tech-invite   World Map     

IETF     RFCs     Groups     SIP     ABNFs    |    3GPP     Specs     Glossaries     Architecture     IMS     UICC    |    search

RFC 3720

 
 
 

Internet Small Computer Systems Interface (iSCSI)

Part 7 of 9, p. 160 to 187
Prev RFC Part       Next RFC Part

 


prevText      Top      Up      ToC       Page 160 
10.13.  Login Response

   The Login Response indicates the progress and/or end of the Login
   Phase.

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x23      |T|C|.|.|CSG|NSG| Version-max   | Version-active|
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| ISID                                                          |
     +                               +---------------+---------------+
   12|                               | TSIH                          |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Status-Class  | Status-Detail | Reserved                      |
     +---------------+---------------+---------------+---------------+
   40/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48/ DataSegment - Login Parameters in Text request Format         /
    +/                                                               /
     +---------------+---------------+---------------+---------------+

10.13.1.  Version-max

   This is the highest version number supported by the target.

   All Login Responses within the Login Phase MUST carry the same
   Version-max.

   The initiator MUST use the value presented as a response to the first
   Login Request.

Top      Up      ToC       Page 161 
10.13.2.  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 supported by the target.

   All Login Responses within the Login Phase MUST carry the same
   Version-active.

   The initiator MUST use the value presented as a response to the first
   Login Request.

10.13.3.  TSIH

   The TSIH is the target assigned session identifying handle.  Its
   internal format and content are not defined by this protocol except
   for the value 0 that is reserved.  With the exception of the Login
   Final-Response in a new session, this field should be set to the TSIH
   provided by the initiator in the Login Request.  For a new session,
   the target MUST generate a non-zero TSIH and ONLY return it in the
   Login Final-Response (see Section 5.3 Login Phase).

10.13.4.  StatSN

   For the first Login Response (the response to the first Login
   Request), this is the starting status Sequence Number for the
   connection.  The next response of any kind, including the next Login
   Response, if any, in the same Login Phase, will carry this number +
   1.  This field is only valid if the Status-Class is 0.

10.13.5.  Status-Class and Status-Detail

   The Status returned in a Login Response indicates the execution
   status of the Login Phase.  The status includes:

     Status-Class
     Status-Detail

   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 exceptions, without having to look at the Status-Detail.
   The Status-Detail allows finer-grained exception handling for more
   sophisticated initiators and for better information for logging.

Top      Up      ToC       Page 162 
   The status classes are as follows:

      0 - Success - indicates that the iSCSI target successfully
          received, understood, and accepted the request.  The numbering
          fields (StatSN, ExpCmdSN, MaxCmdSN) are only valid 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
          parameters of the type "TargetAddress", which indicates the
          target's new address.  A redirection response MAY be issued by
          a target prior or after completing a security negotiation if a
          security negotiation is required.  A redirection SHOULD be
          accepted by an initiator even without having the target
          complete a security negotiation if any security negotiation is
          required, and MUST be accepted by the initiator after the
          completion of the security negotiation if any security
          negotiation is required.

      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 initiator may re-try the same
          Login Request later.

   The table below shows all of the currently allocated status codes.
   The codes are in hexadecimal; the first byte is the status class and
   the second byte is the status detail.

   -----------------------------------------------------------------
   Status        | Code | Description
                 |(hex) |
   -----------------------------------------------------------------
   Success       | 0000 | Login is proceeding OK (*1).
   -----------------------------------------------------------------
   Target moved  | 0101 | The requested 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.
   -----------------------------------------------------------------

Top      Up      ToC       Page 163 
   Initiator     | 0200 | Miscellaneous iSCSI initiator
   error         |      | errors.
   ----------------------------------------------------------------
   Authentication| 0201 | The initiator could not be
   failure       |      | successfully authenticated or target
                 |      | authentication is not supported.
   -----------------------------------------------------------------
   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 | Too many connections on this SSID.
   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 Initiator.
   -----------------------------------------------------------------
   Session does  | 020a | Attempt to add a connection
   not exist     |      | to a non-existent session.
   -----------------------------------------------------------------
   Invalid during| 020b | Invalid Request type during Login.
   login         |      |
   -----------------------------------------------------------------
   Target error  | 0300 | Target hardware or software error.
   -----------------------------------------------------------------
   Service       | 0301 | The iSCSI service or target is not
   unavailable   |      | currently operational.
   -----------------------------------------------------------------
   Out of        | 0302 | The target has insufficient session,
   resources     |      | connection, or other resources.
   -----------------------------------------------------------------

Top      Up      ToC       Page 164 
   (*1) If the response T bit is 1 in both the request and the matching
   response, and the NSG is FullFeaturePhase in both the request and the
   matching 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.

