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Network Working Group                                    R. R. Stewart
INTERNET-DRAFT                                           M. A. Ramalho
                                                         Cisco Systems
                                                                Q. Xie
                                                              Motorola
                                                             M. Tuexen
                                                            Siemens AG
                                                             I. Rytina
                                                              Ericsson
                                                             P. Conrad
                                                     Temple University


expires in six months                                      May 7, 2001


                  SCTP Dynamic Addition of IP addresses
                   <draft-ietf-tsvwg-addip-sctp-00.txt>

    Status of This Memo

    This document is an Internet-Draft and is in full conformance with all
    provisions of Section 10 of RFC 2026 [RFC2026]. Internet-Drafts are
    working documents of the Internet Engineering Task Force (IETF), its areas,
    and its working groups. Note that other groups may also distribute
    working documents as Internet-Drafts.

    The list of current Internet-Drafts can be accessed at
    http://www.ietf.org/ietf/1id-abstracts.txt

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


   Abstract

    This document describes extensions to the Stream Control
    Transmission Protocol (SCTP) [RFC2960] that provide a method to
    reconfigure IP address information on an existing association or
    to request that a peer set a stream flow limit.


                        TABLE OF CONTENTS
    1. Introduction............................................... 2
    2. Conventions................................................ 3
    3. Additional Chunks and Parameters........................... 3
    3.1 New Chunk Types........................................... 3
    3.1.1  Address Configuration Change Chunk (ASCONF)............ 3
    3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK)
    3.2 New Parameter Types....................................... 4
    3.2.1 Add IP Address.......................................... 6
    3.2.2 Delete IP Address....................................... 6
    3.2.3 Stream Flow Limit Change................................ 7
    3.2.4 Error Cause Indication.................................. 7
    3.2.5 Set Primary IP Address.................................. 8

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    3.2.6 Success Indication...................................... 8
    3.3 New Error Causes.......................................... 9
    3.3.1 Error Cause: Request to Delete Last remaining IP Address 9
    3.3.2 Error Cause: Operation Refused due to Resource Shortage.10
    3.3.3 Error Cause: Request to Delete Source IP Address........10
    4. Procedures.................................................11
    4.1 ASCONF Chunk Procedures...................................11
    4.1.1 Congestion Control of ASCONF Chunks.....................12
    4.2 Upon reception of a ASCONF Chunk..........................13
    4.3 General rules for address manipulation....................15
    4.3.1 A special case for OOTB ABORT chunks....................17
    4.4 Setting of the primary address............................18
    4.5 Steam Flow Limit Procedures...............................18
    4.5.1 Stream Receiver side procedures.........................19
    4.5.2 Stream Sender side procedures...........................19
    4.5.3 ULP considerations on the use of SCTP flow limit
          facility................................................20
    5. Security Considerations....................................20
    6. IANA considerations........................................20
    7. Authors' Addresses.........................................20
    8. References.................................................21


    1. Introduction

    To extend the utility and application senarios of SCTP, this
    document introduces optional extensions that provide SCTP with the
    ability to reconfigure IP address information on an existing
    association or to request the peer set a stream flow limit.

    These extensions enable SCTP to be utilized in the following
    applications:

    - Dynamic IP addresses added and subtracted extension: For
    computational or networking platforms that allow addition/removal of
    physical interface cards this feature can provide:

     A) a graceful method to add to the interfaces of an existing
        association. For the multi-homed IPv6 case this feature will
        allow renumbering of existing associations.

     B) provides a method for an endpoint to request that its peer set
        its primary destination address: This can be useful
        when an address is about to be deleted. Or when an endpoint
        has some predetermined knowledge about which is the
        preferred address to receive SCTP packets upon.

    - The SCTP flow limit extension: This extension enables the
      ability to request a sender to set a limit to the
      outstanding data sent to each stream. This in turn will
      provide:

        A) The ability to minimize the occurrence of a single stream
           monopolizing all transport level resources (e.g. a_rwnd

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           "deadlock").

        B) The ability to dynamically change the stream buffering
           limits as the application deems appropriate at any particular
           instant.


    2. Conventions

    The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
    SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
    they appear in this document, are to be interpreted as described in
    RFC 2119 [RFC2119].

    3. Additional Chunks and Parameters

    This section describes the addition of two new chunks and, six
    new parameters to allow:

         - Dynamic addition of IP Addresses to an association.
         - Dynamic deletion of IP Addresses to an association.
         - A request to set the primary address the peer will
           use when sending to an endpoint.
         - The setting of stream flow limits.

    Additionally, this section describes three new error causes that
    support these new chunks and parameters.

    3.1 New Chunk Types

    This section defines two new Chunk types that will be used to
    transfer the control information reliably. Table 1 illustrates the two
    new chunk types.

