndian). (See [NDT] on how this affects the principle
of "conservative reuse").
The Qualifier field is a 16 bit unsigned integer value that provides
a range of possible values for the ISID within the Type and Naming
Authority namespace. It may be set to any value, within the
constraints specified in the iSCSI protocol (see 2.5.3 and 9.1.1).
3.12.7 TSID
The TSID is the target assigned component of the session identifier
(SSID). Together with the ISID provided by the initiator, this
uniquely identifies the session with that initiator.
On a Login request a TSID value of 0 indicates a request to open a
new session.
A non-zero TSID indicates a request to add a connection to an
existing session.
3.12.8 Connection ID - CID
This is a unique ID for this connection within the session.
All Login requests within the Login phase MUST carry the same CID.
The target MUST use the value presented with the first login request.
3.12.9 CmdSN
CmdSN is either the initial command sequence number of a session (for
the first Login request of a session - the "leading" login) or the
command sequence number in the command stream (e.g., if the leading
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login carries the CmdSN 123 all other Login requests carry the CmdSN
123 and the first non-immediate command also carries the CmdSN 123).
The target MUST use the value presented with the first login request.
3.12.10 ExpStatSN
This is ExpStatSN for the old connection.
This field is valid only if the Login request restarts a connection
(i.e., X bit is 1 and TSID is not zero).
3.12.11 Login Parameters
The initiator MAY provide some basic parameters in order to enable
the target to determine if the initiator may use the target's
resources and the initial text parameters for the security exchange.
All the rules specified in 3.10.4 for text requests/responses hold
also for login requests/responses. Keys and their explanations are
listed in the Appendix A (security negotiation keys) and Appendix D
(operational parameter negotiation keys). All keys in Appendix D,
except for the X- extension format, MUST be supported by iSCSI
initiators and targets. Keys in Appendix A MUST be supported only
when the function they refer to is mandatory to implement.
3.13 Login Response
The Login Response indicates the progress and/or end of the login
phase.
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x23 |T|0 0 0|CSG|NSG| Version-max | Version-active|
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| ISID |
+ +---------------+---------------+
12| |TSID |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
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20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| Status-Class | Status-Detail | Reserved |
+---------------+---------------+---------------+---------------+
40/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment - Login Parameters in Text request Format /
+/ /
+---------------+---------------+---------------+---------------+
3.13.1 Version-max
This is the highest version number supported by the target.
All Login responses within the Login phase MUST carry the same
Version-max.
The initiator MUST use the value presented as response to the first
login request.
3.13.2 Version-active
Indicates the version supported (the highest version supported by the
target and initiator). If the target does not support a version
within the range specified by the initiator, the target rejects the
login and this field indicates the lowest version supported by the
target.
All Login responses within the Login phase MUST carry the same
Version-active.
The initiator MUST use the value presented as response to the first
login request.
3.13.3 TSID
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The TSID is the target assigned component of the session identifier
(SSID). Together with the ISID provided by the initiator, it
uniquely identifies the session with that initiator. It MUST be valid
only in the final response.
3.13.4 StatSN
For the first Login Response (the response to the first Login
Request) this is the starting status Sequence Number for the
connection (the next response of any kind, including the next login
response if any in the same login phase, will carry this number + 1).
This field is valid only if the Status Class is 0.
3.13.5 Status-Class and Status-Detail
The Status returned in a Login Response indicates the execution
status of the login phase. The status includes:
Status-Class
Status-Detail
A 0 Status-Class indicates success.
A non-zero Status-Class indicates exception. In this case, Status-
Class is sufficient for a simple initiator to use when handling
errors, without having to look at the Status-Detail. The Status-
Detail allows finer-grained error recovery for more sophisticated
initiators, as well as better information for error logging.
The status classes are as follows:
0 - Success - indicates that the iSCSI target successfully
received, understood, and accepted the request. The numbering
fields (StatSN, ExpCmdSN, MaxCmdSN are valid only if Status-
Class is 0).
1 - Redirection - indicates that further action must be taken
by the initiator to complete the request. This is usually due
to the target moving to a different address. All of the
redirection status class responses MUST return one or more text
key parameters of the type "TargetAddress", which indicates the
target's new address.
2 - Initiator Error (not a format error) - indicates that the
initiator likely caused the error. This MAY be due to a request
for a resource for which the initiator does not have
permission. The request should not be tried again.
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3 - Target Error - indicates that the target sees no errors in
the initiator's login request, but is currently incapable of
fulfilling the request. The client may re-try the same login
request later.
The table below shows all of the currently allocated status codes.
The codes are in hexadecimal; the first byte is the status class and
the second byte is the status detail.
-----------------------------------------------------------------
Status | Code | Description
|(hex) |
-----------------------------------------------------------------
Success | 0000 | Login is proceeding OK (*1)
-----------------------------------------------------------------
Target Moved | 0101 | The requested ITN has moved
Temporarily | | temporarily to the address provided.
-----------------------------------------------------------------
Target Moved | 0102 | The requested ITN has moved
Permanently | | permanently to the address provided.
-----------------------------------------------------------------
Initiator | 0200 | Miscellaneous iSCSI initiator
Error | | errors
----------------------------------------------------------------
Authentication| 0201 | The initiator could not be
Failure | | successfully authenticated.
-----------------------------------------------------------------
Authorization | 0202 | The initiator is not allowed access
Failure | | to the given target.
-----------------------------------------------------------------
Not Found | 0203 | The requested ITN does not
| | exist at this address.
-----------------------------------------------------------------
Target Removed| 0204 | The requested ITN has been removed
| | No forwarding address is provided.
-----------------------------------------------------------------
Unsupported | 0205 | The requested iSCSI version range is
Version | | not supported by the target.
-----------------------------------------------------------------
Too many | 0206 | No more connections accepted on this SID
connections | |
-----------------------------------------------------------------
Missing | 0207 | Missing parameters (e.g., iSCSI
parameter | | Initiator and/or Target Name)
-----------------------------------------------------------------
Can't include | 0208 | Target does not support session
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in session | | spanning to this connection (address)
-----------------------------------------------------------------
Session type | 0209 | Target does not support this type of
Not supported | | of session or not from this Initiator
-----------------------------------------------------------------
Target Error | 0300 | Target hardware or software error.
-----------------------------------------------------------------
Service | 0301 | The iSCSI service or target is not
Unavailable | | currently operational.
-----------------------------------------------------------------
Out of | 0302 | The target has insufficient session,
Resources | | connection, or other resources.
-----------------------------------------------------------------
(*1)If the response T bit is 1 and the NSG is FullFeaturePhase in
both the request and the response) the login phase is finished and
the initiator may proceed to issue SCSI commands.
If the Status Class is not 0, the initiator and target MUST close the
TCP connection.
If the target wishes to reject the login request for more than one
reason, it should return the primary reason for the rejection.
3.13.6 T (Transit) bit
T bit is set to 1 as an indicator of end of stage. If the T bit is
set to 1 and NSG is FullFeaturePhase then this is also the Final
Login Response (see chapter 1). A T bit of 0 indicates a "partial"
response, which means "more negotiation needed".
A login response with a T bit set to 1 MUST NOT contain key=value
pairs that may require additional answers from the initiator within
the same stage.
If the status class is 0, the T bit MUST NOT be set to 1 if the
T bit in the request was set to 0.
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3.14 Logout Request
The Logout request is used to perform a controlled closing of a
connection.
An initiator MAY use a logout command to remove a connection from a
session or to close an entire session.
After sending the Logout PDU, an initiator MUST NOT send any new
iSCSI commands on the closing connection except SNACK and task
management commands required for recovery. If the Logout is
intended to close the session, new iSCSI commands MUST NOT be sent on
any of the connections participating in the session.
When receiving a Logout request with the reason code of "close the
connection" or "close the session", the target MUST abort all pending
commands, whether acknowledged or not, on that connection
respectively session. When receiving a Logout request with the reason
code "remove connection for recovery", the target MUST discard all
requests not yet acknowledged that were issued on the specified
connection and suspend all data/status/R2T transfers on behalf of
pending commands on the specified connection. The target then issues
the Logout response and half-closes the TCP connection (sends FIN).
After receiving the Logout response and attempting to receive the FIN
(if still possible), the initiator MUST completely close the logging-
out connection. For the aborted commands, no additional responses
should be expected after that.
Note that a Logout for a CID may be performed on a different
transport connection when the TCP connection for the CID had already
been terminated. In such a case, only a logical "closing" of the
iSCSI connection for the CID is implied with a Logout.
All commands that were not aborted or not completed (with status) and
acknowledged when the connection is closed completely can be
reassigned to a new connection if the target supports connection
recovery.
If an initiator intends to start recovery for a failing connection it
MUST use either the Logout command to "clean-up" the target end of a
failing connection and enable recovery to start, or use the restart
option of the Login command for the same effect. In sessions with a
single connection, this may imply the opening of a second connection
with the sole purpose of cleaning-up the first. In this case, the
restart option of the Login should be used.
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Sending a logout request with the reason code of "close the
connection" or "remove the connection for recovery" may result in
some unacknowledged commands to be discarded. Those holes in command
sequence numbers will have to be handled by appropriate recovery (see
section 8) unless the session is also closed.
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| 0x06 |1| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved |
+---------------+---------------+---------------+---------------+
8| Reserved |
+---------------+---------------+---------------+---------------+
12| Reserved |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| CID or Reserved | Reserved |Reason Code |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------------------------------------------------------+
3.14.1 CID
This is the connection ID of the connection to be closed (including
closing the TCP stream). This field is valid only if the reason code
is not "close session".
3.14.2 ExpStatSN
This is the last ExpStatSN value for the connection to be closed.
3.14.3 Reason Code
Indicate the reason for Logout:
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0 - closes the session - the session is closed - all commands
associated with the session (if any) are aborted
1 - closes the connection - the connection is closed - all
commands associated with connection (if any) are aborted
2 - removes the connection for recovery - connection is closed
and all commands associated with it (if any) are to be prepared
for a new allegiance
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3.15 Logout Response
The logout response is used by the target to indicate that the
cleanup operation for the connection has completed.
After Logout, the TCP connection referred by the CID MUST be closed
at both ends (or all connections must be closed if the logout reason
was session close).
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x26 |1| Reserved | Response | Reserved |
+---------------+---------------+---------------+---------------+
4/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag |
+---------------+---------------+---------------+---------------+
20| Reserved |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| Reserved |
+---------------------------------------------------------------+
40| Time2Wait | Time2Retain |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------------------------------------------------------+
3.15.1 Response
Logout response:
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0 - Connection or session closed successfully
1 - CID not found
2 - Connection recovery not supported (if Logout reason code
was recovery and target does not support it - as indicated by
the ErrorRecoveryLevel
3 - Cleanup failed for various reasons
3.15.2 Time2Wait
Minimum time in seconds to wait before Login for adding or
reinstating a new connection to this session on this target.
3.15.3 Time2Retain
If ErrorRecoveryLevel is less than 2 this is the maximum time that the
target waits for a connection reinstatement Login after which the
connection state is discarded, and if it is the last connection of a
session the whole session state is discarded. Otherwise, this is the
maximum time the target waits for the allegiance reassignment for any
active task after which the task state is discarded.
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3.16 SNACK Request
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x10 |1|Rsrvd| Type | Reserved |
+---------------+---------------+---------------+---------------+
4/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| BegRun |
+---------------+---------------+---------------+---------------+
24| RunLength |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32| Reserved |
+---------------+---------------+---------------+---------------+
36| ExpDataSN or Reserved |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------------------------------------------------------+
Support for SNACK is optional.
SNACK request is used to request retransmission of numbered-
responses, data or R2T PDUs from the target. The SNACK request
indicates to the target the missed numbered-response or data run,
where the run is composed of an initial missed StatSN, DataSN or
R2TSN and the number of additional missed Status, Data or R2T PDUs (0
means only the initial).
The numbered-response or R2T requested by a SNACK have to be
delivered as exact replicas of the ones the initiator missed
including all its flags except for the ExpStatSN and ExpDataSN that
MUST carry the current values.
The numbered Data-In PDUs individually requested by a SNACK have to
be delivered as exact replicas of the ones the initiator missed
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including all its flags. Data-In PDUs requested with RunLength 0
(meaning all after this number) may be different from the ones
originally sent in order to reflect changes in MaxRecvPDULength.
Any SNACK requesting a numbered-response, Data or R2T that was not
sent by the target MUST be rejected with a reason code of "Invalid
SNACK".
3.16.1 Type
This field encodes the SNACK function as follows:
0-Data/R2T SNACK - requesting retransmission of a Data-In or
R2T PDU
1-Status SNACK - requesting retransmission of a numbered
response
2-DataACK - positively acknowledges Data-In PDUs
All other values are reserved.
Data/R2T SNACK for a command MUST precede status acknowledgement for
the given command.
For a Data/R2T SNACK the Initiator Task Tag MUST be set to the
Initiator Task Tag of the referenced Command. Otherwise, it is
reserved.
For a Status SNACK the ExpDataSN field is reserved.
An iSCSI target that does not support recovery within connection MAY
discard status SNACK. If the target supports command recovery within
session it MAY discard the SNACK after which it MUST issue an
Asynchronous Message PDU with an iSCSI event indicating "Request
Logout".
If an initiator operates at ErrorRecoveryLevel 1 or higher it MUST
issue a SNACK of type DataACK after receiving a Data-In PDU with the
A bit set to 1. However, if the initiator has detected holes in the
input sequence, it MUST postpone issuing the SNACK of type DataACK
until the holes are filled. An initiator MAY ignore the A-bit if it
deems that the bit is being set aggressively by the target (i.e.
before the MaxBurstSize limit is reached).
The DataACK is used to free resources at target and not to request or
imply data retransmission.
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3.16.2 BegRun
First missed DataSN, R2TSN or StatSN
3.16.3 RunLength
RunLength is the number of sequential missed DataSN, R2TSN or StatSN.
RunLength 0 signals that all Data-In, R2T or Response PDUs carrying
numbers equal or greater to BegRun have to be resent.
The first data SNACK after a Task Management request of TASK REASSIGN
(see 3.5.1) for a command whose connection allegiance was just
changed MUST use RunLength "0" to request retransmission of any
number of PDUs (including one). The number of retransmitted PDUs in
this case, may or may not be the same as the original transmission,
depending on if there was a change in MaxRecvPDULength in the
reassignment.
The first data SNACK after a MaxRecvPDULength decrease for a command
issued on the same connection before the change in MaxRecvPDULength
MUST use RunLength "0" to request retransmission of any number of
PDUs (including one). The number of retransmitted PDUs in this case,
may or may not be the same as the original transmission, depending if
the loss was before or after the MaxRecvPDULength was senses at the
target or not.
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3.17 Reject
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x3f |1| Reserved | Reason | Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36| DataSN or Reserved |
+---------------+---------------+---------------+---------------+
40| Reserved |
+---------------+---------------+---------------+---------------+
44| Reserved |
+---------------+---------------+---------------+---------------+
48| Digest (if any) |
+---------------+---------------+---------------+---------------+
xx/ Complete Header of Bad PDU /
+/ /
+---------------+---------------+---------------+---------------+
yy/Vendor specific data (if any) /
/ /
+---------------+---------------+---------------+---------------+
zz
Reject is used to indicate an iSCSI error condition (protocol,
unsupported option etc.).
3.17.1 Reason
The reject Reason is coded as follows:
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+------+-----------------------------------------+------------------+
| Code | Explanation | Can the original |
| (hex)| | PDU be re-sent? |
+------+-----------------------------------------+------------------+
| 0x01 | Full Feature Phase Command before login | no |
| | | |
| 0x02 | Data (payload) Digest Error | yes (Note 1) |
| | | |
| 0x03 | Data-SNACK Reject | yes |
| | | |
| 0x04 | Protocol Error (e.g., SNACK request for | no |
| | a status that was already acknowledged) | |
| | | |
| 0x05 | Command not supported in this session | no |
| | type | |
| | | |
| 0x06 | Immediate Command Reject - too many | yes |
| | immediate commands | |
| | | |
| 0x07 | Task in progress | no |
| | | |
| 0x08 | Invalid SNACK | no |
| | | |
| 0x09 | Target Transfer Tag Reject for this | no |
| | Initiator Task Tag | |
| | | |
| 0x0a | Long Operation Reject - Can't generate | yes |
| | Target Transfer Tag - out of resources | |
| | | |
| 0x0b | Negotiation Reset | no |
| | | |
| 0x0c | Waiting for Logout | no |
+------+-----------------------------------------+------------------+
Note 1: For iSCSI data PDUS, this is done only if target requests
retransmission with a recovery R2T. However, if this is the data
digest error on immediate data, no signal from the target is
necessary for PDU retransmission if desired so by the initiator.
All other values for reason are reserved.
In all the cases in which a pre-instantiated SCSI task is terminated
because of the reject, the target must issue a proper SCSI command
response with CHECK CONDITION as described in section 3.4.3. If the
error is detected while data from the initiator is still expected
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(the command PDU did not contain all the data and the target has not
received a Data-out PDU with the final bit Set) the target MUST wait
until it receives the Data-out PDU with the F bit set before sending
the Response PDU.
For additional usage semantics of Reject PDU, please see section 8.2.
3.17.2 DataSN
This field is valid only if the Reason code is "Invalid SNACK" and
the SNACK was a data SNACK. The DataSN is the last sequence number
that the target sent for the task.
3.17.3 Complete Header of Bad PDU
The target returns the header (not including digest) of the PDU in
error as the data of the response.
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3.18 NOP-Out
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|I| 0x00 |1| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| CmdSN |
+---------------+---------------+---------------+---------------+
28| ExpStatSN |
+---------------+---------------+---------------+---------------+
32/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment - Ping Data (optional) /
+/ /
+---------------+---------------+---------------+---------------+
A NOP-Out may be used by an initiator as a "ping command", to verify
that a connection/session is still active and all its components are
operational. The NOP-In response is the "ping echo".
A NOP-Out is also sent by an initiator in response to a NOP-In.
A NOP-Out may also be used to confirm a changed ExpStatSN if there is
no other PDU to carry it for a long time.
When used as a ping command, the Initiator Task Tag MUST be set to
valid value (not the reserved 0xffffffff).
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Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
value (not the reserved 0xffffffff), the initiator MUST respond with
a NOP-Out. In this case, the NOP-Out Target Transfer Tag MUST contain
a copy of NOP-In Target Task Tag.
When a target receives the NOP-Out with a valid Initiator Task Tag,
it MUST respond with a Nop-In Response (see NOP-In).
3.18.1 Initiator Task Tag
An initiator assigned identifier for the operation.
The NOP-Out must have the Initiator Task Tag set to a valid value
only if a response in the form of NOP-In is requested.
If the Initiator Task Tag contains 0xffffffff, the CmdSN field
contains as usual the next CmdSN but CmdSN is not advanced and the I
bit must be set to 1.
3.18.2 Target Transfer Tag
A target assigned identifier for the operation.
The NOP-Out MUST have the Target Transfer Tag set only if it is
issued in response to a NOP-In with a valid Target Transfer Tag, in
which case it copies the Target Transfer Tag from the NOP-In PDU.
When the Target Transfer Tag is set, the LUN field MUST be also
copied from the NOP-In.
3.18.3 Ping Data
Ping data is reflected in the NOP-In Response. Note that the length
of the reflected data is limited to MaxRecvPDULength of the initiator
when the response is received. The length of ping data is indicated
by the Data Segment Length. 0 is a valid value for the Data Segment
Length - and indicates the absence of ping data.
