GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools

Problem, Formatting or Query -  Send Feedback

Was this page helpful?-10+1


rfc:rfc7145

Internet Engineering Task Force (IETF) M. Ko Request for Comments: 7145 Obsoletes: 5046 A. Nezhinsky Category: Standards Track Mellanox ISSN: 2070-1721 April 2014

    Internet Small Computer System Interface (iSCSI) Extensions
      for the Remote Direct Memory Access (RDMA) Specification

Abstract

 Internet Small Computer System Interface (iSCSI) Extensions for
 Remote Direct Memory Access (RDMA) provides the RDMA data transfer
 capability to iSCSI by layering iSCSI on top of an RDMA-Capable
 Protocol.  An RDMA-Capable Protocol provides RDMA Read and Write
 services, which enable data to be transferred directly into SCSI I/O
 Buffers without intermediate data copies.  This document describes
 the extensions to the iSCSI protocol to support RDMA services as
 provided by an RDMA-Capable Protocol.
 This document obsoletes RFC 5046.

Status of This Memo

 This is an Internet Standards Track document.
 This document is a product of the Internet Engineering Task Force
 (IETF).  It represents the consensus of the IETF community.  It has
 received public review and has been approved for publication by the
 Internet Engineering Steering Group (IESG).  Further information on
 Internet Standards is available in Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc7145.

Ko & Nezhinsky Standards Track [Page 1] RFC 7145 iSER Specification April 2014

Copyright Notice

 Copyright (c) 2014 IETF Trust and the persons identified as the
 document authors.  All rights reserved.
 This document is subject to BCP 78 and the IETF Trust's Legal
 Provisions Relating to IETF Documents
 (http://trustee.ietf.org/license-info) in effect on the date of
 publication of this document.  Please review these documents
 carefully, as they describe your rights and restrictions with respect
 to this document.  Code Components extracted from this document must
 include Simplified BSD License text as described in Section 4.e of
 the Trust Legal Provisions and are provided without warranty as
 described in the Simplified BSD License.

Table of Contents

 1. Introduction ....................................................5
    1.1. Motivation .................................................5
    1.2. iSCSI/iSER Layering ........................................6
    1.3. Architectural Goals ........................................7
    1.4. Protocol Overview ..........................................7
    1.5. RDMA Services and iSER .....................................9
         1.5.1. STag ................................................9
         1.5.2. Send ...............................................10
         1.5.3. RDMA Write .........................................11
         1.5.4. RDMA Read ..........................................11
    1.6. SCSI Read Overview ........................................11
    1.7. SCSI Write Overview .......................................12
 2. Definitions and Acronyms .......................................12
    2.1. Definitions ...............................................12
    2.2. Acronyms ..................................................18
    2.3. Conventions ...............................................20
 3. Upper-Layer Interface Requirements .............................20
    3.1. Operational Primitives offered by iSER ....................21
         3.1.1. Send_Control .......................................21
         3.1.2. Put_Data ...........................................21
         3.1.3. Get_Data ...........................................22
         3.1.4. Allocate_Connection_Resources ......................22
         3.1.5. Deallocate_Connection_Resources ....................23
         3.1.6. Enable_Datamover ...................................23
         3.1.7. Connection_Terminate ...............................23
         3.1.8. Notice_Key_Values ..................................24
         3.1.9. Deallocate_Task_Resources ..........................24
    3.2. Operational Primitives Used by iSER .......................24
         3.2.1. Control_Notify .....................................25
         3.2.2. Data_Completion_Notify .............................25
         3.2.3. Data_ACK_Notify ....................................25

Ko & Nezhinsky Standards Track [Page 2] RFC 7145 iSER Specification April 2014

         3.2.4. Connection_Terminate_Notify ........................26
    3.3. iSCSI Protocol Usage Requirements .........................26
 4. Lower-Layer Interface Requirements .............................27
    4.1. Interactions with the RCaP Layer ..........................27
    4.2. Interactions with the Transport Layer .....................28
 5. Connection Setup and Termination ...............................28
    5.1. iSCSI/iSER Connection Setup ...............................28
         5.1.1. Initiator Behavior .................................30
         5.1.2. Target Behavior ....................................31
         5.1.3. iSER Hello Exchange ................................33
    5.2. iSCSI/iSER Connection Termination .........................36
         5.2.1. Normal Connection Termination at the Initiator .....36
         5.2.2. Normal Connection Termination at the Target ........36
         5.2.3. Termination without Logout Request/Response PDUs ...37
 6. Login/Text Operational Keys ....................................38
    6.1. HeaderDigest and DataDigest ...............................38
    6.2. MaxRecvDataSegmentLength ..................................38
    6.3. RDMAExtensions ............................................39
    6.4. TargetRecvDataSegmentLength ...............................40
    6.5. InitiatorRecvDataSegmentLength ............................41
    6.6. OFMarker and IFMarker .....................................41
    6.7. MaxOutstandingUnexpectedPDUs ..............................41
    6.8. MaxAHSLength ..............................................42
    6.9. TaggedBufferForSolicitedDataOnly ..........................43
    6.10. iSERHelloRequired ........................................43
 7. iSCSI PDU Considerations .......................................44
    7.1. iSCSI Data-Type PDU .......................................44
    7.2. iSCSI Control-Type PDU ....................................45
    7.3. iSCSI PDUs ................................................45
         7.3.1. SCSI Command .......................................45
         7.3.2. SCSI Response ......................................47
         7.3.3. Task Management Function Request/Response ..........49
         7.3.4. SCSI Data-out ......................................50
         7.3.5. SCSI Data-in .......................................51
         7.3.6. Ready To Transfer (R2T) ............................53
         7.3.7. Asynchronous Message ...............................55
         7.3.8. Text Request and Text Response .....................55
         7.3.9. Login Request and Login Response ...................55
         7.3.10. Logout Request and Logout Response ................56
         7.3.11. SNACK Request .....................................56
         7.3.12. Reject ............................................56
         7.3.13. NOP-Out and NOP-In ................................57
 8. Flow Control and STag Management ...............................57
    8.1. Flow Control for RDMA Send Messages .......................57
         8.1.1. Flow Control for Control-Type PDUs from the
                Initiator ..........................................58
         8.1.2. Flow Control for Control-Type PDUs from the
                Target .............................................60

Ko & Nezhinsky Standards Track [Page 3] RFC 7145 iSER Specification April 2014

    8.2. Flow Control for RDMA Read Resources ......................61
    8.3. STag Management ...........................................62
         8.3.1. Allocation of STags ................................62
         8.3.2. Invalidation of STags ..............................62
 9. iSER Control and Data Transfer .................................64
    9.1. iSER Header Format ........................................64
    9.2. iSER Header Format for iSCSI Control-Type PDU .............65
    9.3. iSER Header Format for iSER Hello Message .................67
    9.4. iSER Header Format for iSER HelloReply Message ............68
    9.5. SCSI Data Transfer Operations .............................69
         9.5.1. SCSI Write Operation ...............................69
         9.5.2. SCSI Read Operation ................................70
         9.5.3. Bidirectional Operation ............................70
 10. iSER Error Handling and Recovery ..............................71
    10.1. Error Handling ...........................................71
         10.1.1. Errors in the Transport Layer .....................71
         10.1.2. Errors in the RCaP Layer ..........................72
         10.1.3. Errors in the iSER Layer ..........................73
         10.1.4. Errors in the iSCSI Layer .........................75
    10.2. Error Recovery ...........................................76
         10.2.1. PDU Recovery ......................................77
         10.2.2. Connection Recovery ...............................77
 11. Security Considerations .......................................78
 12. IANA Considerations ...........................................79
 13. References ....................................................79
    13.1. Normative References .....................................79
    13.2. Informative References ...................................80
 Appendix A. Summary of Changes from RFC 5046 ......................81
 Appendix B. Message Format for iSER ...............................83
 B.1. iWARP Message Format for iSER Hello Message ..................83
 B.2. iWARP Message Format for iSER HelloReply Message .............84
 B.3. iSER Header Format for SCSI Read Command PDU .................85
 B.4. iSER Header Format for SCSI Write Command PDU ................86
 B.5. iSER Header Format for SCSI Response PDU .....................87
 Appendix C. Architectural discussion of iSER over InfiniBand ......88
 C.1. Host Side of iSCSI and iSER Connections in InfiniBand ........88
 C.2. Storage Side of iSCSI and iSER Mixed Network Environment .....89
 C.3. Discovery Processes for an InfiniBand Host ...................89
 C.4. IBTA Connection Specifications ...............................90
 Appendix D. Acknowledgments .......................................90

Ko & Nezhinsky Standards Track [Page 4] RFC 7145 iSER Specification April 2014

Table of Figures

 Figure 1. Example of iSCSI/iSER Layering in Full Feature Phase .....6
 Figure 2. iSER Header Format ......................................64
 Figure 3. iSER Header Format for iSCSI Control-Type PDU ...........65
 Figure 4. iSER Header Format for iSER Hello Message ...............67
 Figure 5. iSER Header Format for iSER HelloReply Message ..........68
 Figure 6. SendSE Message Containing an iSER Hello Message .........83
 Figure 7. SendSE Message Containing an iSER HelloReply Message ....84
 Figure 8. iSER Header Format for SCSI Read Command PDU ............85
 Figure 9. iSER Header Format for SCSI Write Command PDU ...........86
 Figure 10. iSER Header Format for SCSI Response PDU ...............87
 Figure 11. iSCSI and iSER on IB ...................................88
 Figure 12. Storage Controller with TCP, iWARP, and IB Connections .89

1. Introduction

1.1. Motivation

 The iSCSI protocol ([iSCSI]) is a mapping of the SCSI Architecture
 Model (see [SAM5] and [iSCSI-SAM]) over the TCP protocol.  SCSI
 commands are carried by iSCSI requests, and SCSI responses and status
 are carried by iSCSI responses.  Other iSCSI protocol exchanges and
 SCSI Data are also transported in iSCSI PDUs.
 Out-of-order TCP segments in the Traditional iSCSI model have to be
 stored and reassembled before the iSCSI protocol layer within an end
 node can place the data in the iSCSI buffers.  This reassembly is
 required because not every TCP segment is likely to contain an iSCSI
 header to enable its placement and TCP itself does not have a built-
 in mechanism for signaling ULP (Upper Level Protocol) message
 boundaries to aid placement of out-of-order segments.  This TCP
 reassembly at high network speeds is quite counterproductive for the
 following reasons: wasted memory bandwidth in data copying, need for
 reassembly memory, wasted CPU cycles in data copying, and the general
 store-and-forward latency from an application perspective.
 The generic term RDMA-Capable Protocol (RCaP) is used to refer to
 protocol stacks that provide the Remote Direct Memory Access (RDMA)
 functionality, such as iWARP and InfiniBand.
 With the availability of RDMA-Capable Controllers within a host
 system, it is appropriate for iSCSI to be able to exploit the direct
 data placement function of the RDMA-Capable Controller like other
 applications.

Ko & Nezhinsky Standards Track [Page 5] RFC 7145 iSER Specification April 2014

 iSCSI Extensions for RDMA (iSER) is designed precisely to take
 advantage of generic RDMA technologies -- iSER's goal is to permit
 iSCSI to employ direct data placement and RDMA capabilities using a
 generic RDMA-Capable Controller.  In summary, the iSCSI/iSER protocol
 stack is designed to enable scaling to high speeds by relying on a
 generic data placement process and RDMA technologies and products
 that enable direct data placement of both in-order and out-of-order
 data.
 This document describes iSER as a protocol extension to iSCSI, both
 for convenience of description and also because it is true in a very
 strict protocol sense.  However, it is to be noted that iSER is in
 reality extending the connectivity of the iSCSI protocol defined in
 [iSCSI], and the name "iSER" reflects this reality.
 When the iSCSI protocol as defined in [iSCSI] (i.e., without the iSER
 enhancements) is intended in the rest of the document, the term
 "Traditional iSCSI" is used to make the intention clear.
 This document obsoletes RFC 5046.  See Appendix A for the list of
 changes from RFC 5046.

1.2. iSCSI/iSER Layering

 iSCSI Extensions for RDMA (iSER) is layered between the iSCSI layer
 and the RCaP layer.
       +--------------------------------------------------------+
       |                        SCSI                            |
       +--------------------------------------------------------+
       |                        iSCSI                           |
 DI -> +--------------------------------------------------------+
       |                         iSER                           |
       +-------+--------------------------+---------------------+
       | RDMAP |                          |                     |
       +-------+      InfiniBand          |                     |
       |  DDP  |       Reliable           |       Other         |
       +-------+       Connected          |        RDMA         |
       |  MPA  |       Transport          |       Capable       |
       +-------+        Service           |       Protocol      |
       |  TCP  |                          |                     |
       +-------+--------------------------+---------------------+
       |  IP   | InfiniBand Network Layer | Other Network Layer |
       +-------+--------------------------+---------------------+
  Figure 1: Example of iSCSI/iSER Layering in Full Feature Phase

Ko & Nezhinsky Standards Track [Page 6] RFC 7145 iSER Specification April 2014

 Figure 1 shows an example of the relationship between SCSI, iSCSI,
 iSER, and the different RCaP layers.  For TCP, the RCaP is iWARP.
 For InfiniBand, the RCaP is the Reliable Connected Transport Service.
 Note that the iSCSI layer as described here supports the RDMA
 Extensions as used in iSER.

1.3. Architectural Goals

 This section summarizes the architectural goals that guided the
 design of iSER.
 1.  Provide an RDMA data transfer model for iSCSI that enables direct
     in-order or out-of-order data placement of SCSI data into pre-
     allocated SCSI buffers while maintaining in-order data delivery.
 2.  Do not require any major changes to the SCSI Architecture Model
     [SAM5] and SCSI command set standards.
 3.  Utilize the existing iSCSI infrastructure (sometimes referred to
     as "iSCSI ecosystem") including but not limited to MIB,
     bootstrapping, negotiation, naming and discovery, and security.
 4.  Enable a session to operate in the Traditional iSCSI data
     transfer mode if iSER is not supported by either the initiator or
     the target.  (Do not require iSCSI Full Feature Phase
     interoperability between an end node operating in Traditional
     iSCSI mode and an end node operating in iSER-assisted mode.)
 5.  Allow initiator and target implementations to utilize generic
     RDMA-Capable Controllers such as RNICs or to implement iSCSI and
     iSER in software.  (Do not require iSCSI- or iSER-specific
     assists in the RCaP implementation or RDMA-Capable Controller.)
 6.  Implement a lightweight Datamover protocol for iSCSI with minimal
     state maintenance.

1.4. Protocol Overview

 Consistent with the architectural goals stated in Section 1.3, the
 iSER protocol does not require changes in the iSCSI ecosystem or any
 related SCSI specifications.  The iSER protocol defines the mapping
 of iSCSI PDUs to RCaP Messages in such a way that it is entirely
 feasible to realize iSCSI/iSER implementations that are based on
 generic RDMA-Capable Controllers.  The iSER protocol layer requires
 minimal state maintenance to assist a connection during the iSCSI
 Full Feature Phase, besides being oblivious to the notion of an iSCSI
 session.  The crucial protocol aspects of iSER may be summarized as
 follows:

Ko & Nezhinsky Standards Track [Page 7] RFC 7145 iSER Specification April 2014

 1.  iSER-assisted mode is negotiated during the iSCSI login in the
     leading connection for each session, and an entire iSCSI session
     can only operate in one mode (i.e., a connection in a session
     cannot operate in iSER-assisted mode if a different connection of
     the same session is already in Full Feature Phase in the
     Traditional iSCSI mode).
 2.  Once in iSER-assisted mode, all iSCSI interactions on that
     connection use RCaP Messages.
 3.  A Send Message is used for carrying an iSCSI control-type PDU
     preceded by an iSER header.  See Section 7.2 for more details on
     iSCSI control-type PDUs.
 4.  RDMA Write, RDMA Read Request, and RDMA Read Response Messages
     are used for carrying control and all data information associated
     with the iSCSI data-type PDUs (i.e., SCSI Data-In PDUs and R2T
     PDUs).  iSER does not use SCSI Data-Out PDUs for solicited data,
     and SCSI Data-Out PDUs for unsolicited data are not treated as
     iSCSI data-type PDUs by iSER because RDMA is not used.  See
     Section 7.1 for more details on iSCSI data-type PDUs.
 5.  The target drives all data transfer (with the exception of iSCSI
     unsolicited data) for SCSI writes and SCSI reads, by issuing RDMA
     Read Requests and RDMA Writes, respectively.
 6.  RCaP is responsible for ensuring data integrity.  (For example,
     iWARP includes a CRC-enhanced framing layer called MPA on top of
     TCP; and for InfiniBand, the CRCs are included in the Reliable
     Connection mode).  For this reason, iSCSI header and data digests
     are negotiated to "None" for iSCSI/iSER sessions.
 7.  The iSCSI error recovery hierarchy defined in [iSCSI] is fully
     supported by iSER.  (However, see Section 7.3.11 on the handling
     of SNACK Request PDUs.)
 8.  iSER requires no changes to iSCSI security and text mode
     negotiation mechanisms.
 Note that Traditional iSCSI implementations may have to be adapted to
 employ iSER.  It is expected that the adaptation when required is
 likely to be centered around the upper-layer interface requirements
 of iSER (Section 3).

Ko & Nezhinsky Standards Track [Page 8] RFC 7145 iSER Specification April 2014

1.5. RDMA Services and iSER

 iSER is designed to work with software and/or hardware protocol
 stacks providing the protocol services defined in RCaP documents such
 as [RDMAP], [IB], etc.  The following subsections describe the key
 protocol elements of RCaP services on which iSER relies.

1.5.1. STag

 An STag is the identifier of an I/O Buffer unique to an RDMA-Capable
 Controller that the iSER layer Advertises to the remote iSCSI/iSER
 node in order to complete a SCSI I/O.
 In iSER, Advertisement is the act of informing the target by the
 initiator that an I/O Buffer is available at the initiator for RDMA
 Read or RDMA Write access by the target.  The initiator Advertises
 the I/O Buffer by including the STag and the Base Offset in the
 header of an iSER Message containing the SCSI Command PDU to the
 target.  The buffer length is as specified in the SCSI Command PDU.
 The iSER layer at the initiator Advertises the STag and the Base
 Offset for the I/O Buffer of each SCSI I/O to the iSER layer at the
 target in the iSER header of a Send Message containing the SCSI
 Command PDU, unless the I/O can be completely satisfied by
 unsolicited data alone.  The SendSE Message should be used if
 supported by the RCaP layer (e.g., iWARP).
 The iSER layer at the target provides the STag for the I/O Buffer
 that is the Data Sink of an RDMA Read Operation (Section 1.5.4) to
 the RCaP layer on the initiator node -- i.e., this is completely
 transparent to the iSER layer at the initiator.
 The iSER layer at the initiator SHOULD invalidate the Advertised STag
 upon a normal completion of the associated task.  The Send with
 Invalidate Message, if supported by the RCaP layer (e.g., iWARP), can
 be used for automatic invalidation when it is used to carry the SCSI
 Response PDU.  There are two exceptions to this automatic
 invalidation -- bidirectional commands and abnormal completion of a
 command.  The iSER layer at the initiator SHOULD explicitly
 invalidate the STag in these two cases.  That iSER layer MUST check
 that STag invalidation has occurred whenever receipt of a Send with
 Invalidate message is the expected means of causing an STag to be
 invalidated, and it MUST perform the STag invalidation if the STag
 has not already been invalidated (e.g., because a Send Message was
 used instead of Send with Invalidate).

Ko & Nezhinsky Standards Track [Page 9] RFC 7145 iSER Specification April 2014

 If the Advertised STag is not invalidated as recommended in the
 foregoing paragraph (e.g., in order to cache the STag for future
 reuse), the I/O Buffer remains exposed to the network for access by
 the RCaP.  Such an I/O Buffer is capable of being read or written by
 the RCaP outside the scope of the iSCSI operation for which it was
 originally established; this fact has both robustness and security
 considerations.  The robustness considerations are that the system
 containing the iSER initiator may react poorly to an unexpected
 modification of its memory.  For the security considerations, see
 Section 11.

1.5.2. Send

 Send is the RDMA Operation that is not addressed to an Advertised
 buffer and uses Untagged buffers as the message is received.
 The iSER layer at the initiator uses the Send Operation to transmit
 any iSCSI control-type PDU to the target.  As an example, the
 initiator uses Send Operations to transfer iSER Messages containing
 SCSI Command PDUs to the iSER layer at the target.
 An iSER layer at the target uses the Send Operation to transmit any
 iSCSI control-type PDU to the initiator.  As an example, the target
 uses Send Operations to transfer iSER Messages containing SCSI
 Response PDUs to the iSER layer at the initiator.
 For interoperability, iSER implementations SHOULD accept and
 correctly process SendSE and SendInvSE messages.  However, SendSE and
 SendInvSE messages are to be regarded as optimizations or
 enhancements to the basic Send Message, and their support may vary by
 RCaP protocol and specific implementation.  In general, these
 messages SHOULD NOT be used, unless the RCaP requires support for
 them in all implementations.  If these messages are used, the
 implementation SHOULD be capable of reverting to use of Send in order
 to work with a receiver that does not support these messages.
 Attempted use of these messages with a peer that does not support
 them may result in a fatal error that closes the RCaP connection.
 For example, these messages SHOULD NOT be used with the InfiniBand
 RCaP because InfiniBand does not require support for them in all
 cases.  New iSER implementations SHOULD use Send (and not SendSE or
 SendInvSE) unless there are compelling reasons for doing otherwise.
 Similarly, iSER implementations SHOULD NOT rely on events triggered
 by SendSE and SendInvSE, as these messages may not be used.

Ko & Nezhinsky Standards Track [Page 10] RFC 7145 iSER Specification April 2014

1.5.3. RDMA Write

 RDMA Write is the RDMA Operation that is used to place data into an
 Advertised buffer at the Data Sink.  The Data Source addresses the
 Message using an STag and a Tagged Offset that are valid on the Data
 Sink.
 The iSER layer at the target uses the RDMA Write Operation to
 transfer the contents of a local I/O Buffer to an Advertised I/O
 Buffer at the initiator.  The iSER layer at the target uses the RDMA
 Write to transfer the whole data or part of the data required to
 complete a SCSI Read command.
 The iSER layer at the initiator does not employ RDMA Writes.

