iSCSI 20-January-02
IPS Julian Satran
Internet Draft Daniel Smith
draft-ietf-ips-iscsi-10.txt Kalman Meth
Category: standards-track Ofer Biran
Jim Hafner
IBM
Costa Sapuntzakis
Mark Bakke
Cisco Systems
Matt Wakeley
Agilent Technolo-
gies
Luciano Dalle Ore
Quantum
Paul Von Stamwitz
Adaptec
Randy Haagens
Mallikarjun Chadal-
apaka
Hewlett-Packard Co.
Efri Zeidner
SANGate
iSCSI
Julian Satran Expires August 2002 1
iSCSI 20-January-02
Status of this Memo
This document is an Internet-Draft and fully conforms to
all provisions of Section 10 of [RFC2026].
Internet-Drafts are working documents of the Internet
Engineering Task Force (IETF), its areas, and its working
groups. Note that other groups may also distribute working
documents as Internet-Drafts. Internet-Drafts are draft
documents valid for a maximum of six months and may be
updated, replaced, or 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 trans-
port 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 con-
tributed 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 help-
ing to shape this document: John Hufferd, Prasenjit
Sarkar, Meir Toledano, John Dowdy, Steve Legg, Alain Aza-
gury (IBM), Dave Nagle (CMU), David Black (EMC), John
Matze (Veritas - now with Stonefly Networks), Steve
DeGroote, Mark Shrandt (NuSpeed), Gabi Hecht (Gadzoox),
Robert Snively (Brocade), Nelson Nachum (StorAge), Uri
Julian Satran Expires August 2002 2
iSCSI 20-January-02
Elzur (Broadcom). Many more helped clean up and improve
this document within the IPS working group. We are espe-
cially grateful to David Robinson and Raghavendra Rao
(Sun), Charles Monia, Joshua Tseng (Nishan), Somesh Gupta
(Silverback Systems), Michael Krause, Pierre Labat, San-
tosh Rao, Matthew Burbridge (HP), Stephen Bailey (Sand-
burst), Robert Elliott (Compaq), Steve Senum, Ayman
Ghanem (CISCO), Barry Reinhold (Trebia Networks), Bob
Russell (UNH), Bill Lynn (Adaptec), Doug Otis (Sanlight),
Robert Griswold and Bill Moody (Crossroads). The recovery
chapter was enhanced with help from Stephen Bailey (Sand-
burst), Somesh Gupta (HP), Venkat Rangan (Rhapsody Net-
works), 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 con-
sidered in conjunction with the "Naming & Discov-
ery"[NDT], "Boot"[BOOT] and "Securing iSCSI, iFCP and
FCIP"[SEC-IPS] documents.
The "Naming & Discovery" document 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" document is authored by:
Prasenjit Sarkar (IBM), Duncan Missimer (HP) and
Costa Sapuntzakis (CISCO).
The "Securing iSCSI, iFCP and FCIP" document is authored
by:
Bernard Aboba, William Dixon (Microsoft), David Black
(EMC),
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iSCSI 20-January-02
Joseph Tardo, Uri Elzur (Broadcom), Mark Bakke, Steve
Senum (Cisco Systems), Howard Herbert, Jesse Walker
(Intel), Julian Satran, Ofer Biran and Charles Kun-
zinger (IBM).
We are grateful to all of them for their good work and for
helping us correlate this document with the ones they pro-
duced.
Conventions used in this document
In examples, "I->" and "T->" indicate iSCSI PDUs sent by
the initiator and target respectively.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
"SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be inter-
preted as described in RFC2119.
Change Log
The following changes were made from draft-ietf-ips-
iSCSI-09 to draft-ietf-ips-iSCSI-10:
- Clarifying MaxOutstandingR2T
- Widening the scope of Reject reason code 0x09 to
mean "Invalid PDU field".
- Changes in the "iSCSI connection termination" sec-
tion to make the terminology usage consistent with
the rest of the draft.
- Adding transition T18 in standard connection state
diagram, and its description.
- Other minor wording changes in the state transi-
tions chapter to address "session close" case and
others.
- Adding a new state Q5(IN_CONTINUE) to the target
session state diagram to resolve transitions N8 and
N9 off Q2.
- Removed the AHS drop bit feature.
- Removed the qualifier field in Task Management
Response PDU, and added a new response "Function
authorization failed".
- Clarified the fate of regular SCSI reservations on
a session timeout, compared to a transient session
failure.
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- Added wording in R2T section to address the case of
receiving a smaller write data sequence than was
asked for in an R2T.
- Changes and fixes in recovery algorithms to be con-
sistent with the rest of the draft.
- Changed the "Invalid SNACK" Reject reason code to
"Invalid data ACK" since the invalid SNACK is
already covered under "Protocol error". Also
treating DataSN and R2TSN equivalently in this
case.
- Change in the SNACK section to require a Reject
"Protocol error" on an invalid SNACK.
- Time2Retain 0 in Logout Response indicates connec-
tion/session cant recover
- Coordinate DataSequenceInOrder with Error recovery
level and MaxOutstandingR2T, also stating that only
the last read/write sequence is recoverable under
digest error recovery if DataSequenceInOrder=yes
- Alias designation format appendix is again out(!) -
T10 has decided it will go in SPC3
- Task Management synchronization moved to the target
(task management response given after task manage-
ment action and confirmed delivery of all previous
responses)
- Removed the dont care value in numerical negotia-
tions
- Changed Marker negotiation to allow it to be closed
in one round
- Marker position is not dependent of the length of
the login phase
- Statement made that reserved bits do not have to be
checked at the beginning of Chapter 10
- InitialR2T, BidiInitialR2T and ImmediateData
changed to LO
- I bit (equivalent) in responses made 0
- Added a "double response" version for the ? key
value to Section 2.2.4 Text Mode Negotiation
- ? value can be used only outside Login
- added :, [ and ] as allowed in key values
- allow 0 in LogoutLoginMax and Min
- after task reassign no SNACK mandated, the function
must be performed by target with information made
available by reassign
- removed the third party command section - SCSI now
handles everything needed (including iSCSI alias-
ing)
The following changes were made from draft-ietf-ips-
iSCSI-08 to draft-ietf-ips-iSCSI-09:
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- 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
- 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 fail-
ure
- Changed version to 0x03 - ALL VERSION NUMBERS are
temporary up to "Rafting" (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 Section 10.2.1.7 Initiator Task
Tag
- Added a clarification to Section 2.2.2.1 Command
Numbering and Acknowledging - response to a command
should not precede acknowledgment.
- Added clarification to Section 10.7 SCSI Data-out &
SCSI Data-in - good status in Data-In must be sup-
ported by initiators
- Clarified InitiatorName is required at login in
Section 4.1 Login Phase Start
- Another clarification for SecurityContextComplete
in Section 4.2 iSCSI Security Negotiation
- Added "command not supported in this session type"
to reject reasons
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- Discovery session implies MaxConnections = 1
- Second appearance of TargetAddress deleted
- Padding forbidden for non-end-of-sequence data PDUs
- Removed Boot and Copenhagener Session types
- Changed explanation of ExpDataSN
- Removed/corrected response 05 in Section 10.4.3
Response
- Brought Section 2.2.7 Naming and Addressing 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
Section 2.2.5 iSCSI Full Feature Phase
- Added new Reject reason codes, tabular listing and
a pointer to Section 10.14.3 Reason Code
- Added additional Reject usage semantics on CmdSN
and DataSN to Section 10.14.3 Reason Code
- 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 6 State Transitions.
- 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 10.6 Task Management
Function Response linking SCSI mode pages to Async
Messages
- Changed the ASC/ASCQ values to better mean "not
enough unsolicited data"
- Names examples include date
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- Removed references to S bit in Section 10.4 SCSI
Response
- 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 3, changed all examples
in Appendix D. - Login Phase Examples - 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 Section 3 SCSI Mode
Parameters for iSCSI, out DataPDULength, DataSe-
quenceOrder
- Changed all sense keys to aborted command in the
table in Section 10.4.2 Status
- 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 appen-
dix. 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 8 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 transi-
tions in Chapter 6.
- Several changes in Chapter 7 corresponding to the
new task management function "reassign". Other
language changes in Chapter 7 for better descrip-
tion. Format errors are mandated to cause session
failures.
- Renamed the erstwhile error recovery levels as
error recovery classes, and renamed "within-ses-
sion" recovery to "connection recovery" to better
reflect the mechanics.
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- Added Section 7.12 Error Recovery Hierarchy to
define the error recovery hierarchy.
- Modifications to error recovery algorithms in
Appendix F.
- Added a new Reject reason code "Invalid SNACK",
added DataSN to Reject PDU.
- Changed Section 10.17 Reject to use the "Invalid
SNACK" reason code.
- Removed a Logout reason code in Section 10.14
Logout Request to be consistent with Section 10.9
Asynchronous Message.
- Collapsed the two event fields in Async Event and
added vendor specific event
- Immediate data can be negotiated anytime (consis-
tency)
- Removed replay as a protocol notion and all refer-
ences 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 speci-
fied 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
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- 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
- 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 gov-
erns data PDU ordering within Sequence (DataPDU-
InOrder). 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 authori-
zation 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 "gener-
alized" to all iSCSI tagged commands (they are
named now Task Management command and response).
Their behavior with respect to their CmdSN is clar-
ified 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 (CopyMan-
agerSession) to be used between a Copy Manager and
all of its target; it may help define authentica-
tion 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., ini-
tiate 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!);
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iSCSI 20-January-02
many others can't be changed anymore while the ses-
sion 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
- A response with F=1 during negotiation may not con-
tain key=value pairs that may require additional
answers from the initiator
- Clarified the meaning of the F bit on Write com-
mands with regard to immediate and unsolicited
data; F bit 0 means that unsolicited data will fol-
low 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 Mes-
sage
- Changed "Who" to "Who can send" in appendix
- Clarified meaning of parameters on 2.18.1 - Asyn-
chronous 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
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- Added a Login Response code indicating that a ses-
sion 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 connec-
tion" 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)
- Added more text to the task management command 2.5
- Removed EnableACA and its dependents (in task man-
agement) 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 corre-
spond 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 Condi-
tion 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 rep-
licas 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 sup-
port for command allegiance change (command retry
on another connection)
- Status SNACK for an acknowledged status is a proto-
col error (cause for reject)
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- 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 com-
mand 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 pre-
fixes also reversed names
- text in 8.3 revised (task management implementation
mechanism)
- 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
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- 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 consis-
tencies
- 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 send-
ing 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.
Table of Contents
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Status of this Memo . . . . . . . . . . . . . . . . . . 2
Abstract . . . . . . . . . . . . . . . . . . . . . . . . 2
Acknowledgements . . . . . . . . . . . . . . . . . . . . 2
Conventions used in this document . . . . . . . . . . . 4
Change Log . . . . . . . . . . . . . . . . . . . . . . . 4
1. Definitions . . . . . . . . . . . . . . . . . . . . . 22
2. Overview . . . . . . . . . . . . . . . . . . . . . . 27
2.1 SCSI Concepts . . . . . . . . . . . . . . . . . . 27
2.2 iSCSI Concepts and Functional Overview . . . . . . 28
2.2.1 Layers and Sessions . . . . . . . . . . . . . 29
2.2.2 Ordering and iSCSI Numbering . . . . . . . . . 30
2.2.2.1 Command Numbering and Acknowledging . . . 30
2.2.2.2 Response/Status Numbering and Acknowledging
34
2.2.2.3 Data Sequencing . . . . . . . . . . . . . 34
2.2.3 iSCSI Login . . . . . . . . . . . . . . . . . 35
2.2.4 Text Mode Negotiation . . . . . . . . . . . . 36
2.2.5 iSCSI Full Feature Phase . . . . . . . . . . . 39
2.2.6 iSCSI Connection Termination . . . . . . . . . 41
2.2.7 Naming and Addressing . . . . . . . . . . . . 42
2.2.8 Persistent State . . . . . . . . . . . . . . . 44
2.2.9 Message Synchronization and Steering . . . . . 45
2.2.9.1 Rationale . . . . . . . . . . . . . . . . 45
2.2.9.2 Synchronization (sync) and Steering Functional
Model . . . . . . . . . . . . . . . . . . . . . . . . . 46
2.2.9.3 Sync and Steering and Other Encapsulation Lay-
ers . . . . . . . . . . . . . . . . . . . . . . . . . . 48
2.2.9.4 Sync/Steering and iSCSI PDU Size . . . . 49
2.3 iSCSI Session Types . . . . . . . . . . . . . . . 50
2.4 SCSI to iSCSI Concepts Mapping Model . . . . . . . 50
2.4.1 iSCSI Architecture Model . . . . . . . . . . . 51
2.4.2 SCSI Architecture Model . . . . . . . . . . . 55
2.4.3 Consequences of the Model . . . . . . . . . . 57
2.4.3.1 I_T Nexus State . . . . . . . . . . . . . 58
2.4.3.2 SCSI Mode Pages . . . . . . . . . . . . . 58
2.5 Request/Response Summary . . . . . . . . . . . . . 59
2.5.1 Request/Response types carrying SCSI payload . 59
2.5.1.1 SCSI-Command . . . . . . . . . . . . . . 59
2.5.1.2 SCSI-Response . . . . . . . . . . . . . . 59
2.5.1.3 Task Management Function Request . . . . 60
2.5.1.4 Task Management Function Response . . . . 61
2.5.1.5 SCSI Data-out and SCSI Data-in . . . . . 61
2.5.1.6 Ready To Transfer (R2T) . . . . . . . . . 62
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2.5.1.7 Asynchronous Message . . . . . . . . . . 62
2.5.2 Requests/Responses carrying iSCSI Only Payload 63
2.5.2.1 Text Request and Text Response . . . . . 63
2.5.2.2 Login Request and Login Response . . . . 63
2.5.2.3 Logout Request and Response . . . . . . . 64
2.5.2.4 SNACK Request . . . . . . . . . . . . . 65
2.5.2.5 Reject . . . . . . . . . . . . . . . . . 65
2.5.2.6 NOP-Out Request and NOP-In Response . . . 65
3. SCSI Mode Parameters for iSCSI . . . . . . . . . . . 67
4. Login Phase . . . . . . . . . . . . . . . . . . . . . 68
4.1 Login Phase Start . . . . . . . . . . . . . . . . 70
4.2 iSCSI Security Negotiation . . . . . . . . . . . . 72
4.3 Operational Parameter Negotiation During the Login
Phase . . . . . . . . . . . . . . . . . . . . . . . . . 73
5. Operational Parameter Negotiation Outside the Login Phase
75
6. State Transitions . . . . . . . . . . . . . . . . . . 77
6.1 Standard Connection State Diagrams . . . . . . . . 77
6.1.1 Standard Connection State Diagram for an Initiator
77
6.1.2 Standard Connection State Diagram for a Target 79
6.1.3 State Descriptions for Initiators and Targets 81
6.1.4 State Transition Descriptions for Initiators and
Targets . . . . . . . . . . . . . . . . . . . . . . . . 82
6.2 Connection Cleanup State Diagram for Initiators and
Targets . . . . . . . . . . . . . . . . . . . . . . . . 86
6.2.1 State Descriptions for Initiators and Targets 87
6.2.2 State Transition Descriptions for Initiators and
Targets . . . . . . . . . . . . . . . . . . . . . . . . 88
6.3 Session State Diagram . . . . . . . . . . . . . . 90
6.3.1 Session State Diagram for an Initiator . . . . 90
6.3.2 Session State Diagram for a Target . . . . . . 91
6.3.3 State Descriptions for Initiators and Targets 92
6.3.4 State Transition Descriptions for Initiators and
Targets . . . . . . . . . . . . . . . . . . . . . . . . 93
7. iSCSI Error Handling and Recovery . . . . . . . . . . 95
7.1 Retry and Reassign in Recovery . . . . . . . . . . 95
7.1.1 Usage of Retry . . . . . . . . . . . . . . . . 95
7.1.2 Allegiance Reassignment . . . . . . . . . . . 96
7.2 Usage Of Reject PDU in Recovery . . . . . . . . . 97
7.3 Format Errors . . . . . . . . . . . . . . . . . . 97
7.4 Digest Errors . . . . . . . . . . . . . . . . . . 98
7.5 Sequence Errors . . . . . . . . . . . . . . . . . 99
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7.6 SCSI Timeouts . . . . . . . . . . . . . . . . . 100
7.7 Negotiation Failures . . . . . . . . . . . . . . 101
7.8 Protocol Errors . . . . . . . . . . . . . . . . 102
7.9 Connection Failures . . . . . . . . . . . . . . 102
7.10 Session Errors . . . . . . . . . . . . . . . . 103
7.11 Recovery Classes . . . . . . . . . . . . . . . 103
7.11.1 Recovery Within-command . . . . . . . . . . 104
7.11.2 Recovery Within-connection . . . . . . . . 105
7.11.3 Connection Recovery . . . . . . . . . . . . 106
7.11.4 Session Recovery . . . . . . . . . . . . . 107
7.12 Error Recovery Hierarchy . . . . . . . . . . . 107
8. Security Considerations . . . . . . . . . . . . . . 111
8.1 iSCSI Security Mechanisms . . . . . . . . . . . 111
8.2 In-band Initiator-Target Authentication . . . . 112
8.3 IPsec . . . . . . . . . . . . . . . . . . . . . 113
8.3.1 Data Integrity and Authentication . . . . . 113
8.3.2 Confidentiality . . . . . . . . . . . . . . 114
8.3.3 Security Associations and Key Management . . 114
9. Notes to Implementers . . . . . . . . . . . . . . . 116
9.1 Multiple Network Adapters . . . . . . . . . . . 116
9.1.1 Conservative Reuse of ISIDs . . . . . . . . 116
9.1.2 iSCSI Name and ISID/TSID Use . . . . . . . . 117
9.2 Autosense and Auto Contingent Allegiance (ACA) . 119
9.3 Command Retry and Cleaning Old Command Instances 119
9.4 Synch and Steering Layer and Performance . . . . 120
9.5 Unsolicited Data and Performance . . . . . . . . 120
10. iSCSI PDU Formats . . . . . . . . . . . . . . . . 121
10.1 iSCSI PDU Length and Padding . . . . . . . . . 121
10.2 PDU Template, Header, and Opcodes . . . . . . . 121
10.2.1 Basic Header Segment (BHS) . . . . . . . . 123
10.2.1.1 I . . . . . . . . . . . . . . . . . . 124
10.2.1.2 Opcode . . . . . . . . . . . . . . . . 125
10.2.1.3 Opcode-specific Fields . . . . . . . . 126
10.2.1.4 TotalAHSLength . . . . . . . . . . . . 126
10.2.1.5 DataSegmentLength . . . . . . . . . . 126
10.2.1.6 LUN . . . . . . . . . . . . . . . . . 126
10.2.1.7 Initiator Task Tag . . . . . . . . . . 126
10.2.2 Additional Header Segment (AHS) . . . . . . 126
10.2.2.1 AHSType . . . . . . . . . . . . . . . 127
10.2.2.2 AHSLength . . . . . . . . . . . . . . 127
10.2.2.3 Extended CDB AHS . . . . . . . . . . . 127
10.2.2.4 Bidirectional Expected Read-Data Length AHS
128
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10.2.3 Header Digest and Data Digest . . . . . . . 129
10.2.4 Data Segment . . . . . . . . . . . . . . . 129
10.3 SCSI Command . . . . . . . . . . . . . . . . . . 130
10.3.1 Flags and Task Attributes (byte 1) . . . . 132
10.3.2 CRN . . . . . . . . . . . . . . . . . . . . 133
10.3.3 CmdSN - Command Sequence Number . . . . . . 133
10.3.4 ExpStatSN . . . . . . . . . . . . . . . . . 133
10.3.5 Expected Data Transfer Length . . . . . . . 133
10.3.6 CDB - SCSI Command Descriptor Block . . . . 134
10.3.7 Data Segment - Command Data . . . . . . . . 134
10.4 SCSI Response . . . . . . . . . . . . . . . . . 135
10.4.1 Flags (byte 1) . . . . . . . . . . . . . . 137
10.4.2 Status . . . . . . . . . . . . . . . . . . 138
10.4.3 Response . . . . . . . . . . . . . . . . . 138
10.4.4 Residual Count . . . . . . . . . . . . . . 141
10.4.5 Bidirectional Read Residual Count . . . . . 141
10.4.6 Data Segment - Sense and Response Data Segment
141
10.4.6.1 SenseLength . . . . . . . . . . . . . 142
10.4.7 ExpDataSN . . . . . . . . . . . . . . . . . 142
10.4.8 StatSN - Status Sequence Number . . . . . . 142
10.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator
143
10.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this
Initiator . . . . . . . . . . . . . . . . . . . . . . 143
10.5 Task Management Function Request . . . . . . . . 144
10.5.1 Function . . . . . . . . . . . . . . . . . 145
10.5.2 LUN . . . . . . . . . . . . . . . . . . . . 147
10.5.3 Referenced Task Tag . . . . . . . . . . . . 147
10.5.4 RefCmdSN or ExpDataSN . . . . . . . . . . . 148
10.6 Task Management Function Response . . . . . . . 149
10.6.1 Response . . . . . . . . . . . . . . . . . 151
10.6.2 Referenced Task Tag . . . . . . . . . . . . 152
10.7 SCSI Data-out & SCSI Data-in . . . . . . . . . . 153
10.7.1 F (Final) Bit . . . . . . . . . . . . . . . 157
10.7.2 A (Acknowledge) bit . . . . . . . . . . . . 158
10.7.3 Target Transfer Tag . . . . . . . . . . . . 158
10.7.4 StatSN . . . . . . . . . . . . . . . . . . 158
10.7.5 DataSN . . . . . . . . . . . . . . . . . . 159
10.7.6 Buffer Offset . . . . . . . . . . . . . . . 159
10.7.7 DataSegmentLength . . . . . . . . . . . . . 159
10.7.8 Flags (byte 1) . . . . . . . . . . . . . . 160
10.8 Ready To Transfer (R2T) . . . . . . . . . . . . 161
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10.8.1 R2TSN . . . . . . . . . . . . . . . . . . . 163
10.8.2 StatSN . . . . . . . . . . . . . . . . . . 163
10.8.3 Desired Data Transfer Length and Buffer Offset
163
10.8.4 Target Transfer Tag . . . . . . . . . . . . 164
10.9 Asynchronous Message . . . . . . . . . . . . . . 165
10.9.1 AsyncEvent . . . . . . . . . . . . . . . . 167
10.9.2 AsyncVCode . . . . . . . . . . . . . . . . 169
10.9.3 Sense Data or iSCSI Event Data . . . . . . 169
10.10 Text Request . . . . . . . . . . . . . . . . . 170
10.10.1 F (Final) Bit . . . . . . . . . . . . . . 172
10.10.2 Initiator Task Tag . . . . . . . . . . . . 172
10.10.3 Target Transfer Tag . . . . . . . . . . . 172
10.10.4 Text . . . . . . . . . . . . . . . . . . . 173
10.11 Text Response . . . . . . . . . . . . . . . . . 175
10.11.1 F (Final) Bit . . . . . . . . . . . . . . 177
10.11.2 Initiator Task Tag . . . . . . . . . . . . 178
10.11.3 Target Transfer Tag . . . . . . . . . . . 178
10.11.4 Text Response Data . . . . . . . . . . . . 178
10.12 Login Request . . . . . . . . . . . . . . . . . 180
10.12.1 T (Transit) Bit . . . . . . . . . . . . . 182
10.12.2 X - Restart Connection . . . . . . . . . . 182
10.12.3 CSG and NSG . . . . . . . . . . . . . . . 183
10.12.4 Version-max . . . . . . . . . . . . . . . 183
10.12.5 Version-min . . . . . . . . . . . . . . . 184
10.12.6 ISID . . . . . . . . . . . . . . . . . . . 184
10.12.7 TSID . . . . . . . . . . . . . . . . . . . 185
10.12.8 Connection ID - CID . . . . . . . . . . . 185
10.12.9 CmdSN . . . . . . . . . . . . . . . . . . 186
10.12.10 ExpStatSN . . . . . . . . . . . . . . . . 186
10.12.11 Login Parameters . . . . . . . . . . . . 186
10.13 Login Response . . . . . . . . . . . . . . . . 187
10.13.1 Version-max . . . . . . . . . . . . . . . 189
10.13.2 Version-active . . . . . . . . . . . . . . 189
10.13.3 TSID . . . . . . . . . . . . . . . . . . . 190
10.13.4 StatSN . . . . . . . . . . . . . . . . . . 190
10.13.5 Status-Class and Status-Detail . . . . . . 190
10.13.6 T (Transit) bit . . . . . . . . . . . . . 193
10.14 Logout Request . . . . . . . . . . . . . . . . 194
10.14.1 CID . . . . . . . . . . . . . . . . . . . 197
10.14.2 ExpStatSN . . . . . . . . . . . . . . . . 197
10.14.3 Reason Code . . . . . . . . . . . . . . . 197
10.15 Logout Response . . . . . . . . . . . . . . . . 198
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10.15.1 Response . . . . . . . . . . . . . . . . . 200
10.15.2 Time2Wait . . . . . . . . . . . . . . . . 200
10.15.3 Time2Retain . . . . . . . . . . . . . . . 200
10.16 SNACK Request . . . . . . . . . . . . . . . . 202
10.16.1 Type . . . . . . . . . . . . . . . . . . . 203
10.16.2 BegRun . . . . . . . . . . . . . . . . . . 204
10.16.3 RunLength . . . . . . . . . . . . . . . . 204
10.17 Reject . . . . . . . . . . . . . . . . . . . . 206
10.17.1 Reason . . . . . . . . . . . . . . . . . . 207
10.17.2 DataSN . . . . . . . . . . . . . . . . . . 210
10.17.3 Complete Header of Bad PDU . . . . . . . . 210
10.18 NOP-Out . . . . . . . . . . . . . . . . . . . . 211
10.18.1 Initiator Task Tag . . . . . . . . . . . . 212
10.18.2 Target Transfer Tag . . . . . . . . . . . 213
10.18.3 Ping Data . . . . . . . . . . . . . . . . 213
10.19 NOP-In . . . . . . . . . . . . . . . . . . . . 214
10.19.1 Target Transfer Tag . . . . . . . . . . . 215
10.19.2 LUN . . . . . . . . . . . . . . . . . . . 216
11. iSCSI Security Keys and Values . . . . . . . . . . 217
11.1 AuthMethod . . . . . . . . . . . . . . . . . . 217
11.2 Kerberos . . . . . . . . . . . . . . . . . . . 219
11.3 Simple Public-Key Mechanism (SPKM) . . . . . . 219
11.4 Secure Remote Password (SRP) . . . . . . . . . 221
11.5 Challenge Handshake Authentication Protocol (CHAP)
222
12. Login/Text Operational Keys . . . . . . . . . . . 224
12.1 HeaderDigest and DataDigest . . . . . . . . . . 224
12.2 MaxConnections . . . . . . . . . . . . . . . . 226
12.3 SendTargets . . . . . . . . . . . . . . . . . . 226
12.4 TargetName . . . . . . . . . . . . . . . . . . 226
12.5 InitiatorName . . . . . . . . . . . . . . . . . 227
12.6 TargetAlias . . . . . . . . . . . . . . . . . . 227
12.7 InitiatorAlias . . . . . . . . . . . . . . . . 228
12.8 TargetAddress . . . . . . . . . . . . . . . . . 228
12.9 InitialR2T . . . . . . . . . . . . . . . . . . 229
12.10 BidiInitialR2T . . . . . . . . . . . . . . . . 230
12.11 ImmediateData . . . . . . . . . . . . . . . . 230
12.12 MaxRecvPDULength . . . . . . . . . . . . . . . 232
12.13 MaxBurstSize . . . . . . . . . . . . . . . . . 233
12.14 FirstBurstSize . . . . . . . . . . . . . . . . 233
12.15 LogoutLoginMaxTime . . . . . . . . . . . . . . 233
12.16 LogoutLoginMinTime . . . . . . . . . . . . . . 234
12.17 MaxOutstandingR2T . . . . . . . . . . . . . . 234
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12.18 DataPDUInOrder . . . . . . . . . . . . . . . . 235
12.19 DataSequenceInOrder . . . . . . . . . . . . . 235
12.20 ErrorRecoveryLevel . . . . . . . . . . . . . . 236
12.21 SessionType . . . . . . . . . . . . . . . . . 236
12.22 The Vendor Specific Key Format . . . . . . . . 237
13. IANA Considerations . . . . . . . . . . . . . . . 238
References and Bibliography . . . . . . . . . . . . . 239
Authors' Addresses . . . . . . . . . . . . . . . . . . 241
Appendix A. Sync and Steering with Fixed Interval Markers
244
A.1 Markers At Fixed Intervals . . . . . . . . . . . 245
A.2 Initial Marker-less Interval . . . . . . . . . . 245
A.3 Negotiation . . . . . . . . . . . . . . . . . . 246
Appendix B. Sync and Steering with Constant Overhead Word
Stuffing
(COWS) . . . . . . . . . . . . . . . . . . . . . . . . 248
B.4 Negotiation . . . . . . . . . . . . . . . . . . 251
B.5 Sent PDU processing . . . . . . . . . . . . . . 251
B.6 Received PDU processing . . . . . . . . . . . . 251
B.7 Search for framing processing . . . . . . . . . 251
Appendix C. Examples . . . . . . . . . . . . . . . . . 252
C.8 Read Operation Example . . . . . . . . . . . . . 252
C.9 Write Operation Example . . . . . . . . . . . . 253
C.10 R2TSN/DataSN use Examples . . . . . . . . . . . 254
C.11 CRC Examples . . . . . . . . . . . . . . . . . 259
Appendix D. Login Phase Examples . . . . . . . . . . . 261
Appendix E. SendTargets Operation . . . . . . . . . . 271
Appendix F. Algorithmic Presentation of Error Recovery Class-
es . . . . . . . . . . . . . . . . . . . . . . . . . . 276
F.12 General Data Structure and Procedure Description 276
F.13 Within-command Error Recovery Algorithms . . . 278
F.14 Within-connection Recovery Algorithms . . . . . 283
F.14.1.1 Initiator Algorithms . . . . . . . . . . 284
F.14.1.2 Target Algorithms . . . . . . . . . . . 287
F.14.2.1 Procedure Descriptions . . . . . . . . . 287
F.14.2.2 Initiator Algorithms . . . . . . . . . . 288
F.14.2.3 Target Algorithms . . . . . . . . . . . 291
Full Copyright Statement . . . . . . . . . . . . . . . 294
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1. Definitions
- 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.
