<pre>Network Working Group                                         R. Stewart
Request for Comments: 5061                           Cisco Systems, Inc.
Category: Standards Track                                         Q. Xie
                                                          Motorola, Inc.
                                                               M. Tuexen
                                      Univ. of Applied Sciences Muenster
                                                             S. Maruyama
                                                               M. Kozuka
                                                        Kyoto University
                                                          September 2007


              <span class="h1">Stream Control Transmission Protocol (SCTP)</span>
                    <span class="h1">Dynamic Address Reconfiguration</span>

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

   A local host may have multiple points of attachment to the Internet,
   giving it a degree of fault tolerance from hardware failures.  Stream
   Control Transmission Protocol (SCTP) (<a href="./rfc4960">RFC 4960</a>) was developed to take
   full advantage of such a multi-homed host to provide a fast failover
   and association survivability in the face of such hardware failures.
   This document describes an extension to SCTP that will allow an SCTP
   stack to dynamically add an IP address to an SCTP association,
   dynamically delete an IP address from an SCTP association, and to
   request to set the primary address the peer will use when sending to
   an endpoint.
















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Table of Contents

   <a href="#section-1">1</a>.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-3">3</a>
   <a href="#section-2">2</a>.  Conventions  . . . . . . . . . . . . . . . . . . . . . . . . .  <a href="#page-3">3</a>
   <a href="#section-3">3</a>.  Serial Number Arithmetic . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
   <a href="#section-4">4</a>.  Additional Chunks and Parameters . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
     <a href="#section-4.1">4.1</a>.  New Chunk Types  . . . . . . . . . . . . . . . . . . . . .  <a href="#page-4">4</a>
       <a href="#section-4.1.1">4.1.1</a>.  Address Configuration Change Chunk (ASCONF)  . . . . .  <a href="#page-5">5</a>
       4.1.2.  Address Configuration Acknowledgment Chunk
               (ASCONF-ACK) . . . . . . . . . . . . . . . . . . . . .  <a href="#page-6">6</a>
     <a href="#section-4.2">4.2</a>.  New Parameter Types  . . . . . . . . . . . . . . . . . . .  <a href="#page-7">7</a>
       <a href="#section-4.2.1">4.2.1</a>.  Add IP Address . . . . . . . . . . . . . . . . . . . .  <a href="#page-8">8</a>
       <a href="#section-4.2.2">4.2.2</a>.  Delete IP Address  . . . . . . . . . . . . . . . . . .  <a href="#page-9">9</a>
       <a href="#section-4.2.3">4.2.3</a>.  Error Cause Indication . . . . . . . . . . . . . . . . <a href="#page-10">10</a>
       <a href="#section-4.2.4">4.2.4</a>.  Set Primary IP Address . . . . . . . . . . . . . . . . <a href="#page-11">11</a>
       <a href="#section-4.2.5">4.2.5</a>.  Success Indication . . . . . . . . . . . . . . . . . . <a href="#page-12">12</a>
       <a href="#section-4.2.6">4.2.6</a>.  Adaptation Layer Indication  . . . . . . . . . . . . . <a href="#page-13">13</a>
       <a href="#section-4.2.7">4.2.7</a>.  Supported Extensions Parameter . . . . . . . . . . . . <a href="#page-13">13</a>
     <a href="#section-4.3">4.3</a>.  New Error Causes . . . . . . . . . . . . . . . . . . . . . <a href="#page-14">14</a>
       4.3.1.  Error Cause: Request to Delete Last Remaining IP
               Address  . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
       4.3.2.  Error Cause: Operation Refused Due to Resource
               Shortage . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-15">15</a>
       <a href="#section-4.3.3">4.3.3</a>.  Error Cause: Request to Delete Source IP Address . . . <a href="#page-16">16</a>
       4.3.4.  Error Cause: Association Aborted Due to Illegal
               ASCONF-ACK . . . . . . . . . . . . . . . . . . . . . . <a href="#page-17">17</a>
       <a href="#section-4.3.5">4.3.5</a>.  Error Cause: Request Refused - No Authorization. . . . <a href="#page-17">17</a>
   <a href="#section-5">5</a>.  Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
     <a href="#section-5.1">5.1</a>.  ASCONF Chunk Procedures  . . . . . . . . . . . . . . . . . <a href="#page-18">18</a>
       <a href="#section-5.1.1">5.1.1</a>.  Congestion Control of ASCONF Chunks  . . . . . . . . . <a href="#page-20">20</a>
     <a href="#section-5.2">5.2</a>.  Upon Reception of an ASCONF Chunk  . . . . . . . . . . . . <a href="#page-21">21</a>
     <a href="#section-5.3">5.3</a>.  General Rules for Address Manipulation . . . . . . . . . . <a href="#page-24">24</a>
       <a href="#section-5.3.1">5.3.1</a>.  A Special Case for OOTB ABORT Chunks . . . . . . . . . <a href="#page-29">29</a>
       <a href="#section-5.3.2">5.3.2</a>.  A Special Case for Changing an Address . . . . . . . . <a href="#page-29">29</a>
     <a href="#section-5.4">5.4</a>.  Setting of the Primary Address . . . . . . . . . . . . . . <a href="#page-29">29</a>
     <a href="#section-5.5">5.5</a>.  Bundling of Multiple ASCONFs . . . . . . . . . . . . . . . <a href="#page-30">30</a>
   <a href="#section-6">6</a>.  Security Considerations  . . . . . . . . . . . . . . . . . . . <a href="#page-30">30</a>
   <a href="#section-7">7</a>.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . <a href="#page-33">33</a>
   <a href="#section-8">8</a>.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-34">34</a>
   <a href="#section-9">9</a>.  References . . . . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
     <a href="#section-9.1">9.1</a>.  Normative References . . . . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
     <a href="#section-9.2">9.2</a>.  Informative References . . . . . . . . . . . . . . . . . . <a href="#page-35">35</a>
   <a href="#appendix-A">Appendix A</a>.  Abstract Address Handling . . . . . . . . . . . . . . <a href="#page-36">36</a>
     <a href="#appendix-A.1">A.1</a>.  General Remarks  . . . . . . . . . . . . . . . . . . . . . <a href="#page-36">36</a>
     <a href="#appendix-A.2">A.2</a>.  Generalized Endpoints  . . . . . . . . . . . . . . . . . . <a href="#page-36">36</a>
     <a href="#appendix-A.3">A.3</a>.  Associations . . . . . . . . . . . . . . . . . . . . . . . <a href="#page-37">37</a>
     <a href="#appendix-A.4">A.4</a>.  Relationship with <a href="./rfc4960">RFC 4960</a> . . . . . . . . . . . . . . . . <a href="#page-38">38</a>
     <a href="#appendix-A.5">A.5</a>.  Rules for Address Manipulation . . . . . . . . . . . . . . <a href="#page-38">38</a>