1.5.4. RDMA Read

 RDMA Read is the RDMA Operation that is used to retrieve data from an
 Advertised buffer at the Data Source.  The sender of the RDMA Read
 Request addresses the Message using an STag and a Tagged Offset that
 are valid on the Data Source in addition to providing a valid local
 STag and Tagged Offset that identify the Data Sink.
 The iSER layer at the target uses the RDMA Read Operation to transfer
 the contents of an Advertised I/O Buffer at the initiator to a local
 I/O Buffer at the target.  The iSER layer at the target uses the RDMA
 Read to fetch whole or part of the data required to complete a SCSI
 Write Command.
 The iSER layer at the initiator does not employ RDMA Reads.

1.6. SCSI Read Overview

 The iSER layer at the initiator receives the SCSI Command PDU from
 the iSCSI layer.  The iSER layer at the initiator generates an STag
 for the I/O Buffer of the SCSI Read and Advertises the buffer by
 including the STag and the Base Offset as part of the iSER header for
 the PDU.  The iSER Message is transferred to the target using a Send
 Message.  The SendSE Message should be used if supported by the RCaP
 layer (e.g., iWARP).
 The iSER layer at the target uses one or more RDMA Writes to transfer
 the data required to complete the SCSI Read.
 The iSER layer at the target uses a Send Message to transfer the SCSI
 Response PDU back to the iSER layer at the initiator.  The iSER layer
 at the initiator invalidates the STag and notifies the iSCSI layer of

Ko & Nezhinsky Standards Track [Page 11] RFC 7145 iSER Specification April 2014

 the availability of the SCSI Response PDU.  The Send with Invalidate
 Message, if supported by the RCaP layer (e.g., iWARP), can be used
 for automatic invalidation of the STag.

1.7. SCSI Write Overview

 The iSER layer at the initiator receives the SCSI Command PDU from
 the iSCSI layer.  If solicited data transfer is involved, the iSER
 layer at the initiator generates an STag for the I/O Buffer of the
 SCSI Write and Advertises the buffer by including the STag and the
 Base Offset as part of the iSER header for the PDU.  The iSER Message
 is transferred to the target using a Send Message.  The SendSE
 Message should be used if supported by the RCaP layer (e.g., iWARP).
 The iSER layer at the initiator may optionally send one or more non-
 immediate unsolicited data PDUs to the target using Send Messages.
 If solicited data transfer is involved, the iSER layer at the target
 uses one or more RDMA Reads to transfer the data required to complete
 the SCSI Write.
 The iSER layer at the target uses a Send Message to transfer the SCSI
 Response PDU back to the iSER layer at the initiator.  The iSER layer
 at the initiator invalidates the STag and notifies the iSCSI layer of
 the availability of the SCSI Response PDU.  The Send with Invalidate
 Message, if supported by the RCaP layer (e.g., iWARP), can be used
 for automatic invalidation of the STag.

2. Definitions and Acronyms

2.1. Definitions

 Advertisement (Advertised, Advertise, Advertisements, Advertises) --
    The act of informing a remote iSER (iSCSI Extensions for RDMA)
    layer that a local node's buffer is available to it.  A node makes
    a buffer available for incoming RDMA Read Request Message or
    incoming RDMA Write Message access by informing the remote iSER
    layer of the Tagged Buffer identifiers (STag, Base Offset, and
    buffer length).  Note that this Advertisement of Tagged Buffer
    information is the responsibility of the iSER layer on either end
    and is not defined by the RDMA-Capable Protocol.  A typical method
    would be for the iSER layer to embed the Tagged Buffer's STag,
    Base Offset, and buffer length in a message destined for the
    remote iSER layer.
 Base Offset - A value when added to the Buffer Offset forms the
    Tagged Offset.

Ko & Nezhinsky Standards Track [Page 12] RFC 7145 iSER Specification April 2014

 Completion (Completed, Complete, Completes) - Completion is defined
    as the process by which the RDMA-Capable Protocol layer informs
    the iSER layer that a particular RDMA Operation has performed all
    functions specified for the RDMA Operation.
 Connection - A connection is a logical bidirectional communication
    channel between the initiator and the target, e.g., a TCP
    connection.  Communication between the initiator and the target
    occurs over one or more connections.  The connections carry
    control messages, SCSI commands, parameters, and data within iSCSI
    Protocol Data Units (iSCSI PDUs).
 Connection Handle - An information element that identifies the
    particular iSCSI connection and is unique for a given iSCSI layer
    and the underlying iSER layer.  Every invocation of an Operational
    Primitive is qualified with the Connection Handle.
 Data Sink - The peer receiving a data payload.  Note that the Data
    Sink can be required to both send and receive RCaP (RDMA-Capable
    Protocol) Messages to transfer a data payload.
 Data Source - The peer sending a data payload.  Note that the Data
    Source can be required to both send and receive RCaP Messages to
    transfer a data payload.
 Datamover Interface (DI) - The interface between the iSCSI layer and
    the Datamover Layer as described in [DA].
 Datamover Layer - A layer that is directly below the iSCSI layer and
    above the underlying transport layers.  This layer exposes and
    uses a set of transport-independent Operational Primitives for the
    communication between the iSCSI layer and itself.  The Datamover
    layer, operating in conjunction with the transport layers, moves
    the control and data information on the iSCSI connection.  In this
    specification, the iSER layer is the Datamover layer.
 Datamover Protocol - A Datamover protocol is the wire protocol that
    is defined to realize the Datamover-layer functionality.  In this
    specification, the iSER protocol is the Datamover protocol.
 Inbound RDMA Read Queue Depth (IRD) - The maximum number of incoming
    outstanding RDMA Read Requests that the RDMA-Capable Controller
    can handle on a particular RCaP Stream at the Data Source.  For
    some RDMA-Capable Protocol layers, the term "IRD" may be known by
    a different name.  For example, for InfiniBand, the equivalent to
    IRD is the Responder Resources.

Ko & Nezhinsky Standards Track [Page 13] RFC 7145 iSER Specification April 2014

 I/O Buffer - A buffer that is used in a SCSI Read or Write operation
    so SCSI data may be sent from or received into that buffer.
 iSCSI - The iSCSI protocol as defined in [iSCSI] is a mapping of the
    SCSI Architecture Model of SAM-5 over TCP.
 iSCSI control-type PDU - Any iSCSI PDU that is not an iSCSI data-
    type PDU and also not a SCSI Data-Out PDU carrying solicited data
    is defined as an iSCSI control-type PDU.  Specifically, it is to
    be noted that SCSI Data-Out PDUs for unsolicited data are defined
    as iSCSI control-type PDUs.
 iSCSI data-type PDU - An iSCSI data-type PDU is defined as an iSCSI
    PDU that causes data transfer via RDMA operations at the iSER
    layer, transparent to the remote iSCSI layer, to take place
    between the peer iSCSI nodes on a Full Feature Phase iSCSI
    connection.  An iSCSI data-type PDU, when requested for
    transmission by the sender iSCSI layer, results in the associated
    data transfer without the participation of the remote iSCSI layer,
    i.e., the PDU itself is not delivered as-is to the remote iSCSI
    layer.  The following iSCSI PDUs constitute the set of iSCSI data-
    type PDUs -- SCSI Data-In PDU and R2T PDU.
 iSCSI Layer - A layer in the protocol stack implementation within an
    end node that implements the iSCSI protocol and interfaces with
    the iSER layer via the Datamover Interface.
 iSCSI PDU (iSCSI Protocol Data Unit) - The iSCSI layer at the
    initiator and the iSCSI layer at the target divide their
    communications into messages.  The term "iSCSI Protocol Data Unit"
    (iSCSI PDU) is used for these messages.
 iSCSI/iSER Connection - An iSER-assisted iSCSI connection.  An iSCSI
    connection that is not iSER assisted always maps onto a TCP
    connection at the transport level.  But an iSER-assisted iSCSI
    connection may not have an underlying TCP connection.  For some
    RCaP implementations (e.g., iWARP), an iSER-assisted iSCSI
    connection has an underlying TCP connection.  For other RCaP
    implementations (e.g., InfiniBand), there is no underlying TCP
    connection.  (In the specific example of InfiniBand [IB], an iSER-
    assisted iSCSI connection is directly mapped onto the InfiniBand
    Reliable Connection-based (RC) channel.)
 iSCSI/iSER Session - An iSER-assisted iSCSI session.  All connections
    of an iSCSI/iSER session are iSCSI/iSER connections.
 iSER - iSCSI Extensions for RDMA, the protocol defined in this
    document.

Ko & Nezhinsky Standards Track [Page 14] RFC 7145 iSER Specification April 2014

 iSER-assisted - A term generally used to describe the operation of
    iSCSI when the iSER functionality is also enabled below the iSCSI
    layer for the specific iSCSI/iSER connection in question.
 iSER-IRD - This variable represents the maximum number of incoming
    outstanding RDMA Read Requests that the iSER layer at the
    initiator grants on a particular RCaP Stream.
 iSER-ORD - This variable represents the maximum number of outstanding
    RDMA Read Requests that the iSER layer can initiate on a
    particular RCaP Stream.  This variable is maintained only by the
    iSER layer at the target.
 iSER Layer - The layer that implements the iSCSI Extensions for RDMA
    (iSER) protocol.
 iWARP - A suite of wire protocols comprising of [RDMAP], [DDP], and
    [MPA] when layered above [TCP].  [RDMAP] and [DDP] may be layered
    above SCTP or other transport protocols.
 Local Mapping - A task state record maintained by the iSER layer that
    associates the Initiator Task Tag to the Local STag(s).  The
    specifics of the record structure are implementation dependent.
 Local Peer - The implementation of the RDMA-Capable Protocol on the
    local end of the connection.  Used to refer to the local entity
    when describing protocol exchanges or other interactions between
    two nodes.
 Node - A computing device attached to one or more links of a network.
    A node in this context does not refer to a specific application or
    protocol instantiation running on the computer.  A node may
    consist of one or more RDMA-Capable Controllers installed in a
    host computer.
 Operational Primitive - An Operational Primitive is an abstract
    functional interface procedure that requests another layer to
    perform a specific action on the requestor's behalf or notifies
    the other layer of some event.  The Datamover Interface between an
    iSCSI layer and a Datamover layer within an iSCSI end node uses a
    set of Operational Primitives to define the functional interface
    between the two layers.  Note that not every invocation of an
    Operational Primitive may elicit a response from the requested
    layer.  A full discussion of the Operational Primitive types and
    request-response semantics available to iSCSI and iSER can be
    found in [DA].

Ko & Nezhinsky Standards Track [Page 15] RFC 7145 iSER Specification April 2014

 Outbound RDMA Read Queue Depth (ORD) - The maximum number of
    outstanding RDMA Read Requests that the RDMA-Capable Controller
    can initiate on a particular RCaP Stream at the Data Sink.  For
    some RDMA-Capable Protocol layer, the term "ORD" may be known by a
    different name.  For example, for InfiniBand, the equivalent to
    ORD is the Initiator Depth.
 Phase Collapse - Refers to the optimization in iSCSI where the SCSI
    status is transferred along with the final SCSI Data-In PDU from a
    target.  See Section 4.2 in [iSCSI].
 RCaP Message - One or more packets of the network layer that
    constitute a single RDMA operation or a part of an RDMA Read
    Operation of the RDMA-Capable Protocol.  For iWARP, an RCaP
    Message is known as an RDMAP Message.
 RCaP Stream - A single bidirectional association between the peer
    RDMA-Capable Protocol layers on two nodes over a single transport-
    level stream.  For iWARP, an RCaP Stream is known as an RDMAP
    Stream, and the association is created following a successful
    Login Phase during which iSER support is negotiated.
 RDMA-Capable Protocol (RCaP) - The protocol or protocol suite that
    provides a reliable RDMA transport functionality, e.g., iWARP,
    InfiniBand, etc.
 RDMA-Capable Controller - A network I/O adapter or embedded
    controller with RDMA functionality.  For example, for iWARP, this
    could be an RNIC, and for InfiniBand, this could be a HCA (Host
    Channel Adapter) or TCA (Target Channel Adapter).
 RDMA-enabled Network Interface Controller (RNIC) - A network I/O
    adapter or embedded controller with iWARP functionality.
 RDMA Operation - A sequence of RCaP Messages, including control
    messages, to transfer data from a Data Source to a Data Sink.  The
    following RDMA Operations are defined -- RDMA Write Operation,
    RDMA Read Operation, and Send Operation.
 RDMA Protocol (RDMAP) - A wire protocol that supports RDMA Operations
    to transfer ULP data between a Local Peer and the Remote Peer as
    described in [RDMAP].
 RDMA Read Operation - An RDMA Operation used by the Data Sink to
    transfer the contents of a Data Source buffer from the Remote Peer
    to a Data Sink buffer at the Local Peer.  An RDMA Read operation
    consists of a single RDMA Read Request Message and a single RDMA
    Read Response Message.

Ko & Nezhinsky Standards Track [Page 16] RFC 7145 iSER Specification April 2014

 RDMA Read Request - An RCaP Message used by the Data Sink to request
    the Data Source to transfer the contents of a buffer.  The RDMA
    Read Request Message describes both the Data Source and the Data
    Sink buffers.
 RDMA Read Response - An RCaP Message used by the Data Source to
    transfer the contents of a buffer to the Data Sink, in response to
    an RDMA Read Request.  The RDMA Read Response Message only
    describes the Data Sink buffer.
 RDMA Write Operation - An RDMA Operation used by the Data Source to
    transfer the contents of a Data Source buffer from the Local Peer
    to a Data Sink buffer at the Remote Peer.  The RDMA Write Message
    only describes the Data Sink buffer.
 Remote Direct Memory Access (RDMA) - A method of accessing memory on
    a remote system in which the local system specifies the remote
    location of the data to be transferred.  Employing an RDMA-
    Capable Controller in the remote system allows the access to take
    place without interrupting the processing of the CPU(s) on the
    system.
 Remote Mapping - A task state record maintained by the iSER layer
    that associates the Initiator Task Tag to the Advertised STag(s)
    and the Base Offset(s).  The specifics of the record structure are
    implementation dependent.
 Remote Peer - The implementation of the RDMA-Capable Protocol on the
    opposite end of the connection.  Used to refer to the remote
    entity when describing protocol exchanges or other interactions
    between two nodes.
 SCSI Layer - This layer builds/receives SCSI CDBs (Command Descriptor
    Blocks) and sends/receives them with the remaining command execute
    [SAM5] parameters to/from the iSCSI layer.
 Send - An RDMA Operation that transfers the content of a buffer from
    the Local Peer to an untagged buffer at the Remote Peer.
 SendInvSE Message - A Send with Solicited Event and Invalidate
    Message.
 SendSE Message - A Send with Solicited Event Message.
 Sequence Number (SN) - DataSN for a SCSI Data-In PDU and R2TSN for an
    R2T PDU.  The semantics for both types of sequence numbers are as
    defined in [iSCSI].

Ko & Nezhinsky Standards Track [Page 17] RFC 7145 iSER Specification April 2014

 Session, iSCSI Session - The group of connections that link an
    initiator SCSI port with a target SCSI port form an iSCSI session
    (equivalent to a SCSI Initiator-Target (I-T) nexus).  Connections
    can be added to and removed from a session even while the I-T
    nexus is intact.  Across all connections within a session, an
    initiator sees one and the same target.
 Steering Tag (STag) - An identifier of a Tagged Buffer on a node
    (Local or Remote) as defined in [RDMAP] and [DDP].  For other
    RDMA-Capable Protocols, the Steering Tag may be known by different
    names but will be referred to herein as STags.  For example, for
    InfiniBand, a Remote STag is known as an R-Key, and a Local STag
    is known as an L-Key, and both will be considered STags.
 Tagged Buffer - A buffer that is explicitly Advertised to the iSER
    layer at the remote node through the exchange of an STag, Base
    Offset, and length.
 Tagged Offset - The offset within a Tagged Buffer.
 Traditional iSCSI - Refers to the iSCSI protocol as defined in
    [iSCSI] (i.e., without the iSER enhancements).
 Untagged Buffer - A buffer that is not explicitly Advertised to the
    iSER layer at the remode node.

2.2. Acronyms

 Acronym        Definition
  1. ————————————————————-
 AHS            Additional Header Segment
 BHS            Basic Header Segment
 CO             Connection Only
 CRC            Cyclic Redundancy Check
 DDP            Direct Data Placement Protocol
 DI             Datamover Interface
 HCA            Host Channel Adapter
 IANA           Internet Assigned Numbers Authority

Ko & Nezhinsky Standards Track [Page 18] RFC 7145 iSER Specification April 2014

 IB             InfiniBand
 IETF           Internet Engineering Task Force
 I/O            Input - Output
 IO             Initialize Only
 IP             Internet Protocol
 IPoIB          IP over InfiniBand
 IPsec          Internet Protocol Security
 iSER           iSCSI Extensions for RDMA
 ITT            Initiator Task Tag
 LO             Leading Only
 MPA            Marker PDU Aligned Framing for TCP
 NOP            No Operation
 NSG            Next Stage (during the iSCSI Login Phase)
 PDU            Protocol Data Unit
 R2T            Ready To Transfer
 R2TSN          Ready To Transfer Sequence Number
 RCaP           RDMA-Capable Protocol
 RDMA           Remote Direct Memory Access
 RDMAP          Remote Direct Memory Access Protocol
 RFC            Request For Comments
 RNIC           RDMA-enabled Network Interface Controller
 SAM5           SCSI Architecture Model - 5
 SCSI           Small Computer System Interface

Ko & Nezhinsky Standards Track [Page 19] RFC 7145 iSER Specification April 2014

 SNACK          Selective Negative Acknowledgment - also
                Sequence Number Acknowledgement for data
 STag           Steering Tag
 SW             Session Wide
 TCA            Target Channel Adapter
 TCP            Transmission Control Protocol
 TMF            Task Management Function
 TTT            Target Transfer Tag
 ULP            Upper Level Protocol

2.3. Conventions

 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in [RFC2119].

3. Upper-Layer Interface Requirements

 This section discusses the upper-layer interface requirements in the
 form of an abstract model of the required interactions between the
 iSCSI layer and the iSER layer.  The abstract model used here is
 derived from the architectural model described in [DA].  [DA] also
 provides a functional overview of the interactions between the iSCSI
 layer and the Datamover layer as intended by the Datamover
 Architecture.
 The interface requirements are specified by Operational Primitives.
 An Operational Primitive is an abstract functional interface
 procedure between the iSCSI layer and the iSER layer that requests
 one layer to perform a specific action on behalf of the other layer
 or notifies the other layer of some event.  Whenever an Operational
 Primitive in invoked, the Connection_Handle qualifier is used to
 identify a particular iSCSI connection.  For some Operational
 Primitives, a Data_Descriptor is used to identify the iSCSI/SCSI data
 buffer associated with the requested or completed operation.
 The abstract model and the Operational Primitives defined in this
 section facilitate the description of the iSER protocol.  In the rest
 of the iSER specification, the compliance statements related to the
 use of these Operational Primitives are only for the purpose of the

Ko & Nezhinsky Standards Track [Page 20] RFC 7145 iSER Specification April 2014

 required interactions between the iSCSI layer and the iSER layer.
 Note that the compliance statements related to the Operational
 Primitives in the rest of this specification only mandate functional
 equivalence on implementations, but do not put any requirements on
 the implementation specifics of the interface between the iSCSI layer
 and the iSER layer.
 Each Operational Primitive is invoked with a set of qualifiers which
 specify the information context for performing the specific action
 being requested of the Operational Primitive.  While the qualifiers
 are required, the method of realizing the qualifiers (e.g., by
 passing synchronously with invocation, or by retrieving from task
 context, or by retrieving from shared memory, etc.) is implementation
 dependent.

3.1. Operational Primitives offered by iSER

 The iSER protocol layer MUST support the following Operational
 Primitives to be used by the iSCSI protocol layer.

3.1.1. Send_Control

    Input qualifiers:  Connection_Handle, BHS and AHS (if any) of the
    iSCSI PDU, PDU-specific qualifiers
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request the outbound transfer of an iSCSI control-type PDU (see
 Section 7.2).  Qualifiers that only apply for a particular control-
 type PDU are known as PDU-specific qualifiers, e.g.,
 ImmediateDataSize for a SCSI Write command.  For details on PDU-
 specific qualifiers, see Section 7.3.  The iSCSI layer can only
 invoke the Send_Control Operational Primitive when the connection is
 in iSER-assisted mode.

3.1.2. Put_Data

    Input qualifiers:  Connection_Handle, content of a SCSI Data-In
    PDU header, Data_Descriptor, Notify_Enable
    Return results:  Not specified
 This is used by the iSCSI layer at the target to request the outbound
 transfer of data for a SCSI Data-In PDU from the buffer identified by
 the Data_Descriptor qualifier.  The iSCSI layer can only invoke the
 Put_Data Operational Primitive when the connection is in iSER-
 assisted mode.

Ko & Nezhinsky Standards Track [Page 21] RFC 7145 iSER Specification April 2014

 The Notify_Enable qualifier is used to indicate to the iSER layer
 whether or not it should generate an eventual local completion
 notification to the iSCSI layer.  See Section 3.2.2 on
 Data_Completion_Notify for details.

3.1.3. Get_Data

    Input qualifiers:  Connection_Handle, content of an R2T PDU,
    Data_Descriptor, Notify_Enable
    Return results:  Not specified
 This is used by the iSCSI layer at the target to request the inbound
 transfer of solicited data requested by an R2T PDU into the buffer
 identified by the Data_Descriptor qualifier.  The iSCSI layer can
 only invoke the Get_Data Operational Primitive when the connection is
 in iSER-assisted mode.
 The Notify_Enable qualifier is used to indicate to the iSER layer
 whether or not it should generate the eventual local completion
 notification to the iSCSI layer.  See Section 3.2.2 on
 Data_Completion_Notify for details.

