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Versions: 00 01 02 03 04 05 06 07 08 RFC 5044

   Remote Direct Data Placement Work Group   P. Culley
   INTERNET-DRAFT                              Hewlett-Packard Company
   draft-ietf-rddp-mpa-04.txt                U. Elzur
                                               Broadcom Corporation
                                             R. Recio
                                               IBM Corporation
                                             S. Bailey
                                               Sandburst Corporation
                                             J. Carrier
                                               Cray Inc.

   Expires: November 2006                    May 30, 2006


             Marker PDU Aligned Framing for TCP Specification

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
   applicable patent or other IPR claims of which he or she is aware
   have been or will be disclosed, and any of which he or she becomes
   aware will be disclosed, in accordance with Section 6 of BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/1id-abstracts.html.  The list of Internet-Draft
   Shadow Directories can be accessed at http://www.ietf.org/shadow.html

Abstract

   MPA (Marker Protocol data unit Aligned framing) is designed to work
   as an "adaptation layer" between TCP and the Direct Data Placement
   [DDP] protocol, preserving the reliable, in-order delivery of TCP,
   while adding the preservation of higher-level protocol record
   boundaries that DDP requires.  MPA is fully compliant with applicable
   TCP RFCs and can be utilized with existing TCP implementations.  MPA
   also supports integrated implementations that combine TCP, MPA and
   DDP to reduce buffering requirements in the implementation and
   improve performance at the system level.






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   Table of Contents

   Status of this Memo                                                 1
   Abstract                                                            1
   1      Glossary                                                     7
   2      Introduction                                                10
   2.1    Motivation                                                  10
   2.2    Protocol Overview                                           10
   3      LLP and DDP requirements                                    14
   3.1    TCP implementation Requirements to support MPA              14
   3.1.1  TCP Transmit side                                           14
   3.1.2  TCP Receive side                                            14
   3.2    MPA's interactions with DDP                                 16
   4      FPDU Formats                                                18
   4.1    Marker Format                                               19
   5      Data Transfer Semantics                                     20
   5.1    MPA Markers                                                 20
   5.2    CRC Calculation                                             23
   5.3    MPA on TCP Sender Segmentation                              26
   5.3.1  Effects of MPA on TCP Segmentation                          27
   5.3.2  FPDU Size Considerations                                    29
   5.4    MPA Receiver FPDU Identification                            30
   5.4.1  Re-segmenting Middle boxes and non MPA-aware TCP senders    31
   6      Connection Semantics                                        32
   6.1    Connection setup                                            32
   6.1.1  MPA Request and Reply Frame Format                          34
   6.1.2  Connection Startup Rules                                    35
   6.1.3  Example Delayed Startup sequence                            38
   6.1.4  Use of Private Data                                         41
   6.1.5  "Dual stack" implementations                                44
   6.2    Normal Connection Teardown                                  45
   7      Error Semantics                                             46
   8      Security Considerations                                     47
   8.1    Protocol-specific Security Considerations                   47
   8.1.1  Spoofing                                                    47
   8.1.2  Eavesdropping                                               48
   8.2    Introduction to Security Options                            49
   8.3    Using IPsec With MPA                                        49
   8.4    Requirements for IPsec Encapsulation of MPA/DDP             50
   9      IANA Considerations                                         51
   10     References                                                  52
   10.1   Normative References                                        52
   10.2   Informative References                                      52
   11     Appendix                                                    54
   11.1   Analysis of MPA over TCP Operations                         54
   11.1.1 Assumptions                                                 55
   11.1.2 The Value of FPDU Alignment                                 56
   11.2   Receiver implementation                                     63
   11.2.1 Network Layer Reassembly Buffers                            63
   11.2.2 TCP Reassembly buffers                                      64



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   11.3   IETF Implementation Interoperability with RDMA Consortium
   Protocols                                                          65
   11.3.1 Negotiated Parameters                                       65
   11.3.2 RDMAC RNIC and Non-permissive IETF RNIC                     66
   11.3.3 RDMAC RNIC and Permissive IETF RNIC                         68
   11.3.4 Non-Permissive IETF RNIC and Permissive IETF RNIC           69
   12     Author's Addresses                                          70
   13     Acknowledgments                                             71
   Full Copyright Statement                                           74
   Intellectual Property                                              74


   Table of Figures

   Figure 1 ULP MPA TCP Layering                                      11
   Figure 2 FPDU Format                                               18
   Figure 3 Marker Format                                             19
   Figure 4 Example FPDU Format with Marker                           21
   Figure 5 Annotated Hex Dump of an FPDU                             25
   Figure 6 Annotated Hex Dump of an FPDU with Marker                 26
   Figure 7 MPA Request/Reply Frame                                   34
   Figure 8: Example Delayed Startup negotiation                      39
   Figure 9: Example Immediate Startup negotiation                    42
   Figure 10: Non-aligned FPDU freely placed in TCP octet stream      58
   Figure 11: Aligned FPDU placed immediately after TCP header        59
   Figure 12.  Connection Parameters for the RNIC Types.              66
   Figure 13: MPA negotiation between an RDMAC RNIC and a Non-permissive
   IETF RNIC.                                                         67
   Figure 14: MPA negotiation between an RDMAC RNIC and a Permissive
   IETF RNIC.                                                         68
   Figure 15: MPA negotiation between a Non-permissive IETF RNIC and a
   Permissive IETF RNIC.                                              69

   Revision history [To be deleted prior to RFC publication]

   [draft-ietf-rddp-mpa-04] workgroup draft with following changes:

        Numerous capitalization and "" adjustments, tried to make more
        consistent.

        Added some missing capitalized terms to glossary

        Removed company specific "use as is" boilerplate paragraph

        Fixed up some contact information and cross references.

        Removed reference to expired draft-elzur-iwarp-mpa-tcp-analysis-
        00.txt

        Suggested MTU to be used to determine EMSS, when otherwise not
        available; removed technology specific lengths per AD suggestion


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        Tweaked text around disabling Nagle so that it is no longer
        implied that that is all that is necessary to achieve proper
        segmentation behavior

        Revamped section 5.3.1 for improved clarity

   [draft-ietf-rddp-mpa-03] workgroup draft with following changes:

        Tweaked abstract to give a bit more information.

        Tightened definition and usage of "deliver"

        Cleaned up usage of terms "FPDU Alignment" and "Header
        Alignment"

        Rearranged overview sections with stack and glossary earlier

        Mentioned how an non-MPA-Aware TCP MPA receiver deals with out
        of order segments (it doesn't have to...)

        Fixed description of out of order segment handling in section
        3.1.1

        Added text saying that ordering and completion indications are
        used to deliver to DDP

        Added redundant text indicating low two bits of FPDUPTR must
        always be zero and treated as such in Section 4.1

        Added redundant text indicating Markers are always included in a
        CRC calculation

        Removed indication saying that an implementation can "ignore" an
        administrative input to not use CRCs; clarified that both ends
        have to agree to not use CRC (as originally intended).

        Changed example FPDU hex dump format for greater clarity

        Clarified that EMSS shrinking below 128 bytes is the condition
        (rather than "very small sizes")

        Put connection startup rules after the start frame formats

        Added Initiator Private Data to figure 9

        Removed or Clarified use of RNIC term

        Added intro to IETF/RDMAC interoperability appendix and gave a
        web reference for docs; also recommended use of "permissive IETF
        RNIC"



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        Numerous minor clarifications

        Updated Boilerplates per current requirements

   [draft-ietf-rddp-mpa-02] workgroup draft with following changes:

        Made IPsec must implement, optional to use.

        Updated Marker language to clarify that it points to ULPDU
        Length even when Marker precedes FPDU.

        Clarified when to start Markers use (in Full Operation mode).

        Added informative text on interoperability with RDMAC RNICs.

        Reduced Private Data to 512 octets max.

        Clarified CRC use description, must be used unless data is at
        least as well protected by another means.

        Clarified CRC disabled mode; CRC field is always valid.

        Added Security text.

        Changed DDP and RDMAP version numbers in hex dumps (Fig 5, 6)
        and adjusted CRC accordingly.

   [draft-ietf-rddp-mpa-01] workgroup draft with following changes:

        Added the "R" bit (Rejected) to the MPA Reply Frame and
        described its semantics.

        Added some comments on recent decisions regarding startup.

        Updated RFC3667 boilerplate.

   [draft-ietf-rddp-mpa-00] workgroup draft with following changes:

        Changed "Start Key" to two separate startup frames to facilitate
        identification of incorrect active/active startup.

        Changed Active/Passive nomenclature to Initiator/Responder to
        reduce confusion with TCP startup and verbs doc (which used
        opposite sense).

        Added Private Data to the startup key sequences.  This also
        required describing the motivation and expected usage models
        along with some interface hints.  Removed the Private Data stuff
        from appendix.

        Added example "Immediate" startup with TCP and explanation.


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   [draft-culley-iwarp-mpa-03]

        Add option to allow receivers to specify Marker use.

        Add option that allows both sides to agree not to use CRC.

        Added startup declaration "Start Key" with options and larger
        MPA mode recognition "key".

        Updated MPA/DDP connection startup rules and sequence to deal
        with "Start Key".

        Added Appendix that provides a more detailed analysis of the
        effects of MPA on TCP data streams.

        Added appendix that describes a mechanism to deal with "Private
        Data" prior to full MPA/DDP operation.

   [draft-culley-iwarp-mpa-02]

        Enhanced descriptions of how MPA is used over an unmodified TCP.

        Removed "No Packing" text.

        Made MPA an adaptation layer for DDP, instead of a generalized
        framing solution.

        Added clarifications of the MPA/TCP interaction for optimized
        implementations and that any such optimizations are to be used
        only when requested by MPA.

    [draft-culley-iwarp-mpa-01] initial draft.





















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1  Glossary

   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 RFC 2119.

   Consumer - the ULPs or applications that lie above MPA and DDP.  The
       Consumer is responsible for making TCP connections, starting MPA
       and DDP connections, and generally controlling operations.

   Delivery - (Delivered, Delivers) - For MPA, Delivery is defined as
       the process of informing DDP that a particular PDU is ordered for
       use.  A PDU is Delivered in the exact order that it was sent by
       the original sender; MPA uses TCP's byte stream ordering to
       determine when Delivery is possible.  This is specifically
       different from "passing the PDU to DDP", which may generally
       occur in any order, while the order of Delivery is strictly
       defined.

   EMSS - Effective Maximum Segment Size.  EMSS is the smaller of the
       TCP maximum segment size (MSS) as defined in RFC 793 [RFC793],
       and the current path Maximum Transfer Unit (MTU) [RFC1191].

   FPDU - Framed Protocol Data Unit.  The unit of data created by an MPA
       sender.

   FPDU Alignment - the property that an FPDU is Header Aligned with the
       TCP segment, and the TCP segment includes an integer number of
       FPDUs.  A TCP segment with a FPDU Alignment allows immediate
       processing of the contained FPDUs without waiting on other TCP
       segments to arrive or combining with prior segments.

   FPDU Pointer (FPDUPTR) - This field of the Marker is used to indicate
       the beginning of an FPDU.

   Full Operation (Full Operation Phase) - After the completion of the
       Startup Phase MPA begins exchanging FPDUs.

   Header Alignment - the property that a TCP segment begins with an
       FPDU.  The FPDU is Header Aligned when the FPDU header is exactly
       at the start of the TCP segment (right behind the TCP headers on
       the wire).

   Initiator - The endpoint of a connection that sends the MPA Request
       Frame, i.e. the first to actually send data (which may not be the
       one which sends the TCP SYN).

   Marker - A four octet field that is placed in the MPA data stream at
       fixed octet intervals (every 512 octets).




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   MPA-aware TCP - a TCP implementation that is aware of the receiver
       efficiencies of MPA FPDU Alignment and is capable of sending TCP
       segments that begin with an FPDU.

   MPA-enabled - MPA is enabled if the MPA protocol is visible on the
       wire.  When the sender is MPA-enabled, it is inserting framing
       and Markers.  When the receiver is MPA-enabled, it is
       interpreting framing and Markers.

   MPA Request Frame - Data sent from the MPA Initiator to the MPA
       Responder during the Startup Phase.

   MPA Reply Frame - Data sent from the MPA Responder to the MPA
       Initiator during the Startup Phase.

   MPA - Marker-based ULP PDU Aligned Framing for TCP protocol.  This
       document defines the MPA protocol.

   MULPDU - Maximum ULPDU.  The current maximum size of the record that
       is acceptable for DDP to pass to MPA for transmission.

   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 MPA on TCP devices installed in a host
       computer.

   PAD - A 1-3 octet group of zeros used to fill an FPDU to an exact
       modulo 4 size.

   PDU - protocol data unit

   Private Data - A block of data exchanged between MPA endpoints during
       initial connection setup.

   Protection Domain - An RDMA concept (see [VERBS] and [RDMASEC]) that
       tie use of various endpoint resources (memory access etc.) to the
       specific RDMA/DDP/MPA connection.

   RDMA - Remote Direct Memory Access; a protocol that uses DDP and MPA
       to enable applications to transfer data directly from memory
       buffers.  See [RDMAP].

   Remote Peer - The MPA protocol implementation on the opposite end of
       the connection.  Used to refer to the remote entity when
       describing protocol exchanges or other interactions between two
       Nodes.

   Responder - The connection endpoint which responds to an incoming MPA
       connection request (the MAP Request Frame).  This may not be the
       endpoint which awaited the TCP SYN.


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   Startup Phase - The initial exchanges of an MPA connection which
       serves to more fully identify MPA endpoints to each other and
       pass connection specific setup information to each other.

   ULP - Upper Layer Protocol.  The protocol layer above the protocol
       layer currently being referenced.  The ULP for MPA is DDP [DDP].

   ULPDU - Upper Layer Protocol Data Unit.  The data record defined by
      the layer above MPA (DDP).  ULPDU corresponds to DDP's DDP
      segment.

   ULPDU_Length - a field in the FPDU describing the length of the
      included ULPDU.








































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2  Introduction

   This section discusses the reason for creating MPA on TCP and a
   general overview of the protocol.  Later sections show the MPA
   headers (see section 4 on page 18), and detailed protocol
   requirements and characteristics (see section 5 on page 20), as well
   as Connection Semantics (section 6 on page 31), Error Semantics
   (section 7 on page 46), and Security Considerations (section 8 on
   page 47).

2.1  Motivation

   The Direct Data Placement protocol [DDP], when used with TCP [RFC793]
   requires a mechanism to detect record boundaries.  The DDP records
   are referred to as Upper Layer Protocol Data Units by this document.
   The ability to locate the Upper Layer Protocol Data Unit (ULPDU)
   boundary is useful to a hardware network adapter that uses DDP to
   directly place the data in the application buffer based on the
   control information carried in the ULPDU header.  This may be done
   without requiring that the packets arrive in order.  Potential
   benefits of this capability are the avoidance of the memory copy
   overhead and a smaller memory requirement for handling out of order
   or dropped packets.

   Many approaches have been proposed for a generalized framing
   mechanism.  Some are probabilistic in nature and others are
   deterministic.  A probabilistic approach is characterized by a
   detectable value embedded in the octet stream.  It is probabilistic
   because under some conditions the receiver may incorrectly interpret
   application data as the detectable value.  Under these conditions,
   the protocol may fail with unacceptable frequency.  A deterministic
   approach is characterized by embedded controls at known locations in
   the octet stream.  Because the receiver can guarantee it will only
   examine the data stream at locations that are known to contain the
   embedded control, the protocol can never misinterpret application
   data as being embedded control data.  For unambiguous handling of an
   out of order packet, the deterministic approach is preferred.

   The MPA protocol provides a framing mechanism for DDP running over
   TCP using the deterministic approach.  It allows the location of the
   ULPDU to be determined in the TCP stream even if the TCP segments
   arrive out of order.

2.2  Protocol Overview

   The layering of PDUs with MPA is shown in Figure 1, below.