10.13.6.  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 FullFeaturePhase, then this is also
   the Final Login Response (see Chapter 5).  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.

10.13.7.  C (Continue) Bit

   When set to 1,  indicates that the text (set of key=value pairs) in
   this Login Response is not complete (it will be continued on
   subsequent Login Responses); otherwise, it indicates that this Login
   Response ends a set of key=value pairs.  A Login Response with the C
   bit set to 1 MUST have the T bit set to 0.

10.13.8.  Login Parameters

   The target MUST provide some basic parameters in order to enable the
   initiator to determine if it is connected to the correct port and the
   initial text parameters for the security exchange.

   All the rules specified in Section 10.11.6 Text Response Data for
   text responses also hold for Login 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 formats, MUST be supported by
   iSCSI initiators and targets.  Keys in Chapter 11, only need to be
   supported when the function to which they refer is mandatory to
   implement.

Top      Up      ToC       Page 165 
10.14.  Logout Request

   The Logout Request is used to perform a controlled closing of a
   connection.

   An initiator MAY use a Logout Request to remove a connection from a
   session or to close an entire session.

   After sending the Logout Request PDU, an initiator MUST NOT send any
   new iSCSI requests on the closing connection.  If the Logout Request
   is intended to close the session, new iSCSI requests MUST NOT be sent
   on any of the connections participating in the session.

   When receiving a Logout Request with the reason code of "close the
   connection" or "close the session", the target MUST terminate all
   pending commands, whether acknowledged via ExpCmdSN 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 via ExpCmdSN 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 terminated
   commands, no additional responses should be expected.

   A Logout for a CID may be performed on a different transport
   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 terminated 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 the Logout Request to "clean-up" the target end of a
   failing connection and enable recovery to start, or the Login Request
   with a non-zero TSIH and the same CID on a new connection for the
   same effect (see Section 10.14.3 CID).  In sessions with a single
   connection, the connection can be closed and then a new connection
   reopened.  A connection reinstatement login can be used for recovery
   (see Section 5.3.4 Connection Reinstatement).

Top      Up      ToC       Page 166 
   A successful completion of a Logout Request with the reason code of
   "close the connection" or "remove the connection for recovery"
   results at the target in the discarding of unacknowledged commands
   received on the connection being logged out.  These are commands that
   have arrived on the connection being logged out, but have not been
   delivered to SCSI because one or more commands with a smaller CmdSN
   has not been received by iSCSI.  See Section 3.2.2.1 Command
   Numbering and Acknowledging.  The resulting holes the in command
   sequence numbers will have to be handled by appropriate recovery (see
   Chapter 6) unless the session is also closed.

   The entire logout discussion in this section is also applicable for
   an implicit Logout realized via a connection reinstatement or session
   reinstatement.  When a Login Request performs an implicit Logout, the
   implicit Logout is performed as if having the reason codes specified
   below:

     Reason code        Type of implicit Logout
     -------------------------------------------
         0              session reinstatement
         1              connection reinstatement when
                       the operational ErrorRecoveryLevel < 2
         2              connection reinstatement when
                       the operational ErrorRecoveryLevel = 2

Top      Up      ToC       Page 167 
   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x06      |1| Reason Code | Reserved                      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------------------------------------------------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| CID or Reserved               | Reserved                      |
     +---------------+---------------+---------------+---------------+
   24| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

10.14.1.  Reason Code

   Reason Code indicates the reason for Logout as follows:

      0 - close the session.  All commands associated with the session
          (if any) are terminated.

      1 - close the connection.  All commands associated with connection
          (if any) are terminated.

      2 - remove the connection for recovery.  Connection is closed and
          all commands associated with it, if any, are to be prepared
          for a new allegiance.