3.1.4. Allocate_Connection_Resources

    Input qualifiers:  Connection_Handle, Resource_Descriptor
    (optional)
    Return results:  Status
 This is used by the iSCSI layers at the initiator and the target to
 request the allocation of all connection resources necessary to
 support RCaP for an operational iSCSI/iSER connection.  The iSCSI
 layer may optionally specify the implementation-specific resource
 requirements for the iSCSI connection using the Resource_Descriptor
 qualifier.
 A return result of Status=success means the invocation succeeded, and
 a return result of Status=failure means that the invocation failed.
 If the invocation is for a Connection_Handle for which an earlier
 invocation succeeded, the request will be ignored by the iSER layer
 and the result of Status=success will be returned.  Only one
 Allocate_Connection_Resources Operational Primitive invocation can be
 outstanding for a given Connection_Handle at any time.

Ko & Nezhinsky Standards Track [Page 22] RFC 7145 iSER Specification April 2014

3.1.5. Deallocate_Connection_Resources

    Input qualifiers:  Connection_Handle
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request the deallocation of all connection resources that were
 allocated earlier as a result of a successful invocation of the
 Allocate_Connection_Resources Operational Primitive.

3.1.6. Enable_Datamover

    Input qualifiers:  Connection_Handle,
    Transport_Connection_Descriptor, Final Login_Response_PDU
    (optional)
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request that iSER-assisted mode be used for the connection.  The
 Transport_Connection_Descriptor qualifier is used to identify the
 specific connection associated with the Connection_Handle.  The iSCSI
 layer can only invoke the Enable_Datamover Operational Primitive when
 there was a corresponding prior resource allocation.
 The Final_Login_Response_PDU input qualifier is applicable only for a
 target and contains the final Login Response PDU that concludes the
 iSCSI Login Phase.

3.1.7. Connection_Terminate

    Input qualifiers:  Connection_Handle
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request that a specified iSCSI/iSER connection be terminated and all
 associated connection and task resources be freed.  When this
 Operational Primitive invocation returns to the iSCSI layer, the
 iSCSI layer may assume full ownership of all iSCSI-level resources,
 e.g., I/O Buffers, associated with the connection.

Ko & Nezhinsky Standards Track [Page 23] RFC 7145 iSER Specification April 2014

3.1.8. Notice_Key_Values

    Input qualifiers:  Connection_Handle, number of keys, list of Key-
    Value pairs
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request the iSER layer to take note of the specified Key-Value pairs
 that were negotiated by the iSCSI peers for the connection.

3.1.9. Deallocate_Task_Resources

    Input qualifiers:  Connection_Handle, ITT
    Return results:  Not specified
 This is used by the iSCSI layers at the initiator and the target to
 request the deallocation of all RCaP-specific resources allocated by
 the iSER layer for the task identified by the ITT qualifier.  The
 iSER layer may require a certain number of RCaP-specific resources
 associated with the ITT for each new iSCSI task.  In the normal
 course of execution, these task-level resources in the iSER layer are
 assumed to be transparently allocated on each task initiation and
 deallocated on the conclusion of each task as appropriate.  In
 exception scenarios where the task does not conclude with a SCSI
 Response PDU, the iSER layer needs to be notified of the individual
 task terminations to aid its task-level resource management.  This
 Operational Primitive is used for this purpose and is not needed when
 a SCSI Response PDU normally concludes a task.  Note that RCaP-
 specific task resources are deallocated by the iSER layer when a SCSI
 Response PDU normally concludes a task, even if the SCSI status was
 not success.

3.2. Operational Primitives Used by iSER

 The iSER layer MUST use the following Operational Primitives offered
 by the iSCSI protocol layer when the connection is in iSER-assisted
 mode.

Ko & Nezhinsky Standards Track [Page 24] RFC 7145 iSER Specification April 2014

3.2.1. Control_Notify

    Input qualifiers:  Connection_Handle, an iSCSI control-type PDU
    Return results:  Not specified
 This is used by the iSER layers at the initiator and the target to
 notify the iSCSI layer of the availability of an inbound iSCSI
 control-type PDU.  A PDU is described as "available" to the iSCSI
 layer when the iSER layer notifies the iSCSI layer of the reception
 of that inbound PDU, along with an implementation-specific indication
 as to where the received PDU is.

3.2.2. Data_Completion_Notify

    Input qualifiers:  Connection_Handle, ITT, SN
    Return results:  Not specified
 This is used by the iSER layer to notify the iSCSI layer of the
 completion of the outbound data transfer that was requested by the
 iSCSI layer only if the invocation of the Put_Data Operational
 Primitive (see Section 3.1.2) was qualified with Notify_Enable set.
 SN refers to the DataSN associated with the SCSI Data-In PDU.
 This is used by the iSER layer to notify the iSCSI layer of the
 completion of the inbound data transfer that was requested by the
 iSCSI layer only if the invocation of the Get_Data Operational
 Primitive (see Section 3.1.3) was qualified with Notify_Enable set.
 SN refers to the R2TSN associated with the R2T PDU.

3.2.3. Data_ACK_Notify

    Input qualifier:  Connection_Handle, ITT, DataSN
    Return results:  Not specified
 This is used by the iSER layer at the target to notify the iSCSI
 layer of the arrival of the data acknowledgement (as defined in
 [iSCSI]) requested earlier by the iSCSI layer for the outbound data
 transfer via an invocation of the Put_Data Operational Primitive
 where the A-bit in the SCSI Data-In PDU is set to one.  See Section
 7.3.5.  DataSN refers to the expected DataSN of the next SCSI Data-In
 PDU that immediately follows the SCSI Data-In PDU with the A-bit set
 to which this notification corresponds, with semantics as defined in
 [iSCSI].

Ko & Nezhinsky Standards Track [Page 25] RFC 7145 iSER Specification April 2014

3.2.4. Connection_Terminate_Notify

    Input qualifiers:  Connection_Handle
    Return results:  Not specified
 This is used by the iSER layers at the initiator and the target to
 notify the iSCSI layer of the unsolicited termination or failure of
 an iSCSI/iSER connection.  The iSER layer MUST deallocate the
 connection and task resources associated with the terminated
 connection before the invocation of this Operational Primitive.  Note
 that the Connection_Terminate_Notify Operational Primitive is not
 invoked when the termination of the connection was earlier requested
 by the local iSCSI layer.

3.3. iSCSI Protocol Usage Requirements

 To operate in iSER-assisted mode, the iSCSI layers at both the
 initiator and the target MUST negotiate the RDMAExtensions key (see
 Section 6.3) to "Yes" on the leading connection.  If the
 RDMAExtensions key is not negotiated to "Yes", then iSER-assisted
 mode MUST NOT be used.  If the RDMAExtensons key is negotiated to
 "Yes", but the invocation of the Allocate_Connection_Resources
 Operational Primitive to the iSER layer fails, the iSCSI layer MUST
 fail the iSCSI Login process or terminate the connection as
 appropriate.  See Section 10.1.3.1 for details.
 If the RDMAExtensions key is negotiated to "Yes", the iSCSI layer
 MUST satisfy the following protocol usage requirements from the iSER
 protocol:
 1.  The iSCSI layer at the initiator MUST set ExpDataSN to zero in
     Task Management Function Requests for Task Allegiance
     Reassignment for read/bidirectional commands, so as to cause the
     target to send all unacknowledged read data.
 2.  The iSCSI layer at the target MUST always return the SCSI status
     in a separate SCSI Response PDU for read commands, i.e., there
     MUST NOT be a "phase collapse" in concluding a SCSI Read Command.
 3.  The iSCSI layers at both the initiator and the target MUST
     support the keys as defined in Section 6 on Login/Text
     Operational Keys.  If used as specified, these keys MUST NOT be
     answered with NotUnderstood, and the semantics as defined MUST be
     followed for each iSER-assisted connection.
 4.  The iSCSI layer at the initiator MUST NOT issue SNACKs for PDUs.

Ko & Nezhinsky Standards Track [Page 26] RFC 7145 iSER Specification April 2014

4. Lower-Layer Interface Requirements

4.1. Interactions with the RCaP Layer

 The iSER protocol layer is layered on top of an RCaP layer (see
 Figure 1) and the following are the key features that are assumed to
 be supported by any RCaP layer:
  • The RCaP layer supports all basic RDMA operations, including the

RDMA Write Operation, RDMA Read Operation, and Send Operation.

  • The RCaP layer provides reliable, in-order message delivery and

direct data placement.

  • When the iSER layer initiates an RDMA Read Operation following an

RDMA Write Operation on one RCaP Stream, the RDMA Read Response

    Message processing on the remote node will be started only after
    the preceding RDMA Write Message payload is placed in the memory
    of the remote node.
  • The RCaP layer encapsulates a single iSER Message into a single

RCaP Message on the Data Source side. The RCaP layer decapsulates

    the iSER Message before delivering it to the iSER layer on the
    Data Sink side.
  • For an RCaP layer that supports the Send with Invalidate Message

(e.g., iWARP), when the iSER layer provides the STag to be

    remotely invalidated to the RCaP layer for a Send with Invalidate
    Message, the RCaP layer uses this STag as the STag to be
    invalidated in the Send with Invalidate Message.
  • The RCaP layer uses the STag and Tagged Offset provided by the

iSER layer for the RDMA Write and RDMA Read Request Messages.

  • When the RCaP layer delivers the content of an RDMA Send Message

to the iSER layer, the RCaP layer provides the length of the RDMA

    Send Message.  This ensures that the iSER layer does not have to
    carry a length field in the iSER header.
  • When the RCaP layer delivers the Send Message to the iSER layer,

it notifies the iSER layer with the mechanism provided on that

    interface.
  • For an RCaP layer that supports the Send with Invalidate Message

(e.g., iWARP), when the RCaP layer delivers a Send with Invalidate

    Message to the iSER layer, it passes the value of the STag that
    was invalidated.

Ko & Nezhinsky Standards Track [Page 27] RFC 7145 iSER Specification April 2014

  • The RCaP layer propagates all status and error indications to the

iSER layer.

  • For a transport layer that operates in byte stream mode such as

TCP, the RCaP implementation supports the enabling of the RDMA

    mode after connection establishment and the exchange of Login
    parameters in byte stream mode.  For a transport layer that
    provides message delivery capability such as [IB], the RCaP
    implementation supports the direct use of the messaging capability
    by the iSCSI layer for the Login Phase after connection
    establishment and before enabling iSER-assisted mode.  (In the
    specific example of InfiniBand [IB], the iSCSI layer uses IB
    messages to transfer iSCSI PDUs for the Login Phase after
    connection establishment and before enabling iSER-assisted mode.)
  • Whenever the iSER layer terminates the RCaP Stream, the RCaP layer

terminates the associated connection.

4.2. Interactions with the Transport Layer

 After the iSER connection is established, the RCaP layer and the
 underlying transport layer are responsible for maintaining the
 connection and reporting to the iSER layer any connection failures.

5. Connection Setup and Termination

5.1. iSCSI/iSER Connection Setup

 During connection setup, the iSCSI layer at the initiator is
 responsible for establishing a connection with the target.  After the
 connection is established, the iSCSI layers at the initiator and the
 target enter the Login Phase using the same rules as outlined in
 [iSCSI].  The connection transitions into the iSCSI Full Feature
 Phase in iSER-assisted mode following a successful login negotiation
 between the initiator and the target in which iSER-assisted mode is
 negotiated and the connection resources necessary to support RCaP
 have been allocated at both the initiator and the target.  The same
 connection MUST be used for both the iSCSI Login Phase and the
 subsequent iSER-assisted Full Feature Phase.
 For a transport layer that operates in byte stream mode such as TCP,
 the RCaP implementation supports the enabling of the RDMA mode after
 connection establishment and the exchange of Login parameters in byte
 stream mode.  For a transport layer that provides message delivery
 capability such as [IB], the RCaP implementation supports the use of
 the messaging capability by the iSCSI layer directly for the Login
 Phase after connection establishment before enabling iSER-assisted
 mode.

Ko & Nezhinsky Standards Track [Page 28] RFC 7145 iSER Specification April 2014

 iSER-assisted mode MUST NOT be enabled unless it is negotiated on the
 leading connection during the LoginOperationalNegotiation stage of
 the iSCSI Login Phase.  iSER-assisted mode is negotiated using the
 RDMAExtensions=<boolean-value> key.  Both the initiator and the
 target MUST exchange the RDMAExtensions key with the value set to
 "Yes" to enable iSER-assisted mode.  If both the initiator and the
 target fail to negotiate the RDMAExtensions key set to "Yes", then
 the connection MUST continue with the login semantics as defined in
 [iSCSI].  If the RDMAExtensions key is not negotiated to Yes, then
 for some RCaP implementation (such as [IB]), the existing connection
 may need to be torn down and a new connection may need to be
 established in TCP-capable mode.  (For InfiniBand, this will require
 a connection like [IPoIB].)
 iSER-assisted mode is defined for a Normal session only, and the
 RDMAExtensions key MUST NOT be negotiated for a Discovery session.
 Discovery sessions are always conducted using the transport layer as
 described in [iSCSI].
 An iSER-enabled node is not required to initiate the RDMAExtensions
 key exchange if its preference is for the Traditional iSCSI mode.
 The RDMAExtensions key, if offered, MUST be sent in the first
 available Login Response or Login Request PDU in the
 LoginOperationalNegotiation stage.  This is due to the fact that the
 value of some Login parameters might depend on whether or not iSER-
 assisted mode is enabled.
 iSER-assisted mode is a session-wide attribute.  If both the
 initiator and the target negotiated RDMAExtensions="Yes" on the
 leading connection of a session, then all subsequent connections of
 the same session MUST enable iSER-assisted mode without having to
 exchange RDMAExtensions keys during the iSCSI Login Phase.
 Conversely, if both the initiator and the target failed to negotiate
 RDMAExtensions to "Yes" on the leading connection of a session, then
 the RDMAExtensions key MUST NOT be negotiated further on any
 additional subsequent connection of the session.
 When the RDMAExtensions key is negotiated to "Yes", the HeaderDigest
 and the DataDigest keys MUST be negotiated to "None" on all
 iSCSI/iSER connections participating in that iSCSI session.  This is
 because, for an iSCSI/iSER connection, RCaP is responsible for
 providing error detection that is at least as good as a 32-bit CRC
 for all iSER Messages.  Furthermore, all SCSI Read data are sent
 using RDMA Write Messages instead of the SCSI Data-In PDUs, and all
 solicited SCSI Write data are sent using RDMA Read Response Messages
 instead of the SCSI Data-Out PDUs.  HeaderDigest and DataDigest that
 apply to iSCSI PDUs would not be appropriate for RDMA Read and RDMA
 Write operations used with iSER.

Ko & Nezhinsky Standards Track [Page 29] RFC 7145 iSER Specification April 2014

5.1.1. Initiator Behavior

 If the outcome of the iSCSI negotiation is to enable iSER-assisted
 mode, then on the initiator side, prior to sending the Login Request
 with the T (Transit) bit set to one and the NSG (Next Stage) field
 set to FullFeaturePhase, the iSCSI layer SHOULD request the iSER
 layer to allocate the connection resources necessary to support RCaP
 by invoking the Allocate_Connection_Resources Operational Primitive.
 The connection resources required are defined by the implementation
 and are outside the scope of this specification.  The iSCSI layer may
 invoke the Notice_Key_Values Operational Primitive before invoking
 the Allocate_Connection_Resources Operational Primitive to request
 the iSER layer to take note of the negotiated values of the iSCSI
 keys for the connection.  The specific keys to be passed in as input
 qualifiers are implementation dependent.  These may include, but are
 not limited to, MaxOutstandingR2T and ErrorRecoveryLevel.
 Among the connection resources allocated at the initiator is the
 Inbound RDMA Read Queue Depth (IRD).  As described in Section 9.5.1,
 R2Ts are transformed by the target into RDMA Read operations.  IRD
 limits the maximum number of simultaneously incoming outstanding RDMA
 Read Requests per an RCaP Stream from the target to the initiator.
 The required value of IRD is outside the scope of the iSER
 specification.  The iSER layer at the initiator MUST set IRD to 1 or
 higher if R2Ts are to be used in the connection.  However, the iSER
 layer at the initiator MAY set IRD to zero based on implementation
 configuration; setting IRD to zero indicates that no R2Ts will be
 used on that connection.  Initially, the iSER-IRD value at the
 initiator SHOULD be set to the IRD value at the initiator and MUST
 NOT be more than the IRD value.
 On the other hand, the Outbound RDMA Read Queue Depth (ORD) MAY be
 set to zero since the iSER layer at the initiator does not issue RDMA
 Read Requests to the target.
 Failure to allocate the requested connection resources locally
 results in a login failure, and its handling is described in Section
 10.1.3.1.
 The iSER layer MUST return a success status to the iSCSI layer in
 response to the Allocate_Connection_Resources Operational Primitive.

Ko & Nezhinsky Standards Track [Page 30] RFC 7145 iSER Specification April 2014

 After the target returns the Login Response with the T bit set to one
 and the NSG field set to FullFeaturePhase, and a Status-Class of 0x00
 (Success), the iSCSI layer MUST invoke the Enable_Datamover
 Operational Primitive with the following qualifiers.  (See Section
 10.1.4.6 for the case when the Status-Class is not Success.)
    a. Connection_Handle that identifies the iSCSI connection.
    b. Transport_Connection_Descriptor that identifies the specific
       transport connection associated with the Connection_Handle.
 The iSER layer MUST send the iSER Hello Message as the first iSER
 Message only if iSERHelloRequired is negotiated to "Yes".  See
 Section 5.1.3 on iSER Hello Exchange.
 If the iSCSI layer on the initiator side allocates the connection
 resources to support RCaP only after it receives the final Login
 Response PDU from the target, then it may not be able to handle the
 number of unexpected iSCSI control-type PDUs (as declared by the
 MaxOutstandingUnexpectedPDUs key from the initiator) that can be sent
 by the target before the buffer resources are allocated at the
 initiator side.  In this case, the iSERHelloRequired key SHOULD be
 negotiated to "Yes" so that the initiator can allocate the connection
 resources before sending the iSER Hello Message.  See Section 5.1.3
 for more details.

5.1.2. Target Behavior

 If the outcome of the iSCSI negotiation is to enable iSER-assisted
 mode, then on the target side, prior to sending the Login Response
 with the T (Transit) bit set to one and the NSG (Next Stage) field
 set to FullFeaturePhase, the iSCSI layer MUST request the iSER layer
 to allocate the resources necessary to support RCaP by invoking the
 Allocate_Connection_Resources Operational Primitive.  The connection
 resources required are defined by implementation and are outside the
 scope of this specification.  Optionally, the iSCSI layer may invoke
 the Notice_Key_Values Operational Primitive before invoking the
 Allocate_Connection_Resources Operational Primitive to request the
 iSER layer to take note of the negotiated values of the iSCSI keys
 for the connection.  The specific keys to be passed in as input
 qualifiers are implementation dependent.  These may include, but not
 limited to, MaxOutstandingR2T and ErrorRecoveryLevel.
 Premature allocation of RCaP connection resources can expose an iSER
 target to a resource exhaustion attack on those resources via
 multiple iSER connections that progress only to the point at which
 the implementation allocates the RCaP connection resources.  The
 countermeasure for this attack is initiator authentication; the iSCSI

Ko & Nezhinsky Standards Track [Page 31] RFC 7145 iSER Specification April 2014

 layer MUST NOT request the iSER layer to allocate the connection
 resources necessary to support RCaP until the iSCSI layer is
 sufficiently far along in the iSCSI Login Phase that it is reasonably
 certain that the peer side is not an attacker.  In particular, if the
 Login Phase includes a SecurityNegotiation stage, the iSCSI layer
 MUST defer the connection resource allocation (i.e., invoking the
 Allocate_Connection_Resources Operational Primitive) to the
 LoginOperationalNegotiation stage ([iSCSI]) so that the resource
 allocation occurs after the authentication phase is completed.
 Among the connection resources allocated at the target is the
 Outbound RDMA Read Queue Depth (ORD).  As described in Section 9.5.1,
 R2Ts are transformed by the target into RDMA Read operations.  The
 ORD limits the maximum number of simultaneously outstanding RDMA Read
 Requests per RCaP Stream from the target to the initiator.
 Initially, the iSER-ORD value at the target SHOULD be set to the ORD
 value at the target.
 On the other hand, the IRD at the target MAY be set to zero since the
 iSER layer at the target does not expect RDMA Read Requests to be
 issued by the initiator.
 Failure to allocate the requested connection resources locally
 results in a login failure, and its handling is described in Section
 10.1.3.1.
 If the iSER layer at the target is successful in allocating the
 connection resources necessary to support RCaP, the following events
 MUST occur in the specified sequence:
 1. The iSER layer MUST return a success status to the iSCSI layer in
    response to the Allocate_Connection_Resources Operational
    Primitive.
 2. The iSCSI layer MUST invoke the Enable_Datamover Operational
    Primitive with the following qualifiers:
    a. Connection_Handle that identifies the iSCSI connection.
    b. Transport_Connection_Descriptor that identifies the specific
       transport connection associated with the Connection_Handle.
    c. The final transport-layer (e.g., TCP) message containing the
       Login Response with the T bit set to one and the NSG field set
       to FullFeaturePhase.

Ko & Nezhinsky Standards Track [Page 32] RFC 7145 iSER Specification April 2014

 3. The iSER layer MUST send the final Login Response PDU in the
    native transport mode to conclude the iSCSI Login Phase.  If the
    underlying transport is TCP, then the iSER layer MUST send the
    final Login Response PDU in byte stream mode.
 4. After receiving the iSER Hello Message from the initiator, the
    iSER layer MUST respond with the iSER HelloReply Message to be
    sent as the first iSER Message if iSERHelloRequired is negotiated
    to "Yes".  If the iSER layer receives an iSER Hello Message when
    iSERHelloRequired is negotiated to "No", then this MUST be treated
    as an iSER protocol error.  See Section 5.1.3 on iSER Hello
    Exchange for more details.
 Note: In the above sequence, the operations as described in items 3
 and 4 MUST be performed atomically for iWARP connections.  Failure to
 do this may result in race conditions.