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<span class="h2"><a class="selflink" id="section-1" href="#section-1">1</a>.  Introduction</span>

   A local host may have multiple points of attachment to the Internet,
   giving it a degree of fault tolerance from hardware failures.  SCTP
   was developed to take full advantage of such a multi-homed host to
   provide a fast failover and association survivability in the face of
   such hardware failures.  However, many modern computers allow for the
   dynamic addition and deletion of network cards (sometimes termed a
   hot-pluggable interface).  Complicate this with the ability of a
   provider, in IPv6, to dynamically renumber a network, and there still
   is a gap between full-fault tolerance and the currently defined SCTP
   protocol.  No matter if a card is added or an interface is
   renumbered, in order to take advantage of this new configuration, the
   transport association must be restarted.  For many fault-tolerant
   applications this restart is considered an outage and is undesirable.

   This document describes an extension to SCTP to attempt to correct
   this problem for the more demanding fault-tolerant application.  This
   extension will allow an SCTP stack to:

   o  Dynamically add an IP address to an association.

   o  Dynamically delete an IP address from an association.

   o  Request to set the primary address the peer will use when sending
      to an endpoint.

   The dynamic addition and subtraction of IP addresses allows an SCTP
   association to continue to function through host and network
   reconfigurations.  These changes, brought on by provider or user
   action, may mean that the peer would be better served by using the
   newly added address; however, this information may only be known by
   the endpoint that had the reconfiguration occur.  In such a case this
   extension allows the local endpoint to advise the peer as to what it
   thinks is the better primary address that the peer should be using.

   One last thing this extension adds is a small, 32-bit integer called
   an adaptation indication that can be exchanged at startup.  This is
   useful for applications where there are one or more specific layers
   below the application, yet still above SCTP.  In such a case, the
   exchange of this indication can allow the proper layer to be enabled
   below the application.

<span class="h2"><a class="selflink" id="section-2" href="#section-2">2</a>.  Conventions</span>

   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 [<a href="./rfc2119" title="&quot;Key words for use in RFCs to Indicate Requirement Levels&quot;">RFC2119</a>].



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<span class="h2"><a class="selflink" id="section-3" href="#section-3">3</a>.  Serial Number Arithmetic</span>

   It is essential to remember that the actual Address Configuration
   Change Chunk (ASCONF) Sequence Number space is finite, though very
   large.  This space ranges from 0 to 2**32 - 1.  Since the space is
   finite, all arithmetic dealing with ASCONF Sequence Numbers MUST be
   performed modulo 2**32.  This unsigned arithmetic preserves the
   relationship of sequence numbers as they cycle from 2**32 - 1 to 0
   again.  There are some subtleties to computer modulo arithmetic, so
   great care should be taken in programming the comparison of such
   values.  When referring to ASCONF Sequence Numbers, the symbol "=&lt;"
   means "less than or equal"(modulo 2**32).

   Comparisons and arithmetic on ASCONF sequence numbers in this
   document SHOULD use Serial Number Arithmetic as defined in [<a href="./rfc1982" title="&quot;Serial Number Arithmetic&quot;">RFC1982</a>]
   where SERIAL_BITS = 32.

   ASCONF Sequence Numbers wrap around when they reach 2**32 - 1.  That
   is, the next ASCONF Sequence Number an ASCONF chunk MUST use after
   transmitting an ASCONF Sequence Number = 2**32 - 1 is 0.

   Any arithmetic done on Stream Sequence Numbers SHOULD use Serial
   Number Arithmetic (as defined in [<a href="./rfc1982" title="&quot;Serial Number Arithmetic&quot;">RFC1982</a>]) where SERIAL_BITS = 16.
   All other arithmetic and comparisons in this document use normal
   arithmetic.

<span class="h2"><a class="selflink" id="section-4" href="#section-4">4</a>.  Additional Chunks and Parameters</span>

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

   o  Dynamic addition of IP addresses to an association.

   o  Dynamic deletion of IP addresses from an association.

   o  A request to set the primary address the peer will use when
      sending to an endpoint.

   Additionally, this section describes three new Error Causes that
   support these new chunks and parameters.

<span class="h3"><a class="selflink" id="section-4.1" href="#section-4.1">4.1</a>.  New Chunk Types</span>

   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.