- 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 con-
nections.
- Connection: Communication between the initiator and
target occurs over one or more TCP connections. The TCP
connections carry control messages, SCSI commands, param-
eters, and data within iSCSI Protocol Data Units (iSCSI
PDUs).
- iSCSI Initiator Name: The iSCSI Initiator Name specifies
the worldwide unique name of the initiator.
- iSCSI Initiator Node: The "initiator".
- iSCSI Layer: This layer builds/receives iSCSI PDUs and
relays/receives them to/from one or more TCP connections
that form an initiator-target "session".
- iSCSI Name: The name of an iSCSI initiator or iSCSI tar-
get.
- 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 accessi-
ble 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 Target Name: The iSCSI Target Name specifies the
worldwide unique name of the target.
- iSCSI Target Node: The "target".
- 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 out-
going transfers are transfers from the initiator to the
target, while inbound or incoming transfers are from the
target to the initiator.
- I_T nexus: According to [SAM2], the I_T nexus is a rela-
tionship 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 ses-
sion (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 Tar-
get Name + 't'+ Portal Group Tag). NOTE: The I_T nexus
identifier is not equal to the session identifier (SSID).
- Network Entity: The Network Entity represents a device
or gateway that is accessible from the IP network. A Net-
work Entity must have one or more Network Portals, each of
which can be used to gain access to the IP network by some
iSCSI Nodes contained in that Network Entity.
- 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.
- Originator - in a negotiation or exchange the party that
initiates the negotiation or exchange.
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- 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.
- 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 Por-
tals within a Portal Group need participate in every ses-
sion 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 Por-
tal Group.
- Responder: In a negotiation or exchange, the party that
responds to the originator of the negotiation or exchange.
- SCSI Device: This is the SAM2 term for an entity that
contains other SCSI entities. For example, a SCSI Initia-
tor 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 Layer: This builds/receives SCSI CDBs (Command
Descriptor Blocks) and relays/receives them with the
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remaining command execute parameters to/from the iSCSI
Layer.
- Session: The group of TCP connections that link an ini-
tiator 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".
- SSID (Session ID): A session is defined by a session ID
that is composed of an initiator part (ISID) and a target
part (TSID).
- SCSI Initiator Port: This maps to the endpoint of an
iSCSI normal operational session. An iSCSI normal opera-
tional 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 identi-
fier.
- 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 the SCSI Initiator Port and the SCSI
Target Port are different.
- 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: This maps to an iSCSI Target Portal
Group.
- 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.
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- 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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1. Overview
1.1 SCSI Concepts
The SCSI Architecture Model-2 [SAM2] describes, in
detail, the architecture of the SCSI family of I/O proto-
cols. This section provides a brief background of the SCSI
architecture and is intended to familiarize readers with
its terminology.
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 processes 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 tar-
get 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 dis-
tinguish 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 termi-
nates a SCSI command.
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Command Descriptor Blocks (CDB) are the data structures
used to contain the command parameters that an initiator
hands to a target. The CDB content and structure is
defined by [SAM] and device-type specific SCSI standards.
1.2 iSCSI Concepts and Functional Overview
The iSCSI protocol is a mapping of the SCSI remote proce-
dure invocation model (see [SAM]) over the TCP protocol.
SCSI commands are carried by iSCSI requests and SCSI
responses and status are carried by iSCSI responses. iSCSI
also uses the request response mechanism for iSCSI proto-
col mechanisms.
For the remainder of this document, the terms "initiator"
and "target" refer to "iSCSI initiator node" and "iSCSI
target node", respectively (see Section 1.4.1 iSCSI
Architecture Model) unless otherwise qualified.
In keeping with similar protocols, the initiator and tar-
get divide their communications into messages. This docu-
ment 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 trans-
fers 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 otherwise specified, status, response, or
numbered response have the same meaning.
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1.2.1 Layers and Sessions
The following conceptual layering model is used to specify
initiator and target actions and how they relate to trans-
mitted and received Protocol Data Units:
-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 con-
nections 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 Section 1.4.2 SCSI Architecture Model). A ses-
sion is defined by a session ID that is composed of an
initiator part and a target part. TCP connections can be
added and removed from a session. Connections within a
session are identified by a connection ID (CID).
Across all connections within a session, an initiator sees
one "target image". All target identifying elements, such
as LUN, are the same. In addition, a target sees one "ini-
tiator image" across all connections within a session.
Initiator that identifying elements, such as the Initia-
tor 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 ses-
sion. For error recovery purposes, targets and initiators
that support a single active connection in a session may
have to support two connections during recovery.
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1.2.2 Ordering and iSCSI Numbering
iSCSI uses Command and Status numbering schemes and a Data
sequencing scheme.
Command numbering is session-wide and is used for ordered
command delivery over multiple connections. It can also be
used as a mechanism for command flow control over a ses-
sion.
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.
Typically, fields in the iSCSI PDUs communicate the
Sequence Numbers between the initiator and target. During
periods when traffic on a connection is unidirectional,
iSCSI NOPOut/In PDUs may be utilized to synchronize the
command and status ordering counters of the target and
initiator.
1.2.2.1 Command Numbering and Acknowledging
iSCSI supports ordered command delivery within a session.
All commands (initiator-to-target 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.
Commands in transit from the initiator to the target are
numbered by iSCSI; the number is carried by the iSCSI PDU
as CmdSN (Command-Sequence-Number). The numbering is ses-
sion-wide. Outgoing iSCSI request PDUs carry this number.
The iSCSI initiator allocates CmdSNs with a 32-bit
unsigned counter (modulo 2**32). Comparisons and arith-
metic on CmdSN SHOULD use Serial Number Arithmetic as
defined in [RFC1982] where SERIAL_BITS = 32.
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Commands meant for immediate delivery are marked with an
immediate delivery flag; they also carry CmdSN. 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 command numbers are incre-
mented by 1 for every non-immediate command issued after-
wards.
If immediate delivery is used with task management com-
mands, these commands may reach the target task management
before the tasks on which they are supposed to act. How-
ever, their CmdSN is a marker of their position in the
stream of commands. The task management command MUST carry
the CmdSN that is given to the next non-immediate command.
The initiator and target must ensure that the task manage-
ment commands act as specified by SAM2. For example, both
commands and responses appear as if delivered in order.
Beyond the scope of this document is the means by which
one may request immediate delivery for a command or by
which iSCSI decides by itself to mark a PDU for immediate
delivery.
The number of commands used for immediate delivery is not
limited and their delivery to execution is not acknowl-
edged through the numbering scheme. Immediate commands
can be rejected by the iSCSI target due to a 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.
With the exception of 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 commands for execution if
required by a prior SCSI or iSCSI action (e.g., clear task
set Task Management request received before all the com-
mands on which it was supposed to act). Delivery for exe-
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cution means delivery to the 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 commands
that are retransmitted due to digest error recovery and
connection recovery.
The initiator and target are assumed to have the following
three registers that are unique session wide and 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. CmdsN
always contains the number to be assigned next.
- ExpCmdSN - the next expected command by the tar-
get. The target acknowledges all commands up to,
but not including, this number. 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 can
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-initia-
tor PDU fields. Comparisons and arithmetic on ExpCmdSN and
MaxCmdSN SHOULD use Serial Number Arithmetic as defined in
[RFC1982] where SERIAL_BITS = 32.
MaxCmdSN and ExpCmdSN fields are processed by the initia-
tor 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; other-
wise, it updates the local MaxCmdSN.
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-If the PDU ExpCmdSN is less than the local ExpCmdSN
(in Serial Arithmetic Sense), it is ignored; other-
wise, it updates the local ExpCmdSN.
This sequence is required since updates may arrive out of
order being that 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 of this range or non-immediate duplicates within
the range.
iSCSI initiators and targets MUST support the command num-
bering 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 state related to its execution (execution state);
afterwards, CmdSN becomes irrelevant. Testing for the
execution state (represented by identifying the Initiator
Task Tag) 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 an execution state
is found.
When the current value of the CmdSN register is Q, an ini-
tiator MUST not advance CmdSN past R + 2**31 - 1 after
reissuing a command with CmdSN R on a connection while
this connection is operational, unless a new non-immedi-
ate command with CmdSN equal or greater than Q was issued
on the given connection and its reception acknowledged by
the target (see Section 9.3 Command Retry and Cleaning Old
Command Instances). 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.
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1.2.2.2 Response/Status Numbering and Acknowledging
Responses in transit from the target to the initiator are
numbered. The StatSN (Status Sequence Number) is used for
this purpose. StatSN is a counter maintained per connec-
tion. ExpStatSN is used by the initiator to acknowledge
status. The status sequence number space is 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 (any ini-
tial value is valid).
To enable command recovery, the target MAY maintain enough
state information to enable data and status recovery after
a connection failure. A target can discard all the state
information maintained for recovery after the status
delivery is acknowledged through ExpStatSN.
A large 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 SHOULD NOT exceed
2**31-1.
Initiators and Targets MUST support the response-number-
ing scheme.
1.2.2.3 Data Sequencing
Data and R2T PDUs, transferred as part of some command
execution, MUST be sequenced. The DataSN field is used for
data sequencing. For input (read) data PDUs, DataSN starts
with 0 for the first data PDU 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. For example, 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
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Data-In and R2T PDUs in one continuous sequence (undiffer-
entiated). Unlike command and status, data PDUs and R2Ts
are not acknowledged by a field in regular outgoing PDUs.
Data-In PDUs can be acknowledged on demand by a special
form of the SNACK PDU. Data and R2T PDUs are implicitly
acknowledged by status. The DataSN/R2TSN field enables
the initiator to detect missing data or R2T PDUs.
For any given write command, a target must have issued
less than 2**32 R2Ts. Any input or output data sequence
MUST contain less than 2**32 numbered PDUs.
1.2.3 iSCSI Login
The purpose of the iSCSI login is to enable a TCP connec-
tion for iSCSI use, authenticate the parties, negotiate
the session's parameters and mark the connection as
belonging to an iSCSI session.
A session is used to identify all the connections with a
given initiator that belong to the same I_T nexus to a
target. (See Section 1.4.2 SCSI Architecture Model 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 associ-
ation protocol for 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 8
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
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authorize an initiator is beyond the scope of this docu-
ment. A more detailed description of the Login Phase can
be found in Chapter 4.
The login PDU includes a session ID that is composed of an
initiator part ISID and a target part TSID. For a new ses-
sion, the TSID is null. As part of the response, the tar-
get 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 that is 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 Section 1.4.1
iSCSI Architecture Model) and internally in an implemen-
tation dependent way. As ISID is used to identify a per-
sistent state, it is subject to reuse restrictions (see
Section 1.4.3 Consequences of the Model).
Before the 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.
1.2.4 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).
The general format of text negotiation is:
Originator-> <key>=<valuex>
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Responder-> <key>=<valuey>|NotUnderstood|Irrelevant
The originator can either be the initiator or the target
and the responder can either be 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 a list
of options (literal constants which may include "None")
for each key in its order of preference.
The responding party answers with the first value that it
supports and is allowed to use for the specific originator
selected from the originator list.
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 does not support or is not allowed to use
all of the offered options with a specific originator, it
may use the constant "Reject".
For numerical and single literal negotiations, the
responding party MUST respond with the required key. The
value it selects, based on the selection rule specific to
the key, becomes the negotiation result. The selection of
a value not admissible under the selection rules is con-
sidered a protocol error and is handled accordingly.
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
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value does not determine that result by itself. The last
value transmitted becomes the negotiation result. The
rules for selecting the value with which to respond 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 negoti-
ation, the responder may answer with the constant "Irrel-
evant" for all types of negotiation.
Any other key not understood by the responder may be
ignored by the responder without affecting the basic func-
tion. However, the Text Response for a key 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 value "?" MUST be used ONLY in Full
Feature Phase. Whenever the responder has 2 two values
for a key - one for the offering-to-responding-party
direction and a second one for the responding-to-offer-
ing-party direction it will answer with the two values
separated by a comma starting with the requesting-to-
offering-party direction.
The constants "None", "Reject", "Irrelevant", and
"NotUnderstood" are reserved and must only be used as
described here.
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Some basic key=value pairs are described in Chapter 12.
All keys in Chapter 12, except for the X- extension for-
mat, 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
1.2.5 iSCSI Full Feature Phase
Once the initiator is authorized to do so, the iSCSI ses-
sion is in the 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 session is in
Full Feature Phase and the connection login has completed
successfully. An iSCSI connection is not in Full Feature
Phase a) when it does not have an established transport
connection, or b) when it has a valid transport connec-
tion, but a successful login was not performed or the con-
nection is currently logged out. In a 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 alle-
giance of the command may be explicitly reassigned to a
different transport connection as described in detail in
Section 7.1 Retry and Reassign in Recovery.
For SCSI commands that require data and/or a 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, illustrating the
above rule.
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Thus, if an initiator issues a READ command, the target
MUST send the requested data, if any, followed by the sta-
tus 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. 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) and 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 initi-
ator and target MAY interleave unrelated SCSI commands,
their SCSI Data, and responses over the session.
Outgoing SCSI data (initiator to target user data or com-
mand parameters) is sent as either solicited data or unso-
licited 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 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 that allows a transfer up to the FirstBurst-
Size 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 out-
going data and the R2T specifies data within the command
bounds.
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It is considered an error for an initiator to send unso-
licited data PDUs to a target that operates 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.
A target SHOULD NOT silently discard data and request
retransmission through R2T. Initiators SHOULD NOT keep
track of the data transferred to or from the target
(scoreboarding); targets perform residual count calcula-
tion. Incoming data for initiators is always implicitly
solicited. SCSI data packets are matched to their corre-
sponding SCSI commands by using Tags specified in the pro-
tocol.
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 tar-
get 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 order-
ing rules. Unsolicited data MUST be sent on every connec-
tion in the same order in which commands were sent. A
target that receives data out of order MAY terminate the
session.
1.2.6 iSCSI Connection Termination
An iSCSI connection may be terminated by use of a trans-
port connection shutdown, or a transport reset. Transport
reset is assumed to be an exceptional event.
Graceful TCP connection shutdowns are done by sending TCP
FINs. A graceful transport connection shutdown SHOULD be
initiated by either party only when the connection is not
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in iSCSI full-feature phase. A target MAY terminate a
full-feature phase connection on internal exception
events, but it SHOULD announce the fact through an Asyn-
chronous Message PDU. Connection termination with out-
standing commands may require recovery actions.
If a connection is terminated while in full-feature phase,
connection cleanup (section 6) is required as a prelude to
recovery. By doing connection cleanup before starting
recovery, the initiator and target can avoid receiving
stale PDUs after recovery. In this case, the initiator
sends a Logout request on one of the operational connec-
tions of a session that indicates which iSCSI connection
should be logged out.
1.2.7 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 to generate names.
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.
- An identifier for initiators and targets to enable
them to recognize each other regardless of IP
address and port mapping on intermediary firewalls.
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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 excep-
tion is if a discovery session (see Section 1.3 iSCSI Ses-
sion Types) 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 the
iSCSI layer; they are opaque and case-sensitive for pur-
poses 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-pro-
vider.users.customer235.host90
eui.02004567A425678D
iSCSI nodes also have addresses. An iSCSI address speci-
fies a single path to an iSCSI node and has the following
format:
<domain-name>[:<port>]
Where <domain-name> is one of:
- IPv4 address, in dotted decimal notation. Assumed
if the name contains exactly four numbers, sepa-
rated by dots (.), where each number is in the
range 0..255.
- IPv6 address, in colon-separated hexadecimal nota-
tion, 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.
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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,
the default port 3260, 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]
[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 inter-
face for devices that contain iSCSI targets and initia-
tors, 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 pro-
tocol-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 Send-
Targets text request, or by other techniques discussed in
[NDT].
1.2.8 Persistent State
iSCSI does not require any persistent state maintenance
across sessions. However in some cases, SCSI requires per-
sistent identification of the SCSI initiator port name
(for iSCSI, the InitiatorName plus the ISID portion of the
session identifier). (See Section 1.4.2 SCSI Architecture
Model and Section 1.4.3 Consequences of the Model.)
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iSCSI sessions do not persist through power cycles and
boot operations.
All iSCSI session and connection parameters are re-ini-
tialized on session and connection creation.
Commands persist beyond connection termination if the
session persists and command recovery within the session
is supported. However, when a connection is dropped, com-
mand execution, as perceived by iSCSI (i.e., involving
iSCSI protocol exchanges for the affected task), is sus-
pended until a new allegiance is established by the 'task
reassign' task management function. (See Section 10.5
Task Management Function Request.)
1.2.9 Message Synchronization and Steering
1.2.9.1 Rationale
iSCSI presents a mapping of the SCSI protocol onto TCP.
This encapsulation is accomplished by sending iSCSI PDUs
of varying lengths. 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 and
messages are processed one after the other. In the pres-
ence of IP packet reordering, (i.e., frames being dropped)
legacy TCP implementations store the "out of order" TCP
segments in temporary buffers until the missing TCP seg-
ments 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
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iSCSI message boundaries in subsequent TCP segments due to
the loss of a TCP segment that contains the iSCSI message
length. The missing TCP segment(s) must be received before
any of the following segments can be steered to the cor-
rect 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 Appendix A. - Sync and
Steering with Fixed Interval Markers -. To make these
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.
1.2.9.2 Synchronization (sync) and Steering Functional
Model
We assume that iSCSI is implemented according to the fol-
lowing layering scheme:
+------------------------+
| SCSI |
+------------------------+
| iSCSI |
+------------------------+
| Sync and Steering |
| +-------------------+ |
| | TCP | |
| +-------------------+ |
+------------------------+
| Lower Functional Layers|
| (LFL) |
+------------------------+
| IP |
+------------------------+
| Link |
+------------------------+
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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. An implementa-
tion 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 layering model, 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 infi-
nitely long streams; stream addressing will wrap around at
2**32-1.
This model assumes that the iSCSI layer will deliver com-
plete PDUs to underlying layers in single (atomic) opera-
tions. The underlying layer does not need to examine the
stream content to discover the PDU boundaries. If a spe-
cific implementation performs 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 that the Sync and Steering Layer can understand.
The Sync and Steering Layer (which 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 is required to add
enough information to every sent data item (IP packet, TCP
packet or some other superstructure) 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 informa-
tion 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
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inserted in the transmission stream when data are first
presented to sync and steering.