5.1.3. iSER Hello Exchange

 If iSERHelloRequired is negotiated to "Yes", the first iSER Message
 sent by the iSER layer at the initiator to the target MUST be the
 iSER Hello Message.  The iSER Hello Message is used by the iSER layer
 at the initiator to declare iSER parameters to the target.  See
 Section 9.3 on iSER Header Format for iSER Hello Message.
 Conversely, if iSERHelloRequired is negotiated to "No", then the iSER
 layer at the initiator MUST NOT send an iSER Hello Message.
 In response to the iSER Hello Message, the iSER layer at the target
 MUST return the iSER HelloReply Message as the first iSER Message
 sent by the target if iSERHelloRequired is negotiated to "Yes".  The
 iSER HelloReply Message is used by the iSER layer at the target to
 declare iSER parameters to the initiator.  See Section 9.4 on iSER
 Header Format for iSER HelloReply Message.  If the iSER layer
 receives an iSER Hello Message when iSERHelloRequired is negotiated
 to "No", then this MUST be treated as an iSER protocol error.  See
 Section 10.1.3.4 on iSER Protocol Errors on for more details.
 In the iSER Hello Message, the iSER layer at the initiator declares
 the iSER-IRD value to the target.
 Upon receiving the iSER Hello Message, the iSER layer at the target
 MUST set the iSER-ORD value to the minimum of the iSER-ORD value at
 the target and the iSER-IRD value declared by the initiator.  In
 order to free up the unused resources, the iSER layer at the target
 MAY adjust (lower) its ORD value to match the iSER-ORD value if the
 iSER-ORD value is smaller than the ORD value at the target.

Ko & Nezhinsky Standards Track [Page 33] RFC 7145 iSER Specification April 2014

 In the iSER HelloReply Message, the iSER layer at the target declares
 the iSER-ORD value to the initiator.
 Upon receiving the iSER HelloReply Message, the iSER layer at the
 initiator MAY adjust (lower) its IRD value to match the iSER-ORD
 value in order to free up the unused resources, if the iSER-ORD value
 declared by the target is smaller than the iSER-IRD value declared by
 the initiator.
 It is an iSER-level negotiation failure if the iSER parameters
 declared in the iSER Hello Message by the initiator are unacceptable
 to the target.  This includes the following:
  • The initiator-declared iSER-IRD value is greater than 0, and the

target-declared iSER-ORD value is 0.

  • The initiator-supported and the target-supported iSER protocol

versions do not overlap.

 See Section 10.1.3.2 on the handling of the error situation.
 An initiator that conforms to [RFC5046] allocates connection
 resources before sending the Login Request with the T (Transit) bit
 set to one and the NSG (Next Stage) field set to FullFeaturePhase.
 (For brevity, this is referred to as "early" connection allocation.)
 The current iSER specification relaxes this requirement to allow an
 initiator to allocate connection resources after it receives the
 final Login Response PDU from the target.  (For brevity, this is
 referred to as "late" connection allocation.)  An initiator that
 employs "late" connection allocation may encounter problems (e.g.,
 RCaP connection closure) with a target that sends unexpected iSCSI
 PDUs immediately upon transitioning to Full Feature Phase, as allowed
 by the negotiated value of the MaxOutstandingUnexpectedPDUs key.  The
 only way to prevent this situation in full generality is to use iSER
 Hello Messages, as they enable the initiator to allocate its
 connection resources before sending its iSER Hello Message.  The
 iSERHelloRequired key is used by the initiator to determine if it is
 dealing with a target that supports the iSER Hello exchanges.
 Fortunately, known iSER target implementations do not take full
 advantage of the number of allowed unexpected PDUs immediately upon
 transitioning into Full Feature Phase, thus enabling an initiator
 workaround that involves a smaller quantity of connection resources
 prior to Full Feature Phase, as explained further below.
 In the following summary, where "late" connection allocation is
 practiced, an initiator that follows [RFC5046] is referred to as an
 "old" initiator; otherwise, it is referred to as a "new" initiator.
 Similarly, a target that does not support the iSERHelloRequired key

Ko & Nezhinsky Standards Track [Page 34] RFC 7145 iSER Specification April 2014

 (and responds with "NotUnderstood" when negotiating the
 iSERHelloRequired key) is referred to as an "old" target; otherwise,
 it is referred to as a "new" target.  Note that an "old" target can
 still support the iSER Hello exchanges, but this fact is not known by
 the initiator.  A "new" target can also respond with "No" when
 negotiating the iSERHelloRequired key.  In this case, its behavior
 with respect to "late" connection allocation is similar to an "old"
 target.
 A "new" initiator will work fine with a "new" target.
 For an "old" initiator and an "old" target, the failure by the
 initiator to handle the number of unexpected iSCSI control-type PDUs
 that are sent by the target before the buffer resources are allocated
 at the initiator can result in the failure of the iSER session caused
 by closure of the underlying RCaP connection.  For the "old" target,
 there is a known implementation that sends one unexpected iSCSI
 control-type PDU after sending the final Login Response and then
 waits awhile before sending the next one.  This tends to alleviate
 somewhat the buffer allocation problem at the initiator.
 For a "new" initiator and an "old" target, the failure by the
 initiator to handle the number of unexpected iSCSI control-type PDUs
 that are sent by the target before the buffer resources are allocated
 at the initiator can result in the failure of the iSER session caused
 by closure of the underlying RCaP connection.  A "new" initiator MAY
 choose to terminate the connection; otherwise, it SHOULD do one of
 the following:
 1. Allocate the connection resources before sending the final Login
    Request PDU.
 2. Allocate one or more buffers for receiving unexpected control-type
    PDUs from the target before sending the final Login Request PDU.
    This reduces the possibility of the unexpected control-type PDUs
    causing the RCaP connection to close before the connection
    resources have been allocated.

Ko & Nezhinsky Standards Track [Page 35] RFC 7145 iSER Specification April 2014

 For an "old" initiator and a "new" target, if the iSERHelloRequired
 key is not negotiated, a "new" target MUST still respond with the
 iSER HelloReply Message when it receives the iSER Hello Message.  If
 the iSERHelloRequired key is negotiated to "No" or "NotUnderstood", a
 "new" target MAY choose to terminate the connection; otherwise, it
 SHOULD delay sending any unexpected control-type PDUs until one of
 the following events has occurred:
 1. A PDU is received from the initiator after it sends the final
    Login Response PDU.
 2. A system-configurable timeout period (say, one second) has
    expired.

5.2. iSCSI/iSER Connection Termination

5.2.1. Normal Connection Termination at the Initiator

 The iSCSI layer at the initiator terminates an iSCSI/iSER connection
 normally by invoking the Send_Control Operational Primitive qualified
 with the Logout Request PDU.  The iSER layer at the initiator MUST
 use a Send Message to send the Logout Request PDU to the target.  The
 SendSE Message should be used if supported by the RCaP layer (e.g.,
 iWARP).  After the iSER layer at the initiator receives the Send
 Message containing the Logout Response PDU from the target, it MUST
 notify the iSCSI layer by invoking the Control_Notify Operational
 Primitive qualified with the Logout Response PDU.
 After the iSCSI logout process is complete, the iSCSI layer at the
 target is responsible for closing the iSCSI/iSER connection as
 described in Section 5.2.2.  After the RCaP layer at the initiator
 reports that the connection has been closed, the iSER layer at the
 initiator MUST deallocate all connection and task resources (if any)
 associated with the connection, and invalidate the Local Mappings (if
 any) before notifying the iSCSI layer by invoking the
 Connection_Terminate_Notify Operational Primitive.

5.2.2. Normal Connection Termination at the Target

 Upon receiving the Send Message containing the Logout Request PDU,
 the iSER layer at the target MUST notify the iSCSI layer at the
 target by invoking the Control_Notify Operational Primitive qualified
 with the Logout Request PDU.  The iSCSI layer completes the logout
 process by invoking the Send_Control Operational Primitive qualified
 with the Logout Response PDU.  The iSER layer at the target MUST use
 a Send Message to send the Logout Response PDU to the initiator.  The
 SendSE Message should be used if supported by the RCaP layer (e.g.,
 iWARP).  After the iSCSI logout process is complete, the iSCSI layer

Ko & Nezhinsky Standards Track [Page 36] RFC 7145 iSER Specification April 2014

 at the target MUST request the iSER layer at the target to terminate
 the RCaP Stream by invoking the Connection_Terminate Operational
 Primitive.
 As part of the termination process, the RCaP layer MUST close the
 connection.  When the RCaP layer notifies the iSER layer after the
 RCaP Stream and the associated connection are terminated, the iSER
 layer MUST deallocate all connection and task resources (if any)
 associated with the connection, and invalidate the Local and Remote
 Mappings (if any).

5.2.3. Termination without Logout Request/Response PDUs

5.2.3.1. Connection Termination Initiated by the iSCSI layer

 The Connection_Terminate Operational Primitive MAY be invoked by the
 iSCSI layer to request the iSER layer to terminate the RCaP Stream
 without having previously exchanged the Logout Request and Logout
 Response PDUs between the two iSCSI/iSER nodes.  As part of the
 termination process, the RCaP layer will close the connection.  When
 the RCaP layer notifies the iSER layer after the RCaP Stream and the
 associated connection are terminated, the iSER layer MUST perform the
 following actions.
 If the Connection_Terminate Operational Primitive is invoked by the
 iSCSI layer at the target, then the iSER layer at the target MUST
 deallocate all connection and task resources (if any) associated with
 the connection, and invalidate the Local and Remote Mappings (if
 any).
 If the Connection_Terminate Operational Primitive is invoked by the
 iSCSI layer at the initiator, then the iSER layer at the initiator
 MUST deallocate all connection and task resources (if any) associated
 with the connection, and invalidate the Local Mappings (if any).

5.2.3.2. Connection Termination Notification to the iSCSI layer

 If the iSCSI/iSER connection is terminated without the invocation of
 Connection_Terminate from the iSCSI layer, the iSER layer MUST notify
 the iSCSI layer that the iSCSI/iSER connection has been terminated by
 invoking the Connection_Terminate_Notify Operational Primitive.
 Prior to invoking Connection_Terminate_Notify, the iSER layer at the
 target MUST deallocate all connection and task resources (if any)
 associated with the connection, and invalidate the Local and Remote
 Mappings (if any).

Ko & Nezhinsky Standards Track [Page 37] RFC 7145 iSER Specification April 2014

 Prior to invoking Connection_Terminate_Notify, the iSER layer at the
 initiator MUST deallocate all connection and task resources (if any)
 associated with the connection, and invalidate the Local Mappings (if
 any).
 If the remote iSCSI/iSER node initiated the closing of the connection
 (e.g., by sending a TCP FIN or TCP RST), the iSER layer MUST notify
 the iSCSI layer after the RCaP layer reports that the connection is
 closed by invoking the Connection_Terminate_Notify Operational
 Primitive.
 Another example of a connection termination without a preceding
 logout is when the iSCSI layer at the initiator does an implicit
 logout (connection reinstatement).

6. Login/Text Operational Keys

 Certain iSCSI login/text operational keys have restricted usage in
 iSER, and additional keys are used to support the iSER protocol
 functionality.  All other keys defined in [iSCSI] and not discussed
 in this section may be used on iSCSI/iSER connections with the same
 semantics.

6.1. HeaderDigest and DataDigest

 Irrelevant when: RDMAExtensions=Yes
 Negotiations resulting in RDMAExtensions=Yes for a session imply
 HeaderDigest=None and DataDigest=None for all connections in that
 session and override the settings, whether default or configured.

6.2. MaxRecvDataSegmentLength

 For an iSCSI connection belonging to a session in which
 RDMAExtensions=Yes was negotiated on the leading connection of the
 session, MaxRecvDataSegmentLength need not be declared in the Login
 Phase, and MUST be ignored if it is declared.  Instead,
 InitiatorRecvDataSegmentLength (as described in Section 6.5) and
 TargetRecvDataSegmentLength (as described in Section 6.4) keys are
 negotiated.  The values of the local and remote
 MaxRecvDataSegmentLength are derived from the
 InitiatorRecvDataSegmentLength and TargetRecvDataSegmentLength keys.
 In the Full Feature Phase, the initiator MUST consider the value of
 its local MaxRecvDataSegmentLength (that it would have declared to
 the target) as having the value of InitiatorRecvDataSegmentLength,
 and the value of the remote MaxRecvDataSegmentLength (that would have
 been declared by the target) as having the value of

Ko & Nezhinsky Standards Track [Page 38] RFC 7145 iSER Specification April 2014

 TargetRecvDataSegmentLength.  Similarly, the target MUST consider the
 value of its local MaxRecvDataSegmentLength (that it would have
 declared to the initiator) as having the value of
 TargetRecvDataSegmentLength, and the value of the remote
 MaxRecvDataSegmentLength (that would have been declared by the
 initiator) as having the value of InitiatorRecvDataSegmentLength.
 Note that RFC 3720 requires that when a target receives a NOP-Out
 request with a valid Initiator Task Tag, it responds with a NOP-In
 with the same Initiator Task Tag that was provided in the NOP-Out
 request.  Furthermore, it returns the first MaxRecvDataSegmentLength
 bytes of the initiator-provided Ping Data.  Since there is no
 MaxRecvDataSegmentLength common to the initiator and the target in
 iSER, the length of the data sent with the NOP-Out request MUST NOT
 exceed InitiatorMaxRecvDataSegmentLength.
 The MaxRecvDataSegmentLength key is applicable only for iSCSI
 control-type PDUs.

6.3. RDMAExtensions

 Use: LO (leading only)
 Senders: Initiator and Target
 Scope: SW (session-wide)
 RDMAExtensions=<boolean-value>
 Irrelevant when: SessionType=Discovery
 Default is No
 Result function is AND
 This key is used by the initiator and the target to negotiate the
 support for iSER-assisted mode.  To enable the use of iSER-assisted
 mode, both the initiator and the target MUST exchange
 RDMAExtensions=Yes.  iSER-assisted mode MUST NOT be used if either
 the initiator or the target offers RDMAExtensions=No.
 An iSER-enabled node is not required to initiate the RDMAExtensions
 key exchange if it prefers to operate in the Traditional iSCSI mode.
 However, if the RDMAExtensions key is to be negotiated, an initiator
 MUST offer the key in the first Login Request PDU in the
 LoginOperationalNegotiation stage of the leading connection, and a
 target MUST offer the key in the first Login Response PDU with which
 it is allowed to do so (i.e., the first Login Response PDU issued

Ko & Nezhinsky Standards Track [Page 39] RFC 7145 iSER Specification April 2014

 after the first Login Request PDU with the C bit set to zero) in the
 LoginOperationalNegotiation stage of the leading connection.  In
 response to the offered key=value pair of RDMAExtensions=yes, an
 initiator MUST respond in the next Login Request PDU with which it is
 allowed to do so, and a target MUST respond in the next Login
 Response PDU with which it is allowed to do so.
 Negotiating the RDMAExtensions key first enables a node to negotiate
 the optimal value for other keys.  Certain iSCSI keys such as
 MaxBurstLength, MaxOutstandingR2T, ErrorRecoveryLevel, InitialR2T,
 ImmediateData, etc., may be negotiated differently depending on
 whether the connection is in Traditional iSCSI mode or iSER-assisted
 mode.

6.4. TargetRecvDataSegmentLength

 Use: IO (Initialize only)
 Senders: Initiator and Target
 Scope: CO (connection-only)
 Irrelevant when: RDMAExtensions=No
 TargetRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)>
 Default is 8192 bytes
 Result function is minimum
 This key is relevant only for the iSCSI connection of an iSCSI
 session if RDMAExtensions=Yes was negotiated on the leading
 connection of the session.  It is used by the initiator and the
 target to negotiate the maximum size of the data segment that an
 initiator may send to the target in an iSCSI control-type PDU in the
 Full Feature Phase.  For SCSI Command PDUs and SCSI Data-Out PDUs
 containing non-immediate unsolicited data to be sent by the
 initiator, the initiator MUST send all non-Final PDUs with a data
 segment size of exactly TargetRecvDataSegmentLength whenever the PDUs
 constitute a data sequence whose size is larger than
 TargetRecvDataSegmentLength.

Ko & Nezhinsky Standards Track [Page 40] RFC 7145 iSER Specification April 2014

6.5. InitiatorRecvDataSegmentLength

 Use: IO (Initialize only)
 Senders: Initiator and Target
 Scope: CO (connection-only)
 Irrelevant when: RDMAExtensions=No
 InitiatorRecvDataSegmentLength=<numerical-value-512-to-(2**24-1)>
 Default is 8192 bytes
 Result function is minimum
 This key is relevant only for the iSCSI connection of an iSCSI
 session if RDMAExtensions=Yes was negotiated on the leading
 connection of the session.  It is used by the initiator and the
 target to negotiate the maximum size of the data segment that a
 target may send to the initiator in an iSCSI control-type PDU in the
 Full Feature Phase.

6.6. OFMarker and IFMarker

 Irrelevant when: RDMAExtensions=Yes
 Negotiations resulting in RDMAExtensions=Yes for a session imply
 OFMarker=No and IFMarker=No for all connections in that session and
 override the settings, whether default or configured.

6.7. MaxOutstandingUnexpectedPDUs

 Use: LO (leading only), Declarative
 Senders: Initiator and Target
 Scope: SW (session-wide)
 Irrelevant when: RDMAExtensions=No
 MaxOutstandingUnexpectedPDUs=
    <numerical-value-from-2-to-(2**32-1) | 0>
 Default is 0

Ko & Nezhinsky Standards Track [Page 41] RFC 7145 iSER Specification April 2014

 This key is used by the initiator and the target to declare the
 maximum number of outstanding "unexpected" iSCSI control-type PDUs
 that it can receive in the Full Feature Phase.  It is intended to
 allow the receiving side to determine the amount of buffer resources
 needed beyond the normal flow control mechanism available in iSCSI.
 An initiator or target should select a value such that it would not
 impose an unnecessary constraint on the iSCSI layer under normal
 circumstances.  The value of 0 is defined to indicate that the
 declarer has no limit on the maximum number of outstanding
 "unexpected" iSCSI control-type PDUs that it can receive.  See
 Sections 8.1.1 and 8.1.2 for the usage of this key.  Note that iSER
 Hello and HelloReply Messages are not iSCSI control-type PDUs and are
 not affected by this key.
 For interoperability with implementations based on [RFC5046], this
 key SHOULD be negotiated because the default value of 0 in [RFC5046]
 is problematic for most implementations as it does not impose a bound
 on resources consumable by unexpected PDUs.

6.8. MaxAHSLength

 Use: LO (leading only), Declarative
 Senders: Initiator and Target
 Scope: SW (session-wide)
 Irrelevant when: RDMAExtensions=No
 MaxAHSLength=<numerical-value-from-2-to-(2**32-1) | 0>
 Default is 256
 This key is used by the initiator and target to declare the maximum
 size of AHS in an iSCSI control-type PDU that it can receive in the
 Full Feature Phase.  It is intended to allow the receiving side to
 determine the amount of resources needed for receive buffering.  An
 initiator or target should select a value such that it would not
 impose an unnecessary constraint on the iSCSI layer under normal
 circumstances.  The value of 0 is defined to indicate that the
 declarer has no limit on the maximum size of AHS in iSCSI control-
 type PDUs that it can receive.
 For interoperability with implementations based on [RFC5046], an
 initiator or target MAY terminate the connection if it anticipates
 MaxAHSLength to be greater than 256 and the key is not understood by
 its peer.

Ko & Nezhinsky Standards Track [Page 42] RFC 7145 iSER Specification April 2014

6.9. TaggedBufferForSolicitedDataOnly

 Use: LO (leading only), Declarative
 Senders: Initiator
 Scope: SW (session-wide)
 RDMAExtensions=<boolean-value>
 Irrelevant when: RDMAExtensions=No
 Default is No
 This key is used by the initiator to declare to the target the usage
 of the Write Base Offset in the iSER header of an iSCSI control-type
 PDU.  When set to No, the Base Offset is associated with an I/O
 buffer that contains all the write data, including both unsolicited
 and solicited data.  When set to Yes, the Base Offset is associated
 with an I/O buffer that only contains solicited data.

6.10. iSERHelloRequired

 Use: LO (leading only), Declarative
 Senders: Initiator
 Scope: SW (session-wide)
 RDMAExtensions=<boolean-value>
 Irrelevant when: RDMAExtensions=No
 Default is No
 This key is relevant only for the iSCSI connection of an iSCSI
 session if RDMAExtensions=Yes was negotiated on the leading
 connection of the session.  It is used by the initiator to declare to
 the target whether the iSER Hello Exchange is required.  When set to
 Yes, the iSER layers MUST perform the iSER Hello Exchange as
 described in Section 5.1.3.  When set to No, the iSER layers MUST NOT
 perform the iSER Hello Exchange.

Ko & Nezhinsky Standards Track [Page 43] RFC 7145 iSER Specification April 2014

7. iSCSI PDU Considerations

 When a connection is in the iSER-assisted mode, two types of message
 transfers are allowed between the iSCSI layer (at the initiator) and
 the iSCSI layer (at the target).  These are known as the iSCSI data-
 type PDUs and the iSCSI control-type PDUs, and these terms are
 described in the following sections.

7.1. iSCSI Data-Type PDU

 An iSCSI data-type PDU is defined as an iSCSI PDU that causes data
 transfer, transparent to the remote iSCSI layer, to take place
 between the peer iSCSI nodes in the Full Feature Phase of an
 iSCSI/iSER connection.  An iSCSI data-type PDU, when requested for
 transmission by the iSCSI layer in the sending node, results in the
 data's transfer without the participation of the iSCSI layers at the
 sending and the receiving nodes.  This is due to the fact that the
 PDU itself is not delivered as-is to the iSCSI layer in the receiving
 node.  Instead, the data transfer operations are transformed into the
 appropriate RDMA operations, which are handled by the RDMA-Capable
 Controller.  The set of iSCSI data-type PDUs consists of SCSI Data-In
 PDUs and R2T PDUs.
 If the invocation of the Operational Primitive by the iSCSI layer to
 request the iSER layer to process an iSCSI data-type PDU is qualified
 with Notify_Enable set, then upon completing the RDMA operation, the
 iSER layer at the target MUST notify the iSCSI layer at the target by
 invoking the Data_Completion_Notify Operational Primitive qualified
 with the ITT and SN.  There is no data completion notification at the
 initiator since the RDMA operations are completely handled by the
 RDMA-Capable Controller at the initiator and the iSER layer at the
 initiator is not involved with the data transfer associated with
 iSCSI data-type PDUs.
 If the invocation of the Operational Primitive by the iSCSI layer to
 request the iSER layer to process an iSCSI data-type PDU is qualified
 with Notify_Enable cleared, then upon completing the RDMA operation,
 the iSER layer at the target MUST NOT notify the iSCSI layer at the
 target and MUST NOT invoke the Data_Completion_Notify Operational
 Primitive.
 If an operation associated with an iSCSI data-type PDU fails for any
 reason, the contents of the Data Sink buffers associated with the
 operation are considered indeterminate.