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               +------------------+
               |     ULP client   |
               +------------------+  <- Consumer messages
               |        DDP       |
               +------------------+  <- ULPDUs
               |        MPA       |
               +------------------+  <- FPDUs (containing ULPDUs)
               |        TCP*      |
               +------------------+  <- TCP Segments (containing FPDUs)
               |      IP etc.     |
               +------------------+
                                      * TCP or MPA-aware TCP.

                       Figure 1 ULP MPA TCP Layering

   MPA is described as an extra layer above TCP and below DDP.  The
   operation sequence is:

   1.  A TCP connection is established by ULP action.  This is done
       using methods not described by this specification.  The ULP may
       exchange some amount of data in streaming mode prior to starting
       MPA, but is not required to do so.

   2.  The Consumer negotiates the use of DDP and MPA at both ends of a
       connection.  The mechanisms to do this are not described in this
       specification.  The negotiation may be done in streaming mode, or
       by some other mechanism (such as a pre-arranged port number).

   3.  The ULP activates MPA on each end in the Startup Phase, either as
       an Initiator or a Responder, as determined by the ULP.  This mode
       verifies the usage of MPA, specifies the use of CRC and Markers,
       and allows the ULP to communicate some additional data via a
       Private Data exchange.  See section 6.1 Connection setup for more
       details on the startup process.

   4.  At the end of the Startup Phase, the ULP puts MPA (and DDP) into
       Full Operation and begins sending DDP data as further described
       below.  In this document, DDP data chunks are called ULPDUs.  For
       a description of the DDP data, see [DDP].

   Following is a description of data transfer when MPA is in Full
   Operation.

   1.  DDP determines the Maximum ULPDU (MULPDU) size by querying MPA
       for this value.  MPA derives this information from TCP or IP,
       when it is available, or chooses a reasonable value.

   2.  DDP creates ULPDUs of MULPDU size or smaller, and hands them to
       MPA at the sender.




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   3.  MPA creates a Framed Protocol Data Unit (FPDU) by pre-pending a
       header, optionally inserting Markers, and appending a CRC field
       after the ULPDU and PAD (if any).  MPA delivers the FPDU to TCP.

   4.  The TCP sender puts the FPDUs into the TCP stream.  If the TCP
       Sender is MPA-aware, it segments the TCP stream in such a way
       that a TCP Segment boundary is also the boundary of an FPDU.  TCP
       then passes each segment to the IP layer for transmission.

   5.  The TCP receiver may be MPA-aware or may not be MPA-aware.  If it
       is MPA-aware, it may separate passing the TCP payload to MPA from
       passing the TCP payload ordering information to MPA.  In either
       case, RFC compliant TCP wire behavior is observed at both the
       sender and receiver.

   6.  The MPA receiver locates and assembles complete FPDUs within the
       stream, verifies their integrity, and removes MPA Markers (when
       present), ULPDU_Length, PAD and the CRC field.

   7.  MPA then provides the complete ULPDUs to DDP.  MPA may also
       separate passing MPA payload to DDP from passing the MPA payload
       ordering information.

   MPA-aware TCP is a TCP layer which potentially contains some
   additional semantics as defined in this document.  MPA is implemented
   as a data stream ULP for TCP and is therefore RFC compliant.  MPA-
   aware TCP is RFC compliant.

   An MPA-aware TCP sender is able to segment the data stream such that
   TCP segments begin with FPDUs (FPDU Alignment).  This has significant
   advantages for receivers.  When segments arrive with aligned FPDUs
   the receiver usually need not buffer any portion of the segment,
   allowing DDP to place it in its destination memory immediately, thus
   avoiding copies from intermediate buffers (DDP's reason for
   existence).

   MPA with an MPA-aware TCP receiver allows a DDP on MPA implementation
   to locate the start of ULPDUs that may be received out of order.  It
   also allows the implementation to determine if the entire ULPDU has
   been received.  As a result, MPA can pass out of order ULPDUs to DDP
   for immediate use.  This enables a DDP on MPA implementation to save
   a significant amount of intermediate storage by placing the ULPDUs in
   the right locations in the application buffers when they arrive,
   rather than waiting until full ordering can be restored.

   The ability of a receiver to recover out of order ULPDUs is optional
   and declared to the transmitter during startup.  When the receiver
   declares that it does not support out of order recovery, the
   transmitter does not add the control information to the data stream
   needed for out of order recovery.



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   If TCP is not MPA-aware, then MPA receives a strictly ordered stream
   of data and does not deal with out of order ULPDUs.  In this case MPA
   passes each ULPDU to DDP when the last bytes arrive from TCP, along
   with the indication that they are in order.

   MPA implementations that support recovery of out of order ULPDUs MUST
   support a mechanism to indicate the ordering of ULPDUs as the sender
   transmitted them and indicate when missing intermediate segments
   arrive.  These mechanisms allow DDP to reestablish record ordering
   and report Delivery of complete messages (groups of records).

   MPA also addresses enhanced data integrity.  Some users of TCP have
   noted that the TCP checksum is not as strong as could be desired (see
   [CRCTCP]).  Studies such as [CRCTCP] have shown that the TCP checksum
   indicates segments in error at a much higher rate than the underlying
   link characteristics would indicate.  With these higher error rates,
   the chance that an error will escape detection, when using only the
   TCP checksum for data integrity, becomes a concern.  A stronger
   integrity check can reduce the chance of data errors being missed.

   MPA includes a CRC check to increase the ULPDU data integrity to the
   level provided by other modern protocols, such as SCTP [RFC2960].  It
   is possible to disable this CRC check, however CRCs MUST be enabled
   unless it is clear that the end to end connection through the network
   has data integrity at least as good as a MPA with CRC enabled (for
   example when IPsec is implemented end to end).  DDP's ULP expects
   this level of data integrity and therefore the ULP does not have to
   provide its own duplicate data integrity and error recovery for lost
   data.
























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3  LLP and DDP requirements

   The following sections describe requirements on TCP and DDP to
   utilize MPA.  The DDP requirements enable the correct operation over
   MPA and TCP (as opposed to DDP over SCTP or other LLPs).

   The TCP requirements are mostly intended to support the MPA-aware TCP
   variation, which allows implementations that require less buffer
   memory and may provide better overall system performance.

3.1  TCP implementation Requirements to support MPA

   The TCP implementation MUST inform MPA when the TCP connection is
   closed or has begun closing the connection (e.g. received a FIN).

3.1.1  TCP Transmit side

   To provide optimum performance, an MPA-aware transmit side TCP
   implementation SHOULD be enabled to:

   *   With an EMSS large enough to contain the FPDU(s), segment the
       outgoing TCP stream such that the first octet of every TCP
       Segment begins with an FPDU.  Multiple FPDUs MAY be packed into a
       single TCP segment as long as they are entirely contained in the
       TCP segment.

   *   Report the current EMSS to the MPA transmit layer.

   An MPA-aware TCP transmit side implementation MUST continue to use
   the method of segmentation expected by non-MPA applications (and
   described in TCP RFCs) when MPA is not enabled on the connection.
   When MPA is enabled above an MPA-aware TCP, it SHOULD specifically
   enable the segmentation rules described above for the DDP segments
   (FPDUs) posted for transmission.

   If the transmit side TCP implementation is not able to segment the
   TCP stream as indicated above, MPA SHOULD make a best effort to
   achieve that result.  For example, using the TCP_NODELAY socket
   option to disable the Nagle algorithm will usually result in many of
   the segments starting with an FPDU.

   If the transmit side TCP implementation is not able to report the
   EMSS, MPA SHOULD use the current MTU value to establish a likely FPDU
   size, taking into account the various expected header sizes.

3.1.2  TCP Receive side

   When an MPA receive implementation and the MPA-aware receive side TCP
   implementation support handling out of order ULPDUs, the TCP receive
   implementation SHOULD be enabled to:



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   *   Pass incoming TCP segments to MPA as soon as they have been
       received and validated, even if not received in order.  The TCP
       layer MUST have committed to keeping each segment before it can
       be passed to the MPA.  This means that the segment must have
       passed the TCP, IP, and lower layer data integrity validation
       (i.e., checksum), must be in the receive window, must not be a
       duplicate, must be part of the same epoch (if timestamps are used
       to verify this) and any other checks required by TCP RFCs.  The
       segment MUST NOT be passed to MPA more than once unless
       explicitly requested (see Section 7).

       This is not to imply that the data must be completely ordered
       before use.  An implementation MAY accept out of order segments,
       SACK them [RFC2018], and pass them to DDP immediately, before the
       reception of the segments needed to fill in the gaps arrive.
       Such an implementation MUST "commit" to the data early on, and
       MUST NOT overwrite it even if (or when) duplicate data arrives.
       MPA expects to utilize this "commit" to allow the passing of
       ULPDUs to DDP when they arrive, independent of ordering.  DDP
       uses the passed ULPDU to "place" the DDP segments (see [DDP] for
       more details).

   *   Provide a mechanism to indicate the ordering of TCP segments as
       the sender transmitted them.  One possible mechanism might be
       attaching the TCP sequence number to each segment.

   *   Provide a mechanism to indicate when a given TCP segment (and the
       prior TCP stream) is complete.  One possible mechanism might be
       to utilize the leading (left) edge of the TCP Receive Window.

       MPA uses the ordering and completion indications to inform DDP
       when a ULPDU is complete; MPA Delivers the FPDU to DDP.  DDP uses
       the indications to "deliver" its messages to the DDP consumer
       (see [DDP] for more details).

       DDP on MPA MUST utilize these two mechanisms to establish the
       Delivery semantics that DDP's consumers agree to.  These
       semantics are described fully in [DDP].  These include
       requirements on DDP's consumer to respect ownership of buffers
       prior to the time that DDP delivers them to the Consumer.

   An MPA-aware TCP receive side implementation MUST continue to buffer
   TCP segments until completely ordered and then deliver them as
   expected by non-MPA applications (and described in TCP RFCs) when MPA
   is not enabled on the connection.  When MPA is enabled above an MPA-
   aware TCP, TCP SHOULD enable the in and out of order passing of data,
   and the separate ordering information as described above.

   When an MPA receive implementation is coupled with a TCP receive
   implementation that does not support the preceding mechanisms, TCP
   passes and Delivers incoming stream data to MPA in order.


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3.2  MPA's interactions with DDP

   DDP requires MPA to maintain DDP record boundaries from the sender to
   the receiver.  When using MPA on TCP to send data, DDP provides
   records (ULPDUs) to MPA.  MPA will use the reliable transmission
   abilities of TCP to transmit the data, and will insert appropriate
   additional information into the TCP stream to allow the MPA receiver
   to locate the record boundary information.

   As such, MPA accepts complete records (ULPDUs) from DDP at the sender
   and returns them to DDP at the receiver.

   MPA combined with an MPA-aware TCP can only ensure FPDU Alignment
   with the TCP Header if the FPDU is less than or equal to TCP's EMSS.
   Since FPDU Alignment is generally desired by the receiver, DDP must
   cooperate with MPA to ensure FPDUs' lengths do not exceed the EMSS
   under normal conditions.  This is done with the MULPDU mechanism.

   MPA provides information to DDP on the current maximum size of the
   record that is acceptable to send (MULPDU).  DDP SHOULD limit each
   record size to MULPDU.  The range of MULPDU values MUST be between
   128 octets and 64768 octets, inclusive.

   The sending DDP MUST NOT post a ULPDU larger than 64768 octets to
   MPA.  DDP MAY post a ULPDU of any size between one and 64768 octets,
   however MPA is not REQUIRED to support a ULPDU Length that is greater
   than the current MULPDU.

   While the maximum theoretical length supported by the MPA header
   ULPDU_Length field is 65535, TCP over IP requires the IP datagram
   maximum length to be 65535 octets.  To enable MPA to support FPDU
   Alignment, the maximum size of the FPDU must fit within an IP
   datagram.  Thus the ULPDU limit of 64768 octets was derived by taking
   the maximum IP datagram length, subtracting from it the maximum total
   length of the sum of the IPv4 header, TCP header, IPv4 options, TCP
   options, and the worst case MPA overhead, and then rounding the
   result down to a 128 octet boundary.

   On receive, MPA MUST pass each ULPDU with its length to DDP when it
   has been validated.

   If an MPA implementation supports passing out of order ULPDUs to DDP,
   the MPA implementation SHOULD:

   *   Pass each ULPDU with its length to DDP as soon as it has been
       fully received and validated.

   *   Provide a mechanism to indicate the ordering of ULPDUs as the
       sender transmitted them.  One possible mechanism might be
       providing the TCP sequence number for each ULPDU.



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   *   Provide a mechanism to indicate when a given ULPDU (and prior
       ULPDUs) are complete (Delivered to DDP).  One possible mechanism
       might be to allow DDP to see the current outgoing TCP Ack
       sequence number.

   *   Provide an indication to DDP that the TCP has closed or has begun
       to close the connection (e.g. received a FIN).

   MPA MUST provide the protocol version negotiated with its peer to
   DDP.  DDP will use this version to set the version in its header and
   to report the version to [RDMAP].










































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4  FPDU Formats

   MPA senders create FPDUs out of ULPDUs.  The format of an FPDU shown
   below MUST be used for all MPA FPDUs.  For purposes of clarity,
   Markers are not 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          ULPDU_Length         |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
      |                                                               |
      ~                                                               ~
      ~                            ULPDU                              ~
      |                                                               |
      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |          PAD (0-3 octets)     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                             CRC                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                           Figure 2 FPDU Format

   ULPDU_Length: 16 bits (unsigned integer).  This is the number of
   octets of the contained ULPDU.  It does not include the length of the
   FPDU header itself, the pad, the CRC, or of any Markers that fall
   within the ULPDU.  The 16-bit ULPDU Length field is large enough to
   support the largest IP datagrams for IPv4 or IPv6.

   PAD: The PAD field trails the ULPDU and contains between zero and
   three octets of data.  The pad data MUST be set to zero by the sender
   and ignored by the receiver (except for CRC checking).  The length of
   the pad is set so as to make the size of the FPDU an integral
   multiple of four.

   CRC: 32 bits, When CRCs are enabled, this field contains a CRC32C
   check value, which is used to verify the entire contents of the FPDU,
   using CRC32C.  See section 5.2 CRC Calculation on page 23.  When CRCs
   are not enabled, this field is still present, may contain any value,
   and MUST NOT be checked.

   The FPDU adds a minimum of 6 octets to the length of the ULPDU.  In
   addition, the total length of the FPDU will include the length of any
   Markers and from 0 to 3 pad octets added to round-up the ULPDU size.










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4.1  Marker Format

   The format of a Marker MUST be as specified 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |           RESERVED            |            FPDUPTR            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Figure 3 Marker Format

   RESERVED: The Reserved field MUST be set to zero on transmit and
   ignored on receive (except for CRC calculation).

   FPDUPTR: The FPDU Pointer is a relative pointer, 16-bits long,
   interpreted as an unsigned integer that indicates the number of
   octets in the TCP stream from the beginning of the ULPDU Length field
   to the first octet of the entire Marker.  The least significant two
   bits MUST always be set to zero at the transmitter, and the receivers
   MUST always treat these as zero for calculations.

































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5  Data Transfer Semantics

   This section discusses some characteristics and behavior of the MPA
   protocol as well as implications of that protocol.

5.1  MPA Markers

   MPA Markers are used to identify the start of FPDUs when packets are
   received out of order.  This is done by locating the Markers at fixed
   intervals in the data stream (which is correlated to the TCP sequence
   number) and using the Marker value to locate the preceding FPDU
   start.

   All MPA Markers are included in the containing FPDU CRC calculation
   (when both CRCs and Markers are in use).

   The MPA receiver's ability to locate out of order FPDUs and pass the
   ULPDUs to DDP is implementation dependent.  MPA/DDP allows those
   receivers that are able to deal with out of order FPDUs in this way
   to require the insertion of Markers in the data stream.  When the
   receiver cannot deal with out of order FPDUs in this way, it may
   disable the insertion of Markers at the sender.  All MPA senders MUST
   be able to generate Markers when their use is declared by the
   opposing receiver (see section 6.1 Connection setup on page 32).