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        Chunk Type  Chunk Name
        --------------------------------------------------------------
        0xC1    Address Configuration Change Chunk        (ASCONF)
        0x80    Address Configuration Acknowledgment      (ASCONF-ACK)

              Table 1: Address Configuration Chunks

<span class="h4"><a class="selflink" id="section-4.1.1" href="#section-4.1.1">4.1.1</a>.  Address Configuration Change Chunk (ASCONF)</span>

   This chunk is used to communicate to the remote endpoint one of the
   configuration change requests that MUST be acknowledged.  The
   information carried in the ASCONF Chunk uses the form of a Type-
   Length-Value (TLV), as described in "3.2.1 Optional/Variable-length
   Parameter Format" in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>] for all variable parameters.  This
   chunk MUST be sent in an authenticated way by using the mechanism
   defined in [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].  If this chunk is received unauthenticated it
   MUST be silently discarded as described in [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].

        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             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Sequence Number                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                    Address Parameter                          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     ASCONF Parameter #1                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       \                                                               \
       /                             ....                              /
       \                                                               \
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     ASCONF Parameter #N                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number: 32 bits (unsigned integer)

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

   Address Parameter: 8 or 20 bytes (depending on the address type)

   This field contains an address parameter, either IPv6 or IPv4, from
   [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>].  The address is an address of the sender of the ASCONF
   Chunk; the address MUST be considered part of the association by the
   peer endpoint (the receiver of the ASCONF Chunk).  This field may be



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   used by the receiver of the ASCONF to help in finding the
   association.  If the address 0.0.0.0 or ::0 is provided, the receiver
   MAY lookup the association by other information provided in the
   packet.  This parameter MUST be present in every ASCONF message, i.e.
   it is a mandatory TLV parameter.

   Note: The host name address MUST NOT be sent and MUST be ignored if
   received in any ASCONF message.

   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 <a href="./rfc4960#section-3.2">[RFC4960], Section&nbsp;3.2</a>.  Note that the upper two bits in
   the ASCONF Chunk are set to one.  As defined in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>], <a href="#section-3.2">Section</a>
   <a href="#section-3.2">3.2</a>, when setting these upper bits in this manner the receiver that
   does not understand this chunk MUST skip the chunk and continue
   processing, and report in an Operation Error Chunk using the
   'Unrecognized Chunk Type' cause of error.  This will NOT abort the
   association but indicates to the sender that it MUST not send any
   further ASCONF chunks.

   ASCONF Parameter: TLV format

   Each address configuration change is represented by a TLV parameter,
   as defined in <a href="#section-4.2">Section 4.2</a>.  One or more requests may be present in an
   ASCONF Chunk.

<span class="h4"><a class="selflink" id="section-4.1.2" href="#section-4.1.2">4.1.2</a>.  Address Configuration Acknowledgment Chunk (ASCONF-ACK)</span>

   This chunk is used by the receiver of an ASCONF Chunk to acknowledge
   the reception.  It carries zero or more results for any ASCONF
   parameters that were processed by the receiver.  This chunk MUST be
   sent in an authenticated way by using the mechanism defined in
   [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].  If this chunk is received unauthenticated it MUST be
   silently discarded as described in [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].
















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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 = 0x80   |  Chunk Flags  |      Chunk Length             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Sequence Number                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 ASCONF Parameter Response#1                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       \                                                               \
       /                             ....                              /
       \                                                               \
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 ASCONF Parameter Response#N                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Sequence Number: 32 bits (unsigned integer)

   This value represents the Sequence Number for the received ASCONF
   Chunk that is acknowledged by this chunk.  This value is copied from
   the received ASCONF Chunk.

   ASCONF Parameter Response: TLV format

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

<span class="h3"><a class="selflink" id="section-4.2" href="#section-4.2">4.2</a>.  New Parameter Types</span>

   The seven new parameters added follow the format defined in <a href="./rfc4960#section-3.2.1">Section</a>
   <a href="./rfc4960#section-3.2.1">3.2.1 of [RFC4960]</a>.  Tables 2, 3, and 4 describe the parameters.

        Address Configuration Parameters   Parameter Type
        -------------------------------------------------
        Set Primary Address                  0xC004
        Adaptation Layer Indication          0xC006
        Supported Extensions                 0x8008

        Table 2: Parameters That Can Be Used in an INIT/INIT-ACK Chunk








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        Address Configuration Parameters   Parameter Type
        -------------------------------------------------
        Add IP Address                       0xC001
        Delete IP Address                    0xC002
        Set Primary Address                  0xC004

        Table 3: Parameters Used in an ASCONF Parameter


        Address Configuration Parameters   Parameter Type
        -------------------------------------------------
        Error Cause Indication               0xC003
        Success Indication                   0xC005

        Table 4: Parameters Used in an ASCONF Parameter Response

   Any parameter that appears where it is not allowed (for example, a
   0xC002 parameter appearing within an INIT or INIT-ACK) MAY be
   responded to with an ABORT by the receiver of the invalid parameter.
   If the receiver chooses NOT to abort, the parameter MUST be ignored.
   A robust implementation SHOULD ignore the parameter and leave the
   association intact.

<span class="h4"><a class="selflink" id="section-4.2.1" href="#section-4.2.1">4.2.1</a>.  Add IP Address</span>

        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          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               ASCONF-Request Correlation ID                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Address Parameter                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASCONF-Request Correlation ID: 32 bits

   This is an opaque integer assigned by the sender to identify each
   request parameter.  The receiver of the ASCONF Chunk will copy this
   2-bit value into the ASCONF Response Correlation ID field of the
   ASCONF-ACK response parameter.  The sender of the ASCONF can use this
   same value in the ASCONF-ACK to find which request the response is
   for.  Note that the receiver MUST NOT change this 32-bit value.








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   Address Parameter: TLV

   This field contains an IPv4 or IPv6 address parameter as described in
   <a href="./rfc4960#section-3.3.2.1">Section&nbsp;3.3.2.1 of [RFC4960]</a>.  The complete TLV is wrapped within
   this parameter.  It informs the receiver that the address specified
   is to be added to the existing association.  This parameter MUST NOT
   contain a broadcast or multicast address.  If the address 0.0.0.0 or
   ::0 is provided, the source address of the packet MUST be added.

