SCTP DDP Adaptation: Stream Control Transmission Protocol (SCTP) Direct Data Placement (DDP) Adaptation

Network Working Group                                    C. Bestler, Ed.
Request for Comments: 5043                                      Neterion
Category: Standards Track                                R. Stewart, Ed.
                                                     Cisco Systems, Inc.
                                                            October 2007


              Stream Control Transmission Protocol (SCTP)
                 Direct Data Placement (DDP) Adaptation

Status of This Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Abstract

   This document specifies an adaptation layer to provide a Lower Layer
   Protocol (LLP) service for Direct Data Placement (DDP) using the
   Stream Control Transmission Protocol (SCTP).

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Motivation . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Overview . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   5.  Data Formats . . . . . . . . . . . . . . . . . . . . . . . . .  5
     5.1.  Adaptation Layer Indicator . . . . . . . . . . . . . . . .  5
     5.2.  Payload Data Chunks  . . . . . . . . . . . . . . . . . . .  6
       5.2.1.  DDP Source Sequence Number (DDP-SSN) . . . . . . . . .  6
       5.2.2.  DDP Segment Chunk  . . . . . . . . . . . . . . . . . .  7
       5.2.3.  DDP Stream Session Control . . . . . . . . . . . . . .  7
   6.  DDP Stream Sessions  . . . . . . . . . . . . . . . . . . . . .  8
     6.1.  Sequencing . . . . . . . . . . . . . . . . . . . . . . . .  9
     6.2.  Legal Sequence: Active/Passive Session Accepted  . . . . .  9
     6.3.  Legal Sequence: Active/Passive Session Rejected  . . . . .  9
     6.4.  Legal Sequence: Active/Passive Session Non-ULP Rejected  . 10
     6.5.  ULP-Specific Sequencing  . . . . . . . . . . . . . . . . . 10
     6.6.  Other Sequencing Rules . . . . . . . . . . . . . . . . . . 10
   7.  SCTP Endpoints . . . . . . . . . . . . . . . . . . . . . . . . 11
     7.1.  Adaptation Layer Indication Restriction  . . . . . . . . . 11
     7.2.  Multihoming Implications . . . . . . . . . . . . . . . . . 11
   8.  Number of Streams  . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Fragmentation  . . . . . . . . . . . . . . . . . . . . . . . . 12
   10. Sequenced Unordered Operation  . . . . . . . . . . . . . . . . 13
   11. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     11.1. Association Initialization . . . . . . . . . . . . . . . . 13
     11.2. Chunk Bundling . . . . . . . . . . . . . . . . . . . . . . 14
     11.3. Association Termination  . . . . . . . . . . . . . . . . . 14
   12. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 15
   13. Security Considerations  . . . . . . . . . . . . . . . . . . . 15
   14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 16
   15. Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 16
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 16
     16.2. Informative References . . . . . . . . . . . . . . . . . . 16

1.  Introduction

   This document describes a method to adapt Direct Data Placement
   [RFC5041] to Stream Control Transmission Protocol (SCTP) [RFC4960].

   Some implementations may include this adaptation layer within their
   SCTP implementations to obtain maximum performance, but the behavior
   of SCTP will be unaffected.  An SCTP layer used solely by this
   adaptation layer is able to take certain optimizations based on the
   limited subset of SCTP capabilities used.  In order to allow
   optimization for these implementations, we specify the use of the new
   adaptation layer indication as defined in [RFC5061]

1.1.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Definitions

   DDP -  See Direct Data Placement Protocol.

   DDP Endpoint -  The logical sender/receiver of DDP Segments.  An SCTP
      stream pair is not assumed to have a DDP Endpoint.  DDP Segments
      may only be sent once a DDP Endpoint has been assigned to an SCTP
      stream pair by a local interface.

   DDP Source Stream Sequence Number (DDP-SSN) -  A stream-specific
      sequence number assigned by the adaptation layer for each SCTP
      Data Chunk sent.  This is the order that chunks were submitted to
      SCTP, no matter in what order they are actually sent or received.

   DDP Segment -  The smallest unit of data transfer for the DDP
      protocol.  It includes a DDP Header and ULP Payload (if present).
      A DDP Segment should be sized to fit within the Lower Layer
      Protocol MULPDU (Marker PDU Aligned (MPA) Upper Layer PDU).