The retained information can be released whenever the
transmitted data is acknowledged by the receiver. (in the
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. It
then 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 to which it
refers 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 notifi-
cations generated by TCP are passed through to iSCSI
1.2.9.3 Sync and Steering and Other Encapsulation Layers
We recognize that in many environments the following is a
more appropriate layering model:
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+----------------------------------+
| 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 that changes
the TCP stream, but that is 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 must be left out of any UFL trans-
formation (encryption, compression, padding etc.). How-
ever, 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.
1.2.9.4 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 must be buff-
ered (in temporary buffers) since the iSCSI header that
indicates to which SCSI buffers the data is to be steered
was lost. To minimize the amount of buffering, it is rec-
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ommended 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
iSCSI PDU size it will accept.
1.3 iSCSI Session Types
iSCSI defines two types of sessions:
a) Normal operational session - an unrestricted ses-
sion.
b) Discovery-session - a session opened only for tar-
get discovery; the target MAY accept only text requests
with the SendTargets key and a logout request with rea-
son "close the session".
The session type is defined during login with key=value
parameter in the login command.
1.4 SCSI to iSCSI Concepts Mapping Model
The following diagram shows an example of how multiple
iSCSI Nodes (targets in this case) can coexist within
the same Network Entity and can share Network Portals
(IP addresses and TCP ports). Other more complex configu-
rations are also possible. See Section 1.4.1 iSCSI Archi-
tecture Model for detailed descriptions of the components
of these diagrams.
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+-----------------------------------+
| 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) |
+-----------------------------------+
1.4.1 iSCSI Architecture Model
This section describes the part of the iSCSI architecture
model that has the most bearing on the relationship
between iSCSI and the SCSI Architecture Model.
a) 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
d), each of which can be used by some iSCSI Nodes (see
item (b)) contained in that Network Entity to gain
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access to the IP network.
b) 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 d). An iSCSI Node is
identified by its iSCSI Name (see Section 1.2.7 Naming
and Addressing and Chapter 12). 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.
c) An alias string could also be associated with an
iSCSI Node. The alias allows an organization to associ-
ate a user friendly string with the iSCSI Name. How-
ever, the alias string is not a substitute for the
iSCSI Name.
d) Network Portal - 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. In an
initiator, it is identified by its IP address. In a
target, it is identified by its IP address and its lis-
tening TCP port.
e) 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 collec-
tively supports the capability of coordinating a ses-
sion with connections that span these portals. Not all
Network Portals within a Portal Group need to partici-
pate 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 Section 12.3 SendTar-
gets). All Network Portals with the same portal group
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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 SendTar-
gets). See Section Section 9.1.1 Conservative Reuse of
ISIDs for references to the Initiator Portal Groups.
f) 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 Section 1.4.3.2 SCSI Mode Pages).
The following diagram shows an example of one such config-
uration on a target and how a session that shares Network
Portals within a Portal Group may be established.
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----------------------------IP Network----------------
-----
| | |
+--------|---------------|--------------------|----------
-----------+
| +----|---------------|-----+ +----|---------+
|
| | +---------+ +---------+ | | +---------+ |
|
| | | Network | | Network | | | | Network | |
|
| | | Portal | | Portal | | | | Portal | |
|
| | +--|------+ +---------+ | | +---------+ |
|
| | | | | | | |
|
| | | Portal | | | | Portal |
|
| | | Group 1 | | | | Group 2 |
|
| +--------------------------+ +--------------+
|
| | | |
|
| +----------------------------+ +--------------------
---------+ |
| | iSCSI Session (Target side)| | iSCSI Session (Tar-
get side) | |
| | | |
| |
| | (iSCSI Name + TSID=2) | | (iSCSI Name + TSID=1)
| |
| +----------------------------+ +--------------------
---------+ |
|
|
| iSCSI Target Node
|
| (within Network Entity, not shown)
|
+--------------------------------------------------------
-----------+
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1.4.2 SCSI Architecture Model
This section describes the relationship between the SCSI
Architecture Model [SAM2] and constructs of the 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 opera-
tional functions. These requirements are detailed in Sec-
tion 1.4.3 Consequences of the Model.
a) SCSI Device - the SAM2 term for an entity that
contains other SCSI entities. For example, a SCSI
Initiator Device contains one or more SCSI Initia-
tor 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 one SCSI Device, at most, within a
given iSCSI Node. Access to the SCSI Device can
only be achieved in an iSCSI normal operational
session (see Section 1.3 iSCSI Session Types). The
SCSI Device Name is defined to be the iSCSI Name of
the node and its use is mandatory in the iSCSI pro-
tocol.
b) SCSI Port - 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 Initi-
ator Port and SCSI Target Port are different.
SCSI Initiator Port: This maps to the endpoint of an
iSCSI normal operational session (see Section 1.3
iSCSI Session Types). 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 Ini-
tiator 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 Por-
tal 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 should be format-
ted 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 for-
mat is a multiple of four bytes long, followed by
- 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 (Big-
Endian).
SCSI port names have a maximum length of 264 bytes
for initiator ports, 260 bytes for target ports,
and must be a multiple of four bytes long. The
ASCII character 'i' or 't' is the label that iden-
tifies this port as either a SCSI Initiator Port or
a SCSI Target Port. This ASCII character also pro-
vides the interpretation and size of the remaining
six bytes (initiator) or two bytes (target).
c) I_T nexus - a relationship between a SCSI Initia-
tor Port and a SCSI Target Port, according to
[SAM2]. For iSCSI, this relationship is a session,
defined as a relationship between an iSCSI Initia-
tor'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).
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1.4.3 Consequences of the Model
This section describes implementation and behavioral
requirements that result from the mapping of SCSI con-
structs to the iSCSI constructs defined above. The follow-
ing are the two assumptions that are the basis of these
requirements:
a) Between a given iSCSI Initiator and iSCSI Target,
at any given time, only one session can exist with a
given session identifier (SSID).
b) Between a given SCSI initiator port and SCSI target
port, only one I_T nexus (session) can exist. 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 Tar-
get Portal Group (SCSI target port), there can be only one
session with a given value for ISID that identifies the
SCSI initiator port. See Section 10.12.6 ISID.
The structure of the ISID that contains a naming authority
component (see Section 10.12.6 ISID and [NDT]) provides a
mechanism to facilitate compliance with the ISID rule (See
also Section 9.1.1 Conservative Reuse of ISIDs).
The iSCSI Initiator Node is expected to manage the assign-
ment 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 Section
9.1.1 Conservative Reuse of ISIDs). Allowing this would be
analogous to a single SCSI Initiator Port having relation-
ships (nexus) with multiple SCSI target ports on the same
SCSI target device or SCSI target ports on other SCSI tar-
get devices. It is also possible to have multiple sessions
with different ISIDs to the same Target Portal Group. Each
such session would be considered to be with a different
initiator even when the sessions originate from the same
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initiator device. 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 is that two nexus with the
same identifier should never exist at the same time.
TSID RULE: The iSCSI Target SHOULD NOT select a TSID for a
given login request if the resulting SSID is already in
use by an existing session between the target and the
requesting iSCSI Initiator. See Section 9.1.1 Conserva-
tive Reuse of ISIDs.
1.4.3.1 I_T Nexus State
Certain nexus relationships contain an explicit state
(e.g., initiator-specific mode pages or reservation
state) that may need to be preserved by the target (or
more correctly stated, 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 perform session
recovery as described in Chapter 7. 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.
1.4.3.2 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.
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
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serves multiple iSCSI Target Nodes in the same Network
Entity.
1.5 Request/Response Summary
This section lists and briefly describes all the iSCSI PDU
types (request and responses).
All iSCSI PDUs are built as a set of one or more header
segments (basic and auxiliary) and zero or one data seg-
ments. The header group and the data segment may be fol-
lowed by a CRC (digest).
The basic header segment has a fixed length of 48 bytes.
1.5.1 Request/Response types carrying SCSI payload
1.5.1.1 SCSI-Command
This request carries the SCSI CDB and all the other SCSI
execute command procedure call output parameters such as
task attributes, Command Reference Number, Expected Data
Transfer Length for one or both transfer directions (the
later for bidirectional commands), and Task Tag. The I_T_L
nexus is derived by the initiator and target from the LUN
field in the request and the I_T nexus implicit in the
session identification.
In addition, the SCSI-command PDU carries information
required for the proper operation of the iSCSI protocol -
the command sequence number (CmdSN) and the expected sta-
tus number on the connection it is issued (ExpStatSN).
Part or all of the SCSI output (write) data associated
with the SCSI command may be sent as part of the SCSI-Com-
mand PDU as a data segment.
1.5.1.2 SCSI-Response
The SCSI-Response carries all the SCSI execute command
procedure call input parameters and the SCSI execute com-
mand procedure call return value.
It contains the residual counts from the operation if any,
and an indication of whether the counts represent an over-
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flow or an underflow, and the SCSI status if the status is
valid or a response code (a non-zero return value for the
execute-command procedure call) if the status is not
valid.
For a valid status that indicates that the command is exe-
cuted but resulted in a exception (e.g., a SCSI CHECK CON-
DITION), the PDU data segment contains the associated
sense data.
Some data segment content may also be associated (in the
data segment) with a non-zero response code.
In addition, the SCSI-Response PDU carries information
required for the proper operation of the iSCSI protocol -
the number of Data-In PDU that a target has sent (to
enable the initiator to check that all arrived) - Exp-
DataSN, the Status Sequence Number on this connection -
StatSN and the next Expected Command Sequence Number at
target - ExpCmdSN, the Maximum CmdSN acceptable at target
from this initiator.
1.5.1.3 Task Management Function Request
The task management function request provides an initia-
tor with a way to explicitly control the execution of one
or more SCSI Tasks or iSCSI functions. The PDU carries a
function identifier (which task management function to
perform) and enough information to unequivocally identify
the task or task-set on which to perform the action even
if the task(s) to act upon has not yet arrived or has been
discarded due to an error.
The referenced tag identifies an individual task if the
function refers to an individual task.
The I_T_L nexus identifies task sets and is carried by the
LUN (and implied by the session identification).
For task sets, the CmdSN of the task management function
request helps identify the tasks upon which to act,
namely all tasks associated with a LUN and having a CmdSN
preceding the task management function request CmdSN.
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The task management function request execution is com-
pletely performed at the target, (i.e., any coordination
between responses to the tasks affected and the task man-
agement function request response is done by the target).
1.5.1.4 Task Management Function Response
The Task Management Function Response carries an indica-
tion of function completion for a Task Management Function
Request including how it completed (response and quali-
fier) and additional information for failure responses
(Referenced Task Tag - if an abort task failed).
After the task management response indicating task man-
agement function completion, the initiator will not
receive any additional responses from the affected tasks.
1.5.1.5 SCSI Data-out and SCSI Data-in
The SCSI Data-out and SCS Data-in are the main vehicles by
which SCSI data payload is carried between initiator and
target. Data payload is associated with a specific SCSI
command through the Initiator Task Tag. For the target,
convenience, outgoing solicited data also carries a Tar-
get Transfer Tag (copied from R2T) and the LUN.
Each PDU contains the payload length and the data offset
relative to the buffer address contained in the SCSI exec
command procedure call.
In each direction, the data transfer is split into
"sequences". An end-of-sequence is indicated by the F bit.
An outgoing sequence is either unsolicited (only the first
sequence can be unsolicited) or is a complete payload sent
in response to an R2T "prompt".
Input sequences are built to enable the direction switch-
ing for bidirectional commands.
For input the target may request positive acknowledgement
of input data. This is limited to sessions that support
error recovery and is implemented through the A bit in the
SCSI Data-in PDU header.
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Data-in and Data-out PDUs also carry the DataSN to enable
the initiator and target to detect missing PDUs (discarded
due to an error).
StatSN is also carried by the Data-In PDUs.
To enable a SCSI command to be executed involving a mini-
mum number of messages, the last SCSI Data-in PDU passed
for a command may also contain the status if the status
indicated termination with no exceptions (no sense or
response involved).
1.5.1.6 Ready To Transfer (R2T)
R2T is the mechanism by which the SCSI target "prompts"
the initiator for output data. R2T passes the offset of
the requested data relative of the buffer address from the
execute command procedure call and the length of the
solicited data to the initiator.
To help the SCSI target to associate resulting Data-out
with an R2T, the R2T carries the Target Transfer Tag cop-
ied by the initiator in the solicited SCSI Data-out PDUs.
There are no protocol specific requirements with regard to
the value of these tags, but it is assumed that together
with the LUN, they will enable the target to associate
data with an R2T.
R2T also carries information required for proper opera-
tion of the iSCSI protocol, such as an R2TSN (to enable an
initiator to detect a missing R2T), StatSN, ExpCmdSN and
MaxCmdSN.
1.5.1.7 Asynchronous Message
Asynchronous Messages are used to carry SCSI asynchronous
events (AEN) and iSCSI asynchronous messages.
When carrying an AEN, the event details are reported as
sense data in the data segment.
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1.5.2 Requests/Responses carrying iSCSI Only Payload
1.5.2.1 Text Request and Text Response
Text requests and responses are designed as a parameter
negotiation vehicle and as a vehicle for future extension.
In the data segment key=value, Text Requests/Responses
carry text information with a simple syntax.
Text Request/Responses may form extended sequences using
the same Initiator Task Tag. The initiator uses the F
(Final) flag bit in the text request header to indicate
its readiness to terminate a sequence. The target uses the
F (Final) flag bit in the text response header to indicate
its consent to sequence termination.
Text Request/Responses also use the Target Transfer Tag to
indicate continuation of an operation or a new beginning.
A target that wishes to continue an operation will set the
Target Transfer Tag in a Text Response to a value differ-
ent from the default 0xffffffff. An initiator willing to
continue will copy this value into the Target Transfer Tag
of the next Text Request. If the initiator wants to reset
the target (start fresh) it will set the Target Transfer
Tag to 0xffffffff.
Although a complete exchange is always started by the ini-
tiator, specific parameter negotiations may be initiated
by the initiator or target.
1.5.2.2 Login Request and Login Response
Login Requests and Responses are used exclusively during
the login phase of each connection to set up the session
and connection parameters (the login phase consists of a
sequence of login requests and responses carrying the same
Initiator Task Tag).
A connection is identified by an arbitrarily selected con-
nection-ID (CID) that is unique within a session.
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Similar to the Text Requests and Responses, Login
Requests/Responses carry key=value text information with
a simple syntax in the data segment.
The Login phase proceeds through several stages (security
negotiation, operational parameter negotiation) that are
selected with two binary coded fields in the header - the
"current stage" (CSG) and the "next stage" (NSG) with the
appearance of the later being signaled by the "transit"
flag (T).
The first login phase of a session plays a special role
(it is called the leading login) and some header fields
are determined by the leading login (e.g., the version
number, the maximum number of connections, the session
identification etc.).
The command counting initial value is also set by the
leading login.
Status counting for each connection is initiated by the
connection login.
Login Requests are always immediate.
A login request may indicate an implied logout (cleanup)
of the connection to be logged in (we call this a connec-
tion restart) through the X flag in the first login
request header.
1.5.2.3 Logout Request and Response
Logout Requests and Responses are used for the orderly
closing of connections for recovery or maintenance. The
logout request may be issued following a target prompt
(through an asynchronous message) or at an initiators ini-
tiative. When issued on the connection to be logged out no
other request may follow it.
The Logout response indicates that the connection or ses-
sion cleanup is completed and no other responses will
arrive on the connection (if received on the logging-out
connection). The Logout Response indicates also how long
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the target will keep on holding resources for recovery
(e.g., command execution that continues on a new connec-
tion) in Time2Retain and how long the initiator must wait
before proceeding with recovery in Time2Wait.
1.5.2.4 SNACK Request
With the SNACK Request, the initiator requests retrans-
mission of numbered-responses or data from the target. A
single SNACK request covers a contiguous set of missing
items called a run of a given type of items (the type is
indicate in a type field in the PDU header). The run is
composed of an initial item (StatSN, DataSN, R2TSN) and
the number of additional missed Status, Data, or R2T PDUs
(0 means only the initial). For long data-in sequences,
the target may request (at predefined minimum intervals) a
positive acknowledgement for the data sent. A SNACK
request with a type field that indicates ACK and the num-
ber of Data-In PDUs acknowledged conveys this positive
acknowledgement.
1.5.2.5 Reject
Reject enables the target to report an iSCSI error condi-
tion (protocol, unsupported option etc.) that uses a Rea-
son field in the PDU header and includes the complete
header of the bad PDU in the Reject PDU data segment.
1.5.2.6 NOP-Out Request and NOP-In Response
This request/response pair may be used by an initiator and
target as a "ping" mechanism to verify that a connection/
session is still active and all its components are opera-
tional. Such a ping may be triggered by the initiator or
target. The triggering party indicates that it wants a
reply by setting a value different from the default
0xffffffff in the corresponding Initiator/Target Transfer
Tag.
NOP-In/NOP-Out may also be used "unidirectional" to con-
vey to the initiator/target command, status or data
counter values when there is no other "carrier" and there
is a need to update the initiator/target.
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1. SCSI Mode Parameters for iSCSI
There are no iSCSI specific mode pages.
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1. Login Phase
The login phase establishes an iSCSI session between an
initiator and a target. It sets the iSCSI protocol param-
eters, security parameters, and authenticates the initia-
tor 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 pro-
ceeds 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 connec-
tion 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 Com-
mand.
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
except for the mandatory names.
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 LoginOperation-
alNegotiation.
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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 8) and in [SEC-IPS]).
In some environments, a target or an initiator is not
interested in authenticating its counterpart. It is pos-
sible to bypass authentication through the Login request
and response.
The initiator and target MAY want to negotiate authentica-
tion parameters. Once this negotiation is completed, the
channel is considered secure.
Most of the negotiation keys are only allowed in a spe-
cific stage. The SecurityNegotiation keys appear in Chap-
ter 12 and the LoginOperationalNegotiation keys appear in
Chapter 12.
Only a limited set of keys (marked as Declarative in Chap-
ter 12) may be used in any of the two stages.
Neither the initiator nor the target should attempt to
negotiate a parameter more than once during any login
stage. Attempting to do so will result in the termination
of the login and connection.
Any given Login request or response belongs to a specific
stage; this determines the negotiation keys allowed with
the command or response.
Stage transition is performed through a command exchange
(request/response) that carries the T bit and the same
current stage code. During this exchange, the next stage
is selected by the target and MUST NOT exceed the value
stated by the initiator. The initiator can request a tran-
sition whenever it is ready, but a target can respond with
a transition only after one is offered 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
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settings of the next pair. An initiator that has a T bit
set to 1 in one pair and is answered with a T bit setting
of 0 may issue the next request with T bit set to 0.
Targets MUST NOT submit parameters that require an addi-
tional 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:
+--------------------------------------------------------
---+
|From To -> | Security | Operational | FullFea-
ture |
| | | | | |
| 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.
1.1 Login Phase Start
The login phase starts with a login request from the ini-
tiator to the target. The initial login request includes:
-Protocol version supported by the initiator.
-Session and connection Ids.
-The negotiation stage that the initiator is ready to
enter.
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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 immedi-
ate rejection from the target that causes the con-
nection to terminate and the session to terminate
if this is the first (or only) connection of a new
session. The T bit of the response MUST be set to 1
and the CSG and NSG are reserved.
-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 tar-
get and the session ID, and may include iSCSI oper-
ational or security parameters (that depend on the
current stage).
-Login Response with Login Accept as a partial
response (NSG not set to FullFeaturePhase in both
request and response) that indicates 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 SecurityNegotia-
tion stage, it issues the Login with the CSG set to Logi-
nOperationalNegotiation and the target may reply with a
Login Response that indicates that it is unwilling to
accept the connection without SecurityNegotiation and
will terminate the connection.
If the initiator is willing to negotiate security, but 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 SecurityNegotia-
tion, 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
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SecurityNegotiation, and NSG set to LoginOperationalNego-
tiation.
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 FullFea-
turePhase. 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 LoginOpera-
tionalNegotiation, and NSG set to FullFeaturePhase in the
next stage.
1.2 iSCSI Security Negotiation
The security exchange sets the security mechanism and
authenticates
the initiator user and the target to each other. The
exchange proceeds according authentication method chosen
in the negotiation phase and is conducted using the login
requests and responses key=value parameters.
An initiator directed negotiation proceeds as follows:
-The initiator sends a login request with an ordered
list of the options it supports (authentication
algorithm). The options are listed in the initia-
tor'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 to use for the spe-
cific initiator unless it does not support any in
which case it MUST answer with "Reject" (see also
Section 2.2.4 Text Mode Negotiation). The parame-
ters are encoded in UTF8 as key=value. For security
parameters, see Chapter 11.
-The initiator must be aware of the imminent comple-
tion 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
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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 ini-
tiator SHOULD close the connection.
It should be noted that the negotiation might also be
directed by the target if the initiator does support secu-
rity, but is not ready to direct the negotiation (offer
options).
1.3 Operational Parameter Negotiation During the Login
Phase
Operational parameter negotiation during the login MAY be
done:
- Starting with the first Login request if the initi-
ator does not offer any security/ integrity option.
- Starting immediately after the security negotiation
if the initiator and target perform such a negotia-
tion.
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 should keep sending the Login request (even
empty) with the T bit set to 1, while it still wants to
switch stage, until it receives the Login Response with
the T bit set to 1.
Whenever parameter action or acceptance are dependent on
other parameters, the dependent parameters MUST be sent
after the parameters on which they depend. If they are
sent within the same command, a response for a parameter
might imply responses for others.
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Some session specific parameters can be specified only
during the login phase begun by a login command that con-
tains a null TSID - the leading login phase (e.g., the
maximum number of connections that can be used for this
session).
A session is operational once it has at least one connec-
tion in FullFeaturePhase. New or replacement connections
can be added to a session only after the session is oper-
ational.
For operational parameters, see Chapter 12.
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1. 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 parame-
ter negotiation MAY involve several text request-response
exchanges, which the indicator always starts and termi-
nates and uses 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 to a text request with the F bit set to 1 the target
responds with a text response with the F bit set to 0, the
initiator should keep sending the text request (even
empty) with the F bit set to 1, while it still wants to
finish the negotiation, until it receives 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 that require an addi-
tional 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 that has 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 on which they depend; if sent within
the same command, a response for a parameter might imply
responses for others.
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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 negotia-
tion 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.
Neither the initiator nor the target should attempt to
negotiate a parameter more than once during any negotia-
tion sequence without an intervening reset. If detected by
the target this MUST result in a Reject with a reason of
"protocol error". The initiator MUST reset the negotia-
tion as outlined above.
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1. State Transitions
iSCSI connections and iSCSI sessions go through several
well-defined states from connection creation and session
creation to the time they are cleared.
An iSCSI connection is a transport connection used for
carrying out iSCSI activity. The connection state transi-
tions are described in two separate, but dependent state
diagrams for ease in understanding. The first diagram,
"standard connection state diagram", describes the con-
nection state transitions when the iSCSI connection is not
waiting for or undergoing a cleanup by way of an explicit
or implicit Logout. The second diagram, "connection
cleanup state diagram", describes the connection state
transitions while performing the iSCSI connection
cleanup.
The "session state diagram" describes the state transi-
tions an iSCSI session would go through during its life-
time, and it depends on the states of possibly multiple
iSCSI connections that participate in the session.
1.1 Standard Connection State Diagrams
1.1.1 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 is as follows:
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-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T2 \ | |
| T8 | |T1 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S2 \ / |
| | \ / / |
| | ---+--- / |
| | |T4 / |
| | V / | T18
| | ------- / |
| | / 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
diagram. 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 con-
nection 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|T18 |- |- | - |T10|T12 |T16|
---+-----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+-----+---+---+---+---+----+---+
1.1.2 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 is as follows:
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-------<-------------+
+--------->/ S1 \<----+ |
T13| +->\ /<-+ \ |
| / ---+--- \ \ |
| / | T6 \ | |
| T8 | |T3 | | |
| | | / |T7 |
| | | / | |
| | | / | |
| | V / / |
| | ------- / / |
| | / S3 \ / |
| | \ / / | T18
| | ---+--- / |
| | |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, and follows 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|T18 |- |- | - |T10|T12 |T16|
---+-----+---+---+---+---+----+---+
S8| - |- |- | - | - | - | - |
---+-----+---+---+---+---+----+---+
1.1.3 State Descriptions for Initiators and Targets
State descriptions for the standard connection state dia-
gram are as follows:
-S1: FREE
-initiator: State on instantiation, or after suc-
cessful connection closure.
-target: State on instantiation, or after success-
ful 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 con-
clude, 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.
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-target: In full-feature phase, waiting for all
internal, iSCSI, and transport events.