   An example TLV requesting that the IPv4 address 192.0.2.1 be added to
   the association would look as follows:

           +--------------------------------+
           |  Type=0xC001   | Length = 16   |
           +--------------------------------+
           |       C-ID = 0x01023474        |
           +--------------------------------+
           |  Type=5        | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

   Valid Chunk Appearance

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

<span class="h4"><a class="selflink" id="section-4.2.2" href="#section-4.2.2">4.2.2</a>.  Delete IP Address</span>

        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          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               ASCONF-Request Correlation ID                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Address Parameter                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASCONF-Request Correlation ID: 32 bits

   This is an opaque integer assigned by the sender to identify each
   request parameter.  The receiver of the ASCONF Chunk will copy this
   32-bit value into the ASCONF Response Correlation ID field of the
   ASCONF-ACK response parameter.  The sender of the ASCONF can use this
   same value in the ASCONF-ACK to find which request the response is
   for.  Note that the receiver MUST NOT change this 32-bit value.




<span class="grey">Stewart, et al.             Standards Track                     [Page 9]</span></pre>
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<span class="grey"><a href="./rfc5061">RFC 5061</a>          SCTP Dynamic Address Reconfiguration    September 2007</span>


   Address Parameter: TLV

   This field contains an IPv4 or IPv6 address parameter, as described
   in <a href="./rfc4960#section-3.3.2.1">Section&nbsp;3.3.2.1 of [RFC4960]</a>.  The complete TLV is wrapped within
   this parameter.  It informs the receiver that the address specified
   is to be removed from the existing association.  This parameter MUST
   NOT contain a broadcast or multicast address.  If the address 0.0.0.0
   or ::0 is provided, all addresses of the peer except the source
   address of the packet MUST be deleted.

   An example TLV deleting the IPv4 address 192.0.2.1 from an existing
   association would look as follows:

           +--------------------------------+
           |  Type=0xC002   | Length = 16   |
           +--------------------------------+
           |       C-ID = 0x01023476        |
           +--------------------------------+
           |  Type=5        | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

   Valid Chunk Appearance

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

<span class="h4"><a class="selflink" id="section-4.2.3" href="#section-4.2.3">4.2.3</a>.  Error Cause Indication</span>

        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        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             ASCONF-Response Correlation ID                    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |             Error Cause(s) or Success Indication              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASCONF-Response Correlation ID: 32 bits

   This is an opaque integer assigned by the sender to identify each
   request parameter.  The receiver of the ASCONF Chunk will copy this
   32-bit value from the ASCONF-Request Correlation ID into the ASCONF
   Response Correlation ID field so the peer can easily correlate the
   request to this response.  Note that the receiver MUST NOT change
   this 32-bit value.



<span class="grey">Stewart, et al.             Standards Track                    [Page 10]</span></pre>
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   Error Cause(s): TLV(s)

   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 [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>]).  The Error
   Cause(s) follow the format defined in <a href="./rfc4960#section-3.3.10">Section&nbsp;3.3.10 of [RFC4960]</a>.

   Valid Chunk Appearance

   The Error Cause Indication parameter may only appear in the ASCONF-
   ACK Chunk Type.

<span class="h4"><a class="selflink" id="section-4.2.4" href="#section-4.2.4">4.2.4</a>.  Set Primary IP Address</span>

        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          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               ASCONF-Request Correlation ID                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                       Address Parameter                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   ASCONF-Request Correlation ID: 32 bits

   This is an opaque integer assigned by the sender to identify each
   request parameter.  The receiver of the ASCONF Chunk will copy this
   32-bit value into the ASCONF Response Correlation ID field of the
   ASCONF-ACK response parameter.  The sender of the ASCONF can use this
   same value in the ASCONF-ACK to find which request the response is
   for.  Note that the receiver MUST NOT change this 32-bit value.

   Address Parameter: TLV

   This field contains an IPv4 or IPv6 address parameter as described in
   <a href="./rfc4960#section-3.3.2.1">Section&nbsp;3.3.2.1 of [RFC4960]</a>.  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 <a href="./rfc4960#section-5.1.2">Section&nbsp;5.1.2 of
   [RFC4960]</a>).  The receiver MAY mark this as its primary address upon
   receiving this request.  If the address 0.0.0.0 or ::0 is provided,
   the receiver MAY mark the source address of the packet as its
   primary.

   An example TLV requesting that the IPv4 address 192.0.2.1 be made the
   primary destination address would look as follows:





<span class="grey">Stewart, et al.             Standards Track                    [Page 11]</span></pre>
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           +--------------------------------+
           |  Type=0xC004   | Length = 16   |
           +--------------------------------+
           |       C-ID = 0x01023479        |
           +--------------------------------+
           |  Type=5        | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

   Valid Chunk Appearance

   The Set Primary IP Address parameter may appear in the ASCONF, 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.

<span class="h4"><a class="selflink" id="section-4.2.5" href="#section-4.2.5">4.2.5</a>.  Success Indication</span>

        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 = 8               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |               ASCONF-Response Correlation ID                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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

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

   ASCONF-Response Correlation ID: 32 bits

   This is an opaque integer assigned by the sender to identify each
   request parameter.  The receiver of the ASCONF Chunk will copy this
   32-bit value from the ASCONF-Request Correlation ID into the ASCONF
   Response Correlation ID field so the peer can easily correlate the
   request to this response.







<span class="grey">Stewart, et al.             Standards Track                    [Page 12]</span></pre>
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   Valid Chunk Appearance

   The Success Indication parameter may only appear in the ASCONF-ACK
   Chunk Type.