   DDP Segment Chunk -  An SCTP Payload Data Chunk that encapsulates the
      DDP-SSN and a DDP Segment.

   DDP Stream -  A sequence of DDP Segments whose ordering is defined by
      the LLP.  For SCTP, a DDP stream maps directly to a bidirectional
      pair of SCTP streams with the same Stream IDs.  Note that DDP has
      no ordering guarantees between DDP streams.

   DDP Stream Session -  A single pairing of DDP Endpoints over a DDP
      stream that lasts from an Initiation message through the
      Termination message(s).

   DDP Stream Session Control Message -  A message that is used to
      control the association of the DDP Endpoint with the DDP stream.

   Direct Data Placement Protocol (DDP) -  A wire protocol that supports
      Direct Data Placement by associating explicit memory buffer
      placement information with the LLP payload units.

   Lower Layer Protocol (LLP) -  In the context of DDP, the protocol
      layer beneath RDMA that provides a reliable transport service.
      The SCTP DDP adaption is one of the initially defined LLPs for
      DDP.

   Protection Domain -  A common local interface convention to control
      which Steering Tags (STags) are valid with which DDP Endpoints.
      Under this convention, both the Steering Tag and DDP Endpoint are
      created within the context of a Protection Domain, and the
      Steering Tag may only be enabled for DDP Endpoints created under
      the same Protection Domain.

   RDMA -  Remote Direct Memory Access.

   RNIC -  RDMA Network Interface Card.

   SCTP association -  A protocol relationship between two SCTP
      endpoints.  An SCTP association supports multiple SCTP streams.

   SCTP Data Chunk -  An SCTP Chunk used to convey Payload Data.  There
      can be multiple Chunks within each SCTP packet.  Other Chunks are
      used to control the SCTP Association.

   SCTP endpoint -  The logical sender/receiver of SCTP packets.  On a
      multihomed host, an SCTP endpoint is represented to its peers as a
      combination of an SCTP port number and a set of eligible
      destination transport addresses to which SCTP packets can be sent.

   SCTP Stream -  A unidirectional logical channel established from one
      to another associated SCTP endpoint.  There can be multiple SCTP
      streams within each SCTP association.  An SCTP stream is used to
      form one direction of a DDP stream.

   Transmission Sequence Number (TSN) -  A 32-bit sequence number used
      internally by SCTP.  One TSN is attached to each chunk containing
      user data to permit the receiving SCTP endpoint to acknowledge its
      receipt and detect duplicate deliveries.

   Upper Layer Protocol (ULP) -  In the context of RDMA protocol
      specifications, this is the layer using RDMA services.  Typically,
      this is an application or middleware.  A primary goal of RDMA
      protocols is to enable direct transfer of payload to/from ULP
      Buffers.

3.  Motivation

   This document specifies an adaptation layer which fulfills the
   requirements of a Lower Layer Protocol (LLP) for DDP using a specific
   subset of SCTP capabilities.

   The defined protocol is intended to be implementable over existing
   SCTP stacks, while clearly defining what portions of SCTP are
   required to enable an implementation to be optimized specifically to
   support DDP.

4.  Overview

   The adaptation layer uses a pair of like-numbered SCTP streams within
   an SCTP Association to provide a reliable DDP stream between two DDP
   Endpoints.  Except as specifically noted, each DDP Segment submitted
   by the DDP layer is encoded as a single unordered SCTP Data Chunk.
   In addition to the DDP Segment, the Data Chunk also contains a
   sequence number (DDP-SSN) that reflects the order in which DDP
   submitted the segments for that stream.

   A DDP Stream Session is defined by DDP Stream Session Control Chunks
   that manage the state of the DDP Stream Session.  These Chunks
   dynamically bind DDP Endpoints to the DDP Stream Session, and DDP
   Segment Chunks are used to reliably deliver DDP Segments with the
   session.

5.  Data Formats

5.1.  Adaptation Layer Indicator

   The DDP/SCTP adaptation layer uses all streams within an SCTP
   association.  An SCTP Association that has had the DDP Adaptation
   Indication negotiated will carry only SCTP Data Chunks as defined in
   this document.