-S6: IN_LOGOUT
-initiator: Waiting for a Logout response.
-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 Mes-
sage.
-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.
1.1.4 State Transition Descriptions for Initiators and Tar-
gets
-T1:
-initiator: Transport connect request was made (ex:
TCP SYN sent).
-target: Illegal
-T2:
-initiator: Transport connection request timed
out, or a transport reset was received, or an
internal event of receiving a Logout response
(success) on another connection for a close the
session Logout command was received.
-target:Illegal
-T3:
-initiator: Illegal
-target: Received a valid transport connection
request that establishes the transport connection.
-T4:
-initiator: Transport connection established, thus
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.
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-target: The final iSCSI Login command to conclude
the Login phase was received, thus 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, or an internal event
indicating a transport timeout was received, or an
internal event of sending a Logout response (suc-
cess) on another connection for a close the ses-
sion Logout command was received. In all these
cases, the connection is to be closed.
-T7:
-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, or an
internal event indicating a transport timeout was
received, or an internal event of receiving a
Logout response (success) on another connection
for a close the session Logout command was
received. In all these cases, the transport con-
nection is 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 trans-
port disconnect indication was received, or trans-
port reset was received, or an internal event
indicating a transport timeout was received, or an
internal event of sending a Logout response (suc-
cess) on another connection for a close the ses-
sion Logout command was received. In all these
cases, the connection is to be closed.
-T8:
-initiator: An internal event of receiving a Logout
response (success) on a another connection for a
close the session Logout command was received,
thus closing this connection requiring no further
cleanup.
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-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 that indicates the
readiness to start the Logout process was
received, thus prompting an iSCSI Logout to be
sent by the initiator.
-target: An iSCSI Logout command was received.
-T11, T12:
-initiator: Async PDU with AsyncEvent "Request
Logout" was received.
-target: An internal event that requires the decom-
missioning of the connection is received, thus
causing an Async PDU with an AsyncEvent "Request
Logout" to be sent.
-T13:
-initiator: An iSCSI Logout response (success) was
received, or an internal event of receiving a
Logout response (success) on another connection
for a close the session Logout command was
received.
-target: An internal event was received that indi-
cates successful processing of the Logout, which
prompts an iSCSI Logout response (success) to be
sent, or an internal event of sending a Logout
response (success) on another connection for a
"close the session" Logout command was received.
In both these cases, the transport connection is
closed.
-T14:
-initiator: Async PDU with AsyncEvent "Request
Logout" was received again.
-target: Illegal
-T15, T16:
-initiator: One or more of the following events
caused this transition:
-Internal event that indicates a transport con-
nection timeout was received thus prompting trans-
port RESET or transport connection closure.
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-A transport RESET.
-A transport disconnect indication.
-Async PDU with AsyncEvent "Drop connection"
(for this CID).
-Async PDU with AsyncEvent "Drop all connec-
tions".
-target: One or more of the following events caused
this transition:
-Internal event that indicates a transport con-
nection timeout was received, thus prompting
transport RESET or transport connection closure.
-A transport RESET.
-A transport disconnect indication.
-Internal emergency cleanup event was received
which prompts an Async PDU with AsyncEvent "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, i.e. a non-zero sta-
tus) was received.
-Any of the events specified for T15 and T16.
-target: One or more of the following events
caused this transition:
-Internal event that indicates a failure of the
Logout processing was received, which prompts a
Logout response (failure, i.e. a non-zero status)
to be sent.
-Any of the events specified for T15 and T16.
-T18:
-initiator: An internal event of receiving a Logout
response (success) on another connection for a
"close the session" Logout command was received.
-target: An internal event of sending a Logout
response (success) on another connection for a
"close the session" Logout command was received.
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The CLEANUP_WAIT state (S8) implies that there are possi-
ble iSCSI tasks that have not reached conclusion and are
still considered busy.
1.2 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 (e.g., 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-fea-
ture phase connection (lets call it CSM-E) in the
LOGGED_IN state in the same session, or b) using a new
transport connection (lets 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 that corresponds to
CSM-C (either as a connection or session logout) needs to
be performed to complete the cleanup. In the CSM-I case,
an implicit logout for the CID that corresponds to CSM-C
needs to be performed by way of connection reinstatement
(see Section 10.12.2 X - Restart Connection) for that CID.
In either case, the protocol exchanges on CSM-E or CSM-I
to determine the state transitions for CSM-C. Therefore,
this cleanup state diagram 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.
The following state diagram applies to both initiators and
targets.
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-------
/ R1 \
+--\ /<-+
/ ---+--- \
/ | \ M3
M1 | |M2 |
| | /
| | /
| | /
| V /
| ------- /
| / R2 \
| \ /
| -------
| |
| |M4
| |
| |
| |
| V
| -------
| / R3 \
+---->\ /
-------
The following state transition table represents the above
diagram, and follows the same conventions as in earlier
sections.
+----+----+----+
|R1 |R2 |R3 |
-----+----+----+----+
R1 | - |M2 |M1 |
-----+----+----+----+
R2 |M3 | - |M4 |
-----+----+----+----+
R3 | - | - | - |
-----+----+----+----+
1.2.1 State Descriptions for Initiators and Targets
-R1: CLEANUP_WAIT (Same as S8)
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-initiator: Waiting for the internal event to ini-
tiate the cleanup processing for CSM-C.
-target: Waiting for the cleanup process to start
for CSM-C.
-R2: IN_CLEANUP
-initiator: Waiting for the connection cleanup pro-
cess 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.
1.2.2 State Transition Descriptions for Initiators and Tar-
gets
-M1: One or more of the following events was received:
-initiator:
-An internal event that indicates connection
state timeout.
-An internal event of receiving a successful
Logout response on a different connection for a
"close the session" Logout.
-target:
-An internal event that indicates 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, thus prompting a
connection reinstatement Login to be sent transi-
tioning to state IN_LOGIN.
-target: A connection reinstatement Login was
received while in state XPT_UP.
-In CSM-E usage:
-initiator: An internal event that indicates
that an explicit logout was sent for this CID in
state LOGGED_IN.
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-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 and
arrived into FREE instead.
-target: CSM-I failed to reach LOGGED_IN and
arrived into FREE instead.
-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.
-target: CSM-E either moved out of LOGGED_IN,
or Logout timed out and/or aborted, or an internal
event that indicates 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, or
an internal event of receiving a Logout response
(success) on another connection for a "close the
session" Logout command was received.
-target: CSM-I reached state LOGGED_IN, or an
internal event of sending a Logout response (suc-
cess) on a different connection for a "close the
session" Logout command was received.
- In CSM-E usage:
-initiator: CSM-E stayed in LOGGED_IN and
received a Logout response (success), or an inter-
nal event of receiving a Logout response (success)
on another connection for a "close the session"
Logout command was received.
-target: CSM-E stayed in LOGGED_IN and an
internal event indicating a successful Logout pro-
cessing was received, or an internal event of
sending a Logout response (success) on a different
connection for a "close the session" Logout com-
mand was received.
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1.3 Session State Diagram
Session continuation is the process by which the state of
a pre-existing session continues to be in use by either
connection reinstatement (see Section 10.12.2 X - Restart
Connection), or by adding a connection with a new CID.
Either of these actions associates the new transport con-
nection with the pre-existing session state.
1.3.1 Session State Diagram for an Initiator
Symbolic Names for States:
Q1: FREE
Q3: LOGGED_IN
Q4: FAILED
The state diagram is as follows:
-------
/ Q1 \
+------>\ /<-+
/ ---+--- |
/ | |N3
N6 | |N1 |
| | |
| N4 | |
| +--------+ | /
| | | | /
| | | | /
| | V V /
-+--+-- -----+-
/ Q4 \ N5 / Q3 \
\ /<---\ /
------- -------
State transition table:
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+----+----+----+
|Q1 |Q3 |Q4 |
-----+----+----+----+
Q1 | - |N1 | - |
-----+----+----+----+
Q3 |N3 | - |N5 |
-----+----+----+----+
Q4 |N6 |N4 | - |
-----+----+----+----+
1.3.2 Session State Diagram for a Target
Symbolic Names for States:
Q1: FREE
Q2: ACTIVE
Q3: LOGGED_IN
Q4: FAILED
Q5: IN_CONTINUE
The state diagram is as follows:
-------
/ Q1 \
+---------------->\ /<-+
/ ---+--- |
/ ^ | |N3
N6 | N9| V N1 |
| +------ |
| / Q2 \ |
| \ / |
| ------- +--+--- |
| / Q5 \ | |
| \ / N10 | |
| +-+---+------------+ |N2 /
| ^ | | | /
|N7| |N8 | | /
| | | | V /
-+--+-V V----+-
/ Q4 \ N5 / Q3 \
\ /<-------------\ /
------- -------
State transition table:
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+----+----+----+----+----+
|Q1 |Q2 |Q3 |Q4 |Q5 |
-----+----+----+----+----+----+
Q1 | - |N1 | - | - | - |
-----+----+----+----+----+----+
Q2 |N9 | - |N2 | - | - |
-----+----+----+----+----+----+
Q3 |N3 | - | - |N5 | - |
-----+----+----+----+----+----+
Q4 |N6 | - | - | - |N7 |
-----+----+----+----+----+----+
Q5 | - | - |N10 |N8 | - |
-----+----+----+----+----+----+
1.3.3 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: The first iSCSI connection in the session
transitioned to IN_LOGIN, waiting for it to com-
plete the login process.
-Q3: LOGGED_IN
-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.
-Q5: IN_CONTINUE
-initiator: Illegal
-target: Waiting for session continuation attempt
to reach a conclusion.
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1.3.4 State Transition Descriptions for Initiators and Tar-
gets
-N1:
-initiator: At least one transport connection
reached the LOGGED_IN state.
-target: The first iSCSI connection in the session
had reached the IN_LOGIN state.
-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 com-
pleted either via a "close the session" Logout,
or last successful "close the connection" Logout.
-N4:
-initiator: A session continuation attempt suc-
ceeded.
-target: Illegal
-N5:
-initiator: Session failure occurred (all connec-
tions reported CLEANUP_WAIT).
-target: Session failure occurred (all connections
reported CLEANUP_WAIT).
-N6:
-initiator: Session state timeout occurred, or an
implicit session logout (by reuse of ISID with
TSID=0) cleared this session instance. This
results in the freeing of all associated resources
and the session state is discarded.
-target: Session state timeout occurred, or an
implicit session logout (by reuse of ISID with
TSID=0) cleared this session instance. This
results in the freeing of all associated resources
and the session state is discarded.
-N7:
-initiator: Illegal
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-target: A session continuation attempt is initi-
ated.
-N8:
-initiator: Illegal
-target: The last session continuation attempt
failed.
-N9:
-initiator: Illegal
-target: Login attempt on the leading connection
failed.
-N10:
-initiator: Illegal
-target: A session continuation attempt succeeded.
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1. 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 com-
mand PDU, and that outgoing data is available (in host
memory) for retransmission while the command is outstand-
ing. 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 sta-
tus retransmission.
Many of the recovery details in an iSCSI implementation
are a local matter, beyond the scope of protocol standard-
ization. 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. See Appendix F. - Algorithmic Pre-
sentation of Error Recovery Classes - for further detail.
Compliant implementations do not have to match the imple-
mentation details of this model as presented, but the
external behavior of such implementations must correspond
to the externally observable characteristics of the pre-
sented model.
1.1 Retry and Reassign in Recovery
This section summarizes two important and somewhat
related iSCSI protocol features used in error recovery.
1.1.1 Usage of Retry
By resending the same iSCSI command PDU ("retry") in the
absence of a command acknowledgement or response, an ini-
tiator attempts to "plug" (what it thinks are) the discon-
tinuities in CmdSN ordering on the target end. Discarded
command PDUs, due to digest errors, may have created these
discontinuities.
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Retry MUST NOT be used for reasons other than plugging
command sequence gaps. In particular, all PDU retransmis-
sion (for data, or status) requests for a currently alle-
giant command in progress must be conveyed to the target
using only the SNACK mechanism already described. This,
however, does not constitute a requirement on initiators
to use SNACK.
If initiators, as part of plugging command sequence gaps
as described above, inadvertently issue retries for alle-
giant commands already in progress (i.e., targets did not
see the discontinuities in CmdSN ordering), targets MUST
silently discard the duplicate requests if the CmdSN win-
dow 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 (e.g., 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 origi-
nal command unless the original connection was already
successfully logged out.
1.1.2 Allegiance Reassignment
By issuing a "task reassign" task management command (Sec-
tion 10.5.1 Function), the 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 established
for the command, that associates 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 (which must be set to zero
if there was 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.
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It is optional for targets to support the allegiance reas-
signment. This capability is negotiated via the ErrorRe-
coveryLevel 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, the target MUST respond with a task management
response code of "Task still allegiant".
1.2 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 fur-
ther responses since the command itself is being dis-
carded.
The above rule means that the initiators can eventually
expect a response even on Rejects, if the Reject is not
for the command itself. The non-command Rejects only have
diagnostic value in logging the errors, and they can be
used for retransmission decisions by the initiators.
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. The target MAY advance
its ExpDataSN if it does not attempt to recover the lost
data PDU.
1.3 Format Errors
Explicit violations of the PDU layout rules stated in this
document are format errors. Violations, when detected,
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usually indicate 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 immediately terminate all transport
connections in the session either with a connection close
or with a connection reset and escalate the format error
to session recovery (see Section 1.11.4 Session Recov-
ery).
1.4 Digest Errors
The discussion of the legal choices in handling digest
errors below excludes session recovery as an explicit
option, but either party 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 Rea-
son-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), the target
MUST do one of the following:
a) Request retransmission with a recovery R2T. [OR]
b) Terminate the task with a response PDU with the
reason "protocol service CRC error" (Section 10.4.3
Response). If the target chooses to implement this
option, it MUST wait to receive all the data (signaled
by a Data PDU with the final bit set for all outstand-
ing R2Ts) before sending the response PDU. A task man-
agement command (similar to 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.
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LS: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, the ini-
tiator MUST do one of the following:
a) Request the desired data PDU through SNACK. In its
turn, the target MUST either resend the data PDU or,
reject the SNACK with a Reject PDU with a reason-code
of "Data-SNACK Reject" in which case -
i) if the status had not already been sent
for the command, the target MUST terminate the
command with an iSCSI response reason(Section
10.4.3 Response) of "SNACK rejected".
ii) if the status was already sent, no fur-
ther action is necessary for the target. Ini-
tiator in this case MUST internally signal the
completion with the "SNACK rejected" reason
(Section 10.4.3 Response) disregarding any
received status PDU, but must wait for the sta-
tus to be received before doing so. [OR]
b) Abort the task and terminate the command with an
error.
- If the discarded PDU is a response PDU, the initi-
ator 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 1.1 Retry and Reassign in Recovery. [OR]
c) Logout to close the connection (abort all the com-
mands associated with the connection).
- No further action is necessary for initiators if
the discarded PDU is an unsolicited PDU (e.g.,
Async, Reject).
1.5 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 that implies 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. The initiator
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MUST address these implied digest errors as described in
Section 1.4 Digest Errors. 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 digest error on at least
one of the earlier data PDUs. Target MUST address these
implied digest errors as described in Section 1.4 Digest
Errors.
When an initiator receives an iSCSI status PDU with an
out-of-order StatSN that implies missing responses, it
MUST address the one or more missing status PDUs as
described in Section 1.4 Digest Errors. As a side effect
of receiving the missing responses, the initiator may dis-
cover missing data PDUs. If the initiator wants to recover
the missing data for a command, it MUST NOT acknowledge
the received responses that start 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 proac-
tive retransmission of R2Ts by the target) or duplicate
DataSNs (due to proactive SNACKs by the initiator), it
MUST discard the duplicates.
1.6 SCSI Timeouts
An iSCSI initiator MAY attempt to plug a command sequence
gap on the target end (in the absence of an acknowledge-
ment of the command by way of ExpCmdSN) before the ULP
timeout by retrying the unacknowledged command, as
described in Section 1.1 Retry and Reassign in Recovery.
On a ULP timeout for a command (that carried a CmdSN of
n), the iSCSI initiator MUST abort the command by either
using the Abort Task task management function request, or
a "close the connection" Logout if it intends to continue
the session. 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.
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- The connection on which the original command was
sent was successfully logged out (on logout, the
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 manage-
ment response with the response code: "Task does not
exist". This response concludes the task on both ends.
1.7 Negotiation Failures
Text request and response sequences, when used to set/
negotiate operational parameters, constitute the negotia-
tion/parameter setting. A negotiation failure is consid-
ered one or more of the following:
- None of the choices or the stated value is accept-
able 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 negoti-
ation failures:
- During Login, any failure in negotiation MUST be
considered a login process failure and the login
phase must be terminated, and with it the connec-
tion. If the target detects the failure, it must
terminate the login with the appropriate login
response code.
- A failure in negotiation, while in the full-feature
phase, will terminate the entire negotiation
sequence that may consist of a series of text
requests that use the same Initiator Task Tag. The
operational parameters of the session or the con-
nection 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).
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1.8 Protocol Errors
The authors recognize that mapping framed messages over a
"stream" connection, such as TCP, make the proposed mech-
anisms vulnerable to simple software framing errors. On
the other hand, the introduction of framing mechanisms to
limit the effects of these errors may be onerous on per-
formance for simple implementations. Command Sequence
Numbers and the above mechanisms for connection drop and
re-establishment 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 only be
addressed by fixing the implementations; iSCSI defines
Reject and response codes to enable this.
1.9 Connection Failures
iSCSI can keep a session in operation if it is able to
keep/establish at least one TCP connection between the
initiator and the target in a timely fashion. It is
assumed that targets and/or initiators recognize a fail-
ing connection by either transport level means (TCP), a
gap in the command, a 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 imple-
mentations. 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:
- Attempt connection recovery within the session
(Section 1.11.3 Connection Recovery).
- Logout the connection with the reason code "closes
the connection" (Section 10.14.3 Reason Code), re-
issue missing commands, and implicitly terminate
all active commands. This option requires support
for the within-connection recovery class (Section
1.11.2 Recovery Within-connection).
- Perform session recovery (Section 1.11.4 Session
Recovery).
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Either side may choose to escalate to session recovery,
and the other side MUST give it precedence. On a connec-
tion 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).
1.10 Session Errors
If all the connections of a session fail and cannot be re-
established in a short time, or if initiators detect pro-
tocol errors repeatedly, an initiator may choose to termi-
nate 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 ses-
sion.
When the session timeout (the connection state timeout for
the last failed connection) 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 corre-
sponding initiator.
1.11 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 con-
nections to be rebuilt and commands to be reis-
sued).
- Session recovery.
The recovery scenarios detailed in the rest of this sec-
tion are representative rather than exclusive. In every
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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, which impacts a larger number of
iSCSI tasks in any of the cases identified in the follow-
ing discussion.
In all classes, the implementer has the choice of defer-
ring 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, such as
ACA, must be considered.
Use of within-connection and within-command recovery
classes MUST NOT be attempted before the connection is in
full feature phase.
1.11.1 Recovery Within-command
At the target, the following cases lend themselves to
within-command recovery:
- Lost data PDU - realized through one of the follow-
ing:
a) Data digest error - dealt with as specified in Sec-
tion 1.4 Digest Errors, using the option of a recovery
R2T.
b) Sequence reception timeout (no data or partial-
data-and-no-F-bit) - considered an implicit sequence
error and dealt with as specified in Section 1.5
Sequence Errors, using the option of a recovery R2T.
c) Header digest error, which manifests as a sequence
reception timeout, or a sequence error - dealt with as
specified in Section 1.5 Sequence Errors, using the
option of a recovery R2T.
At the initiator, the following cases lend themselves to
within-command recovery:
Lost data PDU or lost R2T - realized through one of
the following:
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a) Data digest error - dealt with as specified in Sec-
tion 1.4 Digest Errors, using the option of a SNACK.
b) Sequence reception timeout (no status) - dealt with
as specified in Section 1.5 Sequence Errors, using the
option of a SNACK.
c) Header digest error, which manifests as a sequence
reception timeout, or a sequence error - dealt with as
specified in Section 1.5 Sequence Errors, using the
option of a SNACK.
To avoid a race with the target, which may already have a
recovery R2T or a termination response on its way, an ini-
tiator SHOULD NOT originate a SNACK for an R2T based on
its internal timeouts (if any). Recovery in this case is
better left to the target.
The timeout values used by the initiator and target are
outside the scope of this document. Sequence reception
timeout is generally a large enough value to allow the
data sequence transfer to be complete.
1.11.2 Recovery Within-connection
At the initiator, the following cases lend themselves to
within-connection recovery:
- 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 1.1 Retry and Reassign in
Recovery.
- 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 by receiving a Response PDU with a higher StatSN
than expected. In the first case, digest error han-
dling is done as specified in Section 1.4 Digest
Errors using the option of a SNACK. In the second
case, sequence error handling is done as specified
in Section 1.5 Sequence Errors, using the option of
a SNACK.
At the target, the following cases lend themselves to
within-connection recovery:
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- 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.
The timeout values used by the initiator and the target
are outside the scope of this document.
1.11.3 Connection Recovery
At an iSCSI initiator, the following cases lend themselves
to connection recovery:
- TCP connection failure. The initiator MUST close
the connection. It then 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 connec-
tion) using the "Task reassign" task management
function (see Section 10.5.1 Function).
- 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.
- Receiving an Asynchronous Message that indicates
one or all connections in a session has 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:
- TCP connection failure. The target MUST close the
connection and if more than one connection is
available, the target SHOULD send an Asynchronous
Message that indicates it has dropped the connec-
tion. Then, the target will wait for the initiator
to continue recovery.
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1.11.4 Session Recovery
Session recovery should be performed when all other recov-
ery attempts have failed. Very simple initiators and tar-
gets MAY perform session recovery on all iSCSI errors and
therefore, place the burden of recovery on the SCSI layer
and above.
Session recovery implies the closing of all TCP connec-
tions, internally aborting all executing and queued tasks
for the given initiator at the target, terminating all
outstanding SCSI commands with an appropriate SCSI ser-
vice response at the initiator, and restarting a session
on a new set of connection(s) (TCP connection establish-
ment and login on all new connections).
Reserve-Release managed SCSI reservations ("Regular" res-
ervations) that are secured during a given iSCSI session
persist until they are cleared using regular SCSI means or
(in the absence of such,) until the session object is
cleared - i.e. when the FREE state is reached. Only the
session continuation (section 6.3) therefore preserves
the Regular reservations.
Persistent SCSI reservations are not affected by iSCSI
session failures, and only the regular SCSI means can be
used to handle these reservations when the session is
reconstructed (necessarily between the same SCSI ports
and so with the same nexus identifier).
1.12 Error Recovery Hierarchy
The error recovery classes and features described are
organized into a hierarchy for ease in understanding and
to limit the myriad of implementation possibilities, with
hopes that this significantly contributes to highly
interoperable implementations. The attributes of this
hierarchy are as follows:
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.
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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.
The following diagram represents the error recovery hier-
archy.
+
/ \
/ 2 \ <-- Connection recovery
+-----+
/ 1 \ <-- Digest failure
recovery
+---------+
/ 0 \ <-- Session failure
recovery
+-------------+
The following table lists the error recovery capabilities
expected from the implementations that support each error
recovery level.
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+-------------------+------------------------------------
--------+
|ErrorRecoveryLevel | Associated Error recovery capabil-
ities |
+-------------------+------------------------------------
--------+
| 0 | Session recovery class
|
| | (Section 1.11.4 Session Recovery)
|
+-------------------+------------------------------------
--------+
| 1 | Digest failure recovery (See Note
below.) |
+-------------------+------------------------------------
--------+
| 2 | Connection recovery class
|
| | (Section 1.11.3 Connection Recovery)
|
+-------------------+------------------------------------
--------+
Note: Digest failure recovery is comprised of two recovery
classes: Within-Connection recovery class (Section 1.11.2
Recovery Within-connection) and Within-Command recovery
class (Section 1.11.1 Recovery Within-command).
Supporting error recovery level "0" is mandatory, while
the rest are optional to implement. In implementation
terms, the above striation means that the following incre-
mental sophistication with each level is required.
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+-------------------+------------------------------------
---------+
|Level transition | Incremental require-
ment |
+-------------------+------------------------------------
---------+
| 0->1 | PDU retransmissions on the same con-
nection |
+-------------------+------------------------------------
---------+
| 1->2 | Retransmission across connections
and |
| | allegiance reassign-
ment |
+-------------------+------------------------------------
---------+
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1. Security Considerations
Historically, native storage systems have not had to con-
sider security because their environments offered minimal
security risks. That is, these environments consisted of
storage devices either directly attached to hosts or con-
nected via a subnet distinctly separate from the communi-
cations 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 (e.g., pretending to be
another identity, message insertion, deletion, modifica-
tion, and replaying) and passive attacks (e.g.,eavesdrop-
ping, gaining advantage by analyzing the data sent over
the line).