<span class="h4"><a class="selflink" id="section-4.2.6" href="#section-4.2.6">4.2.6</a>.  Adaptation Layer Indication</span>

        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 = 8                 |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                   Adaptation Code point                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   This parameter is specified for the communication of peer upper-layer
   protocols.  It is envisioned to be used for flow control and other
   adaptation layers that require an indication to be carried in the
   INIT and INIT-ACK.  Each adaptation layer that is defined that wishes
   to use this parameter MUST specify an adaptation code point in an
   appropriate RFC defining its use and meaning.  This parameter SHOULD
   NOT be examined by the receiving SCTP implementation and should be
   passed opaquely to the upper-layer protocol.

   Note: This parameter is not used in either the addition or deletion
   of addresses but is for the convenience of the upper layer.  This
   document includes this parameter to minimize the number of SCTP
   documents.

   Valid Chunk Appearance

   The Adaptation Layer Indication parameter may appear in INIT or INIT-
   ACK chunk and SHOULD be passed to the receiver's upper-layer protocol
   based upon the upper-layer protocol configuration of the SCTP stack.
   This parameter MUST NOT be sent in any other chunks, and if it is
   received in another chunk, it MUST be ignored.

<span class="h4"><a class="selflink" id="section-4.2.7" href="#section-4.2.7">4.2.7</a>.  Supported Extensions Parameter</span>

   This parameter is used at startup to identify any additional
   extensions that the sender supports.  The sender MUST support both
   the sending and the receiving of any chunk types listed within the
   Supported Extensions Parameter.  An implementation supporting this
   extension MUST list the ASCONF,the ASCONF-ACK, and the AUTH chunks in
   its INIT and INIT-ACK parameters.






<span class="grey">Stewart, et al.             Standards Track                    [Page 13]</span></pre>
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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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Parameter Type = 0x8008   |      Parameter Length         |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | CHUNK TYPE 1  |  CHUNK TYPE 2 |  CHUNK TYPE 3 |  CHUNK TYPE 4 |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |                             ....                              |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | CHUNK TYPE N  |      PAD      |      PAD      |      PAD      |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Parameter Type This field holds the IANA-defined parameter type for
   the Supported Extensions Parameter.  The value of this field is
   0x8008.

   Parameter Type Length This field holds the length of the parameter,
   including the Parameter Type, Parameter Length, and any additional
   supported extensions.  Note: The length MUST NOT include any padding.

   CHUNK TYPE X This field(s) hold the chunk type of any SCTP
   extension(s) that are currently supported by the sending SCTP.
   Multiple chunk types may be defined listing each additional feature
   that the sender supports.  The sender MUST NOT include multiple
   Supported Extensions Parameter within any chunk.

   Parameter Appearance This parameter may appear in the INIT or INIT-
   ACK chunk.  This parameter MUST NOT appear in any other chunk.

<span class="h3"><a class="selflink" id="section-4.3" href="#section-4.3">4.3</a>.  New Error Causes</span>

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

       Cause Code
       Value          Cause Code
       ---------      ----------------
       0x00A0          Request to Delete Last Remaining IP Address
       0x00A1          Operation Refused Due to Resource Shortage
       0x00A2          Request to Delete Source IP Address
       0x00A3          Association Aborted Due to Illegal ASCONF-ACK
       0x00A4          Request Refused - No Authorization

             Table 5: New Error Causes







<span class="grey">Stewart, et al.             Standards Track                    [Page 14]</span></pre>
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<span class="grey"><a href="./rfc5061">RFC 5061</a>          SCTP Dynamic Address Reconfiguration    September 2007</span>


<span class="h4"><a class="selflink" id="section-4.3.1" href="#section-4.3.1">4.3.1</a>.  Error Cause: Request to Delete Last Remaining IP Address</span>

   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=0x00A0         |      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 = 0xC003  | Length = 28   |
           +----------------+---------------+
           |       C-ID = 0x01023476        |
           +--------------------------------+
           |  Cause=0x00A0  | Length = 20   |
           +----------------+---------------+
           |  Type= 0xC002  | Length = 16   |
           +----------------+---------------+
           |       C-ID = 0x01023476        |
           +--------------------------------+
           |   Type=0x0005  | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

<span class="h4"><a class="selflink" id="section-4.3.2" href="#section-4.3.2">4.3.2</a>.  Error Cause: Operation Refused Due to Resource Shortage</span>

   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 into the Error
   Cause.






<span class="grey">Stewart, et al.             Standards Track                    [Page 15]</span></pre>
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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Cause Code=0x00A1         |      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 = 0xC003  | Length = 28   |
           +--------------------------------+
           |       C-ID = 0x01023474        |
           +--------------------------------+
           |  Cause=0x00A1  | Length = 20   |
           +----------------+---------------+
           |  Type=0xC001   | Length = 16   |
           +--------------------------------+
           |       C-ID = 0x01023474        |
           +--------------------------------+
           |  Type=0x0005   | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

<span class="h4"><a class="selflink" id="section-4.3.3" href="#section-4.3.3">4.3.3</a>.  Error Cause: Request to Delete Source IP Address</span>

   Cause of error

   Request to Delete Source IP Address: The receiver of this error sent
   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=0x00A2         |      Cause Length=Variable    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       \                    TLV-Copied-From-ASCONF                     /
       /                                                               \
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+







<span class="grey">Stewart, et al.             Standards Track                    [Page 16]</span></pre>
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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 = 0xC003  | Length = 28   |
           +--------------------------------+
           |       C-ID = 0x01023476        |
           +--------------------------------+
           |  Cause=0x00A2  | Length = 20   |
           +----------------+---------------+
           |  Type=0xC002   | Length = 16   |
           +----------------+---------------+
           |       C-ID = 0x01023476        |
           +--------------------------------+
           |   Type=0x0005  | Length = 8    |
           +----------------+---------------+
           |       Value=0xC0000201         |
           +----------------+---------------+

   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.