   It is presumed that the handling of incoming data chunks for DDP-
   enabled associations is sufficiently different than for routine SCTP
   associations that it is undesirable to require support for mixing DDP
   and non-DDP streams in a single association.  More than a single
   association is required if an application desires to utilize both DDP
   and non-DDP traffic with the same remote host.

   We define an Adaptation Indication that MUST appear in the INIT or
   INIT-ACK with the following format as defined in [RFC5061].

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |        Type =0xC006           |    Length = Variable          |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                    Adaptation Indication                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Adaptation Indication:

   The following value has been assigned for DDP.

         DDP                        - 0x00000001


5.2.  Payload Data Chunks

   The DDP SCTP adaptation uses two types of SCTP Payload Data Chunks,
   differentiated by the Payload Protocol Identifier:

      DDP Segment Chunks are used to reliably deliver DDP Segments sent
      between DDP Endpoints.

      DDP Stream Session Control Messages are used to establish and tear
      down DDP Stream Sessions, specifically by controlling the binding
      of DDP Endpoints with SCTP streams.


   Payload Protocol Identifier:

   The following value are defined for DDP in this document
   and have been assigned by IANA:

         DDP Segment Chunk          - 16
         DDP Stream Session Control - 17


5.2.1.  DDP Source Sequence Number (DDP-SSN)

   All SCTP Payload Data Chunks used by this adaptation layer include a
   DDP Source Sequence Number (DDP-SSN).  The DDP-SSN tracks the
   sequence in which the messages were submitted to the SCTP layer for
   the SCTP stream in use.  The DDP-SSN MUST have the same value that
   the SCTP Stream Sequence Number (SSN) would have been assigned had
   ordered SCTP Payload Data Chunks been used rather than unordered.

   The rationale for specifying the DDP-SSN is as follows:

   o  The SCTP Stream Sequence Number (SSN) is not suitable for this
      purpose because all messages defined by this document use
      unordered Payload Data Chunks to ensure prompt delivery from the
      receiving SCTP layer.

   o  The SCTP Transmission Sequence Number (TSN) is not suitable for
      determining the original order of Data Chunks within a stream.
      The sending SCTP layer is allowed to optimize the transmission
      sequence of unordered Data Chunks to encourage Chunk Bundling, or
      for other purposes.

5.2.2.  DDP Segment Chunk

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          DDP-SSN              |         DDP Segment           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
   |                                                               |
   |                         ...                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   DDP Segments are as defined in [RFC5041].  The DDP Segment Chunk
   serves the same purpose as the MPA [RFC5044] Upper Layer PDU (MULPDU)
   in that it carries DDP Segments over a reliable protocol with added
   sequencing information.

5.2.3.  DDP Stream Session Control

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          DDP-SSN              |    Function Code              |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |            Private Data (Dependent on Function Code)          |
   |                         ...                                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The following function code values are defined for DDP in
   this document:

         DDP Stream Session Initiate         - 0x001
         DDP Stream Session Accept           - 0x002
         DDP Stream Session Reject           - 0x003
         DDP Stream Session Terminate        - 0x004

   ULP-supplied Private Data MUST be included for DDP Stream Session
   Initiate, DDP Stream Session Accept, and DDP Stream Session Reject
   messages.  However, the ULP supplied Private DATA MAY be of zero
   length.

   Private Data length MUST NOT exceed 512 bytes in any message.

   Private Data MUST NOT be included in the DDP Stream Session Terminate
   message.

   Received DDP Stream Session Control messages SHOULD be reported to
   the ULP.  If reported, any supplied Private Data MUST be available
   for the ULP to examine.

   The DDP/SCTP adaptation layer MAY limit the number of Session
   Initiate requests that it has submitted to the ULP.  When a DDP
   Stream Session Initiate cannot be forwarded to the ULP due to such a
   limit, the adaptation layer MUST respond with a DDP Stream Session
   Terminate message.

6.  DDP Stream Sessions

   A DDP Endpoint is the logical sender/receiver of DDP Segments.  A DDP
   stream connects two DDP Endpoints using a matched pair of SCTP
   streams having the same SCTP Stream Identifiers.