   All other values are reserved.

Top      Up      ToC       Page 168 
10.14.2.  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.

10.14.3.  CID

   This is the connection ID of the connection to be closed (including
   closing the TCP stream).  This field is only valid if the reason code
   is not "close the session".

10.14.4.  ExpStatSN

   This is the last ExpStatSN value for the connection to be closed.

10.14.5.  Implicit termination of tasks

   A target implicitly terminates the active tasks due to the iSCSI
   protocol in the following cases:

      a)  When a connection is implicitly or explicitly logged out with
          the reason code of "Close the connection" and there are active
          tasks allegiant to that connection.

      b)  When a connection fails and eventually the connection state
          times out (state transition M1 in Section 7.2.2 State
          Transition Descriptions for Initiators and Targets) and there
          are active tasks allegiant to that connection.

      c)  When a successful recovery Logout is performed while there are
          active tasks allegiant to that connection, and those tasks
          eventually time out after the Time2Wait and Time2Retain
          periods without allegiance reassignment.

      d)  When a connection is implicitly or explicitly logged out with
          the reason code of "Close the session" and there are active
          tasks in that session.

   If the tasks terminated in any of the above cases are SCSI tasks,
   they must be internally terminated as if with CHECK CONDITION status.
   This status is only meaningful for appropriately handling the
   internal SCSI state and SCSI side effects with respect to ordering
   because this status is never communicated back as a terminating
   status to the initiator. However additional actions may have to be
   taken at SCSI level depending on the SCSI context as defined by the
   SCSI standards (e.g., queued commands and ACA, in cases a), b), and
   c), after the tasks are terminated, the target MUST report a Unit
   Attention condition on the next command processed on any connection
   for each affected I_T_L nexus with the status of CHECK CONDITION, and

Top      Up      ToC       Page 169 
   the ASC/ASCQ value of 47h/7Fh - "SOME COMMANDS CLEARED BY ISCSI
   PROTOCOL EVENT" - etc. - see [SAM2] and [SPC3]).

10.15.  Logout Response

   The Logout Response is used by the target to indicate if the cleanup
   operation for the connection(s) has completed.

   After Logout, the TCP connection referred by the CID MUST be closed
   at both ends (or all connections must be closed if the logout reason
   was session close).

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x26      |1| Reserved    | Response      | Reserved      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------------------------------------------------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag                                            |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| Reserved                                                      |
     +---------------------------------------------------------------+
   40| Time2Wait                     | Time2Retain                   |
     +---------------+---------------+---------------+---------------+
   44| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

Top      Up      ToC       Page 170 
10.15.1.  Response

   Logout Response:

      0 - connection or session closed successfully.

      1 - CID not found.

      2 - connection recovery is not supported.  If Logout reason code
         was recovery and target does not support it as indicated by the
         ErrorRecoveryLevel.

      3 - cleanup failed for various reasons.

10.15.2.  TotalAHSLength and DataSegmentLength

   For this PDU TotalAHSLength and DataSegmentLength MUST be 0.

10.15.3.  Time2Wait

   If the Logout Response code is 0 and if the operational
   ErrorRecoveryLevel is 2, this is the minimum amount of time, in
   seconds, to wait before attempting task reassignment.  If the Logout
   Response code is 0 and if the operational ErrorRecoveryLevel is less
   than 2, this field is to be ignored.

   This field is invalid if the Logout Response code is 1.

   If the Logout response code is 2 or 3, this field specifies the
   minimum time to wait before attempting a new implicit or explicit
   logout.

   If Time2Wait is 0, the reassignment or a new Logout may be attempted
   immediately.

10.15.4.  Time2Retain

   If the Logout response code is 0 and if the operational
   ErrorRecoveryLevel is 2, this is the maximum amount of 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.  If the Logout response code is 0 and if the
   operational ErrorRecoveryLevel is less than 2, this field is to be
   ignored.

   This field is invalid if the Logout response code is 1.

Top      Up      ToC       Page 171 
   If the Logout response code is 2 or 3, this field specifies the
   maximum amount of time, in seconds, after the initial wait
   (Time2Wait), the target waits for a new implicit or explicit logout.