<span class="h4"><a class="selflink" id="section-4.3.4" href="#section-4.3.4">4.3.4</a>.  Error Cause: Association Aborted Due to Illegal ASCONF-ACK</span>

   This error is to be included in an ABORT that is generated due to the
   reception of an ASCONF-ACK that was not expected but is larger than
   the current Sequence Number (see <a href="#section-5.3">Section 5.3</a>, Rule F0 ).  Note that a
   Sequence Number is larger than the last acked Sequence Number if it
   is either the next sequence or no more than 2**31-1 greater than the
   current Sequence Number.  Sequence Numbers smaller than the last
   acked Sequence Number are silently ignored.

        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=0x00A3         |      Cause Length=4           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

<span class="h4"><a class="selflink" id="section-4.3.5" href="#section-4.3.5">4.3.5</a>.  Error Cause: Request Refused - No Authorization.</span>

   Cause of error

   This Error Cause may be included to reject a request based on local
   security policies.






<span class="grey">Stewart, et al.             Standards Track                    [Page 17]</span></pre>
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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     Cause Code=0x00A4         |      Cause Length=Variable    |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       \                     TLV-Copied-From-ASCONF                    /
       /                                                               \
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

<span class="h2"><a class="selflink" id="section-5" href="#section-5">5</a>.  Procedures</span>

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

<span class="h3"><a class="selflink" id="section-5.1" href="#section-5.1">5.1</a>.  ASCONF Chunk Procedures</span>

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

   A1)  Create an ASCONF Chunk as defined in <a href="#section-4.1.1">Section 4.1.1</a>.  The chunk
        MUST 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 Sequence Number MUST be assigned to the Chunk.  The Sequence
        Number MUST be larger by one.  The Sequence Number MUST be
        initialized at the start of the association to the same value as
        the Initial Transmission Sequence Number (TSN) and every time a
        new ASCONF Chunk is created, it MUST be incremented by one after
        assigning the Sequence Number to the newly created chunk.

   A3)  If no SCTP packet with one or more ASCONF Chunk(s) is
        outstanding (unacknowledged) with the remote peer, send the
        chunk and proceed to step A4.  If an ASCONF chunk is
        outstanding, then the ASCONF chunk should be queued for later
        transmission and no further action should be taken until the
        previous ASCONF is acknowledged or a timeout occurs.

   A4)  The sender MUST Start a T-4 Retransmission Timeout (RTO) timer,
        using the RTO value of the selected destination address
        (normally the primary path; see <a href="./rfc4960#section-6.4">[RFC4960], Section&nbsp;6.4</a> for
        details).









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   A5)  When the ASCONF-ACK that acknowledges the Sequence Number last
        sent arrives, the sender MUST stop the T-4 RTO timer, and clear
        the appropriate association and destination error counters as
        defined in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>], Sections <a href="#section-8.1">8.1</a> and <a href="#section-8.2">8.2</a>.

   A6)  The endpoint MUST process all of the TLVs within the ASCONF-
        ACK(s) 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 for a TLV parameter, 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 is no response(s) to specific TLV parameter(s), and no
        failures are indicated, then all request(s) are considered
        successful.

   A9)  If the peer responds to an ASCONF with an ERROR Chunk reporting
        that it did not recognize the ASCONF Chunk Type, the sender of
        the ASCONF MUST NOT send any further ASCONF Chunks and MUST stop
        its T-4 timer.

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

   B1)  Increment the error counters and perform path failure detection
        on the appropriate destination address as defined in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>],
        Sections <a href="#section-8.1">8.1</a> and <a href="#section-8.2">8.2</a>.

   B2)  Increment the association error counters and perform endpoint
        failure detection on the association as defined in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>],
        Sections <a href="#section-8.1">8.1</a> and <a href="#section-8.2">8.2</a>.

   B3)  Backoff the destination address RTO value to which the ASCONF
        chunk was sent by doubling the RTO timer value.

        Note: The RTO value is used in the setting of all timer types
        for SCTP.  Each destination address has a single RTO estimate.











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   B4)  Re-transmit the ASCONF Chunk last sent and if possible choose an
        alternate destination address (please refer to <a href="./rfc4960#section-6.4.1">[RFC4960],
        Section&nbsp;6.4.1</a>).  An endpoint MUST NOT add new parameters to this
        chunk; it MUST be the same (including its Sequence Number) as
        the last ASCONF sent.  An endpoint MAY, however, bundle an
        additional ASCONF with new ASCONF parameters with the next
        Sequence Number.  For details, see <a href="#section-5.5">Section 5.5</a>.

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

   Note: The total number of retransmissions is limited by B2 above.  If
   the maximum is reached, the association will fail and enter into the
   CLOSED state (see <a href="./rfc4960#section-6.4.1">[RFC4960], Section&nbsp;6.4.1</a> for details).

<span class="h4"><a class="selflink" id="section-5.1.1" href="#section-5.1.1">5.1.1</a>.  Congestion Control of ASCONF Chunks</span>

   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:

   C1)  One and only one SCTP packet-holding ASCONF Chunk(s) MAY be in
        transit and unacknowledged at any one time.  If a sender, after
        sending an 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).  However, when an ASCONF Chunk is
        retransmitted due to a time-out, the additionally held ASCONF
        Chunks can be bundled into the retransmission packet as
        described in <a href="#section-5.5">Section 5.5</a>.

   C2)  An ASCONF Chunk may be bundled with any other chunk type
        including other ASCONF Chunks.  If bundled with other ASCONF
        Chunks, the chunks MUST appear in sequential order with respect
        to their Sequence Number.