   A DDP Stream Session defines the sequence of Data Chunks exchanged
   between two DDP Endpoints over a DDP stream that has a distinct
   beginning and end as defined in the following section.  Data Chunks
   from one DDP Stream Session are never carried over to the next
   session.  Each Data Chunk unambiguously belongs to exactly one
   session.  The DDP-SSNs assigned to the Data Chunks for a session MUST
   NOT have any gaps.

   The local interface MAY dynamically associate a DDP Endpoint with the
   DDP stream based upon the initial exchanges of a DDP Session, and
   dynamically terminate that association at the session's end.
   Alternately, a specialized local interface could simply statically
   map DDP Endpoints to DDP streams.

   Conventionally, local interfaces for RDMA have deferred the selection
   of the DDP Endpoint until after the ULP decides to accept an RDMA
   connection request.  But that is a local interface choice and not a
   wire protocol requirement.

   A DDP stream is associated with at most one Protection Domain during
   a single DDP Stream Session.  On the passive side, the association is
   typically deferred until the DDP Stream Session Accept message.

6.1.  Sequencing

   The DDP-SSN is reset to zero at the beginning of each DDP Stream
   Session.

   The normative sequence for considering Payload Data Chunks within a
   given session is based upon each Data Chunk's DDP-SSN.  When
   considered in this normative sequence, all sessions MUST conform to
   one of the patterns defined in this section.

   If the adaptation layer receives a Payload Data Chunk that conforms
   to none of the enumerated legal patterns, the DDP Stream Session MUST
   be terminated.

6.2.  Legal Sequence: Active/Passive Session Accepted

   In this DDP Stream Session sequence, one DDP Endpoint assumes the
   active role in requesting a DDP Stream Session, which the other side
   accepts.

      Active side sends a DDP Stream Session Initiate message.

      Passive side sends a DDP Stream Session Accept message.

      Each side may then send zero or more DDP Segments with increasing
      DDP-SSNs, subject to any flow control imposed by other protocol
      layers.

      The final User Data Chunk for each side MAY be a DDP Stream
      Terminate.  At least one side MUST send a DDP Stream Terminate.
      Note that this would follow any RDMAP Terminate message, which to
      the adaptation layer is simply another DDP Segment.

6.3.  Legal Sequence: Active/Passive Session Rejected

   DDP Stream Sessions allow each party to send a single non-payload
   message before the other end commits specific resources to the
   session.  This allows each end to determine which resources are to be
   used, and how they are to be configured, or even if the session
   should be granted.

   These decisions MAY be influenced by the need to assign a specific
   Protection Domain, to determine how many RDMA Read Credits are
   required, or to determine how many receive operations the ULP should
   enable.

   Because of these or other factors, the passive side MAY choose to
   reject a DDP Stream Session Request.  This results in the following
   legal sequence:

      Active side sends a DDP Stream Session Initiate message.

      Passive side sends a DDP Stream Session Reject message.

   A DDP Stream Session Reject message MUST NOT be sent unless the
   rejection is at the direction of the ULP.

6.4.  Legal Sequence: Active/Passive Session Non-ULP Rejected

   Acceptance or rejection of DDP Stream Session Initiate messages
   SHOULD be under the control of the ULP.  This MAY require passing an
   event to the ULP.  There MUST be a finite limit on the number of such
   requests that are pending a ULP decision.  When more session requests
   are received, the passive side MUST respond to the Initiate message
   with a DDP Stream Terminate Message.

6.5.  ULP-Specific Sequencing

   An implementation MAY choose to support additional ULP-specific
   sequences, but MUST NOT do so unless requested to do so by the ULP.

   A defined ULP MUST be able to operate using only the defined
   mandatory session sequences.  Any additional sequences must be used
   only for optional optimizations.

6.6.  Other Sequencing Rules

   A DDP Stream Session Control message MUST NOT be sent if it may be
   received before a prior DDP Stream Session Control message within the
   same DDP Stream Session.

   An active side of a DDP Stream Session MUST NOT send a DDP Segment
   that might be received before the DDP Stream Session Initiate
   message.

   This MAY be determined by SCTP acking of the Data Chunk used to carry
   the DDP Stream Session Initiate message, or by receipt of a
   responsive DDP Stream Session Control message.