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3.19 NOP-In
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0|0|1| 0x20 |1| Reserved |
+---------------+---------------+---------------+---------------+
4| Reserved | DataSegmentLength |
+---------------+---------------+---------------+---------------+
8| LUN or Reserved |
+ +
12| |
+---------------+---------------+---------------+---------------+
16| Initiator Task Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
20| Target Transfer Tag or 0xffffffff |
+---------------+---------------+---------------+---------------+
24| StatSN |
+---------------+---------------+---------------+---------------+
28| ExpCmdSN |
+---------------+---------------+---------------+---------------+
32| MaxCmdSN |
+---------------+---------------+---------------+---------------+
36/ Reserved /
+/ /
+---------------+---------------+---------------+---------------+
48| Digests if any... |
+---------------+---------------+---------------+---------------+
/ DataSegment - Return Ping Data /
+/ /
+---------------+---------------+---------------+---------------+
NOP-In is either sent by a target as a response to a NOP-Out, as a
"ping" to an initiator, or a means to carry a changed ExpCmdSN and/or
MaxCmdSN if there is no other PDU to carry them for a long time.
When a target receives the NOP-Out with a valid Initiator Task Tag
(not the reserved value 0xffffffff), it MUST respond with a NOP-In
with the same Initiator Task Tag that was provided in the NOP-Out
Command. It MUST also duplicate up to first MaxRecvPDULength bytes of
the initiator provided Ping Data. For such a response, the Target
Transfer Tag MUST be 0xffffffff.
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3.19.1 Target Transfer Tag
A target assigned identifier for the operation.
If the target is responding to a NOP-Out, this is set to the reserved
value 0xffffffff.
If the target is sending a NOP-In as a Ping (intending to receive a
corresponding NOP-Out), this field is set to a valid value (not the
reserved 0xffffffff).
If the target is initiating a NOP-In without wanting to receive a
corresponding NOP-Out, this field MUST hold the reserved value of
0xffffffff.
Whenever the NOP-In is sent as a "ping" to an initiator (not as a
response to a NOP-Out) the StatSN field will contain as usual
the next StatSN but StatSN for this connection is not advanced.
3.19.2 LUN
A LUN MUST be set to a correct value when the Target Transfer Tag is
valid (not the reserved value 0xffffffff).
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4. SCSI Mode Parameters for iSCSI
There are no iSCSI specific mode pages.
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5. Login Phase
The login phase establishes an iSCSI session between initiator and
target. It sets the iSCSI protocol parameters, security parameters,
and authenticates the initiator and target to each other.
The login phase is implemented via login request and responses only.
The whole login phase is considered as a single task and has a single
Initiator Task Tag (similar to the linked SCSI commands).
The default MaxRecvPDULength is used during Login.
The login phase sequence of commands and responses proceeds as
follows:
- Login initial request
- Login partial response (optional)
- More Login requests and responses (optional)
- Login Final-Response (mandatory)
The initial login request of any connection MUST include the
InitiatorName key=value pair. The initial login request of the first
connection of a session MAY also include the SessionType key=value
pair. For any connection within a session whose type is not
"discovery" the first login request MUST also include the key=value
pair TargetName.
The Login Final-response accepts or rejects the Login Command.
The Login Phase MAY include a SecurityNegotiation stage and a
LoginOperationalNegotiation stage and MUST include at least one of
them, but the included stage MAY be empty.
The login requests and responses contain a field that indicates the
negotiation stage (SecurityNegotiation or
LoginOperationalNegotiation). If both stages are used the
SecurityNegotiation MUST precede the LoginOperationalNegotiation.
Some operational parameters can be negotiated outside login, through
text request/response.
Security MUST be completely negotiated within the Login Phase (using
underlying IPsec security is specified in chapter 10 and in [SEC-
IPS]).
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In some environments, a target or an initiator is not interested in
authenticating its counterpart. It is possible to bypass
authentication through the Login request and response.
The initiator and target MAY want to negotiate authentication
parameters. Once this negotiation is completed, the channel is
considered secure.
Most of the negotiation keys are allowed only in a specific stage -
the SecurityNegotiation keys appear all in Appendix A while the
LoginOperationalNegotiation keys appear in Appendix D.
Only a limited set of keys (marked as Declarative in Appendix D) may
be used in any of the 2 stages.
Any given Login request or response belongs to a specific stage and
this determines the negotiation keys allowed with the command or
response.
Stage transition is performed through a command exchange
(request/response) carrying the T bit and the same current stage
code. During this exchange, the next stage selected by the target
and MUST NOT exceed the value stated by the initiator. The initiator
can request a transition whenever it is ready but a target can
respond with a transition only after it is offered one by the
initiator.
In a negotiation sequence, the T bit settings in one pair of login
request-responses have no bearing on the T bit settings of the next
pair. An initiator having T bit set to 1 in one pair and being
answered with an T bit setting of 0 may issue the next request with T
bit set to 0.
Targets MUST NOT submit parameters requiring an additional initiator
login request in a login response with the T bit set to 1.
Stage transitions during login (including entering and exit) are
possible only as outlined in the following table:
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+-----------------------------------------------------------+
|From To -> | Security | Operational | FullFeature |
| | | | | |
| V | | | |
+-----------------------------------------------------------+
| (start) | yes | yes | no |
+-----------------------------------------------------------+
| Security | no | yes | yes |
+-----------------------------------------------------------+
| Operational | no | no | yes |
+-----------------------------------------------------------+
The Login Final-Response that accepts a Login Command can come only
as a response to a Login command with the T bit set to 1 and both the
command and response MUST have FullFeaturePhase in the NSG field.
Both initiator and target MUST NOT attempt to negotiate a parameter
more than once during any login stage. Attempting to do so MUST
result in the login (and connection) being terminated.
5.1 Login Phase Start
The login phase starts with a login request from the initiator to the
target. The initial login request includes:
-Protocol version supported by the initiator (currently 0x'02')
-Session and connection Ids
-The negotiation stage that the initiator is ready to enter
Optionally the login request may include:
-Security parameters OR
-iSCSI operational parameters AND/OR
-The next negotiation stage that the initiator is ready to
enter
The target can answer the login in the following ways:
-Login Response with Login Reject. This is an immediate
rejection from the target that causes the session to terminate.
The T bit of the response MUST be set to 1 and the CSG and NSG
are reserved.
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-Login Response with Login Accept as a final response (T bit
set to 1 and the NSG in both command and response are set to
FullFeaturePhase). The response includes the protocol version
supported by the target and the session ID and may include
iSCSI operational or security parameters (depending on the
current stage).
-Login Response with Login Accept as a partial response (NSG
not set to FullFeaturePhase in both request and response)
indicating the start of a negotiation sequence. The response
includes the protocol version supported by the target and
either security or iSCSI parameters (when no security mechanism
is chosen) supported by the target.
If the initiator decides to forego the SecurityNegotiation stage, it
issues the Login with the CSG set to LoginOperationalNegotiation and
the target may reply with a Login Response indicating that it is
unwilling to accept the connection without SecurityNegotiation and
terminate the connection.
If the initiator is willing to negotiate security but it is unwilling
to make the initial parameter offer and may accept a connection
without security it issues the Login with the T bit set to 1, the CSG
set to SecurityNegotiation and NSG set to
LoginOperationalNegotiation. If the target is also ready to forego
security the Login response is empty and has T bit set to 1, the CSG
set to SecurityNegotiation and NSG set to
LoginOperationalNegotiation.
An initiator that can operate without security and with all the
operational parameters taking the default values issues the Login
with the T bit set to 1, the CSG set to LoginOperationalNegotiation
and NSG set to FullFeaturePhase. If the target is also ready to
forego security and can finish its LoginOperationalNegotiation the
Login response has T bit set to 1, the CSG set to
LoginOperationalNegotiation and NSG set to FullFeaturePhase in the
next stage.
The iSCSI Names MUST be in text request format.
5.2 iSCSI Security and Integrity Negotiation
The security exchange sets the security mechanism and authenticates
the user and the target to each other. The exchange proceeds
according to the algorithms that were chosen in the negotiation phase
and is conducted by the login requests and responses key=value
parameters.
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The negotiable security mechanisms include the following modes:
-Initiator-target authentication - the host and the target
authenticate themselves to each other. A negotiable algorithm
such as SRP provides this feature.
Using IPsec for encryption or authentication may eliminate part
of the security negotiation at the iSCSI level but not
necessarily all.
An initiator directed negotiation proceeds as follows:
-The initiator sends a login request with an ordered list of
the options it supports for each subject (authentication
algorithm, iSCSI parameters and so on). The options are listed
in the initiator's order of preference. The initiator MAY also
send proprietary options.
-The target MUST reply with the first option in the list it
supports and is allowed for the specific initiator unless it
does not support any in which case it MUST answer with "reject"
(see also 2.2.4). The parameters are encoded in UTF8 as
key=value. For a list of security parameters see Appendix A.
-The initiator must be aware of the imminent completion of the
SecurityNegotiation stage and MUST set the T bit to 1 and the
NSG to what it would like the next stage to be. The target will
answer with a Login response with the T bit set to 1 and the
NSG to what it would like the next stage to be. The next stage
selected will be the one the target selected. If the next stage
is FullFeaturePhase, the target MUST respond with a Login
Response with the Session ID and the protocol version.
If the security negotiation fails at the target then the target MUST
send the appropriate Login Response PDU. If the security negotiation
fails at the initiator, the initiator SHALL close the connection.
It should be noted that the negotiation might also be directed by the
target if the initiator does support security but is not ready to
direct the negotiation (offer options).
5.3 Operational Parameter Negotiation During the Login Phase
Operational parameter negotiation during the login MAY be done:
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- starting with the first Login request if the initiator does
not offer any security/ integrity option
- starting immediately after the security negotiation if the
initiator and target perform such a negotiation
An operational parameter negotiation on a connection MUST NOT start
before the security negotiation if a security negotiation exists.
Operational parameter negotiation MAY involve several Login request-
response exchanges started and terminated by the initiator. The
initiator MUST indicate its intent to terminate the negotiation by
setting the T bit to 1; the target sets the T bit to 1 on the last
response.
If the target responds to a Login request with the T bit set to 1,
with a Login response with the T bit set to 0, the initiator must
keep sending the Login request (even empty) with the T bit set to 1
until it gets the Login Response with the T bit set to 1.
Whenever parameter action or acceptance is dependent on other
parameters, the dependent parameters MUST be sent after the
parameters they depend on. If they are sent within the same command
a response for a parameter might imply responses for others.
Session specific parameters can be specified only during the login
phase begun by a login command containing a null TSID (e.g., the
maximum number of connections that can be used for this session) -
the leading login phase.
Connection specific parameters, if any, can be specified during the
login phase begun by any login command. Thus, a session is
operational once it has at least one connection.
For a list of operational parameters, see Appendix D.
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6. Operational Parameter Negotiation Outside the Login Phase
Some operational parameters MAY be negotiated outside (after) the
login phase.
Parameter negotiation in full feature phase is done through Text
requests and responses. Operational parameter negotiation MAY involve
several text request-response exchanges always started and terminated
by the initiator and using the same Initiator Task Tag. The initiator
MUST indicate its intent to terminate the negotiation by setting the
F bit to 1; the target sets the F bit to 1 on the last response.
If the target responds to a text request with the F bit set to 1,
with a text response with the F bit set to 0, the initiator must keep
sending the text request (even empty) with the F bit set to 1 until
it gets the text response with the F bit set to 1. Responding to a
text request with the F bit set to 1 with an empty (no key=value
pairs) response with the F bit set to 0 is not an error but is
discouraged.
Targets MUST NOT submit parameters requiring an additional initiator
text request in a text response with the F bit set to 1.
In a negotiation sequence, the F bit settings in one pair of text
request-responses have no bearing on the F bit settings of the next
pair. An initiator having the F bit set to 1 in a request and being
answered with an F bit setting of 0 may have the next request issued
with the F bit set to 0.
Whenever parameter action or acceptance is dependent on other
parameters, the dependent parameters MUST be sent after the
parameters they depend on; if they are sent within the same command a
response for a parameter might imply responses for others.
Whenever the target responds with the F bit set to 0 it MUST set the
Target Transfer Tag to a value other than the default 0xffffffff.
An initiator MAY reset an operational parameter negotiation by
issuing a Text request with the Target Transfer Tag set to the value
0xffffffff after receiving a response with the Target Transfer Tag
set to a value other than 0xffffffff. A target may reset an
operational parameter negotiation by answering a Text request with a
Reject.
Both initiator and target MUST NOT attempt to negotiate a parameter
more than once during any negotiation sequence without an intervening
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reset. If detected by the target this MUST result in a Reject with a
reason of "protocol error". The initiator MUST reset the negotiation
as outlined above.
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7. State transitions
An iSCSI connection and an iSCSI session go through several well-
defined states from the time the connection and the session are
created to the time they are cleared.
An iSCSI connection is a transport connection that is used for
carrying out iSCSI activity. The connection state transitions are
described in two separate but dependent state diagrams for ease of
understanding. The first of these two is called a "standard
connection state diagram" and it describes the connection state
transitions when the iSCSI connection is not waiting for a cleanup by
way of an explicit or implicit Logout. The second diagram is called
a "connection cleanup state diagram" which describes the connection
state transitions while performing the iSCSI connection cleanup.
The "session state diagram" describes the state transitions an iSCSI
session would go through during its lifetime, and it depends on the
states of possibly multiple iSCSI connections that are participating
in the session.
7.1 Standard connection state diagrams
7.1.1 Standard connection state diagram for an initiator
Symbolic names for States:
S1: FREE
S2: XPT_WAIT
S4: IN_LOGIN
S5: LOGGED_IN (full-feature phase)
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
The state diagram follows.
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-------
+--------->/ S1 \<----+
T13| +->\ /<-+ \
| / ---+--- \ \
| / | T2 \ |
| T8 | |T1 | |
| | | / |T7
| | | / |
| | | / |
| | V / /
| | ------- / /
| | / S2 \ /
| | \ / /
| | ---+--- /
| | |T4 /
| | V /
| | ------- /
| | / S4 \
| | \ /
| | ---+--- T15
| | |T5 +------------------+
| | | /T16+------------+ |
| | | / -+-----+--+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V +----+ \ /
| | ---+-+- ----+-- | -------
| | / S5 \T9 / S6 \<+ ^
| +-----\ /--->\ / T14 |
| ------- --+----+------+T17
+---------------------------+
The following state transition table represents the above in a
tabular form. Each row represents the starting state for a given
transition, which after taking a transition marked in a table cell
would end in the state represented by the column of the cell (for
example, from state S1, the connection takes the T1 transition to
arrive at state S2). The fields marked "-" correspond to undefined
transitions.
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+-----+---+---+---+---+----+---+
|S1 |S2 |S4 |S5 |S6 |S7 |S8 |
---+-----+---+---+---+---+----+---+
S1| - |T1 | - | - | - | - | - |
---+-----+---+---+---+---+----+---+
S2|T2 |- |T4 | - | - | - | - |
---+-----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+-----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+-----+---+---+---+---+----+---+
S6|T13 |- |- | - |T14|- |T17|
---+-----+---+---+---+---+----+---+
S7|- |- |- | - |T10|T12 |T16|
---+-----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+-----+---+---+---+---+----+---+
7.1.2 Standard connection state diagram for a target
Symbolic names for States:
S1: FREE
S3: XPT_UP
S4: IN_LOGIN
S5: LOGGED_IN (full-feature phase)
S6: IN_LOGOUT
S7: LOGOUT_REQUESTED
S8: CLEANUP_WAIT
The state diagram follows.
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-------
+--------->/ S1 \<----+
T13| +->\ /<-+ \
| / ---+--- \ \
| / | T6 \ |
| T8 | |T3 | |
| | | / |T7
| | | / |
| | | / |
| | V / /
| | ------- / /
| | / S3 \ /
| | \ / /
| | ---+--- /
| | |T4 /
| | V /
| | ------- /
| | / S4 \
| | \ /
| | ---+--- T15
| | |T5 +------------------+
| | | /T16+------------+ |
| | | / -+-----+--+ | |
| | | / / S7 \ |T12| |
| | | / +->\ /<-+ V V
| | | / / -+----- -------
| | | / /T11 |T10 / S8 \
| | V / / V \ /
| | ---+-+- ------- -------
| | / S5 \T9 / S6 \ ^
| +-----\ /--->\ / |
| ------- --+----+------+T17
+---------------------------+
The following state transition table represents the above
diagram, following the conventions described for the initiator
diagram.
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+-----+---+---+---+---+----+---+
|S1 |S3 |S4 |S5 |S6 |S7 |S8 |
---+-----+---+---+---+---+----+---+
S1| - |T3 | - | - | - | - | - |
---+-----+---+---+---+---+----+---+
S3|T6 |- |T4 | - | - | - | - |
---+-----+---+---+---+---+----+---+
S4|T7 |- |- |T5 | - | - | - |
---+-----+---+---+---+---+----+---+
S5|T8 |- |- | - |T9 |T11 |T15|
---+-----+---+---+---+---+----+---+
S6|T13 |- |- | - |- |- |T17|
---+-----+---+---+---+---+----+---+
S7|- |- |- | - |T10|T12 |T16|
---+-----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+-----+---+---+---+---+----+---+
7.1.3 State descriptions for initiators and targets
State descriptions for the standard connection state diagram
-S1: FREE
-initiator: state on instantiation, or after successful
connection closure.
-target: state on instantiation, or after successful
connection closure.
-S2: XPT_WAIT
-initiator: waiting for a response to its transport
connection establishment request.
-target: illegal
-S3: XPT_UP
-initiator: illegal
-target: waiting for the Login process to commence.
-S4: IN_LOGIN
-initiator: waiting for the Login process to conclude,
possibly involving several PDU exchanges.
-target: waiting for the Login process to conclude, possibly
involving several PDU exchanges.
-S5: LOGGED_IN
-initiator: in full-feature phase, waiting for all internal,
iSCSI and transport events.
-target: in full-feature phase, waiting for all internal,
iSCSI and transport events.
-S6: IN_LOGOUT
-initiator: waiting for a Logout response.
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-target: waiting for an internal event signaling completion
of logout processing.
-S7: LOGOUT_REQUESTED
-initiator: waiting for an internal event signaling
readiness to proceed with Logout.
-target: waiting for the Logout process to start after
having requested a Logout via an Async Message.
-S8: CLEANUP_WAIT
-initiator: waiting for the context and/or resources to
initiate the cleanup processing for this CSM.
-target: waiting for the cleanup process to start for this
CSM.
7.1.4 State transition descriptions for initiators and targets
-T1:
-initiator: Transport connect request was made (ex: TCP SYN
sent).
-target: illegal
-T2:
-initiator: Transport connection request timed out, or
failed.
-target: illegal
-T3:
-initiator: illegal
-target: Received a valid transport connection request,
establishing the transport connection.
-T4:
-initiator: Transport connection established, prompting the
initiator to start the iSCSI Login.
-target: Initial iSCSI Login command was received.
-T5:
-initiator: The final iSCSI Login response with a status
class of zero was received.
-target: The final iSCSI Login command to conclude the Login
phase was received, prompting the target to send the final
iSCSI Login response with a status class of zero.
-T6:
-initiator: illegal
-target: Timed out waiting for an iSCSI Login, or transport
disconnect indication was received, or transport reset was
received. In all these cases, the connection is to be
closed.
-T7:
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-initiator: The final iSCSI Login response was received with
a non-zero status class, or Login timed out, or transport
disconnect indication was received, or transport reset was
received, prompting the connection to be closed.
-target: The final iSCSI Login command to conclude the Login
phase was received, prompting the target to send the final
iSCSI Login response with a non-zero status class, or Login
timed out, or transport disconnect indication was received,
or transport reset was received. In all these cases, the
connection is to be closed.
-T8:
-initiator: A disconnect indication was received after a
Logout response (success) was received on another connection
in response to a "close the session" Logout command, thus
closing this connection requiring no further cleanup.
-target: An internal event of sending a Logout response
(success) on another connection for a "close the session"
Logout command was received, thus prompting the target to
close this connection cleanly.
-T9, T10:
-initiator: An internal event indicating the readiness to
start the Logout process was received, prompting an iSCSI
Logout to be sent by the initiator.
-target: An iSCSI Logout command was received.
-T11, T12:
-initiator: Async PDU with iSCSI event "Request Logout" was
received.