   If it is the last connection of a session, the whole session state is
   discarded after Time2Retain.

   If Time2Retain is 0, the target has already discarded the connection
   (and possibly the session) state along with the task states.  No
   reassignment or Logout is required in this case.

10.16.  SNACK Request

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x10      |1|.|.|.| Type  | Reserved                      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or SNACK Tag or 0xffffffff                |
     +---------------+---------------+---------------+---------------+
   24| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   28| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   40| BegRun                                                        |
     +---------------------------------------------------------------+
   44| RunLength                                                     |
     +---------------------------------------------------------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+

   If the implementation supports ErrorRecoveryLevel greater than zero,
   it MUST support all SNACK types.

Top      Up      ToC       Page 172 
   The SNACK is used by the initiator to request the retransmission of
   numbered-responses, data, or R2T PDUs from the target.  The SNACK
   request indicates the numbered-responses or data "runs" whose
   retransmission is requested by the target, where the run starts with
   the first StatSN, DataSN, or R2TSN whose retransmission is requested
   and indicates the number of Status, Data, or R2T PDUs requested
   including the first.  0 has special meaning when used as a starting
   number and length:

     - When used in RunLength, it means all PDUs starting with the
       initial.
     - When used in both BegRun and RunLength, it means all
       unacknowledged PDUs.

   The numbered-response(s) or R2T(s), requested by a SNACK, MUST be
   delivered as exact replicas of the ones that the target transmitted
   originally except for the fields ExpCmdSN, MaxCmdSN, and ExpDataSN,
   which MUST carry the current values.  R2T(s)requested by SNACK MUST
   also carry the current value of StatSN.

   The numbered Data-In PDUs, requested by a Data SNACK MUST be
   delivered as exact replicas of the ones that the target transmitted
   originally except for the fields ExpCmdSN and MaxCmdSN, which MUST
   carry the current values and except for resegmentation (see Section
   10.16.3 Resegmentation).

   Any SNACK that requests a numbered-response, Data, or R2T that was
   not sent by the target or was already acknowledged by the initiator,
   MUST be rejected with a reason code of "Protocol error".

10.16.1.  Type

   This field encodes the SNACK function as follows:

      0-Data/R2T SNACK - requesting retransmission of one or more Data-
        In or R2T PDUs.

      1-Status SNACK - requesting retransmission of one or more numbered
        responses.

      2-DataACK - positively acknowledges Data-In PDUs.

      3-R-Data SNACK - requesting retransmission of Data-In PDUs with
        possible resegmentation and status tagging.

Top      Up      ToC       Page 173 
   All other values are reserved.

   Data/R2T SNACK, Status SNACK, or R-Data SNACK for a command MUST
   precede status acknowledgement for the given command.

10.16.2.  Data Acknowledgement

   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 MaxBurstLength limit is reached).

   The DataACK is used to free resources at the target and not to
   request or imply data retransmission.

   An initiator MUST NOT request retransmission for any data it had
   already acknowledged.

10.16.3.  Resegmentation

   If the initiator MaxRecvDataSegmentLength changed between the
   original transmission and the time the initiator requests
   retransmission, the initiator MUST issue a R-Data SNACK (see Section
   10.16.1 Type).  With R-Data SNACK, the initiator indicates that it
   discards all the unacknowledged data and expects the target to resend
   it.  It also expects resegmentation.  In this case, the retransmitted
   Data-In PDUs MAY be different from the ones originally sent in order
   to reflect changes in MaxRecvDataSegmentLength.  Their DataSN starts
   with the BegRun of the last DataACK received by the target if any was
   received; otherwise it starts with 0 and is increased by 1 for each
   resent Data-In PDU.

   A target that has received a R-Data SNACK MUST return a SCSI Response
   that contains a copy of the SNACK Tag field from the R-Data SNACK in
   the SCSI Response SNACK Tag field as its last or only Response.  For
   example, if it has already sent a response containing another value
   in the SNACK Tag field or had the status included in the last Data-In
   PDU, it must send a new SCSI Response PDU.  If a target sends more
   than one SCSI Response PDU due to this rule, all SCSI responses must
   carry the same StatSN (see Section 10.4.4 SNACK Tag).  If an
   initiator attempts to recover a lost SCSI Response (with a
   Status SNACK, see Section 10.16.1 Type) when more than one response
   has been sent, the target will send the SCSI Response with the latest
   content known to the target, including the last SNACK Tag for the
   command.