Although technically possible, iSCSI SHOULD NOT be con-
figured 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
provided by an iSCSI implementation.
1.1 iSCSI Security Mechanisms
The entities involved in iSCSI security are the initiator,
target, and the IP communication end points. iSCSI scenar-
ios 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 the tar-
get 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 the target,
while IPsec provides a secure channel between the IP com-
munication end points.
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Further details on typical iSCSI scenarios and the rela-
tion between the initiators, targets, and the communica-
tion end points can be found in [SEC-IPS].
1.2 In-band Initiator-Target Authentication
With this mechanism, the target authenticates the initia-
tor and the initiator optionally authenticates the tar-
get. The authentication is performed on every new iSCSI
connection by an exchange of iSCSI Login PDUs using a
negotiated authentication method.
The authentication method cannot assume an underlying
IPsec protection, since IPsec is optional to use. An
attacker should gain as little advantage as possible by
inspecting the authentication phase PDUs. Therefore, 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 the under-
lying 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 eavesdrop-
ping, message insertion, deletion, modification, and
replaying.
The CHAP authentication method (see Chapter 13) is vulner-
able to an off-line dictionary attack. In environments
where this attack is a concern, CHAP SHOULD NOT be used
without additional protection. Underlying IPsec encryp-
tion provides protection against this attack.
The strength of the SRP authentication method (specified
in Chapter 13) 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
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GF(n). 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 oth-
erwise, abort the connection). This verification MAY
start by trying to match N and g with a well-known group
that satisfies the above requirements.
Well-known SRP groups are provided in [SEC-IPS].
Compliant iSCSI initiators and targets MUST at least
implement the SRP authentication method [RFC2945] (see
Chapter 11).
1.3 IPsec
The IPsec mechanism is used by iSCSI for packet protection
(cryptographic integrity, authentication, and confidenti-
ality) at the IP level between the iSCSI communicating end
points. The following sections describe the IPsec proto-
cols that must be implemented for data integrity and
authentication, confidentiality, and key management.
Detailed considerations and recommendations for using
IPsec for iSCSI are provided in [SEC-IPS].
1.3.1 Data Integrity and Authentication
Data authentication and integrity is provided by a keyed
Message Authentication Code in every sent packet. This
code protects against message insertion, deletion, and
modification. Protection against message replay is real-
ized 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 fol-
lowing iSCSI specific requirements:
- HMAC-SHA1 MUST be implemented [RFC2404].
- AES CBC MAC with XCBC extensions SHOULD be imple-
mented [AES], [XCBC] (NOTE: Still subject to the
IETF-IPsec WG's standardization plans).
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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, an iSCSI implementation that operates at
speeds of 1 Gbps or less MAY implement the IPsec sequence
number extension [SEQ-EXT].
Implementation operation at speeds of 10 Gbps or faster
SHOULD implement the sequence number extension.
1.3.2 Confidentiality
Confidentiality is provided by encrypting the data in
every packet. Confidentiality SHOULD always be used
together with data integrity and authentication to pro-
vide comprehensive protection against eavesdropping, mes-
sage insertion, deletion, modification, and replaying.
An iSCSI compliant initiator or target MUST provide confi-
dentiality by implementing IPsec [RFC2401] with ESP in
tunnel mode [RFC2406] with the following iSCSI specific
requirements:
- 3DES in CBC mode MUST be implemented [RFC2451].
- 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.
1.3.3 Security Associations and Key Management
A compliant iSCSI implementation MUST meet the key manage-
ment requirements of the IPsec protocol suite. Authenti-
cation, security association negotiation, and key
management MUST be provided by implementing IKE [RFC2409]
using the IPsec DOI [RFC2407] with the following iSCSI
specific requirements:
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- Peer authentication using a pre-shared key MUST be
supported. 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 authen-
tication, an IKE negotiator SHOULD use IKE Certifi-
cate Request Payload(s) to specify the certificate
authority. IKE negotiators SHOULD check the perti-
nent Certificate Revocation List (CRL) before
accepting a PKI certificate for use in IKE authen-
tication procedures.
- Both IKE Main Mode and Aggressive Mode MUST be sup-
ported. IKE main mode with pre-shared key authenti-
cation 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 a man-in-the-middle attack.
- In the IKE Phase 2 Quick Mode exchanges for creat-
ing the Phase 2 SA, the Identity Payload fields
MUST be present, and MUST carry individual
addresses and 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. The receipt of an IKE Phase 2 delete message SHOULD
NOT be interpreted as a reason for tearing down the con-
nection. If additional traffic is sent on it, a new IKE
Phase 2 SA will be created to protect it.
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1. 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 imple-
mentations. 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 is that targets are resource constrained rela-
tive to initiators.
Implementers are also advised to consider the implementa-
tion consequences of the iSCSI to SCSI mapping model as
outlined in Section 2.4.3 Consequences of the Model.
1.1 Multiple Network Adapters
The iSCSI protocol allows multiple connections, not all of
which need to go over the same network adapter. If multi-
ple network connections are to be utilized with hardware
support, the iSCSI protocol command-data-status alle-
giance to one TCP connection ensures that there is no need
to replicate information across network adapters or oth-
erwise require them to cooperate.
However, some task management commands may require some
loose form of cooperation or replication at least on the
target.
1.1.1 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 world-
wide unique names for these ports. In iSCSI however, the
SCSI initiator ports are the endpoints of dynamically cre-
ated sessions, so the presumption of "static and physical"
does not apply. In any case, the model clauses (particu-
larly, Section 2.4.2 SCSI Architecture Model) provide for
persistent, reusable names for the iSCSI-type SCSI initi-
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ator ports even though there does not need to be any phys-
ical entity bound to these names.
To both minimize the disruption of legacy applications and
to better facilitate the SCSI features that rely on per-
sistent 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 to which they connect). 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). The ISID RULE
(Section 2.4.3 Consequences of the Model) only prohibits
reuse to the same target portal group. It does not "pre-
clude" 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 ses-
sions 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.
1.1.2 iSCSI Name and ISID/TSID Use
The designers of the iSCSI protocol envisioned there being
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. It
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
coordinated as a single iSCSI Node, there must be some
(logical) entity that represents the iSCSI Node that makes
the iSCSI Node Name available to all components involved
in session creation and login. Similarly, this entity that
represents the iSCSI Node must be able to coordinate ses-
sion identifier resources (ISID for initiators and TSID
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for targets) to enforce both the ISID and TSID RULES (see
Section Section 2.4.3 Consequences of the Model).
For targets, because of the closed environment, implemen-
tation of this entity should be straightforward. However,
vendors of iSCSI hardware (e.g., NICs or HBAs) intended
for targets to provide mechanisms for configuration of the
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 mecha-
nism is to allow for static or dynamic partitioning of the
TSID namespace among the portal groups. Such a partition-
ing allows each portal group to act independently of other
portal groups when assigning TSIDs, and facilitates
enforcement of the TSID RULE (Section 2.4.3 Consequences
of the Model).
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 compo-
nents 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.
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-spe-
cific location for this datum or to a system-wide loca-
tion. The structure of the ISID namespace (see Section
10.12.6 ISID and [NDT]) facilitates implementation of the
ISID coordination by allowing each component vendor to
independently (of other vendor's components) coordinate
allocation and use and reuse its own partition of the ISID
namespace in a vendor-specific manner. 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 select-
ing an ISID for a login; this facilitates enforcement of
the ISID RULE (see Section 2.4.3 Consequences of the
Model) at the initiator.
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A vendor of iSCSI hardware (e.g., NICs or HBAs) intended
for use in the initiators must allow, in addition to a
mechanism for configuring the iSCSI Node Name, for a mech-
anism to configure and/or coordinate ISIDs for all ses-
sions 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 nec-
essarily 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, such as the
OS vendor) or via private APIs driven by the vendor's own
SW.
1.2 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 success-
fully. iSCSI mandates support for autosense.
ACA helps preserve ordered command execution in the pres-
ence of errors.
As iSCSI can have many commands in-flight between initia-
tor and target, iSCSI mandates support for ACA.
1.3 Command Retry and Cleaning Old Command Instances
To avoid having old, retried command instances appear in a
valid command window after a command sequence number wrap
around, the protocol requires (see Section 2.2.2.1 Com-
mand Numbering and Acknowledging) that on every connec-
tion on which a retry has been issued, a non-immediate
command be issued and acknowledged within a 2**31-1 com-
mands interval since the retry was issued. This require-
ment can be fulfilled by an implementation in several
ways.
The simplest technique to use is to send 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 on which the retry was attempted. As errors
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are deemed rare events, this technique is probably the
most effective, as it does not involve additional checks
at the initiator when issuing commands.
1.4 Synch and Steering Layer and Performance
While a synch and steering layer is optional, an initia-
tor/target that does not have it working against a target/
initiator that demands synch and steering may experience
performance degradation caused by packet reordering and
loss. Providing a synch and steering mechanism is recom-
mended for all high-speed implementations.
1.5 Unsolicited Data and Performance
Unsolicited data on write are meant to reduce the effect
of latency on throughput (no R2T is needed to start send-
ing data). In addition, immediate data are meant to
reduce the protocol overhead (both bandwidth and execu-
tion 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 perfor-
mance and may not be supported by all the targets.
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1. 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 that appears 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 all bits not defined and all
reserved fields to zero unless specified otherwise. Any
compliant receiver MUST ignore any bit not defined and all
reserved fields unless specified otherwise.
Reserved fields are marked by the word "reserved", some
abbreviation of "reserved" or by "." for individual bits
when no other form of marking is technically feasible.
1.1 iSCSI PDU Length and Padding
iSCSI PDUs are padded to the closest integer number of
four byte words. The padding bytes SHOULD be 0.
1.2 PDU Template, Header, and Opcodes
All iSCSI PDUs have one or more header segments and,
optionally, a data segment. After the entire header seg-
ment group a header-digest may follow. The data segment
MAY also be followed by a data-digest.
The Basic Header Segment (BHS) is the first segment in all
of the 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 Seg-
ment(optional) /
+/
/
+---------------+---------------+---------------+------
---------+
m/ Data-Digest (optional)
/
+/
/
+---------------+---------------+---------------+------
---------+
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All PDU segments and digests are padded to an integer num-
ber of four byte words. The padding bytes SHOULD be sent
as 0.
1.2.1 Basic Header Segment (BHS)
The BHS is 48 bytes long. The Opcode, TotalAHSLength, and
DataSegmentLength fields appear in all iSCSI PDUs. In
addition, when used, the Initiator Task Tag and Logical
Unit Number always appear in the same location in the
header.
The format of the BHS is:
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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|.|I| Opcode | Opcode-specific fields
|
+---------------+---------------+---------------+------
---------+
4|TotalAHSLength | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| LUN or Opcode-specific fields
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag or Opcode-specific fields
|
+---------------+---------------+---------------+------
---------+
20/ Opcode-specific fields
/
+/
/
+---------------+---------------+---------------+------
---------+
48
1.2.1.1 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).
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1.2.1.2 Opcode
The Opcode indicates the 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). 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
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.
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1.2.1.3 Opcode-specific Fields
These fields have different meanings for different opcode
types.
1.2.1.4 TotalAHSLength
Total length of all AHS header segments in four byte words
including padding, if any.
1.2.1.5 DataSegmentLength
This is the data segment payload length in bytes (exclud-
ing padding).
1.2.1.6 LUN
Some opcodes operate on a specific Logical Unit. The Log-
ical Unit Number (LUN) field identifies which Logical
Unit. If the opcode does not relate to a Logical Unit,
this field is either ignored or may be used in an opcode
specific way. The LUN field is 64-bits and should be for-
matted in accordance with [SAM2] i.e., LUN[0] from [SAM2]
is BHS byte 8 and so on up to LUN[8] from [SAM2] that is
BHS byte 15..
1.2.1.7 Initiator Task Tag
The initiator assigns a Task Tag to each iSCSI task it
issues. While a task exists, this tag MUST uniquely iden-
tify it session-wide.
SCSI may also use the initiator task tag as part of the
SCSI task identifier when the time span during which an
iSCSI initiator task tag must be unique extends over the
time span during which a SCSI task tag must be unique.
However, the iSCSI Initiator Task Tag has to exist and be
unique even for untagged SCSI commands.
1.2.2 Additional Header Segment (AHS)
The general format of an AHS is:
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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| AHSLength | AHSType | AHS-
Specific |
+---------------+---------------+---------------+------
---------+
4/ AHS-Spe-
cific /
+/
/
+---------------+---------------+---------------+------
---------+
x
1.2.2.1 AHSType
The AHSType field is coded as follows:
bit 7-6 - 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
1.2.2.2 AHSLength
This field contains the effective length in bytes of the
AHS excluding AHSType and AHSLength (not including pad-
ding). The AHS is padded to the smallest integer number of
4 byte words (i.e., from 0 up to 3 padding bytes).
1.2.2.3 Extended CDB AHS
The format of the Extended CDB AHS is:
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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| AHSLength (CDBLength-15) | 0x01 |
Reserved |
+---------------+---------------+---------------+------
---------+
4/ ExtendedCDB...+pad-
ding /
+/
/
+---------------+---------------+---------------+------
---------+
x
1.2.2.4 Bidirectional Expected Read-Data Length AHS
The format of the Bidirectional Read Expected Data Trans-
fer Length AHS is:
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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| AHSLength (0x0005) | 0x02 |
Reserved |
+---------------+---------------+---------------+------
---------+
4| Expected Read-Data Length
|
+---------------+---------------+---------------+------
---------+
8
1.2.3 Header Digest and Data Digest
Optional header and data digests protect the integrity of
the 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 also implies a zero-length
data-digest.
1.2.4 Data Segment
The (optional) Data Segment contains PDU associated data.
Its payload effective length is provided in the BHS field
- DataSegmentLength. The Data Segment is also padded to an
integer number of 4 byte words.
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1.3 SCSI Command
The format of the SCSI Command PDU is:
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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|.|I| 0x01 |F|R|W|0 0|ATTR | Reserved | CRN or
Rsvd |
+---------------+---------------+---------------+------
---------+
4|TotalAHSLength | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| Logical Unit Number (LUN)
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Expected Data Transfer Length
|
+---------------+---------------+---------------+------
---------+
24| CmdSN
|
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32/ SCSI Command Descriptor Block (CDB)
/
+/
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/
+---------------+---------------+---------------+------
---------+
48| AHS (if any), Header Digest (if any)
|
+---------------+---------------+---------------+------
---------+
/ DataSegment - Command Data (optional)
/
+/
/
+---------------+---------------+---------------+------
---------+
1.3.1 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 DataSeg-
mentLength 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
bit 2-0 contains Task Attributes.
Task Attributes (ATTR) have 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
Setting both the W and the F bit to 0 is an error.
The R and W MAY both be 1 when the corresponding Expected
Data Transfer Lengths are 0, but they CANNOT both be 0
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when the corresponding Expected Data Transfer Lengths are
not 0.
1.3.2 CRN
SCSI command reference number - if present in the SCSI
execute command arguments (according to [SAM2]).
1.3.3 CmdSN - Command Sequence Number
Enables ordered delivery across multiple connections in a
single session.
1.3.4 ExpStatSN
Command responses up to ExpStatSN-1 (mod 2**32) have been
received (acknowledges status) on the connection.
1.3.5 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 oper-
ation (W flag set to 1 and R flag set to 0), the initiator
uses this field to specify the number of bytes of data it
expects to transfer for this operation. For a unidirec-
tional read operation (W flag set to 0 and R flag set to
1), 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 transfer. For bidirectional opera-
tions, an additional header segment MUST be present in the
header sequence that indicates 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 the immediate data part that follows the command
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(if any) are the same, than 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 unsolic-
ited data the target will accept), the initiator SHOULD
send the maximum size of unsolicited data. The target MAY
terminate a command in error for which the Expected Data
Transfer Length is higher than the FirstBurstSize and for
which the initiator sent less than the FirstBurstSize
unsolicited data.
Upon completion of a data transfer, the target informs the
initiator (through residual counts) of how many bytes were
actually processed (sent and/or received) by the target.
1.3.6 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.
1.3.7 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 (for example, from a WRITE oper-
ation) can be placed in the same PDU (both cases are
referred to as immediate data). These data are governed by
the general rules for solicited vs. unsolicited data.
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1.4 SCSI Response
The format of the SCSI Response PDU is:
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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|.|.| 0x21 |1 . .|o|u|O|U|.| Response | Status
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Residual Count
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
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---------+
36| ExpDataSN or Reserved
|
+---------------+---------------+---------------+------
---------+
40| Reserved
|
+---------------+---------------+---------------+------
---------+
44| Bidirectional Read Residual Count
|
+---------------+---------------+---------------+------
---------+
48| Digests if any...
|
+---------------+---------------+---------------+------
---------+
/ Data Segment (Optional)
/
+/
/
+---------------+---------------+---------------+------
---------+
1.4.1 Flags (byte 1)
bit 6-5 Reserved
bit 4 - (o) set for Bidirectional Read Residual Over-
flow. In this case, the b Bidirectional Read Resid-
ual Count indicates the number of bytes that were
not transferred to the initiator because the initi-
ator's Expected Bidirectional Read Data Transfer
Length was not sufficient.
bit 3 - (u) set for Bidirectional Read Residual
Underflow. In this case, 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.
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.
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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 bidi-
rectional operation, the Residual Count contains
the residual for the write operation.
bit 0 - (0) Reserved
Bits O and U and bits o and u are mutually exclusive.
For a response other than "Command Completed at Target"
bit 4-1 MUST be 0.
1.4.2 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 con-
tain all the data and the target has not received a Data
PDU with the final bit Set), the target MUST wait until it
receives a Data PDU with the F bit set in the last
expected sequence, before sending the Response PDU.
1.4.3 Response
This field contains the iSCSI service response.
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iSCSI service response codes defined in this specifica-
tion 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 ter-
minated at the target (response Command Completed at Tar-
get) with a SCSI Check Condition Status as outlined in the
next table:
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+--------------------------+----------+------------------
---------+
| Reason |Sense | Additional Sense
Code & |
| |Key | Quali-
fier |
+--------------------------+----------+------------------
---------+
| 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
|
+--------------------------+----------+------------------
---------+
The target reports the "Not enough unsolicited data" con-
dition only if it does not support output (write) opera-
tions in which the total data length is higher than
FirstBurstSize, but the initiator sent less than First-
BurstSize amount of unsolicited data, and out-of-order
R2Ts cannot be used.
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1.4.4 Residual Count
The Residual Count field is only valid 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.
1.4.5 Bidirectional Read Residual Count
The Bidirectional Read Residual Count field is only valid
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 Bidirec-
tional 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.
1.4.6 Data Segment - Sense and Response Data Segment
iSCSI targets MUST support and enable autosense. If Sta-
tus is CHECK CONDITION (0x02), then the Data Segment con-
tains 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 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|SenseLength | Sense Data
|
+---------------+---------------+---------------+------
---------+
x/ Sense Data
/
+---------------+---------------+---------------+------
---------+
y/ Response Data
/
/
/
+---------------+---------------+---------------+------
---------+
z|
1.4.6.1 SenseLength
Length of Sense Data.
1.4.7 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 or the command is a write command.
1.4.8 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 con-
nection except for responses sent as a result of a retry
or SNACK. In the case of responses sent due to a retrans-
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mission request, the StatSN MUST be the same as the first
time the PDU was sent unless the connection has since been
restarted.
1.4.9 ExpCmdSN - Next Expected CmdSN from this Initiator
ExpCmdSN is a Sequence Number that the target iSCSI
returns to the initiator to acknowledge command recep-
tion. 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.
1.4.10 MaxCmdSN - Maximum CmdSN Acceptable from this Initi-
ator
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,
this indicates to the initiator that the target cannot
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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1.5 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|.|I| x02 |1| 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| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32| RefCmdSN or Exp-
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DataSN |
+---------------+---------------+---------------+------
---------+
36/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
48
1.5.1 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 func-
tions are listed below. 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 via
this session on the logical unit.
3 CLEAR ACA - clears the Auto Contingent Alle-
giance condition.
4 CLEAR TASK SET - aborts all Tasks for the Logi-
cal Unit.
5 LOGICAL UNIT RESET
6 TARGET WARM RESET
7 TARGET COLD RESET
8 TASK REASSIGN - reassigns connection allegiance
for the task identified by the Initiator Task Tag
field to this connection, thus resuming the iSCSI
exchanges for the task.
For all these functions, the Task Management Function
Response MUST be returned as detailed in Section 1.6 Task
Management Function Response. All these functions apply
to the referenced tasks regardless of whether they are
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proper SCSI tasks or tagged iSCSI operations. Task man-
agement requests must act on all the commands having a
CmdSN lower than the task management CmdSN. If the task
management request is marked for immediate delivery it
must be considered immediately for execution but the oper-
ations involved (all or part of them) may be postponed to
allow the target to receive all relevant tasks. According
to [SAM2] for all the tasks covered by the task management
response (i.e., with CmdSN not higher than the task man-
agement command CmdSN), additional responses MUST NOT be
delivered to the SCSI layer after the task management
response. The iSCSI initiator MAY deliver to the SCSI
layer all responses received before the task management
response (i.e., it is a matter of implementation if the
SCSI responses - received before the task management
response but after the task management requests - are
delivered to the SCSI layer by the iSCSI layer in the ini-
tiator). The iSCSI target MUST ensure that no responses
for the tasks covered by a task management function are
delivered to the iSCSI initiator after the task management
response.
If the connection is still active (it is not undergoing an
implicit or explicit logout), 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 being implicitly or explic-
itly 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 establish a new alle-
giance for the command to be aborted as well as abort it
(i.e., the task to be aborted will not have to be retried
or reassigned, and its status, if issued but not acknowl-
edged, will be reissued followed by the task management
response).
For the LOGICAL UNIT RESET function, the target MUST
behave as dictated by the Logical Unit Reset function in
[SAM2].
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The TARGET RESET function (WARM and COLD) implementation
is OPTIONAL and when implemented, should act as described
below. Target Reset MAY also be subject to SCSI access
controls for the requesting initiator. When authorization
fails at the target, the appropriate response as described
in Section 1.6 Task Management Function Response must be
returned by the target.
For the TARGET WARM RESET and TARGET COLD RESET functions,
the target cancels all pending operations. Both functions
are equivalent to the Target Reset function specified by
[SAM2]. They can affect many other initiators.
In addition, for the TARGET COLD RESET, the target MUST
then terminate all of its TCP connections to all initia-
tors (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 suc-
cessfully logged-out. For additional usage semantics see
Section 7.1 Retry and Reassign in Recovery.
TASK REASSIGN MUST be issued as an immediate command.
1.5.2 LUN
This field is required for functions that address a spe-
cific LU (ABORT TASK, CLEAR TASK SET, ABORT TASK SET,
CLEAR ACA, LOGICAL UNIT RESET) and is reserved in all oth-
ers.
1.5.3 Referenced Task Tag
The Initiator Task Tag of the task to be aborted for the
TASK ABORT function or reassigned for the TASK REASSIGN
function.
For all the other functions this field is reserved.
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1.5.4 RefCmdSN or ExpDataSN
For ABORT TASK, this is the task CmdSN of the task to be
aborted. If RefCmdSN does not match the CmdSN of the com-
mand 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, which establishes 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 execu-
tion. The target MUST retransmit all data previously
transmitted in DataIN PDUs (if any) starting with Exp-
DataSN. The number of retransmitted PDUs, may or may not
be the same as the original transmission, depending on if
there was a change in MaxRecvPDULength in the reassign-
ment.
Otherwise, this field is reserved.
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1.6 Task Management Function Response
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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|.|.| 0x22 |1| Reserved | Response |
Reserved |
+---------------+---------------+---------------+------
---------+
4/ Reserved
/
/
/
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Referenced Task Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
---------+
36/ Reserved
/
+/
/
+---------------+---------------+---------------+------
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---------+
48| Digest (if any)
|
+------------------------------------------------------
---------+
For the functions ABORT TASK, ABORT TASK SET, CLEAR ACA,
CLEAR TASK SET, LOGICAL UNIT RESET, and TARGET WARM RESET,
the target performs the requested Task Management func-
tion and sends a Task Management Response back to the ini-
tiator.