Ko & Nezhinsky Standards Track [Page 44] RFC 7145 iSER Specification April 2014

7.2. iSCSI Control-Type PDU

 Any iSCSI PDU that is not an iSCSI data-type PDU and also not a SCSI
 Data-Out PDU carrying solicited data is defined as an iSCSI control-
 type PDU.  The iSCSI layer invokes the Send_Control Operational
 Primitive to request the iSER layer to process an iSCSI control-type
 PDU.  iSCSI control-type PDUs are transferred using Send Messages of
 RCaP.  Specifically, it is to be noted that SCSI Data-Out PDUs
 carrying unsolicited data are defined as iSCSI control-type PDUs.
 See Section 7.3.4 on the treatment of SCSI Data-Out PDUs.
 When the iSER layer receives an iSCSI control-type PDU, it MUST
 notify the iSCSI layer by invoking the Control_Notify Operational
 Primitive qualified with the iSCSI control-type PDU.

7.3. iSCSI PDUs

 This section describes the handling of each of the iSCSI PDU types by
 the iSER layer.  The iSCSI layer requests the iSER layer to process
 the iSCSI PDU by invoking the appropriate Operational Primitive.  A
 Connection_Handle MUST qualify each of these invocations.  In
 addition, the BHS and the optional AHS of the iSCSI PDU as defined in
 [iSCSI] MUST qualify each of the invocations.  The qualifying
 Connection_Handle, the BHS, and the AHS are not explicitly listed in
 the subsequent sections.

7.3.1. SCSI Command

    Type:  control-type PDU
    PDU-specific qualifiers (for SCSI Write or bidirectional command):
    ImmediateDataSize, UnsolicitedDataSize, DataDescriptorOut
    PDU-specific qualifiers (for SCSI Read or bidirectional command):
    DataDescriptorIn
 The iSER layer at the initiator MUST send the SCSI command in a Send
 Message to the target.  The SendSE Message should be used if
 supported by the RCaP layer (e.g., iWARP).

Ko & Nezhinsky Standards Track [Page 45] RFC 7145 iSER Specification April 2014

 For a SCSI Write or bidirectional command, the iSCSI layer at the
 initiator MUST invoke the Send_Control Operational Primitive as
 follows:
  • If there is immediate data to be transferred for the SCSI write or

bidirectional command, the qualifier ImmediateDataSize MUST be

    used to define the number of bytes of immediate unsolicited data
    to be sent with the write or bidirectional command, and the
    qualifier DataDescriptorOut MUST be used to define the initiator's
    I/O Buffer containing the SCSI Write data.
  • If there is unsolicited data to be transferred for the SCSI Write

or bidirectional command, the qualifier UnsolicitedDataSize MUST

    be used to define the number of bytes of immediate and non-
    immediate unsolicited data for the command.  The iSCSI layer will
    issue one or more SCSI Data-Out PDUs for the non-immediate
    unsolicited data.  See Section 7.3.4 on SCSI Data-Out.
  • If there is solicited data to be transferred for the SCSI Write or

bidirectional command, as indicated when the Expected Data

    Transfer Length in the SCSI Command PDU exceeds the value of
    UnsolicitedDataSize, the iSER layer at the initiator MUST do the
    following:
    a. It MUST allocate a Write STag for the I/O Buffer defined by the
       qualifier DataDescriptorOut.  DataDescriptorOut describes the
       I/O buffer starting with the immediate unsolicited data (if
       any), followed by the non-immediate unsolicited data (if any)
       and solicited data.  When TaggedBufferForSolicitedDataOnly is
       negotiated to No, the Base Offset is associated with this I/O
       Buffer.  When TaggedBufferForSolicitedDataOnly is negotiated to
       Yes, the Base Offset is associated with an I/O Buffer that
       contains only solicited data.
    b. It MUST establish a Local Mapping that associates the Initiator
       Task Tag (ITT) to the Write STag.
    c. It MUST Advertise the Write STag and the Base Offset to the
       target by sending them in the iSER header of the iSER Message
       (the payload of the Send Message of RCaP) containing the SCSI
       Write or bidirectional command PDU.  The SendSE Message should
       be used if supported by the RCaP layer (e.g., iWARP).  See
       Section 9.2 on iSER Header Format for iSCSI Control-Type PDU.

Ko & Nezhinsky Standards Track [Page 46] RFC 7145 iSER Specification April 2014

 For a SCSI Read or bidirectional command, the iSCSI layer at the
 initiator MUST invoke the Send_Control Operational Primitive
 qualified with DataDescriptorIn, which defines the initiator's I/O
 Buffer for receiving the SCSI Read data.  The iSER layer at the
 initiator MUST do the following:
    a. It MUST allocate a Read STag for the I/O Buffer and note the
       Base Offset for this I/O Buffer.
    b. It MUST establish a Local Mapping that associates the Initiator
       Task Tag (ITT) to the Read STag.
    c. It MUST Advertise the Read STag and the Base Offset to the
       target by sending them in the iSER header of the iSER Message
       (the payload of the Send Message of RCaP) containing the SCSI
       Read or bidirectional command PDU.  The SendSE Message should
       be used if supported by the RCaP layer (e.g., iWARP).  See
       Section 9.2 on iSER Header Format for iSCSI Control-Type PDU.
 If the amount of unsolicited data to be transferred in a SCSI Command
 exceeds TargetRecvDataSegmentLength, then the iSCSI layer at the
 initiator MUST segment the data into multiple iSCSI control-type
 PDUs, with the data segment length in all generated PDUs (except the
 last one) having exactly the size TargetRecvDataSegmentLength.  The
 data segment length of the last iSCSI control-type PDU carrying the
 unsolicited data can be up to TargetRecvDataSegmentLength.
 When the iSER layer at the target receives the SCSI Command, it MUST
 establish a Remote Mapping that associates the ITT to the Base
 Offset(s) and the Advertised STag(s) in the iSER header.  The Write
 STag is used by the iSER layer at the target in handling the data
 transfer associated with the R2T PDU(s) as described in Section
 7.3.6.  The Read STag is used in handling the SCSI Data-In PDU(s)
 from the iSCSI layer at the target as described in Section 7.3.5.

7.3.2. SCSI Response

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorStatus
 The iSCSI layer at the target MUST invoke the Send_Control
 Operational Primitive qualified with DataDescriptorStatus, which
 defines the buffer containing the sense and response information.
 The iSCSI layer at the target MUST always return the SCSI status for
 a SCSI command in a separate SCSI Response PDU.  "Phase collapse" for

Ko & Nezhinsky Standards Track [Page 47] RFC 7145 iSER Specification April 2014

 transferring SCSI status in a SCSI Data-In PDU MUST NOT be used. The
 iSER layer at the target sends the SCSI Response PDU according to the
 following rules:
  • If no STags were Advertised by the initiator in the iSER Message

containing the SCSI command PDU, then the iSER layer at the target

    MUST send a Send Message containing the SCSI Response PDU.  The
    SendSE Message should be used if supported by the RCaP layer
    (e.g., iWARP).
  • If the initiator Advertised a Read STag in the iSER Message

containing the SCSI Command PDU, then the iSER layer at the target

    MUST send a Send Message containing the SCSI Response PDU.  The
    header of the Send Message MUST carry the Read STag to be
    invalidated at the initiator.  The Send with Invalidate Message,
    if supported by the RCaP layer (e.g., iWARP), can be used for the
    automatic invalidation of the STag.
  • If the initiator Advertised only the Write STag in the iSER

Message containing the SCSI command PDU, then the iSER layer at

    the target MUST send a Send Message containing the SCSI Response
    PDU.  The header of the Send Message MUST carry the Write STag to
    be invalidated at the initiator.  The Send with Invalidate
    Message, if supported by the RCaP layer (e.g., iWARP), can be used
    for the automatic invalidation of the STag.
 When the iSCSI layer at the target invokes the Send_Control
 Operational Primitive to send the SCSI Response PDU, the iSER layer
 at the target MUST invalidate the Remote Mapping before transferring
 the SCSI Response PDU to the initiator.
 Upon receiving a Send Message containing the SCSI Response PDU from
 the target, the iSER layer at the initiator MUST invalidate the
 STag(s) specified in the header.  (If a Send with Invalidate Message
 is supported by the RCaP layer (e.g., iWARP) and is used to carry the
 SCSI Response PDU, the RCaP layer at the initiator will invalidate
 the STag.  The iSER layer at the initiator MUST ensure that the
 correct STag is invalidated.  If both the Read and the Write STags
 were Advertised earlier by the initiator, then the iSER layer at the
 initiator MUST explicitly invalidate the Write STag upon receiving
 the Send with Invalidate Message because the header of the Send with
 Invalidate Message can only carry one STag (in this case, the Read
 STag) to be invalidated.)
 The iSER layer at the initiator MUST ensure the invalidation of the
 STag(s) used in a command before notifying the iSCSI layer at the
 initiator by invoking the Control_Notify Operational Primitive
 qualified with the SCSI Response.  This precludes the possibility of

Ko & Nezhinsky Standards Track [Page 48] RFC 7145 iSER Specification April 2014

 using the STag(s) after the completion of the command; such use would
 cause data corruption.
 When the iSER layer at the initiator receives a Send Message
 containing the SCSI Response PDU, it SHOULD invalidate the Local
 Mapping.  The iSER layer MUST ensure that all local STag(s)
 associated with the ITT are invalidated before notifying the iSCSI
 layer of the SCSI Response PDU by invoking the Control_Notify
 Operational Primitive qualified with the SCSI Response PDU.

7.3.3. Task Management Function Request/Response

    Type:  control-type PDU
    PDU-specific qualifiers (for TMF Request):  DataDescriptorOut,
    DataDescriptorIn
 The iSER layer MUST use a Send Message to send the Task Management
 Function Request/Response PDU.  The SendSE Message should be used if
 supported by the RCaP layer (e.g., iWARP).
 For the Task Management Function Request with the TASK REASSIGN
 function, the iSER layer at the initiator MUST do the following:
  • It MUST use the ITT as specified in the Referenced Task Tag from

the Task Management Function Request PDU to locate the existing

    STags (if any) in the Local Mappings.
  • It MUST invalidate the existing STags (if any) and the Local

Mappings.

  • It MUST allocate a Read STag for the I/O Buffer and note the Base

Offset associated with the I/O Buffer as defined by the qualifier

    DataDescriptorIn if the Send_Control Operational Primitive
    invocation is qualified with DataDescriptorIn.
  • It MUST allocate a Write STag for the I/O Buffer and note the Base

Offset associated with the I/O Buffer as defined by the qualifier

    DataDescriptorOut if the Send_Control Operational Primitive
    invocation is qualified with DataDescriptorOut.
  • If STags are allocated, it MUST establish new Local Mapping(s)

that associate the ITT to the allocated STag(s).

  • It MUST Advertise the STags and the Base Offsets, if allocated, to

the target in the iSER header of the Send Message carrying the

    iSCSI PDU, as described in Section 9.2.  The SendSE Message should
    be used if supported by the RCaP layer (e.g., iWARP).

Ko & Nezhinsky Standards Track [Page 49] RFC 7145 iSER Specification April 2014

 For the Task Management Function Request with the TASK REASSIGN
 function for a SCSI Read or bidirectional command, the iSCSI layer at
 the initiator MUST set ExpDataSN to zero since the data transfer and
 acknowledgements happen transparently to the iSCSI layer at the
 initiator.  This provides the flexibility to the iSCSI layer at the
 target to request transmission of only the unacknowledged data as
 specified in [iSCSI].
 When the iSER layer at the target receives the Task Management
 Function Request with the TASK REASSIGN function, it MUST do the
 following:
  • It MUST use the ITT as specified in the Referenced Task Tag from

the Task Management Function Request PDU to locate the Local and

    Remote Mappings (if any).
  • It MUST invalidate the local STags (if any) associated with the

ITT.

  • It MUST replace the Base Offset(s) and the Advertised STag(s) in

the Remote Mapping with the Base Offset(s) and the Advertised

    STag(s) in the iSER header.  The Write STag is used in the
    handling of the R2T PDU(s) from the iSCSI layer at the target as
    described in Section 7.3.6.  The Read STag is used in the handling
    of the SCSI Data-In PDU(s) from the iSCSI layer at the target as
    described in Section 7.3.5.

7.3.4. SCSI Data-Out

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorOut
 The iSCSI layer at the initiator MUST invoke the Send_Control
 Operational Primitive qualified with DataDescriptorOut, which defines
 the initiator's I/O Buffer containing unsolicited SCSI Write data.
 If the amount of unsolicited data to be transferred as SCSI Data-Out
 exceeds TargetRecvDataSegmentLength, then the iSCSI layer at the
 initiator MUST segment the data into multiple iSCSI control-type
 PDUs, where the DataSegmentLength has the value of
 TargetRecvDataSegmentLength in all generated PDUs except the last
 one.  The DataSegmentLength of the last iSCSI control-type PDU
 carrying the unsolicited data can be up to
 TargetRecvDataSegmentLength.  The iSCSI layer at the target MUST
 perform the reassembly function for the unsolicited data.

Ko & Nezhinsky Standards Track [Page 50] RFC 7145 iSER Specification April 2014

 For unsolicited data, the iSER layer at the initiator MUST use a Send
 Message to send the SCSI Data-Out PDU.  If the F bit is set to 1, the
 SendSE Message should be used if supported by the RCaP layer (e.g.,
 iWARP).
 Note that for solicited data, the SCSI Data-Out PDUs are not used
 since R2T PDUs are not delivered to the iSCSI layer at the initiator;
 instead, R2T PDUs are transformed by the iSER layer at the target
 into RDMA Read operations.  (See Section 7.3.6.)

7.3.5. SCSI Data-In

    Type:  data-type PDU
    PDU-specific qualifiers:  DataDescriptorIn
 When the iSCSI layer at the target is ready to return the SCSI Read
 data to the initiator, it MUST invoke the Put_Data Operational
 Primitive qualified with DataDescriptorIn, which defines the SCSI
 Data-In buffer.  See Section 7.1 on the general requirement on the
 handling of iSCSI data-type PDUs.  SCSI Data-In PDU(s) are used in
 SCSI Read data transfer as described in Section 9.5.2.
 The iSER layer at the target MUST do the following for each
 invocation of the Put_Data Operational Primitive:
 1. It MUST use the ITT in the SCSI Data-In PDU to locate the remote
    Read STag and the Base Offset in the Remote Mapping.  The Remote
    Mapping was established earlier by the iSER layer at the target
    when the SCSI Read Command was received from the initiator.
 2. It MUST generate and send an RDMA Write Message containing the
    read data to the initiator.
    a. It MUST use the remote Read STag as the Data Sink STag of the
       RDMA Write Message.
    b. It MUST add the Buffer Offset from the SCSI Data-In PDU to the
       Base Offset from the Remote Mapping as the Data Sink Tagged
       Offset of the RDMA Write Message.
    c. It MUST use DataSegmentLength from the SCSI Data-In PDU to
       determine the amount of data to be sent in the RDMA Write
       Message.
 3. It MUST associate the DataSN and ITT from the SCSI Data-In PDU
    with the RDMA Write operation.  If the Put_Data Operational
    Primitive invocation was qualified with Notify_Enable set, then

Ko & Nezhinsky Standards Track [Page 51] RFC 7145 iSER Specification April 2014

    when the iSER layer at the target receives a completion from the
    RCaP layer for the RDMA Write Message, the iSER layer at the
    target MUST notify the iSCSI layer by invoking the
    Data_Completion_Notify Operational Primitive qualified with the
    DataSN and ITT.  Conversely, if the Put_Data Operational Primitive
    invocation was qualified with Notify_Enable cleared, then the iSER
    layer at the target MUST NOT notify the iSCSI layer on completion
    and MUST NOT invoke the Data_Completion_Notify Operational
    Primitive.
 When the A-bit is set to one in the SCSI Data-In PDU, the iSER layer
 at the target MUST notify the iSCSI layer at the target when the data
 transfer is complete at the initiator.  To perform this additional
 function, the iSER layer at the target can take advantage of the
 operational ErrorRecoveryLevel if previously disclosed by the iSCSI
 layer via an earlier invocation of the Notice_Key_Values Operational
 Primitive.  There are two approaches that can be taken:
 1. If the iSER layer at the target knows that the operational
    ErrorRecoveryLevel is 2, or if the iSER layer at the target does
    not know the operational ErrorRecoveryLevel, then the iSER layer
    at the target MUST issue a zero-length RDMA Read Request Message
    following the RDMA Write Message.  When the iSER layer at the
    target receives a completion for the RDMA Read Request Message
    from the RCaP layer, implying that the RDMA-Capable Controller at
    the initiator has completed processing the RDMA Write Message due
    to the completion ordering semantics of RCaP, the iSER layer at
    the target MUST notify the iSCSI layer at the target by invoking
    the Data_ACK_Notify Operational Primitive qualified with ITT and
    DataSN (see Section 3.2.3).
 2. If the iSER layer at the target knows that the operational
    ErrorRecoveryLevel is 1, then the iSER layer at the target MUST do
    one of the following:
    a. It MUST notify the iSCSI layer at the target by invoking the
       Data_ACK_Notify Operational Primitive qualified with ITT and
       DataSN (see Section 3.2.3) when it receives the local
       completion from the RCaP layer for the RDMA Write Message.
       This is allowed since digest errors do not occur in iSER (see
       Section 10.1.4.2) and a CRC error will cause the connection to
       be terminated and the task to be terminated anyway.  The local
       RDMA Write completion from the RCaP layer guarantees that the
       RCaP layer will not access the I/O Buffer again to transfer the
       data associated with that RDMA Write operation.

Ko & Nezhinsky Standards Track [Page 52] RFC 7145 iSER Specification April 2014

    b. Alternatively, it MUST use the same procedure for handling the
       data transfer completion at the initiator as for
       ErrorRecoveryLevel 2.
 It should be noted that the iSCSI layer at the target cannot set the
 A-bit to 1 if the ErrorRecoveryLevel=0.
 SCSI status MUST always be returned in a separate SCSI Response PDU.
 The S bit in the SCSI Data-In PDU MUST always be set to zero.  There
 MUST NOT be a "phase collapse" in the SCSI Data-In PDU.
 Since the RDMA Write Message only transfers the data portion of the
 SCSI Data-In PDU but not the control information in the header, such
 as ExpCmdSN, if timely updates of such information are crucial, the
 iSCSI layer at the initiator MAY issue NOP-Out PDUs to request the
 iSCSI layer at the target to respond with the information using
 NOP-In PDUs.

7.3.6. Ready To Transfer (R2T)

    Type:  data-type PDU
    PDU-specific qualifiers:  DataDescriptorOut
 In order to send an R2T PDU, the iSCSI layer at the target MUST
 invoke the Get_Data Operational Primitive qualified with
 DataDescriptorOut, which defines the I/O Buffer for receiving the
 SCSI Write data from the initiator.  See Section 7.1 on the general
 requirements on the handling of iSCSI data-type PDUs.
 The iSER layer at the target MUST do the following for each
 invocation of the Get_Data Operational Primitive:
 1. It MUST ensure a valid local STag for the I/O Buffer and a valid
    Local Mapping.  This may involve allocating a valid local STag and
    establishing a Local Mapping.
 2. It MUST use the ITT in the R2T to locate the remote Write STag and
    the Base Offset in the Remote Mapping.  The Remote Mapping was
    established earlier by the iSER layer at the target when the iSER
    Message containing the Advertised Write STag, the Base Offset, and
    the SCSI Command PDU for a SCSI Write or bidirectional command was
    received from the initiator.
 3. If the iSER-ORD value at the target is set to zero, the iSER layer
    at the target MUST terminate the connection and free up the
    resources associated with the connection (as described in Section
    5.2.3) if it received the R2T PDU from the iSCSI layer at the

Ko & Nezhinsky Standards Track [Page 53] RFC 7145 iSER Specification April 2014

    target.  Upon termination of the connection, the iSER layer at the
    target MUST notify the iSCSI layer at the target by invoking the
    Connection_Terminate_Notify Operational Primitive.
 4. If the iSER-ORD value at the target is set to greater than 0, the
    iSER layer at the target MUST transform the R2T PDU into an RDMA
    Read Request Message.  While transforming the R2T PDU, the iSER
    layer at the target MUST ensure that the number of outstanding
    RDMA Read Request Messages does not exceed the iSER-ORD value.  To
    transform the R2T PDU, the iSER layer at the target:
    a. MUST derive the local STag and local Tagged Offset from the
       DataDescriptorOut that qualified the Get_Data invocation.
    b. MUST use the local STag as the Data Sink STag of the RDMA Read
       Request Message.
    c. MUST use the local Tagged Offset as the Data Sink Tagged Offset
       of the RDMA Read Request Message.
    d. MUST use the Desired Data Transfer Length from the R2T PDU as
       the RDMA Read Message Size of the RDMA Read Request Message.
    e. MUST use the remote Write STag as the Data Source STag of the
       RDMA Read Request Message.
    f. MUST add the Buffer Offset from the R2T PDU to the Base Offset
       from the Remote Mapping as the Data Source Tagged Offset of the
       RDMA Read Request Message.
 5. It MUST associate the R2TSN and ITT from the R2T PDU with the RDMA
    Read operation.  If the Get_Data Operational Primitive invocation
    was qualified with Notify_Enable set, then when the iSER layer at
    the target receives a completion from the RCaP layer for the RDMA
    Read operation, the iSER layer at the target MUST notify the iSCSI
    layer by invoking the Data_Completion_Notify Operational Primitive
    qualified with the R2TSN and ITT.  Conversely, if the Get_Data
    Operational Primitive invocation was qualified with Notify_Enable
    cleared, then the iSER layer at the target MUST NOT notify the
    iSCSI layer on completion and MUST NOT invoke the
    Data_Completion_Notify Operational Primitive.
 When the RCaP layer at the initiator receives a valid RDMA Read
 Request Message, it will return an RDMA Read Response Message
 containing the solicited write data to the target.  When the RCaP
 layer at the target receives the RDMA Read Response Message from the
 initiator, it will place the solicited data in the I/O Buffer
 referenced by the Data Sink STag in the RDMA Read Response Message.