   When Markers are enabled, MPA senders MUST insert a Marker into the
   data stream at a 512 octet periodic interval in the TCP Sequence
   Number Space.  The Marker contains a 16 bit unsigned integer referred
   to as the FPDUPTR (FPDU Pointer).

   If the FPDUPTR's value is non-zero, the FPDU Pointer is a 16 bit
   relative back-pointer.  FPDUPTR MUST contain the number of octets in
   the TCP stream from the beginning of the ULPDU Length field to the
   first octet of the Marker, unless the Marker falls between FPDUs.
   Thus the location of the first octet of the previous FPDU header can
   be determined by subtracting the value of the given Marker from the
   current octet-stream sequence number (i.e. TCP sequence number) of
   the first octet of the Marker.  Note that this computation MUST take
   into account that the TCP sequence number could have wrapped between
   the Marker and the header.

   An FPDUPTR value of 0x0000 is a special case - it is used when the
   Marker falls exactly between FPDUs (between the preceding FPDU CRC
   field, and the next FPDU's ULPDU Length field).  In this case, the
   Marker is considered to be contained in the following FPDU; the
   Marker MUST be included in the CRC calculation of the FPDU following
   the Marker (if CRCs are being generated or checked).  Thus an FPDUPTR
   value of 0x0000 means that immediately following the Marker is an
   FPDU header (the ULPDU Length field).




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   Since all FPDUs are integral multiples of 4 octets, the bottom two
   bits of the FPDUPTR as calculated by the sender are zero.  MPA
   reserves these bits so they MUST be treated as zero for computation
   at the receiver.

   When Markers are enabled (see section 6.1 Connection setup on page
   32), the MPA Markers MUST be inserted immediately preceding the first
   FPDU of Full Operation phase, and at every 512th octet of the TCP
   octet stream thereafter.  As a result, the first Marker has an
   FPDUPTR value of 0x0000.  If the first Marker begins at octet
   sequence number SeqStart, then Markers are inserted such that the
   first octet of the Marker is at octet sequence number SeqNum if the
   remainder of (SeqNum - SeqStart) mod 512 is zero.  Note that SeqNum
   can wrap.

   For example, if the TCP sequence number were used to calculate the
   insertion point of the Marker, the starting TCP sequence number is
   unlikely to be zero, and 512 octet multiples are unlikely to fall on
   a modulo 512 of zero.  If the MPA connection is started at TCP
   sequence number 11, then the 1st Marker will begin at 11, and
   subsequent Markers will begin at 523, 1035, etc.

   If an FPDU is large enough to contain multiple Markers, they MUST all
   point to the same point in the TCP stream: the first octet of the
   ULPDU Length field for the FPDU.

   If a Marker interval contains multiple FPDUs (the FPDUs are small),
   the Marker MUST point to the start of the ULPDU Length field for the
   FPDU containing the Marker unless the Marker falls between FPDUs, in
   which case the Marker MUST be zero.

   The following example shows an FPDU containing a Marker.

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |       ULPDU Length (0x0010)   |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
      |                                                               |
      +                                                               +
      |                         ULPDU (octets 0-9)                    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |            (0x0000)           |        FPDU ptr (0x000C)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        ULPDU (octets 10-15)                   |
      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |          PAD (2 octets:0,0)   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                              CRC                              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                 Figure 4 Example FPDU Format with Marker


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   MPA Receivers MUST preserve ULPDU boundaries when passing data to
   DDP.  MPA Receivers MUST pass the ULPDU data and the ULPDU Length to
   DDP and not the Markers, headers, and CRC.


















































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5.2  CRC Calculation

   An MPA implementation MUST implement CRC support and MUST either:

   (1) always use CRCs; The MPA provider at is not REQUIRED to support
       an administrator's request that CRCs not be used.

       or

   (2a) only indicate a preference to not use CRCs on the explicit
       request of the system administrator, via an interface not defined
       in this spec.  The default configuration for a connection MUST be
       to use CRCs.

   (2b) disable CRC checking (and possibly generation) if both the local
       and remote endpoints indicate preference to not use CRCs.

   The decision for hosts to request CRC suppression MAY be made on an
   administrative basis for any path that provides equivalent protection
   from undetected errors as an end-to-end CRC32c.

   The process MUST be invisible to the ULP.

   After receipt of an MPA startup declaration indicating that its peer
   requires CRCs, an MPA instance MUST continue generating and checking
   CRCs until the connection terminates.  If an MPA instance has
   declared that it does not require CRCs, it MUST turn off CRC checking
   immediately after receipt of an MPA mode declaration indicating that
   its peer also does not require CRCs.  It MAY continue generating
   CRCs.  See section 6.1 Connection setup on page 32 for details on the
   MPA startup.

   When sending an FPDU, the sender MUST include a CRC field.  When CRCs
   are enabled, the CRC field in the MPA FPDU MUST be computed using the
   CRC32C polynomial in the manner described in the iSCSI Protocol
   [iSCSI] document for Header and Data Digests.















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   The fields which MUST be included in the CRC calculation when sending
   an FPDU are as follows:

   1)  If a Marker does not immediately precede the ULPDU Length field,
       the CRC-32c is calculated from the first octet of the ULPDU
       Length field, through all the ULPDU and Markers (if present), to
       the last octet of the PAD (if present), inclusive.  If there is a
       Marker immediately following the PAD, the Marker is included in
       the CRC calculation for this FPDU.

   2)  If a Marker immediately precedes the first octet of the ULPDU
       Length field of the FPDU, (i.e. the Marker fell between FPDUs,
       and thus is required to be included in the second FPDU), the CRC-
       32c is calculated from the first octet of the Marker, through the
       ULPDU Length header, through all the ULPDU and Markers (if
       present), to the last octet of the PAD (if present), inclusive.

   3)  After calculating the CRC-32c, the resultant value is placed into
       the CRC field at the end of the FPDU.

   When an FPDU is received, and CRC checking is enabled, the receiver
   MUST first perform the following:

   1)  Calculate the CRC of the incoming FPDU in the same fashion as
       defined above.

   2)  Verify that the calculated CRC-32c value is the same as the
       received CRC-32c value found in the FPDU CRC field.  If not, the
       receiver MUST treat the FPDU as an invalid FPDU.

   The procedure for handling invalid FPDUs is covered in the Error
   Section (see section 7 on page 46)

   The following is an annotated hex dump of an example FPDU sent as the
   first FPDU on the stream.  As such, it starts with a Marker.  The
   FPDU contains a 42 octet ULPDU (an example DDP segment) which in turn
   contains 24 octets of the contained ULPDU, which is a data load that
   is all zeros.  The CRC32c has been correctly calculated and can be
   used as a reference.  See the [DDP] and [RDMAP] specification for
   definitions of the DDP Control field, Queue, MSN, MO, and Send Data.













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       Octet Contents  Annotation
       Count

       0000    00      Marker: Reserved
       0001    00
       0002    00      Marker: FPDUPTR
       0003    00
       0004    00      ULPDU Length
       0005    2a
       0006    41      DDP Control Field, Send with Last flag set
       0007    43
       0008    00      Reserved (DDP STag position with no STag)
       0009    00
       000a    00
       000b    00
       000c    00      DDP Queue = 0
       000d    00
       000e    00
       000f    00
       0010    00      DDP MSN = 1
       0011    00
       0012    00
       0013    01
       0014    00      DDP MO = 0
       0015    00
       0016    00
       0017    00
       0018    00      DDP Send Data (24 octets of zeros)
       ...
       002f    00
       0030    52      CRC32c
       0031    23
       0032    99
       0033    83
                  Figure 5 Annotated Hex Dump of an FPDU


















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   The following is an example sent as the second FPDU of the stream
   where the first FPDU (which is not shown here) had a length of 492
   octets and was also a Send to Queue 0 with Last Flag set.  This
   example contains a Marker.

       Octet Contents  Annotation
       Count

       01ec    00      Length
       01ed    2a
       01ee    41      DDP Control Field: Send with Last Flag set
       01ef    43
       01f0    00      Reserved (DDP STag position with no STag)
       01f1    00
       01f2    00
       01f3    00
       01f4    00      DDP Queue = 0
       01f5    00
       01f6    00
       01f7    00
       01f8    00      DDP MSN = 2
       01f9    00
       01fa    00
       01fb    02
       01fc    00      DDP MO = 0
       01fd    00
       01fe    00
       01ff    00
       0200    00      Marker: Reserved
       0201    00
       0202    00      Marker: FPDUPTR
       0203    14
       0204    00      DDP Send Data (24 octets of zeros)
       ...
       021b    00
       021c    84      CRC32c
       021d    92
       021e    58
       021f    98
            Figure 6 Annotated Hex Dump of an FPDU with Marker

5.3  MPA on TCP Sender Segmentation

   The various TCP RFCs allow considerable choice in segmenting a TCP
   stream.  In order to optimize FPDU recovery at the MPA receiver, MPA
   specifies additional segmentation rules.

   MPA MUST encapsulate the ULPDU such that there is exactly one ULPDU
   contained in one FPDU.




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   An MPA-aware TCP sender SHOULD, when enabled for MPA, on TCP
   implementations that support this, and with an EMSS large enough to
   contain at least one FPDU, segment the outbound TCP stream such that
   each TCP segment begins with an FPDU, and fully contains all included
   FPDUs.

        Implementation note: To achieve the previous segmentation rule,
        an MPA-aware TCP sender implementation SHOULD disable TCP's
        Nagle [RFC0896] algorithm, communicate the FPDU boundaries to
        TCP, and make other minor changes such as the reporting of EMSS
        to MPA.

   There are exceptions to the above rule.  Once an ULPDU is provided to
   MPA, the MPA on TCP sender MUST transmit it or fail the connection;
   it cannot be repudiated.  As a result, during changes in MTU and
   EMSS, or when TCP's Receive Window size (RWIN) becomes too small, it
   may be necessary to send FPDUs that do not conform to the
   segmentation rule above.

   A possible, but less desirable, alternative is to use IP
   fragmentation on accepted FPDUs to deal with MTU reductions or
   extremely small EMSS.

   The sender MUST still format the FPDU according to FPDU format as
   shown in Figure 2.

   On a retransmission, TCP does not necessarily preserve original TCP
   segmentation boundaries.  This can lead to the loss of FPDU Alignment
   and containment within a TCP segment during TCP retransmissions.  An
   MPA-aware TCP sender SHOULD try to preserve original TCP segmentation
   boundaries on a retransmission.

5.3.1  Effects of MPA on TCP Segmentation

   DDP/MPA senders will fill TCP segments to the EMSS with a single FPDU
   when a DDP message is large enough.  Since the DDP message may not
   exactly fit into TCP segments, a "message tail" often occurs that
   results in an FPDU that is smaller than a single TCP segment.
   Additionally some DDP messages may be considerably shorter than the
   EMSS.  If a small FPDU is sent in a single TCP segment the result is
   a "short" TCP segment.

   Applications expected to see strong advantages from Direct Data
   Placement include transaction-based applications and throughput
   applications.  Request/response protocols typically send one FPDU per
   TCP segment and then wait for a response.  Under these conditions,
   these "short" TCP segments are an appropriate and expected effect of
   the segmentation.

   Another possibility is that the application might be sending multiple
   messages (FPDUs) to the same endpoint before waiting for a response.


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   In this case, the segmentation policy would tend to reduce the
   available connection bandwidth by under-filling the TCP segments.

   TCP implementations often utilize the Nagle [RFC0896] algorithm to
   ensure that segments are filled to the EMSS whenever the round trip
   latency is large enough that the source stream can fully fill
   segments before Acks arrive.  The algorithm does this by delaying the
   transmission of TCP segments until a ULP can fill a segment, or until
   an ACK arrives from the far side.  The algorithm thus allows for
   smaller segments when latencies are shorter to keep the ULP's end to
   end latency to reasonable levels.

   The Nagle algorithm is not mandatory to use [RFC1122].

   If Nagle or other algorithms for detecting the availability of
   multiple FPDUs for transmission is used, "packing" of multiple FPDUs
   into TCP segments can occur.

   If a "message tail", small DDP messages, or the start of a larger DDP
   message are available, MPA MAY pack multiple FPDUs into TCP segments.
   When this is done, the TCP segments can be more fully utilized, but,
   due to the size constraints of FPDUs, segments may not be filled to
   the EMSS.

        Note that MPA receivers must do more processing of a TCP segment
        that contains multiple FPDUs, this may affect the performance of
        some receiver implementations.

   It is up to the ULP to decide if Nagle is useful with DDP/MPA.  Note
   that many of the applications expected to take advantage of MPA/DDP
   prefer to avoid the extra delays caused by Nagle.  In such scenarios
   it is anticipated there will be minimal opportunity for packing at
   the transmitter and receivers may choose to optimize their
   performance for this anticipated behavior.

   Therefore, the application is expected to set TCP parameters such
   that it can trade off latency and wire efficiency.  This is
   accomplished by setting the TCP_NODELAY socket option (which disables
   Nagle).

   When latency is not critical, application is expected to leave Nagle
   enabled.  In this case the TCP implementation may pack any available
   stream data into TCP segments so that the segments are filled to the
   EMSS.  If the amount of data available is not enough to fill the TCP
   segment when it is prepared for transmission, TCP can send the
   segment partly filled, or use the Nagle algorithm to wait for the ULP
   to post more data (discussed below).






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5.3.2  FPDU Size Considerations

   MPA defines the Maximum Upper Layer Protocol Data Unit (MULPDU) as
   the size of the largest ULPDU fitting in an FPDU.  For an empty TCP
   Segment, MULPDU is EMSS minus the FPDU overhead (6 octets) minus
   space for Markers and pad octets.

        The maximum ULPDU Length for a single ULPDU when Markers are
        present MUST be computed as:

        MULPDU = EMSS - (6 + 4 * Ceiling(EMSS / 512) + EMSS mod 4)

   The formula above accounts for the worst-case number of Markers.

        The maximum ULPDU Length for a single ULPDU when Markers are NOT
        present MUST be computed as:

        MULPDU = EMSS - (6 + EMSS mod 4)

   As a further optimization of the wire efficiency an MPA
   implementation MAY dynamically adjust the MULPDU (see section 5.3.1
   for latency and wire efficiency trade-offs).  When one or more FPDUs
   are already packed into a TCP Segment, MULPDU MAY be reduced
   accordingly.

   DDP SHOULD provide ULPDUs that are as large as possible, but less
   than or equal to MULPDU.

   If the TCP implementation needs to adjust EMSS to support MTU
   changes, the MULPDU value is changed accordingly.

   In certain rare situations, the EMSS may shrink below 128 octets in
   size.  If this occurs, the MPA on TCP sender MUST NOT shrink the
   MULPDU below 128 octets and is not REQUIRED to follow the
   segmentation rules in Section 5.3 MPA on TCP Sender Segmentation on
   page 26.

   If one or more FPDUs are already packed into a TCP segment, such that
   the remaining room is less than 128 octets, MPA MUST NOT provide a
   MULPDU smaller than 128.  In this case, MPA would typically provide a
   MULPDU for the next full sized segment, but may still pack the next
   FPDU into the small remaining room, provide that the next FPDU is
   small enough to fit.

   The value 128 is chosen as to allow DDP designers room for the DDP
   Header and some user data.







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5.4  MPA Receiver FPDU Identification

   An MPA receiver MUST first verify the FPDU before passing the ULPDU
   to DDP.  To do this, the receiver MUST:

   *   locate the start of the FPDU unambiguously,

   *   verify its CRC (if CRC checking is enabled).

   If the above conditions are true, the MPA receiver passes the ULPDU
   to DDP.

   To detect the start of the FPDU unambiguously one of the following
   MUST be used:

   1:  In an ordered TCP stream, the ULPDU Length field in the current
       FPDU when FPDU has a valid CRC, can be used to identify the
       beginning of the next FPDU.

   2:  For receivers that support out of order reception of FPDUs (see
       section 5.1 MPA Markers on page 20) a Marker can always be used
       to locate the beginning of an FPDU (in FPDUs with valid CRCs).
       Since the location of the Marker is known in the octet stream
       (sequence number space), the Marker can always be found.