1.6.1 Response
The target provides a Response, which may take on the fol-
lowing values:
a) 0 - Function Complete
b) 1 - Task does not exist
c) 2 - LUN does not exist.
d) 3 - Task still allegiant.
e) 4 - Task failover not supported.
f) 5 - Task management function not supported.
g) 6 - Function authorization failed.
h) 255 - Function Rejected.
All other values are reserved.
For a discussion on usage of response codes 3 and 4, see
Section 7.1.2 Allegiance Reassignment.
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 ses-
sions).
The mapping of the response code into a SCSI service
response code, if needed, is outside the scope of this
document.
The response to ABORT TASK SET and CLEAR TASK SET MUST be
issued by the target only after all the commands affected
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have been received by the target, the corresponding task
management functions have been executed by the SCSI target
and the delivery of all previous responses has been con-
firmed (acknowledged through ExpStatSN) by the initiator
on all connections of this session.
1.6.2 Referenced Task Tag
If the Request was ABORT TASK and the Response is "task
not found", the Referenced Task Tag contains the Initiator
Task Tag of the task that was to be aborted. In other
cases, it MUST be set to 0xffffffff.
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1.7 SCSI Data-out & SCSI Data-in
The SCSI Data-out PDU for WRITE operations has the follow-
ing format:
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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|.|.| 0x05 |F| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| LUN or Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| Reserved
|
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32| Reserved
|
+---------------+---------------+---------------+------
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---------+
36| DataSN
|
+---------------+---------------+---------------+------
---------+
40| Buffer Off-
set |
+---------------+---------------+---------------+------
---------+
44| Reserved
|
+---------------+---------------+---------------+------
---------+
48| Digests if any...
|
+---------------+---------------+---------------+------
---------+
/ DataSeg-
ment /
+/
/
+---------------+---------------+---------------+------
---------+
The SCSI Data-in PDU for READ operations has the following
format:
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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|.|.| 0x25 |F|A|0 0 0|O|U|S| Reserved |Status
or Rsvd |
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Residual Count
|
+---------------+---------------+---------------+------
---------+
24| StatSN or Reserved
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
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---------+
36| DataSN
|
+---------------+---------------+---------------+------
---------+
40| Buffer Off-
set |
+---------------+---------------+---------------+------
---------+
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 (i.e., the status is "good
status" - GOOD, CONDITION MET or INTERMEDIATE CONDITION
MET). The 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.
1.7.1 F (Final) Bit
For outgoing data, this bit is 1 for the last PDU of unso-
licited data or the last PDU of a sequence that answers an
R2T.
For incoming data, this bit is 1 for the last input (read)
data PDU of a sequence. Input can be split into several
sequences, each having its own F bit. Splitting the data
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stream into sequences does not affect DataSN counting on
Data-In PDUs. It MAY be used as a "change direction" indi-
cation for Bidirectional operations that need such a
change.
For Bidirectional operations, the F bit is 1 for both the
end of the input sequences as well as the end of the out-
put sequences.
1.7.2 A (Acknowledge) bit
For sessions with ErrorRecoveryLevel 1 or higher, the tar-
get sets this bit to 1 to indicate that it requests a pos-
itive acknowledgement from the initiator for the data
received. The target should use the A bit moderately; it
MAY set the A bit to 1 only once every MaxBurstSize bytes
and MUST NOT do so more frequently than this.
On receiving a Data-In PDU with the A bit set to 1, the
initiator MUST issue a SNACK of type DataACK. If the ini-
tiator has detected holes in the input sequence, it MUST
postpone issuing the SNACK of type DataACK until the holes
are filled.
1.7.3 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.
1.7.4 StatSN
This field MUST ONLY be set if the S bit is set to 1.
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1.7.5 DataSN
For input (read) data PDUs, the DataSN is the data PDU
number (starting with 0) within the data transfer for the
command identified by the Initiator Task Tag.
For output (write) data PDUs, the DataSN is the data PDU
number (starting with 0) within the current output
sequence. The current output sequence is either identi-
fied by the Initiator Task Tag (for unsolicited data) or
is a data sequence generated for one R2T (for data solic-
ited through R2T).
Any input or output data sequence MUST contain less than
2**32 numbered PDUs.
1.7.6 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 DataSe-
quenceInOrder. When set to yes, it means that sequences
have to be in increasing Buffer Offset order and overlays
are forbidden.
1.7.7 DataSegmentLength
This is the data payload length of a SCSI Data-In or SCSI
Data-Out PDU. The 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 the integer number of 4 byte words (real pay-
load) unless the F bit is set to 1.
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1.7.8 Flags (byte 1)
The last SCSI Data packet sent from a target to an initi-
ator for a SCSI command that completed successfully (with
a status of GOOD, CONDITION MET, INTERMEDIATE or INTERME-
DIATE CONDITION MET) may also optionally contain the Sta-
tus for the data transfer. In this case, Sense Data
cannot be sent together with the Command Status. If the
command is completed with an error, then the response and
sense data MUST be sent in a SCSI Response PDU (i.e., MUST
NOT be sent in a SCSI Data packet). For Bidirectional com-
mands, the status MUST be sent in a SCSI Response PDU.
bit 3-5 - not used (should be set to 0).
bit 1-2 - used the same as in a 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 and Residual Count have meaning-
ful content only if the S bit is set to 1 and they values
are as define in Section 1.4 SCSI Response.
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1.8 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|.|.| 0x31 |1| Reserved
|
+---------------+---------------+---------------+------
---------+
4/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
---------+
36| R2TSN
|
+---------------+---------------+---------------+------
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---------+
40| Buffer Off-
set |
+---------------+---------------+---------------+------
---------+
44| Desired Data Transfer Length
|
+------------------------------------------------------
---------+
48| Digest (if any)
|
+------------------------------------------------------
---------+
When an initiator has submitted a SCSI Command with data
that passes 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 by
sending the InitialR2T=no key-pair to each other, which
occurs either during Login or through the Text request/
Response mechanism.
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, and the last PDU SHOULD have the F bit set to 1. If
the last PDU (marked with the F bit) is received before
the Desired Data Transfer Length is transferred, a target
MAY choose to Reject that PDU with "Protocol error" reason
code. DataPDUInOrder governs the Data-Out PDU ordering.
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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). It, therefore, can have a number of pending data
transfers. Within a connection, outstanding R2Ts MUST be
fulfilled by the initiator in the order in which they were
received.
DataSequenceInOrder governs the buffer offset ordering in
consecutive R2Ts. If DataSequenceInOrder is yes, then
consecutive R2Ts SHOULD refer to continuous non-overlap-
ping ranges.
1.8.1 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.
1.8.2 StatSN
The StatSN field will contain the next StatSN. The StatSN
for this connection is not advanced.
1.8.3 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 neces-
sarily 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, rela-
tive to the beginning of the total data transfer. The
Desired Data Transfer Length SHOULD not be 0 and MUST not
exceed MaxBurstSize.
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1.8.4 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
the Target Transfer Tag, but it is assumed that it is used
to tag the response data to the target (alone or in combi-
nation with the LUN).
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1.9 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.
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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|.|.| 0x32 |1| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| LUN
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
---------+
36| AsyncEvent | AsyncVCode | Parameter1 or Reserved
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|
+---------------+---------------+---------------+------
---------+
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].
StatSN counts this PDU as an acknowledgeable event (StatSN
is advanced), which allows for initiator and target state
synchronization.
1.9.1 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. The
sending of a SCSI Event (Asynchronous Event Notifi-
cation 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 request-
ing to be logged out. The initiator MUST honor
Julian Satran Expires August 2002 47
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this request by issuing a Logout as early as possi-
ble, but no later than Parameter3 seconds. Initi-
ator MUST send a Logout with a reason code of
"Close the
connection" (if not the only connection) OR "Close
the session"
(if using multiple connections). Once this message
is received, the 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 ini-
tiator does not Logout in Parameter3 seconds, the
target should send an Async PDU with iSCSI event
code "Dropped the connection" if possible, or sim-
ply terminate the transport connection. Parameter1
and Parameter2 are reserved.
2 - target indicates it will drop the connection.
The Parameter1 field indicates the CID of the con-
nection going to be dropped.
The Parameter2 field (Time2Wait) indicates, in sec-
onds, the minimum time to wait before attempting to
reconnect.
The Parameter3 field (Time2Retain) indicates the
maximum time to reconnect and/or restart commands
after the initial wait (Time2Wait).
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 com-
mands on this connection (Time2Retain).
A value of 0 for Parameter2 indicates that recon-
nect can be attempted immediately.
3 - target indicates it will drop all the connections
of this session.
The Parameter1 field indicates the CID of the con-
nection going to be dropped.
The Parameter2 field (Time2Wait) indicates, in sec-
onds, the minimum time to wait before attempting to
reconnect.
The Parameter3 field (Time2Retain) indicates the
maximum time to reconnect and/or restart commands
after the initial wait (Time2Wait).
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
session is terminated. In this case, the target
Julian Satran Expires August 2002 48
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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.
1.9.2 AsyncVCode
AsyncVCode is a vendor specific detail code that is valid
only if the AsyncEvent field indicates a vendor specific
event. Otherwise, it is reserved.
1.9.3 Sense Data or iSCSI Event Data
For a SCSI Event, this data accompanies the report in the
data segment and identifies the condition.
For an iSCSI Event, additional vendor-unique data MAY
accompany the Async event. Initiators MAY ignore the data
when not understood while processing the rest of the PDU.
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1.10 Text Request
The Text Request is provided to allow for the exchange of
information and for future extensions. It permits the ini-
tiator 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.
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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|.|I| 0x04 |F| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| CmdSN
|
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32/ Reserved
/
+/
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/
+---------------+---------------+---------------+------
---------+
48| Digests if any
|
+---------------+---------------+---------------+------
---------+
/ DataSegment (Text)
/
+/
/
+---------------+---------------+---------------+------
---------+
1.10.1 F (Final) Bit
When set to 1, indicates that this is the last or only
text request in a sequence of commands; otherwise, it
indicates that more commands will follow.
1.10.2 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).
1.10.3 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 the Target Transfer Tag in a text response
to a value other than the reserved value 0xffffffff when-
ever it indicates that it has more data to send or more
operations to perform that are associated with the speci-
fied 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
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for the specific Initiator Task Tag. The initiator MUST
ignore the Target Transfer Tag in the Text Response when
the F bit is set to 1.
This mechanism allows the initiator and target to transfer
a large amount of textual data over a sequence of text-
command/text-response exchanges 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 run-
ning out of resources.
Long text responses are handled as in the following exam-
ple:
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)
1.10.4 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 pre-
sented and interpreted in the case they appear in this
document. They are case sensitive. Text keys and values
MUST ONLY contain letters (a-z, A-Z), digits (0-9), space
(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 one null (0x00) delimiter.
A list is a set of values separated by comma (0x2c). Text
values may also contain colon (:) and brackets ([ and ]).
Character strings are represented as plain text. Binary
items can be encoded using their decimal representation
(with or without leading zeros) or hexadecimal represen-
tation (e.g., 8190 is 0x1ffe). Upper and lower case let-
ters may be used interchangeably in hexadecimal notation
Julian Satran Expires August 2002 53
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(i.e., 0x1aBc, 0x1AbC, 0X1aBc, and 0x1ABC are equiva-
lent). Binary items can also be encoded using the more
compact Base64 encoding as specified by [RFC2045] pre-
ceded by the 0b. Key names MUST NOT exceed 63 bytes.
If not otherwise specified, the maximum length of an indi-
vidual 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 bound-
aries (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 also be used to perform some long
lasting operations.
Text operations that take a long time should be placed in
their own Text request.
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1.11 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.
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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|.|.| 0x24 |F| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
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---------+
36/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
48| Digests if any...
|
+---------------+---------------+---------------+------
---------+
/ DataSegment (Text)
/
+/
/
+---------------+---------------+---------------+------
---------+
1.11.1 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.
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 1 MUST have a Target
Transfer Tag field set to the reserved value of
0xffffffff.
A text response with the F bit set to 0 MUST have a Target
Transfer Tag field set to a value other than the reserved
0xffffffff.
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1.11.2 Initiator Task Tag
The Initiator Task Tag matches the tag used in the initial
Text request.
1.11.3 Target Transfer Tag
When a target has more work to do (e.g., cannot 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
other than 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
Transfer Tag set to the reserved value of 0xffffffff, it
discards its internal information (resets state) associ-
ated with the given Initiator Task Tag.
When a target cannot finish the operation in a single text
response, and does not have enough resources to continue
it rejects the Text request with the appropriate Reject
code. A target may reset its internal state associated
with an Initiator Task Tag, state expressed through the
Target Transfer Tag if the initiator fails to continue the
exchange for some time. The target may reject subsequent
Text requests with the Target Transfer Tag set to the
"stale" value.
1.11.4 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. Chapter 11 and Chapter
12 list some basic Text key=value pairs, some of which can
be used in Login Request/Response and some in Text
Request/Response.
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
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MAY refer to key=value pairs presented in an earlier text
request.
Although the initiator is the requesting party and con-
trols 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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1.12 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 4) consists of a sequence of
Login requests and responses that carry the same Initiator
Task Tag.
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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|.|.| 0x03 |T|X|0 0|CSG|NSG| Version-max | Ver-
sion-min |
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| ISID
|
+ +---------------+------
---------+
12| |TSID
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| CID | Reserved
|
+---------------+---------------+---------------+------
---------+
24| CmdSN
|
+---------------+---------------+---------------+------
---------+
28| ExpStatSN or Reserved
|
+---------------+---------------+---------------+------
---------+
32| Reserved
|
+---------------+---------------+---------------+------
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---------+
36| Reserved
|
+---------------+---------------+---------------+------
---------+
40/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
48/ DataSegment - Login Parameters in Text request Format
/
+/
/
+---------------+---------------+---------------+------
---------+
1.12.1 T (Transit) Bit
If set to 1, indicates that the initiator is ready to
transit to the next stage.
If the T bit is set to 1 and NSG is FullFeaturePhase, then
this also indicates that the initiator is ready for the
Final Login Response (see Chapter 4).
If the response class is 0 the target MAY answer with a
Login response with the T bit set to 1 ONLY if the T bit
is set to 1 in the request.
If the response class is not 0 the T bit value MUST be
ignored by the initiator.
1.12.2 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 func-
tion 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
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sole purpose of cleaning up the first. Targets should sup-
port opening a second connection even when they do not
support 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 reinstate-
ment refers to the replacement of the old CID without
enabling task reassignment.
1.12.3 CSG and NSG
Through these fields, Current Stage (CSG) and Next Stage
(NSG), the Login negotiation commands and responses are
associated with a specific stage in the session (Security-
Negotiation, LoginOperationalNegotiation, FullFea-
turePhase) and may indicate the next stage they want to
move to (see Chapter 4).
The next stage value is valid only when the T bit is 1;
otherwise, it is reserved.
The stage codes are:
- 0 - SecurityNegotiation
- 1 - LoginOperationalNegotiation
- 3 - FullFeaturePhase
1.12.4 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.
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1.12.5 Version-min
Minimum Version supported. The version number of the cur-
rent 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.
1.12.6 ISID
This is an initiator-defined component of the session
identifier (SSID). The ISID is structured as follows. See
[NDT] and Section 9.1.1 Conservative Reuse of ISIDs for
details.
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 Author-
ity |
+---------------+---------------+---------------+------
---------+
4| Qualifier |
+---------------+---------------+
The Type field identifies the format of the Naming Author-
ity field and takes on three defined values with all other
possible values reserved as indicated bellow:
Type naming authority format
0x00 IEEE OUI
0x01 IANA Enterprise Number (EN)
0x02 "Random"
0x03-0xFF Reserved
The Naming Authority field identifies the vendor or orga-
nization whose component (SW or HW) generates this ISID.
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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] for 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 Section 2.4.3 Consequences of the
Model and Section 9.1.1 Conservative Reuse of ISIDs).
1.12.7 TSID
The TSID is the target assigned component of the session
identifier (SSID). Together with the ISID, provided by
the initiator, TSID uniquely identifies the session from
that specific target 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.
1.12.8 Connection ID - CID
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.
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1.12.9 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 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.
1.12.10 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).
1.12.11 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 Section 1.10.4 Text for text
requests/responses also hold for login requests/
responses. Keys and their explanations are listed in
Chapter 11 (security negotiation keys) and Chapter 12
(operational parameter negotiation keys). All keys in
Chapter 12, except for the X- extension format, MUST be
supported by iSCSI initiators and targets. Keys in Chapter
12, only need to be supported when the function to which
they refer is mandatory to implement.
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1.13 Login Response
The Login Response indicates the progress and/or end of
the login phase.
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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|.|.| 0x23 |T|0 0 0|CSG|NSG| Version-max | Ver-
sion-active|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| ISID
|
+ +---------------+------
---------+
12| |TSID
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Reserved
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
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---------+
36| Status-Class | Status-Detail | Reserved
|
+---------------+---------------+---------------+------
---------+
40/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
48/ DataSegment - Login Parameters in Text request Format
/
+/
/
+---------------+---------------+---------------+------
---------+
1.13.1 Version-max
This is the highest version number supported by the tar-
get.
All Login responses within the Login phase MUST carry the
same Version-max.
The initiator MUST use the value presented as a response
to the first login request.
1.13.2 Version-active
Indicates 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 sup-
ported by the target.
All Login responses within the Login phase MUST carry the
same Version-active.
The initiator MUST use the value presented as a response
to the first login request.
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1.13.3 TSID
The TSID is the target assigned component of the session
identifier (SSID). TSID and the ISID provided by the ini-
tiator uniquely identify the session with that initiator.
TSID MUST be valid only in the final response.
1.13.4 StatSN
For the first Login Response (the response to the first
Login Request), this is the starting status Sequence Num-
ber 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.
1.13.5 Status-Class and Status-Detail
The Status returned in a Login Response indicates the exe-
cution status of the login phase. The status includes:
Status-Class
Status-Detail
0 Status-Class indicates success.
A non-zero Status-Class indicates an 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 suc-
cessfully received, understood, and accepted the
request. The numbering fields (StatSN, ExpCmdSN,
MaxCmdSN) are valid only if Status-Class is 0.
1 - Redirection - indicates that the initiator must
take further action 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 parame-
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ters of the type "TargetAddress", which indicates
the target's new address.
2 - Initiator Error (not a format error) - indicates
that the initiator most 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.
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 sta-
tus 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 iSCSI Target Name
(ITN) Temporarily | | has temporarily moved
| | to the address provided.
---------------------------------------------------------
--------
Target Moved | 0102 | The requested ITN has permanently
moved
Permanently | | to the address provided.
---------------------------------------------------------
--------
Initiator | 0200 | Miscellaneous iSCSI initiator
Error | | errors.
---------------------------------------------------------
-------
Authentication| 0201 | The initiator could not be
Failure | | successfully authenticated.
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---------------------------------------------------------
--------
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
and
| |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 are 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
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 Initi-
ator.
---------------------------------------------------------
--------
Target Error | 0300 | Target hardware or software error.
---------------------------------------------------------
--------
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Service | 0301 | The iSCSI service or target is not
Unavailable | | currently operational.
---------------------------------------------------------
--------
Out of | 0302 | The target has insufficient ses-
sion,
Resources | | connection, or other resources.
---------------------------------------------------------
--------
(*1)If the response T bit is 1 and the NSG is FullFea-
turePhase 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.
1.13.6 T (Transit) bit
The T bit is set to 1 as an indicator of the end of the
stage. If the T bit is set to 1 and NSG is FullFea-
turePhase, then this is also the Final Login Response (see
Chapter 4). 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.
If the status class is not 0 the T bit value MUST be set
to 1 by the target and ignored by the initiator.
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1.14 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 connec-
tion 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. If the
Logout is intended to close the session, new iSCSI com-
mands MUST NOT be sent on any of the connections partici-
pating 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 or session respectively. 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 com-
mands, no additional responses should be expected.
A Logout for a CID may be performed on a different trans-
port connection when the TCP connection for the CID has
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
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"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.
Sending a logout request with the reason code of "close
the connection" or "remove the connection for recovery"
may result in the discarding of some unacknowledged com-
mands. Those holes in command sequence numbers will have
to be handled by appropriate recovery (see Chapter 7)
unless the session is also closed.
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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|.|I| 0x06 |1| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved
|
+---------------+---------------+---------------+------
---------+
8| Reserved
|
+---------------+---------------+---------------+------
---------+
12| Reserved
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| CID or Reserved | Reserved |Reason
Code |
+---------------+---------------+---------------+------
---------+
24| CmdSN
|
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32/ Reserved
/
+/
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/
+---------------+---------------+---------------+------
---------+
48| Digest (if any)
|
+------------------------------------------------------
---------+
1.14.1 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 the session".
1.14.2 ExpStatSN
This is the last ExpStatSN value for the connection to be
closed.
1.14.3 Reason Code
Indicates the reason for Logout:
0 - closes the session. All commands associated with
the session (if any) are aborted.
1 - closes the connection. 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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1.15 Logout Response
The logout response is used by the target to indicate if
the cleanup operation for the connection(s) has com-
pleted.
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).
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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|.|.| 0x26 |1| Reserved | Response |
Reserved |
+---------------+---------------+---------------+------
---------+
4/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag
|
+---------------+---------------+---------------+------
---------+
20| Reserved
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
---------+
36| Reserved
|
+------------------------------------------------------
---------+
40| Time2Wait | Time2Retain
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|
+---------------+---------------+---------------+------
---------+
44| Reserved
|
+---------------+---------------+---------------+------
---------+
48| Digest (if any)
|
+------------------------------------------------------
---------+
1.15.1 Response
Logout response:
0 - connection or session closed successfully.
1 - CID not found.
2 - connection recovery not supported (if Logout rea-
son code was recovery and target does not support
it- as indicated by the ErrorRecoveryLevel.
3 - cleanup failed for various reasons.
1.15.2 Time2Wait
The minimum amount of time, in seconds, to wait before
Login to add or reinstate a new connection to this session
on this target. If Time2Wait is 0 a new Login may be
attempted immediately.
1.15.3 Time2Retain
If ErrorRecoveryLevel is less than 2, the maximum time, in
seconds, that the target waits for a connection reinstate-
ment Login, after the initial wait (Time2Wait), after
which the connection state is discarded. If it is the last
connection of a session, the whole session state is dis-
carded after Time2Retain. If ErrorRecoveryLevel is 2,
this is the maximum time, in seconds, after the initial
wait (Time2Wait), the target waits for the allegiance
reassignment for any active task after which the task
state is discarded.
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If Time2Retain is 0 the connection (or session state) is
discarded by the target.
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1.16 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|.|.| 0x10 |1|Rsrvd| Type | Reserved
|
+---------------+---------------+---------------+------
---------+
4/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
20| BegRun
|
+---------------+---------------+---------------+------
---------+
24| Run-
Length |
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
48| Digest (if any)
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|
+------------------------------------------------------
---------+
Support for SNACK is optional.
The SNACK request is used to request the retransmission of
numbered-responses, data, or R2T PDUs from the target.
The SNACK request indicates the missed numbered-response
or data "run" to the target, where the run starts with the
first missed StatSN, DataSN, or R2TSN and indicates also
the number of missed Status, Data, or R2T PDUs (0 has the
special meaning of "all after the initial").
The numbered-response(s) or R2T(s), requested by a SNACK,
MUST be delivered as exact replicas of the ones the initi-
ator missed and MUST include all its flags. However, the
fields ExpCmdSN, MaxCmdSN and ExpDataSN MUST carry the
current values.
The numbered Data-In PDUs, requested by a SNACK with a
RunLength different from 0, have to be delivered as exact
replicas of the ones the initiator missed and MUST include
all its flags. However, the fields ExpCmdSN and MaxCmdSN
MUST carry the current values. Data-In PDUs requested
with RunLength 0 (meaning all PDUs after this number) may
be different from the ones originally sent, in order to
reflect changes in MaxRecvPDULength.
Any SNACK that requests a numbered-response, Data, or R2T
that was not sent by the target MUST be rejected with a
reason code of "Protocol error".
1.16.1 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 num-
bered response.
2-DataACK - positively acknowledges Data-In PDUs.
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All other values are reserved.
Data/R2T SNACK for a command MUST precede status acknowl-
edgement 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. Oth-
erwise, it is reserved.
An iSCSI target that does not support recovery within con-
nection MAY discard the status SNACK. If the target sup-
ports recovery within connection, it MAY discard the SNACK
after which it MUST issue an Asynchronous Message PDU with
an iSCSI event that indicates "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 the target and
not to request or imply data retransmission.