   A DDP Stream Identifier MUST NOT be reused for another DDP Stream
   Session while any Data Chunk from a prior session might be
   outstanding.

7.  SCTP Endpoints

7.1.  Adaptation Layer Indication Restriction

   The local interface MUST allow the ULP to specify an SCTP endpoint to
   use a specific Adaptation Indication.  It MAY require the ULP to do
   so.

   Once an endpoint decides on its acceptable Adaptation Indication(s),
   it SHOULD terminate all requests to establish an association with any
   different Adaptation Indication.

   An SCTP implementation MAY choose to accept association requests for
   a given SCTP endpoint only until one association for the endpoint has
   been established.  At that point, it MAY choose to restrict all
   further associations for the same endpoint to use the same Adaptation
   Indication.

7.2.  Multihoming Implications

   SCTP allows an SCTP endpoint to be associated with multiple IP
   addresses, potentially representing different interface devices.
   Distribution of the logic for a single DDP stream across multiple
   input devices can be very undesirable, resulting in complex cache
   coherency challenges.  Therefore, the local interface MAY restrict
   DDP-enabled SCTP endpoints to a single IP address, or to a set of IP
   addresses that are all assigned to the same input device ("RNIC").

   The default binding of a DDP-enabled SCTP endpoint SHOULD NOT cover
   more than a single IP address unless doing so results in neither
   additional bus traffic nor duplication of memory registration
   resources.  This will frequently result in a different default than
   for SCTP endpoints that are not DDP enabled.

   Applications MAY choose to avoid using out-of-band methods for
   communicating the set of IP addresses used by an SCTP endpoint when
   there is potential confusion as to the intended scope of the SCTP
   endpoint.  For example, assuming the SCTP endpoint consists of all IP
   addresses Advertised by DNS may work for a general purpose SCTP
   endpoint but not a DDP-enabled one.

   Even when multihoming is supported, ULPs are cautioned that they
   SHOULD NOT use ULP control of the source address in an attempt to
   load-balance a stream across multiple paths.  A receiving DDP/SCTP
   implementation that chooses to support multihoming SHOULD optimize
   its design on the assumption that multihoming will be used for
   network fault tolerance, and not to load-balance between paths.  This
   is consistent with recommended SCTP practices.

8.  Number of Streams

   DDP streams are bidirectional.  They are always composed by pairing
   the inbound and outbound SCTP streams with the same SCTP Stream
   Identifier.

   The adaptation layer should request the maximum number of SCTP
   streams it will wish to use over the lifetime of the association.
   SCTP streams must still be bound to DDP Endpoints, and a DDP-enabled
   SCTP association does not support ordered Data Chunks.  Therefore,
   the mere existence of an SCTP stream is unlikely to require
   significant supporting resources.

   This mapping uses an SCTP association to carry one or more DDP
   streams.  Each DDP stream will be mapped to a pair of SCTP streams
   with the same SCTP stream number.  The adaptation MUST initialize all
   of its SCTP associations with the same number of inbound and outbound
   streams.

9.  Fragmentation

   A DDP/SCTP Receiver already deals with fragmentation at both the IP
   and DDP layers.  Therefore, use of SCTP layer segmenting will be
   avoided for most cases.

   As a Lower Layer Protocol (LLP) for DDP, the SCTP adaptation layer
   MUST inform the DDP layer of the maximum DDP Segment size that will
   be supported.  This should be the largest value that can be supported
   without use of IP or SCTP fragmentation, or 516 bytes, whichever is
   larger.

   A minimum of 516 bytes is required to allow a DDP Stream Session
   Control Message with 512 bytes of Private Data.

   SCTP data chunk fragmentation MUST NOT be used unless the alternative
   is IP fragmentation.

   The SCTP adaptation layer SHOULD set the maximum DDP Segment size
   below the theoretical maximum in order to allow bundling of Control
   Chunks in the same SCTP packet.

   The SCTP adaptation layer MUST reject DDP Segments that are larger
   than the maximum size specified.

10.  Sequenced Unordered Operation

   The adaptation layer MUST use the Unordered option on all Data Chunks
   (U Flag set to one).  The SCTP layer is expected to deliver unordered
   Data Chunks without delay.