Top      Up      ToC       Page 174 
   For considerations in allegiance reassignment of a task to a
   connection with a different MaxRecvDataSegmentLength, refer to
   Section 6.2.2 Allegiance Reassignment.

10.16.4.  Initiator Task Tag

   For Status SNACK and DataACK, the Initiator Task Tag MUST be set to
   the reserved value 0xffffffff.  In all other cases, the Initiator
   Task Tag field MUST be set to the Initiator Task Tag of the
   referenced command.

10.16.5.  Target Transfer Tag or SNACK Tag

   For an R-Data SNACK, this field MUST contain a value that is
   different from 0 or 0xffffffff and is unique for the task (identified
   by the Initiator Task Tag).  This value MUST be copied by the iSCSI
   target in the last or only SCSI Response PDU it issues for the
   command.

   For DataACK, the Target Transfer Tag MUST contain a copy of the
   Target Transfer Tag and LUN provided with the SCSI Data-In PDU with
   the A bit set to 1.

   In all other cases, the Target Transfer Tag field MUST be set to the
   reserved value of 0xffffffff.

10.16.6.  BegRun

   The DataSN, R2TSN, or StatSN of the first PDU whose retransmission is
   requested (Data/R2T and Status SNACK), or the next expected DataSN
   (DataACK SNACK).

   BegRun 0 when used in conjunction with RunLength 0 means resend all
   unacknowledged Data-In, R2T or Response PDUs.

   BegRun MUST be 0 for a R-Data SNACK.

10.16.7.  RunLength

   The number of PDUs whose retransmission is requested.

   RunLength 0 signals that all Data-In, R2T, or Response PDUs carrying
   the numbers equal to or greater than BegRun have to be resent.

   The RunLength MUST also be 0 for a DataACK SNACK in addition to
   R-Data SNACK.

Top      Up      ToC       Page 175 
10.17.  Reject

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x3f      |1| Reserved    | Reason        | Reserved      |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   16| 0xffffffff                                                    |
     +---------------+---------------+---------------+---------------+
   20| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36| DataSN/R2TSN or Reserved                                      |
     +---------------+---------------+---------------+---------------+
   40| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   44| Reserved                                                      |
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
   xx/ Complete Header of Bad PDU                                    /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   yy/Vendor specific data (if any)                                  /
     /                                                               /
     +---------------+---------------+---------------+---------------+
   zz| Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

   Reject is used to indicate an iSCSI error condition (protocol,
   unsupported option, etc.).

Top      Up      ToC       Page 176 
10.17.1.  Reason

   The reject Reason is coded as follows:

   +------+----------------------------------------+------------------+
   | Code | Explanation                            | Can the original |
   | (hex)|                                        | PDU be re-sent?  |
   +------+----------------------------------------+------------------+
   | 0x01 | Reserved                               | no               |
   |      |                                        |                  |
   | 0x02 | Data (payload) Digest Error            | yes  (Note 1)    |
   |      |                                        |                  |
   | 0x03 | SNACK Reject                           | yes              |
   |      |                                        |                  |
   | 0x04 | Protocol Error (e.g., SNACK request for| no               |
   |      | a status that was already acknowledged)|                  |
   |      |                                        |                  |
   | 0x05 | Command not supported                  | no               |
   |      |                                        |                  |
   | 0x06 | Immediate Command Reject - too many    | yes              |
   |      | immediate commands                     |                  |
   |      |                                        |                  |
   | 0x07 | Task in progress                       | no               |
   |      |                                        |                  |
   | 0x08 | Invalid Data ACK                       | no               |
   |      |                                        |                  |
   | 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 only done 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,  a response, or a
   data transfer.  Some examples are invalid TTT/ITT, buffer offset, LUN
   qualifying a TTT, and an invalid sequence number in a SNACK.

   All other values for Reason are reserved.