Ko & Nezhinsky Standards Track [Page 54] RFC 7145 iSER Specification April 2014

 Since the RDMA Read Request Message from the target does not transfer
 the control information in the R2T PDU such as ExpCmdSN, if timely
 updates of such information are crucial, the iSCSI layer at the
 initiator MAY issue NOP-Out PDUs to request the iSCSI layer at the
 target to respond with the information using NOP-In PDUs.
 Similarly, since the RDMA Read Response Message from the initiator
 only transfers the data but not the control information normally
 found in the SCSI Data-Out PDU, such as ExpStatSN, if timely updates
 of such information are crucial, the iSCSI layer at the target MAY
 issue NOP-In PDUs to request the iSCSI layer at the initiator to
 respond with the information using NOP-Out PDUs.

7.3.7. Asynchronous Message

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorSense
 The iSCSI layer MUST invoke the Send_Control Operational Primitive
 qualified with DataDescriptorSense, which defines the buffer
 containing the sense and iSCSI event information.  The iSER layer
 MUST use a Send Message to send the Asynchronous Message PDU.  The
 SendSE Message should be used if supported by the RCaP layer (e.g.,
 iWARP).

7.3.8. Text Request and Text Response

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorTextOut (for Text
    Request), DataDescriptorIn (for Text Response)
 The iSCSI layer MUST invoke the Send_Control Operational Primitive
 qualified with DataDescriptorTextOut (or DataDescriptorIn), which
 defines the Text Request (or Text Response) buffer.  The iSER layer
 MUST use Send Messages to send the Text Request (or Text Response
 PDUs).  The SendSE Message should be used if supported by the RCaP
 layer (e.g., iWARP).

7.3.9. Login Request and Login Response

 During the login negotiation, the iSCSI layer interacts with the
 transport layer directly, and the iSER layer is not involved.  See
 Section 5.1 on iSCSI/iSER Connection Setup.  If the underlying
 transport is TCP, the Login Request PDUs and the Login Response PDUs
 are exchanged when the connection between the initiator and the
 target is still in the byte stream mode.

Ko & Nezhinsky Standards Track [Page 55] RFC 7145 iSER Specification April 2014

 The iSCSI layer MUST NOT send a Login Request (or a Login Response)
 PDU during the Full Feature Phase.  A Login Request (or a Login
 Response) PDU, if used, MUST be treated as an iSCSI protocol error.
 The iSER layer MAY reject such a PDU from the iSCSI layer with an
 appropriate error code.  If a Login Request PDU is received by the
 iSCSI layer at the target, it MUST respond with a Reject PDU with a
 reason code of "protocol error".

7.3.10. Logout Request and Logout Response

    Type:  control-type PDU
    PDU-specific qualifiers:  None
 The iSER layer MUST use a Send Message to send the Logout Request or
 Logout Response PDU.  The SendSE Message should be used if supported
 by the RCaP layer (e.g., iWARP).  Sections 5.2.1 and 5.2.2 describe
 the handling of the Logout Request and the Logout Response at the
 initiator and the target and the interactions between the initiator
 and the target to terminate a connection.

7.3.11. SNACK Request

 Since HeaderDigest and DataDigest must be negotiated to "None", there
 are no digest errors when the connection is in iSER-assisted mode.
 Also, since RCaP delivers all messages in the order they were sent,
 there are no sequence errors when the connection is in iSER-assisted
 mode.  Therefore, the iSCSI layer MUST NOT send SNACK Request PDUs.
 A SNACK Request PDU, if used, MUST be treated as an iSCSI protocol
 error.  The iSER layer MAY reject such a PDU from the iSCSI layer
 with an appropriate error code.  If a SNACK Request PDU is received
 by the iSCSI layer at the target, it MUST respond with a Reject PDU
 with a reason code of "protocol error".

7.3.12. Reject

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorReject
 The iSCSI layer MUST invoke the Send_Control Operational Primitive
 qualified with DataDescriptorReject, which defines the Reject buffer.
 The iSER layer MUST use a Send Message to send the Reject PDU.  The
 SendSE Message should be used if supported by the RCaP layer (e.g.,
 iWARP).

Ko & Nezhinsky Standards Track [Page 56] RFC 7145 iSER Specification April 2014

7.3.13. NOP-Out and NOP-In

    Type:  control-type PDU
    PDU-specific qualifiers:  DataDescriptorNOPOut (for NOP-Out),
    DataDescriptorNOPIn (for NOP-In)
 The iSCSI layer MUST invoke the Send_Control Operational Primitive
 qualified with DataDescriptorNOPOut (or DataDescriptorNOPIn), which
 defines the Ping (or Return Ping) data buffer.  The iSER layer MUST
 use Send Messages to send the NOP-Out (or NOP-In) PDU.  The SendSE
 Message should be used if supported by the RCaP layer (e.g., iWARP).

8. Flow Control and STag Management

8.1. Flow Control for RDMA Send Messages

 Send Messages in RCaP are used by the iSER layer to transfer iSCSI
 control-type PDUs.  Each Send Message in RCaP consumes an Untagged
 Buffer at the Data Sink.  However, neither the RCaP layer nor the
 iSER layer provides an explicit flow control mechanism for the Send
 Messages.  Therefore, the iSER layer SHOULD provision enough Untagged
 buffers for handling incoming Send Messages to prevent buffer
 exhaustion at the RCaP layer.  If buffer exhaustion occurs, it may
 result in the termination of the connection.
 An implementation may choose to satisfy the buffer requirement by
 using a common buffer pool shared across multiple connections, with
 usage limits on a per-connection basis and usage limits on the buffer
 pool itself.  In such an implementation, exceeding the buffer usage
 limit for a connection or the buffer pool itself may trigger
 interventions from the iSER layer to replenish the buffer pool and/or
 to isolate the connection causing the problem.
 iSER also provides the MaxOutstandingUnexpectedPDUs key to be used by
 the initiator and the target to declare the maximum number of
 outstanding "unexpected" control-type PDUs that it can receive.  It
 is intended to allow the receiving side to determine the amount of
 buffer resources needed beyond the normal flow control mechanism
 available in iSCSI.
 The buffer resources required at both the initiator and the target as
 a result of control-type PDUs sent by the initiator are described in
 Section 8.1.1.  The buffer resources required at both the initiator
 and target as a result of control-type PDUs sent by the target are
 described in Section 8.1.2.

Ko & Nezhinsky Standards Track [Page 57] RFC 7145 iSER Specification April 2014

8.1.1. Flow Control for Control-Type PDUs from the Initiator

 The control-type PDUs that can be sent by an initiator to a target
 can be grouped into the following categories:
 1. Regulated:  Control-type PDUs in this category are regulated by
    the iSCSI CmdSN window mechanism, and the immediate flag is not
    set.
 2. Unregulated but Expected:  Control-type PDUs in this category are
    not regulated by the iSCSI CmdSN window mechanism but are expected
    by the target.
 3. Unregulated and Unexpected:  Control-type PDUs in this category
    are not regulated by the iSCSI CmdSN window mechanism and are
    "unexpected" by the target.

8.1.1.1. Control-Type PDUs from the Initiator in the Regulated Category

 Control-type PDUs that can be sent by the initiator in this category
 are regulated by the iSCSI CmdSN window mechanism, and the immediate
 flag is not set.
 The queuing capacity required of the iSCSI layer at the target is
 described in Section 4.2.2.1 of [iSCSI].  For each of the control-
 type PDUs that can be sent by the initiator in this category, the
 initiator MUST provision for the buffer resources required for the
 corresponding control-type PDU sent as a response from the target.
 The following is a list of the PDUs that can be sent by the initiator
 and the PDUs that are sent by the target in response:
    a. When an initiator sends a SCSI Command PDU, it expects a SCSI
       Response PDU from the target.
    b. When the initiator sends a Task Management Function Request
       PDU, it expects a Task Management Function Response PDU from
       the target.
    c. When the initiator sends a Text Request PDU, it expects a Text
       Response PDU from the target.
    d. When the initiator sends a Logout Request PDU, it expects a
       Logout Response PDU from the target.
    e. When the initiator sends a NOP-Out PDU as a ping request with
       ITT != 0xffffffff and TTT = 0xffffffff, it expects a NOP-In PDU
       from the target with the same ITT and TTT as in the ping
       request.

Ko & Nezhinsky Standards Track [Page 58] RFC 7145 iSER Specification April 2014

 The response from the target for any of the PDUs enumerated here may
 alternatively be in the form of a Reject PDU sent before the task is
 active, as described in Section 7.3 of [iSCSI].

8.1.1.2. Control-Type PDUs from the Initiator in the Unregulated but

        Expected Category
 For the control-type PDUs in the Unregulated but Expected category,
 the amount of buffering resources required at the target can be
 predetermined.  The following is a list of the PDUs in this category:
    a. SCSI Data-Out PDUs are used by the initiator to send
       unsolicited data.  The amount of buffer resources required by
       the target can be determined using FirstBurstLength.  Note that
       SCSI Data-Out PDUs are not used for solicited data since the
       R2T PDU, which is used for solicitation, is transformed into
       RDMA Read operations by the iSER layer at the target.  See
       Section 7.3.4.
    b. A NOP-Out PDU with TTT != 0xffffffff is sent as a ping response
       by the initiator to the NOP-In PDU sent as a ping request by
       the target.

8.1.1.3. Control-Type PDUs from the Initiator in the Unregulated and

        Unexpected Category
 PDUs in the Unregulated and Unexpected category are PDUs with the
 immediate flag set.  The number of PDUs that are in this category and
 can be sent by an initiator is controlled by the value of
 MaxOutstandingUnexpectedPDUs declared by the target.  (See Section
 6.7.)  After a PDU in this category is sent by the initiator, it is
 outstanding until it is retired.  At any time, the number of
 outstanding unexpected PDUs MUST NOT exceed the value of
 MaxOutstandingUnexpectedPDUs declared by the target.
 The target uses the value of MaxOutstandingUnexpectedPDUs that it
 declared to determine the amount of buffer resources required for
 control-type PDUs in this category that can be sent by an initiator.
 For the initiator, for each of the control-type PDUs that can be sent
 in this category, the initiator MUST provision for the buffer
 resources if required for the corresponding control-type PDU that can
 be sent as a response from the target.
 An outstanding PDU in this category is retired as follows.  If the
 CmdSN of the PDU sent by the initiator in this category is x, the PDU
 is outstanding until the initiator sends a non-immediate control-type

Ko & Nezhinsky Standards Track [Page 59] RFC 7145 iSER Specification April 2014

 PDU on the same connection with CmdSN = y (where y is at least x) and
 the target responds with a control-type PDU on any connection where
 ExpCmdSN is at least y+1.
 When the number of outstanding unexpected control-type PDUs equals
 MaxOutstandingUnexpectedPDUs, the iSCSI layer at the initiator MUST
 NOT generate any unexpected PDUs, which otherwise it would have
 generated, even if the unexpected PDU is intended for immediate
 delivery.

8.1.2. Flow Control for Control-Type PDUs from the Target

 Control-type PDUs that can be sent by a target and are expected by
 the initiator are listed in the Regulated category.  (See Section
 8.1.1.1.)
 For the control-type PDUs that can be sent by a target and are
 unexpected by the initiator, the number is controlled by
 MaxOutstandingUnexpectedPDUs declared by the initiator.  (See Section
 6.7.)  After a PDU in this category is sent by a target, it is
 outstanding until it is retired.  At any time, the number of
 outstanding unexpected PDUs MUST NOT exceed the value of
 MaxOutstandingUnexpectedPDUs declared by the initiator.  The
 initiator uses the value of MaxOutstandingUnexpectedPDUs that it
 declared to determine the amount of buffer resources required for
 control-type PDUs in this category that can be sent by a target.  The
 following is a list of the PDUs in this category and the conditions
 for retiring the outstanding PDU:
    a. For an Asynchronous Message PDU with StatSN = x, the PDU is
       outstanding until the initiator sends a control-type PDU with
       ExpStatSN set to at least x+1.
    b. For a Reject PDU with StatSN = x, which is sent after a task is
       active, the PDU is outstanding until the initiator sends a
       control-type PDU with ExpStatSN set to at least x+1.
    c. For a NOP-In PDU with ITT = 0xffffffff and StatSN = x, the PDU
       is outstanding until the initiator responds with a control-type
       PDU on the same connection where ExpStatSN is at least x+1.
       But if the NOP-In PDU is sent as a ping request with
       TTT != 0xffffffff, the PDU can also be retired when the
       initiator sends a NOP-Out PDU with the same ITT and TTT as in
       the ping request.  Note that when a target sends a NOP-In PDU
       as a ping request, it must provision a buffer for the NOP-Out
       PDU sent as a ping response from the initiator.

Ko & Nezhinsky Standards Track [Page 60] RFC 7145 iSER Specification April 2014

 When the number of outstanding unexpected control-type PDUs equals
 MaxOutstandingUnexpectedPDUs, the iSCSI layer at the target MUST NOT
 generate any unexpected PDUs, which otherwise it would have
 generated, even if its intent is to indicate an iSCSI error condition
 (e.g., Asynchronous Message, Reject).  Task timeouts, as in the
 initiator's waiting for a command completion or other connection and
 session-level exceptions, will ensure that correct operational
 behavior will result in these cases despite not generating the PDU.
 This rule overrides any other requirements elsewhere that require
 that a Reject PDU MUST be sent.
 (Implementation note:  SCSI task timeout and recovery can be a
 lengthy process and hence SHOULD be avoided by proper provisioning of
 resources.)
 (Implementation note:  To ensure that the initiator has a means to
 inform the target that outstanding PDUs have been retired, the target
 should reserve the last unexpected control-type PDU allowable by the
 value of MaxOutstandingUnexpectedPDUs declared by the initiator for
 sending a NOP-In ping request with TTT != 0xffffffff to allow the
 initiator to return the NOP-Out ping response with the current
 ExpStatSN.)

8.2. Flow Control for RDMA Read Resources

 If iSERHelloRequired is negotiated to "Yes", then the total number of
 RDMA Read operations that can be active simultaneously on an
 iSCSI/iSER connection depends on the amount of resources allocated as
 declared in the iSER Hello exchange described in Section 5.1.3.
 Exceeding the number of RDMA Read operations allowed on a connection
 will result in the connection being terminated by the RCaP layer.
 The iSER layer at the target maintains the iSER-ORD to keep track of
 the maximum number of RDMA Read Requests that can be issued by the
 iSER layer on a particular RCaP Stream.
 During connection setup (see Section 5.1), iSER-IRD is known at the
 initiator and iSER-ORD is known at the target after the iSER layers
 at the initiator and the target have respectively allocated the
 connection resources necessary to support RCaP, as directed by the
 Allocate_Connection_Resources Operational Primitive from the iSCSI
 layer before the end of the iSCSI Login Phase.  In the Full Feature
 Phase, if iSERHelloRequired is negotiated to "Yes", then the first
 message sent by the initiator is the iSER Hello Message (see Section
 9.3), which contains the value of iSER-IRD.  In response to the iSER
 Hello Message, the target sends the iSER HelloReply Message (see
 Section 9.4), which contains the value of iSER-ORD.  The iSER layer
 at both the initiator and the target MAY adjust (lower) the resources
 associated with iSER-IRD and iSER-ORD, respectively, to match the

Ko & Nezhinsky Standards Track [Page 61] RFC 7145 iSER Specification April 2014

 iSER-ORD value declared in the HelloReply Message.  The iSER layer at
 the target MUST control the flow of the RDMA Read Request Messages so
 that it does not exceed the iSER-ORD value at the target.
 If iSERHelloRequired is negotiated to "No", then the maximum number
 of RDMA Read operations that can be active is negotiated via other
 means outside the scope of this document.  For example, in
 InfiniBand, iSER connection setup uses InfiniBand Connection Manager
 (CM) Management Datagrams (MADs), with additional iSER information
 exchanged in the private data.

8.3. STag Management

 An STag is an identifier of a Tagged Buffer used in an RDMA
 operation.  If the STags are exposed on the wire by being Advertised
 in the iSER header or declared in the header of an RCaP Message, then
 the allocation and the subsequent invalidation of the STags are as
 specified in this document.

8.3.1. Allocation of STags

 When the iSCSI layer at the initiator invokes the Send_Control
 Operational Primitive to request the iSER layer at the initiator to
 process a SCSI Command, zero, one, or two STags may be allocated by
 the iSER layer.  See Section 7.3.1 for details.  The number of STags
 allocated depends on whether the command is unidirectional or
 bidirectional and whether or not solicited write data transfer is
 involved.
 When the iSCSI layer at the initiator invokes the Send_Control
 Operational Primitive to request the iSER layer at the initiator to
 process a Task Management Function Request with the TASK REASSIGN
 function, besides allocating zero, one, or two STags, the iSER layer
 MUST invalidate the existing STags (if any) associated with the ITT.
 See Section 7.3.3 for details.
 The iSER layer at the target allocates a local Data Sink STag when
 the iSCSI layer at the target invokes the Get_Data Operational
 Primitive to request the iSER layer to process an R2T PDU.  See
 Section 7.3.6 for details.

8.3.2. Invalidation of STags

 The invalidation of the STags at the initiator at the completion of a
 unidirectional or bidirectional command when the associated SCSI
 Response PDU is sent by the target is described in Section 7.3.2.

Ko & Nezhinsky Standards Track [Page 62] RFC 7145 iSER Specification April 2014

 When a unidirectional or bidirectional command concludes without the
 associated SCSI Response PDU being sent by the target, the iSCSI
 layer at the initiator MUST request the iSER layer at the initiator
 to invalidate the STags by invoking the Deallocate_Task_Resources
 Operational Primitive qualified with ITT.  In response, the iSER
 layer at the initiator MUST locate the STags (if any) in the Local
 Mapping.  The iSER layer at the initiator MUST invalidate the STags
 (if any) and the Local Mapping.
 For an RDMA Read operation used to realize a SCSI Write data
 transfer, the iSER layer at the target SHOULD invalidate the Data
 Sink STag at the conclusion of the RDMA Read operation referencing
 the Data Sink STag (to permit the immediate reuse of buffer
 resources).
 For an RDMA Write operation used to realize a SCSI Read data
 transfer, the Data Source STag at the target is not declared to the
 initiator and is not exposed on the wire.  Invalidation of the STag
 is thus not specified.
 When a unidirectional or bidirectional command concludes without the
 associated SCSI Response PDU being sent by the target, the iSCSI
 layer at the target MUST request the iSER layer at the target to
 invalidate the STags by invoking the Deallocate_Task_Resources
 Operational Primitive qualified with ITT.  In response, the iSER
 layer at the target MUST locate the local STags (if any) in the Local
 Mapping.  The iSER layer at the target MUST invalidate the local
 STags (if any) and the Local Mapping.

Ko & Nezhinsky Standards Track [Page 63] RFC 7145 iSER Specification April 2014

9. iSER Control and Data Transfer

 For iSCSI data-type PDUs (see Section 7.1), the iSER layer uses RDMA
 Read and RDMA Write operations to transfer the solicited data.  For
 iSCSI control-type PDUs (see Section 7.2), the iSER layer uses Send
 Messages of RCaP.

9.1. iSER Header Format

 An iSER header MUST be present in every Send Message of RCaP.  The
 iSER header is located in the first 28 bytes of the message payload
 of the Send Message of RCaP, as shown in Figure 2.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | Opcode|                  Opcode Specific Fields               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Opcode Specific Fields (32 bits)           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                    Opcode Specific Fields (64 bits)           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                    Opcode Specific Fields (32 bits)           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                    Opcode Specific Fields (64 bits)           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                   Figure 2: iSER Header Format
 Opcode - Operation Code: 4 bits
       The Opcode field identifies the type of iSER Messages:
            0001b = iSCSI control-type PDU
            0010b = iSER Hello Message
            0011b = iSER HelloReply Message
            All other Opcodes are unassigned.