-target: An internal event requiring decommissioning of the
connection is received, causing an Async PDU with iSCSI
event "Request Logout" to be sent.
-T13:
-initiator: An iSCSI Logout response (success) was received.
-target: An internal event indicating successful processing
of the Logout was received, prompting an iSCSI Logout
response (success) to be sent and the transport connection
to be closed.
-T14:
-initiator: Async PDU with iSCSI event "Request Logout" was
received again.
-target: illegal.
-T15, T16:
-initiator: One or more of the following events caused this
transition
-internal event indicating a transport connection timeout
was received prompting transport RESET or transport
connection closure,
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-a transport RESET,
-a transport disconnect indication.
-Async PDU with iSCSI event "Drop connection" (for this
CID),
-Async PDU with iSCSI event "Drop all connections".
-target: One or more of the following events caused this
transition
-internal event indicating a transport connection timeout
was received prompting transport RESET or transport
connection closure,
-a transport RESET,
-a transport disconnect indication,
-internal emergency cleanup event was received prompting
an Async PDU with iSCSI event "Drop connection" (for this
CID), or event "Drop all connections".
-T17:
-initiator: One or more of the following events caused this
transition
-Logout response (failure) was received,
-any of the events specified for T15 and T16.
-target: One or more of the following events caused this
transition
-internal event indicating a failure of the Logout
processing was received, prompting a Logout response
(failure) to be sent,
-any of the events specified for T15 and T16.
The CLEANUP_WAIT state (S8) implies that there are possibly iSCSI
tasks that have not reached conclusion and are still considered busy.
7.2 Connection cleanup state diagram for initiators and targets
Symbolic names for states:
R1: CLEANUP_WAIT (same as S8)
R2: IN_CLEANUP
R3: FREE (same as S1)
Whenever a connection state machine (say, CSM-C) enters the
CLEANUP_WAIT state (S8), it must go through the state transitions
additionally described in the connection cleanup state diagram either
a) using a separate full-feature phase connection (let us call it
CSM-E) in the LOGGED_IN state in the same session, or b) using a new
transport connection (let us call it CSM-I) in the FREE state that is
to be added to the same session. In the CSM-E case, an explicit
logout for the CID corresponding to CSM-C (either as a connection or
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session logout) needs to be performed to complete the cleanup. In
the CSM-I case, an implicit logout for the CID corresponding to CSM-C
needs to be performed by way of connection reinstatement (section
3.12.2) for that CID. In either case, the protocol exchanges on CSM-
E or CSM-I determine the state transitions for CSM-C. This cleanup
state diagram hence is applicable only to the instance of the
connection in cleanup, i.e. CSM-C. In the case of an implicit logout
for example, CSM-C reaches FREE (R3) at the time CSM-I reaches
LOGGED_IN. In the case of an explicit logout, CSM-C reaches FREE
(R3) when CSM-E receives a successful logout response while
continuing to be in the LOGGED_IN state.
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The following state diagram applies to both initiators and targets.
-------
/ R1 \
+--\ /<-+
/ ---+--- \
/ | \ M3
M1 | |M2 |
| | /
| | /
| | /
| V /
| ------- /
| / R2 \
| \ /
| -------
| |
| |M4
| |
| |
| |
| V
| -------
| / R3 \
+---->\ /
-------
The following state transition table represents the above diagram,
following the same conventions as in earlier sections.
+----+----+----+
|R1 |R2 |R3 |
-----+----+----+----+
R1 | - |M2 |M1 |
-----+----+----+----+
R2 |M3 | - |M4 |
-----+----+----+----+
R3 | - | - | - |
-----+----+----+----+
7.2.1 State descriptions for initiators and targets
-R1: CLEANUP_WAIT (Same as S8)
-initiator: waiting for the internal event to initiate the
cleanup processing for CSM-C.
-target: waiting for the cleanup process to start for CSM-C.
-R2: IN_CLEANUP
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-initiator: waiting for the connection cleanup process to
conclude for CSM-C.
-target: waiting for the connection cleanup process to
conclude for CSM-C.
-R3: FREE (Same as S1)
-initiator: end state for CSM-C.
-target: end state for CSM-C.
7.2.2 State transition descriptions for initiators and targets
-M1: One or more of the following events was received
-initiator:
-an internal event indicating connection state timeout,
-a successful Logout response was received on a different
connection for a "close the session" Logout.
-target:
-an internal event indicating connection state timeout,
-an internal event of sending a Logout response (success)
on a different connection for a "close the session"
Logout command.
-M2: An implicit /explicit logout process was initiated by the
initiator.
-In CSM-I usage:
-initiator: An internal event requesting the CID
reinstatement was received prompting a connection
reinstatement Login to be sent transitioning to state
IN_LOGIN.
-target: A connection reinstatement Login was received
while in state XPT_UP.
-In CSM-E usage:
-initiator: An internal event indicating that an explicit
logout was sent for this CID in state LOGGED_IN.
-target: An explicit logout was received for this CID in
state LOGGED_IN.
-M3: Logout failure detected
-In CSM-I usage:
-initiator: CSM-I failed to reach LOGGED_IN, instead
arrived into FREE.
-target: CSM-I failed to reach LOGGED_IN, instead arrived
into FREE.
-In CSM-E usage:
-initiator: CSM-E either moved out of LOGGED_IN, or
Logout timed out and/or aborted, or Logout response
(failure) was received.
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-target: CSM-E either moved out of LOGGED_IN, or Logout
timed out and/or aborted, or an internal event indicating
a failed Logout processing was received. A Logout
response (failure) was sent in the last case.
-M4: Successful implicit/explicit logout was performed.
- In CSM-I usage:
-initiator: CSM-I reached state LOGGED_IN.
-target: CSM-I reached state LOGGED_IN.
- In CSM-E usage:
-initiator: CSM-E stayed in LOGGED_IN, and received a
Logout response (success).
-target: CSM-E stayed in LOGGED_IN, and sent a Logout
response (success).
7.3 Session state diagram
Session continuation is the process by which the state of a pre-
existing session is continued to be in use by either connection
reinstatement (section 3.12.2), or by adding a connection with a new
CID. Either of these actions associates the new transport connection
with the pre-existing session state.
7.3.1 Session state diagram for an initiator
Symbolic Names for States:
Q1: FREE
Q3: LOGGED_IN
Q4: FAILED
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The state diagram follows.
-------
/ Q1 \
+------>\ /<-+
/ ---+--- |
/ | |N3
N6 | |N1 |
| | |
| N4 | |
| +--------+ | /
| | | | /
| | | | /
| | V V /
-+--+-- -----+-
/ Q4 \ N5 / Q3 \
\ /<---\ /
------- -------
State transition table:
+----+----+----+
|Q1 |Q3 |Q4 |
-----+----+----+----+
Q1 | - |N1 | - |
-----+----+----+----+
Q3 |N3 | - |N5 |
-----+----+----+----+
Q4 |N6 |N4 | - |
-----+----+----+----+
7.3.2 Session state diagram for a target
Symbolic Names for States:
Q1: FREE
Q2: ACTIVE
Q3: LOGGED_IN
Q4: FAILED
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The state diagram follows.
-------
/ Q1 \
+------>\ /<-+
/ ---+--- |
/ ^ | |N3
N6 | N9| V N1 |
| +------ |
| / Q2 \ |
| +-->\ / |
| N7 / +--+--- |
| / / | |
| / / | |
| + /N8 |N2 /
| | / | /
| | / | /
| | / V /
-+--+-V -----+-
/ Q4 \ N5 / Q3 \
\ /<---\ /
------- -------
State transition table:
+----+----+----+----+
|Q1 |Q2 |Q3 |Q4 |
-----+----+----+----+----+
Q1 | - |N1 | - | - |
-----+----+----+----+----+
Q2 |N9 | - |N2 |N8 |
-----+----+----+----+----+
Q3 |N3 | - | - |N5 |
-----+----+----+----+----+
Q4 |N6 |N7 | - | - |
-----+----+----+----+----+
7.3.3 State descriptions for initiators and targets
-Q1: FREE
-initiator: state on instantiation or after cleanup.
-target: state on instantiation or after cleanup.
-Q2: ACTIVE
-initiator: illegal
-target: at least one connection is XPT_UP, waiting for the
first connection to be LOGGED_IN.
-Q3: LOGGED_IN
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-initiator: waiting for all session events.
-target: waiting for all session events.
-Q4: FAILED
-initiator: waiting for session recovery or session
continuation.
-target: waiting for session recovery or session
continuation.
7.3.4 State transition descriptions for initiators and targets
-N1:
-initiator: At least one transport connection reached the
LOGGED_IN state.
-target: At least one transport connection was established
for the session.
-N2:
-initiator: illegal
-target: At least one transport connection reached the
LOGGED_IN state.
-N3:
-initiator: Graceful closing of the session was completed -
either via a "close the session" Logout, or last successful
"close the connection" Logout.
-target: Graceful closing of the session was completed -
either via a "close the session" Logout, or last successful
"close the connection" Logout.
-N4:
-initiator: A session continuation attempt has succeeded.
-target: illegal
-N5:
-initiator: Session failure occurred (all connections
reported CLEANUP_WAIT).
-target: Session failure occurred (all connections reported
CLEANUP_WAIT).
-N6:
-initiator: Session state timeout had happened, or an
implicit session logout by reuse of ISID with TSID=0 cleared
this session instance. This results in all associated
resources to be freed and the session state discarded.
-target: Session state timeout had happened, or an implicit
session logout by reuse of ISID with TSID=0 cleared this
session instance. This results in all associated resources
to be freed and the session state discarded.
-N7:
-initiator: illegal
-target: A session continuation attempt is initiated.
-N8:
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-initiator: illegal
-target: A session continuation attempt failed.
-N9:
-initiator: illegal
-target: Login attempt on the leading connection failed.
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8. iSCSI Error Handling and Recovery
For any outstanding SCSI command, it is assumed that iSCSI in
conjunction with SCSI at the initiator is able to keep enough
information to be able to rebuild the command PDU, and that outgoing
data is available (in host memory) for retransmission while the
command is outstanding. It is also assumed that at target, incoming
data (read data) MAY be kept for recovery or it can be re-read from a
device server.
It is further assumed that a target will keep the "status & sense"
for a command it has executed, if it supports status retransmission.
Many of the recovery details in an iSCSI implementation are a local
matter, beyond the scope of protocol standardization. However, some
external aspects of the processing must be standardized to ensure
interoperability. This section describes a general model for
recovery in support of interoperability, and the corresponding
appendix illustrates the required behavior in more detail. Compliant
implementations need not match implementation details of this model
as presented, but the external behavior of such implementations must
correspond to the externally observable characteristics of the
presented model.
8.1 Retry and Reassign in Recovery
This section summarizes two important and somewhat related iSCSI
protocol features used in error recovery.
8.1.1 Usage of Retry
By resending the same iSCSI command PDU in the absence of a command
acknowledgement or response ("retry"), an initiator attempts to
"plug" (what it thinks are) the discontinuities in CmdSN ordering on
the target end. These discontinuities may have been created because
of discarded command PDUs due to digest errors.
Note that retry MUST NOT be used for any reasons other than plugging
command sequence gaps. In particular, all PDU retransmission (for
data, or status) requests for a currently allegiant command in
progress must be conveyed to the target using only the SNACK
mechanism already described. This does not however constitute a
requirement on initiators to use SNACK.
If initiators as part of plugging command sequence gaps described
above inadvertently issue retries for allegiant commands already in
progress (i.e. targets did not see the discontinuities in CmdSN
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ordering), targets MUST silently issue the duplicate CmdSNs if the
CmdSN window had not advanced by then. Targets MUST support the
retry functionality described above.
When an iSCSI command is retried, the command PDU MUST carry the
original Initiator Task Tag and the original operational attributes
(ex. flags, function names, LUN, CDB etc.) as well as the original
CmdSN. The command being retried MUST be sent on the same connection
as the original command unless the original connection was already
successfully logged out.
8.1.2 Allegiance Reassignment
By issuing a "task reassign" task management command (section 3.5.1),
initiator signals its intent to continue an already active command
(but with no current connection allegiance) as part of connection
recovery. This means that a new connection allegiance is being
established for the command, associating it to the connection on
which the task management command is being issued.
In reassigning connection allegiance for a command, the targets
SHOULD continue the command from its current state, for example
taking advantage of ExpDataSN in the command PDU for read commands
(must be set to zero if there had been no data transfer). However,
targets MAY choose to send/receive the entire data on a reassignment
of connection allegiance, and it is not considered an error.
It is optional for targets to support the allegiance reassignment.
This capability is negotiated via the ErrorRecoveryLevel text key at
the login time. When a target does not support allegiance
reassignment, it MUST respond with a task management response code of
"Task failover not supported". If allegiance reassignment is
supported by the target but the task is still allegiant to a
different connection, target MUST respond with a task management
response code of "Task still allegiant".
8.2 Usage Of Reject PDU in Recovery
Targets MUST NOT implicitly terminate an active task by sending a
Reject PDU for any PDU exchanged during the life of the task. If the
target decides to terminate the task, a Response PDU (SCSI, Text,
Task etc.) must be returned by the target to conclude the task. If
the task had never been active before the Reject (i.e. the Reject is
on the command PDU), targets should not send any further responses
since the command itself is being discarded.
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The above rule means that the initiators can eventually expect a
response even on seeing Rejects, if the Reject is not for the command
itself. The non-command Rejects only have diagnostic value in
logging the errors, and they may be used for retransmission decisions
as well by the initiators.
It should also be noted that the CmdSN of the rejected PDU (if it
carried one) MUST NOT be considered received by the target (i.e. a
command sequence gap must be assumed for the CmdSN). This is true
even when the CmdSN can be reliably ascertained as in the case of a
data digest error on immediate data. However, when the DataSN of a
rejected data PDU can be ascertained, a target MUST advance ExpDataSN
for the current burst if a recovery R2T is being generated. Target
MAY advance its ExpDataSN if it does not attempt to recover the lost
data PDU.
8.3 Format Errors
Explicit violations of the PDU layout rules stated in this document
are format errors. This when detected, usually indicates a major
implementation flaw in one of the parties.
When a target or an initiator receives an iSCSI PDU with a format
error, it MUST terminate all transport connections in the session
either with a connection close or with a connection reset immediately
and escalate the format error to session recovery (section 8.11.4).
8.4 Digest Errors
The discussion of legal choices of handling digest errors below
excludes session recovery as an explicit option, but either party on
detecting a digest error may choose to escalate the error to session
recovery.
When a target receives any iSCSI PDU with a header digest error, it
MUST silently discard the PDU.
When a target receives any iSCSI PDU with a payload digest error, it
MUST answer with a Reject iSCSI PDU with a Reason-code of Data-
Digest-Error and discard the PDU.
- If the discarded PDU is a solicited or unsolicited iSCSI
data PDU (for immediate data in a command PDU, non-data PDU
rule below applies), target MUST do one of the following:
a) Request retransmission with a recovery R2T. [OR]
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b) Terminate the task with a response PDU with the reason
"protocol service CRC error" (section 3.4.3). If the
target chooses to implement this, it MUST wait to receive
all the data (signaled by a Data PDU with the final bit
set for all outstanding R2Ts) before sending the response
PDU. A task management command (like an abort task) from
the initiator during this wait may also conclude the task.
- No further action is necessary for targets if the discarded
PDU is a non-data PDU.
When an initiator receives any iSCSI PDU with a header digest error,
it MUST discard the PDU.
When an initiator receives any iSCSI PDU with a payload digest error,
it MUST discard the PDU.
- If the discarded PDU is an iSCSI data PDU, initiator MUST
do one of the following -
a) Request the desired data PDU through SNACK. In its turn,
the target MUST either reject the SNACK with a Reject PDU
with a reason-code of "Data-SNACK Reject" in which case
the target MUST terminate the command with an iSCSI reason
of "SNACK rejected", or resend the data PDU. [OR]
b) Abort the task and terminate the command with an error.
- If the discarded PDU is a response PDU, initiator MUST do
one of the following -
a) Request PDU retransmission with a status SNACK.
[OR]
b) Logout the connection for recovery and continue
the tasks on a different connection instance as
described in section 7.1. [OR]
c) Logout to close the connection (abort all the
commands associated with the connection)
- No further action is necessary for initiators if the
discarded PDU is an unsolicited PDU (ex. Async, Reject).
8.5 Sequence Errors
When an initiator receives an iSCSI R2T/data PDU with an out-of-order
R2TSN/DataSN or a SCSI response PDU with an ExpDataSN implying
missing data PDU(s), it means that the initiator must have hit a
header or payload digest error on one or more earlier R2T/data PDUs.
Initiator MUST address these implied digest errors as described in
section 8.4. When a target receives a data PDU with an out-of-order
DataSN, it means that the target must have hit a header or payload
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digest error on at least one of the earlier data PDUs. Target MUST
address these implied digest errors as described in section 8.4.
When an initiator receives an iSCSI status PDU with an out-of-order
StatSN implying missing responses, it MUST address the one or more
missing status PDUs as described in section 8.4. As a side effect of
receiving the missing responses, the initiator may discover missing
data PDUs. If the initiator wants to recover the missing data for a
command, it MUST NOT acknowledge the received responses starting from
the StatSN of the interested command, until it has completed
receiving all the data PDUs of the command.
When an initiator receives duplicate R2TSNs (due to proactive
retransmission of R2Ts by the target) or duplicate DataSNs (due to
proactive SNACKs by the initiator), it MUST discard the duplicates.
8.6 SCSI Timeouts
An iSCSI initiator MAY attempt to plug a command sequence gap on the
target end (in the absence of an acknowledgement of the command by
way of ExpCmdSN) before the ULP timeout by retrying the
unacknowledged command, as described in section 8.1.
On a ULP timeout for a command (that carried a CmdSN of n), the iSCSI
initiator MUST abort the command if it intends to continue the
session - either using the Abort Task task management function
request, or a "close the connection" Logout. In using an explicit
Abort, if the ExpCmdSN is still less than (n+1), the target may see
the abort request while missing the original command itself due to
one of the following reasons:
- the original command was dropped due to digest error, or
- the connection the original command sent on was successfully
logged out (on logout unacknowledged commands issued on the
connection being logged out are discarded)
If the abort request is received and the original command is missing,
targets MUST consider the original command with that RefCmdSN to be
received and issue a task management response with the response code
"Task specified in the Referenced Task Tag field was not in task set"
and any state referring to the aborted task (if any) at the initiator
can be discarded. If the original command exists, as with any abort
the initiator expects a concluding status (that will not be delivered
to SCSI) and the target MUST supply a status at abort time if it was
not delivered earlier. The task management response is issued after
the status.
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8.7 Negotiation failures
Text request and response sequences when used to set/negotiate
operational parameters constitute the negotiation/parameter setting.
A negotiation failure is considered one or more of the following:
- None of the choices or the stated value is acceptable to one
negotiating side.
- The text request timed out, and possibly aborted.
- The text request was answered with a reject.
The following two rules are to be used to address negotiation
failures.
- During Login, any failure in negotiation MUST be considered
as the login process failure and the login phase must be
terminated - and with it the connection. If the failure is
detected by the target, it must terminate the login with the
appropriate login response code.
- A failure in negotiation while in the full-feature phase MUST
terminate the entire negotiation sequence possibly consisting
of a series of text requests using the same Initiator Task Tag.
The operational parameters of the session or the connection
MUST continue to be the values agreed upon during an earlier
successful negotiation - i.e. any partial results of this
unsuccessful negotiation must be undone.
8.8 Protocol Errors
The authors recognize that mapping framed messages over a "stream"
connection, such as TCP, makes the proposed mechanisms vulnerable to
simple software framing errors. On the other hand, the introduction
of framing mechanisms to limit the effects of those errors may be
onerous for performance and bandwidth. Command Sequence Numbers and
the above mechanisms for connection drop and reestablishment help
handle this type of mapping errors.