Top      Up      ToC       Page 177 
   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 10.4.3
   Response.  In these 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
   (i.e., the command PDU did not contain all the data and the target
   has not received a Data-Out PDU with the Final bit set to 1 for the
   unsolicited data, if any, and all outstanding R2Ts, if any), the
   target MUST wait until it receives the last expected Data-Out PDUs
   with the F bit set to 1 before sending the Response PDU.

   For additional usage semantics of Reject PDU, see Section 6.3 Usage
   Of Reject PDU in Recovery.

10.17.2.  DataSN/R2TSN

   This field is only valid if the rejected PDU is a Data/R2T SNACK and
   the Reject reason code is "Protocol error" (see Section 10.16 SNACK
   Request).  The DataSN/R2TSN is the next Data/R2T sequence number that
   the target would send for the task, if any.

10.17.3.  StatSN, ExpCmdSN and MaxCmdSN

   These fields carry their usual values and are not related to the
   rejected command. StatSN is advanced after a Reject.

10.17.4.  Complete Header of Bad PDU

   The target returns the header (not including digest) of the PDU in
   error as the data of the response.

Top      Up      ToC       Page 178 
10.18.  NOP-Out

   Byte/     0       |       1       |       2       |       3       |
      /              |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|I| 0x00      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or 0xffffffff                             |
     +---------------+---------------+---------------+---------------+
   24| CmdSN                                                         |
     +---------------+---------------+---------------+---------------+
   28| ExpStatSN                                                     |
     +---------------+---------------+---------------+---------------+
   32/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Ping Data (optional)                            /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

   A NOP-Out may be used by an initiator as a "ping request" 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.

   Upon receipt of a NOP-In with the Target Transfer Tag set to a valid
   value (not the reserved 0xffffffff), the initiator MUST respond with
   a NOP-Out.  In this case, the NOP-Out Target Transfer Tag MUST
   contain a copy of the NOP-In Target Transfer Tag.

Top      Up      ToC       Page 179 
10.18.1.  Initiator Task Tag

   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 (i.e., the
   NOP-Out is used as a ping request).  Otherwise, the Initiator Task
   Tag MUST be set to 0xffffffff.

   When a target receives the NOP-Out with a valid Initiator Task Tag,
   it MUST respond with a Nop-In Response (see Section 10.19 NOP-In).

   If the Initiator Task Tag contains 0xffffffff, the I bit MUST be set
   to 1 and the CmdSN is not advanced after this PDU is sent.

10.18.2.  Target Transfer Tag

   A target assigned identifier for the operation.

   The NOP-Out MUST only have the Target Transfer Tag set 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.
   Otherwise, the Target Transfer Tag MUST be set to 0xffffffff.

   When the Target Transfer Tag is set to a value other than 0xffffffff,
   the LUN field MUST also be copied from the NOP-In.

10.18.3.  Ping Data

   Ping data are reflected in the NOP-In Response.  The length of the
   reflected data are limited to MaxRecvDataSegmentLength.  The length
   of ping data are indicated by the DataSegmentLength.  0 is a valid
   value for the DataSegmentLength and indicates the absence of ping
   data.

Top      Up      ToC       Page 180 
10.19.  NOP-In

   Byte/     0       |       1       |       2       |       3       |
      /             |               |               |               |
     |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|
     +---------------+---------------+---------------+---------------+
    0|.|.| 0x20      |1| Reserved                                    |
     +---------------+---------------+---------------+---------------+
    4|TotalAHSLength | DataSegmentLength                             |
     +---------------+---------------+---------------+---------------+
    8| LUN or Reserved                                               |
     +                                                               +
   12|                                                               |
     +---------------+---------------+---------------+---------------+
   16| Initiator Task Tag or 0xffffffff                              |
     +---------------+---------------+---------------+---------------+
   20| Target Transfer Tag or 0xffffffff                             |
     +---------------+---------------+---------------+---------------+
   24| StatSN                                                        |
     +---------------+---------------+---------------+---------------+
   28| ExpCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   32| MaxCmdSN                                                      |
     +---------------+---------------+---------------+---------------+
   36/ Reserved                                                      /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
   48| Header-Digest (Optional)                                      |
     +---------------+---------------+---------------+---------------+
     / DataSegment - Return Ping Data                                /
    +/                                                               /
     +---------------+---------------+---------------+---------------+
     | Data-Digest (Optional)                                        |
     +---------------+---------------+---------------+---------------+

   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 target).