   Because DDP employs unordered SCTP delivery, the receiver MUST NOT
   rely upon the SCTP Transmission Sequence Number (TSN) to imply
   ordering of DDP Segments.  The fact that the SCTP Data Chunk for a
   DDP Segment is prior to the cumulative ack point does not guarantee
   that all prior DDP segments have been placed.  The SCTP sender is not
   obligated to transmit unordered Data Chunks in the order presented.

   The DDP-SSN can be used without special logic to determine the
   submission sequence when the maximum number of in-flight messages is
   less than 32768.  This also applies if the sending SCTP accepts no
   more than 32767 Data Chunks for a single stream without assigning
   TSNs.

   If SCTP does accept more than 32768 Data chunks for a single stream
   without assigning TSNs, the sending DDP must simply refrain from
   sending more than 32767 Data Chunks for a single stream without
   acknowledgment.  Note that it MUST NOT rely upon ULP flow control for
   this purpose.  Typical ULP flow control will deal exclusively with
   untagged messages, not with DDP segments.

   The receiver MAY perform a validity check on received DDP-SSNs to
   ensure that any gap could be accounted for by unreceived Data Chunks.
   Implementations SHOULD NOT allocate resources on the assumption that
   DDP-SSNs are valid without first performing such a validity check.
   An invalid DDP-SSN MAY result in termination of the DDP stream.

11.  Procedures

11.1.  Association Initialization

   At the startup of an association, a DDP/SCTP adaptation layer MUST
   include an adaptation layer indication in its INIT or INIT-ACK (as
   defined in Section 5.1).  After the exchange of the initial first two
   SCTP chunks (INIT and INIT-ACK), an endpoint MUST verify and inspect
   the Adaptation Indication and compare it to the following table to
   determine proper action.

          Indication |           Action
            type     |
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                     | This indicates that the peer DOES NOT
         NONE        | support ANY DDP or RDMA adaptation, and thus
                     | RDMA and DDP procedures MUST NOT be
                     | performed upon this association.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                     | This indicates that the peer DOES support
         DDP         | the DDP/SCTP adaptation layer defined here.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                     | This indicates that the peer DOES NOT
       ANY-OTHER     | support the DDP adaptation, and thus
       Indication    | DDP procedures MUST NOT be performed
                     | upon this association.
   ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

   An implementation MAY require that all associations for a given SCTP
   endpoint be placed in the same mode.

   The local interface MAY allow the ULP to accept only requests to
   establish an association in a specified mode.

11.2.  Chunk Bundling

   SCTP allows multiple Data Chunks to be bundled in a single SCTP
   packet.  Data chunks containing DDP Segments with untagged messages
   SHOULD NOT be delayed to facilitate bundling.  Data chunks containing
   DDP Segments with tagged messages will generally be full sized, and
   hence not subject to bundling.  However, partial-size tagged messages
   MAY be delayed, as they are frequently followed by a short untagged
   message.

11.3.  Association Termination

   Termination of an SCTP Association due to errors should be handled at
   the SCTP layer.  The RDMAP-defined RDMAP Terminate Message SHOULD NOT
   be sent on each DDP stream when a determination has been made to
   terminate an SCTP association.  Sending that message on each SCTP
   stream could severely delay the termination of the association.

   The local interface SHOULD notify all consumers of DDP streams when
   the underlying SCTP stream has been terminated.

   Other RDMAP-defined Terminate Messages MUST be generated as specified
   when a DDP stream is terminated.  Note that with the SCTP mapping,
   termination of a DDP Stream does not mandate termination of the
   Association.

12.  IANA Considerations

   This document defines a new SCTP Adaptation Layer Indication
   codepoint for DDP (0x00000001).  [RFC5061] creates the registry from
   which this codepoint has been assigned.

   This document also defines two new SCTP Payload Protocol Identifiers
   (PPIDs).  RFC 4960 [RFC4960] creates the registry from which these
   identifiers have been assigned.  The following values have been
   assigned:

         DDP Segment Chunk           - 16
         DDP Stream Session Control  - 17

13.  Security Considerations

   Any direct placement of memory could pose a significant security risk
   if adequate local controls are not provided.  These threats are
   addressed in the appropriate DDP [RFC5041], RDMA [RFC5040], or
   Security [RFC5042] documents.  This document does not add any
   additional security risks over those found in RFC 4960 [RFC4960].