All violations of iSCSI PDU exchange sequences specified in this
draft are also protocol errors. This category of errors can be
addressed only by fixing the implementations; iSCSI defines Reject
and response codes to enable this.
8.9 Connection Failures
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iSCSI can keep a session in operation if it is able to keep/establish
at least one TCP connection between the initiator and target in a
timely fashion. It is assumed that targets and/or initiators
recognize a failing connection by either transport level means (TCP),
a gap in the command or response stream that is not filled for a long
time, or by a failing iSCSI NOP-ping. The latter MAY be used
periodically by highly reliable implementations. Initiators and
targets MAY also use the keep-alive option on the TCP connection to
enable early link failure detection on otherwise idle links.
On connection failure, the initiator and target MUST do one of the
following:
a) Attempt connection recovery within the session (section 8.11.3)
[OR]
b) Logout the connection with the reason code "closes the
connection" (section 3.14.3) and re-issue missing commands, and
implicitly terminate all active commands. Note that this option
requires support for the within-connection recovery class
(section 8.11.2) [OR]
c) Perform session recovery (section 8.11.4).
Either side may choose to escalate to session recovery, and the other
side MUST give precedence to it. On a connection failure, a target
MUST terminate and/or discard all the active immediate commands
regardless of which of the above options is used - i.e. immediate
commands are not recoverable across connection failures.
8.10 Session Errors
If all the connections of a session fail and cannot be reestablished
in a short time or if initiators detect protocol errors repeatedly,
an initiator may choose to terminate a session and establish a new
session.
The initiator takes the following actions:
- It resets or closes all the transport connections.
- It terminates all outstanding requests with an appropriate
response before initiating a new session.
When the session timeout (0) happens on the target, it takes the
following actions:
- Resets or closes the TCP connections (closes the session).
- Aborts all Tasks in the task set for the corresponding
initiator.
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8.11 Recovery Classes
iSCSI enables the following classes of recovery (in the order of
increasing scope of affected iSCSI tasks):
- within a command (i.e., without requiring command restart).
- within a connection (i.e., without requiring the connection
to be rebuilt but perhaps requiring command restart).
- connection recovery (i.e., perhaps requiring connections to
be rebuilt and commands to be reissued).
- session recovery.
The recovery scenarios detailed in the rest of this section are
representative rather than exclusive. In every case, they detail the
lowest class recovery that MAY be attempted. The implementer is left
to decide under which circumstances to escalate to the next recovery
class and/or what recovery classes to implement. Both the iSCSI
target and initiator MAY escalate the error handling to an error
recovery class impacting larger number of iSCSI tasks in any of the
cases identified in the following discussion.
In all classes, the implementer has the choice of deferring errors to
the SCSI initiator (with an appropriate response code), in which case
the task, if any, has to be removed from the target and all the side-
effects (like ACA) have to be considered.
Usage of within-connection and within-command recovery classes MUST
NOT be attempted before the connection is in full feature phase.
8.11.1 Recovery Within-command
At the target, the following cases lend themselves to within-command
recovery:
- Lost data PDU - realized through one of the following:
a) a data digest error - to be dealt with as specified in
section 8.4, using the option of a recovery R2T.
b) a sequence reception timeout (no data or partial-data-and-no-
F-bit) - to be considered as an implicit sequence error and
dealt with as specified in section 8.5, using the option of a
recovery R2T.
c) a header digest error which manifests as a sequence reception
timeout, or a sequence error - to be dealt with as specified
in section 8.5, using the option of a recovery R2T.
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At the initiator, the following cases lend themselves to within-
command recovery:
Lost data PDU or lost R2T - realized through one of the
following:
a) a data digest error - to be dealt with as specified in
section 8.4, using the option of a SNACK.
b) a sequence reception timeout (no status) - to be dealt with
as specified in section 8.5, using the option of a SNACK.
c) a header digest error which manifests as a sequence reception
timeout, or a sequence error - to be dealt with as specified
in section 8.5, using the option of a SNACK.
Please note that an initiator SHOULD NOT originate a SNACK for an R2T
based on its internal timeouts (if any) to avoid a race with the
target which may already have a recovery R2T or a termination
response on its way. Recovery in this case is better left to the
target.
All the timeout values to be used by the initiator and target are
outside the scope of this document.
8.11.2 Recovery Within-connection
At the initiator, the following cases lend themselves to within-
connection recovery:
a) Requests not acknowledged for a long time. Requests are
acknowledged explicitly through ExpCmdSN or implicitly by
receiving data and/or status. The initiator MAY retry non-
acknowledged commands as specified in section 8.1.
b) Lost iSCSI numbered Response. It is recognized by either
identifying a data digest error on a Response PDU or a Data-
In PDU carrying the status, or receiving a Response PDU with
a higher StatSN than expected. In the first case, digest
error handling is done as specified in section 8.4 using the
option of a SNACK, and in the second case, sequence error
handling is done as specified in section 8.5, using the
option of a SNACK.
At the target, the following cases lend themselves to within-
connection recovery:
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a) Status/Response not acknowledged for a long time. The target
MAY issue a NOP-IN (with a valid Target Transfer Tag or
otherwise) that carries the next status sequence number it is
going to use in the StatSN field. This helps the initiator
detect any missing StatSN(s) and issue a SNACK for the
status.
Both the timeout values to be used by the initiator and target are
outside the scope of this document.
8.11.3 Connection Recovery
At an iSCSI initiator, the following cases lend themselves to
connection recovery:
a) TCP connection failure. The initiator MUST close the
connection following which it MUST either Logout the failed
connection, or Login with an implied Logout, and reassign
connection allegiance for all commands associated with the
failed connection on another connection (that MAY be a newly
established connection) using the "Task reassign" task
management function (section 3.5.1).
N.B. The logout function is mandatory, while a new connection
establishment is mandatory only if the failed connection was
the last or only connection in the session.
b) Receiving an Asynchronous Message indicating one or all
connections in a session had been dropped. The initiator
MUST handle it as a TCP connection failure for the
connection(s) referred to in the Message.
At an iSCSI target, the following cases lend themselves to connection
recovery:
a) TCP connection failure. The target MUST close the connection
and then, if more than one connection is available, the
target SHOULD send an Asynchronous Message indicating it has
dropped the connection. Following that, the target will wait
for the initiator to continue recovery.
8.11.4 Session Recovery
Session recovery is to be performed when all other recovery attempts
have failed. Very simple initiators and targets MAY perform session
recovery on all iSCSI errors and therefore place the burden of
recovery on the SCSI layer and above.
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Session recovery implies closing of all TCP connections, internally
aborting all executing and queued tasks for the given initiator at
the target, terminating all outstanding SCSI commands with an
appropriate SCSI service response at the initiator and restarting a
session on a new set of connection(s) (TCP connection establishment
and login on all new connections). It is to be noted that neither
Reserve-Release managed SCSI reservations ("Regular" reservations)
nor Persistent SCSI reservations are affected by session failures.
Regular SCSI means are to be used to handle these reservations when
the session is reconstructed (necessarily between the same SCSI ports
and so with the same nexus identifier).
8.12 Error Recovery Hierarchy
The error recovery classes and features described so far are
organized into a hierarchy for ease of understanding and to limit the
myriad of implementation possibilities. It is hoped that this would
significantly contribute to highly interoperable implementations.
The attributes of this hierarchy are:
a) Each level is a superset of the capabilities of the
previous level. For example, Level 1 support implies
supporting all capabilities of Level 0 and more.
b) As a corollary, supporting a higher error recovery
level means increased sophistication and possibly an
increase in resource requirement.
c) Supporting error recovery level "n" is advertised and
negotiated by each iSCSI entity by exchanging the text
key "ErrorRecoveryLevel=n". The lower of the two
exchanged values is the operational ErrorRecoveryLevel
for the session.
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The following picture represents the error recovery hierarchy.
+
/ \
/ 2 \ <-- Connection recovery
+-----+
/ 1 \ <-- Digest failure recovery
+---------+
/ 0 \ <-- Session failure recovery
+-------------+
The following table lists the error recovery capabilities expected of
implementations supporting each error recovery level.
+-------------------+--------------------------------------------+
|ErrorRecoveryLevel | Associated Error recovery capabilities |
+-------------------+--------------------------------------------+
| 0 | Session recovery class (8.11.4) |
+-------------------+--------------------------------------------+
| 1 | Digest failure recovery (Note below) |
+-------------------+--------------------------------------------+
| 2 | Connection recovery class (8.11.3) |
+-------------------+--------------------------------------------+
Note: Digest failure recovery is comprised of two recovery classes -
Within-Connection recovery class (8.11.2) and Within-Command recovery
class (8.11.1).
Supporting error recovery level "0" is mandatory, while the rest are
optional to implement. In implementation terms, the above striation
means that the following incremental sophistication with each level
is required.
+-------------------+---------------------------------------------+
|Level transition | Incremental requirement |
+-------------------+---------------------------------------------+
| 0->1 | PDU retransmissions on the same connection |
+-------------------+---------------------------------------------+
| 1->2 | Retransmission across connections and |
| | allegiance reassignment |
+-------------------+---------------------------------------------+
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9. Notes to Implementers
This section notes some of the performance and reliability
considerations of the iSCSI protocol. This protocol was designed to
allow efficient silicon and software implementations. The iSCSI tag
mechanism was designed to enable RDMA at the iSCSI level or lower.
The guiding assumption made throughout the design of this protocol
was that targets are resource constrained relative to initiators.
Implementers are also advised to consider the implementation
consequences of the iSCSI to SCSI mapping model as outlined in 2.5.3.
9.1 Multiple Network Adapters
The iSCSI protocol allows multiple connections, not all of which need
go over the same network adapter. If multiple network connections are
to be utilized with hardware support, the iSCSI protocol command-
data-status allegiance to one TCP connection insure that there is no
need to replicate information across network adapters or otherwise
require them to cooperate.
However, some task management commands may require some loose form of
cooperation or replication at least on the target.
9.1.1 Conservative reuse of ISIDs
Historically, the SCSI model (and implementations and applications
based on that model) has assumed that SCSI ports are static, physical
entities. Recent extensions to the SCSI model have taken advantage
of persistent worldwide unique names for these ports. In iSCSI
however, the SCSI initiator ports are the endpoints of dynamically
created sessions, so the presumption of "static and physical" does
not apply. In any case, the model clauses (particularly, 2.5.2)
provide for persistent, reusable names for iSCSI-type SCSI initiator
ports even though there need not be any physical entity bound to
those names.
To both minimize the disruption of legacy applications and to better
facilitate the SCSI features that rely on persistent names for SCSI
ports, iSCSI implementations should attempt to provide a stable
presentation of SCSI Initiator Ports (both to the upper OS-layers and
to the targets they connect to). This can be achieved in an
initiator implementation by conservatively reusing ISIDs. In other
words, the same ISID should be used in the Login process to multiple
target portal groups (of the same iSCSI Target or different iSCSI
Targets). Note that the ISID RULE (2.5.3) only prohibits reuse to
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the same target portal group. It also does not "preclude" reuse to
other target portal groups.
The principle of conservative reuse "encourages" reuse to other
target portal groups. When a SCSI target device sees the same
(InitiatorName, ISID) pair in different sessions to different target
portal groups, it can identify the underlying SCSI Initiator Port on
each session as the same SCSI port (in effect, it can recognize
multiple paths from the same source).
9.1.2 iSCSI Name and ISID/TSID use
The designers of the iSCSI protocol envision there should be one
iSCSI Initiator Node Name per operating system image on a machine.
This enables SAN resource configuration and authentication schemes
based on a system's identity. This supports the notion that it
should be possible to assign access to storage resources based on
"initiator device" identity.
When there are multiple hardware or software components that are
coordinated as a single iSCSI Node, there must be some (logical)
entity representing the iSCSI Node that makes available the iSCSI
Node Name to all components involved in session creation and login.
Similarly, this entity representing the iSCSI Node must be able to
coordinate session identifier resources (ISID for initiators and TSID
for targets) to enforce both the ISID and TSID RULES (see 2.5.3).
For targets, because of the closed environment, implementation of
this entity should be straightforward. However, vendors of iSCSI
hardware (e.g., NICs or HBAs) intended for use in targets must
provide mechanisms for configuration of iSCSI Node Name and for
configuration and/or coordination of TSIDs across the portal groups
instantiated by multiple instances of these components within a
target. One mechanism is to allow for static or dynamic partitioning
of the TSID namespace among the portal groups. Such a partitioning
allows each portal group to act independently of other portal groups
when assigning TSIDs and facilitates enforcement of the TSID RULE
(see 2.5.3).
For initiators, in the long term, it is expected that operating
system vendors will take on the role of this entity and provide
standard APIs that can inform components of their iSCSI Node Name and
can configure and/or coordinate ISID allocation, use and reuse.
Recognizing that such initiator APIs are not available today, other
implementations of the role of this entity are possible.
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For example, a human may instantiate the (common) Node name as part
of the installation process of each iSCSI component involved in
session creation and login. This may be done either by pointing the
component to a vendor-specific location for this datum or to a
system-wide location. The structure of the ISID namespace (see
3.12.6 and [NDT]) facilitates implementation of the ISID coordination
by allowing each component vendor to independently (of other vendor's
components) coordinate allocation, use and reuse of its own partition
of the ISID namespace in a vendor-specific manner. Note that
partitioning of the ISID namespace within initiator portal groups
managed by that vendor allows each such initiator portal group to act
independently of all other portal groups when selecting an ISID for a
login; this facilitates enforcement of the ISID RULE (see 2.5.3) at
the initiator.
A vendor of iSCSI hardware (e.g., NICs or HBAs) intended for use in
initiators must allow, in addition to a mechanism for configuring the
iSCSI Node Name, for a mechanism to configure and/or coordinate ISIDs
for all sessions managed by multiple instances of that hardware
within a given iSCSI Node. Such configuration might be either
permanently pre-assigned at the factory (in a necessarily globally
unique way), statically assigned (e.g., partitioned across all the
NICs at initialization in a locally unique way) or dynamically
assigned (e.g., on-line allocator, also in a locally unique way). In
the latter two cases, the configuration may be via public APIs
(perhaps driven by an independent vendor's SW, e.g., the OS vendor)
or via private APIs driven by the vendor's own SW.
9.2 Autosense and Auto Contingent Allegiance (ACA)
Autosense refers to the automatic return of sense data to the
initiator in case a command did not complete successfully. iSCSI
mandates support for autosense.
ACA helps preserve ordered command execution in presence of errors.
As iSCSI can have many commands in-flight between initiator and
target iSCSI mandates support for ACA.
9.3 Command retry and cleaning old command instances
In order to avoid having old instances of commands that have been
retried appear in a valid command window after a command sequence
number wrap around the protocol requires that on every connection on
which a retry has been issued a non-immediate command be issued and
acknowledged within a 2**31-1 commands interval since the retry was
issued. This requirement can be fulfilled by an implementation in
several ways.
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The simplest technique to use is sending a (non-retry) non-immediate
SCSI command (or a NOP if no SCSI command is available for a while)
after every command retry on the connection the retry was attempted
on. As errors are deemed rare events, this technique is probably the
most effective, as it does not involve additional checks at the
initiator when issuing commands.
9.4 Task Management Commands and Immediate Delivery
When immediate delivery is requested, a task management command may
reach the target and be executed before all of the tasks it was meant
to act upon have been delivered or even reached the target.
It is assumed that, while pending delivery from iSCSI to SCSI at the
target, commands are kept in an iSCSI queue at both the initiator and
the target and that the target queue contains both commands and
"holes" (placeholders for commands not received yet).
The following general mechanism can be used to achieve the effect of
ordered delivery for task management commands while enabling the
"urgent" delivery that some of them imply and immediate execution of
the task management commands. The mechanism manages discarding
commands while they are in the iSCSI layer at the target and prevents
these discarded commands from being delivered to the target's SCSI
layer. The initiator must keep a record of these commands to
determine which will not receive a response. The target does not
generate a response to a command that is aborted while in the iSCSI
layer. The "barrier list" described in the following sections is a
list containing information relating to all task management commands
marked for immediate delivery.
At the Initiator when a relevant task management command marked
for immediate delivery is issued:
a) if ExpCmdSN is equal to CmdSN (there are no commands in
the queue) skip to step c;
b) mark all pending commands with a CmdSN field between the
current ExpCmdSN and the current CmdSN as candidates for
cleanup and retain CmdSN of the task management command in a
"barrier list";
c) send the task management command for immediate delivery
to the target.
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Note: for clarity, the barrier list contains "items" and the
command queue contains "entries"
At initiator when updating ExpCmdSN:
a) if the "barrier list" is empty or ExpCmdSN is less than
the CmdSN of the oldest item in the barrier list then
skip to step d;
b) remove the oldest barrier list item, and remove and
silently discard all entries marked for cleanup having a
CmdSN field less than ExpCmdSN;
c) go to step a;
d) release all queued entries between the old and new
ExpCmdSN from the queue. Note: Any entries that had been
marked as a candidate for cleanup have now been delivered
by the target to its SCSI layer. The SCSI layer will
have to determine if they are to be aborted.
At the target when receiving a relevant task management command
for immediate delivery:
a) if ExpCmdSN is equal to CmdSN skip to step c;
b) mark all pending entries (commands received and
placeholders) with a CmdSN field between ExpCmdSN and the
current CmdSN as candidates for cleanup and retain CmdSN in
a "barrier list" including the referenced LUN (or an ALL
marker);
c) send the task management command to SCSI for immediate
execution.
At target when updating ExpCmdSN (releasing ordered commands to
SCSI):
a) if the "barrier list" is empty or ExpCmdSN is less than
the oldest item in the barrier list then skip to step d;
b) remove the oldest barrier list item and evaluate all
queued entries that have a CmdSN field less than
ExpCmdSN, removing and silently discarding each queued
command that meets the criteria for cleanup candidacy (as
specified by the task management function);
c) go to step a;
d) release all queued entries between the old and new
ExpCmdSN from the queue.
Note that this scheme will withstand connection recovery.
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The following table details the candidates for cleanup:
+------------------+------------------------------------------+
| Function | Candidacy Selection |
+------------------+------------------------------------------+
| Abort Task Set | All tasks associated with the specified |
| | LUN and initiator. |
+------------------+------------------------------------------+
| Clear Task Set | All tasks associated with the specified |
| | LUN and initiator. For all other |
| | initiators all tasks at LUN with no |
| | regard to order. |
+------------------+------------------------------------------+
9.5 Synch and steering layer and performance
Although a synch and steering layer is optional, an initiator/target
without synch and steering working against a target/initiator
demanding synch and steering may experience performance degradation
caused by packet reordering and loss. Providing a synch and steering
mechanism is recommended for all high-speed implementations.
9.6 Unsolicited data and performance
Unsolicited data on write are meant to reduce the effect of latency
on throughput (no R2T is needed to start sending data). In addition,
immediate data are meant to reduce the protocol overhead (both
bandwidth and execution time).
However, negotiating an amount of unsolicited data for writes and
sending less than the negotiated amount when the total data amount to
be sent by a command is larger than the negotiated amount may
negatively impact performance and may not be supported by all the
targets.
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10. Security Considerations
Historically, native storage systems have not had to consider
security because their environments offered minimal security risks.
That is, these environments consisted of storage devices either
directly attached to hosts or connected via a subnet distinctly
separate from the communications network. The use of storage
protocols, such as SCSI, over IP networks requires that security
concerns be addressed. iSCSI implementations MUST provide means of
protection against active attacks (pretending as another identity,
message insertion, deletion, modification and replaying) and passive
attacks (eavesdropping, gaining advantage by analyzing the data sent
over the line).
Although technically possible, iSCSI SHOULD NOT be configured without
security. iSCSI without security should be confined, in extreme
cases, to closed environments without any security risk.
The following section describes the security mechanisms to be
provided by an iSCSI implementation.