   C3)  An ASCONF-ACK Chunk may be bundled with any other chunk type
        including other ASCONF-ACK Chunks.  If bundled with other
        ASCONF-ACK Chunks, the chunks MUST appear in sequential order
        with respect to their Sequence Number.







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   C4)  Both ASCONF and ASCONF-ACK Chunks MUST NOT be sent in any SCTP
        state except ESTABLISHED, SHUTDOWN-PENDING, SHUTDOWN-RECEIVED,
        and SHUTDOWN-SENT.

   C5)  An ASCONF Chunk and an ASCONF-ACK Chunk SHOULD not be larger
        than the PMTU.  If the PMTU is unknown, then the PMTU should be
        set to the minimum PMTU.  The minimum PMTU depends on the IP
        version used for transmission, and is the lesser of 576 octets
        and the first-hop MTU for IPv4 [<a href="./rfc1122" title="&quot;Requirements for Internet Hosts - Communication Layers&quot;">RFC1122</a>] and 1280 octets for
        IPv6 [<a href="./rfc2460" title="&quot;Internet Protocol, Version 6 (IPv6) Specification&quot;">RFC2460</a>].

   An ASCONF sender without these restrictions could possibly flood the
   network with a large number of separate address-change operations,
   thus causing network congestion.

   If the sender of an ASCONF Chunk receives an 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-layer application that the peer
   endpoint does not support any of the extensions detailed in this
   document.

<span class="h3"><a class="selflink" id="section-5.2" href="#section-5.2">5.2</a>.  Upon Reception of an ASCONF Chunk</span>

   When an endpoint receives an ASCONF Chunk from the remote peer,
   special procedures may be needed to identify the association the
   ASCONF Chunk is associated with.  To properly find the association,
   the following procedures SHOULD be followed:

   D1)  Use the source address and port number of the sender to attempt
        to identify the association (i.e., use the same method defined
        in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>] used for all other SCTP Chunks).  If found proceed
        to rule D4.

   D2)  If the association is not found, use the address found in the
        Address Parameter TLV combined with the port number found in the
        SCTP common header.  If found, proceed to rule D4.

   D2-ext)  If more than one ASCONF Chunks are packed together, use the
            address found in the ASCONF Address Parameter TLV of each of
            the subsequent ASCONF Chunks.  If found, proceed to rule D4.










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   D3)  If neither D1, D2, nor D2-ext locates the association, treat the
        chunk as an Out Of The Blue packet as defined in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>].

   D4)  Follow the normal rules to validate the SCTP verification tag
        found in [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>].

   D5)  After the verification tag has been validated, normal chunk
        processing should occur.  Prior to finding the ASCONF chunk, the
        receiver MUST encounter an AUTH chunk as described in [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].
        If either authentication fails, or the AUTH chunk is missing,
        the receiver MUST silently discard this chunk and the rest of
        the packet.

   After identification and verification of the association, the
   following should be performed to properly process the ASCONF Chunk:

   E1)  If the value found in the Sequence Number of the ASCONF Chunk is
        equal to the ('Peer-Sequence-Number' + 1) and the Sequence
        Number of the ASCONF Chunk is the first in the SCTP Packet, the
        endpoint MAY clean any old cached ASCONF-ACK up to the 'Peer-
        Sequence-Number' and then proceed to rule E4.

   E1-ext)  If the value found in the Sequence Number of the ASCONF
            Chunk is equal to the ('Peer-Sequence-Number' + 1) and the
            ASCONF chunk is NOT the first Sequence Number in the SCTP
            packet, proceed to rule E4 but do NOT clear any cached
            ASCONF- ACK or state information.

   E2)  If the value found in the Sequence Number is less than the
        ('Peer- Sequence-Number' + 1), simply skip to the next ASCONF,
        and include in the outbound response packet any previously
        cached ASCONF-ACK response that was sent and saved that matches
        the Sequence Number of the ASCONF.  Note: It is possible that no
        cached ASCONF-ACK Chunk exists.  This will occur when an older
        ASCONF arrives out of order.  In such a case, the receiver
        should skip the ASCONF Chunk and not include ASCONF-ACK Chunk
        for that chunk.

   E3)  Then, process each ASCONF one by one as above while the Sequence
        Number of the ASCONF is less than the ('Peer-Sequence-Number' +
        1).










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   E4)  When the Sequence Number matches the next one expected, process
        the ASCONF as described below and after processing the ASCONF
        Chunk, append an ASCONF-ACK Chunk to the response packet and
        cache a copy of it (in the event it later needs to be
        retransmitted).

        V1)  Process the TLVs contained within the Chunk performing the
             appropriate actions as indicated by each TLV type.  The
             TLVs MUST be processed in order within the Chunk.  For
             example, if the sender puts 3 TLVs in one chunk, the first
             TLV (the one closest to the Chunk Header) in the Chunk MUST
             be processed first.  The next TLV in the chunk (the middle
             one) MUST be processed second and finally, the last TLV in
             the Chunk MUST be processed last.

        V2)  In processing the chunk, the receiver should build a
             response message with the appropriate error TLVs, as
             specified in the Parameter type bits, for any ASCONF
             Parameter it does not understand.  To indicate an
             unrecognized parameter, Cause Type 8 should be used as
             defined in the ERROR in <a href="#section-3.3.10.8">Section 3.3.10.8</a>, [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>].  The
             endpoint 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 responses MUST copy the ASCONF-Request Correlation ID
             field received in the ASCONF parameter from the TLV being
             responded to, into the ASCONF-Request Correlation ID field
             in the response parameter.

        V4)  After processing the entire Chunk, the receiver of the
             ASCONF MUST queue the response ASCONF-ACK Chunk for
             transmission after the rest of the SCTP packet has been
             processed.  This allows the ASCONF-ACK Chunk to be bundled
             with other ASCONF-ACK Chunks as well as any additional
             responses, e.g., a Selective Acknowledgment (SACK) Chunk.