    Chunk Type  Chunk Name
    --------------------------------------------------------------
    11000001    Address/Stream Configuration Change Chunk (ASCONF)
    10000000    Address Configuration Acknowledgment     (ASCONF-ACK)

          Table 1: Address/Stream Configuration Chunks

    It should be noted that the ASCONF Chunk format requires the
    receiver to report to the sender if it does not understand the
    ASCONF chunk. This is accomplished by setting the upper bits in the
    Chunk type as described in [RFC2960] section 3.2. Note that the
    upper two bits in the ASCONF chunk are set to one.  As defined in
    [RFC2960] section 3.2, setting these upper bits in this manner will
    cause the receiver that does not understand this chunk to skip the
    chunk and continue processing, but report in an Operation Error
    Chunk using the 'Unrecognized Chunk Type' cause of error.

    3.1.1  Address Configuration Change Chunk (ASCONF)

    This chunk is used to communicate to the remote endpoint one of the

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    configuration change requests that MUST be acknowledged.  The
    information carried in the ASCONF chunk is always in the form of a
    Tag-Length-Value (TLV) as described in "3.2.1
    Optional/Variable-length Parameter Format" in [RFC2960].

    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 = 0xC1   |  Chunk Flags  |      Chunk Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Serial Number                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               ASCONF-Request Correlation ID #1                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     ASCONF Parameter #1                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                                                               \
    /                             ....                              /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               ASCONF-Request Correlation ID #N                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                     ASCONF Parameter #N                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Serial Number : 32 bits (unsigned integer)

    This value represents a Serial Number for the ASCONF Chunk. The
    valid range of Serial Number is from 0 to 4294967295 (2**32 - 1).
    Serial Numbers wrap back to 0 after reaching 4294967295.

    ASCONF-Request Correlation ID: 32 bits (unsigned integer)

    This is an opaque integer assigned by the sender to identify each
    request parameter. It is in host byte order and is only meaningful
    to the sender. The receiver of the ASCONF chunk will copy this 32
    bit value into the ASCONF Correlation ID field of the
    ASCONF-ACK. The sender of the ASCONF can use this same value in the
    ASCONF-ACK to find which request the response is for.

    ASCONF Parameter: TLV format

    Each Address configuration change is represented by a TLV
    parameter has defined in Section 3.2. One or more request
    may be present in a ASCONF chunk.

    3.1.2 Address Configuration Acknowledgment Chunk (ASCONF-ACK)

    This chunk is used by the receiver of an ASCONF chunk to acknowledge
    its reception. It carries zero or more results for any ASCONF
    Parameters that were processed by the receiver.

    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

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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Type = 0x80   |  Chunk Flags  |      Chunk Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Serial Number                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               ASCONF-Request Correlation ID #1                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 ASCONF Parameter Response#1                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                                                               \
    /                             ....                              /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               ASCONF-Request Correlation ID #N                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                 ASCONF Parameter Response#N                   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Serial Number : 32 bits (unsigned integer)

    This value represents the Serial Number for the ASCONF chunk that
    was received to which this Chunk is acknowledgment of. This value is
    copied from the received ASCONF chunk.

    ASCONF-Request Correlation ID: 32 bits (unsigned integer)

    This value is copied from the ASCONF Correlation ID received in the
    ASCONF chunk. It is used by the receiver of the ASCONF-ACK to identify
    which ASCONF parameter this response is associated with.

    ASCONF Parameter Response : TLV format

    The ASCONF Parameter Response is used in the ASCONF-ACK to report
    status of ASCONF processing. By default, if a responding endpoint
    does not include any Error cause a success is indicated. Thus a
    sender of a ASCONF-ACK MAY indicate complete success of all TLV's in
    a ASCONF by returning only the Chunk Type, Chunk Flags, Chunk Length
    (set to 8) and the Serial Number.

    3.2 New Parameter Types

    The six new parameters added follow the format defined in section
    3.2.1 of [RFC2960]. Table 2 describes the Parameters.

    Address Configuration Parameters   Parameter Type
    -------------------------------------------------
    Add IP Address                     49153 (0xC001)
    Delete IP Address                  49154 (0xC002)
    Stream Flow limit Request          49155 (0xC003)
    Error Cause Indication             49156 (0xC004)
    Set Primary Address                49157 (0xC005)
    Success report                     49158 (0xC006)

          Table 2: Address Configuration Parameters

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    3.2.1 Add IP Address

    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 = 0xC001          |    Length = Variable          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Address Parameter                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Address Parameter: TLV

    This field contains an IPv4 or IPv6 address parameter as described
    in 3.3.2.1 of RFC2960. The complete TLV is wrapped within this
    parameter.  It informs the receiver that the Address specified is to
    be added to the existing association.

    An example TLV requesting that the IPv4 address 10.1.1.1 should be
    made the primary destination address would look as follows:

        +--------------------------------+
        |  Type=0xC001   | Length = 12   |
        +--------------------------------+
        |  Type=5        | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+

    Valid Chunk Appearance

    The Add IP Address parameter may only appear in the ASCONF chunk
    type.