10.1 iSCSI Security mechanisms
The entities involved in iSCSI security are the initiator, target,
and the IP communication end points. iSCSI scenarios where multiple
initiators or targets share a single communication end point are
expected. To accommodate such scenarios iSCSI uses two separate
security mechanisms: in-band authentication between the initiator and
target at the iSCSI connection level (carried out by exchange of
iSCSI Login PDUs), and packet protection (integrity, authentication
and confidentiality) by IPsec at the IP level. The two security
mechanisms complement each other: the in-band authentication provides
end-to-end trust (at login time) between the iSCSI initiator and
target, while IPsec provides a secure channel between the IP
communication end points.
Further details on typical iSCSI scenarios and the relation between
the initiators, targets and the communication end points can be found
in [SEC-IPS].
10.2 In-band Initiator-Target Authentication
With this mechanism, the target authenticates the initiator and the
initiator optionally authenticates the target. The authentication is
performed on every new iSCSI connection, by an exchange of iSCSI
Login PDUs and using a negotiated authentication method.
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The authentication method cannot assume an underlying IPsec
protection, since IPsec is optional to use. An attacker should gain
as minimal advantage as possible by inspecting the authentication
phase PDUs. In this spirit, a method using clear text (or equivalent)
passwords is not acceptable; on the other hand, identity protection
is not strictly required.
This mechanism protects against an unauthorized login to storage
resources by using a false identity (spoofing). Once the
authentication phase is completed, if underlying IPsec is not used -
all PDUs are sent and received in clear. This mechanism alone
(without underlying IPsec) should only be used when there is no risk
of eavesdropping, message insertion, deletion, modification and
replaying.
The CHAP authentication method (specified in Appendix A) is
vulnerable to off-line dictionary attack. CHAP SHOULD NOT be used
without additional protection in environments where this attack is a
concern. Underlying IPsec, encryption provides protection against
this attack.
The strength of the SRP authentication method (specified in Appendix
A) is dependent on the characteristics of the group being used (i.e.,
the prime modulus N and generator g). As described in [RFC2945], N is
required to be a Sophie-German prime (of the form N = 2q + 1, where q
is also prime) and the generator g is a primitive root of GF(n). For
use in iSCSI authentication, the prime modulus N MUST be at least 768
bits.
Upon receiving N and g from the Target, the Initiator MUST verify
that they satisfy the above requirements (and abort the connection
otherwise). This verification MAY start by trying to match them with
a well-known group that satisfies the above requirements.
SRP well-known groups are given in [SEC-IPS].
Compliant iSCSI initiators and targets MUST implement at least the
SRP authentication method [RFC2945] (see Appendix A).
10.3 IPsec
The IPsec mechanism is used by iSCSI for packet protection
(cryptographic integrity, authentication and confidentiality) at the
IP level between the iSCSI communicating end points. The following
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sections describe the IPsec protocols that must be implemented for
data integrity and authentication, confidentiality and key
management.
Detailed considerations and recommendations on using IPsec for iSCSI
are given in [SEC-IPS].
10.3.1 Data Integrity and Authentication
Data authentication and integrity is provided by usage of a keyed
Message Authentication Code in every sent packet. This protects
against message insertion, deletion and modification. Protection
against message replay is realized by using a sequence counter.
An iSCSI compliant initiator or target MUST provide data integrity
and authentication by implementing IPsec [RFC2401] with ESP in tunnel
mode [RFC2406] with the following iSCSI specific requirements:
- HMAC-SHA1 MUST be implemented [RFC2404].
- AES CBC MAC with XCBC extensions SHOULD be implemented [AES],
[XCBC] (NOTE - this is still subject to the IETF-IPsec WG's
standardization plans).
The ESP anti-replay service MUST also be implemented.
At the high speeds iSCSI is expected to operate, a single IPsec SA
could rapidly cycle through the 32-bit IPsec sequence number space.
In view of this, iSCSI implementation operating at speeds of 1 Gbps
or less MAY implement the IPsec sequence number extension [SEQ-EXT].
Implementation operating at speeds of 10 Gbps or faster SHOULD
implement the sequence number extension.
10.3.2 Confidentiality
Confidentiality is provided by encrypting the data in every packet.
Confidentiality SHOULD always be used together with data integrity
and authentication to provide comprehensive protection against
eavesdropping, message insertion, deletion, modification and
replaying.
An iSCSI compliant initiator or target MUST provide confidentiality
by implementing IPsec [RFC2401] with ESP in tunnel mode [RFC2406]
with the following iSCSI specific requirements:
- 3DES in CBC mode MUST be implemented [RFC2451].
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- AES in Counter mode SHOULD be implemented [AESCTR] (NOTE - this is
still subject to the IPsec WG's standardization plans).
DES in CBC mode SHOULD NOT be used due to its inherent weakness.
The NULL encryption algorithm MUST also be implemented.
10.3.3 Security Associations and Key Management
A compliant iSCSI implementation MUST meet the key management
requirements of the IPsec protocol suite. Authentication, security
association negotiation and key management MUST be provided by
implementing IKE [RFC2409] using the IPsec DOI [RFC2407] with the
following iSCSI specific requirements:
- Peer authentication using a pre-shared key MUST be supported,
and certificate-based peer authentication using digital
signatures MAY be supported. Peer authentication using the
public key encryption methods outlined in IKE sections 5.2 and
5.3[7] SHOULD NOT be used.
- When digital signatures are used to achieve authentication,
an IKE negotiator SHOULD use IKE Certificate Request Payload(s)
to specify the certificate authority. IKE negotiators SHOULD
check the pertinent Certificate Revocation List (CRL) before
accepting a PKI certificate for use in IKE authentication
procedures.
- Both IKE Main Mode and Aggressive Mode MUST be supported. IKE
main mode with pre-shared key authentication method SHOULD NOT
be used when either the initiator or the target uses
dynamically assigned IP addresses (while pre-shared keys in
many cases offer good security, situations where dynamically
assigned addresses are used force the use of a group pre-shared
key which creates vulnerability to man-in-the-middle attack).
- In the IKE Phase 2 Quick Mode exchanges for creating the
Phase 2 SA, the Identity Payload fields MUST be present, and
MUST carry individual addresses (MUST NOT use the IP Subnet or
IP Address Range formats).
Manual keying MUST NOT be used since it does not provide the
necessary re-keying support.
When IPsec is used, each iSCSI TCP connection within an iSCSI
session MUST be protected by a separate IKE Phase 2 SA.
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11. IANA Considerations
The temporary (user) well-known port number for iSCSI connections
assigned by IANA is 3260.
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12. References and Bibliography
[AC] A Detailed Proposal for Access Control, Jim Hafner,
T10/99-245
[AES] J. Daemen, V. Rijman, "AES Proposal: Rijndael" NIST
AES proposal,
http://csrc.nist.gov/encryption/aes/rijndael/Rijndael.pdf ,
September 1999.
[XCBC] J. Black, P. Rogaway "Comments to NIST concerning AES
Modes of Operations: A Suggestion for Handling Arbitrary-Length
Messages with the CBC MAC",
http://csrc.nist.gov/encryption/modes/proposedmodes/xcbc-
mac/xcbc-mac-spec.pdf , NIST proposed modes of operations, August
2001.
[AESCTR] J. Etienne, "The counter-mode and its use with ESP",
Internet draft (work in progress), draft-etienne-ipsec-esp-ctr-
mode-00.txt, May 2001.
[BOOT] P. Sarkar & team draft-ietf-ips-iscsi-boot-01.txt
[CAM] ANSI X3.232-199X, Common Access Method-3 (Cam)
[Castagnoli93] G. Castagnoli, S. Braeuer and M. Herrman
"Optimization of Cyclic Redundancy-Check Codes with 24 and 32
Parity Bits", IEEE Transact. on Communications, Vol. 41, No. 6,
June 1993
[CRC] ISO 3309, High-Level Data Link Control (CRC 32)
[NDT] M. Bakke & team, draft-ietf-ips-iscsi-name-disc-03.txt
[RFC790] J. Postel, ASSIGNED NUMBERS, September 1981
[RFC791] INTERNET PROTOCOL, DARPA INTERNET PROGRAM PROTOCOL
SPECIFICATION, September 1981
[RFC793] TRANSMISSION CONTROL PROTOCOL, DARPA INTERNET PROGRAM
PROTOCOL SPECIFICATION, September 1981
[RFC1035] P. Mockapetris, DOMAIN NAMES - IMPLEMENTATION AND
SPECIFICATION, November 1987
[RFC1122] Requirements for Internet Hosts-Communication Layer
RFC1122, R. Braden (editor)
[RFC1510] J. Kohl, C. Neuman, "The Kerberos Network
Authentication Service (V5)", September 1993.
[RFC1766] H. Alvestrand, "Tags for the Identification of
Languages", March 1995.
[RFC1964] J. Linn, "The Kerberos Version 5 GSS-API Mechanism",
June 1996.
[RFC1982] Elz, R., Bush, R., "Serial Number Arithmetic", RFC
1982, August 1996.
[RFC1994] "W. Simpson, PPP Challenge Handshake Authentication
Protocol (CHAP)", RFC 1994, August 1996.
[RFC2025] C. Adams, "The Simple Public-Key GSS-API Mechanism
(SPKM)", October 1996.
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iSCSI 19-Nov-01
[RFC2026] Bradner, S., "The Internet Standards Process --
Revision 3", RFC 2026, October 1996.
[RFC2044] Yergeau, F., "UTF-8, a Transformation Format of
Unicode and ISO 10646", October 1996.
[RFC2045] N. Borenstein, N. Freed, "MIME (Multipurpose Internet
Mail Extensions) Part One: Mechanisms for Specifying and
Describing the Format of Internet Message Bodies", November
1996
[RFC2119] Bradner, S. "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2234] D. Crocker, P. Overell Augmented BNF for Syntax
Specifications: ABNF
[RFC2246] T. Dierks, C. Allen, " The TLS Protocol Version 1.0
[RFC2373] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 2373, July 1998.
[RFC2434] T. Narten, and H. Avestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs.", RFC2434, October
1998.
[RFC2401] S. Kent, R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998
[RFC2404] C. Madson, R. Glenn, "The Use of HMAC-SHA-1-96 within
ESP and AH", RFC 2404, November 1998.
[RFC2406] S. Kent, R. Atkinson, "IP Encapsulating Security
Payload (ESP)", RFC 2406, November 1998
[RFC2407] D. Piper, "The Internet IP Security Domain of
Interpretation of ISAKMP", RFC 2407, November 1998
[RFC2409] D. Harkins, D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998
[RFC2451] R. Pereira, R. Adams " The ESP CBC-Mode Cipher
Algorithms"
[RFC2732] R. Hinden, B. Carpenter, L. Masinter, "Format for
Literal IPv6 Addresses in URL's", RFC 2732, December 1999.
[RFC2945], Wu, T., "The SRP Authentication and Key Exchange
System", September 2000.
[SAM] ANSI X3.270-1998, SCSI-3 Architecture Model (SAM)
[SAM2] T10/1157D, SCSI Architecture Model - 2 (SAM-2)
[SBC] NCITS.306-1998, SCSI-3 Block Commands (SBC)
[Schneier] B. Schneier, "Applied Cryptography: Protocols,
Algorithms, and Source Code in C", 2nd edition, John Wiley &
Sons, New York, NY, 1996.
[SEC-IPS] B. Aboba & team "Securing iSCSI, iFCP and FCIP" -
draft-ietf-ips-security-03.txt
[SEQ-EXT] Steve Kent, IPsec sequence number extension
proposal, IETF 50.
[SPC] NCITS.351:200, SCSI-3 Primary Commands (SPC)
[SPC3]T10/1416-D, SCSI-3 Primary Commands (SPC)
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iSCSI 19-Nov-01
[XCBC] J. Black, P. Rogaway "Comments to NIST concerning AES
Modes of Operations: A Suggestion for Handling Arbitrary-Length
Messages with the CBC MAC",
http://csrc.nist.gov/encryption/modes/proposedmodes/xcbc-
mac/xcbc-mac-spec.pdf , NIST proposed modes of operations, August
2001.
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13. Author's Addresses
Julian Satran
IBM, Haifa Research Lab
MATAM - Advanced Technology Center
Haifa 31905, Israel
Phone +972.4.829.6264
E-mail: Julian_Satran@vnet.ibm.com
Kalman Meth
IBM, Haifa Research Lab
MATAM - Advanced Technology Center
Haifa 31905, Israel
Phone +972.4.829.6341
E-mail: meth@il.ibm.com
Ofer Biran
IBM, Haifa Research Lab
MATAM - Advanced Technology Center
Haifa 31905, Israel
Phone +972.4.829.6253
E-mail: biran@il.ibm.com
Daniel F. Smith
IBM Almaden Research Center
650 Harry Road
San Jose, CA 95120-6099, USA
Phone: +1.408.927.2072
E-mail: dfsmith@almaden.ibm.com
Jim Hafner
IBM Almaden Research Center
650 Harry Road
San Jose, CA 95120
Phone: +1.408.927.1892
E-mail: hafner@almaden.ibm.com
Costa Sapuntzakis
Cisco Systems, Inc.
170 W. Tasman Drive
San Jose, CA 95134, USA
Phone: +1.408.525.5497
E-mail: csapuntz@cisco.com
Mark Bakke
Cisco Systems, Inc.
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iSCSI 19-Nov-01
6450 Wedgwood Road
Maple Grove, MN
USA 55311
Phone: +1.763.398.1000
E-Mail: mbakke@cisco.com
Randy Haagens
Hewlett-Packard Company
8000 Foothills Blvd.
Roseville, CA 95747-5668, USA
Phone: +1.916.785.4578
E-mail: Randy_Haagens@hp.com
Matt Wakeley (current address)
Sierra Logic, Inc.
Phone: +1.916.772.1234 ext 116
E-mail: matt_wakeley@sierralogic.com
Efri Zeidner
SANgate Systems, Inc.
41 Hameyasdim Street
P.O.B. 1486
Even-Yehuda, Israel 40500
Phone: +972.9.891.9555
E-mail: efri@sangate.com
Paul von Stamwitz (current address)
TrueSAN Networks, Inc.
Phone: +1.408.869.4219
E-mail: pvonstamwitz@truesan.com
Luciano Dalle Ore
Quantum Corp.
Phone: +1.408.232.6524
E-mail: ldalleore@snapserver.com
Mallikarjun Chadalapaka
Hewlett-Packard Company
8000 Foothills Blvd.
Roseville, CA 95747-5668, USA
Phone: +1.916.785.5621
E-mail: cbm@rose.hp.com
Yaron Klein
SANRAD
24 Raul Valenberg St.
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Tel-Aviv, 69719 Israel
Phone: +972.3.765.9998
E-mail: klein@sanrad.com
Comments may be sent to Julian Satran
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Appendix A. iSCSI Security and Integrity
01 Security Keys and Values
The security negotiation main item is the authentication method
(AuthMethod).
The following table details authentication methods:
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+------------------------------------------------------------+
| Name | Description |
+------------------------------------------------------------+
| KRB5 | Kerberos V5 |
+------------------------------------------------------------+
| SPKM1 | Simple Public-Key GSS-API Mechanism |
+------------------------------------------------------------+
| SPKM2 | Simple Public-Key GSS-API Mechanism |
+------------------------------------------------------------+
| SRP | Secure Remote Password |
+------------------------------------------------------------+
| CHAP | Challenge Handshake Authentication Protocol|
+------------------------------------------------------------+
| none | No authentication |
+------------------------------------------------------------+
KRB5 is defined in [RFC1510], SPKM1, SPKM2 are defined in
[RFC2025], SRP is defined in [RFC2945] and CHAP is defined in
[RFC1994].
Initiator and target MUST implement SRP.
02 Authentication
The authentication exchange authenticates the initiator to the
target, and optionally the target to the initiator. Authentication
is not mandatory and is distinct from the data integrity exchange.
The authentication methods to be used are KRB5, SPKM1, SPKM2, SRP,
CHAP, or proprietary.
For KRB5 (Kerberos V5) [RFC1510], the initiator MUST use:
KRB_AP_REQ=<KRB_AP_REQ>
where KRB_AP_REQ is the client message as defined in [RFC1510].
If the initiator authentication fails, the target MUST answer with a
Login reject with the "Authentication Failure" status. Otherwise, if
the initiator has selected the mutual authentication option (by
setting MUTUAL-REQUIRED in the ap-options field of the KRB_AP_REQ),
the target MUST reply with:
KRB_AP_REP=<KRB_AP_REP>
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where KRB_AP_REP is the server's response message as defined in
[RFC1510].
If mutual authentication was selected and target authentication
fails, the initiator MUST close the connection.
KRB_AP_REQ, KRB_AP_REP are binary items and their binary length (not
the encoded length) MUST not exceed 4096 bytes.
For SPKM1,SPKM2 [RFC2025], the initiator MUST use:
SPKM_REQ=<SPKM-REQ>
where SPKM-REQ is the first initiator token as defined in [RFC2025].
[RFC2025] defines situations where each side may send an error token
which may cause the peer to re-generate and resend his last token.
This scheme is followed in iSCSI, and the error token syntax is:
SPKM_ERROR=<SPKM-ERROR>
However, SPKM-DEL tokens that are defined by [RFC2025] for fatal
errors will not be used by iSCSI. If the target needs (by
[RFC2025]) to send SPKM-DEL token, it will, instead, send a Login
"login reject" message with the "Authentication Failure" status and
terminate the connection. If the initiator needs to send SPKM-DEL
token, it will just close the connection.
In what follows, we assume that no SPKM-ERROR tokens are required:
If the initiator authentication fails, the target MUST return an
error. Otherwise, if the AuthMethod is SPKM1 or if the initiator has
selected the mutual authentication option (by setting mutual-state
bit in the options field of the REQ-TOKEN in the SPKM-REQ), the
target MUST reply with:
SPKM_REP_TI=<SPKM-REP-TI>
where SPKM-REP-TI is the target token as defined in [RFC2025].
If mutual authentication was selected and target authentication
fails, the initiator MUST close the connection. Otherwise, if the
AuthMethod is SPKM1, the initiator MUST continue with:
SPKM_REP_IT=<SPKM-REP-IT>
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where SPKM-REP-IT is the second initiator token as defined in
[RFC2025], and if the initiator authentication fails, the target MUST
answer with a Login reject with the "Authentication Failure" status.
All the SPKM-* tokens are large binary items and their binary length
(not the encoded length) MUST not exceed 4096 bytes.
For SRP [RFC2945], the initiator MUST use:
SRP_U=<user> TargetAuth=yes /* or TargetAuth=no */
The target MUST either answer with a Login reject with the
"Authorization Failure" status or reply with:
SRP_N=<N> SRP_g=<g> SRP_s=<s>
The initiator MUST either close the connection or continue with:
SRP_A=<A>
The target MUST either answer with a Login reject with the
"Authentication Failure" status or reply with:
SRP_B=<B>
The initiator MUST either close the connection or continue with:
SRP_M=<M>
If the initiator authentication fails, target MUST answer with a
Login reject with the "Authentication Failure" status. Otherwise, if
the initiator sent TargetAuth=yes in the first message (requiring
target authentication) the target MUST reply with:
SRP_HM=<H(A | M | K)>
If target authentication fails, the initiator MUST close the
connection.
Where U, N, g, s, A, B, M and H(A | M | K) are defined in [RFC2945]
(using the SHA1 hash function, i.e., SRP-SHA1).
U is a text string, N,g,s,A,B,M and H(A | M | K) are binary items and
their binary length (not the encoded length) MUST not exceed 1024
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bytes. Further restrictions on allowed N,g values are specified in
Section 10.2.
For CHAP [RFC1994], the initiator MUST use:
CHAP_A=<A1,A2...>
Where A1,A2... are proposed algorithms, in order of preference.
The target MUST either answer with a Login reject with the
"Authentication Failure" status or reply with:
CHAP_A=<A> CHAP_I=<I> CHAP_C=<C>
Where A is one of A1,A2... that were proposed by the initiator.