   3:  Having found an FPDU by means of a Marker, following contiguous
       FPDUs can be found by using the ULPDU Length fields (from FPDUs
       with valid CRCs) to establish the next FPDU boundary.

   The ULPDU Length field (see section 4) MUST be used to determine if
   the entire FPDU is present before forwarding the ULPDU to DDP.

   CRC calculation is discussed in section 5.2 on page 23 above.


















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5.4.1  Re-segmenting Middle boxes and non MPA-aware TCP senders

   Since MPA on MPA-aware TCP senders start FPDUs on TCP segment
   boundaries, a receiving DDP on MPA on TCP implementation may be able
   to optimize the reception of data in various ways.

   However, MPA receivers MUST NOT depend on FPDU Alignment on TCP
   segment boundaries.

   Some MPA senders may be unable to conform to the sender requirements
   because their implementation of TCP is not designed with MPA in mind.
   Even if the sender is MPA-aware, the network may contain "middle
   boxes" which modify the TCP stream by changing the segmentation.
   This is generally interoperable with TCP and its users and MPA must
   be no exception.

   The presence of Markers in MPA (when enabled) allows an MPA receiver
   to recover the FPDUs despite these obstacles, although it may be
   necessary to utilize additional buffering at the receiver to do so.

   Some of the cases that a receiver may have to contend with are listed
   below as a reminder to the implementer:

   *   A single Aligned and complete FPDU, either in order, or out of
       order:  This can be passed to DDP as soon as validated, and
       Delivered when ordering is established.

   *   Multiple FPDUs in a TCP segment, aligned and fully contained,
       either in order, or out of order:  These can be passed to DDP as
       soon as validated, and Delivered when ordering is established.

   *   Incomplete FPDU: The receiver should buffer until the remainder
       of the FPDU arrives.  If the remainder of the FPDU is already
       available, this can be passed to DDP as soon as validated, and
       Delivered when ordering is established.

   *   Unaligned FPDU start: The partial FPDU must be combined with its
       preceding portion(s).  If the preceding parts are already
       available, and the whole FPDU is present, this can be passed to
       DDP as soon as validated, and Delivered when ordering is
       established.  If the whole FPDU is not available, the receiver
       should buffer until the remainder of the FPDU arrives.

   *   Combinations of Unaligned or incomplete FPDUs (and potentially
       other complete FPDUs) in the same TCP segment:  If any FPDU is
       present in its entirety, or can be completed with portions
       already available, it can be passed to DDP as soon as validated,
       and Delivered when ordering is established.



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6  Connection Semantics

6.1  Connection setup

   MPA requires that the Consumer MUST activate MPA, and any TCP
   enhancements for MPA, on a TCP half connection at the same location
   in the octet stream at both the sender and the receiver.  This is
   required in order for the Marker scheme to correctly locate the
   Markers (if enabled) and to correctly locate the first FPDU.

   MPA, and any TCP enhancements for MPA are enabled by the ULP in both
   directions at once at an endpoint.

   This can be accomplished several ways, and is left up to DDP's ULP:

   *   DDP's ULP MAY require DDP on MPA startup immediately after TCP
       connection setup.  This has the advantage that no streaming mode
       negotiation is needed.  An example of such a protocol is shown in
       Figure 9: Example Immediate Startup negotiation on page 42.

       This may be accomplished by using a well-known port, or a service
       locator protocol to locate an appropriate port on which DDP on
       MPA is expected to operate.

   *   DDP's ULP MAY negotiate the start of DDP on MPA sometime after a
       normal TCP startup, using TCP streaming data exchanges on the
       same connection.  The exchange establishes that DDP on MPA (as
       well as other ULPs) will be used, and exactly locates the point
       in the octet stream where MPA is to begin operation.  Note that
       such a negotiation protocol is outside the scope of this
       specification.  A simplified example of such a protocol is shown
       in Figure 8: Example Delayed Startup negotiation on page 39.

   An MPA endpoint operates in two distinct phases.

   The Startup Phase is used to verify correct MPA setup, exchange CRC
   and Marker configuration, and optionally pass Private Data between
   endpoints prior to completing a DDP connection.  During this phase,
   specifically formatted frames are exchanged as TCP byte streams
   without using CRCs or Markers.  During this phase a DDP endpoint need
   not be "bound" to the MPA connection.  In fact, the choice of DDP
   endpoint and its operating parameters may not be known until the
   Consumer supplied Private Data (if any) has been examined by the
   Consumer.

   The second distinct phase is Full Operation during which FPDUs are
   sent using all the rules that pertain (CRCs, Markers, MULPDU
   restrictions etc.).  A DDP endpoint MUST be "bound" to the MPA
   connection at entry to this phase.




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   When Private Data is passed between ULPs in the Startup Phase, the
   ULP is responsible for interpreting that data, and then placing MPA
   into Full Operation.

   Note: The following text differentiates the two endpoints by calling
       them Initiator and Responder.  This is quite arbitrary and is NOT
       related to the TCP startup (SYN, SYN/ACK sequence).  The
       Initiator is the side that sends first in the MPA startup
       sequence (the MPA Request Frame).

   Note: The possibility that both endpoints would be allowed to make a
       connection at the same time, sometimes called an active/active
       connection, was considered by the work group and rejected.  There
       were several motivations for this decision.  One was that
       applications needing this facility were few (none other than
       theoretical at the time of this draft).  Another was that the
       facility created some implementation difficulties, particularly
       with the "dual stack" designs described later on.  A last issue
       was that dealing with rejected connections at startup would have
       required at least an additional frame type, and more recovery
       actions, complicating the protocol.  While none of these issues
       was overwhelming, the group and implementers were not motivated
       to do the work to resolve these issues.  The protocol includes a
       method of detecting these active/active startup attempts so that
       they can be rejected and an error reported.

   The ULP is responsible for determining which side is Initiator or
   Responder.  For client/server type ULPs this is easy.  For peer-peer
   ULPs (which might utilize a TCP style active/active startup), some
   mechanism (not defined by this specification) must be established, or
   some streaming mode data exchanged prior to MPA startup to determine
   the side which starts in Initiator and which starts in Responder MPA
   mode.




















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6.1.1  MPA Request and Reply Frame Format

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   0  |                                                               |
      +         Key (16 bytes containing "MPA ID Req Frame")          +
   4  |      (4D 50 41 20 49 44 20 52 65 71 20 46 72 61 6D 65)        |
      +         Or  (16 bytes containing "MPA ID Rep Frame")          +
   8  |      (4D 50 41 20 49 44 20 52 65 70 20 46 72 61 6D 65)        |
      +                                                               +
   12 |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   16 |M|C|R| Res     |     Rev       |          PD_Length            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                                                               ~
      ~                   Private Data                                ~
      |                                                               |
      |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     Figure 7 MPA Request/Reply Frame

   Key: This field contains the "key" used to validate that the sender
       is an MPA sender.  Initiator mode senders MUST set this field to
       the fixed value "MPA ID Req frame" or (in byte order) 4D 50 41 20
       49 44 20 52 65 71 20 46 72 61 6D 65 (in hexadecimal).  Responder
       mode receivers MUST check this field for the same value, and
       close the connection and report an error locally if any other
       value is detected.  Responder mode senders MUST set this field to
       the fixed value "MPA ID Rep frame" or (in byte order) 4D 50 41 20
       49 44 20 52 65 70 20 46 72 61 6D 65 (in hexadecimal).  Initiator
       mode receivers MUST check this field for the same value, and
       close the connection and report an error locally if any other
       value is detected.

   M: This bit, when sent in an MPA Request Frame or an MPA Reply Frame,
       declares a receiver's requirement for Markers.  When in a
       received MPA Request Frame or MPA Reply Frame and the value is
       '0', Markers MUST NOT be added to the data stream by the sender.
       When '1' Markers MUST be added as described in section 5.1 MPA
       Markers on page 20.

   C: This bit declares an endpoint's preferred CRC usage.  When this
       field is '0' in the MPA Request Frame and the MPA Reply Frame,
       CRCs MUST not be checked and need not be generated by either
       endpoint.  When this bit is '1' in either the MPA Request Frame
       or MPA Reply Frame, CRCs MUST be generated and checked by both
       endpoints.  Note that even when not in use, the CRC field remains
       present in the FPDU.  When CRCs are not in use, the CRC field


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       MUST be considered valid for FPDU checking regardless of its
       contents.

   R: This bit is set to zero, and not checked on reception in the MPA
       Request Frame.  In the MPA Reply Frame, this bit is the Rejected
       Connection bit, set by the Responders ULP to indicate acceptance
       '0', or rejection '1', of the connection parameters provided in
       the Private Data.

   Res: This field is reserved for future use.  It MUST be set to zero
       when sending, and not checked on reception.

   Rev: This field contains the Revision of MPA.  For this version of
       the specification senders MUST set this field to one.  MPA
       receivers compliant with this version of the specification MUST
       check this field.  If the MPA receiver cannot interoperate with
       the received version, then it MUST close the connection and
       report an error locally.  Otherwise, the MPA receiver should
       report the received version to the ULP.

   PD_Length: This field MUST contain the length in Octets of the
       Private Data field.  A value of zero indicates that there is no
       Private Data field present at all.  If the receiver detects that
       the PD_Length field does not match the length of the Private Data
       field, or if the length of the Private Data field exceeds 512
       octets, the receiver MUST close the connection and report an
       error locally.  Otherwise, the MPA receiver should pass the
       PD_Length value and Private Data to the ULP.

   Private Data: This field may contain any value defined by ULPs or may
       not be present.  The Private Data field MUST between 0 and 512
       octets in length.  ULPs define how to size, set, and validate
       this field within these limits.

6.1.2  Connection Startup Rules

   The following rules apply to MPA connection Startup Phase:

   1.  When MPA is started in the Initiator mode, the MPA implementation
       MUST send a valid MPA Request Frame.  The MPA Request Frame MAY
       include ULP supplied Private Data.

   2.  When MPA is started in the Responder mode, the MPA implementation
       MUST wait until a MPA Request Frame is received and validated
       before entering full MPA/DDP operation.

       If the MPA Request Frame is improperly formatted, the
       implementation MUST close the TCP connection and exit MPA.

       If the MPA Request Frame is properly formatted but the Private
       Data is not acceptable, the implementation SHOULD return an MPA


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       Reply Frame with the Rejected Connection bit set to '1'; the MPA
       Reply Frame MAY include ULP supplied Private Data; the
       implementation MUST exit MPA, leaving the TCP connection open.
       The ULP may close TCP or use the connection for other purposes.

       If the MPA Request Frame is properly formatted and the Private
       Data is acceptable, the implementation SHOULD return an MPA Reply
       Frame with the Rejected Connection bit set to '0'; the MPA Reply
       Frame MAY include ULP supplied Private Data; and the Responder
       SHOULD prepare to interpret any data received as FPDUs and pass
       any received ULPDUs to DDP.

       Note: Since the receiver's ability to deal with Markers is
           unknown until the Request and Reply frames have been
           received, sending FPDUs before this occurs is not possible.

       Note: The requirement to wait on a Request Frame before sending a
           Reply frame is a design choice, it makes for well ordered
           sequence of events at each end, and avoids having to specify
           how to deal with situations where both ends start at the same
           time.

   3.  MPA Initiator mode implementations MUST receive and validate a
       MPA Reply Frame.

       If the MPA Reply Frame is improperly formatted, the
       implementation MUST close the TCP connection and exit MPA.

       If the MPA Reply Frame is properly formatted but is the Private
       Data is not acceptable, or if the Rejected Connection bit set to
       '1', the implementation MUST exit MPA, leaving the TCP connection
       open.  The ULP may close TCP or use the connection for other
       purposes.

       If the MPA Reply Frame is properly formatted and the Private Data
       is acceptable, and the Reject Connection bit is set to '0', the
       implementation SHOULD enter full MPA/DDP operation mode;
       interpreting any received data as FPDUs and sending DDP ULPDUs as
       FPDUs.

   4.  MPA Responder mode implementations MUST receive and validate at
       least one FPDU before sending any FPDUs or Markers.

       Note: this requirement is present to allow the Initiator time to
           get its receiver into Full Operation before an FPDU arrives,
           avoiding potential race conditions at the Initiator.  This
           was also subject to some debate in the work group before
           rough consensus was reached.  Eliminating this requirement
           would allow faster startup in some types of applications.
           However, that would also make certain implementations
           (particularly "dual stack") much harder.


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   5.  If a received "Key" does not match the expected value, (See 6.1.1
       MPA Request and Reply Frame Format above) the TCP/DDP connection
       MUST be closed, and an error returned to the ULP.

   6.  The received Private Data fields may be used by Consumers at
       either end to further validate the connection, and set up DDP or
       other ULP parameters.  The Initiator ULP MAY close the
       TCP/MPA/DDP connection as a result of validating the Private Data
       fields.  The Responder SHOULD return a MPA Reply Frame with the
       "Reject Connection" Bit set to '1' if the validation of the
       Private Data is not acceptable to the ULP.

   7.  When the first FPDU is to be sent, then if Markers are enabled,
       the first octets sent are the special Marker 0x00000000, followed
       by the start of the FPDU (the FPDU's ULPDU Length field).  If
       Markers are not enabled, the first octets sent are the start of
       the FPDU (the FPDU's ULPDU Length field).

   8.  MPA implementations MUST use the difference between the MPA
       Request Frame and the MPA Reply Frame to check for incorrect
       "Initiator/Initiator" startups.  Implementations SHOULD put a
       timeout on waiting for the MPA Request Frame when started in
       Responder mode, to detect incorrect "Responder/Responder"
       startups.

   9.  MPA implementations MUST validate the PD_Length field.  The
       buffer that receives the Private Data field MUST be large enough
       to receive that data; the amount of Private Data MUST not exceed
       the PD_Length, or the application buffer.  If any of the above
       fails, the startup frame MUST be considered improperly formatted.

   10. MPA implementations SHOULD implement a reasonable timeout while
       waiting for the entire startup frames; this prevents certain
       denial of service attacks.  ULPs SHOULD implement a reasonable
       timeout while waiting for FPDUs, ULPDUs and application level
       messages to guard against application failures and certain denial
       of service attacks.
















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6.1.3  Example Delayed Startup sequence

   A variety of startup sequences are possible when using MPA on TCP.
   Following is an example of an MPA/DDP startup that occurs after TCP
   has been running for a while and has exchanged some amount of
   streaming data.  This example does not use any Private Data (an
   example that does is shown later in 6.1.4.2 Example Immediate Startup
   using Private Data on page 42), although it is perfectly legal to
   include the Private Data.  Note that since the example does not use
   any Private Data, there are no ULP interactions shown between
   receiving "Startup frames" and putting MPA into Full Operation.










































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          Initiator                                 Responder

   +---------------------------+
   |ULP streaming mode         |
   | <Hello> request to        |
   | transition to DDP/MPA     |           +--------------------------+
   | mode (optional)           | --------> |ULP gets request;         |
   +---------------------------+           |enables MPA Responder mode|
                                           |with last (optional)      |
                                           |streaming mode <Hello Ack>|
                                           |for MPA to send.          |
   +---------------------------+           |MPA waits for incoming    |
   |ULP receives streaming     | <-------- |  <MPA Request frame>     |
   | <Hello Ack>;              |           +--------------------------+
   |Enters MPA Initiator mode; |
   |MPA sends                  |
   |  <MPA Request Frame>;     |
   |MPA waits for incoming     |           +--------------------------+
   |  <MPA Reply Frame         | - - - - > |MPA receives              |
   +---------------------------+           |  <MPA Request Frame>     |
                                           |Consumer binds DDP to MPA,|
                                           |MPA sends the             |
                                           |  <MPA Reply Frame>.      |
                                           |DDP/MPA enables FPDU      |
   +---------------------------+           |decoding, but does not    |
   |MPA receives the           | < - - - - |send any FPDUs.           |
   |  <MPA Reply Frame>        |           +--------------------------+
   |Consumer binds DDP to MPA, |
   |DDP/MPA begins full        |
   |operation.                 |
   |MPA sends first FPDU (as   |           +--------------------------+
   |DDP ULPDUs become          | ========> |MPA Receives first FPDU.  |
   |available).                |           |MPA sends first FPDU (as  |
   +---------------------------+           |DDP ULPDUs become         |
                                   <====== |available.                |
                                           +--------------------------+
               Figure 8: Example Delayed Startup negotiation
















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   An example Delayed Startup sequence is described below:

       *   Active and passive sides start up a TCP connection in the
           usual fashion, probably using sockets APIs.  They exchange
           some amount of streaming mode data.  At some point one side
           (the MPA Initiator) sends streaming mode data that
           effectively says "Hello, Lets go into MPA/DDP mode."