1.16.2 BegRun
The first missed DataSN, R2TSN, or StatSN or the next
expected DataSN for a DataACK type SNACK request.
1.16.3 RunLength
The number of sequential missed DataSN, R2TSN or StatSN.
RunLength of "0" signals that all Data-In, R2T or Response
PDUs carrying the numbers equal to or greater to BegRun
have to be resent.
The first data SNACK, issued after initiators MaxRecvPD-
ULength decreased, for a command issued on the same con-
nection before the change in MaxRecvPDULength, MUST use
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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 whether loss was before or
after the MaxRecvPDULength was changed at the target.
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1.17 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|.|.| 0x3f |1| Reserved | Reason |
Reserved |
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8/ Reserved
/
+/
/
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
mdSN |
+---------------+---------------+---------------+------
---------+
36| DataSN or Reserved
|
+---------------+---------------+---------------+------
---------+
40| Reserved
|
+---------------+---------------+---------------+------
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---------+
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 (pro-
tocol, unsupported option etc.).
1.17.1 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 Data ACK | no
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|
| | |
|
| 0x09 | Invalid PDU field | no
(Note 2) |
| | |
|
| 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-Out PDU retransmission is done only
if the target requests retransmission with a recovery R2T.
However, if this is the data digest error on immediate
data, the initiator may choose to retransmit the whole PDU
including the immediate data.
Note 2: A target should use this reason code for all
invalid values of PDU fields that are meant to describe a
task or a data transfer. Some examples are invalid TTT/
ITT, buffer offset, LUN qualifying a TTT.
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 1.4.3 Response. In those cases in
which a status for the SCSI task was already sent before
the reject no additional status is required. If the error
is detected while data from the initiator is still
expected (the command PDU did not contain all the data and
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the target has not received a Data-out PDU with the Final
bit 1), the target MUST wait until it receives the Data-
out PDU with the F bit set to 1 before sending the
Response PDU.
For additional usage semantics of Reject PDU, see Section
7.2 Usage Of Reject PDU in Recovery.
1.17.2 DataSN
This field is valid only if the Reason code is "Protocol
error" and the SNACK was a Data/R2T SNACK. The DataSN/
R2TSN is the last valid sequence number that the target
sent for the task.
1.17.3 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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1.18 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|.|I| 0x00 |1| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| LUN or Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| CmdSN
|
+---------------+---------------+---------------+------
---------+
28| Exp-
StatSN |
+---------------+---------------+---------------+------
---------+
32/ Reserved
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/
+/
/
+---------------+---------------+---------------+------
---------+
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 another PDU will not be available for a long time.
When used as a ping command, the Initiator Task Tag MUST
be set to a valid value (not the reserved 0xffffffff).
Upon receipt of a NOP-In with the Target Transfer Tag set
to a valid value (not the reserved 0xffffffff), the initi-
ator MUST respond with a NOP-Out. In this case, the NOP-
Out Target Transfer Tag MUST contain a copy of the NOP-In
Target Transfer 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).
1.18.1 Initiator Task Tag
An initiator assigned identifier for the operation.
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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 the next CmdSN. However, CmdSN is not
advanced and the I bit must be set to 1.
1.18.2 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 this case, it copies the Target Transfer
Tag from the NOP-In PDU.
When the Target Transfer Tag is set, the LUN field MUST
also be copied from the NOP-In.
1.18.3 Ping Data
Ping data is reflected in the NOP-In Response. The length
of the reflected data is limited to MaxRecvPDULength. 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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1.19 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|.|.| 0x20 |1| Reserved
|
+---------------+---------------+---------------+------
---------+
4| Reserved | DataSeg-
mentLength |
+---------------+---------------+---------------+------
---------+
8| LUN or Reserved
|
+
+
12|
|
+---------------+---------------+---------------+------
---------+
16| Initiator Task Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
20| Target Transfer Tag or 0xffffffff
|
+---------------+---------------+---------------+------
---------+
24| StatSN
|
+---------------+---------------+---------------+------
---------+
28| ExpC-
mdSN |
+---------------+---------------+---------------+------
---------+
32| MaxC-
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mdSN |
+---------------+---------------+---------------+------
---------+
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 as a means to carry a
changed ExpCmdSN and/or MaxCmdSN if another PDU will not
be available for a long time (as determined by the tar-
get).
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 the first MaxRecvPDULength bytes of the
initiator provided Ping Data. For such a response, the
Target Transfer Tag MUST be 0xffffffff.
When a target send a NOP-In as a "ping" (the Initiator
Task Tag is 0xffffffff) it MUST NOT send any data in the
data segment (DataSegmentLength MUST be 0).
1.19.1 Target Transfer Tag
A target assigned identifier for the operation.
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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 the next StatSN. However, StatSN for this connec-
tion is not advanced.
1.19.2 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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1. iSCSI Security Keys and Values
The following keys can only be used during the SecurityNe-
gotiatian stage of the Login Phase.
All security keys have connection-wide applicability.
1.1 AuthMethod
Senders: Initiator and Target
AuthMethod = <list-of-options>
The main item of security negotiation is the authentica-
tion method (AuthMethod).
The authentication methods that can be used (appear in the
list-of-options) are either those listed in the following
table or are vendor-unique methods:
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+--------------------------------------------------------
----+
| Name | Description
|
+--------------------------------------------------------
----+
| KRB5 | Kerberos V5
|
+--------------------------------------------------------
----+
| SPKM1 | Simple Public-Key GSS-API Mecha-
nism |
+--------------------------------------------------------
----+
| SPKM2 | Simple Public-Key GSS-API Mecha-
nism |
+--------------------------------------------------------
----+
| SRP | Secure Remote Pass-
word |
+--------------------------------------------------------
----+
| CHAP | Challenge Handshake Authentication Pro-
tocol|
+--------------------------------------------------------
----+
| none | No authentication
|
+--------------------------------------------------------
----+
KRB5 is defined in [RFC1510].
SPKM1 and SPKM2 are defined in [RFC2025].
SRP is defined in [RFC2945] and CHAP is defined in
[RFC1994].
The AuthMethod selection is followed by an "authentica-
tion exchange" specific to the authentication method
selected.
The authentication exchange authenticates the initiator
to the target, and optionally, the target to the initia-
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tor. Authentication is not mandatory to use but must be
supported by the target and initiator.
The initiator and target MUST implement SRP.
1.2 Kerberos
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 "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>
where KRB_AP_REP is the server's response message as
defined in
[RFC1510].
If mutual authentication was selected and target authen-
tication fails, the initiator MUST close the connection.
KRB_AP_REQ and KRB_AP_REP are large binary items and their
binary length (not the length of the character string that
represents them in encoded form) MUST not exceed 65536
bytes.
1.3 Simple Public-Key Mechanism (SPKM)
For SPKM1 and SPKM2 [RFC2025], the initiator MUST use:
SPKM_REQ=<SPKM-REQ>
where SPKM-REQ is the first initiator token as defined in
[RFC2025].
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[RFC2025] defines situations where each side may send an
error token
that may cause the peer to re-generate and resend its 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 to send a SPKM-DEL token(by[RFC2025], it will,
instead, send a Login "login reject" message with the
"Authentication Failure" status and terminate the connec-
tion. If the initiator needs to send a SPKM-DEL token, it
will close the connection.
In the following sections, 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 authen-
tication fails, the initiator MUST close the connection.
Otherwise, if the AuthMethod is SPKM1, the initiator MUST
continue with:
SPKM_REP_IT=<SPKM-REP-IT>
where SPKM-REP-IT is the second initiator token as defined
in [RFC2025]. If the initiator authentication fails, the
target MUST answer with a Login reject with "Authentica-
tion Failure" status.
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All the SPKM-* tokens are large binary items and their
binary length (not the length of the character string that
represents them in encoded form) MUST not exceed 65536
bytes.
1.4 Secure Remote Password (SRP)
For SRP [RFC2945], the initiator MUST use:
SRP_U=<user> TargetAuth=yes /* or TargetAuth=no */
The target MUST 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 answer with a Login reject with the
"Authentication Failure" status or reply with:
SRP_B=<B>
The initiator MUST close the connection or continue with:
SRP_M=<M>
If the initiator authentication fails, the target MUST
answer with a Login reject with "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 the target authentication fails, the initiator MUST
close the connection.
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iSCSI 20-January-02
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 length of
the character string that represents them in encoded form)
MUST not exceed 1024 bytes. Further restrictions on
allowed N,g values are specified in Section 8.2 In-band
Initiator-Target Authentication.
1.5 Challenge Handshake Authentication Protocol (CHAP)
For CHAP [RFC1994], the initiator MUST use:
CHAP_A=<A1,A2...>
Where A1,A2... are proposed algorithms, in order of pref-
erence.
The target MUST 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 ini-
tiator.
The initiator MUST continue with:
CHAP_N=<N> CHAP_R=<R>
or, if it 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 "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.
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Where N, (A,A1,A2), I, C, and R are (correspondingly) the
Name, Algorithm, Identifier, Challenge, and Response as
defined in [RFC1994], N is a text string, A,A1,A2, and I
are numbers, and C and R are binary items and their binary
length (not the length of the character string that repre-
sents them in encoded form) 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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1. Login/Text Operational Keys
The ISID and TSID collectively form the SSID (session id).
A TSID of zero indicates a leading connection. Some ses-
sion specific parameters MUST only be carried on the lead-
ing connection and cannot be changed after the leading
connection login (e.g., MaxConnections, the maximum num-
ber of connections). This holds for a single connection
session with regard to connection restart. The keys that
fall into this category have the use LO (Leading Only).
Keys that can be used only during login have the use IO
(initialize only) while those that can be used in both the
login phase and full feature phase have the use ALL.
Keys that can only be used during full feature phase use
FFPO (full feature phase only).
Keys marked as "declarative" may appear also in the Secu-
rityNegotiation stage while all other keys described in
this chapter are operational keys.
Key scope is indicated as session-wide (SW) or connection-
only (CO).
1.1 HeaderDigest and DataDigest
Use: IO
Senders: Initiator and Target
Scope: CO
HeaderDigest = <list-of-options>
DataDigest = <list-of-options>
Digests enable the checking of end-to-end non-crypto-
graphic data integrity beyond the integrity checks pro-
vided by the link layers and the covering of the whole
communication path including all elements that may change
the network level PDUs such as routers, switches, and
proxies.
The following table lists cyclic integrity checksums that
can be negotiated for the digests and that MUST be imple-
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mented by every iSCSI initiator and target. These digest
options only have error detection significance.
+---------------------------------------------+
| Name | Description | Generator |
+---------------------------------------------+
| CRC32C | 32 bit CRC |0x11edc6f41|
+---------------------------------------------+
| none | no digest |
+---------------------------------------------+
The generator polynomial for this digest is given in hex-
notation, for example 0x3b stands for 0011 1011. The poly-
nomial x**5+X**4+x**3+x+1.
When the 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 and starts with byte 0 bit 0 to
7 continues with byte 1 bit 0 etc. (Big Endian on
bytes / Little Endian on bits).
- The first 32 bits of the message are complemented.
- 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 then divided
by G(x). The generator polynomial produces 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.
(when examples are provided, the value to be speci-
Julian Satran Expires August 2002 2
iSCSI 20-January-02
fied in the examples follows the same rules of rep-
resentation as the rest of this document).
- A receiver of a "good" segment (data or header)
including the CRC built using the generator
0x11edc6f41 will get the value 0x1c2d19ed as its
CRC (this is a polynomial 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.
1.2 MaxConnections
Use: LO
Senders: Initiator and Target
Scope: SW
MaxConnections=<number-from-1-to-65535>
Default is 1.
Initiator and target negotiate the maximum number of con-
nections requested/acceptable. The lower of the two num-
bers is selected.
1.3 SendTargets
Use: FFPO
Senders: Initiator
Scope: SW
For a complete description, see Appendix E. - SendTargets
Operation -.
1.4 TargetName
Use: IO by initiator ALL by target, Declarative
Senders: Initiator and Target
Scope: SW
TargetName=<iSCSI-Name>
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Examples:
TargetName=iqn.1993-11.com.disk-vendor.diskar-
rays.sn.45678
TargetName=eui.020000023B040506
The initiator of the TCP connection must provide this key
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 "SendTar-
gets" text request (which is its only use when issued by a
target).
1.5 InitiatorName
Use: IO, Declarative
Senders: Initiator
Scope: SW
InitiatorName=<iSCSI-Name>
Examples:
InitiatorName=iqn.1992-04.com.os-ven-
dor.plan9.cdrom.12345
InitiatorName=iqn.2001-
02.com.ssp.users.customer235.host90
InitiatorName=iSCSI
The initiator of the TCP connection must provide this key
to the remote endpoint at the first Login of the login
phase for every connection. The Initiator key enables the
initiator to identify itself to the remote endpoint.
1.6 TargetAlias
Use: ALL, Declarative
Senders: Target
Scope: SW
TargetAlias=<UTF-8 string>
Examples:
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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 ini-
tiator during a Login Response PDU. This string is not
used as an identifier, but can be displayed by the initi-
ator's user interface in a list of targets to which it is
connected.
1.7 InitiatorAlias
Use: ALL, Declarative
Senders: Initiator
Scope: SW
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 dis-
played by the target's user interface in a list of initi-
ators to which it is connected.
This key SHOULD be sent by an initiator within the Login
phase, if available.
1.8 TargetAddress
Use: ALL, Declarative
Senders: Target
Scope: SW
TargetAddress=domainname[:port][,portal-group-tag]
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If the TCP port is not specified, it is assumed to be the
IANA-assigned default port for iSCSI.
If the TargetAddress is returned as the result of a redi-
rect status in a login response, the comma and portal
group tag are omitted.
If the TargetAddress is 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 further described in Appendix E.
- SendTargets Operation -.
1.9 InitialR2T
Use: LO
Senders: Initiator and Target
Scope: SW
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 (First-
BurstSize, 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
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InitialR2T=no. Only the first outgoing data burst
(immediate data and/or separate PDUs) can be sent unsolic-
ited (i.e., not requiring an explicit R2T).
1.10 BidiInitialR2T
Use: LO
Senders: Initiator and Target
Scope: SW
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 initi-
ator 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'. Only
the first outgoing data burst (immediate data and/or sep-
arate PDUs) can be sent unsolicited by an R2T.
1.11 ImmediateData
Use: LO
Senders: Initiator and Target
Scope: SW
ImmediateData=<yes|no>
Default is yes.
Result function is AND.
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iSCSI 20-January-02
The initiator and target negotiate support for immediate
data. To turn immediate data off, the initiator or target
must state its desire to do so. ImmediateData can be
turned on if both the initiator and target have Immediate-
Data=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:
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+----------+-------------+-------------------------------
--------+
|InitialR2T|ImmediateData| Result (up to FirstBurst-
Size) |
+----------+-------------+-------------------------------
--------+
| no | no | Unsolicited data in data PDUs
only. |
+----------+-------------+-------------------------------
--------+
| no | yes | Immediate & separate unsolicited
data.|
+----------+-------------+-------------------------------
--------+
| yes | no | Unsolicited data disal-
lowed. |
+----------+-------------+-------------------------------
--------+
| yes | yes | Immediate unsolicited data only.
|
+----------+-------------+-------------------------------
--------+
1.12 MaxRecvPDULength
Use: ALL
Senders: Initiator and Target
Scope: CO
MaxRecvPDULength=<number-512-to-(2**24-1)>
Default is 8191 bytes.
This is a connection specific parameter.
The initiator or target declares the maximum data segment
length in bytes they can receive in an iSCSI PDU.
For a target the value limiting the size of the receive
PDUs is the lower of the declared MaxRecvPDULength and the
negotiated MaxBurstSize for solicited data or FirstBurst-
Size for unsolicited data.
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1.13 MaxBurstSize
Use: LO
Senders: Initiator and Target
Scope: SW
MaxBurstSize=<number-512-to-(2**24-1)>
Default is 262144 (256 Kbytes).
The initiator and target negotiate maximum SCSI data pay-
load 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 two numbers is selected.
1.14 FirstBurstSize
Use: LO
Senders: Initiator and Target
Scope: SW
FirstBurstSize=<number-512-to-(2**24-1)>
Default is 65536 (64 Kbytes).
The initiator and target negotiate the maximum amount in
bytes of unsolicited data an iSCSI initiator may send to
the target, during 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 com-
mand.
The minimum of the two numbers is selected.
FirstBurstSize MUST NOT exceed MaximumBurstSize.
1.15 LogoutLoginMaxTime
Use: LO
Senders: Initiator and Target
Scope: SW
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LogoutLoginMaxTime=<number-0-to-3600>
Default is 3.
The initiator and target negotiate the maximum time, in
seconds after an initial wait (Time2Wait), before which
the connection reinstatement is still possible after a
connection termination or a connection reset.
This value is also the session state timeout if the con-
nection in question is the last LOGGED_IN connection in
the session.
The lesser of the two values is selected and will be used
anywhere a explicit value is not otherwise provided
(Time2Retain).
A value of 0 indicates that connection state is immedi-
ately discarded by the target.
1.16 LogoutLoginMinTime
Use: LO
Senders: Initiator and Target
Scope: SW
LogoutLoginMinTime=<number-0-to-3600>
Default is 3.
The initiator and target negotiate the minimum time, in
seconds, to wait before attempting connection reinstate-
ment after a connection termination or a connection reset.
The maximum of the two values is selected and will be used
anywhere an explicit value is not otherwise pro-
vided(Time2Wait).
A value of 0 indicates that connection reinstatement can
be attempted immediately.
1.17 MaxOutstandingR2T
Use: LO
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Senders: Initiator and Target
Scope: SW
MaxOutstandingR2T=<number-from-1-to-65535>
Default is 1.
Initiator and target negotiate the maximum number of out-
standing R2Ts per task, excluding any implied initial R2T
that might be part of that task. An R2T is considered
outstanding until the last data PDU (with the F bit set to
1) is transferred, or a sequence reception timeout (sec-
tion 7.11.1) is encountered for that data sequence.
1.18 DataPDUInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
DataPDUInOrder=<yes|no>
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.
1.19 DataSequenceInOrder
Use: LO
Senders: Initiator and Target
Scope: SW
DataSequenceInOrder=<yes|no>
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
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iSCSI 20-January-02
to one. A Data-out 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 non-decreasing sequence
offsets (R2T buffer offset for writes, or the smallest
SCSI Data-In buffer offset within a read data sequence).
If ErrorRecoveryLevel is not 0 and if DataSequenceInOrder
is set to yes, a target may retry at most the last R2T,
and an initiator may at most request retransmission for
the last read data sequence. MaxOustandingR2T MUST be set
to 1 in this case.
1.20 ErrorRecoveryLevel
Use: LO
Senders: Initiator and Target
Scope: SW
ErrorRecoveryLevel=<0 to 2>
Default is 0.
The initiator and target negotiate the recovery level sup-
ported.
The minimum of the two values is selected.
Recovery levels represent a combination of recovery capa-
bilities.
Each recovery level includes all the capabilities of the
lower recovery levels and adds some new ones to them.
In the description of recovery mechanisms, certain recov-
ery classes are specified. Section 7.12 Error Recovery
Hierarchy describes the mapping between the classes and
the levels.
1.21 SessionType
Use: LO, Declarative
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Senders: Initiator
Scope: SW
SessionType= <discovery|normal>
Default is Normal.
The Initiator indicates the type of session it wants to
create. The target can either accept it or reject it.
A discovery session indicates to the Target that the only
purpose of this Session is discovery. The only requests a
target accepts in this type of session are a text request
with a SendTargets key and a logout request with reason
"close the session".
The discovery session implies MaxConnections = 1 and over-
rides both the default and an explicit setting.
1.22 The Vendor Specific Key Format
Use: ALL
Senders: Initiator and Target
Scope: specific key dependent
X-reversed.vendor.dns_name.do_something=
Keys with this format are used for vendor-specific pur-
poses. These keys always start with X-.
To identify the vendor, we suggest you use the reversed
DNS-name as a prefix to the key-proper.
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iSCSI 20-January-02
1. IANA Considerations
The temporary (user) well-known port number for iSCSI con-
nections assigned by IANA is 3260.
Julian Satran Expires August 2002 1
iSCSI 20-January-02
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 Concern-
ing 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.
[Castagnoli93] G. Castagnoli, S. Braeuer and M. Her-
rman "Optimization of Cyclic Redundancy-Check Codes
with 24 and 32 Parity Bits", IEEE Transact. on Com-
munications, Vol. 41, No. 6, June 1993.
[COBS] S. Cheshire and M. Baker, Consistent Overhead
Byte Stuffing, IEEE Transactions on Networking,
April 1999.
[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 INTER-
NET PROGRAM PROTOCOL SPECIFICATION, September 1981.
[RFC1035] P. Mockapetris, DOMAIN NAMES - IMPLEMENTA-
TION AND SPECIFICATION, November 1987.
[RFC1122] Requirements for Internet Hosts-Communica-
tion 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 Arith-
metic", RFC 1982, August 1996.
Julian Satran Expires August 2002 1
iSCSI 20-January-02
[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.
[RFC2026] Bradner, S., "The Internet Standards Pro-
cess -- Revision 3", RFC 2026, October 1996.
[RFC2044] Yergeau, F., "UTF-8, a Transformation For-
mat of Unicode and ISO 10646", October 1996.
[RFC2045] N. Borenstein, N. Freed, "MIME (Multipur-
pose Internet Mail Extensions) Part One: Mechanisms
for Specifying and Describing the Format of Inter-
net 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 Architec-
ture 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 Secu-
rity 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, "For-
mat for Literal IPv6 Addresses in URL's", RFC 2732,
December 1999. [RFC2945], Wu, T., "The SRP Authen-
tication 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).
Julian Satran Expires August 2002 2
iSCSI 20-January-02
[Schneier] B. Schneier, "Applied Cryptography: Pro-
tocols, Algorithms, and Source Code in C", 2nd edi-
tion, 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).
[XCBC] J. Black, P. Rogaway "Comments to NIST Concern-
ing 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.
Authors' 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
Julian Satran Expires August 2002 3
iSCSI 20-January-02
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.
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
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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.
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. Sync and Steering with Fixed Interval Markers
This appendix presents a simple scheme for synchroniza-
tion (PDU boundary retrieval). It uses markers that
include 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 schemes uses payload byte stream counting that
includes every byte placed by iSCSI in the TCP stream
except for the markers themselves. It also excludes any
bytes that TCP counts but are not originated by iSCSI.
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 marker uses two copies of the pointer so that
a marker that spans a TCP packet boundary should leave at
least one valid copy in one of the packets.
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 mark-
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ers during login separately for each connection. The
default is NO. In certain environments, a sender not will-
ing to supply markers to a receiver willing to accept
markers MAY suffer from a considerable performance degra-
dation.
A.1 Markers At Fixed Intervals
A marker is inserted at fixed intervals in the TCP byte
stream. During login, each end of the iSCSI session spec-
ifies the interval at which it is willing to receive the
marker, or it disables the marker altogether. If a
receiver indicates that it desires a marker, the sender
SHOULD agree (during negotiation) and provide the marker
at the desired interval.
The marker interval and the initial marker-less interval
are counted in terms of the bytes placed in the TCP stream
data by iSCSI.
When reduced to iSCSI terms, markers MUST indicate the
offset to a 4-byte word boundary in the stream. The last
two bits of each marker word are reserved and are consid-
ered 0 for offset computation.
Padding iSCSI PDU payloads to 4-byte word boundaries sim-
plifies marker manipulation.
A.2 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. However,
in order to enable the marker inclusion and exclusion
mechanism to work without knowledge of the length of the
login phase, the first marker will be placed in the TCP
stream as if the Marker-less interval had included mark-
ers.
As an example if the marker interval is 512 and the login
ended at byte 1003 (first iSCSI placed byte is 0) the
first marker will be inserted after byte 1031 in the
stream.
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A.3 Negotiation
The following operational key=value pairs are used to
negotiate the fixed interval markers.
A.3.1 FMarker
Use: IO
Senders: 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 the Marker being used in both directions while
I->FMarker=send-receive
T->FMarker=receive
Results in Marker being used from the initiator to the
target, but not from the target to initiator.
A.3.2 RFMarkInt, SFMarkInt - offering
Use: IO
Senders: Initiator and Target
RFMarkInt=<number-from-1-to-65535>[,<number-from-1-to-
65535>]
SFMarkInt=<number-from-1-to-65535>[,<number-from-1-to-
65535>]
This is a connection specific parameter.