The initiator MUST continue either with:
CHAP_N=<N> CHAP_R=<R>
or, if he requires target authentication, with:
CHAP_N=<N> CHAP_R=<R> CHAP_I=<I> CHAP_C=<C>
If the initiator authentication fails, the target MUST answer with a
Login reject with the "Authentication Failure" status. Otherwise, if
the initiator required target authentication, the target MUST reply
with
CHAP_N=<N> CHAP_R=<R>
If target authentication fails, the initiator MUST close the
connection.
Where N, (A,A1,A2), I, C, R are (correspondingly) the Name,
Algorithm, Identifier, Challenge and Response as defined in
[RFC1994]. N is a text string, A,A1,A2,I are numbers and C,R are
binary items and their binary length (not the encoded length) MUST
not exceed 1024 bytes.
For the Algorithm, as stated in [RFC1994], one value is required
to be implemented:
5 (CHAP with MD5)
To guarantee interoperability, initiators SHOULD always offer it as
one of the proposed algorithms.
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03 Login Phase Examples
In the first example, the initiator and target authenticate each
other via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=KRB5,SRP,none
T-> Login (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=<krb_ap_req>
(krb_ap_req contains the Kerberos V5 ticket and authenticator
with MUTUAL-REQUIRED set in the ap-options field)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REP=<krb_ap_rep>
(krb_ap_rep is the Kerberos V5 mutual authentication reply)
If the authentication is successful, the initiator may proceed
with:
I-> Login (CSG,NSG=1,0 T=0) FirstBurstSize=0
T-> Login (CSG,NSG=1,0 T=0) FirstBurstSize=8192
MaxBurstSize=8192
I-> Login (CSG,NSG=1,0 T=0) MaxBurstSize=8192
... more iSCSI Operational Parameters
T-> Login (CSG,NSG=1,0 T=0)
... more iSCSI Operational Parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
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If the initiator authentication by the target is not
successful, the target responds with:
T-> Login "login reject"
instead of the Login KRB_AP_REP message, and terminates the
connection.
If the target authentication by the initiator is not
successful, the initiator terminates the connection (without
responding to the Login KRB_AP_REP message).
In the next example only the initiator is authenticated by the target
via Kerberos:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=SRP,KRB5,none
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=KRB5
I-> Login (CSG,NSG=0,1 T=1)
KRB_AP_REQ=krb_ap_req
(MUTUAL-REQUIRED not set in the ap-options field of krb_ap_req)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
. . .
T-> Login (CSG,NSG=1,3 T=1)"login accept"
In the next example, the initiator and target authenticate each other
via SPKM1:
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I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=SPKM1,KRB5,none
T-> Login (CSG,NSG=0,0 T=0)
AuthMethod=SPKM1
I-> Login (CSG,NSG=0,0 T=0)
SPKM_REQ=<spkm-req>
(spkm-req is the SPKM-REQ token with the mutual-state bit in
the options field of the REQ-TOKEN set)
T-> Login (CSG,NSG=0,0 T=0)
SPKM_REP_TI=<spkm-rep-ti>
If the authentication is successful, the initiator proceeds:
I-> Login (CSG,NSG=0,1 T=1)
SPKM_REP_IT=<spkm-rep-it>
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
The initiator may proceed:
I-> Login (CSG,NSG=1,0 T=0) ... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0) ... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the target authentication by the initiator is not
successful, the initiator terminates the connection (without
responding to the Login SPKM_REP_TI message).
If the initiator authentication by the target is not
successful, the target responds with:
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T-> Login "login reject"
instead of the Login "proceed and change stage" message, and
terminates the connection.
In the next example, the initiator and target authenticate each other
via SPKM2:
I-> Login (CSG,NSG=0,0 T=0)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=SPKM1,SPKM2
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SPKM2
I-> Login (CSG,NSG=0,1 T=1)
SPKM_REQ=<spkm-req>
(spkm-req is the SPKM-REQ token with the mutual-state bit in
the options field of the REQ-TOKEN not set)
If the authentication is successful, the target proceeds with:
T-> Login (CSG,NSG=0,1 T=1)
The initiator may proceed:
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example, the initiator and target authenticate each other
via SRP:
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I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=KRB5,SRP,none
T-> Login-PR (CSG,NSG=0,1 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=yes
T-> Login (CSG,NSG=0,0 T=0)
SRP_N=<N>
SRP_g=<g>
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
SRP_HM=<H(A | M | K)>
Where N, g, s, A, B, M, and H(A | M | K) are defined in [RFC2945].
If the target authentication is not successful, the initiator
terminates the connection. Otherwise it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
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I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the T-> Login SRP_HM=<H(A | M | K)> message and
terminates the connection.
In the next example only the initiator is authenticated by the target
via SRP:
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=KRB5,SRP,none
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=SRP
I-> Login (CSG,NSG=0,0 T=0)
SRP_U=<user>
TargetAuth=no
T-> Login (CSG,NSG=0,0 T=0)
SRP_N=<N>
SRP_g=<g>
SRP_s=<s>
I-> Login (CSG,NSG=0,0 T=0)
SRP_A=<A>
T-> Login (CSG,NSG=0,0 T=0)
SRP_B=<B>
I-> Login (CSG,NSG=0,1 T=1)
SRP_M=<M>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
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I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example the initiator and target authenticate each other
via CHAP:
I-> Login (CSG,NSG=0,0 T=0)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=KRB5,CHAP,none
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
CHAP_I=<I>
CHAP_C=<C>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
CHAP_N=<N>
CHAP_R=<R>
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If the target authentication is not successful, the initiator
aborts the connection. Otherwise it proceeds.
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
If the initiator authentication is not successful, the target
responds with:
T-> Login "login reject"
Instead of the Login CHAP_R=<response> "proceed and change
stage"
message and terminates the connection.
In the next example only the initiator is authenticated by the target
via CHAP:
I-> Login (CSG,NSG=0,1 T=0)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod=KRB5,CHAP,none
T-> Login-PR (CSG,NSG=0,0 T=0)
AuthMethod=CHAP
I-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1,A2>
T-> Login (CSG,NSG=0,0 T=0)
CHAP_A=<A1>
CHAP_I=<I>
CHAP_C=<C>
I-> Login (CSG,NSG=0,1 T=1)
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CHAP_N=<N>
CHAP_R=<R>
If the initiator authentication is successful, the target
proceeds:
T-> Login (CSG,NSG=0,1 T=1)
I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
In the next example, the initiator does not offer any security
parameters, so it may offer iSCSI parameters on the Login PDU with
the T bit set to 1, and the target may respond with a final Login
Response PDU immediately:
I-> Login (CSG,NSG=1,3 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
... iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
... ISCSI parameters
In the next example, the initiator does offer security parameters
on the Login PDU, but the target does not choose any (i.e.,
chooses the "none" values):
I-> Login (CSG,NSG=0,1 T=1)
InitiatorName=iqn.1999-07.com.os.hostid.77
TargetName=iqn.1999-07.com.acme.diskarray.sn.88
AuthMethod:KRB5,SRP,none
T-> Login-PR (CSG,NSG=0,1 T=1)
AuthMethod=none
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I-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
T-> Login (CSG,NSG=1,0 T=0)
... iSCSI parameters
And at the end:
I-> Login (CSG,NSG=1,3 T=1)
optional iSCSI parameters
T-> Login (CSG,NSG=1,3 T=1) "login accept"
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Appendix B. Examples
04 Read Operation Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+----------------------+
| | | Prepare Data Transfer|
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
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05 Write Operation Example
+------------------+-----------------------+---------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+---------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+---------------------+
| | | Process old commands|
+------------------+-----------------------+---------------------+
| | | Ready to process |
| | <<< R2T | WRITE command |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| | <<< R2T | Ready for data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
+------------------+-----------------------+---------------------+
| | <<< SCSI Response |Send Status and Sense|
+------------------+-----------------------+---------------------+
| Command Complete | | |
+------------------+-----------------------+---------------------+
06 R2TSN/DataSN use examples
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Output (write) data DataSN/R2TSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) | | and queue it |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for data |
| | R2TSN = 0 | |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 1 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=0 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 1, F=1 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Data >>> | Receive Data |
| for R2TSN 1 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 0 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
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Input (read) data DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (READ)>>> | |
| (read) | | |
+------------------+-----------------------+----------------------+
| | | Prepare Data Transfer|
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 0, F=0 | |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 1, F=0 | |
+------------------+-----------------------+----------------------+
| Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 2, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 3 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
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Bidirectional DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command >>> | |
| (Read-Write) | Read-Write | |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready to process |
| | R2TSN = 0 | WRITE command |
+------------------+-----------------------+----------------------+
| * Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 0, F=0 | |
+------------------+-----------------------+----------------------+
| * Receive Data | <<< SCSI Data-in | Send Data |
| | DataSN = 1, F=1 | |
+------------------+-----------------------+----------------------+
| * Send Data | SCSI Data-out >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 2 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
*) Send data and Receive Data may be transferred simultaneously as in
an atomic Read-Old-Write-New or sequential as in an atomic Read-
Update-Write (in the alter case the R2T may follow the received data)
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Unsolicited and immediate output (write) data with DataSN Example
+------------------+-----------------------+----------------------+
|Initiator Function| PDU Type & Content | Target Function |
+------------------+-----------------------+----------------------+
| Command request |SCSI Command (WRITE)>>>| Receive command |
| (write) |F=0 | and data |
|+ immediate data | | and queue it |
+------------------+-----------------------+----------------------+
| Send Unsolicited | SCSI Write Data >>> | Receive more Data |
| Data | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | | Process old commands |
+------------------+-----------------------+----------------------+
| | <<< R2T | Ready for more data |
| | R2TSN = 0 | |
+------------------+-----------------------+----------------------+
| Send Data | SCSI Write Data >>> | Receive Data |
| for R2TSN 0 | DataSN = 0, F=1 | |
+------------------+-----------------------+----------------------+
| | <<< SCSI Response |Send Status and Sense |
| | ExpDataSN = 0 | |
+------------------+-----------------------+----------------------+
| Command Complete | | |
+------------------+-----------------------+----------------------+
07 CRC Examples
N.B. all Values are Hexadecimal
32 bytes of zeroes:
Byte: 0 1 2 3
0: 00 00 00 00
...
28: 00 00 00 00
CRC: aa 36 91 8a
32 bytes of ones:
Byte: 0 1 2 3
0: ff ff ff ff
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...
28: ff ff ff ff
CRC: 43 ab a8 62
32 bytes of incrementing 00..1f:
Byte: 0 1 2 3
0: 00 01 02 03
...
28: 1c 1d 1e 1f
CRC: 4e 79 dd 46
32 bytes of decrementing 1f..00:
Byte: 0 1 2 3
0: 1f 1e 1d 1c
...
28: 03 02 01 00
CRC: 5c db 3f 11
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Appendix C. Sync and Steering with Fixed Interval Markers
This appendix presents a simple scheme for synchronization (PDU
boundary retrieval). It uses markers including synchronization
information placed at fixed intervals in the TCP stream.
A Marker consists of:
Byte / 0 | 1 | 2 | 3 |
/ | | | |
|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|7 6 5 4 3 2 1 0|
+---------------+---------------+---------------+---------------+
0| Next-iSCSI-PDU-start pointer - copy #1 |
+---------------+---------------+---------------+---------------+
4| Next-iSCSI-PDU-start pointer - copy #2 |
+---------------+---------------+---------------+---------------+
The Marker indicates the offset to the next iSCSI PDU header. The
Marker is eight bytes in length, and contains two 32-bit offset
fields that indicate how many bytes to skip in the TCP stream in
order to find the next iSCSI PDU header. The offset is counted from
the marker end to the beginning of the next header. The marker uses
two copies of the pointer so that a marker spanning a TCP packet
boundary should leave at least one valid copy in one of the packets.
The offset to the next iSCSI PDU header is counted in terms of the
TCP stream data. Anything counted in the TCP sequence-number is
counted for the offset. Specifically this includes any bytes
"inserted" in the TCP stream by an UFL and it excludes any other
markers inserted between the one we are examining and the next PDU
header. The inserted value is independent of the marker interval.
The use of markers is negotiable. The initiator and target MAY
indicate their readiness to receive and/or send markers during login
separately for each connection. The default is NO. In certain
environments a sender not willing to supply markers to a receiver
willing to accept markers MAY suffer from a considerable performance
degradation.
08 Markers At Fixed Intervals
At fixed intervals in the TCP byte stream, a marker is inserted.
Each end of the iSCSI session specifies during login the interval at
which it is willing to receive the marker or disables the marker
altogether. If a receiver indicates that it desires a marker, the
sender SHOULD agree (during negotiation) and provide the marker at
the desired interval.
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The marker interval and the initial marker-less interval are counted
in terms of the TCP stream data. Anything counted in the TCP
sequence-number is counted for the interval and the initial marker-
less interval. Specifically this includes any bytes "inserted" in the
TCP stream by an UFL.
When reduced to iSCSI terms markers MUST indicate the offset to a 4-
byte word boundary in the stream. The last 2 bits of each marker
word are reserved and are considered 0 for offset computation.
Padding iSCSI PDU payloads to 4-byte word boundaries simplifies
marker manipulation.
09 Initial Marker-less Interval
To enable the connection setup including the login phase negotiation,
marking (if any) is started only at the first marker interval after
the end of the login phase.
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Appendix D. Login/Text Operational Keys
The ISID and TSID form collectively the SSID (session id). A TSID of
zero indicates a leading connection. Some session specific parameters
MUST be carried only on the leading connection and cannot be changed
after the leading connection login (e.g., MaxConnections, the maximum
number of connections). This holds even for a single connection
session with regard to connection restart. The keys that fall into
this category have the use defined as LO (Leading Only).
Keys that can be used only during login have the use defined as IO
(initialize only) while those that can be used in both the login
phase and full feature phase have the use defined as ALL.
Keys that can be used only during full feature phase have the use
defined as FFPO (full feature phase only).
Unless explicitly stated otherwise, all key=value pairs specified
here are session specific.
10 HeaderDigest and DataDigest
Use: IO
Who can send: Initiator and Target
HeaderDigest = <list-of-options>
DataDigest = <list-of-options>
Digests enable checking end-to-end non-cryptographic data integrity
beyond the integrity checks provided by the link layers and covering
the whole communication path including all elements that may change
the network level PDUs like routers, switches, proxies, etc.
The following table lists cyclic integrity checksums that can be
negotiated for the digests and MUST be implemented by every iSCSI
initiator and target. Note that these digest options have only error
detection significance.
+---------------------------------------------+
| Name | Description | Generator |
+---------------------------------------------+
| CRC32C | 32 bit CRC |0x11edc6f41|
+---------------------------------------------+
| none | no digest |
+---------------------------------------------+
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The generator polynomial for this digest is given in hex-notation,
for example 0x3b stands for 0011 1011 - the polynomial
x**5+X**4+x**3+x+1.
When Initiator and Target agree on a digest, this digest MUST be used
for every PDU in Full Feature Phase.
Padding bytes, when present, in a segment covered by a CRC, should be
set to 0 and are included in the CRC. The CRC should be calculated as
follows:
- data are assumed to be in the numbering order that appears
in the draft - start with byte 0 bit 0 continue byte 1 bit 0
etc. (Big Endian on bytes / Little Endian on bits)
- the CRC register is initialized with all 1s (equivalent to
complementing the first 32 bits of the message)
- the n PDU bits are considered coefficients of a polynomial
M(x) of order n-1, with bit 0 of byte 0 being x^(n-1)
- the polynomial is multiplied by x^32 and divided by G(x)- the
generator polynomial - producing a remainder R(x) of degree <=
31
- the coefficients of R(x) are considered a 32 bit sequence
- the bit sequence is complemented and the result is the CRC
- after the last bit of the original segment the CRC bits are
transmitted with x^31 first followed by x^30 etc. ( whenever
examples are given the value to be specified in examples
follows the same rules of representation as the rest of this
document)
- a receiver of a "good" segment (data or header) built using
the generator 0x11edc6f41 will end-up having in the CRC
register the value 0x1c2d19ed (this a register value and not a
word as outlined in this draft)
Proprietary algorithms MAY also be negotiated for digests. Whenever a
proprietary algorithm is negotiated, "none" or "CRC32C" should be
listed as an option in order to guarantee interoperability.
11 MaxConnections
Use: LO
Who can send: Initiator and Target
MaxConnections=<number-from-1-to-65535>
Default is 1.
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Initiator and target negotiate the maximum number of connections
requested/acceptable. The lower of the 2 numbers is selected.
12 SendTargets
Use: FFPO
Who can send: Initiator
For a complete description see Appendix E.
13 TargetName
Use: IO by initiator ALL by target, Declarative
Who can send: Initiator and Target
TargetName=<iSCSI-Name>
Examples:
TargetName=iqn.1993-11.com.disk-vendor.diskarrays.sn.45678
TargetName=eui.020000023B040506
This key must be provided by the initiator of the TCP connection to
the remote endpoint in the first login request if the initiator is
not establishing a discovery session. The iSCSI Target Name specifies
the worldwide unique name of the target.
The TargetName key may also be returned by the "SendTargets" text
request (and that is its only use when issued by a target).
14 InitiatorName
Use: IO, Declarative
Who can send: Initiator
InitiatorName=<iSCSI-Name>
Examples:
InitiatorName=iqn.1992-04.com.os-vendor.plan9.cdrom.12345
InitiatorName=iqn.2001-02.com.ssp.users.customer235.host90
InitiatorName=iSCSI
This key MUST be provided by the initiator of the TCP connection to
the remote endpoint at the first Login of login phase for every
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connection. The Initiator key enables the initiator to identify
itself to the remote endpoint.
15 TargetAlias
Use: ALL
Who can send: Target
TargetAlias=<UTF-8 string>
Examples:
TargetAlias=Bob's Disk
TargetAlias=Database Server 1 Log Disk
TargetAlias=Web Server 3 Disk 20
If a target has been configured with a human-readable name or
description, this name MUST be communicated to the initiator during a
Login Response PDU. This string is not used as an identifier, but
can be displayed by the initiator's user interface in a list of
targets to which it is connected.
16 InitiatorAlias
Use: ALL
Who can send: Initiator
InitiatorAlias=<UTF-8 string>
Examples:
InitiatorAlias=Web Server 4
InitiatorAlias=spyalley.nsa.gov
InitiatorAlias=Exchange Server
If an initiator has been configured with a human-readable name or
description, it may be communicated to the target during a Login
Request PDU. If not, the host name can be used instead.
This string is not used as an identifier, but can be displayed by the
target's user interface in a list of initiators to which it is
connected.
This key SHOULD be sent by an initiator within the Login phase if
available.
17 TargetAddress
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Use: ALL
Who can send: Target
TargetAddress=domainname[:port][,portal-group-tag]
If the TCP port is not specified, it is assumed to be the IANA-
assigned default port for iSCSI.
If the TargetAddress is being returned in a login response as the
result of a redirect status, the comma and portal group tag are
omitted.
If the TargetAddress is being returned within a SendTargets response,
the portal group tag is required.
Examples:
TargetAddress=10.0.0.1:5003,1
TargetAddress=[1080:0:0:0:8:800:200C:417A],65
TargetAddress=[1080::8:800:200C:417A]:5003,1
TargetAddress=computingcenter.acme.com,23
The TargetAddress key is more fully described in Appendix E.
18 FMarker
Use: IO
Who can send: Initiator and Target
FMarker=<send|receive|send-receive|no>
Default is no.
This is a connection specific parameter.
Examples:
I->FMarker=send-receive
T->FMarker=send-receive
results in Marker being used in both directions while
I->FMarker=send-receive
T->FMarker=receive
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results in Marker being used from the initiator to the target but not
from the target to initiator.
19 RFMarkInt
Use: IO
Who can send: Initiator and Target
RFMarkInt=<number-from-1-to-65535>[,<number-from-1-to-65535>]
This is a connection specific parameter.
The receiver indicates the minimum to maximum interval (in 4-byte
words) that the receiver wants the markers. In case the receiver
wants only a specific value, only a single value has to be specified.