   The IPsec requirements for Remote Direct Data Placement (RDDP) are
   based on the version of IPsec specified in RFC 2401 [RFC2401] and
   related RFCs, as profiled by RFC 3723 [RFC3723], despite the
   existence of a newer version of IPsec specified in RFC 4301 [RFC4301]
   and related RFCs.  One of the important early applications of the
   RDDP protocols is their use with iSCSI iSER [RFC5046]; RDDP's IPsec
   requirements follow those of IPsec in order to facilitate that usage
   by allowing a common profile of IPsec to be used with iSCSI and the
   RDDP protocols.  In the future, RFC 3723 may be updated to the newer
   version of IPsec; the IPsec security requirements of any such update
   should apply uniformly to iSCSI and the RDDP protocols.

   Additional requirements apply to security for RDDP over SCTP, due to
   the use of SCTP as the transport protocol.  An implementation of
   IPsec for RDDP over SCTP:

   1)  MUST support IPsec functionality for SCTP equivalent to the IPsec
       functionality for TCP that is required by RFC 3723,

   2)  SHOULD support the same level of IPsec functionality for SCTP and
       TCP unless there is no support for TCP, and

   3)  MUST support at least the level of protocol and port selector
       functionality for SCTP that is supported for TCP.

14.  Contributors

   Many thanks to our contributors who have spent many hours reading and
   reviewing keeping us straight: Sukanta Ganguly an independent
   consultant, Vivek Kashyap of IBM, Jim Pinkerton of Microsoft, and
   Hemal Shah of Broadcom.  Thanks for all your hard work.

15.  Acknowledgments

   The authors would like to thank the following people that have
   provided comments and input: Stephen Bailey, David Black, Douglas
   Otis, Allyn Romanow, and Jim Williams.

16.  References

16.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3723]  Aboba, B., Tseng, J., Walker, J., Rangan, V., and F.
              Travostino, "Securing Block Storage Protocols over IP",
              RFC 3723, April 2004.

   [RFC4960]  Stewart, R., "Stream Control Transmission Protocol",
              RFC 4960, September 2007.

   [RFC5040]  Recio, R., Metzler, B., Culley, P., Hilland, J., and D.
              Garcia, "A Remote Direct Memory Access Protocol
              Specification", RFC 5040, October 2007.

   [RFC5041]  Shah, H., Pinkerton, J., Recio, R., and P. Culley, "Direct
              Data Placement over Reliable Transports", RFC 5041,
              October 2007.

   [RFC5042]  Pinkerton, J. and E. Deleganes, "Direct Data Placement
              Protocol (DDP) / Remote Direct Memory Access Protocol
              (RDMAP) Security", RFC 5042, October 2007.

   [RFC5061]  Stewart, R., Xie, Q., Tuexen, M., Maruyama, S., and M.
              Kozuka, "Stream Control Transmission Protocol (SCTP)
              Dynamic Address Reconfiguration", RFC 5061,
              September 2007.

16.2.  Informative References

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

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005.

   [RFC5044]  Culley, P., Elzur, U., Recio, R., Bailey, S., and J.
              Carrier, "Marker PDU Aligned Framing for TCP
              Specification", RFC 5044, October 2007.

   [RFC5046]  Ko, M., Chadalapaka, M., Elzur, U., Shah, H., and P.
              Thaler, "Internet Small Computer System Interface (iSCSI)
              Extensions for Remote Direct Memory Access (RDMA)",
              RFC 5046, October 2007.

Authors' Addresses

   Caitlin Bestler (editor)
   Neterion
   20230 Stevens Creek Blvd.
   Suite C
   Cupertino, CA  95014
   USA

   Phone: 408-366-4639
   EMail: caitlin.bestler@neterion.com


   Randall R. Stewart (editor)
   Cisco Systems, Inc.
   Forest Drive
   Columbia, SC  29036
   USA

   Phone: +1-815-342-5222
   EMail: rrs@cisco.com

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