   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
   request.  It MUST also duplicate up to the first
   MaxRecvDataSegmentLength bytes of the initiator provided Ping Data.
   For such a response, the Target Transfer Tag MUST be 0xffffffff.

Top      Up      ToC       Page 181 
   Otherwise, when a target sends a NOP-In that is not a response to a
   Nop-Out received from the initiator, the Initiator Task Tag MUST be
   set to 0xffffffff and the Data Segment MUST NOT contain any data
   (DataSegmentLength MUST be 0).

10.19.1.  Target Transfer Tag

   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.

10.19.2.  StatSN

   The StatSN field will always contain the next StatSN.  However, when
   the Initiator Task Tag is set to 0xffffffff, StatSN for the
   connection is not advanced after this PDU is sent.

10.19.3.  LUN

   A LUN MUST be set to a correct value when the Target Transfer Tag is
   valid (not the reserved value 0xffffffff).

11.  iSCSI Security Text Keys and Authentication Methods

   Only the following keys are used during the SecurityNegotiation stage
   of the Login Phase:

     SessionType
     InitiatorName
     TargetName
     TargetAddress
     InitiatorAlias
     TargetAlias
     TargetPortalGroupTag
     AuthMethod and the keys used by the authentication methods
       specified under Section 11.1 AuthMethod along with all of
       their associated keys as well as Vendor Specific
       Authentication Methods.

Top      Up      ToC       Page 182 
   Other keys MUST NOT be used.

   SessionType, InitiatorName, TargetName, InitiatorAlias, TargetAlias,
   and TargetPortalGroupTag are described in Chapter 12 as they can be
   used also in the OperationalNegotiation stage.

   All security keys have connection-wide applicability.

11.1.  AuthMethod

   Use: During Login - Security Negotiation Senders: Initiator and
   Target Scope: connection

   AuthMethod = <list-of-values>

   The main item of security negotiation is the authentication method
   (AuthMethod).

   The authentication methods that can be used (appear in the
   list-of-values) are either those listed in the following table or are
   vendor-unique methods:

   +------------------------------------------------------------+
   | Name          | Description                                |
   +------------------------------------------------------------+
   | KRB5          | Kerberos V5 - defined in [RFC1510]         |
   +------------------------------------------------------------+
   | SPKM1         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SPKM2         | Simple Public-Key GSS-API Mechanism        |
   |               | defined in [RFC2025]                       |
   +------------------------------------------------------------+
   | SRP           | Secure Remote Password                     |
   |               | defined in [RFC2945]                       |
   +------------------------------------------------------------+
   | CHAP          | Challenge Handshake Authentication Protocol|
   |               | defined in [RFC1994]                       |
   +------------------------------------------------------------+
   | None          | No authentication                          |
   +------------------------------------------------------------+

   The AuthMethod selection is followed by an "authentication exchange"
   specific to the authentication method selected.

   The authentication method proposal may be made by either the
   initiator or the target.  However the initiator MUST make the first
   step specific to the selected authentication method as soon as it is

Top      Up      ToC       Page 183 
   selected.  It follows that if the target makes the authentication
   method proposal the initiator sends the first keys(s) of the exchange
   together with its authentication method selection.

   The authentication exchange authenticates the initiator to the
   target, and optionally, the target to the initiator.  Authentication
   is OPTIONAL to use but MUST be supported by the target and initiator.

   The initiator and target MUST implement CHAP.  All other
   authentication methods are OPTIONAL.

   Private or public extension algorithms MAY also be negotiated for
   authentication methods.  Whenever a private or public extension
   algorithm is part of the default offer (the offer made in absence of
   explicit administrative action) the implementer MUST ensure that CHAP
   is listed as an alternative  in the default offer and "None" is not
   part of the default offer.

   Extension authentication methods MUST be named using one of the
   following two formats:

       a)  Z-reversed.vendor.dns_name.do_something=
       b)  Z<#><IANA-registered-string>=

   Authentication methods named using the Z- format are used as private
   extensions.  Authentication methods named using the Z# format are
   used as public extensions that must be registered with IANA and MUST
   be described by an informational RFC.