The sender selects a value within the minimum and maximum the
receiver requires (or the only value the receiver requires) or
indicates through the FMarker key=value its inability to set markers.
The interval is measured from the end of a marker to the beginning of
the next marker. For example, a value of 1024 means 1024 words (4096
bytes of "pure" payload between markers). Whenever FMarker and
RFMarkInt are both sent they MUST appear on the same Login
Request/Response.
Default is 2048.
20 SFMarkInt
Use: IO
Who can send: Initiator and Target
SFMarkInt=<number-from-1-to-65535>
This is a connection specific parameter.
Indicates at what interval (in 4-byte words) the sender agrees to
send the markers. The number MUST be within the range required by the
receiver. The interval is measured from the end of a marker to the
beginning of the next marker. For example, a value of 1024 means 1024
words (4096 bytes of "pure" payload between markers).
Default is 2048.
21 InitialR2T
Use: ALL
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Who can send: Initiator and Target
InitialR2T=<yes|no>
Examples:
I->InitialR2T=no
T->InitialR2T=no
Default is yes.
Result function is OR.
The InitialR2T key is used to turn off the default use of R2T, thus
allowing an initiator to start sending data to a target as if it has
received an initial R2T with Buffer Offset=0 and Desired Data
Transfer Length=min (FirstBurstSize, Expected Data Transfer Length).
The default action is that R2T is required, unless both the initiator
and the target send this key-pair attribute specifying InitialR2T=no.
Once InitialR2T has been set to 'no', it cannot be set back to 'yes'.
Note that only the first outgoing data burst (immediate data and/or
or separate PDUs) can be sent unsolicited by an R2T.
22 BidiInitialR2T
Use: ALL
Who can send: Initiator and Target
BidiInitialR2T=<yes|no>
Examples:
I->BidiInitialR2T=no
T->BidiInitialR2T=no
Default is yes.
Result function is OR.
The BidiInitialR2T key is used to turn off the default use of
BiDiR2T, thus allowing an initiator to send data to a target without
the target having sent an R2T to the initiator for the output data
(write part) of a Bidirectional command (having both the R and the W
bits set). The default action is that R2T is required, unless both
the initiator and the target send this key-pair attribute specifying
BidiInitialR2T=no. Once BidiInitialR2T has been set to 'no', it
cannot be set back to 'yes'. Note that only the first outgoing data
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burst (immediate data and/or or separate PDUs) can be sent
unsolicited by an R2T.
23 ImmediateData
Use: ALL
Who can send: Initiator and Target
ImmediateData=<yes|no>
Default is yes.
Result function is AND.
Initiator and target negotiate support for immediate data. If
initiator or target wants to turn immediate data off they have to
state that. ImmediateData can be turned on if both initiator and
target have ImmediateData=yes.
If ImmediateData is set to yes and InitialR2T is set to yes (default)
then only immediate data are accepted in the first burst.
If ImmediateData is set to no and InitialR2T is set to yes then the
initiator MUST NOT send unsolicited data and the target MUST reject
them with the corresponding response code.
If ImmediateData is set to no and InitialR2T is set to no then the
initiator MUST NOT send unsolicited immediate data but MAY send one
unsolicited burst of Data-OUT PDUs.
If ImmediateData is set to yes and InitialR2T is set to no then the
initiator MAY send unsolicited immediate data and/or one unsolicited
burst of Data-OUT PDUs.
The following table is a summary of unsolicited data options:
+----------+-------------+--------------------------------------+
|InitialR2T|ImmediateData| Result (up to FirstBurstSize) |
+----------+-------------+--------------------------------------+
| no | no | Unsolicited data in data PDUs only |
+----------+-------------+--------------------------------------+
| no | yes | Immediate & separate unsolicited data|
+----------+-------------+--------------------------------------+
| yes | no | Unsolicited data disallowed |
+----------+-------------+--------------------------------------+
| yes | yes | Immediate unsolicited data only |
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+----------+-------------+--------------------------------------+
24 MaxRecvPDULength
Use: All
Who can send: Initiator and Target
MaxRecvPDULength=<number-512-to-2**24>
Default is 8192 bytes.
This is a connection specific parameter.
Initiator or target declares the maximum data segment length in bytes
they can receive in an iSCSI PDU.
A value of 0 MAY be used as a "don't care" offer in negotiations.
25 MaxBurstSize
Use: LO
Who can send: Initiator and Target
MaxBurstSize=<number-512-to-2**24>
Default is 256 Kbytes.
Initiator and target negotiate maximum SCSI data payload in bytes in
an Data-In or a solicited Data-Out iSCSI sequence (a sequence of
Data-In or Data-Out PDUs ending with a Data-In or Data-Out PDU with
the F bit set to one).
The minimum of the 2 numbers is selected.
A value of 0 MAY be used as a "don't care" offer in negotiations.
26 FirstBurstSize
Use: LO
Who can send: Initiator and Target
FirstBurstSize=<number-512-to-2**24>
Default is 64 Kbytes.
Initiator and target negotiate the maximum amount in bytes of
unsolicited data an iSCSI initiator may send to the target, during
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the execution of a single SCSI command. This covers the immediate
data (if any) and the sequence of unsolicited Data-Out PDUs (if any)
that follow the command.
The minimum of the 2 numbers is selected.
FirstBurstSize MUST NOT exceed MaximumBurstSize.
A value of 0 MAY be used as a "don't care" offer in negotiations.
27 LogoutLoginMaxTime
Use: LO
Who can send: Initiator and Target
LogoutLoginMaxTime=<number-from-2-3600>
Default is 3.
Initiator and target negotiate the maximum time in seconds before
whom connection reinstatement is still possible after a connection
termination, or a connection reset.
This value is also the session state timeout if the connection in
question is the last LOGGED_IN connection in the session.
The minimum of the 2 values is selected and will be used anywhere no
explicit value is provided otherwise (Time2Retain).
A value of 0 MAY be used as a "don't care" offer in negotiations.
28 LogoutLoginMinTime
Use: LO
Who can send: Initiator and Target
LogoutLoginMinTime=<number-from-2-3600>
Default is 3.
Initiator and target negotiate the minimum time in seconds to wait
before attempting connection reinstatement after a connection
termination, or a connection reset.
This value is also the session state timeout if the connection in
question is the last LOGGED_IN connection in the session.
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The maximum of the 2 values is selected and will be used anywhere no
explicit value is provided otherwise (Time2Wait).
A value of 0 MAY be used as a "don't care" offer in negotiations.
29 MaxOutstandingR2T
Use: LO
Who can send: Initiator and Target
MaxOutstandingR2T=<number-from-1-to-65535>
The default is 1.
Initiator and target negotiate the maximum number of outstanding R2Ts
per task. The minimum of the two values is selected.
A value of 0 MAY be used as a "don't care" offer in negotiations.
30 DataPDUInOrder
Use: LO
Who can send: Initiator and Target
DataPDUInOrder=<yes|no>
The default is yes.
Result function is OR.
No is used by iSCSI to indicate that the data PDUs within sequences
can be in any order. Yes is used to indicate that data PDUs within
sequences have to be at continuously increasing addresses and
overlays are forbidden.
31 DataSequenceInOrder
Use: LO
Who can send: Initiator and Target
DataSequenceInOrder=<yes|no>
The default is yes.
Result function is OR.
A Data Sequence is a sequence of Data-In or Data-Out PDUs ending with
a Data-In or Data-Out PDU with the F bit set to one (a Data-out
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sequence is sent either unsolicited or in response to an R2T).
Sequences cover an offset-range.
If DataSequenceInOrder is set to no, Data PDU sequences may be
transferred in any order. If DataSequenceInOrder is set to yes, Data
Sequences MUST be transferred using continuously increasing offsets
except for error recovery.
32 ErrorRecoveryLevel
Use: LO
Who can send: Initiator and Target
ErrorRecoveryLevel=<0 to 2>
Default is 0.
Initiator and target negotiate the recovery level supported.
The minimum of the two values is selected.
Recovery levels represent a combination of recovery capabilities.
Each recovery level includes all the capabilities of the lower
recovery levels and adds to them some new ones.
In the description of recovery mechanisms, certain recovery classes
are specified. Section 8.12 describes the mapping between the
classes and the levels.
33 SessionType
Use: LO, Declarative
Who can send: Initiator
SessionType= <discovery|normal>
Default is Normal.
The Initiator indicates the type of session it wants to create. The
target can accept or reject it.
A discovery session indicates to the Target that the only purpose of
this Session is discovery. The only requests accepted by a target in
this type of session are a text request with a SendTargets key and a
close session type of logout request.
Discovery session implies MaxConnections = 1 and overrides both the
default and an explicit setting.
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34 The Vendor Specific Key Format
Use: ALL
Who can send: Initiator and Target
X-reversed.vendor.dns_name.do_something=
Keys with this format are used for vendor-specific purposes. These
keys always start with X-.
To identify the vendor it is suggested to use the reversed DNS-name
as a prefix to the key-proper.
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Appendix E. SendTargets operation
To reduce the amount of configuration required on an initiator, iSCSI
provides the SendTargets text request. This command is sent by the
initiator to request a list of targets to which it may have access,
as well as the list of addresses (IP address and TCP port) on which
these targets may be accessed.
To make use of SendTargets, an initiator must first establish one of
two types of sessions. If the initiator establishes the session
using the key "SessionType=discovery", the session is a discovery
session, and a target name need not be specified. Otherwise, the
session is a normal, operational session. The SendTargets command
MUST be sent only during the full feature phase of a normal or
discovery session.
A system containing targets MUST support discovery sessions on each
of its IP addresses, and MUST support the SendTargets command on the
discovery session. A target MUST support the SendTargets command on
operational sessions; these will only return address information
about the target to which the session is connected, and do not return
information about other targets.
An initiator MAY make use of the SendTargets as it sees fit.
A SendTargets command consists of a single Text request PDU.
This PDU contains exactly one text key and value. The text key MUST
be SendTargets. The expected response depends upon the value, as
well as whether the session is a discovery or operational session.
The value must be one of:
all
The initiator is requesting that information on all relevant
targets known to the implementation be returned. This value
MUST be supported on a discovery session, and MAY NOT be
supported on an operational session.
<iSCSI-target-name>
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If an iSCSI target name is specified, the session should
respond with addresses for only the named target, if
possible. This value MUST be supported on discovery
sessions. A discovery session MUST be capable of returning
addresses for those targets that would have been returned had
value=all been designated.
<nothing>
The session should respond with addresses only for the target
to which the session is logged in. This MUST be supported on
operational sessions, and MAY NOT return targets other than
the one to which the session is logged in.
The response to this command is a text response containing a list of
zero or more targets and, optionally, their addresses. Each target
is returned as a target record. A target record begins with the
TargetName text key, followed by a list of TargetAddress text keys,
and bounded by the end of the text response or the next TargetName
key, which begins a new record. No text keys other than TargetName
and TargetAddress are permitted within a SendTargets response.
For the format of the TargetName see Appendix D-13.
A discovery session MAY respond to a SendTargets request with its
complete list of targets, or with a list of targets that is based on
the name of the initiator logged in to the session.
A SendTargets response MAY contain no target names, if there are no
targets for the requesting initiator to access.
Each target record returned includes zero or more TargetAddress
fields.
A SendTargets response MUST NOT contain iSCSI default target names.
Each target record starts with one text key of the form:
TargetName=<target-name-goes-here>
Followed by zero or more address keys of the form:
TargetAddress=<hostname-or-ipaddress>[:<tcp-port>],<portal-
group-tag>
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The hostname-or-ipaddress and tcp port are as specified in the
"Naming and Addressing" section.
Each TargetAddress belongs to a portal group, identified by its
numeric, decimal portal group tag. The iSCSI target name, together
with this tag, constitutes the SCSI port identifier; the tag need be
unique only within a given target name's list of addresses.
Multiple-connection sessions can span iSCSI addresses belonging to
the same portal group.
Multiple-connection sessions cannot span iSCSI addresses belonging to
different portal groups.
If a SendTargets response reports an iSCSI address for a target, it
SHOULD also report all other addresses in its portal group in the
same response.
A SendTargets text response can be longer than a single Text Response
PDU, and makes use of the long text responses as specified.
After obtaining a list of targets from the discovery target session,
an iSCSI initiator may initiate new sessions to log in to the
discovered targets for full operation. The initiator MAY keep the
session to a default target open, and MAY send subsequent SendTargets
commands to discover new targets.
Examples:
This example is the SendTargets response from a single target that
has no other interface ports.
Initiator sends text request containing:
SendTargets=all
Target sends text response containing:
TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
Note that all it really had to return in the simple case was the
target name. It is assumed by the initiator that the IP address and
TCP port for this target are the same as used on the current
connection to the default iSCSI target.
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The next example has two internal iSCSI targets, each accessible via
two different ports with different IP addresses. Here's the text
response:
TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.45:3000,2
TargetName=iqn.1993-11.com.acme.diskarray.sn.1234567
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.45:3000,2
Note that both targets share both addresses; the multiple addresses
are likely used to provide multi-path support. The initiator may
connect to either target name on either address. Each of the
addresses has its own portal group tag; they do not support spanning
multiple-connection sessions with each other. Keep in mind also that
the portal group tags for the two named targets are independent of
one another; portal group "1" on the first target is not necessarily
the same as portal group "1" on the second.
Also note that in the above example, a DNS host name could have been
returned instead of an IP address, and that an IPv6 addresses (5 to
16 dotted-decimal numbers) could have been returned as well.
The next text response shows a target that supports spanning sessions
across multiple addresses, indicating this using the portal group
tags:
TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
TargetAddress=10.1.0.45:3000,1
TargetAddress=10.1.1.46:3000,1
TargetAddress=10.1.0.47:3000,2
TargetAddress=10.1.1.48:3000,2
TargetAddress=10.1.1.49:3000,3
In this example, any of the target addresses can be used to reach the
same target. A single-connection session can be established to any
of these TCP addresses. A multiple-connection session could span
addresses .45 and .46, or .47 and .48, but cannot span any other
combination. A TargetAddress with its own tag (.49) cannot be
combined with any other address within the same session.
Note that this SendTargets response does not indicate whether .49
supports multiple connections per session; this is communicated via
the MaxConnections text key upon login to the target.
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Appendix F. SCSI Alias designation formats
35 Format codes
The SCSI command set (see [SPC3]) defines an alias mechanism (CHANGE
ALIASES and REPORT ALIASES commands) for mapping long identifiers
(such as iSCSI Names) into shorter values for use in parameter data,
such as third party commands.
This appendix defines the alias entry formats and codes used in these
commands to designate iSCSI devices or ports. Error! Reference
source not found.The protocol identifier used in these formats SHALL
be set to 0x05 (see [SPC3]) and the format code values are defined in
the following table:
------------------------------------------------------------------
Format | Description | Max | Content
Code | | Length |
| | (bytes) |
------------------------------------------------------------------
00h | iSCSI Name | 256 | Name in UTF-8 format (null
| | | terminated with pad). See Y.2.
------------------------------------------------------------------
01h | iSCSI Name | 268 | Name in UTF-8 format (null
| with IPv4 | | terminated with pad), binary IPv4
| address | | address, binary TCP port, binary
| | | Internet Protocol Number. See Y.3
------------------------------------------------------------------
02h | iSCSI Name | 520 | Name in UTF-8 format (null
| with IPName | | terminated), IPName (null
| | | terminated with pad), binary
| | | TCP port, binary Internet
| | | Protocol Number. See Y.4
------------------------------------------------------------------
01h | iSCSI Name | 268 | Name in UTF-8 format (null
| with IPv6 | | terminated with pad), binary IPv6
| address | | address, binary TCP port, binary
| | | Internet Protocol Number. See Y.5
------------------------------------------------------------------
04-FFh | reserved | n/a | n/a
------------------------------------------------------------------
In all cases, if the length is not a multiple of 4, then zero to
three pad bytes are added (as indicated).
A designation that contains no IP addressing information or contains
IP addressing information that does not address the named SCSI device
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may require the SCSI logical unit device server to have access to a
name server or to other discovery protocols to resolve the given
iSCSI Name to an IP address through which the device server may
establish iSCSI Login.
36 iSCSI Name designation format
The following table describes the iSCSI Name designation 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| iSCSI Name + Null (00h) + pad (0) (if necessary) |
+/ /
+---------------+---------------+---------------+---------------+
x
The iSCSI Name field SHALL contain the iSCSI Name of an iSCSI Node.
A Null (00h) byte SHALL terminate the iSCSI Name.
Zero to three bytes set to zero SHALL be appended as padding so that
the total length of the designation is a multiple of four. The pad
field SHALL be ignored.
An iSCSI Name designation is valid if the device server has access to
a SCSI domain containing an IP network and there exists an iSCSI Node
on that network with the specified iSCSI Name.
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37 iSCSI Name with binary IPv4 address designation format
The following table describes the iSCSI Name with IPv4 address
designation 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| iSCSI Name + Null (00h) + pad (0) (if necessary) |
+/ /
+---------------+---------------+---------------+---------------+
x| IPv4 address |
+---------------+---------------+---------------+---------------+
x+4| Reserved | Port Number |
+---------------+---------------+---------------+---------------+
x+8| Reserved | Internet Protocol Number |
+---------------+---------------+---------------+---------------+
x+12
The iSCSI Name field SHALL contain the iSCSI Name of an iSCSI Node.
A Null (00h) byte SHALL terminate the iSCSI Name.
Zero to three bytes set to zero SHALL be appended as padding so that
the total length of the designation is a multiple of four. The pad
field SHALL be ignored.
The IPv4 Address field SHALL contain an IPv4 address. See [RFC791]
for a description of IPv4 addresses.
The Port Number field SHALL contain a port number. See [RFC790] for a
description of port numbers.
The internet protocol number field SHALL contain an Internet protocol
number. See [RFC790] for a description of Internet protocol numbers.
An iSCSI Name with IPv4 address designation is valid if the device
server has access to a SCSI domain containing an IP network and there
exists an iSCSI Node on that network with the specified iSCSI Name.
The IPv4 address, port number and internet protocol number provided
in the designation may be used by a device server for addressing to
discover and establish communication with the named iSCSI Node.
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Alternatively, the device server may use other protocol specific or
vendor specific methods to discover and establish communication with
the named iSCSI Node.
38 iSCSI Name with IPname designation format
The following table describes the iSCSI Name with IPname designation
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| iSCSI Name + Null (00h) + IPname + Null (00h) + |
+/ pad (0) (if necessary) /
+---------------+---------------+---------------+---------------+
x| Reserved | Port Number |
+---------------+---------------+---------------+---------------+
x+4| Reserved | Internet Protocol Number |
+---------------+---------------+---------------+---------------+
x+8
The iSCSI name field SHALL contain the iSCSI Name of an iSCSI Node.
See [NDT] for a description of iSCSI Names. The iSCSI name field
SHALL not include a byte set to 00h.
A Null (00h) byte SHALL terminate the iSCSI Name.
The IPname field SHALL contain a Internet protocol domain name. See
[RFC1035] for a description of domain names.
A Null (00h) byte SHALL terminate the Internet protocol domain name.
Zero to three bytes set to zero SHALL be appended as padding so that
the total length of the designation is a multiple of four. The pad
field SHALL be ignored.
An iSCSI Name with IPname designation is valid if the device server
has access to a SCSI domain containing an IP network and there exists
an iSCSI Node on that network with the specified iSCSI Name. The
domain name, port number and internet protocol number provided in the
designation may be used by a device server for addressing to discover
and establish communication with the named iSCSI Node. Alternatively,
the device server may use other protocol specific or vendor specific
methods to discover and establish communication with the named iSCSI
Node.
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39 iSCSI Name with binary IPv6 address designation format
The following table describes the iSCSI Name with IPv6 address
designation 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| iSCSI Name + Null (00h) + pad (0) (if necessary) |
+/ /
+---------------+---------------+---------------+---------------+
x| IPv6 address |
+/ /
+---------------+---------------+---------------+---------------+
x+16| Reserved | Port Number |
+---------------+---------------+---------------+---------------+
x+20| Reserved | Internet Protocol Number |
+---------------+---------------+---------------+---------------+
x+24
The iSCSI Name field SHALL contain the iSCSI Name of an iSCSI Node.