    3.2.2 Delete IP Address

    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 =0xC002           |    Length = Variable          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Address Parameter                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Address Parameter: TLV

    This field contains an IPv4 or IPv6 address parameter as described in
    3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this
    parameter.  It informs the receiver that the Address specified is to
    be removed from the existing association.

    An example TLV deleting the IPv4 address 10.1.1.1 from an existing
    association would look as follows:


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        +--------------------------------+
        |  Type=0xC002   | Length = 12   |
        +--------------------------------+
        |  Type=5        | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+


    Valid Chunk Appearance

    The Delete IP Address parameter may only appear in the ASCONF chunk
    type.

    3.2.3 Stream Flow Limit Change

    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 =0xC003           |    Length = Variable          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Stream Number 1          |    Flow Limit 1             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                                                               /
    /                                                               \
    \                                                               /
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        Stream Number N          |    Flow Limit N             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Stream Number n :  16 bits (unsigned integer)

    This is the stream number that is requesting a limit be placed
    on the sender based on the applications receive buffer sizes.

    Flow Limit n :  16 bits (unsigned integer)

    This is the limit the receiver is requesting (in bytes) as to the
    maximum amount of data that the receiver may accept. Note that the
    value 0 holds a special meaning described in Section 4.5.

    Valid Chunk Appearance

    The Stream Flow Limit Change parameter may only appear in the ASCONF
    chunk type.


    3.2.4 Error Cause Indication

    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 = 0xC004              |      Length = Variable        |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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    |             Error Cause(s) or Return Info on Success          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    When reporting an error this response parameter is used to wrap
    one or more standard error causes normally found within an SCTP
    Operational Error or SCTP Abort (as defined in [RFC2960]). The
    Error Cause(s) follow the format defined in section 3.3.10 of
    [RFC2960].

    Valid Chunk Appearance

    The Error Cause Indication parameter may only appear in the
    ASCONF-ACK chunk type.

    3.2.5 Set Primary IP Address

    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 =0xC005           |    Length = Variable          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Address Parameter                       |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    Address Parameter: TLV

    This field contains an IPv4 or IPv6 address parameter as described in
    3.3.2.1 of [RFC2960]. The complete TLV is wrapped within this
    parameter.  It requests the receiver to mark the specified address
    as the primary address to send data to (see section 5.1.2 of
    [RFC2960]). The receiver MAY mark this as its primary upon
    receiving this request.

    An example TLV requesting that the IPv4 address 10.1.1.1 be made the
    primary destination address would look as follows:

        +--------------------------------+
        |  Type=0xC005   | Length = 12   |
        +--------------------------------+
        |  Type=5        | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+

    Valid Chunk Appearance

    The Set Primary IP Address parameter may appear in the ASCONF chunk,
    the INIT, or the INIT-ACK chunk type. The inclusion of this parameter
    in the INIT or INIT-ACK can be used to indicate an initial preference
    of primary address.


    3.2.6 Success Indication


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    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 = 4               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    By default if a responding endpoint does not report an error for any
    requested TLV, a success is implicitly indicated. Thus a sender of a
    ASCONF-ACK MAY indicate complete success of all TLV's in a ASCONF by
    returning only the Chunk Type, Chunk Flags, Chunk Length (set to 8)
    and the Serial Number.

    The responding endpoint MAY also choose to explicitly report a
    success for a requested TLV, by returning a success report ASCONF
    Parameter Response.

    Valid Chunk Appearance

    The Success Indication parameter may only appear in the ASCONF-ACK
    chunk type.


    3.3  New Error Causes

    Three new Error Causes are added to the SCTP Operational Errors,
    primarily for use in the ASCONF-ACK chunk.

    Cause Code
    Value          Cause Code
    ---------      ----------------
    12             Request to delete last remaining IP address.
    13             Operation Refused due to resource shortage.
    14             Request to delete source IP address.

          Table 3: New Error Causes

    3.3.1 Error Cause: Request to Delete Last remaining IP Address

    Cause of error
    ---------------
    Request to delete last remaining IP address: The receiver of this
    error sent a request to delete the last IP address from its
    association with its peer. This error indicates that the request is
    rejected.