   For all of the public or private extension authentication methods,
   the method specific keys MUST conform to the format specified in
   Section 5.1 Text Format for standard-label.

   To identify the vendor for private extension authentication methods,
   we suggest you use the reversed DNS-name as a prefix to the proper
   digest names.

   The part of digest-name following Z- and Z# MUST conform to the
   format for standard-label specified in Section 5.1 Text Format.

   Support for public or private extension authentication methods is
   OPTIONAL.

   The following subsections define the specific exchanges for each of
   the standardized authentication methods.  As mentioned earlier the
   first step is always done by the initiator.

Top      Up      ToC       Page 184 
11.1.1.  Kerberos

   For KRB5 (Kerberos V5) [RFC1510] and [RFC1964], the initiator MUST
   use:

      KRB_AP_REQ=<KRB_AP_REQ>

   where KRB_AP_REQ is the client message as defined in [RFC1510].

   The default principal name assumed by an iSCSI initiator or target
   (prior to any administrative configuration action) MUST be the iSCSI
   Initiator Name or iSCSI Target Name respectively, prefixed by the
   string "iscsi/".

   If the initiator authentication fails, the target MUST respond 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 authentication
   fails, the initiator MUST close the connection.

   KRB_AP_REQ and KRB_AP_REP are binary-values and their binary length
   (not the length of the character string that represents them in
   encoded form) MUST not exceed 65536 bytes.

11.1.2.  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].

   [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>

Top      Up      ToC       Page 185 
   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, it will, instead, send a Login "login reject" message
   with the "Authentication Failure" status and terminate the
   connection.  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 authentication
   fails, the initiator MUST close the connection.  Otherwise, if the
   AuthMethod is SPKM1, the initiator MUST continue with:

      SPKM_REP_IT=<SPKM-REP-IT>

   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 "Authentication Failure" status.

   SPKM requires support for very long authentication items.

   All the SPKM-* tokens are binary-values and their binary length (not
   the length of the character string that represents them in encoded
   form) MUST not exceed 65536 bytes.

11.1.3.  Secure Remote Password (SRP)

   For SRP [RFC2945], the initiator MUST use:

      SRP_U=<U> TargetAuth=Yes   /* or TargetAuth=No */

   The target MUST answer with a Login reject with the "Authorization
   Failure" status or reply with:

   SRP_GROUP=<G1,G2...> SRP_s=<s>

   Where G1,G2... are proposed groups, in order of preference.

Top      Up      ToC       Page 186 
   The initiator MUST either close the connection or continue with:

   SRP_A=<A> SRP_GROUP=<G>

   Where G is one of G1,G2... that were proposed by the target.

   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.

   Where U, s, A, B, M, and H(A | M | K) are defined in [RFC2945] (using
   the SHA1 hash function, such as SRP-SHA1) and G,Gn (Gn stands for
   G1,G2...) are identifiers of SRP groups specified in [RFC3723].  G,
   Gn, and U are text strings, s,A,B,M, and H(A | M | K) are
   binary-values.  The length of s,A,B,M and H(A | M | K) in binary form
   (not the length of the character string that represents them in
   encoded form) MUST not exceed 1024 bytes.

   For the SRP_GROUP, all the groups specified in [RFC3723] up to 1536
   bits (i.e., SRP-768, SRP-1024, SRP-1280, SRP-1536) must be supported
   by initiators and targets.  To guarantee interoperability, targets
   MUST always offer "SRP-1536" as one of the proposed groups.

11.1.4.  Challenge Handshake Authentication Protocol (CHAP)

   For CHAP [RFC1994], in the first step, the initiator MUST send:

      CHAP_A=<A1,A2...>

   Where A1,A2... are proposed algorithms, in order of preference.

Top      Up      ToC       Page 187 
   In the second step, 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 initiator.

   In the third step, 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 either
   answer with a Login reject with "Authentication Failure" or reply
   with:

      CHAP_N=<N> CHAP_R=<R>

   If target authentication fails, the initiator MUST close the
   connection.

   Where N, (A,A1,A2), I, C, 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 large-binary-values and their binary length (not the length of
   the character string that represents 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 MUST always offer it as one
   of the proposed algorithms.



(page 187 continued on part 8)

Next RFC Part