Ko & Nezhinsky Standards Track [Page 64] RFC 7145 iSER Specification April 2014

9.2. iSER Header Format for iSCSI Control-Type PDU

 The iSER layer uses Send Messages of RCaP to transfer iSCSI control-
 type PDUs (see Section 7.2).  The message payload of each of the Send
 Messages of RCaP used for transferring an iSER Message contains an
 iSER Header followed by an iSCSI control-type PDU.
 The iSER header in a Send Message of RCaP carrying an iSCSI control-
 type PDU MUST have the format as described in Figure 3.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       |W|R|                                                   |
 | 0001b |S|S|                  Reserved                         |
 |       |V|V|                                                   |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                            Write STag                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                         Write Base Offset                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                             Read STag                         |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                         Read Base Offset                      |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 3: iSER Header Format for iSCSI Control-Type PDU
 WSV - Write STag Valid flag: 1 bit
    This flag indicates the validity of the Write STag field and the
    Write Base Offset field of the iSER Header.  If set to one, the
    Write STag field and the Write Base Offset field in this iSER
    Header are valid.  If set to zero, the Write STag field and the
    Write Base Offset field in this iSER Header MUST be ignored at the
    receiver.  The Write STag Valid flag is set to one when there is
    solicited data to be transferred for a SCSI Write or bidirectional
    command, or when there are non-immediate unsolicited and solicited
    data to be transferred for the referenced task specified in a Task
    Management Function Request with the TASK REASSIGN function.
 RSV - Read STag Valid flag: 1 bit
    This flag indicates the validity of the Read STag field and the
    Read Base Offset field of the iSER Header.  If set to one, the
    Read STag field and the Read Base Offset field in this iSER Header

Ko & Nezhinsky Standards Track [Page 65] RFC 7145 iSER Specification April 2014

    are valid.  If set to zero, the Read STag field and the Read Base
    Offset field in this iSER Header MUST be ignored at the receiver.
    The Read STag Valid flag is set to one for a SCSI Read or
    bidirectional command, or a Task Management Function Request with
    the TASK REASSIGN function.
 Write STag - Write Steering Tag: 32 bits
    This field contains the Write STag when the Write STag Valid flag
    is set to one.  For a SCSI Write or bidirectional command, the
    Write STag is used to Advertise the initiator's I/O Buffer
    containing the solicited data.  For a Task Management Function
    Request with the TASK REASSIGN function, the Write STag is used to
    Advertise the initiator's I/O Buffer containing the non-immediate
    unsolicited data and solicited data.  This Write STag is used as
    the Data Source STag in the resultant RDMA Read operation(s).
    When the Write STag Valid flag is set to zero, this field MUST be
    set to zero and ignored on receive.
 Write Base Offset: 64 bits
    This field contains the Base Offset associated with the I/O Buffer
    for the SCSI Write command when the Write STag Valid flag is set
    to one.  When the Write STag Valid flag is set to zero, this field
    MUST be set to zero and ignored on receive.
 Read STag - Read Steering Tag: 32 bits
    This field contains the Read STag when the Read STag Valid flag is
    set to one.  The Read STag is used to Advertise the initiator's
    Read I/O Buffer of a SCSI Read or bidirectional command, or a Task
    Management Function Request with the TASK REASSIGN function.  This
    Read STag is used as the Data Sink STag in the resultant RDMA
    Write operation(s).  When the Read STag Valid flag is zero, this
    field MUST be set to zero and ignored on receive.
 Read Base Offset: 64 bits
    This field contains the Base Offset associated with the I/O Buffer
    for the SCSI Read command when the Read STag Valid flag is set to
    one.  When the Read STag Valid flag is set to zero, this field
    MUST be set to zero and ignored on receive.
 Reserved:
    Reserved fields MUST be set to zero on transmit and MUST be
    ignored on receive.

Ko & Nezhinsky Standards Track [Page 66] RFC 7145 iSER Specification April 2014

9.3. iSER Header Format for iSER Hello Message

 An iSER Hello Message MUST only contain the iSER header, which MUST
 have the format as described in Figure 4.  If iSERHelloRequired is
 negotiated to "Yes", then iSER Hello Message is the first iSER
 Message sent on the RCaP Stream from the iSER layer at the initiator
 to the iSER layer at the target.
     0                   1                   2                   3
     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |       |       |       |       |                               |
    | 0010b | Rsvd  | MaxVer| MinVer|           iSER-IRD            |
    |       |       |       |       |                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Reserved                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                           Reserved                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                           Reserved                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                           Reserved                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
          Figure 4: iSER Header Format for iSER Hello Message
 MaxVer - Maximum Version: 4 bits
    This field specifies the maximum version of the iSER protocol
    supported.  It MUST be set to 10 to indicate the version of the
    specification described in this document.
 MinVer - Minimum Version: 4 bits
    This field specifies the minimum version of the iSER protocol
    supported.  It MUST be set to 10 to indicate the version of the
    specification described in this document.
 iSER-IRD: 16 bits
    This field contains the value of the iSER-IRD at the initiator.
 Reserved (Rsvd):
    Reserved fields MUST be set to zero on transmit and MUST be
    ignored on receive.

Ko & Nezhinsky Standards Track [Page 67] RFC 7145 iSER Specification April 2014

9.4. iSER Header Format for iSER HelloReply Message

 An iSER HelloReply Message MUST only contain the iSER header, which
 MUST have the format as described in Figure 5.  If iSERHelloRequired
 is negotiated to "Yes", then the iSER HelloReply Message is the first
 iSER Message sent on the RCaP Stream from the iSER layer at the
 target to the iSER layer at the initiator.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |       |     |R|       |       |                               |
 | 0011b |Rsvd |E| MaxVer| CurVer|           iSER-ORD            |
 |       |     |J|       |       |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Reserved                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           Reserved                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           Reserved                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           Reserved                            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 5: iSER Header Format for iSER HelloReply Message
 REJ - Reject flag: 1 bit
    This flag indicates whether the target is rejecting this
    connection.  If set to one, the target is rejecting the
    connection.
 MaxVer - Maximum Version: 4 bits
    This field specifies the maximum version of the iSER protocol
    supported.  It MUST be set to 10 to indicate the version of the
    specification described in this document.
 CurVer - Current Version: 4 bits
    This field specifies the current version of the iSER protocol
    supported.  It MUST be set to 10 to indicate the version of the
    specification described in this document.

Ko & Nezhinsky Standards Track [Page 68] RFC 7145 iSER Specification April 2014

 iSER-ORD: 16 bits
    This field contains the value of the iSER-ORD at the target.
 Reserved (Rsvd):
    Reserved fields MUST be set to zero on transmit and MUST be
    ignored on receive.

9.5. SCSI Data Transfer Operations

 The iSER layer at the initiator and the iSER layer at the target
 handle each SCSI Write, SCSI Read, and bidirectional operation as
 described below.

9.5.1. SCSI Write Operation

 The iSCSI layer at the initiator MUST invoke the Send_Control
 Operational Primitive to request the iSER layer at the initiator to
 send the SCSI Write Command.  The iSER layer at the initiator MUST
 request the RCaP layer to transmit a Send Message with the message
 payload consisting of the iSER header followed by the SCSI Command
 PDU and immediate data (if any).  The SendSE Message should be used
 if supported by the RCaP layer (e.g., iWARP).  If there is solicited
 data, the iSER layer MUST Advertise the Write STag and the Base
 Offset in the iSER header of the Send Message, as described in
 Section 9.2.  Upon receiving the Send Message, the iSER layer at the
 target MUST notify the iSCSI layer at the target by invoking the
 Control_Notify Operational Primitive qualified with the SCSI Command
 PDU.  See Section 7.3.1 for details on the handling of the SCSI Write
 Command.
 For the non-immediate unsolicited data, the iSCSI layer at the
 initiator MUST invoke a Send_Control Operational Primitive qualified
 with the SCSI Data-Out PDU.  Upon receiving each Send Message
 containing the non-immediate unsolicited data, the iSER layer at the
 target MUST notify the iSCSI layer at the target by invoking the
 Control_Notify Operational Primitive qualified with the SCSI Data-Out
 PDU.  See Section 7.3.4 for details on the handling of the SCSI Data-
 Out PDU.
 For the solicited data, when the iSCSI layer at the target has an I/O
 Buffer available, it MUST invoke the Get_Data Operational Primitive
 qualified with the R2T PDU.  See Section 7.3.6 for details on the
 handling of the R2T PDU.

Ko & Nezhinsky Standards Track [Page 69] RFC 7145 iSER Specification April 2014

 When the data transfer associated with this SCSI Write operation is
 complete, the iSCSI layer at the target MUST invoke the Send_Control
 Operational Primitive when it is ready to send the SCSI Response PDU.
 Upon receiving a Send Message containing the SCSI Response PDU, the
 iSER layer at the initiator MUST notify the iSCSI layer at the
 initiator by invoking the Control_Notify Operational Primitive
 qualified with the SCSI Response PDU.  See Section 7.3.2 for details
 on the handling of the SCSI Response PDU.

9.5.2. SCSI Read Operation

 The iSCSI layer at the initiator MUST invoke the Send_Control
 Operational Primitive to request the iSER layer at the initiator to
 send the SCSI Read Command.  The iSER layer at the initiator MUST
 request the RCaP layer to transmit a Send Message with the message
 payload consisting of the iSER header followed by the SCSI Command
 PDU.  The SendSE Message should be used if supported by the RCaP
 layer (e.g., iWARP).  The iSER layer at the initiator MUST Advertise
 the Read STag and the Base Offset in the iSER header of the Send
 Message, as described in Section 9.2.  Upon receiving the Send
 Message, the iSER layer at the target MUST notify the iSCSI layer at
 the target by invoking the Control_Notify Operational Primitive
 qualified with the SCSI Command PDU.  See Section 7.3.1 for details
 on the handling of the SCSI Read Command.
 When the requested SCSI data is available in the I/O Buffer, the
 iSCSI layer at the target MUST invoke the Put_Data Operational
 Primitive qualified with the SCSI Data-In PDU.  See Section 7.3.5 for
 details on the handling of the SCSI Data-In PDU.
 When the data transfer associated with this SCSI Read operation is
 complete, the iSCSI layer at the target MUST invoke the Send_Control
 Operational Primitive when it is ready to send the SCSI Response PDU.
 The SendInvSE Message should be used if supported by the RCaP layer
 (e.g., iWARP).  Upon receiving the Send Message containing the SCSI
 Response PDU, the iSER layer at the initiator MUST notify the iSCSI
 layer at the initiator by invoking the Control_Notify Operational
 Primitive qualified with the SCSI Response PDU.  See Section 7.3.2
 for details on the handling of the SCSI Response PDU.

9.5.3. Bidirectional Operation

 The initiator and the target handle the SCSI Write and the SCSI Read
 portions of this bidirectional operation the same as described in
 Sections 9.5.1 and 9.5.2, respectively.

Ko & Nezhinsky Standards Track [Page 70] RFC 7145 iSER Specification April 2014

10. iSER Error Handling and Recovery

 RCaP provides the iSER layer with reliable in-order delivery.
 Therefore, the error management needs of an iSER-assisted connection
 are somewhat different than those of a Traditional iSCSI connection.

10.1. Error Handling

 iSER error handling is described in the following sections,
 classified loosely based on the sources of errors:
 1. Those originating at the transport layer (e.g., TCP).
 2. Those originating at the RCaP layer.
 3. Those originating at the iSER layer.
 4. Those originating at the iSCSI layer.

10.1.1. Errors in the Transport Layer

 If the transport layer is TCP, then TCP packets with detected errors
 are silently dropped by the TCP layer and result in retransmission at
 the TCP layer.  This has no impact on the iSER layer.  However,
 connection loss (e.g., link failure) and unexpected termination
 (e.g., TCP graceful or abnormal close without the iSCSI Logout
 exchanges) at the transport layer will cause the iSCSI/iSER
 connection to be terminated as well.

10.1.1.1. Failure in the Transport Layer Before RCaP Mode is Enabled

 If the connection is lost or terminated before the iSCSI layer
 invokes the Allocate_Connection_Resources Operational Primitive, the
 login process is terminated and no further action is required.
 If the connection is lost or terminated after the iSCSI layer has
 invoked the Allocate_Connection_Resources Operational Primitive, then
 the iSCSI layer MUST request the iSER layer to deallocate all
 connection resources by invoking the Deallocate_Connection_Resources
 Operational Primitive.

Ko & Nezhinsky Standards Track [Page 71] RFC 7145 iSER Specification April 2014

10.1.1.2. Failure in the Transport Layer After RCaP Mode is Enabled

 If the connection is lost or terminated after the iSCSI layer has
 invoked the Enable_Datamover Operational Primitive, the iSER layer
 MUST notify the iSCSI layer of the connection loss by invoking the
 Connection_Terminate_Notify Operational Primitive.  Prior to invoking
 the Connection_Terminate_Notify Operational Primitive, the iSER layer
 MUST perform the actions described in Section 5.2.3.2.

10.1.2. Errors in the RCaP Layer

 The RCaP layer does not have error recovery operations built in.  If
 errors are detected at the RCaP layer, the RCaP layer will terminate
 the RCaP Stream and the associated connection.

10.1.2.1. Errors Detected in the Local RCaP Layer

 If an error is encountered at the local RCaP layer, the RCaP layer
 MAY send a Send Message to the Remote Peer to report the error if
 possible.  (For iWARP, see [RDMAP] for the list of errors where a
 Terminate Message is sent.)  The RCaP layer is responsible for
 terminating the connection.  After the RCaP layer notifies the iSER
 layer that the connection is terminated, the iSER layer MUST notify
 the iSCSI layer by invoking the Connection_Terminate_Notify
 Operational Primitive.  Prior to invoking the
 Connection_Terminate_Notify Operational Primitive, the iSER layer
 MUST perform the actions described in Section 5.2.3.2.

10.1.2.2. Errors Detected in the RCaP Layer at the Remote Peer

 If an error is encountered at the RCaP layer at the Remote Peer, the
 RCaP layer at the Remote Peer may send a Send Message to report the
 error if possible.  If it is unable to send a Send Message, the
 connection is terminated.  This is treated the same as a failure in
 the transport layer after RDMA is enabled, as described in Section
 10.1.1.2.
 If an error is encountered at the RCaP layer at the Remote Peer and
 it is able to send a Send Message, the RCaP layer at the Remote Peer
 is responsible for terminating the connection.  After the local RCaP
 layer notifies the iSER layer that the connection is terminated, the
 iSER layer MUST notify the iSCSI layer by invoking the
 Connection_Terminate_Notify Operational Primitive.  Prior to invoking
 the Connection_Terminate_Notify Operational Primitive, the iSER layer
 MUST perform the actions described in Section 5.2.3.2.

Ko & Nezhinsky Standards Track [Page 72] RFC 7145 iSER Specification April 2014

10.1.3. Errors in the iSER Layer

 The error handling due to errors at the iSER layer is described in
 the following sections.

10.1.3.1. Insufficient Connection Resources to Support RCaP at

         Connection Setup
 After the iSCSI layer at the initiator invokes the
 Allocate_Connection_Resources Operational Primitive during the iSCSI
 login negotiation phase, if the iSER layer at the initiator fails to
 allocate the connection resources necessary to support RCaP, it MUST
 return a status of failure to the iSCSI layer at the initiator.  The
 iSCSI layer at the initiator MUST terminate the connection as
 described in Section 5.2.3.1.
 After the iSCSI layer at the target invokes the
 Allocate_Connection_Resources Operational Primitive during the iSCSI
 login negotiation phase, if the iSER layer at the target fails to
 allocate the connection resources necessary to support RCaP, it MUST
 return a status of failure to the iSCSI layer at the target.  The
 iSCSI layer at the target MUST send a Login Response with a Status-
 Class of 0x03 (Target Error), and a Status-Code of 0x02 (Out of
 Resources).  The iSCSI layers at the initiator and the target MUST
 terminate the connection as described in Section 5.2.3.1.

10.1.3.2. iSER Negotiation Failures

 If iSERHelloRequired is negotiated to "Yes" and the RCaP or iSER
 related parameters declared by the initiator in the iSER Hello
 Message are unacceptable to the iSER layer at the target, the iSER
 layer at the target MUST set the Reject (REJ) flag, as described in
 Section 9.4, in the iSER HelloReply Message.  The following are the
 cases when the iSER layer MUST set the REJ flag to 1 in the
 HelloReply Message:
  • The initiator-declared iSER-IRD value is greater than 0, and the

target-declared iSER-ORD value is 0.

  • The initiator-supported and the target-supported iSER protocol

versions do not overlap.

 After requesting the RCaP layer to send the iSER HelloReply Message,
 the handling of the error situation is the same as that for iSER
 format errors as described in Section 10.1.3.3.

Ko & Nezhinsky Standards Track [Page 73] RFC 7145 iSER Specification April 2014

10.1.3.3. iSER Format Errors

 The following types of errors in an iSER header are considered format
 errors:
  • Illegal contents of any iSER header field
  • Inconsistent field contents in an iSER header
  • Length error for an iSER Hello or HelloReply Message (see Sections

9.3 and 9.4)

 When a format error is detected, the following events MUST occur in
 the specified sequence:
 1. The iSER layer MUST request the RCaP layer to terminate the RCaP
    Stream.  The RCaP layer MUST terminate the associated connection.
 2.  The iSER layer MUST notify the iSCSI layer of the connection
    termination by invoking the Connection_Terminate_Notify
    Operational Primitive.  Prior to invoking the
    Connection_Terminate_Notify Operational Primitive, the iSER layer
    MUST perform the actions described in Section 5.2.3.2.

10.1.3.4. iSER Protocol Errors

 If iSERHelloRequired is negotiated to "Yes", then the first iSER
 Message sent by the iSER layer at the initiator MUST be the iSER
 Hello Message (see Section 9.3).  In this case the first iSER Message
 sent by the iSER layer at the target MUST be the iSER HelloReply
 Message (see Section 9.4).  Failure to send the iSER Hello or
 HelloReply Message, as indicated by the wrong Opcode in the iSER
 header, is a protocol error.  Conversely, if the iSER Hello Message
 is sent by the iSER layer at the initiator when iSERHelloRequired is
 negotiated to "No", the iSER layer at the target MAY treat this as a
 protocol error or respond with an iSER HelloReply Message.  The
 handling of iSER protocol errors is the same as that for iSER format
 errors as described in Section 10.1.3.3.
 If the sending side of an iSER-enabled connection acts in a manner
 not permitted by the negotiated or declared login/text operational
 key values as described in Section 6, this is a protocol error and
 the receiving side MAY handle this the same as for iSER format errors
 as described in Section 10.1.3.3.

Ko & Nezhinsky Standards Track [Page 74] RFC 7145 iSER Specification April 2014

10.1.4. Errors in the iSCSI Layer

 The error handling due to errors at the iSCSI layer is described in
 the following sections.  For error recovery, see Section 10.2.

10.1.4.1. iSCSI Format Errors

 When an iSCSI format error is detected, the iSCSI layer MUST request
 the iSER layer to terminate the RCaP Stream by invoking the
 Connection_Terminate Operational Primitive.  For more details on
 connection termination, see Section 5.2.3.1.

10.1.4.2. iSCSI Digest Errors

 In the iSER-assisted mode, the iSCSI layer will not see any digest
 error because both the HeaderDigest and the DataDigest keys are
 negotiated to "None".

10.1.4.3. iSCSI Sequence Errors

 For Traditional iSCSI, sequence errors are caused by dropped PDUs due
 to header or data digest errors.  Since digests are not used in iSER-
 assisted mode and the RCaP layer will deliver all messages in the
 order they were sent, sequence errors will not occur in iSER-assisted
 mode.

10.1.4.4. iSCSI Protocol Error

 When the iSCSI layer handles certain protocol errors by dropping the
 connection, the error handling is the same as that for iSCSI format
 errors as described in Section 10.1.4.1.
 When the iSCSI layer uses the iSCSI Reject PDU and response codes to
 handle certain other protocol errors, no special handling at the iSER
 layer is required.

10.1.4.5. SCSI Timeouts and Session Errors

 This is handled at the iSCSI layer, and no special handling at the
 iSER layer is required.

10.1.4.6. iSCSI Negotiation Failures

 For negotiation failures that happen during the Login Phase at the
 initiator after the iSCSI layer has invoked the
 Allocate_Connection_Resources Operational Primitive and before the
 Enable_Datamover Operational Primitive has been invoked, the iSCSI
 layer MUST request the iSER layer to deallocate all connection

Ko & Nezhinsky Standards Track [Page 75] RFC 7145 iSER Specification April 2014

 resources by invoking the Deallocate_Connection_Resources Operational
 Primitive.  The iSCSI layer at the initiator MUST terminate the
 connection.
 For negotiation failures during the Login Phase at the target, the
 iSCSI layer can use a Login Response with a Status-Class other than 0
 (success) to terminate the Login Phase.  If the iSCSI layer has
 invoked the Allocate_Connection_Resources Operational Primitive and
 has not yet invoked the Enable_Datamover Operational Primitive, the
 iSCSI layer at the target MUST request the iSER layer at the target
 to deallocate all connection resources by invoking the
 Deallocate_Connection_Resources Operational Primitive.  The iSCSI
 layer at both the initiator and the target MUST terminate the
 connection.
 During the iSCSI Login Phase, if the iSCSI layer at the initiator
 receives a Login Response from the target with a Status-Class other
 than 0 (Success) after the iSCSI layer at the initiator has invoked
 the Allocate_Connection_Resources Operational Primitive, the iSCSI
 layer MUST request the iSER layer to deallocate all connection
 resources by invoking the Deallocate_Connection_Resources Operational
 Primitive.  The iSCSI layer MUST terminate the connection in this
 case.
 For negotiation failures during the Full Feature Phase, the error
 handling is left to the iSCSI layer and no special handling at the
 iSER layer is required.

10.2. Error Recovery

 Error recovery requirements of iSCSI/iSER are the same as that of
 Traditional iSCSI.  All three ErrorRecoveryLevels as defined in
 [iSCSI] are supported in iSCSI/iSER.
  • For ErrorRecoveryLevel 0, session recovery is handled by iSCSI and

no special handling by the iSER layer is required.

  • For ErrorRecoveryLevel 1, see Section 10.2.1 on PDU Recovery.
  • For ErrorRecoveryLevel 2, see Section 10.2.2 on Connection

Recovery.

 The iSCSI layer may invoke the Notice_Key_Values Operational
 Primitive during connection setup to request the iSER layer to take
 note of the value of the operational ErrorRecoveryLevel, as described
 in Sections 5.1.1 and 5.1.2.

Ko & Nezhinsky Standards Track [Page 76] RFC 7145 iSER Specification April 2014

10.2.1. PDU Recovery

 As described in Sections 10.1.4.2 and 10.1.4.3, digest and sequence
 errors will not occur in the iSER-assisted mode.  If the RCaP layer
 detects an error, it will close the iSCSI/iSER connection, as
 described in Section 10.1.2.  Therefore, PDU recovery is not useful
 in the iSER-assisted mode.
 The iSCSI layer at the initiator SHOULD disable iSCSI timeout-driven
 PDU retransmissions.