    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Cause Code=12             |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                     TLV-Copied-From-ASCONF                    /
    /                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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    An example of a failed delete in an Error Cause TLV would look as
    follows in the response ASCONF-ACK message:

        +--------------------------------+
        | Type = 0xC004  | Length = 20   |
        +--------------------------------+
        |  Cause=12      | Length = 16   |
        +----------------+---------------+
        |  Type= 0xC002  | Length = 12   |
        +----------------+---------------+
        |   Type=5       | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+

    3.3.2 Error Cause: Operation Refused due to Resource Shortage

    Cause of error
    ---------------
    This error cause is used to report a failure by the receiver to
    perform the requested operation due to a lack of resources.  The
    entire TLV that is refused is copied from the ASCONF-REQ into the
    error cause.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Cause Code=13             |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                  TLV-Copied-From-ASCONF                      /
    /                                                              \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    An example of a failed addition in an Error Cause TLV would look as
    follows in the response ASCONF-ACK message:

        +--------------------------------+
        | Type = 0xC004  | Length = 20   |
        +--------------------------------+
        |  Cause=13      | Length = 16   |
        +----------------+---------------+
        |  Type=0xC001   | Length = 12   |
        +--------------------------------+
        |  Type=5        | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+

    3.3.3 Error Cause: Request to Delete Source IP Address

    Cause of error
    ---------------
    Request to delete source IP address: The receiver of this error sent

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    a request to delete the source IP address of the ASCONF
    message. This error indicates that the request is rejected.

    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Cause Code=14             |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \                    TLV-Copied-From-ASCONF                     /
    /                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    An example of a failed delete in an Error Cause TLV would look as
    follows in the response ASCONF-ACK message:

        +--------------------------------+
        | Type = 0xC004  | Length = 20   |
        +--------------------------------+
        |  Cause=14      | Length = 16   |
        +----------------+---------------+
        |  Type=0xC002   | Length = 12   |
        +----------------+---------------+
        |   Type=5       | Length = 8    |
        +----------------+---------------+
        |       Value=0x0a010101         |
        +----------------+---------------+

    IMPLEMENTATION NOTE: It is unlikely that an endpoint would source
    a packet from the address being deleted, unless the endpoint
    does not do proper source address selection.


    4. Procedures

    This section will lay out the specific procedures for address/stream
    configuration change chunk type and its processing.

    4.1 ASCONF Chunk Procedures

    When an endpoint has an ASCONF signaled change to be sent to the
    remote endpoint it should do the following:

    A1) Create a ASCONF Chunk as defined in section 3.1.1. The chunk
    should contain all of the TLV('s) of information necessary to be
    sent to the remote endpoint, and unique correlation identities for
    each request.

    A2) A serial number should be assigned to the Chunk. The serial
    number should be a monotonically increasing number. All serial
    numbers are defined to be initialized at the start of the
    association to the same value as the Initial TSN.

    A3) If no ASCONF chunk is outstanding (un-acknowledged) with the
    remote peer AND there is less than cwnd bytes of user data

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    outstanding send the chunk.

    A4) Start a T-4 RTO timer, using the RTO value of the selected
    destination address (normally the primary path see [RFC2960] section
    6.4 for details).

    A5) When the ASCONF-ACK which acknowledges the serial number last
    sent arrives, stop the T-4 RTO timer and clear the appropriate
    association and destination error counters as defined in [RFC2960]
    section 8.1 and 8.2.

    A6) Process all of the TLV's within the ASCONF-ACK to find out
    particular status information returned to the various requests that
    were sent. Use the Correlation IDs to correlate the request and the
    responses.

    A7) If an error response is received to a TLV whose parameter type
    all TLVs with no response before the failed TLV are considered
    successful if not reported.  All TLVs after the failed response are
    considered unsuccessful unless a specific success indication is
    present for the parameter.

    A8) If there are no responses to TLVs whose parameter type begins
    all TLVs not responded to are considered successful.

If the T-4 RTO timer expires the endpoint should do the following:

    B1) Increment the error counter and perform path failure detection
    on the appropriate destination address as defined in [RFC2960]
    section 8.2.

    B2) Increment the association error counter and perform endpoint
    failure detection on the association as defined in [RFC2960] section
    8.1.

    B3) Back-off the destination address RTO timer to which the ASCONF
    chunk was sent.

    B4) Re-transmit the ASCONF chunk last sent and if possible choose an
    alternate destination address (please refer to [RFC2960] section
    6.4.1). An endpoint MUST NOT add new parameters to this chunk, it
    MUST be the same (including its serial number) as the last ASCONF
    sent.

    B5) Restart the T-4 RTO timer. Note if a different destination is
    selected, then the RTO used will be that of the new destination
    address.

    Note: That the the total number of re-transmissions is limited by B2
    above. If the maximum is reached the association will fail and enter
    a CLOSED state (see [RFC2960] section 6.4.1 for details).

    4.1.1 Congestion Control of ASCONF Chunks


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    In defining the ASCONF chunk transfer procedures it is essential
    that these transfers MUST NOT cause congestion within the network.
    To achieve this we place these restrictions on the transfer of
    ASCONF chunks:

    R1) One and only one ASCONF Chunk MAY be in transit and
    unacknowledged at any one time.  If a sender, after sending a ASCONF
    chunk, decides it needs to transfer another ASCONF Chunk, it MUST
    wait until the ASCONF-ACK Chunk returns from the previous ASCONF
    Chunk before sending a subsequent ASCONF. Note this restriction
    binds each side, so at any time two ASCONF may be in-transit on any
    given association (one sent from each endpoint).