   *   When the remote side (the MPA Responder) gets this streaming mode
       message, the Consumer would send a last streaming mode message
       that effectively says "I Acknowledge your Hello, and am now in
       MPA Responder Mode".  The exchange of these messages establishes
       the exact point in the TCP stream where MPA is enabled.  The
       Responding Consumer enables MPA in the Responder mode and waits
       for the initial MPA startup message.

       *   The Initiating Consumer would enable MPA startup in the
           Initiator mode which then sends the MPA Request Frame.  It is
           assumed that no Private Data messages are needed for this
           example, although it is possible to do so.  The Initiating
           MPA (and Consumer) would also wait for the MPA connection to
           be accepted.

   *   The Responding MPA would receive the initial MPA Request Frame
       and would inform the Consumer that this message arrived.  The
       Consumer can then accept the MPA/DDP connection or close the TCP
       connection.

   *   To accept the connection request, the Responding Consumer would
       use an appropriate API to bind the TCP/MPA connections to a DDP
       endpoint, thus enabling MPA/DDP into Full Operation.  In the
       process of going to Full Operation, MPA sends the MPA Reply
       Frame.  MPA/DDP waits for the first incoming FPDU before sending
       any FPDUs.

   *   If the initial TCP data was not a properly formatted MPA Request
       Frame MPA will close or reset the TCP connection immediately.

       *   The Initiating MPA would receive the MPA Reply Frame and
           would report this message to the Consumer.  The Consumer can
           then accept the MPA/DDP connection, or close or reset the TCP
           connection to abort the process.

       *   On determining that the Connection is acceptable, the
           Initiating Consumer would use an appropriate API to bind the
           TCP/MPA connections to a DDP endpoint thus enabling MPA/DDP
           into Full Operation.  MPA/DDP would begin sending DDP
           messages as MPA FPDUs.





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6.1.4  Use of Private Data

   This section is advisory in nature, in that it suggests a method that
   a ULP can deal with pre-DDP connection information exchange.

6.1.4.1  Motivation

   Prior RDMA protocols have been developed that provide Private Data
   via out of band mechanisms.  As a result, many applications now
   expect some form of Private Data to be available for application use
   prior to setting up the DDP/RDMA connection.  Following are some
   examples of the use of Private Data.

   An RDMA Endpoint (referred to as a Queue Pair, or QP, in InfiniBand
   and the [VERBS]) must be associated with a Protection Domain.  No
   receive operations may be posted to the endpoint before it is
   associated with a Protection Domain.  Indeed under both the
   InfiniBand and proposed RDMA/DDP verbs [VERBS] an endpoint/QP is
   created within a Protection Domain.

   There are some applications where the choice of Protection Domain is
   dependent upon the identity of the remote ULP client.  For example,
   if a user session requires multiple connections, it is highly
   desirable for all of those connections to use a single Protection
   Domain.  Note: use of Protection Domains is further discussed in
   [RDMASEC].

   InfiniBand, the DAT APIs [DAT-API] and the [IT-API] all provide for
   the active side ULP to provide Private Data when requesting a
   connection.  This data is passed to the ULP to allow it to determine
   whether to accept the connection, and if so with which endpoint (and
   implicitly which Protection Domain).

   The Private Data can also be used to ensure that both ends of the
   connection have configured their RDMA endpoints compatibly on such
   matters as the RDMA Read capacity (see [RDMAP]).  Further ULP-
   specific uses are also presumed, such as establishing the identity of
   the client.

   Private Data is also allowed for when accepting the connection, to
   allow completion of any negotiation on RDMA resources and for other
   ULP reasons.

   There are several potential ways to exchange this Private Data.  For
   example, the InfiniBand specification includes a connection
   management protocol that allows a small amount of Private Data to be
   exchanged using datagrams before actually starting the RDMA
   connection.





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   This draft allows for small amounts of Private Data to be exchanged
   as part of the MPA startup sequence.  The actual Private Data fields
   are carried in the MPA Request Frame, and the MPA Reply Frame.

   If larger amounts of Private Data or more negotiation is necessary,
   TCP streaming mode messages may be exchanged prior to enabling MPA.

6.1.4.2  Example Immediate Startup using Private Data

          Initiator                                 Responder

   +---------------------------+
   |TCP SYN sent               |           +--------------------------+
   +---------------------------+ --------> |TCP gets SYN packet;      |
   +---------------------------+           |  Sends SYN-Ack           |
   |TCP gets SYN-Ack           | <-------- +--------------------------+
   |  Sends Ack                |
   +---------------------------+ --------> +--------------------------+
   +---------------------------+           |Consumer enables MPA      |
   |Consumer enables MPA       |           |Responder Mode, waits for |
   |Initiator mode with        |           |  <MPA Request frame>     |
   |Private Data; MPA sends    |           +--------------------------+
   |  <MPA Request Frame>;     |
   |MPA waits for incoming     |           +--------------------------+
   |  <MPA Reply Frame         | - - - - > |MPA receives              |
   +---------------------------+           |  <MPA Request Frame>     |
                                           |Consumer examines Private |
                                           |Data, provides MPA with   |
                                           |return Private Data,      |
                                           |binds DDP to MPA, and     |
                                           |enables MPA to send an    |
                                           |  <MPA Reply Frame>.      |
                                           |DDP/MPA enables FPDU      |
   +---------------------------+           |decoding, but does not    |
   |MPA receives the           | < - - - - |send any FPDUs.           |
   |  <MPA Reply Frame>        |           +--------------------------+
   |Consumer examines Private  |
   |Data, binds DDP to MPA,    |
   |and enables DDP/MPA to     |
   |begin Full Operation.      |
   |MPA sends first FPDU (as   |           +--------------------------+
   |DDP ULPDUs become          | ========> |MPA Receives first FPDU.  |
   |available).                |           |MPA sends first FPDU (as  |
   +---------------------------+           |DDP ULPDUs become         |
                                   <====== |available.                |
                                           +--------------------------+
              Figure 9: Example Immediate Startup negotiation

   Note: the exact order of when MPA is started in the TCP connection
       sequence is implementation dependent; the above diagram shows one
       possible sequence.  Also, the Initiator "Ack" to the Responder's


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       "SYN-Ack" may be combined into the same TCP segment containing
       the MPA Request Frame (as is allowed by TCP RFCs).

   The example immediate startup sequence is described below:

   *   The passive side (Responding Consumer) would listen on the TCP
       destination port, to indicate its readiness to accept a
       connection.

       *   The active side (Initiating Consumer) would request a
           connection from a TCP endpoint (that expected to upgrade to
           MPA/DDP/RDMA and expected the Private Data) to a destination
           address and port.

       *   The Initiating Consumer would initiate a TCP connection to
           the destination port.  Acceptance/rejection of the connection
           would proceed as per normal TCP connection establishment.

   *   The passive side (Responding Consumer) would receive the TCP
       connection request as usual allowing normal TCP gatekeepers, such
       as INETD and TCPserver, to exercise their normal
       safeguard/logging functions.  On acceptance of the TCP
       connection, the Responding Consumer would enable MPA in the
       Responder mode and wait for the initial MPA startup message.

       *   The Initiating Consumer would enable MPA startup in the
           Initiator mode to send an initial MPA Request Frame with its
           included Private Data message to send.  The Initiating MPA
           (and Consumer) would also wait for the MPA connection to be
           accepted, and any returned Private Data.

   *   The Responding MPA would receive the initial MPA Request Frame
       with the Private Data message and would pass the Private Data
       through to the Consumer.  The Consumer can then accept the
       MPA/DDP connection, close the TCP connection, or reject the MPA
       connection with a return message.

   *   To accept the connection request, the Responding Consumer would
       use an appropriate API to bind the TCP/MPA connections to a DDP
       endpoint, thus enabling MPA/DDP into Full Operation.  In the
       process of going to Full Operation, MPA sends the MPA Reply Frame
       which includes the Consumer supplied Private Data containing any
       appropriate Consumer response.  MPA/DDP waits for the first
       incoming FPDU before sending any FPDUs.

   *   If the initial TCP data was not a properly formatted MPA Request
       Frame, MPA will close or reset the TCP connection immediately.

   *   To reject the MPA connection request, the Responding Consumer
       would send an MPA Reply Frame with any ULP supplied Private Data



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       (with reason for rejection), with the "Rejected Connection" bit
       set to '1', and may close the TCP connection.

       *   The Initiating MPA would receive the MPA Reply Frame with the
           Private Data message and would report this message to the
           Consumer, including the supplied Private Data.

           If the "rejected Connection" bit is set to a '1', MPA will
           close the TCP connection and exit.

           If the "Rejected Connection" bit is set to a '0', and on
           determining from the MPA Reply Frame Private Data that the
           Connection is acceptable, the Initiating Consumer would use
           an appropriate API to bind the TCP/MPA connections to a DDP
           endpoint thus enabling MPA/DDP into Full Operation.  MPA/DDP
           would begin sending DDP messages as MPA FPDUs.



6.1.5  "Dual stack" implementations

   MPA/DDP implementations are commonly expected to be implemented as
   part of a "dual stack" architecture.  One "stack" is the traditional
   TCP stack, usually with a sockets interface API (Application
   Programming Interface).  The second stack is the MPA/DDP "stack" with
   its own API, and potentially separate code or hardware to deal with
   the MPA/DDP data.  Of course, implementations may vary, so the
   following comments are of an advisory nature only.

   The use of the two "stacks" offers advantages:

        TCP connection setup is usually done with the TCP stack.  This
        allows use of the usual naming and addressing mechanisms.  It
        also means that any mechanisms used to "harden" the connection
        setup against security threats are also used when starting
        MPA/DDP.

        Some applications may have been originally designed for TCP, but
        are "enhanced" to utilize MPA/DDP after a negotiation reveals
        the capability to do so.  The negotiation process takes place in
        TCP's streaming mode, using the usual TCP APIs.

        Some new applications, designed for RDMA or DDP, still need to
        exchange some data prior to starting MPA/DDP.  This exchange can
        be of arbitrary length or complexity, but often consists of only
        a small amount of Private Data, perhaps only a single message.
        Using the TCP streaming mode for this exchange allows this to be
        done using well understood methods.





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   The main disadvantage of using two stacks is the conversion of an
   active TCP connection between them.  This process must be done with
   care to prevent loss of data.

   To avoid some of the problems when using a "dual stack" architecture
   the following additional restrictions may be required by the
   implementation:

   1.  Enabling the DDP/MPA stack SHOULD be done only when no incoming
       stream data is expected.  This is typically managed by the ULP
       protocol.  When following the recommended startup sequence, the
       Responder side enters DDP/MPA mode, sends the last streaming mode
       data, and then waits for the MPA Request Frame.  No additional
       streaming mode data is expected.  The Initiator side ULP receives
       the last streaming mode data, and then enters DDP/MPA mode.
       Again, no additional streaming mode data is expected.

   2.  The DDP/MPA MAY provide the ability to send a "last streaming
       message" as part of its Responder DDP/MPA enable function.  This
       allows the DDP/MPA stack to more easily manage the conversion to
       DDP/MPA mode (and avoid problems with a very fast return of the
       MPA Request Frame from the Initiator side).

   Note: Regardless of the "stack" architecture used, TCP's rules MUST
       be followed.  For example, if network data is lost, re-segmented
       or re-ordered, TCP MUST recover appropriately even when this
       occurs while switching stacks.

6.2  Normal Connection Teardown

   Each half connection of MPA terminates when DDP closes the
   corresponding TCP half connection.

   A mechanism SHOULD be provided by MPA to DDP for DDP to be made aware
   that a graceful close of the LLP connection has been received by the
   LLP (e.g. FIN is received).

















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7  Error Semantics

   The following errors MUST be detected by MPA and the codes SHOULD be
   provided to DDP or other Consumer:

    Code Error

    1    TCP connection closed, terminated or lost.  This includes lost
         by timeout, too many retries, RST received or FIN received.

    2    Received MPA CRC does not match the calculated value for the
         FPDU.

    3    In the event that the CRC is valid, received MPA Marker (if
         enabled) and ULPDU Length fields do not agree on the start of
         a FPDU.  If the FPDU start determined from previous ULPDU
         Length fields does not match with the MPA Marker position, MPA
         SHOULD deliver an error to DDP.  It may not be possible to
         make this check as a segment arrives, but the check SHOULD be
         made when a gap creating an out of order sequence is closed
         and any time a Marker points to an already identified FPDU.
         It is OPTIONAL for a receiver to check each Marker, if
         multiple Markers are present in an FPDU, or if the segment is
         received in order.

    4    Invalid MPA Request Frame or MPA Response Frame received.  In
         this case, the TCP connection MUST be immediately closed.  DDP
         and other ULPs should treat this similar to code 1, above.

   When conditions 2 or 3 above are detected, an MPA-aware TCP
   implementation MAY choose to silently drop the TCP segment rather
   than reporting the error to DDP.  In this case, the sending TCP will
   retry the segment, usually correcting the error, unless the problem
   was at the source.  In that case, the source will usually exceed the
   number of retries and terminate the connection.

   Once MPA delivers an error of any type, it MUST NOT pass or deliver
   any additional FPDUs on that half connection.

   For Error codes 2 and 3, MPA MUST NOT close the TCP connection
   following a reported error.  Closing the connection is the
   responsibility of DDP's ULP.

        Note that since MPA will not Deliver any FPDUs on a half
        connection following an error detected on the receive side of
        that connection, DDP's ULP is expected to tear down the
        connection.  This may not occur until after one or more last
        messages are transmitted on the opposite half connection.  This
        allows a diagnostic error message to be sent.




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8  Security Considerations

   This section discusses the security considerations for MPA.

8.1  Protocol-specific Security Considerations

   The vulnerabilities of MPA to third-party attacks are no greater than
   any other protocol running over TCP.  A third party, by sending
   packets into the network that are delivered to an MPA receiver, could
   launch a variety of attacks that take advantage of how MPA operates.
   For example, a third party could send random packets that are valid
   for TCP, but contain no FPDU headers.  An MPA receiver reports an
   error to DDP when any packet arrives that cannot be validated as an
   FPDU when properly located on an FPDU boundary.  A third party could
   also send packets that are valid for TCP, MPA, and DDP, but do not
   target valid buffers.  These types of attacks ultimately result in
   loss of connection and thus become a type of DOS (Denial Of Service)
   attack.  Communication security mechanisms such as IPsec [RFC2401]
   may be used to prevent such attacks.

   Independent of how MPA operates, a third party could use ICMP
   messages to reduce the path MTU to such a small size that performance
   would likewise be severely impacted.  Range checking on path MTU
   sizes in ICMP packets may be used to prevent such attacks.

   [RDMAP] and [DDP] are used to control, read and write data buffers
   over IP networks.  Therefore, the control and the data packets of
   these protocols are vulnerable to the spoofing, tampering and
   information disclosure attacks listed below.  In addition, Connection
   to/from an unauthorized or unauthenticated endpoint is a potential
   problem with most applications using RDMA, DDP, and MPA.

8.1.1  Spoofing

   Spoofing attacks can be launched by the Remote Peer, or by a network
   based attacker.  A network based spoofing attack applies to all
   Remote Peers.  Because the MPA Stream requires a TCP Stream in the
   ESTABLISHED state, certain types of traditional forms of wire attacks
   do not apply -- an end-to-end handshake must have occurred to
   establish the MPA Stream.  So, the only form of spoofing that applies
   is one when a remote node can both send and receive packets.  Yet
   even with this limitation the Stream is still exposed to the
   following spoofing attacks.