A Null (00h) byte SHALL terminate the iSCSI Name.
Zero to three bytes set to zero SHALL be appended as padding so that
the total length of the designation is a multiple of four. The pad
field SHALL be ignored.
The IPv6 Address field SHALL contain an IPv6 address. See [RFC2373]
for a description of IPv6 addresses.
The Port Number field SHALL contain a port number. See [RFC790] for a
description of port numbers.
The Internet Protocol Number field SHALL contain an Internet protocol
number. See [RFC790] for a description of Internet protocol numbers.
An iSCSI Name with IPv6 address designation is valid if the device
server has access to a SCSI domain containing an IP network and there
exists an iSCSI Node on that network with the specified iSCSI Name.
The IPv6 address, port number and internet protocol number provided
in the designation may be used by a device server for addressing to
discover and establish communication with the named iSCSI Node.
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Alternatively, the device server may use other protocol specific or
vendor specific methods to discover and establish communication with
the named iSCSI Node.
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Appendix G. Algorithmic presentation of error recovery classes
This appendix illustrates the error recovery classes using a pseudo-
programming-language. The procedure names are chosen to be obvious
to most implementers, and each of the recovery classes described has
initiator procedures as well as target procedures. Readers may
please note that these algorithms focus on outlining the mechanics of
error recovery classes, and ignore all other aspects/cases. Examples
of this approach are:
- Handling for only certain Opcode types is shown.
- Only certain reason codes (for example, Recovery in Logout
command) are outlined.
- Resultant cases like recovery of Synchronization on a
header digest error are considered out-of-scope in these
algorithms. In this particular example, header digest error
may lead to connection recovery if sync and steering layer is
not implemented.
It may also be noted that these algorithms strive to convey the iSCSI
error recovery concepts in simplest terms, and are not designed to be
optimal.
40 General Data structure and procedure description
This section defines the procedures and data structures that are
commonly used by all the error recovery algorithms. Please note that
the structures may not be the exhaustive representations of what is
required for a typical implementation.
Data structure definitions -
struct TransferContext {
int TargetTransferTag;
int ExpectedDataSN;
};
struct TCB {
Boolean SoFarInOrder;
int ExpectedDataSN; /* used for both R2Ts, and Data */
int MissingDataSNList[MaxMissingDPDU];
Boolean FbitReceived;
Boolean StatusXferd;
Boolean CurrentlyAllegiant;
int ActiveR2Ts;
int Response;
char *Reason;
struct TransferContext
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TransferContextList[MaxOutStandingR2T];
int InitiatorTaskTag;
int CmdSN;
};
struct Connection {
struct Session SessionReference;
Boolean SoFarInOrder;
int CID;
int State;
int ExpectedStatSN;
int MissingStatSNList[MaxMissingSPDU];
Boolean PerformConnectionRecovery;
};
struct Session {
int NumConnections;
int NextCmdSN;
int Maxconnections;
Boolean FailoverSupport;
struct iSCSIEndpoint OtherEndInfo;
struct Connection ConnectionList[MaxSupportedConns];
};
Procedure descriptions -
Receive-a-In-PDU(transport connection, inbound PDU);
check-basic-validity(inbound PDU);
Start-Timer(timeout handler, argument, timeout value);
Build-And-Send-Reject(transport connection, bad PDU, reason code);
41 Within-command error recovery algorithms
1 Procedure descriptions
Recover-Data-if-Possible(last required DataSN, task control block);
Build-And-Send-DSnack(task control block);
Build-And-Send-Abort(task control block);
SCSI-Task-Completion(task control block);
Build-And-Send-a-Data-Burst(transport connection, R2T PDU,
task control block);
Build-And-Send-R2T(transport connection, description of data,
task control block);
Build-And-Send-Status(transport connection, task control block);
Transfer-Context-Timeout-Handler(transfer context);
Implementation-specific tunables -
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InitiatorDataSNACKEnabled, TargetDataSNACKSupported,
TargetRecoveryR2TEnabled.
Notes:
- Some procedures used in this section - Recover-Status-if-
Possible, Handle-Status-SNACK-request, Evaluate-a-StatSN -
are defined in Within-connection recovery algorithms.
- The Response processing pseudo-code shown in the target
algorithms applies to all solicited PDUs carrying StatSN -
SCSI Response, Text Response etc.
2 Initiator algorithms
Recover-Data-if-Possible(LastRequiredDataSN, TCB)
{
if (InitiatorDataSNACKEnabled) {
if (# of missing PDUs is trackable) {
Note the missing DataSNs in TCB.
Build-And-Send-DSnack(TCB);
} else {
TCB.Reason = "Delivery subsystem failure";
}
} else {
TCB.Reason = "Delivery subsystem failure";
}
if (TCB.Reason = "Delivery subsystem failure") {
Clear the missing PDU list in the TCB.
if (TCB.StatusXferd is not TRUE)
Build-And-Send-Abort(TCB);
}
}
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if ((CurrentPDU.type = Data)
or (CurrentPDU.type = R2T)) {
if (Data-Digest-Bad) {
send-data-SNACK = TRUE;
LastRequiredDataSN = CurrentPDU.DataSN;
} else {
if (TCB.SoFarInOrder = TRUE) {
if (current DataSN is expected) {
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Increment TCB.ExpectedDataSN.
} else {
TCB.SoFarInOrder = FALSE;
send-data-SNACK = TRUE;
}
} else {
if (current DataSN was considered missing) {
remove current DataSN from missing PDU list.
} else if (current DataSN is higher than expected) {
send-data-SNACK = TRUE;
} else {
discard, return;
}
Adjust TCB.ExpectedDataSN if appropriate.
}
LastRequiredDataSN = CurrentPDU.DataSN - 1;
}
if (current PDU has F-bit set) {
TCB.FbitReceived = TRUE;
}
if (send-data-SNACK is TRUE and
task is not already considered failed) {
Recover-Data-if-Possible(LastRequiredDataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
if (CurrentPDU.type = R2T) {
Increment ActiveR2Ts for this task.
Build-And-Send-A-Data-Burst(Connection, CurrentPDU, TCB);
}
} else if (CurrentPDU.type = Response) {
if (Data-Digest-Bad) {
send-status-SNACK = TRUE;
} else {
TCB.StatusXferd = TRUE;
Store the status information in TCB.
if (ExpDataSN does not match) {
TCB.SoFarInOrder = FALSE;
Recover-Data-if-Possible(current DataSN, TCB);
}
if (missing data PDU list is empty) {
TCB.SoFarInOrder = TRUE;
}
send-status-SNACK = Evaluate-a-StatSN(Connection,
CurrentPDU.StatSN);
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}
if (send-status-SNACK is TRUE)
Recover-Status-if-Possible(Connection, CurrentPDU);
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN
*/
}
if (TCB.SoFarInOrder is TRUE ) {
if (TCB.StatusXferd is TRUE and
(TCB.FbitReceived is TRUE or
task is already considered failed)) {
SCSI-Task-Completion(TCB);
}
}
}
3 Target algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type = Data) {
Retrieve TContext from CurrentPDU.TargetTransferTag;
if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
} else {
if (current DataSN is not expected) {
Note the missing data PDUs in MissingDataRange[].
send-recovery-R2T = TRUE;
}
if (CurrentPDU.Fbit = TRUE) {
Decrement TCB.ActiveR2Ts.
if (current PDU is unsolicited and
data received is less than I/O size and
data received is less than FirstBurstSize) {
send-recovery-R2T = TRUE;
Note the missing data PDUs in MissingDataRange[].
}
}
}
Increment TContext.ExpectedDataSN.
if (send-recovery-R2T is TRUE and
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task is not already considered failed) {
if (TargetRecoveryR2TEnabled is TRUE) {
Increment TCB.ActiveR2Ts.
Build-And-Send-R2T(Connection, MissingDataRange, TCB);
} else {
if (current PDU is the last unsolicited)
TCB.Reason = "Not enough unsolicited data";
else
TCB.Reason = "Delivery subsystem failure";
}
}
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
} else if (CurrentPDU.type = SNACK) {
if (this is data retransmission request) {
if (TargetDataSNACKSupported) {
if (the request is satisfiable) {
Build-And-Send-A-Data-Burst(CurrentPDU, TCB);
} else {
TCB.Reason = "SNACK Rejected";
}
} else {
TCB.Reason = "SNACK Rejected";
}
if (TCB.Reason = "SNACK Rejected") {
Build-And-Send-Reject(Connection, CurrentPDU,
Data-SNACK-Reject);
Build-And-Send-Status(Connection, TCB);
}
} else {
Handle-Status-SNACK-request(Connection, CurrentPDU);
}
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY, NOT SHOWN */
}
}
Transfer-Context-Timeout-Handler(TContext)
{
Retrieve TCB and Connection from TContext.
Decrement TCB.ActiveR2Ts.
if (TargetRecoveryR2TEnabled is TRUE and
task is not already considered failed) {
Note the missing data PDUs in MissingDataRange[].
Build-And-Send-R2T(Connection, MissingDataRange, TCB);
} else {
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TCB.Reason = "Delivery subsystem failure";
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
}
}
42 Within-connection recovery algorithms
4 Procedure descriptions
Procedure descriptions:
Recover-Status-if-Possible(transport connection,
currently received PDU);
Evaluate-a-StatSN(transport connection, current StatSN);
Retransmit-Command-if-Possible(transport connection, CmdSN);
Build-And-Send-SSnack(transport connection);
Build-And-Send-Command(transport connection, task control block);
Command-Acknowledge-Timeout-Handler(task control block);
Status-Expect-Timeout-Handler(transport connection);
Build-And-Send-Nop-Out(transport connection);
Handle-Status-SNACK-request(transport connection, status SNACK PDU);
Retransmit-Status-Burst(status SNACK, task control block);
Is-Acknowledged(beginning StatSN, run size);
Implementation-specific tunables -
InitiatorCommandRetryEnabled, InitiatorStatusExpectNopEnabled,
InitiatorProactiveSNACKEnabled, InitiatorStatusSNACKEnabled,
TargetStatusSNACKSupported.
Notes:
The initiator algorithms deal only with unsolicited Nop-In PDUs for
generating status SNACKs. Solicited Nop-In PDU has an assigned
StatSN which when out-of-order could trigger the out-of-order StatSN
handling in Within-command algorithms, again leading to Recover-
Status-if-Possible.
The pseudo-code shown may result in retransmission of unacknowledged
commands in more cases than is necessary. This will not however
affect the correctness of operation since the target is required to
discard the duplicate CmdSNs.
The procedure Build-And-Send-Async is defined in Connection recovery
algorithms.
The procedure Status-Expect-Timeout-Handler describes how initiators
may proactively attempt to retrieve Status if they choose to. This
procedure is assumed to be triggered much before the standard ULP
timeout.
Satran, J. Standards-Track, Expires July 2002 222
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1. Initiator algorithms
Recover-Status-if-Possible(Connection, CurrentPDU)
{
if ((Connection.state = LOGGED_IN) and
connection is not already considered failed) {
if (InitiatorStatusSNACKEnabled) {
if (# of missing PDUs is trackable) {
Note the missing StatSNs in Connection;
Build-And-Send-SSnack(Connection);
} else {
Connection.PerformConnectionRecovery = TRUE;
}
} else {
Connection.PerformConnectionRecovery = TRUE;
}
if (Connection.PerformConnectionRecovery is TRUE) {
Start-Timer(Connection-Recovery-Handler, Connection, 0);
}
}
}
Retransmit-Command-if-Possible(Connection, CmdSN)
{
if (InitiatorCommandRetryEnabled) {
Retrieve the InitiatorTaskTag, and thus TCB for the CmdSN.
Build-And-Send-Command(Connection, TCB);
}
}
Evaluate-a-StatSN(Connection, StatSN)
{
send-status-SNACK = FALSE;
if (Connection.SoFarInOrder is TRUE) {
if (current StatSN is the expected) {
Increment Connection.ExpectedStatSN.
} else {
Connection.SoFarInOrder = FALSE;
send-status-SNACK = TRUE;
}
} else {
if (current StatSN was considered missing) {
remove current StatSN from the missing list.
} else {
if (current StatSN is higher than expected){
send-status-SNACK = TRUE;
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iSCSI 19-Nov-01
} else {
discard, return;
}
}
Adjust Connection.ExpectedStatSN if appropriate.
if (missing StatSN list is empty) {
Connection.SoFarInOrder = TRUE;
}
}
return send-status-SNACK;
}
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB for CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type = Nop-In) {
if (the PDU is unsolicited) {
if (current StatSN is not expected) {
Recover-Status-if-Possible(Connection, CurrentPDU);
}
if (current ExpCmdSN is not our NextCmdSN) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.ExpCmdSN);
}
}
} else if (CurrentPDU.type = Reject) {
if (it is a data digest error on immediate data) {
Retransmit-Command-if-Possible(Connection,
CurrentPDU.BadPDUHeader.CmdSN);
}
} else if (CurrentPDU.type = Response) {
send-status-SNACK = Evaluate-a-StatSN(Connection,
CurrentPDU.StatSN);
if (send-status-SNACK is TRUE)
Recover-Status-if-Possible(Connection, CurrentPDU);
} else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Command-Acknowledge-Timeout-Handler(TCB)
{
Retrieve the Connection for TCB.
Retransmit-Command-if-Possible(Connection, TCB.CmdSN);
Satran, J. Standards-Track, Expires July 2002 224
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}
Status-Expect-Timeout-Handler(Connection)
{
if (InitiatorStatusExpectNopEnabled) {
Build-And-Send-Nop-Out(Connection);
} else if (InitiatorProactiveSNACKEnabled){
if ((Connection.state = LOGGED_IN) and
connection is not already considered failed) {
Build-And-Send-SSnack(Connection);
}
}
}
2. Target algorithms
Handle-Status-SNACK-request(Connection, CurrentPDU)
{
if (TargetStatusSNACKSupported) {
if (request for an acknowledged run) {
Build-And-Send-Reject(Connection, CurrentPDU,
Protocol-Error);
} else if (request for an untransmitted run) {
discard, return;
} else {
Retransmit-Status-Burst(CurrentPDU, TCB);
}
} else {
Build-And-Send-Async(Connection, DroppedConnection,
0, TargetConnectionRecoveryTimeout);
}
}
5 Connection recovery algorithms
3. Procedure descriptions
Build-And-Send-Async(transport connection, reason code,
minimum time, maximum time);
Pick-A-Logged-In-Connection(session);
Build-And-Send-Logout(transport connection, logout connection
identifier, reason code);
PerformImplicitLogout(transport connection, logout connection
identifier, target information);
PerformLogin(transport connection, target information);
CreateNewTransportConnection(target information);
Build-And-Send-Command(transport connection, task control block);
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Connection-Recovery-Handler(transport connection);
Connection-Resource-Timeout-Handler(transport connection);
Quiesce-And-Prepare-for-New-Allegiance(session, task control block);
Build-And-Send-Logout-Response(transport connection,
CID of connection in recovery, reason code);
Build-And-Send-TaskMgmt-Response(transport connection,
task mgmt command PDU, response code);
Establish-New-Allegiance(task control block, transport connection);
Schedule-Command-To-Continue(task control block);
Notes:
Transport exception conditions such as unexpected connection
termination, connection reset, hung connection while the connection
is in the full-feature phase, are all assumed to be asynchronously
signaled to iSCSI layer using the Transport_Exception_Handler
procedure.
4. Initiator algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
Retrieve TCB from CurrentPDU.InitiatorTaskTag.
if (CurrentPDU.type = Async) {
if ((CurrentPDU.iSCSIEvent = LogoutRequest) or
(CurrentPDU.iSCSIEvent = ConnectionDropped)) {
Retrieve the AffectedConnection for CurrentPDU.Parameter1.
AffectedConnection.State = ASYNC_MSG_RCVD;
AffectedConnection.PerformConnectionRecovery = TRUE;
Start-Timer(Connection-Recovery-Handler,
AffectedConnection, CurrentPDU.Parameter2);
}
} else if (CurrentPDU.type = LogoutResponse) {
Retrieve the RecoveryConnection for CurrentPDU.CID.
if (CurrentPDU.Response = failure) {
RecoveryConnection.State = RECOVERY_START;
Start-Timer(Connection-Resource-Timeout-Handler,
RecoveryConnection, InitiatorRecoveryTimeout);
} else {
RecoveryConnection.State = FREE;
}
} else if (CurrentPDU.type = LoginResponse) {
if (this is a response to an implicit Logout) {
Retrieve the RecoveryConnection.
if (successful) {
RecoveryConnection.State = FREE;
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Connection.State = LOGGED_IN;
} else {
RecoveryConnection.State = RECOVERY_START;
DestroyTransportConnection(Connection);
Start-Timer(Connection-Resource-Timeout-Handler,
RecoveryConnection, InitiatorRecoveryTimeout);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
if (RecoveryConnection.State = FREE) {
for (each command that was active on RecoveryConnection) {
NewConnection = Pick-A-Logged-In-Connection(Session);
Build-And-Send-Command(NewConnection, TCB);
}
}
}
Connection-Recovery-Handler(Connection)
{
Retrieve Session from Connection.
if (Connection can still exchange iSCSI PDUs) {
NewConnection = Connection;
} else {
if (there are other logged-in connections) {
NewConnection = Pick-A-Logged-In-Connection(Session);
} else {
NewConnection =
CreateTransportConnection(Session.OtherEndInfo);
Initiate an implicit Logout on NewConnection for
Connection.CID.
return;
}
}
Build-And-Send-Logout(NewConnection, Connection.CID,
RecoveryRemove);
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionRecovery = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = XPT_CLEANUP;
} else {
Connection.State = RECOVERY_START;
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}
Start-Timer(Connection-Recovery-Handler, Connection, 0);
}
5. Target algorithms
Receive-a-In-PDU(Connection, CurrentPDU)
{
check-basic-validity(CurrentPDU);
if (Header-Digest-Bad) discard, return;
else if (Data-Digest-Bad) {
Build-And-Send-Reject(Connection, CurrentPDU,
Payload-Digest-Error);
discard, return;
}
Retrieve TCB and Session.
if (CurrentPDU.type = Logout) {
if (CurrentPDU.ReasonCode = RecoveryRemove) {
Retrieve the RecoveryConnection from CurrentPDU.CID).
for (each command active on RecoveryConnection) {
Quiesce-And-Prepare-for-New-Allegiance(Session, TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(RecoveryConnection);
if ((quiescing successful) and (cleanup successful)) {
Build-And-Send-Logout-Response(Connection,
RecoveryConnection.CID, Sucess);
} else {
Build-And-Send-Logout-Response(Connection,
RecoveryConnection.CID, Failure);
}
}
} else if (CurrentPDU.type = TaskManagement) {
if (CurrentPDU.function = "TaskReassign") {
if (Session.FailoverSupport is not TRUE) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task failover not supported");
} else if (task is not found) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task not in task set");
} else if (task is currently allegiant) {
Build-And-Send-TaskMgmt-Response(Connection,
CurrentPDU, "Task still allegiant");
} else {
Establish-New-Allegiance(TCB, Connection);
TCB.CurrentlyAllegiant = TRUE;
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Schedule-Command-To-Continue(TCB);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionRecovery = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = XPT_CLEANUP;
} else {
Connection.State = RECOVERY_START;
}
Start-Timer(Connection-Resource-Timeout-Handler, Connection,
TargetConnectionRecoveryTimeout);
if (this Session has full-feature phase connections left) {
DifferentConnection = Pick-A-Logged-In-Connection(Session);
Build-And-Send-Async(DifferentConnection, DroppedConnection,
0, TargetConnectionRecoveryTimeout);
}
}
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included on all such copies and derivative works. However, this
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Satran, J. Standards-Track, Expires July 2002 230
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