    R2) A ASCONF MUST NOT be sent if there is no room in the current
    cwnd. If there is room in the cwnd of the destination network the
    Chunk may be sent regardless of the value of rwnd.

    R3) A ASCONF may be bundled with any other Chunk type except other
    ASCONF chunks.

    R4) A ASCONF-ACK may be bundled with any other Chunk type except
    other ASCONF-ACK's.

    R5) Both ASCONF and ASCONF-ACK chunks MUST NOT be sent in any SCTP
    state except ESTABLISHED.

    R6) An ASCONF and respective ASCONF-ACK MUST NOT be larger than the
    path MTU of the destination.

    If the sender of a ASCONF chunk receives a Operational Error
    indicating that the ASCONF chunk type is not understood, then the
    sender MUST not send subsequent ASCONF chunks to the peer. The
    endpoint should also inform the upper level application that the
    peer endpoint does not support any of the extensions detailed in this
    document.


    4.2 Upon reception of a ASCONF Chunk.

    When an endpoint receives a ASCONF chunk from the remote peer it
    should perform the following:

    C1) Compare the value of the serial number to the value the endpoint
    stored in a new association variable 'Peer-Serial-Number'.  This
    value MUST be initialized to the Initial TSN value minus 1.

    C2) If the value found in the serial number is equal to the the
    ('Peer-Serial-Number' + 1), the endpoint should:

      V1) Process the TLV's contained within the Chunk performing the
      appropriate actions as indicated by each TLV type.  The TLV's MUST
      be processed in order within the Chunk. In other words if the sender
      puts 3 TLV's in one chunk the first TLV (the one closest to the
      Chunk Header) in the Chunk MUST be processed first. The next TLV in

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      the chunk (the middle one) would be processed second and finally the
      last TLV in the Chunk would be processed last.

      V2) In processing the chunk, the receiver should build a response
      message with the appropriate error TLV's, as specified in the
      Parameter type bits for any ASCONF Parameter it does not understand.
      To indicate an unrecognized parameter, parameter type 8 as defined
      in in the INIT-ACK in 3.3.3 of [RFC2960] should be used. It may also
      use the response to carry rejections for other reasons such as
      resource shortages etc using the Error Cause TLV and an appropriate
      error condition.

      Note: a positive response is implied if no error is indicated by the
      sender.

      V3) All error responses must copy the ASCONF-Request Correlation ID
      field received in the ASCONF, from the TLV being responded to, into
      the ASCONF-Request Correlation ID field. The ASCONF-Request
      Correlation ID always precedes the request TLV.

      V4) After processing the entire Chunk, it MUST send all TLV's for
      both unrecognized parameters and any other status TLV's inside the
      ASCONF-ACK chunk that acknowledges the arrival and processing of the
      ASCONF Chunk.

      V5) Update the 'Peer-Serial-Number' to the value found in the serial
      number field.

    C3) If the value found in the serial number is equal to the value
    stored in the 'Peer-Serial-Number', the endpoint should:

      X1) Parse the ASCONF Chunk TLV's but the endpoint MUST not take any
      action on the TLV's parsed (since it has already performed these
      actions).

      X2) Build a response message with the appropriate response TLV's
      as specified in the ASCONF Parameter type bits, for any
      parameter it does not understand or could not process.

      X3) After parsing the entire Chunk, it MUST send any response
      TLV errors and status with a ASCONF-ACK chunk acknowledging the
      arrival and processing of the ASCONF Chunk.

      X4) The endpoint MUST NOT update its 'Peer-Serial-Number'.

    IMPLEMENTATION NOTE: As an optimization a receiver may wish to save
    the last ASCONF-ACK for some predetermined period of time and
    instead of re-processing the ASCONF (with the same serial number) it
    may just re-transmit the ASCONF-ACK. It may wish to use the arrival
    of a new serial number to discard the previously saved ASCONF-ACK or
    any other means it may choose to expire the saved ASCONF-ACK.

    C4) Otherwise, the ASCONF chunk is discarded since it must be either
    a stale packet or from an attacker. A receiver of such a packet MAY

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    log the event for security purposes.

    C5) In both cases C2 and C3 the ASCONF-ACK MUST be sent back to the
    source address contained in the IP header of the ASCONF being
    responded to.


    4.3 General rules for address manipulation

    When building TLV parameters for the ASCONF Chunk that
    will add or delete IP addresses the following rules should be
    applied:

    D1) When adding an IP address to an association, the IP address is
    NOT considered fully added to the association until the ASCONF-ACK
    arrives. This means that until such time as the ASCONF containing
    the add is acknowledged the sender MUST NOT use the new IP address
    as a source for ANY SCTP packet. The receiver of the add IP address
    request may use the address has a destination immediately.