8.1.1.1  Impersonation

   A network based attacker can impersonate a legal MPA/DDP/RDMAP peer
   (by spoofing a legal IP address), and establish an MPA/DDP/RDMAP
   Stream with the victim.  End to end authentication (i.e. IPsec or ULP
   authentication) provides protection against this attack.



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8.1.1.2  Stream Hijacking

   Stream hijacking happens when a network based attacker follows the
   Stream establishment phase, and waits until the authentication phase
   (if such a phase exists) is completed successfully.  He can then
   spoof the IP address and re-direct the Stream from the victim to its
   own machine.  For example, an attacker can wait until an iSCSI
   authentication is completed successfully, and hijack the iSCSI
   Stream.

   The best protection against this form of attack is end-to-end
   integrity protection and authentication, such as IPsec to prevent
   spoofing.  Another option is to provide physical security.
   Discussion of physical security is out of scope for this document.

8.1.1.3  Man in the Middle Attack

   If a network based attacker has the ability to delete, inject replay,
   or modify packets which will still be accepted by MPA (e.g., TCP
   sequence number is correct, FPDU is valid etc.) then the Stream can
   be exposed to a man in the middle attack.  The attacker could
   potentially use the services of [DDP] and [RDMAP] to read the
   contents of the associated data buffer, modify the contents of the
   associated data buffer, or to disable further access to the buffer.
   The only countermeasure for this form of attack is to either secure
   the MPA/DDP/RDMAP Stream (i.e. integrity protect) or attempt to
   provide physical security to prevent man-in-the-middle type attacks.

   The best protection against this form of attack is end-to-end
   integrity protection and authentication, such as IPsec, to prevent
   spoofing or tampering.  If Stream or session level authentication and
   integrity protection are not used, then a man-in-the-middle attack
   can occur, enabling spoofing and tampering.

   Another approach is to restrict access to only the local subnet/link,
   and provide some mechanism to limit access, such as physical security
   or 802.1.x.  This model is an extremely limited deployment scenario,
   and will not be further examined here.

8.1.2  Eavesdropping

   Generally speaking, Stream confidentiality protects against
   eavesdropping.  Stream and/or session authentication and integrity
   protection is a counter measurement against various spoofing and
   tampering attacks.  The effectiveness of authentication and integrity
   against a specific attack, depend on whether the authentication is
   machine level authentication (as the one provided by IPsec), or ULP
   authentication.





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8.2  Introduction to Security Options

   The following security services can be applied to an MPA/DDP/RDMAP
   Stream:

   1.  Session confidentiality - protects against eavesdropping.

   2.  Per-packet data source authentication - protects against the
   following spoofing attacks: network based impersonation, Stream
   hijacking, and man in the middle.

   3.  Per-packet integrity - protects against tampering done by
   network based modification of FPDUs (indirectly affecting buffer
   content through DDP services).

   4.  Packet sequencing - protects against replay attacks, which is
   a special case of the above tampering attack.

   If an MPA/DDP/RDMAP Stream may be subject to impersonation attacks,
   or Stream hijacking attacks, it is recommended that the Stream be
   authenticated, integrity protected, and protected from replay
   attacks; it may use confidentiality protection to protect from
   eavesdropping (in case the MPA/DDP/RDMAP Stream traverses a public
   network).

   IPsec is capable of providing the above security services for IP and
   TCP traffic.

   ULP protocols may be able to provide part of the above security
   services.  See [NFSv4CHANNEL] for additional information on a
   promising approach called "channel binding".  From [NFSv4CHANNEL]:

        "The concept of channel bindings allows applications to prove
        that the end-points of two secure channels at different network
        layers are the same by binding authentication at one channel to
        the session protection at the other channel.  The use of channel
        bindings allows applications to delegate session protection to
        lower layers, which may significantly improve performance for
        some applications."

8.3  Using IPsec With MPA

   IPsec can be used to protect against the packet injection attacks
   outlined above.  Because IPsec is designed to secure individual IP
   packets, MPA can run above IPsec without change.  IPsec packets are
   processed (e.g., integrity checked and decrypted) in the order they
   are received, and an MPA receiver will process the decrypted FPDUs
   contained in these packets in the same manner as FPDUs contained in
   unsecured IP packets.




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   MPA Implementations MUST implement IPsec as described in Section 8.4
   below.  The use of IPsec is up to ULPs and administrators.

8.4  Requirements for IPsec Encapsulation of MPA/DDP

   The IP Storage working group has spent significant time and effort to
   define the normative IPsec requirements for IP Storage [RFC3723].
   Portions of that specification are applicable to a wide variety of
   protocols, including the RDDP protocol suite.  In order to not
   replicate this effort, an MPA ON TCP implementation MUST follow the
   requirements defined in RFC3723 Section 2.3 and Section 5, including
   the associated normative references for those sections.

   Additionally, since IPsec acceleration hardware may only be able to
   handle a limited number of active IKE Phase 2 SAs, Phase 2 delete
   messages MAY be sent for idle SAs, as a means of keeping the number
   of active Phase 2 SAs to a minimum.  The receipt of an IKE Phase 2
   delete message MUST NOT be interpreted as a reason for tearing down
   an DDP/RDMA Stream.  Rather, it is preferable to leave the Stream up,
   and if additional traffic is sent on it, to bring up another IKE
   Phase 2 SA to protect it.  This avoids the potential for continually
   bringing Streams up and down.

   Note that there are serious security issues if IPsec is not
   implemented end-to-end.  For example, if IPsec is implemented as a
   tunnel in the middle of the network, any hosts between the peer and
   the IPsec tunneling device can freely attack the unprotected Stream.


























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9  IANA Considerations

   No IANA actions are required by this document.

   If a well-known port is chosen as the mechanism to identify a DDP on
   MPA on TCP, the well-known port must be registered with IANA.
   Because the use of the port is DDP specific, registration of the port
   with IANA is left to DDP.













































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10 References

10.1 Normative References

   [iSCSI] Satran, J., Internet Small Computer Systems Interface
       (iSCSI), RFC 3720, April 2004.

   [RFC1191] Mogul, J., and Deering, S., "Path MTU Discovery", RFC 1191,
       November 1990.

   [RFC2018] Mathis, M., Mahdavi, J., Floyd, S., Romanow, A., "TCP
       Selective Acknowledgment Options", RFC 2018, October 1996.

   [RFC3723] Aboba B., et al, "Securing Block Storage Protocols over
       IP", RFC3723, April 2004.

   [RFC793] Postel, J., "Transmission Control Protocol - DARPA Internet
       Program Protocol Specification", RFC 793, September 1981.

   [RDMASEC]  Pinkerton J., Deleganes E., Bitan S., "DDP/RDMAP
       Security", draft-ietf-rddp-security-09.txt (work in progress),
       MAY 2006.

10.2 Informative References

   [CRCTCP] Stone J., Partridge, C., "When the CRC and TCP checksum
       disagree", ACM Sigcomm, Sept. 2000.

   [DAT-API] DAT Collaborative, "kDAPL (Kernel Direct Access Programming
       Library) and uDAPL (User Direct Access Programming Library)",
       http://www.datcollaborative.org.

   [DDP] H. Shah et al., "Direct Data Placement over Reliable
       Transports", draft-ietf-rddp-ddp-06.txt (Work in progress), May
       2006.

   [IT-API] The Open Group, "Interconnect Transport API (IT-API)"
       Version 2.1, http://www.opengroup.org.

   [RFC2401]  Atkinson, R., Kent, S., "Security Architecture for the
       Internet Protocol", RFC 2401, November 1998.

   [RFC0896] J. Nagle, "Congestion Control in IP/TCP Internetworks", RFC
       896, January 1984.

   [NagleDAck] Minshall G., Mogul, J., Saito, Y., Verghese, B.,
       "Application performance pitfalls and TCP's Nagle algorithm",
       Workshop on Internet Server Performance, May 1999.





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   [NFSv4CHANNEL] Williams, N., "On the Use of Channel Bindings to
       Secure Channels", Internet-Draft draft-ietf-nfsv4-channel-
       bindings-02.txt, July 2004.

   [RDMAP] R. Recio et al., "RDMA Protocol Specification",
       draft-ietf-rddp-rdmap-06.txt, May 2006.

   [RFC2960] R. Stewart et al., "Stream Control Transmission Protocol",
       RFC 2960, October 2000.

   [RFC792] Postel, J., "Internet Control Message Protocol", September
       1981

   [RFC1122] Braden, R.T., "Requirements for Internet hosts -
       communication layers", October 1989.

   [VERBS] J. Hilland et al., "RDMA Protocol Verbs Specification",
       draft-hilland-iwarp-verbs-v1.0-RDMAC.pdf April 2003,
       http://www.rdmaconsortium.org.


































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11 Appendix

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

   The appendix covers three topics;

   Section 11.1 is an analysis of MPA on TCP and why it is useful to
   integrate MPA with TCP (with modifications to typical TCP
   implementations) to reduce overall system buffering and overhead.

   Section 11.2 covers some MPA receiver implementation notes.

   Section 11.3 covers methods of making MPA implementations
   interoperate with both IETF and RDMA Consortium versions of the
   protocols.

11.1 Analysis of MPA over TCP Operations

   This appendix analyzes the impact of MPA on the TCP sender, receiver,
   and wire protocol.

   One of MPA's high level goals is to provide enough information, when
   combined with the Direct Data Placement Protocol [DDP], to enable
   out-of-order placement of DDP payload into the final Upper Layer
   Protocol (ULP) buffer.  Note that DDP separates the act of placing
   data into a ULP buffer from that of notifying the ULP that the ULP
   buffer is available for use.  In DDP terminology, the former is
   defined as "Placement", and the later is defined as "Delivery".  MPA
   supports in-order Delivery of the data to the ULP, including support
   for Direct Data Placement in the final ULP buffer location when TCP
   segments arrive out-of-order.  Effectively, the goal is to use the
   pre-posted ULP buffers as the TCP receive buffer, where the
   reassembly of the ULP Protocol Data Unit (PDU) by TCP (with MPA and
   DDP) is done in place, in the ULP buffer, with no data copies.

   This Appendix walks through the advantages and disadvantages of the
   TCP sender modifications proposed by MPA:

   1) that MPA prefers that the TCP sender to do Header Alignment, where
   a TCP segment should begin with an MPA Framing Protocol Data Unit
   (FPDU) (if there is payload present).

   2) that there be an integral number of FPDUs in a TCP segment (under
   conditions where the Path MTU is not changing).

   This Appendix concludes that the scaling advantages of FPDU Alignment
   are strong, based primarily on fairly drastic TCP receive buffer
   reduction requirements and simplified receive handling.  The analysis
   also shows that there is little effect to TCP wire behavior.



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11.1.1 Assumptions

11.1.1.1 MPA is layered beneath DDP [DDP]

   MPA is an adaptation layer between DDP and TCP.  DDP requires
   preservation of DDP segment boundaries and a CRC32C digest covering
   the DDP header and data.   MPA adds these features to the TCP stream
   so that DDP over TCP has the same basic properties as DDP over SCTP.

11.1.1.2 MPA preserves DDP message framing

   MPA was designed as a framing layer specifically for DDP and was not
   intended as a general-purpose framing layer for any other ULP using
   TCP.

   A framing layer allows ULPs using it to receive indications from the
   transport layer only when complete ULPDUs are present.  As a framing
   layer, MPA is not aware of the content of the DDP PDU, only that it
   has received and, if necessary, reassembled a complete PDU for
   Delivery to the DDP.

11.1.1.3 The size of the ULPDU passed to MPA is less than EMSS under
      normal conditions

   To make reception of a complete DDP PDU on every received segment
   possible, DDP passes to MPA a PDU that is no larger than the EMSS of
   the underlying fabric.  Each FPDU that MPA creates contains
   sufficient information for the receiver to directly place the ULP
   payload in the correct location in the correct receive buffer.

   Edge cases when this condition does not occur are dealt with, but do
   not need to be on the fast path

11.1.1.4 Out-of-order placement but NO out-of-order Delivery

   DDP receives complete DDP PDUs from MPA.  Each DDP PDU contains the
   information necessary to place its ULP payload directly in the
   correct location in host memory.

   Because each DDP segment is self-describing, it is possible for DDP
   segments received out of order to have their ULP payload placed
   immediately in the ULP receive buffer.

   Data delivery to the ULP is guaranteed to be in the order the data
   was sent.  DDP only indicates data delivery to the ULP after TCP has
   acknowledged the complete byte stream.







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11.1.2 The Value of FPDU Alignment

   Significant receiver optimizations can be achieved when Header
   Alignment and complete FPDUs are the common case.  The optimizations
   allow utilizing significantly fewer buffers on the receiver and less
   computation per FPDU.  The net effect is the ability to build a
   "flow-through" receiver that enables TCP-based solutions to scale to
   10G and beyond in an economical way.  The optimizations are
   especially relevant to hardware implementations of receivers that
   process multiple protocol layers - Data Link Layer (e.g., Ethernet),
   Network and Transport Layer (e.g., TCP/IP), and even some ULP on top
   of TCP (e.g., MPA/DDP).  As network speed increases, there is an
   increasing desire to use a hardware based receiver in order to
   achieve an efficient high performance solution.

   A TCP receiver, under worst case conditions, has to allocate buffers
   (BufferSizeTCP) whose capacities are a function of the bandwidth-
   delay product.  Thus:

       BufferSizeTCP = K * bandwidth [octets/Second] * Delay [Seconds].

   Where bandwidth is the end-to-end bandwidth of the connection, delay
   is the round trip delay of the connection, and K is an implementation
   dependent constant.

   Thus BufferSizeTCP scales with the end-to-end bandwidth (10x more
   buffers for a 10x increase in end-to-end bandwidth).  As this
   buffering approach may scale poorly for hardware or software
   implementations alike, several approaches allow reduction in the
   amount of buffering required for high-speed TCP communication.

   The MPA/DDP approach is to enable the ULP's buffer to be used as the
   TCP receive buffer.  If the application pre-posts a sufficient amount
   of buffering, and each TCP segment has sufficient information to
   place the payload into the right application buffer, when an out-of-
   order TCP segment arrives it could potentially be placed directly in
   the ULP buffer.  However, placement can only be done when a complete
   FPDU with the placement information is available to the receiver, and
   the FPDU contents contain enough information to place the data into
   the correct ULP buffer (e.g., there is a DDP header available).

   For the case when the FPDU is not aligned with the TCP segment, it
   may take, on average, 2 TCP segments to assemble one FPDU.
   Therefore, the receiver has to allocate BufferSizeNAF (Buffer Size,
   Non-Aligned FPDU) octets:

       BufferSizeNAF = K1* EMSS * number_of_connections + K2 * EMSS

   Where K1 and K2 are implementation dependent constants and EMSS is
   the effective maximum segment size.



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   For example, a 1 Gbps link with 10,000 connections and an EMSS of
   1500B would require 15 MB of memory.  Often the number of connections
   used scales with the network speed, aggravating the situation for
   higher speeds.

   FPDU Alignment would allow the receiver to allocate BufferSizeAF
   (Buffer Size, Aligned FPDU) octets:

       BufferSizeAF = K2 * EMSS

   for the same conditions.  A FPDU Aligned receiver may require memory
   in the range of ~100s of KB - which is feasible for an on-chip memory
   and enables a "flow-through" design, in which the data flows through
   the NIC and is placed directly in the destination buffer.  Assuming
   most of the connections support FPDU Alignment, the receiver buffers
   no longer scale with number of connections.

   Additional optimizations can be achieved in a balanced I/O sub-system
   -- where the system interface of the network controller provides
   ample bandwidth as compared with the network bandwidth.  For almost
   twenty years this has been the case and the trend is expected to
   continue - while Ethernet speeds have scaled by 1000 (from 10
   megabit/sec to 10 gigabit/sec), I/O bus bandwidth of volume CPU
   architectures has scaled from ~2 MB/sec to ~2 GB/sec (PC-XT bus to
   PCI-X DDR).  Under these conditions, the FPDU Alignment approach
   allows BufferSizeAF to be indifferent to network speed.  It is
   primarily a function of the local processing time for a given frame.
   Thus when the FPDU Alignment approach is used, receive buffering is
   expected to scale gracefully (i.e. less than linear scaling) as
   network speed is increased.