10.2.2. Connection Recovery

 The iSCSI layer at the initiator MAY reassign connection allegiance
 for non-immediate commands that are still in progress and are
 associated with the failed connection by using a Task Management
 Function Request with the TASK REASSIGN function.  See Section 7.3.3
 for more details.
 When the iSCSI layer at the initiator does a task reassignment for a
 SCSI Write command, it MUST qualify the Send_Control Operational
 Primitive invocation with DataDescriptorOut, which defines the I/O
 Buffer for both the non-immediate unsolicited data and the solicited
 data.  This allows the iSCSI layer at the target to use recovery R2Ts
 to request data originally sent as unsolicited and solicited from the
 initiator.
 When the iSCSI layer at the target accepts a reassignment request for
 a SCSI Read command, it MUST request the iSER layer to process SCSI
 Data-In for all unacknowledged data by invoking the Put_Data
 Operational Primitive.  See Section 7.3.5 on the handling of SCSI
 Data-In.
 When the iSCSI layer at the target accepts a reassignment request for
 a SCSI Write command, it MUST request the iSER layer to process a
 recovery R2T for any non-immediate unsolicited data and any solicited
 data sequences that have not been received by invoking the Get_Data
 Operational Primitive.  See Section 7.3.6 on the handling of Ready To
 Transfer (R2T).
 The iSCSI layer at the target MUST NOT issue recovery R2Ts on an
 iSCSI/iSER connection for a task for which the connection allegiance
 was never reassigned.  The iSER layer at the target MAY reject such a
 recovery R2T received via the Get_Data Operational Primitive
 invocation from the iSCSI layer at the target, with an appropriate
 error code.

Ko & Nezhinsky Standards Track [Page 77] RFC 7145 iSER Specification April 2014

 The iSER layer at the target will process the requests invoked by the
 Put_Data and Get_Data Operational Primitives for a reassigned task in
 the same way as for the original commands.

11. Security Considerations

 When iSER is layered on top of an RCaP layer and provides the RDMA
 extensions to the iSCSI protocol, the security considerations of iSER
 are the same as that of the underlying RCaP layer.  For iWARP, this
 is described in [RDMAP] and [RDDPSEC], plus the updates to both of
 those RFCs that are contained in [IPSEC-IPS].
 Since iSER-assisted iSCSI protocol is still functionally iSCSI from a
 security considerations perspective, all of the iSCSI security
 requirements as described in [iSCSI] apply.  If iSER is layered on
 top of a non-IP-based RCaP layer, all the security protocol
 mechanisms applicable to that RCaP layer are also applicable to an
 iSCSI/iSER connection.  If iSER is layered on top of a non-IP
 protocol, the IPsec mechanism as specified in [iSCSI] MUST be
 implemented at any point where the iSER protocol enters the IP
 network (e.g., via gateways), and the non-IP protocol SHOULD
 implement (optional to use) a packet-by-packet security protocol
 equal in strength to the IPsec mechanism specified by [iSCSI].
 In order to protect target RCaP connection resources from possible
 resource exhaustion attacks, allocation of such resources for a new
 connection MUST be delayed until it is reasonably certain that the
 new connection is not part of a resource exhaustion attack (e.g.,
 until after the SecurityNegotiation stage of Login); see Section
 5.1.2.
 A valid STag exposes I/O Buffer resources to the network for access
 via the RCaP.  The security measures for the RCAP and iSER described
 in the above paragraphs can be used to protect data in an I/O buffer
 from undesired disclosure or modification, and these measures are of
 heightened importance for implementations that retain (e.g., cache)
 STags for use in multiple tasks (e.g., iSCSI I/O operations) because
 the resources are exposed to the network for a longer period of time.
 A complementary means of controlling I/O Buffer resource exposure is
 invalidation of the STag after completion of the associated task, as
 specified in Section 1.5.1.  The use of Send with Invalidate messages
 (which cause remote STag invalidation) is OPTIONAL, therefore the
 iSER layer MUST NOT rely on use of a Send with Invalidate by its
 Remote Peer to cause local STag invalidation.  If an STag is expected
 to be invalid after completion of a task, the iSER layer MUST check
 the STag and invalidate it if it is still valid.

Ko & Nezhinsky Standards Track [Page 78] RFC 7145 iSER Specification April 2014

12. IANA Considerations

 IANA has added the following entries to the "iSCSI Login/Text Keys"
 registry:
    MaxAHSLength, RFC 7145
    TaggedBufferForSolicitedDataOnly, RFC 7145
    iSERHelloRequired, RFC 7145
 IANA has updated the following entries in the "iSCSI Login/Text Keys"
 registry to reference this RFC.
    InitiatorRecvDataSegmentLength
    MaxOutstandingUnexpectedPDUs
    RDMAExtensions
    TargetRecvDataSegmentLength
 IANA has also changed the reference to RFC 5046 for the "iSCSI
 Login/Text Keys" registry to refer to this RFC.
 IANA has updated the registrations of the iSER Opcodes 1-3 in the
 "iSER Opcodes" registry to reference this RFC.  IANA has also changed
 the reference to RFC 5046 for the "iSER Opcodes" registry to refer to
 this RFC.

13. References

13.1. Normative References

 [RFC5046]   Ko, M., Chadalapaka, M., Hufferd, J., Elzur, U., Shah,
             H., and P. Thaler, "Internet Small Computer System
             Interface (iSCSI) Extensions for Remote Direct Memory
             Access (RDMA)", RFC 5046, October 2007.
 [iSCSI]     Chadalapaka, M., Satran, J., Meth, K., and D. Black,
             "Internet Small Computer System Interface (iSCSI)
             Protocol (Consolidated)", RFC 7143, April 2014.
 [RDMAP]     Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
             Garcia, "A Remote Direct Memory Access Protocol
             Specification", RFC 5040, October 2007.

Ko & Nezhinsky Standards Track [Page 79] RFC 7145 iSER Specification April 2014

 [DDP]       Shah, H., Pinkerton, J., Recio, R., and P. Culley,
             "Direct Data Placement over Reliable Transports", RFC
             5041, October 2007.
 [MPA]       Culley, P., Elzur, U., Recio, R., Bailey, S., and J.
             Carrier, "Marker PDU Aligned Framing for TCP
             Specification", RFC 5044, October 2007.
 [RDDPSEC]   Pinkerton, J. and E. Deleganes, "Direct Data Placement
             Protocol (DDP) / Remote Direct Memory Access Protocol
             (RDMAP) Security", RFC 5042, October 2007.
 [TCP]       Postel, J., "Transmission Control Protocol", STD 7, RFC
             793, September 1981.
 [RFC2119]   Bradner, S., "Key words for use in RFCs to Indicate
             Requirement Levels", BCP 14, RFC 2119, March 1997.
 [IPSEC-IPS] Black, D. and P. Koning, "Securing Block Storage
             Protocols over IP: RFC 3723 Requirements Update for IPsec
             v3", RFC 7146, April 2014.

13.2. Informative References

 [SAM5]      INCITS Technical Committee T10, "SCSI Architecture Model
             - 5 (SAM-5)", T10/BSR INCITS 515 rev 04, Committee Draft.
 [iSCSI-SAM] Knight, F. and M. Chadalapaka, "Internet Small Computer
             System Interface (iSCSI) SCSI Features Update", RFC 7144,
             April 2014.
 [DA]        Chadalapaka, M., Hufferd, J., Satran, J., and H. Shah,
             "DA: Datamover Architecture for the Internet Small
             Computer System Interface (iSCSI)", RFC 5047, October
             2007.
 [IB]        InfiniBand Architecture Specification Volume 1 Release
             1.2, October 2004
 [IPoIB]     Chu, J. and V. Kashyap, "Transmission of IP over
             InfiniBand (IPoIB)", RFC 4391, April 2006.

Ko & Nezhinsky Standards Track [Page 80] RFC 7145 iSER Specification April 2014

Appendix A. Summary of Changes from RFC 5046

 All changes are backward compatible with RFC 5046 except for item #8,
 which reflects all known implementations of iSER, each of which has
 implemented this change, despite its absence in RFC 5046.  As a
 result, a hypothetical implementation based on RFC 5046 will not
 interoperate with an implementation based on this version of the
 specification.
 1.  Removed the requirement that a connection be opened in "normal"
     TCP mode and transitioned to zero-copy mode.  This allows the
     specification to conform to existing implementations for both
     InfiniBand and iWARP.  Changes were made in Sections 1, 3.1.6,
     4.2, 5.1, 5.1.1, 5.1.2, 5.1.3, 10.1.3.4, and 11.
 2.  Added a clause in Section 6.2 to clarify that
     MaxRecvDataSegmentLength must be ignored if it is declared in the
     Login Phase.
 3.  Added a clause in Section 6.2 to clarify that the initiator must
     not send more than InitiatorMaxRecvDataSegmentLength worth of
     data when a NOP-Out request is sent with a valid Initiator Task
     Tag.  Since InitiatorMaxRecvDataSegmentLength can be smaller than
     TargetMaxRecvDataSegmentLength, returning the original data in
     the NOP-Out request in this situation can overflow the receive
     buffer unless the length of the data sent with the NOP-Out
     request is less than InitiatorMaxRecvDataSegmentLength.
 4.  Added a SHOULD negotiate recommendation for
     MaxOutstandingUnexpectedPDUs in Section 6.7.
 5.  Added MaxAHSLength key in Section 6.8 to set a limit on the AHS
     Length.  This is useful when posting receive buffers in knowing
     what the maximum possible message length is in a PDU that
     contains AHS.
 6.  Added TaggedBufferForSolicitedDataOnly key in Section 6.9 to
     indicate how the memory region will be used.  An initiator can
     treat the memory regions intended for unsolicited and solicited
     data differently and can use different registration modes.  In
     contrast, RFC 5046 treats the memory occupied by the data as a
     contiguous (or virtually contiguous, by means of scatter-gather
     mechanisms) and homogenous region.  Adding a new key will allow
     different memory models to be accommodated.  Changes were also
     made in Section 7.3.1.

Ko & Nezhinsky Standards Track [Page 81] RFC 7145 iSER Specification April 2014

 7.  Added iSERHelloRequired key in Section 6.10 to allow an initiator
     to allocate connection resources after the login process by
     requiring the use of the iSER Hello messages before sending iSCSI
     PDUs.  The default is "No" since iSER Hello messages have not
     been implemented and are not in use.  Changes were made in
     Sections 5.1.1, 5.1.2, 5.1.3, 8.2, 9.3, 9.4, 10.1.3.2, and
     10.1.3.4.
 8.  Added two 64-bit fields in iSER header in Section 9.2 for the
     Read Base Offset and the Write Base Offset to accommodate a non-
     zero Base Offset.  This allows one implementation such as the
     Open Fabrics Enterprise Distribution (OFED) stack to be used in
     both the InfiniBand and the iWARP environment.
     Changes were made in the definitions of Base Offset,
     Advertisement, and Tagged Buffer.  Changes were also made in
     Sections 1.5.1, 1.6, 1.7, 7.3.1, 7.3.3, 7.3.5, 7.3.6, 9.1, 9.3,
     9.4, 9.5.1, and 9.5.2.  This change is not backward compatible
     with RFC 5046, but it was part of all known implementations of
     iSER at the time this document was developed.
 9.  Remove iWARP-specific behavior.  Changes were made in the
     definitions of RDMA Operation and Send Message Type.
     Clarifications were added in Section 1.5.2 on the use of SendSE
     and SendInvSE.  These clarifications reflect a removal of the
     requirements in RFC 5046 for the use of these messages, as
     implementations have not followed RFC 5046 in this area.  Changes
     affecting Send with Invalidate were made in Sections 1.5.1, 1.6,
     1.7, 4.1, and 7.3.2.  Changes affecting Terminate were made in
     Sections 10.1.2.1 and 10.1.2.2.  Changes were made in Appendix B
     to remove iWARP headers.
 10. Removed denial-of-service descriptions for the initiator in
     Section 5.1.1 since they are applicable for the target only.
 11. Clarified in Section 1.5.1 that STag invalidation is the
     initiator's responsibility for security reasons, and the
     initiator cannot rely on the target using an Invalidate version
     of Send.  Added text in Section 11 on Stag invalidation.

Ko & Nezhinsky Standards Track [Page 82] RFC 7145 iSER Specification April 2014

Appendix B. Message Format for iSER

 This section is for information only and is NOT part of the standard.

B.1. iWARP Message Format for iSER Hello Message

 The following figure depicts an iSER Hello Message encapsulated in an
 iWARP SendSE Message.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         MPA Header            |  DDP Control  | RDMA Control  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Reserved                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       (Send) Queue Number                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 (Send) Message Sequence Number                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      (Send) Message Offset                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 0010b | Zeros | 0001b | 0001b |           iSER-IRD            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 |                           MPA CRC                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 6: SendSE Message Containing an iSER Hello Message

Ko & Nezhinsky Standards Track [Page 83] RFC 7145 iSER Specification April 2014

B.2. iWARP Message Format for iSER HelloReply Message

 The following figure depicts an iSER HelloReply Message encapsulated
 in an iWARP SendSE Message.  The Reject (REJ) flag is set to zero.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |         MPA Header            |  DDP Control  | RDMA Control  |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Reserved                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       (Send) Queue Number                     |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                 (Send) Message Sequence Number                |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                      (Send) Message Offset                    |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 0011b |Zeros|0| 0001b | 0001b |           iSER-ORD            |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           MPA CRC                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   Figure 7: SendSE Message Containing an iSER HelloReply Message

Ko & Nezhinsky Standards Track [Page 84] RFC 7145 iSER Specification April 2014

B.3. iSER Header Format for SCSI Read Command PDU

 The following figure depicts a SCSI Read Command PDU embedded in an
 iSER Message.  For this particular example, in the iSER header, the
 Write STag Valid flag is set to zero, the Read STag Valid flag is set
 to one, the Write STag field is set to all zeros, the Write Base
 Offset field is set to all zeros, the Read STag field contains a
 valid Read STag, and the Read Base Offset field contains a valid Base
 Offset for the Read Tagged Buffer.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 0001b |0|1|                  All zeros                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         All Zeros                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                         All Zeros                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         Read STag                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                       Read Base Offset                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       SCSI Read Command PDU                   |
 //                                                             //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      Figure 8: iSER Header Format for SCSI Read Command PDU

Ko & Nezhinsky Standards Track [Page 85] RFC 7145 iSER Specification April 2014

B.4. iSER Header Format for SCSI Write Command PDU

 The following figure depicts a SCSI Write Command PDU embedded in an
 iSER Message.  For this particular example, in the iSER header, the
 Write STag Valid flag is set to one, the Read STag Valid flag is set
 to zero, the Write STag field contains a valid Write STag, the Write
 Base Offset field contains a valid Base Offset for the Write Tagged
 Buffer, the Read STag field is set to all zeros since it is not used,
 and the Read Base Offset field is set to all zeros.
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 0001b |1|0|                  All zeros                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                        Write STag                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                      Write Base Offset                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                         All Zeros                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                         All Zeros                             |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       SCSI Write Command PDU                  |
 //                                                             //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     Figure 9: iSER Header Format for SCSI Write Command PDU

Ko & Nezhinsky Standards Track [Page 86] RFC 7145 iSER Specification April 2014

B.5. iSER Header Format for SCSI Response PDU

 The following figure depicts a SCSI Response PDU embedded in an iSER
 Message:
  0                   1                   2                   3
  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 | 0001b |0|0|                  All Zeros                        |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                                                               |
 |                           All Zeros                           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |                       SCSI Response PDU                       |
 //                                                             //
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Figure 10: iSER Header Format for SCSI Response PDU

Ko & Nezhinsky Standards Track [Page 87] RFC 7145 iSER Specification April 2014

Appendix C. Architectural Discussion of iSER over InfiniBand

 This section explains how an InfiniBand network (with Gateways) would
 be structured.  It is informational only and is intended to provide
 insight on how iSER is used in an InfiniBand environment.

C.1. Host Side of iSCSI and iSER Connections in InfiniBand

 Figure 11 defines the topologies in which iSCSI and iSER will be able
 to operate on an InfiniBand Network.
 +---------+ +---------+ +---------+ +---------+ +--- -----+
 |  Host   | |  Host   | |   Host  | |   Host  | |   Host  |
 |         | |         | |         | |         | |         |
 +---+-+---+ +---+-+---+ +---+-+---+ +---+-+---+ +---+-+---+
 |HCA| |HCA| |HCA| |HCA| |HCA| |HCA| |HCA| |HCA| |HCA| |HCA|
 +-v-+ +-v-+ +-v-+ +-v-+ +-v-+ +-v-+ +-v-+ +-v-+ +-v-+ +-v-+
   |----+------|-----+-----|-----+-----|-----+-----|-----+---> To IB
 IB|        IB |        IB |        IB |        IB |    SubNet2 SWTCH
 +-v-----------v-----------v-----------v-----------v---------+
 |                  InfiniBand Switch for Subnet1            |
 +---+-----+--------+-----+--------+-----+------------v------+
     | TCA |        | TCA |        | TCA |            |
     +-----+        +-----+        +-----+            | IB
    /  IB   \      /  IB   \      /       \     +--+--v--+--+
   |  iSER   |    |  iSER   |    |  IPoIB  |    |  | TCA |  |
   | Gateway |    | Gateway |    | Gateway |    |  +-----+  |
   |   to    |    |   to    |    |   to    |    | Storage   |
   |  iSCSI  |    |  iSER   |    |   IP    |    | Controller|
   |   TCP   |    |  iWARP  |    |Ethernet |    +-----+-----+
   +---v-----|    +---v-----|    +----v----+
       | EN           | EN            | EN
       +--------------+---------------+----> to IP based storage
         Ethernet links that carry iSCSI or iWARP
              Figure 11: iSCSI and iSER on IB
 In Figure 11, the Host systems are connected via the InfiniBand Host
 Channel Adapters (HCAs) to the InfiniBand links.  With the use of IB
 switch(es), the InfiniBand links connect the HCA to InfiniBand Target
 Channel Adapters (TCAs) located in gateways or Storage Controllers.
 An iSER-capable IB-IP Gateway converts the iSER Messages encapsulated
 in IB protocols to either standard iSCSI, or iSER Messages for iWARP.
 An [IPoIB] Gateway converts the InfiniBand [IPoIB] protocol to IP
 protocol, and in the iSCSI case, permits iSCSI to be operated on an
 IB Network between the Hosts and the [IPoIB] Gateway.

Ko & Nezhinsky Standards Track [Page 88] RFC 7145 iSER Specification April 2014

C.2. Storage Side of iSCSI and iSER Mixed Network Environment

 Figure 12 shows a storage controller that has three different portal
 groups: one supporting only iSCSI (TPG-4), one supporting iSER/iWARP
 or iSCSI (TPG-2), and one supporting iSER/IB (TPG-1).  Here, "TPG"
 stands for "Target Portal Group".
                |                |                |
                |                |                |
          +--+--v--+----------+--v--+----------+--v--+--+
          |  | IB  |          |iWARP|          | EN  |  |
          |  |     |          | TCP |          | NIC |  |
          |  |(TCA)|          | RNIC|          |     |  |
          |  +-----|          +-----+          +-----+  |
          |   TPG-1            TPG-2            TPG-4   |
          |  9.1.3.3          9.1.2.4          9.1.2.6  |
          |                                             |
          |                  Storage Controller         |
          |                                             |
          +---------------------------------------------+
 Figure 12: Storage Controller with TCP, iWARP, and IB Connections
 The normal iSCSI portal group advertising processes (via the Service
 Location Protocol (SLP), Internet Storage Name Service (iSNS), or
 SendTargets) are available to a Storage Controller.

C.3. Discovery Processes for an InfiniBand Host

 An InfiniBand Host system can gather portal group IP addresses from
 SLP, iSNS, or the SendTargets discovery processes by using TCP/IP via
 [IPoIB].  After obtaining one or more remote portal IP addresses, the
 Initiator uses the standard IP mechanisms to resolve the IP address
 to a local outgoing interface and the destination hardware address
 (Ethernet MAC or InfiniBand Global Identifier (GID) of the target or
 a gateway leading to the target).  If the resolved interface is an
 [IPoIB] network interface, then the target portal can be reached
 through an InfiniBand fabric.  In this case, the Initiator can
 establish an iSCSI/TCP or iSCSI/iSER session with the Target over
 that InfiniBand interface, using the hardware address (InfiniBand
 GID) obtained through the standard Address Resolution Protocol (ARP)
 processes.
 If more than one IP address is obtained through the discovery
 process, the Initiator should select a Target IP address that is on
 the same IP subnet as the Initiator, if one exists.  This will avoid
 a potential overhead of going through a gateway when a direct path
 exists.

Ko & Nezhinsky Standards Track [Page 89] RFC 7145 iSER Specification April 2014

 In addition, a user can configure manual static IP route entries if a
 particular path to the target is preferred.

C.4. IBTA Connection Specifications

 It is outside the scope of this document, but it is expected that the
 InfiniBand Trade Association (IBTA) has or will define:
  • The iSER ServiceID
  • A means for permitting a Host to establish a connection with a

peer InfiniBand end-node, and that peer indicating when that end-

    node supports iSER, so the Host would be able to fall back to
    iSCSI/TCP over [IPoIB].
  • A means for permitting the Host to establish connections with IB

iSER connections on storage controllers or IB iSER-connected

    Gateways in preference to IPoIB-connected Gateways/Bridges or
    connections to Target Storage Controllers that also accept iSCSI
    via [IPoIB].
  • A means for combining the IB ServiceID for iSER and the IP port

number such that the IB Host can use normal IB connection

    processes, yet ensure that the iSER target peer can actually
    connect to the required IP port number.

Appendix D. Acknowledgments

 The authors acknowledge the following individuals for identifying
 implementation issues and/or suggesting resolutions to the issues
 clarified in this document: Robert Russell, Arne Redlich, David
 Black, Mallikarjun Chadalapaka, Tom Talpey, Felix Marti, Robert
 Sharp, Caitlin Bestler, Hemal Shah, Spencer Dawkins, Pete Resnick,
 Ted Lemon, Pete McCann, and Steve Kent.  Credit also goes to the
 authors of the original iSER Specification [RFC5046], including
 Michael Ko, Mallikarjun Chadalapaka, John Hufferd, Uri Elzur, Hemal
 Shah, and Patricia Thaler.  This document benefited from all of their
 contributions.

Ko & Nezhinsky Standards Track [Page 90] RFC 7145 iSER Specification April 2014

Authors' Addresses

 Michael Ko
 EMail: mkosjc@gmail.com
 Alexander Nezhinsky
 Mellanox Technologies
 13 Zarchin St.
 Raanana 43662
 Israel
 Phone: +972-74-712-9000
 EMail: alexandern@mellanox.com, nezhinsky@gmail.com

Ko & Nezhinsky Standards Track [Page 91]

/data/webs/external/dokuwiki/data/pages/rfc/rfc7145.txt · Last modified: 2014/04/04 23:20 (external edit)