    D2) After the ASCONF-ACK of an IP address add arrives, the endpoint
    MAY begin using the added IP address as a source address.

    D3) If an endpoint receives an Error Cause TLV indicating that the
    IP address Add, IP address Deletion, or Set Primary IP Address
    parameters was not understood, the endpoint MUST consider the
    operation failed and MUST NOT attempt to send any subsequent Add,
    Delete or Set Primary requests to the peer.

    D4) When deleting an IP address from an association, the IP address
    MUST be considered a valid destination address for the reception of
    SCTP packets until the ASCONF-ACK arrives and MUST NOT be used has a
    source address for any subsequent packets. This means that any
    datagrams that arrive before the ASCONF-ACK destined to the IP address
    being deleted MUST be considered part of the current
    association. One special consideration is that ABORT chunks arriving
    destined to the IP address being deleted MUST be ignored (see
    Section 4.3.1 for further details).

    D5) An endpoint MUST NOT delete its last remaining IP address from an
    association. In other words if an endpoint is NOT multi-homed it
    MUST NOT use the delete IP address. Or if an endpoint sends multiple
    requests to delete IP addresses it MUST NOT delete all of the IP
    addresses that the peer has listed for the requester.

    D6) An endpoint MUST NOT set a source address for an SCTP packet
    holding the ASCONF chunk to be the same as an address being deleted
    by the ASCONF chunk.

    D7) If a request is received to delete the last remaining IP address
    of a peer endpoint, the receiver MUST send an Error Cause TLV with
    the error cause set to the new error code 'Request to delete last IP
    remaingin address'. The requested delete MUST NOT be performed or
    acted upon, other than to send the ASCONF-ACK.

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    D8) If a request is received to delete an IP address which is also
    the source address of the IP packet which contained the ASCONF
    chunk, the receiver MUST reject this request.  To reject the request
    the receiver MUST send an Error Cause TLV set to the new error code
    "Request to Delete Source IP Address" (unless Rule D5 has also been
    violated, in which case the error code 'Request to delete last
    remaining IP address' is sent).

    D9) If an endpoint receives an ADD IP address request and does not
    have the local resources to add this new address to the association,
    it MUST return an Error Cause TLV set to the new error code
    "Operation Refused due to Resource Shortage".

    D10) If an endpoint receives an 'Out of Resource' error in response
    to its request to ADD an IP address to an association, it must
    either ABORT the association or not consider the address part of the
    association. In other words if the endpoint does not ABORT the
    association, it must consider the add attempt failed and NOT use
    this address and treat SCTP packets destined to the address as Out
    Of The Blue packets.

    D11) When an endpoint receiving a ASCONF to add an IP address sends
    an 'Out of Resource' in its response, it MUST also fail any
    subsequent add or delete requests bundled in the ASCONF.  The
    receiver MUST NOT reject an ADD and then accept a subsequent DELETE
    of an IP address in the same ASCONF chunk. In other words, once a
    receiver begins failing any ADD or DELETE request, it must fail all
    subsequent ADD or DELETE requests contained in that single ASCONF.

    D12) When an endpoint receives a request to delete an IP address
    that is the current primary address, it is an implementation
    decision as to how that endpoint chooses the new primary address.

    D13) When an endpoint receives a valid request to DELETE an IP
    address the endpoint MUST consider the address no longer as part of
    the association. It MUST NOT send SCTP packets for the association
    to that address and it MUST treat subsequent packets received from
    that address as Out Of The Blue.

    During the time interval between sending out the ASCONF and
    receiving the ASCONF-ACK it MAY be possible to receive DATA chunks
    out of order. The following examples illustrate these problems:

    Endpoint-A                                     Endpoint-Z
    ----------                                     ----------
    ASCONF[Add-IP:X]------------------------------>
                                            /--ASCONF-ACK
                                           /
                                 /--------/---New DATA:
                                /        /    Destination
           <-------------------/        /     IP:X
                                       /
           <--------------------------/

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Internet Draft           Address/Stream Configuration           May 2001


    In the above example we see a new IP address (X) being added to
    the Endpoint-A. However due to packet re-ordering in the network
    a new DATA chunk is sent and arrives at Endpoint-A before
    the ASCONF-ACK confirming the add of the address to the association.

    A similar problem exists with the deletion of an IP address as
    follows:

    Endpoint-A                                     Endpoint-Z
    ----------                                     ----------
                                 /------------New DATA:
                                /             Destination
                               /              IP:X
    ASCONF [DEL-IP:X]---------/---------------->
           <-----------------/------------------ASCONF-ACK
                            /
                           /
            <-------------/

    In this example we see a DATA chunk destined to the IP:X (which is
    about to be deleted) arriving after the deletion is complete.
    For the ADD case an endpoint SHOULD consider the newly adding IP
    address valid for the association to receive data from during the
    interval when awaiting the ASCONF-ACK. The endpoint MUST NOT source
    data from this new address until the ASCONF-ACK arrives but it may
    receive out of order data as illustrated and MUST NOT treat this
    data as an OOTB datagram (please see [RFC2960] section 8.4). It MAY
    drop the data silently or it MAY consider it part of the association
    but it MUST NOT respond with an ABORT.