11.1.2.1 Impact of lack of FPDU Alignment on the receiver computational
      load and complexity

   The receiver must perform IP and TCP processing, and then perform
   FPDU CRC checks, before it can trust the FPDU header placement
   information.  For simplicity of the description, the assumption is
   that a FPDU is carried in no more than 2 TCP segments.  In reality,
   with no FPDU Alignment, an FPDU can be carried by more than 2 TCP
   segments (e.g., if the PMTU was reduced).











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   ----++-----------------------------++-----------------------++-----
   +---||---------------+    +--------||--------+   +----------||----+
   |   TCP Seg X-1      |    |     TCP Seg X    |   |  TCP Seg X+1   |
   +---||---------------+    +--------||--------+   +----------||----+
   ----++-----------------------------++-----------------------++-----
                   FPDU #N-1                  FPDU #N

       Figure 10: Non-aligned FPDU freely placed in TCP octet stream

   The receiver algorithm for processing TCP segments (e.g., TCP segment
   #X in Figure 10: Non-aligned FPDU freely placed in TCP octet stream)
   carrying non-aligned FPDUs (in-order or out-of-order) includes:



      Data Link Layer processing (whole frame) - typically including a
          CRC calculation.

      1.  Network Layer processing (assuming not an IP fragment, the
          whole Data Link Layer frame contains one IP datagram.  IP
          fragments should be reassembled in a local buffer.  This is
          not a performance optimization goal)

      2.  Transport Layer processing -- TCP protocol processing, header
          and checksum checks.

          a.  Classify incoming TCP segment using the 5 tuple (IP SRC,
              IP DST, TCP SRC Port, TCP DST Port, protocol)

      3.  Find FPDU message boundaries.

          a.  Get MPA state information for the connection

              If the TCP segment is in-order, use the receiver managed
                  MPA state information to calculate where the previous
                  FPDU message (#N-1) ends in the current TCP segment X.
                  (previously, when the MPA receiver processed the first
                  part of FPDU #N-1, it calculated the number of bytes
                  remaining to complete FPDU #N-1 by using the MPA
                  Length field).

                  Get the stored partial CRC for FPDU #N-1

                  Complete CRC calculation for FPDU #N-1 data (first
                      portion of TCP segment #X)

                  Check CRC calculation for FPDU #N-1

                  If no FPDU CRC errors, placement is allowed




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                  Locate the local buffer for the first portion of
                      FPDU#N-1, CopyData(local buffer of first portion
                      of FPDU #N-1, host buffer address, length)

                  Compute host buffer address for second portion of FPDU
                      #N-1

                  CopyData (local buffer of second portion of FPDU #N-1,
                      host buffer address for second portion, length)

                  Calculate the octet offset into the TCP segment for
                      the next FPDU #N.

                  Start Calculation of CRC for available data for FPDU
                      #N

                  Store partial CRC results for FPDU #N

                  Store local buffer address of first portion of FPDU #N

                  No further action is possible on FPDU #N, before it is
                      completely received

              If TCP out-of-order, receiver must buffer the data until
                  at least one complete FPDU is received.  Typically
                  buffering for more than one TCP segment per connection
                  is required.  Use the MPA based Markers to calculate
                  where FPDU boundaries are.

                  When a complete FPDU is available, a similar procedure
                      to the in-order algorithm above is used.  There is
                      additional complexity, though, because when the
                      missing segment arrives, this TCP segment must be
                      run through the CRC engine after the CRC is
                      calculated for the missing segment.

   If we assume FPDU Alignment, the following diagram and the algorithm
   below apply.  Note that when using MPA, the receiver is assumed to
   actively detect presence or loss of FPDU Alignment for every TCP
   segment received.



      +--------------------------+      +--------------------------+
   +--|--------------------------+   +--|--------------------------+
   |  |       TCP Seg X          |   |  |         TCP Seg X+1      |
   +--|--------------------------+   +--|--------------------------+
      +--------------------------+      +--------------------------+
                FPDU #N                          FPDU #N+1

        Figure 11: Aligned FPDU placed immediately after TCP header


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   The receiver algorithm for FPDU Aligned frames (in-order or out-of-
   order) includes:



       1)  Data Link Layer processing (whole frame) - typically
           including a CRC calculation.

       2)  Network Layer processing (assuming not an IP fragment, the
           whole Data Link Layer frame contains one IP datagram.  IP
           fragments should be reassembled in a local buffer.  This is
           not a performance optimization goal)

       3)  Transport Layer processing -- TCP protocol processing, header
           and checksum checks.

           a.  Classify incoming TCP segment using the 5 tuple (IP SRC,
               IP DST, TCP SRC Port, TCP DST Port, protocol)

       4)  Check for Header Alignment. (Described in detail in Section
           5.4).  Assuming Header Alignment for the rest of the
           algorithm below.

           a.  If the header is not aligned, see the algorithm defined
               in the prior section.

       5)  If TCP is in-order or out-of-order the MPA header is at the
           beginning of the current TCP payload.  Get the FPDU length
           from the FPDU header.

       6)  Calculate CRC over FPDU

       7)  Check CRC calculation for FPDU #N

       8)  If no FPDU CRC errors, placement is allowed

       9)  CopyData(TCP segment #X, host buffer address, length)

       10) Loop to #5 until all the FPDUs in the TCP segment are
           consumed in order to handle FPDU packing.

   Implementation note: In both cases the receiver has to classify the
   incoming TCP segment and associate it with one of the flows it
   maintains.  In the case of no FPDU Alignment, the receiver is forced
   to classify incoming traffic before it can calculate the FPDU CRC.
   In the case of FPDU Alignment the operations order is left to the
   implementer.

   The FPDU Aligned receiver algorithm is significantly simpler.  There
   is no need to locally buffer portions of FPDUs.  Accessing state
   information is also substantially simplified - the normal case does


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   not require retrieving information to find out where a FPDU starts
   and ends or retrieval of a partial CRC before the CRC calculation can
   commence.  This avoids adding internal latencies, having multiple
   data passes through the CRC machine, or scheduling multiple commands
   for moving the data to the host buffer.

   The aligned FPDU approach is useful for in-order and out-of-order
   reception.  The receiver can use the same mechanisms for data storage
   in both cases, and only needs to account for when all the TCP
   segments have arrived to enable Delivery.  The Header Alignment,
   along with the high probability that at least one complete FPDU is
   found with every TCP segment, allows the receiver to perform data
   placement for out-of-order TCP segments with no need for intermediate
   buffering.  Essentially the TCP receive buffer has been eliminated
   and TCP reassembly is done in place within the ULP buffer.

   In case FPDU Alignment is not found, the receiver should follow the
   algorithm for non aligned FPDU reception which may be slower and less
   efficient.

11.1.2.2 FPDU Alignment effects on TCP wire protocol

      An MPA-aware TCP exposes its EMSS to MPA.  MPA uses the EMSS to
      calculate its MULPDU, which it then exposes to DDP, its ULP.  DDP
      uses the MULPDU to segment its payload so that each FPDU sent by
      MPA fits completely into one TCP segment.  This has no impact on
      wire protocol and exposing this information is already supported
      on many TCP implementations, including all modern flavors of BSD
      networking, through the TCP_MAXSEG socket option.

   In the common case, the ULP (i.e. DDP over MPA) messages provided to
   the TCP layer are segmented to MULPDU size.  It is assumed that the
   ULP message size is bounded by MULPDU, such that a single ULP message
   can be encapsulated in a single TCP segment.  Therefore, in the
   common case, there is no increase in the number of TCP segments
   emitted.  For smaller ULP messages, the sender can also apply
   packing, i.e. the sender packs as many complete FPDUs as possible
   into one TCP segment.  The requirement to always have a complete FPDU
   may increase the number of TCP segments emitted.  Typically, a ULP
   message size varies from few bytes to multiple EMSS (e.g., 64
   Kbytes).  In some cases the ULP may post more than one message at a
   time for transmission, giving the sender an opportunity for packing.
   In the case where more than one FPDU is available for transmission
   and the FPDUs are encapsulated into a TCP segment and there is no
   room in the TCP segment to include the next complete FPDU, another
   TCP segment is sent.  In this corner case some of the TCP segments
   are not full size.  In the worst case scenario, the ULP may choose a
   FPDU size that is EMSS/2 +1 and has multiple messages available for
   transmission.  For this poor choice of FPDU size, the average TCP
   segment size is therefore about 1/2 of the EMSS and the number of TCP
   segments emitted is approaching 2x of what is possible without the


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   requirement to encapsulate an integer number of complete FPDUs in
   every TCP segment.  This is a dynamic situation that only lasts for
   the duration where the sender ULP has multiple non-optimal messages
   for transmission and this causes a minor impact on the wire
   utilization.

   However, it is not expected that requiring FPDU Alignment will have a
   measurable impact on wire behavior of most applications.  Throughput
   applications with large I/Os are expected to take full advantage of
   the EMSS.  Another class of applications with many small outstanding
   buffers (as compared to EMSS) is expected to use packing when
   applicable.  Transaction oriented applications are also optimal.

   TCP retransmission is another area that can affect sender behavior.
   TCP supports retransmission of the exact, originally transmitted
   segment (see [RFC793] section 2.6, [RFC793] section 3.7 "managing the
   window" and [RFC1122] section 4.2.2.15).  In the unlikely event that
   part of the original segment has been received and acknowledged by
   the remote peer (e.g., a re-segmenting middle box, as documented in
   5.4.1 Re-segmenting Middle boxes and non MPA-aware TCP senders on
   page 31), a better available bandwidth utilization may be possible by
   re-transmitting only the missing octets.  If an MPA-aware TCP
   retransmits complete FPDUs, there may be some marginal bandwidth
   loss.

   Another area where a change in the TCP segment number may have impact
   is that of Slow Start and Congestion Avoidance.  Slow-start
   exponential increase is measured in segments per second, as the
   algorithm focuses on the overhead per segment at the source for
   congestion that eventually results in dropped segments.  Slow-start
   exponential bandwidth growth for MPA-aware TCP is similar to any TCP
   implementation.  Congestion Avoidance allows for a linear growth in
   available bandwidth when recovering after a packet drop.  Similar to
   the analysis for slow-start, MPA-aware TCP doesn't change the
   behavior of the algorithm.  Therefore the average size of the segment
   versus EMSS is not a major factor in the assessment of the bandwidth
   growth for a sender.  Both Slow Start and Congestion Avoidance for an
   MPA-aware TCP will behave similarly to any TCP sender and allow an
   MPA-aware TCP to enjoy the theoretical performance limits of the
   algorithms.

   In summary, the ULP messages generated at the sender (e.g., the
   amount of messages grouped for every transmission request) and
   message size distribution has the most significant impact over the
   number of TCP segments emitted.  The worst case effect for certain
   ULPs (with average message size of EMSS/2+1 to EMSS), is bounded by
   an increase of up to 2x in the number of TCP segments and
   acknowledges.  In reality the effect is expected to be marginal.





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11.2 Receiver implementation

   Transport & Network Layer Reassembly Buffers:

   The use of reassembly buffers (either TCP reassembly buffers or IP
   fragmentation reassembly buffers) is implementation dependent.  When
   MPA is enabled, reassembly buffers are needed if out of order packets
   arrive and Markers are not enabled.  Buffers are also needed if FPDU
   Alignment is lost or if IP fragmentation occurs.  This is because the
   incoming out of order segment may not contain enough information for
   MPA to process all of the FPDU.  For cases where a re-segmenting
   middle box is present, or where the TCP sender is not MPA-aware, the
   presence of Markers significantly reduces the amount of buffering
   needed.

   Recovery from IP Fragmentation must be transparent to the MPA
   Consumers.

11.2.1 Network Layer Reassembly Buffers

   Most IP implementations set the IP Don't Fragment bit.  Thus upon a
   path MTU change, intermediate devices drop the IP datagram if it is
   too large and reply with an ICMP message which tells the source TCP
   that the path MTU has changed.  This causes TCP to emit segments
   conformant with the new path MTU size.  Thus IP fragments under most
   conditions should never occur at the receiver.  But it is possible.

   There are several options for implementation of network layer
   reassembly buffers:

   1.  drop any IP fragments, and reply with an ICMP message according
       to [RFC792] (fragmentation needed and DF set) to tell the Remote
       Peer to resize its TCP segment

   2.  support an IP reassembly buffer, but have it of limited size
       (possibly the same size as the local link's MTU).  The end Node
       would normally never advertise a path MTU larger than the local
       link MTU.  It is recommended that a dropped IP fragment cause an
       ICMP message to be generated according to RFC792.

   3.  multiple IP reassembly buffers, of effectively unlimited size.

   4.  support an IP reassembly buffer for the largest IP datagram (64
       KB).

   5.  support for a large IP reassembly buffer which could span
       multiple IP datagrams.

   An implementation should support at least 2 or 3 above, to avoid
   dropping packets that have traversed the entire fabric.



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   There is no end-to-end ACK for IP reassembly buffers, so there is no
   flow control on the buffer.  The only end-to-end ACK is a TCP ACK,
   which can only occur when a complete IP datagram is delivered to TCP.
   Because of this, under worst case, pathological scenarios, the
   largest IP reassembly buffer is the TCP receive window (to buffer
   multiple IP datagrams that have all been fragmented).

   Note that if the Remote Peer does not implement re-segmentation of
   the data stream upon receiving the ICMP reply updating the path MTU,
   it is possible to halt forward progress because the opposite peer
   would continue to retransmit using a transport segment size that is
   too large.  This deadlock scenario is no different than if the fabric
   MTU (not last hop MTU) was reduced after connection setup, and the
   remote Node's behavior is not compliant with [RFC1122].

11.2.2 TCP Reassembly buffers

   A TCP reassembly buffer is also needed.  TCP reassembly buffers are
   needed if FPDU Alignment is lost when using TCP with MPA or when the
   MPA FPDU spans multiple TCP segments.  Buffers are also needed if
   Markers are disabled and out of order packets arrive.

   Since lost FPDU Alignment often means that FPDUs are incomplete, an
   MPA on TCP implementation must have a reassembly buffer large enough
   to recover an FPDU that is less than or equal to the MTU of the
   locally attached link (this should be the largest possible advertised
   TCP path MTU).  If the MTU is smaller than 140 octets, the buffer
   MUST be at least 140 octets long to support the minimum FPDU size.
   The 140 octets allows for the minimum MULPDU of 128, 2 octets of pad,
   2 of ULPDU_Length, 4 of CRC, and space for a possible Marker.  As
   usual, additional buffering may provide better performance.

   Note that if the TCP segment were not stored, it is possible to
   deadlock the MPA algorithm.  If the path MTU is reduced, FPDU
   Alignment requires the source TCP to re-segment the data stream to
   the new path MTU.  The source MPA will detect this condition and
   reduce the MPA segment size, but any FPDUs already posted to the
   source TCP will be re-segmented and lose FPDU Alignment.  If the
   destination does not support a TCP reassembly buffer, these segments
   can never be successfully transmitted and the protocol deadlocks.

   When a complete FPDU is received, processing continues normally.











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11.3 IETF Implementation Interoperability with RDMA Consortium Protocols

   The RDMA Consortium created early specifications of the MPA/DDP/RDMA
   protocols and some manufacturers created implementations of those
   protocols before the IETF versions were finalized.  These protocols
   and are very similar to the IETF versions making it possible for
   implementations to be created or modified to support either set of
   specifications.  For those interested, the RDMA Consortium protocol
   documents can be obtained at http://www.rdmaconsortium.org.

   In this section, implementations of MPA/DDP/RDMA that conform to the
   RDMAC specifications are called RDMAC RNICs.  Implementations of
   MPA/DDP/RDMA that conform to the IETF RFCs are called IETF RNICs.