The receiver or sender indicates the minimum to maximum
interval (in 4-byte words) it wants the markers. In case
the receiver or sender only wants a specific value, only a
single value has to be specified. The responding sender or
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receiver selects a value within the minimum and maximum
offered or the only value offered or indicates through the
FMarker key=value its inability to set and/or receive
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 iSCSI payload
between markers). Whenever FMarker and RFMarkInt are both
sent, they MUST appear on the same Login Request/Response.
The default is 2048.
A.3.3 SFMarkInt, RFMarkInt - responding
Use: IO
Senders: Initiator and Target
SFMarkInt=<number-from-1-to-65535>
RFMarkInt=<number-from-1-to-65535>
This is a connection specific parameter.
Indicates at what interval (in 4-byte words) the sender
agrees to send or the receiver wants to receive the mark-
ers. The number MUST be within the range required offering
party. 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 iSCSI payload
between markers).
Default is 2048.
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Appendix A. Sync and Steering with Constant Overhead Word
Stuffing
(COWS)
This appendix presents a simple scheme for synchroniza-
tion (PDU boundary retrieval). The basic mechanism
described is inspired by [COBS]. However, unlike the mech-
anism outlined in [COBS], here the PDU is extended by 2 or
3 4 byte words regardless of the PDU length. With COWS:
- The iSCSI PDU is "prefixed" by an 8 byte COWS
header (CH), including a 4 byte word aligned COWS
framing pattern (CFP) and a 4 byte COWS link chain
element (CLCE).
- Any appearance of the pattern within the PDU is
replaced either by a forward or (for long payloads)
a backward link to the next appearance of the pat-
tern, or to the end (for forward links) or an end of
chain in indicator formatted as a CLCE.
- The iSCSI PDU may be followed by a trailer that
consists of a single CLCE.
All of these elements form a COWS Extended PDU (CEPDU).
COWS uses a framing pattern defined by the sender. A spe-
cial version of COWS that does not require pattern
replacement, but requires the sender to guarantee that a
CH will always appear at the beginning of a TCP segment,
may be used by specialized software stacks and/or hardware
adapters and its use may be negotiated (PDU Alignment
Option - PAO).
The CH format 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|
+---------------+---------------+---------------+----
-----------+
CFP| CFP (COWS Framing Pat-
tern) |
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+---------------+---------------+---------------+----
-----------+
CLCE|N| Res. | Link
|LT|
+---------------+---------------+---------------+----
-----------+
CFP is a pattern selected by the sender and communicated
to the receiver during the login phase. A CFP has to be
specified by the sender for each direction.
Except for the PAO, every occurrence of CFP within the
payload is replaced by a CLCE.
The CLCE is composed of:
- N - a bit is selected to be the complement of the
corresponding bit in the Framing pattern.
- Link - number of non-link 4 byte words to the next/
previous link.
- LT - link type coded as follows:
- 00 - Forward Last Link - no more links follow.
The Link field is the number of words to the end
of PDU.
- 01 - Forward More Links - the link field is
the number of words to the next link.
- 10 - Backward Last Link - the link field is 0.
- 11 - Backward More Links - the link field is
the number of words from the preceding field.
The LT field in the CH MUST be 00 or 01, and all CLCE
within the iSCSI header (if any) MUST have an LT field of
00 or 01 (the iSCSI header is encoded ONLY with forward
links).
The sender can use the backward linking mechanism to avoid
storing very long data payloads before sending them and
MUST be processed by the receiver.
If using backward linking, the sender MUST include a tail-
ing CLCE in the ECPDU. The tailing CLCE is the first CLCE
in the "back-tracking chain" and MUST be linked to by the
last CLCE in the "forward-tracking chain".
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COWS ECPDU can follow one of the following outlines:
a) Only Forward Pointing
CH (mandatory)
.
.
Forward Pointing CLCE (optional)
.
.
.
Forward Pointing CLCE (optional)
.
.
Last Payload Word
b) Forward-and-Backward Pointing
CH (mandatory)
.
.
Forward Pointing CLCE (optional - may point to
trailer if last forward)
.
.
.
Backward Pointing CLCE (optional - may have link
of 0)
.
.
Last Payload Word
Backward Pointing CLCE (mandatory - may have a
link of 0)
c) PDU alignment option
CH (mandatory)
.
.
.
Last Payload Word (also end of TCP segment)
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For cases a) and b), the payload on the wire is guaranteed
not to contain a CFP or a word aligned pattern anywhere
but in CH. For case c), the CFP is supposed the appear
only aligned to TCP segment boundaries and be implement
with specialized software stacks and hardware. For this
case the Link value, LT and the Reserved bits may is used
as a further validity checks (TBD???).
if all cases of the iSCSI PDUs are not constrained to a
one or a limited number of TCP segments.
A.1 Negotiation
A.2 Sent PDU processing
pseudo-language description...
A.3 Received PDU processing
pseudo-language description
A.4 Search for framing processing
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Appendix A. Examples
A.1 Read Operation Example
+------------------+-----------------------+-------------
---------+
|Initiator Function| PDU Type | Target Func-
tion |
+------------------+-----------------------+-------------
---------+
| 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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A.2 Write Operation Example
+------------------+-----------------------+-------------
--------+
|Initiator Function| PDU Type | Target Func-
tion |
+------------------+-----------------------+-------------
--------+
| Command request |SCSI Command (WRITE)>>>| Receive com-
mand |
| (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
|
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+------------------+-----------------------+-------------
--------+
| | <<< SCSI Response |Send Status and
Sense|
+------------------+-----------------------+-------------
--------+
| Command Complete | |
|
+------------------+-----------------------+-------------
--------+
A.3 R2TSN/DataSN use Examples
Output (write) data DataSN/R2TSN Example
+------------------+-----------------------+-------------
---------+
|Initiator Function| PDU Type & Content | Target Func-
tion |
+------------------+-----------------------+-------------
---------+
| Command request |SCSI Command (WRITE)>>>| Receive com-
mand |
| (write) | | and queue it
|
+------------------+-----------------------+-------------
---------+
| | | Process old
commands |
+------------------+-----------------------+-------------
---------+
| | <<< R2T | Ready for data
|
| | R2TSN = 0 |
|
+------------------+-----------------------+-------------
---------+
| | <<< R2T | Ready for more
data |
| | R2TSN = 1 |
|
+------------------+-----------------------+-------------
---------+
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| 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 | |
|
+------------------+-----------------------+-------------
---------+
Input (read) data DataSN Example
+------------------+-----------------------+-------------
---------+
|Initiator Function| PDU Type | Target Func-
tion |
+------------------+-----------------------+-------------
---------+
| Command request |SCSI Command (READ)>>> |
|
| (read) | |
|
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+------------------+-----------------------+-------------
---------+
| | | 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 | |
|
+------------------+-----------------------+-------------
---------+
Bidirectional DataSN Example
+------------------+-----------------------+-------------
---------+
|Initiator Function| PDU Type | Target Func-
tion |
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+------------------+-----------------------+-------------
---------+
| 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 |
|
+------------------+-----------------------+-------------
---------+
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| Command Complete | |
|
+------------------+-----------------------+-------------
---------+
*) Send data and Receive Data may be transferred simulta-
neously 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).
Unsolicited and immediate output (write) data with DataSN
Example
+------------------+-----------------------+-------------
---------+
|Initiator Function| PDU Type & Content | Target Func-
tion |
+------------------+-----------------------+-------------
---------+
| Command request |SCSI Command (WRITE)>>>| Receive com-
mand |
| (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 |
|
+------------------+-----------------------+-------------
---------+
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| Send Data | SCSI Write Data >>> | Receive Data
|
| for R2TSN 0 | DataSN = 0, F=1 |
|
+------------------+-----------------------+-------------
---------+
| | <<< SCSI Response |Send Status and
Sense |
| | |
|
+------------------+-----------------------+-------------
---------+
| Command Complete | |
|
+------------------+-----------------------+-------------
---------+
A.4 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
...
28: ff ff ff ff
CRC: 43 ab a8 62
32 bytes of incrementing 00..1f:
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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 A. Login Phase Examples
In the first example, the initiator and target authenti-
cate 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 pro-
ceeds 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 Max-
BurstSize=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 initiators authentication by the target is
not successful, the target responds with:
T-> Login "login reject"
instead of the Login KRB_AP_REP message, and termi-
nates the connection.
If the targets authentication by the initiator is
not successful, the initiator terminates the con-
nection (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 pro-
ceeds 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 pro-
ceeds 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 targets authentication by the initiator is
not successful, the initiator terminates the con-
nection (without responding to the Login
SPKM_REP_TI message).
If the initiators authentication by the target is
not successful, the target responds with:
T-> Login "login reject"
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instead of the Login "proceed and change stage" mes-
sage, 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 pro-
ceeds 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:
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
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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=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:
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 is not successful,
the target responds with:
T-> Login "login reject"
Instead of the T-> Login SRP_HM=<H(A | M | K)> mes-
sage 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)
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"
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>
If the target authentication is not successful, the
initiator aborts the connection; otherwise, it pro-
ceeds.
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 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)
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)
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... 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. It therefore, may offer iSCSI param-
eters on the Login PDU with the T bit set to 1, and the
target may respond with a final Login Response PDU immedi-
ately:
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 secu-
rity parameters on the Login PDU, but the target
does not choose any (i.e., chooses the "none" val-
ues):
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
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
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T-> Login (CSG,NSG=1,3 T=1) "login accept"
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Appendix A. SendTargets Operation
To reduce the amount of configuration required on an ini-
tiator, iSCSI provides the SendTargets text request. This
initiator sends this command 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 estab-
lish one of two types of sessions. If the initi-
ator establishes the session using the key
"SessionType=discovery", the session is a discovery ses-
sion, and a target name does not need to be specified.
Otherwise, the session is a normal, operational session.
The SendTargets command MUST only be sent during the full
feature phase of a normal or discovery session.
A system that contains targets MUST support discovery ses-
sions 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 ses-
sions; 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 dis-
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covery session, and MAY NOT be supported on an
operational session.
<iSCSI-target-name>
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 only with addresses 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 that con-
tains 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 Tar-
getName 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 Section 12.4 Target-
Name.
A discovery session MAY respond to a SendTargets request
with its complete list of targets, or with a list of tar-
gets that is based on the name of the initiator logged in
to the session.
A SendTargets response MAY not contain target names if
there are no targets for the requesting initiator to
access.
Each target record returned includes zero or more Tar-
getAddress fields.
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A SendTargets response MUST NOT contain iSCSI default tar-
get 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>
The hostname-or-ipaddress and tcp port are as specified in
the Section 2.2.7 Naming and Addressing.
Each TargetAddress belongs to a portal group, identified
by its numeric, decimal portal group tag. The iSCSI tar-
get 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
that belong to the same portal group.
Multiple-connection sessions cannot span iSCSI addresses
that belong 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 speci-
fied.
After obtaining a list of targets from the discovery tar-
get 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 subsequently SendTargets commands to
discover new targets.
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Examples:
This example is the SendTargets response from a single
target that has no other interface ports.
Initiator sends text request that contains:
SendTargets=all
Target sends a text response that contains:
TargetName=iqn.1993-11.com.acme.diskarray.sn.8675309
All the target 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.
The next example has two internal iSCSI targets, each
accessible via two different ports with different IP
addresses. The following is 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
Both targets share both addresses; the multiple addresses
are likely used to provide multi-path support. The initi-
ator 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.
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 also
been returned.
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The next text response shows a target that supports span-
ning sessions across multiple addresses, which indicates
the use of 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 Tar-
getAddress with its own tag (.49), cannot be combined with
any other address within the same session.
This SendTargets response does not indicate whether .49
supports multiple connections per session; it communi-
cated via the MaxConnections text key upon login to the
target.
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Appendix A. 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. Each of the
recovery classes described has initiator procedures as
well as target procedures. 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, such as recovery of Synchroniza-
tion on a header digest error are considered out-
of-scope in these algorithms. In this particular
example a header digest error may lead to connec-
tion recovery if some type of sync and steering
layer is not implemented.
These algorithms strive to convey the iSCSI error recovery
concepts in the simplest terms, and are not designed to be
optimal.
A.1 General Data Structure and Procedure Description
This section defines the procedures and data structures
that are commonly used by all the error recovery algo-
rithms. The structures may not be the exhaustive represen-
tations of what is required for a typical implementation.
Data structure definitions -
struct TransferContext {
int TargetTransferTag;
int ExpectedDataSN;
};
struct TCB { /* task control block */
Boolean SoFarInOrder;
int ExpectedDataSN; /* used for both R2Ts, and
Data */
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int MissingDataSNList[MaxMissingDPDU];
Boolean FbitReceived;
Boolean StatusXferd;
Boolean CurrentlyAllegiant;
int ActiveR2Ts;
int Response;
char *Reason;
struct TransferContext
TransferContextList[MaxOutStandingR2T];
int InitiatorTaskTag;
int CmdSN;
};
struct Connection {
struct Session SessionReference;
Boolean SoFarInOrder;
int CID;
int State;
int ExpectedStatSN;
int MissingStatSNList[MaxMissingSPDU];
Boolean PerformConnectionCleanup;
};
struct Session {
int NumConnections;
int NextCmdSN;
int Maxconnections;
int ErrorRecoveryLevel;
struct iSCSIEndpoint OtherEndInfo;
struct Connection ConnectionList[MaxSupported-
Conns];
};
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, rea-
son code);
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A.2 Within-command Error Recovery Algorithms
A.2.1 Procedure Descriptions
Recover-Data-if-Possible(last required DataSN, task con-
trol 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 -
InitiatorDataSNACKEnabled, TargetDataSNACKSupported,
TargetRecoveryR2TEnabled.
Notes:
- Some procedures used in this section, including:
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
that carry StatSN - SCSI Response, Text Response
etc.
A.2.2 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);
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} else {
TCB.Reason = "Protocol service CRC error";
}
} else {
TCB.Reason = "Protocol service CRC error";
}
if (TCB.Reason = "Protocol service CRC error") {
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) {
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.
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}
LastRequiredDataSN = CurrentPDU.DataSN - 1;
}
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, Current-
PDU, 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);
}
if (send-status-SNACK is TRUE)
Recover-Status-if-Possible(Connection, Current-
PDU);
} else { /* REST UNRELATED TO WITHIN-COMMAND-RECOVERY,
NOT SHOWN */
}
if ((TCB.SoFarInOrder is TRUE) and
(TCB.StatusXferd is TRUE)) {
SCSI-Task-Completion(TCB);
}
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}
A.2.3 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 MissingDat-
aRange[].
send-recovery-R2T = TRUE;
}
if (CurrentPDU.Fbit = TRUE) {
if (current PDU is solicited) {
Decrement TCB.ActiveR2Ts.
}
if ((current PDU is unsolicited and
data received is less than I/O size and
data received is less than First-
BurstSize)
or {current PDU is solicited and the size
of
this burst is less than expected)) {
send-recovery-R2T = TRUE;
Note the missing data in MissingDat-
aRange[].
}
}
}
Increment TContext.ExpectedDataSN.
if (send-recovery-R2T is TRUE and
task is not already considered failed) {
if (TargetRecoveryR2TEnabled is TRUE) {
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Increment TCB.ActiveR2Ts.
Build-And-Send-R2T(Connection, MissingDat-
aRange, TCB);
} else {
if (current PDU is the last unsolicited)
TCB.Reason = "Not enough unsolicited
data";
else
TCB.Reason = "Protocol service CRC
error";
}
}
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
} else if (CurrentPDU.type = SNACK) {
snack-failure = FALSE;
if (this is data retransmission request) {
if (TargetDataSNACKSupported) {
if (the request is satisfiable) {
Build-And-Send-A-Data-Burst(CurrentPDU,
TCB);
} else {
snack-failure = TRUE;
}
} else {
snack-failure = TRUE;
}
if (snack-failure is TRUE) {
Build-And-Send-Reject(Connection, Current-
PDU,
Data-
SNACK-Reject);
if (TCB.StatusXferd is not TRUE) {
TCB.Reason = "SNACK Rejected";
Build-And-Send-Status(Connection, TCB);
}
}
} else {
Handle-Status-SNACK-request(Connection, Current-
PDU);
}
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} 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 {
TCB.Reason = "Protocol service CRC error";
if (TCB.ActiveR2Ts = 0) {
Build-And-Send-Status(Connection, TCB);
}
}
}
A.3 Within-connection Recovery Algorithms
A.3.1 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);
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Implementation-specific tunables:
InitiatorCommandRetryEnabled, InitiatorStatusExpectNopEn-
abled, InitiatorProactiveSNACKEnabled, InitiatorStatusS-
NACKEnabled, TargetStatusSNACKSupported.
Notes:
- The initiator algorithms only deal with unsolicited
Nop-In PDUs for generating status SNACKs. Solic-
ited 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 lead-
ing to Recover-Status-if-Possible.
- The pseudo-code shown may result in the retransmis-
sion of unacknowledged commands in more cases than
necessary. This will not however affect the cor-
rectness of the operation since the target is
required to discard the duplicate CmdSNs.
- The procedure Build-And-Send-Async is defined in
the Connection recovery algorithms.
- The procedure Status-Expect-Timeout-Handler
describes how initiators may proactively attempt to
retrieve the Status if they so choose. This proce-
dure is assumed to be triggered much before the
standard ULP timeout.
A.3.1.1 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.PerformConnectionCleanup = TRUE;
}
} else {
Connection.PerformConnectionCleanup = TRUE;
}
if (Connection.PerformConnectionCleanup is TRUE) {
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Start-Timer(Connection-Cleanup-Handler, Connec-
tion, 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;
} else {
discard, return;
}
}
Adjust Connection.ExpectedStatSN if appropriate.
if (missing StatSN list is empty) {
Connection.SoFarInOrder = TRUE;
}
}
return send-status-SNACK;
}
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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(Connec-
tion,
CurrentPDU.ExpCmdSN);
}
}
} else if (CurrentPDU.type = Reject) {
if (it is a data digest error on immediate data)
{
Retransmit-Command-if-Possible(Connection,
CurrentPDU.BadPDU-
Header.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, Cur-
rentPDU);
} else { /* REST UNRELATED TO WITHIN-CONNECTION-RECOV-
ERY,
* NOT SHOWN */
}
}
Command-Acknowledge-Timeout-Handler(TCB)
{
Retrieve the Connection for TCB.
Retransmit-Command-if-Possible(Connection,
TCB.CmdSN);
}
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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);
}
}
}
A.3.1.2 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,
LogoutLoginMinTime, Logout-
LoginMaxTime);
}
}
A.3.2 Connection Recovery Algorithms
A.3.2.1 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 con-
nection
identifier, reason code);
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PerformImplicitLogout(transport connection, logout con-
nection
identifier, target information);
PerformLogin(transport connection, target information);
CreateNewTransportConnection(target information);
Build-And-Send-Command(transport connection, task control
block);
Connection-Cleanup-Handler(transport connection);
Connection-Resource-Timeout-Handler(transport connec-
tion);
Quiesce-And-Prepare-for-New-Allegiance(session, task con-
trol 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, and hung
connection while the connection is in the full-fea-
ture phase, are all assumed to be asynchronously
signaled to the iSCSI layer using the
Transport_Exception_Handler procedure.
A.3.2.2 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.AsyncEvent = ConnectionDropped) {
Retrieve the AffectedConnection for Current-
PDU.Parameter1.
AffectedConnection.State = CLEANUP_WAIT;
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} else if (CurrentPDU.AsyncEvent = LogoutRequest))
{
Retrieve the AffectedConnection for Current-
PDU.Parameter1.
AffectedConnection.State = LOGOUT_REQUESTED;
AffectedConnection.PerformConnectionCleanup =
TRUE;
Start-Timer(Connection-Cleanup-Handler,
AffectedConnection, Current-
PDU.Parameter2);
} else if (CurrentPDU.AsyncEvent = Session-
Dropped)) {
for (each Connection) {
Connection.state = CLEANUP_WAIT;
}
Session.state = FAILED;
Start-Timer(Session-Continuation-Handler,
Session, CurrentPDU.Parameter2);
}
} else if (CurrentPDU.type = LogoutResponse) {
Retrieve the CleanupConnection for CurrentPDU.CID.
if (CurrentPDU.Response = failure) {
CleanupConnection.State = CLEANUP_WAIT;
} else {
CleanupConnection.State = FREE;
}
} else if (CurrentPDU.type = LoginResponse) {
if (this is a response to an implicit Logout) {
Retrieve the CleanupConnection.
if (successful) {
CleanupConnection.State = FREE;
Connection.State = LOGGED_IN;
} else {
CleanupConnection.State = CLEANUP_WAIT;
DestroyTransportConnection(Connection);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
if (CleanupConnection.State = FREE) {
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for (each command that was active on CleanupConnec-
tion) {
/* Establish new connection allegiance */
NewConnection = Pick-A-Logged-In-Connec-
tion(Session);
Build-And-Send-Command(NewConnection, TCB);
}
}
}
Connection-Cleanup-Handler(Connection)
{
Retrieve Session from Connection.
Start-Timer(Connection-Resource-Timeout-Handler,
Connection, LogoutLoginMaxTime);
if (Connection can still exchange iSCSI PDUs) {
NewConnection = Connection;
} else {
if (there are other logged-in connections) {
NewConnection = Pick-A-Logged-In-Connec-
tion(Session);
} else {
NewConnection =
CreateTransportConnection(Session.Other-
EndInfo);
Initiate an implicit Logout on NewConnection
for
Connec-
tion.CID.
return;
}
}
Build-And-Send-Logout(NewConnection, Connection.CID,
RecoveryRemove);
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
Start-Timer(Connection-Cleanup-Handler, Connec-
tion,
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LogooutLogin-
MinTime);
} else {
Connection.State = FREE;
}
}
A.3.2.3 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 CleanupConnection from Current-
PDU.CID).
for (each command active on CleanupConnection)
{
Quiesce-And-Prepare-for-New-Alle-
giance(Session, TCB);
TCB.CurrentlyAllegiant = FALSE;
}
Cleanup-Connection-State(CleanupConnection);
if ((quiescing successful) and (cleanup suc-
cessful)) {
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID,
Sucess);
} else {
Build-And-Send-Logout-Response(Connection,
CleanupConnection.CID,
Failure);
}
}
} else if (CurrentPDU.type = TaskManagement) {
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if (CurrentPDU.function = "TaskReassign") {
if (Session.ErrorRecoveryLevel < 2) {
Build-And-Send-TaskMgmt-Response(Connec-
tion,
CurrentPDU, "Task failover not sup-
ported");
} else if (task is not found) {
Build-And-Send-TaskMgmt-Response(Connec-
tion,
CurrentPDU, "Task not in task set");
} else if (task is currently allegiant) {
Build-And-Send-TaskMgmt-Response(Connec-
tion,
CurrentPDU, "Task still alle-
giant");
} else {
Establish-New-Allegiance(TCB, Connec-
tion);
TCB.CurrentlyAllegiant = TRUE;
Schedule-Command-To-Continue(TCB);
}
}
} else { /* REST UNRELATED TO CONNECTION-RECOVERY,
* NOT SHOWN */
}
}
Transport_Exception_Handler(Connection)
{
Connection.PerformConnectionCleanup = TRUE;
if (the event is an unexpected transport disconnect) {
Connection.State = CLEANUP_WAIT;
Start-Timer(Connection-Resource-Timeout-Handler,
Connection,
(LogoutLoginMinTime+Logout-
LoginMinTime));
if (this Session has full-feature phase connec-
tions left) {
DifferentConnection =
Pick-A-Logged-In-Connection(Session);
Build-And-Send-Async(DifferentConnection,
DroppedConnection, LogoutLoginMinTime,
LogoutLoginMaxTime);
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}
} else {
Connection.State = FREE;
}
}
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Full Copyright Statement
"Copyright (C) The Internet Society (date). All Rights
Reserved. This document and translations of it may be cop-
ied and furnished to others, and derivative works that
comment on or otherwise explain it or assist in its imple-
mentation may be prepared, copied, published and distrib-
uted, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this
paragraph are included on all such copies and derivative
works. However, this document itself may not be modified
in any way, such as by removing the copyright notice or
references to the Internet Society or other Internet orga-
nizations, except as needed for the purpose of developing
Internet standards in which case the procedures for copy-
rights defined in the Internet Standards process must be
followed, or as required to translate it into languages
other than English.
The limited permissions granted above are perpetual and
will not be revoked by the Internet Society or its suc-
cessors or assigns.
This document and the information contained herein is pro-
vided on an "AS IS" basis and THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WAR-
RANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT
INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MER-
CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
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