    For the DELETE case, an endpoint MAY respond to the late arriving DATA
    packet as an OOTB datagram or it MAY hold the deleting IP address for a
    small period of time as still valid. If it treats the DATA packet as
    an OOTB the peer will silently discard the ABORT (since by the time
    the ABORT is sent the peer will have removed the IP address from this
    association). If the endpoint elects to hold the IP address valid for
    a period of time, it MUST NOT hold it valid longer than 2 RTO
    intervals for the destination being removed.

    4.3.1 A special case for OOTB ABORT chunks

    Another case worth mentioning is illustrated below:

    Endpoint-A                                     Endpoint-Z
    ----------                                     ----------

    New DATA:------------\
    Source IP:X           \
                           \
    ASCONF-REQ[DEL-IP:X]----\------------------>
                             \        /---------ASCONF-ACK
                              \      /
                               \----/-----------> OOTB

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Internet Draft           Address/Stream Configuration           May 2001

    (Ignored <---------------------/-------------ABORT
     by rule D4)                  /
           <---------------------/

    For this case, during the deletion of an IP address, an
    Abort MUST be ignored if the destination address of the
    Abort message is that of the destination being deleted.

    4.4 Setting of the primary address

    A sender of this option may elect to send this combined with
    a deletion or addition of an address. A sender SHOULD only send
    a set primary request to an address that is already considered
    part of the association. In other words if a sender combines
    a set primary with an add of a new IP address the set primary
    will be discarded unless the add request is to be processed
    BEFORE the set primary (i.e. it preceeds the set primary).

    A request to set primary MAY also appear in a INIT or INIT-ACK
    chunk. This can give a hint to the peer endpoint as to which
    of its addresses the sender of the INIT or INIT-ACK would like
    to be used as the primary address.

    The request to set an address as the primary path is an option the
    receiver MAY perform. It is considered a hint to the receiver of the
    best destination address to use in sending SCTP packets (in the
    requester's view). It is possible that the receiver may have other
    knowledge that it may act upon and NOT set the specified address as
    primary.  If a request arrives that asks the receiver to set an
    address as primary that does not exist, the receiver should NOT
    honor the request, leaving its existing primary address unchanged.

    4.5 Steam Flow Limit Procedures

    A stream in SCTP is an uni-directional logical channel established
    from one to another associated SCTP endpoint, within which all user
    messages are delivered in sequence except for those submitted to the
    un-ordered delivery service which may arrive out of sequence. Since
    each stream is uni-directional and no feedback mechanism exists to
    limit a sender, it is possible for one unique stream to monopolize
    all of the transport level receiver window space. The mechanism
    defined here attempts to alleviate this problem by allowing the
    receiver side to communicate to the sender a limit on how much
    outstanding data may be sent within a particular stream.

    The procedures defined here are broken down into two sides:

    o The stream receiver side or peer requesting the limit. And,

    o the stream sender side or peer that MUST honor the limit request.

    The receivers side is mainly involved with sending the request to
    the peer. The senders side is where the actual limitations and flow
    limit will occur. Note in section 4.5.1 the stream receiver is the

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Internet Draft           Address/Stream Configuration           May 2001

    endpoint that sends the ASCONF message, in section 4.5.2 the sender
    side is the endpoint that receives the ASCONF message.

    4.5.1 Stream Receiver side procedures

    The receiver side SCTP makes decisions on stream flow limit based on
    upper layer input. Normally the upper layer makes a request to limit
    all or a subset of the active streams that send data to it via an
    API interface. How this decision is made is outside the scope of
    this document.

    Anytime flow limits are made known to the SCTP endpoint by the
    application, the receiver side SHOULD create a ASCONF Chunk and
    attach to it one or more stream flow limits with there respective
    stream number. If the receiver wishes to remove all limits
    (previously placed on a particular stream) it may do so by placing
    the special value '0' in the 'Flow Limit' field. Once acknowledged
    by the peer endpoint the receiver should consider the limit in
    place.

    Note that the parameter type field upper two bits dictates that any
    parameter not understood should be skipped and reported to the
    sender with an Operational Error. If an Operational Error is
    received that indicates that the 'Stream Flow Limit Request' is not
    understood, the sender of the limit request MUST not send subsequent
    limit requests. The endpoint SHOULD also inform the upper level
    application that the peer endpoint does not support this feature.

    4.5.2 Stream Sender side procedures

    When a 'Stream Flow Limit Request' is received the sender MUST
    record each flow limit with its appropriate stream.