   Without the exchange of MPA Request/Reply Frames, there is no
   standard mechanism for enabling RDMAC RNICs to interoperate with IETF
   RNICs.  Even if a ULP uses a well-known port to start an IETF RNIC
   immediately in RDMA mode (i.e., without exchanging the MPA
   Request/Reply messages), there is no reason to believe an IETF RNIC
   will interoperate with an RDMAC RNIC because of the differences in
   the version number in the DDP and RDMAP headers on the wire.

   Therefore, the ULP or other supporting entity at the RDMAC RNIC must
   implement MPA Request/Reply Frames on behalf of the RNIC in order to
   negotiate the connection parameters.  The following section describes
   the results following the exchange of the MPA Request/Reply Frames
   before the conversion from streaming to RDMA mode.

11.3.1 Negotiated Parameters

   Three types of RNICs are considered:

   Upgraded RDMAC RNIC - an RNIC implementing the RDMAC protocols which
       has a ULP or other supporting entity that exchanges the MPA
       Request/Reply Frames in streaming mode before the conversion to
       RDMA mode.

   Non-permissive IETF RNIC - an RNIC implementing the IETF protocols
       which is not capable of implementing the RDMAC protocols.  Such
       an RNIC can only interoperate with other IETF RNICs.

   Permissive IETF RNIC - an RNIC implementing the IETF protocols which
       is capable of implementing the RDMAC protocols on a per
       connection basis.

   The Permissive IETF RNIC is recommended for those implementers that
   want maximum interoperability with other RNIC implementations.




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   The values used by these three RNIC types for the MPA, DDP, and RDMAP
   versions as well as MPA Markers and CRC are summarized in Figure 12.

    +----------------++-----------+-----------+-----------+-----------+
    | RNIC TYPE      || DDP/RDMAP |    MPA    |    MPA    |    MPA    |
    |                ||  Version  | Revision  |  Markers  |    CRC    |
    +----------------++-----------+-----------+-----------+-----------+
    +----------------++-----------+-----------+-----------+-----------+
    | RDMAC          ||     0     |     0     |     1     |     1     |
    |                ||           |           |           |           |
    +----------------++-----------+-----------+-----------+-----------+
    | IETF           ||     1     |     1     |  0 or 1   |  0 or 1   |
    | Non-permissive ||           |           |           |           |
    +----------------++-----------+-----------+-----------+-----------+
    | IETF           ||  1 or 0   |  1 or 0   |  0 or 1   |  0 or 1   |
    | permissive     ||           |           |           |           |
    +----------------++-----------+-----------+-----------+-----------+
           Figure 12.  Connection Parameters for the RNIC Types.
            For MPA Markers and MPA CRC, enabled=1, disabled=0.

   It is assumed there is no mixing of versions allowed between MPA, DDP
   and RDMAP.  The RNIC either generates the RDMAC protocols on the wire
   (version is zero) or the IETF protocols (version is one).

   During the exchange of the MPA Request/Reply Frames, each peer
   provides its MPA Revision, Marker preference (M: 0=disabled,
   1=enabled), and CRC preference.  The MPA Revision provided in the MPA
   Request Frame and the MPA Reply Frame may differ.

   From the information in the MPA Request/Reply Frames, each side sets
   the Version field (V: 0=RDMAC, 1=IETF) of the DDP/RDMAP protocols as
   well as the state of the Markers for each half connection.  Between
   DDP and RDMAP, no mixing of versions is allowed.  Moreover, the DDP
   and RDMAP version MUST be identical in the two directions.  The RNIC
   either generates the RDMAC protocols on the wire (version is zero) or
   the IETF protocols (version is one).

   In the following sections, the figures do not discuss CRC negotiation
   because there is no interoperability issue for CRCs.  Since the RDMAC
   RNIC will always request CRC use, then, according to the IETF MPA
   specification, both peers MUST generate and check CRCs.

11.3.2 RDMAC RNIC and Non-permissive IETF RNIC

   Figure 13 shows that a Non-permissive IETF RNIC cannot interoperate
   with an RDMAC RNIC, despite the fact that both peers exchange MPA
   Request/Reply Frames.  For a Non-permissive IETF RNIC, the MPA
   negotiation has no effect on the DDP/RDMAP version and it is unable
   to interoperate with the RDMAC RNIC.




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   The rows in the figure show the state of the Marker field in the MPA
   Request Frame sent by the MPA Initiator.  The columns show the state
   of the Marker field in the MPA Reply Frame sent by the MPA Responder.
   Each type of RNIC is shown as an Initiator and a Responder.  The
   connection results are shown in the lower right corner, at the
   intersection of the different RNIC types, where V=0 is the RDMAC
   DDP/RDMAP version, V=1 is the IETF DDP/RDMAC version, M=0 means MPA
   Markers are disabled and M=1 means MPA Markers are enabled.  The
   negotiated Marker state is shown as X/Y, for the receive direction of
   the Initiator/Responder.

          +---------------------------++-----------------------+
          |   MPA                     ||          MPA          |
          | CONNECT                   ||       Responder       |
          |   MODE  +-----------------++-------+---------------+
          |         |   RNIC          || RDMAC |     IETF      |
          |         |   TYPE          ||       | Non-permissive|
          |         |          +------++-------+-------+-------+
          |         |          |MARKER|| M=1   | M=0   |  M=1  |
          +---------+----------+------++-------+-------+-------+
          +---------+----------+------++-------+-------+-------+
          |         |   RDMAC  | M=1  || V=0   | close | close |
          |         |          |      || M=1/1 |       |       |
          |         +----------+------++-------+-------+-------+
          |   MPA   |          | M=0  || close | V=1   | V=1   |
          |Initiator|   IETF   |      ||       | M=0/0 | M=0/1 |
          |         |Non-perms.+------++-------+-------+-------+
          |         |          | M=1  || close | V=1   | V=1   |
          |         |          |      ||       | M=1/0 | M=1/1 |
          +---------+----------+------++-------+-------+-------+
   Figure 13: MPA negotiation between an RDMAC RNIC and a Non-permissive
                                IETF RNIC.

11.3.2.1 RDMAC RNIC Initiator

   If the RDMAC RNIC is the MPA Initiator, its ULP sends an MPA Request
   Frame with Rev field set to zero and the M and C bits set to one.
   Because the Non-permissive IETF RNIC cannot dynamically downgrade the
   version number it uses for DDP and RDMAP, it would send an MPA Reply
   Frame with the Rev field equal to one and then gracefully close the
   connection.

11.3.2.2 Non-Permissive IETF RNIC Initiator

   If the Non-permissive IETF RNIC is the MPA Initiator, it sends an MPA
   Request Frame with Rev field equal to one.  The ULP or supporting
   entity for the RDMAC RNIC responds with an MPA Reply Frame that has
   the Rev field equal to zero and the M bit set to one.  The Non-
   permissive IETF RNIC will gracefully close the connection after it
   reads the incompatible Rev field in the MPA Reply Frame.



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11.3.3 RDMAC RNIC and Permissive IETF RNIC

   Figure 14 shows that a Permissive IETF RNIC can interoperate with an
   RDMAC RNIC regardless of its Marker preference.  The figure uses the
   same format as shown with the Non-permissive IETF RNIC.

          +---------------------------++-----------------------+
          |   MPA                     ||          MPA          |
          | CONNECT                   ||       Responder       |
          |   MODE  +-----------------++-------+---------------+
          |         |   RNIC          || RDMAC |     IETF      |
          |         |   TYPE          ||       |  Permissive   |
          |         |          +------++-------+-------+-------+
          |         |          |MARKER|| M=1   | M=0   | M=1   |
          +---------+----------+------++-------+-------+-------+
          +---------+----------+------++-------+-------+-------+
          |         |   RDMAC  | M=1  || V=0   | N/A   | V=0   |
          |         |          |      || M=1/1 |       | M=1/1 |
          |         +----------+------++-------+-------+-------+
          |   MPA   |          | M=0  || V=0   | V=1   | V=1   |
          |Initiator|   IETF   |      || M=1/1 | M=0/0 | M=0/1 |
          |         |Permissive+------++-------+-------+-------+
          |         |          | M=1  || V=0   | V=1   | V=1   |
          |         |          |      || M=1/1 | M=1/0 | M=1/1 |
          +---------+----------+------++-------+-------+-------+
     Figure 14: MPA negotiation between an RDMAC RNIC and a Permissive
                                IETF RNIC.

   A truly Permissive IETF RNIC will recognize an RDMAC RNIC from the
   Rev field of the MPA Req/Rep Frames and then adjust its receive
   Marker state and DDP/RDMAP version to accommodate the RDMAC RNIC.  As
   a result, as an MPA Responder, the Permissive IETF RNIC will never
   return an MPA Reply Frame with the M bit set to zero.  This case is
   shown as a not applicable (N/A) in Figure 14.

11.3.3.1 RDMAC RNIC Initiator

   When the RDMAC RNIC is the MPA Initiator, its ULP or other supporting
   entity prepares an MPA Request message and sets the revision to zero
   and the M bit and C bit to one.

   The Permissive IETF Responder receives the MPA Request message and
   checks the revision field.  Since it is capable of generating RDMAC
   DDP/RDMAP headers, it sends an MPA Reply message with revision set to
   zero and the M and C bits set to one.  The Responder must inform its
   ULP that it is generating version zero DDP/RDMAP messages.

11.3.3.2 Permissive IETF RNIC Initiator

   If the Permissive IETF RNIC is the MPA Initiator, it prepares the MPA
   Request Frame setting the Rev field to one.  Regardless of the value


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   of the M bit in the MPA Request Frame, the ULP or other supporting
   entity for the RDMAC RNIC will create an MPA Reply Frame with Rev
   equal to zero and the M bit set to one.

   When the Initiator reads the Rev field of the MPA Reply Frame and
   finds that its peer is an RDMAC RNIC, it must inform its ULP that it
   should generate version zero DDP/RDMAP messages and enable MPA
   Markers and CRC.

11.3.4 Non-Permissive IETF RNIC and Permissive IETF RNIC

   For completeness, Figure 15 shows the results of MPA negotiation
   between a Non-permissive IETF RNIC and a Permissive IETF RNIC.  The
   important point from this figure is that an IETF RNIC cannot detect
   whether its peer is a Permissive or Non-permissive RNIC.

      +---------------------------++-------------------------------+
      |   MPA                     ||              MPA              |
      | CONNECT                   ||            Responder          |
      |   MODE  +-----------------++---------------+---------------+
      |         |   RNIC          ||     IETF      |     IETF      |
      |         |   TYPE          || Non-permissive|  Permissive   |
      |         |          +------++-------+-------+-------+-------+
      |         |          |MARKER|| M=0   | M=1   | M=0   | M=1   |
      +---------+----------+------++-------+-------+-------+-------+
      +---------+----------+------++-------+-------+-------+-------+
      |         |          | M=0  || V=1   | V=1   | V=1   | V=1   |
      |         |   IETF   |      || M=0/0 | M=0/1 | M=0/0 | M=0/1 |
      |         |Non-perms.+------++-------+-------+-------+-------+
      |         |          | M=1  || V=1   | V=1   | V=1   | V=1   |
      |         |          |      || M=1/0 | M=1/1 | M=1/0 | M=1/1 |
      |   MPA   +----------+------++-------+-------+-------+-------+
      |Initiator|          | M=0  || V=1   | V=1   | V=1   | V=1   |
      |         |   IETF   |      || M=0/0 | M=0/1 | M=0/0 | M=0/1 |
      |         |Permissive+------++-------+-------+-------+-------+
      |         |          | M=1  || V=1   | V=1   | V=1   | V=1   |
      |         |          |      || M=1/0 | M=1/1 | M=1/0 | M=1/1 |
      +---------+----------+------++-------+-------+-------+-------+
    Figure 15: MPA negotiation between a Non-permissive IETF RNIC and a
                           Permissive IETF RNIC.













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12 Author's Addresses

   Stephen Bailey
       Sandburst Corporation
       600 Federal Street
       Andover, MA  01810 USA
       Phone: +1 978 689 1614
       Email: steph@sandburst.com

   Paul R. Culley
       Hewlett-Packard Company
       20555 SH 249
       Houston, Tx. USA 77070-2698
       Phone:  281-514-5543
       Email:  paul.culley@hp.com

   Uri Elzur
       Broadcom
       16215 Alton Parkway
       CA, 92618
       Phone: 949.585.6432
       Email:  uri@broadcom.com

   Renato J Recio
       IBM
       Internal Zip 9043
       11400 Burnett Road
       Austin,  Texas  78759
       Phone:  512-838-3685
       Email:  recio@us.ibm.com

   John Carrier
       Cray Inc.
       411 First Avenue S, Suite 600
       Seattle, WA 98104-2860
       Phone: 206-701-2090
       Email: carrier@cray.com
















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13 Acknowledgments

   Dwight Barron
       Hewlett-Packard Company
       20555 SH 249
       Houston, Tx. USA 77070-2698
       Phone: 281-514-2769
       Email: dwight.barron@hp.com

   Jeff Chase
       Department of Computer Science
       Duke University
       Durham, NC 27708-0129 USA
       Phone: +1 919 660 6559
       Email: chase@cs.duke.edu

   Ted Compton
       EMC Corporation
       Research Triangle Park, NC 27709, USA
       Phone: 919-248-6075
       Email: compton_ted@emc.com

   Dave Garcia
       Hewlett-Packard Company
       19333 Vallco Parkway
       Cupertino, Ca. USA 95014
       Phone: 408.285.6116
       Email: dave.garcia@hp.com

   Hari Ghadia
       Adaptec, Inc.
       691 S. Milpitas Blvd.,
       Milpitas, CA 95035  USA
       Phone: +1 (408) 957-5608
       Email: hari_ghadia@adaptec.com

   Howard C. Herbert
       Intel Corporation
       MS CH7-404
       5000 West Chandler Blvd.
       Chandler, Arizona 85226
       Phone: 480-554-3116
       Email: howard.c.herbert@intel.com










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   Jeff Hilland
       Hewlett-Packard Company
       20555 SH 249
       Houston, Tx. USA 77070-2698
       Phone: 281-514-9489
       Email: jeff.hilland@hp.com

   Mike Ko
       IBM
       650 Harry Rd.
       San Jose, CA 95120
       Phone: (408) 927-2085
       Email: mako@us.ibm.com

   Mike Krause
       Hewlett-Packard Corporation, 43LN
       19410 Homestead Road
       Cupertino, CA 95014 USA
       Phone: +1 (408) 447-3191
       Email: krause@cup.hp.com

   Dave Minturn
       Intel Corporation
       MS JF1-210
       5200 North East Elam Young Parkway
       Hillsboro, Oregon  97124
       Phone: 503-712-4106
       Email: dave.b.minturn@intel.com

   Jim Pinkerton
       Microsoft, Inc.
       One Microsoft Way
       Redmond, WA, USA 98052
       Email: jpink@microsoft.com

   Hemal Shah
       16215 Alton Parkway
       Irvine, California 92619-7013 USA
       Phone: +1 949 926-6941
       Email: hemal@broadcom.com

   Allyn Romanow
       Cisco Systems
       170 W Tasman Drive
       San Jose, CA 95134 USA
       Phone: +1 408 525 8836
       Email: allyn@cisco.com






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   Tom Talpey
       Network Appliance
       375 Totten Pond Road
       Waltham, MA 02451 USA
       Phone: +1 (781) 768-5329
       EMail: thomas.talpey@netapp.com

   Patricia Thaler
       Broadcom
       16215 Alton Parkway
       Irvine, CA 92618
       Phone: 916 570 2707
       pthaler@broadcom.com

   Jim Wendt
       Hewlett Packard Corporation
       8000 Foothills Boulevard MS 5668
       Roseville, CA 95747-5668 USA
       Phone: +1 916 785 5198
       Email: jim_wendt@hp.com

   Jim Williams
       Emulex Corporation
       580 Main Street
       Bolton, MA 01740 USA
       Phone: +1 978 779 7224
       Email: jim.williams@emulex.com


























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