    After a limit is set on a stream the sender MUST obey the following
    rules when sending to the peer on that stream:

    S1) When the upper layer application attempts to send to the peer on
    a stream, check the number of outstanding bytes sent to that stream
    (those TSN's in queue to be sent, which the cumulative TSN
    Acknowledgment has not passed, on this stream) versus the limit set
    for that stream (The last received limit for this stream is
    henceforth termed the current limit).

    S2) If the number of outstanding bytes is greater than or equal to
    the current limit, the SCTP endpoint MUST reject the request and NOT
    queue the data for transmit. Instead it SHOULD return an error to
    the sending application.

    S3) If the number of outstanding bytes is less than the current
    limit, validate that the data to be sent plus the number of
    outstanding bytes is smaller than or equal to this limit. If the
    user data plus the number of outstanding bytes is smaller than or
    equal to the current limit accept the data for transmit and queue
    the user data (increasing the number of outstanding data bytes on

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Internet Draft           Address/Stream Configuration           May 2001

    this stream). If the user data plus the number of outstanding bytes
    is larger than the current limit for this stream, the SCTP endpoint
    MUST reject the request and NOT queue the data for transmit and
    instead SHOULD return an error to the application.

    S4) Any time a stream limit is updated to the value of 0, consider
    this indication to mean no limit is in effect for this stream.

    4.5.3 ULP considerations on the use of SCTP flow limit facility

    The effect of rule S3 in section 4.5.2 places a maximum size upon a
    sender. Once a limit is in effect, if the sending Upper Layer
    Protocol (ULP) wishes to send a message that is larger than that
    permitted by the imposed stream limit, the ULP will need to provide
    a mechanism for fragmentation and re-assembly.

    This ULP mechanism is in addition to any fragmentation and
    re-assembly that may be provided by SCTP. It is the sole
    responsibility of the ULP to handle the case of a single
    user message being larger than the stream flow limit, if
    applicable.

    5. Security Considerations

    The ADD/DELETE of an IP address to an existing association does
    provide an additional mechanism by which existing associations can
    be hijacked.  Where the attacker is able to intercept and or alter
    the packets sent and received in an association the use of this
    feature MAY increase the ease at which an association may be
    overtaken. This threat SHOULD be considered when deploying a version
    of SCTP that use this feature. The IP Authentication Header
    [RFC2402] SHOULD be used when the threat environment requires
    stronger integrity protections, but does not require
    confidentiality. It should be noted that in the base SCTP
    specification [RFC2960], if an attacker is able to intercept and or
    alter packets, even without this feature it is possible to hijack an
    existing association, please refer to Section 11 of RFC2960.


    6. IANA considerations

    This document defines the following new SCTP parameters, chunks
    and errors:

        - Two new Chunk Types,
        - Six Parameter Types, and
        - Three new SCTP Error Causes.

    7.  Acknowledgements

    The authors wish to thank Jon Berger, John Loughney, Ivan Rodriguez,
    Marshall Rose, and Chip Sharp for their invaluable comments.

    8. Authors' Addresses

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Internet Draft           Address/Stream Configuration           May 2001


    Randall R. Stewart                      Tel: +1-815-477-2127
    Cisco Systems, Inc.                     EMail: rrs@cisco.com
    8745 W. Higgins Road, Suite 200
    Chicago, Ill  60631
    USA

    Micheal A. Ramalho                      Tel: +1-732-809-0188
    Cisco Systems, Inc.                EMail: mramalho@cisco.com
    1802 Rue de la Porte
    Wall Township, NJ 0719-3784

    Qiaobing Xie                            Tel: +1-847-632-3028
    Motorola, Inc.                    EMail: qxie1@email.mot.com
    1501 W. Shure Drive, #2309
    Arlington Heights, IL 60004
    USA

    Michael Tuexen                          Tel: +49-89-722-47210
    SIEMENS AG               EMail: Michael.Tuexen@icn.siemens.de
    Hofmannstr. 51
    81359 Munich
    Germany

    Ian Rytina                              Tel: +61-3-9301-6164
    Ericsson Australia                      EMail:ian.rytina@ericsson.com
    37/360 Elizabeth Street
    Melbourne, Victoria 3000
    Australia

    Phil Conrad                            Tel: +1-XXX-XXX-XXXX
    Netlab Research Group       Email conrad@joda.cis.temple.edu
    Dept. Of Computer &
    Information Sciences
    Temple University
    1805 N Broad St.
    Philadelphia, PA 19122
    USA

    9. References

    [RFC2960] R. R. Stewart, Q. Xie, K. Morneault, C. Sharp,
        H. J. Schwarzbauer, T. Taylor, I. Rytina, M. Kalla, L. Zhang,
        and, V. Paxson, "Stream Control Transmission Protocol," RFC
        2960, October 2000.

    [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
        3", RFC 2026, October 1996.

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

    [RFC2402] S. Kent, R. Atkinson., "IP Authentication Header.", RFC
        2402, November 1998.

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