        V5)  Update the 'Peer-Sequence-Number' to the value found in the
             Sequence Number field.









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   E5)  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 log the event for security purposes.

   E6)  When all ASCONF Chunks are processed for this SCTP packet, send
        back the accumulated single response packet with all of the
        ASCONF-ACK Chunks.  The destination address of the SCTP packet
        containing the ASCONF-ACK Chunks MUST be the source address of
        the SCTP packet that held the ASCONF Chunks.

   E7)  While processing the ASCONF Chunks in the SCTP packet, if the
        response packet will exceed the PMTU of the return path, the
        receiver MUST stop adding additional ASCONF-ACKs into the
        response packet but MUST continue to process all of the ASCONF
        Chunks, saving ASCONF-ACK Chunk responses in its cached copy.
        The sender of the ASCONF Chunk will later retransmit the ASCONF
        Chunks that were not responded to, at which time the cached
        copies of the responses that would NOT fit in the PMTU can be
        sent to the peer.

   Note: These rules have been presented with the assumption that the
   implementation is caching old ASCONF-ACKs in case of loss of SCTP
   packets in the ACK path.  It is allowable for an implementation to
   maintain this state in another form it deems appropriate, as long as
   that form results in the same ASCONF-ACK sequences being returned to
   the peer as outlined above.

<span class="h3"><a class="selflink" id="section-5.3" href="#section-5.3">5.3</a>.  General Rules for Address Manipulation</span>

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

   F0)  If an endpoint receives an ASCONF-ACK that is greater than or
        equal to the next Sequence Number to be used but no ASCONF Chunk
        is outstanding, the endpoint MUST ABORT the association.  Note
        that a Sequence Number is greater than if it is no more than
        2^^31-1 larger than the current Sequence Number (using serial
        arithmetic).

   F1)  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 except on
        carrying an ASCONF Chunk.  The receiver of the Add IP Address






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        request may use the address as a destination immediately.  The
        receiver MUST use the path-verification procedure for the added
        address before using that address.  The receiver MUST NOT send
        packets to the new address except for the corresponding ASCONF-
        ACK Chunk or HEARTBEAT Chunks for path verification before the
        new path is verified.  If the ASCONF-ACK is sent to the new
        address, it MAY be bundled with the HEARTBEAT chunk for path
        verification.

   F2)  After the ASCONF-ACK of an IP address Add arrives, the endpoint
        MAY begin using the added IP address as a source address for any
        type of SCTP chunk.

   F3a) If an endpoint receives an Error Cause TLV indicating that the
        IP address Add or IP address Deletion parameters was not
        understood, the endpoint MUST consider the operation failed and
        MUST NOT attempt to send any subsequent Add or Delete requests
        to the peer.

   F3b) If an endpoint receives an Error Cause TLV indicating that the
        IP address Set Primary IP Address parameter was not understood,
        the endpoint MUST consider the operation failed and MUST NOT
        attempt to send any subsequent Set Primary IP Address requests
        to the peer.

   F4)  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 as 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 <a href="#section-5.3.1">Section 5.3.1</a> for further details).

   F5)  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 without an Add IP
        Address preceding the delete parameter in the ASCONF Chunk.  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.









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   F6)  An endpoint MUST NOT set an IP header source address for an SCTP
        packet holding the ASCONF Chunk to be the same as an address
        being deleted by the ASCONF Chunk.

   F7)  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 Remaining IP Address'.  The requested delete MUST
        NOT be performed or acted upon, other than to send the ASCONF-
        ACK.

   F8)  If a request is received to delete an IP address that is also
        the source address of the IP packet that 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 F5 has also been violated, in which case the error code
        'Request to Delete Last Remaining IP Address' is sent).

   F9)  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'.

   F10) 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 since its peer will treat SCTP packets destined
        to the address as Out Of The Blue packets.

   F11) When an endpoint receives an 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.











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   F12) 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.

   F13) When an endpoint receives a valid request to DELETE an IP
        address, the endpoint MUST consider the address no longer 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:

   F14) All addresses added by the reception of an ASCONF Chunk MUST be
        put into the UNCONFIRMED state and MUST have path verification
        performed on them before the address can be used as described in
        <a href="./rfc4960#section-5.4">[RFC4960], Section&nbsp;5.4</a>.

       Endpoint-A                                     Endpoint-Z
       ----------                                     ----------
       ASCONF[Add-IP:X]------------------------------&gt;
                                               /--ASCONF-ACK
                                              /
                                    /--------/---New DATA:
                                   /        /    Destination
              &lt;-------------------/        /     IP:X
                                          /
              &lt;--------------------------/

   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
   confirms the add of the address to the association.
















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   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]---------/----------------&gt;
              &lt;-----------------/------------------ASCONF-ACK
                               /
                              /
               &lt;-------------/

   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 added IP address
   for the purpose of sending data to the association before the ASCONF-
   ACK has been received.  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 <a href="./rfc4960#section-8.4">[RFC4960] section&nbsp;8.4</a>).  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 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.


















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<span class="h4"><a class="selflink" id="section-5.3.1" href="#section-5.3.1">5.3.1</a>.  A Special Case for OOTB ABORT Chunks</span>

   Another case worth mentioning is illustrated below:

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

       New DATA:------------\
       Source IP:X           \
                              \
       ASCONF-REQ[DEL-IP:X]----\------------------&gt;
                                \        /---------ASCONF-ACK
                                 \      /
                                  \----/-----------&gt; OOTB
       (Ignored &lt;---------------------/-------------ABORT
        by rule F4)                  /
              &lt;---------------------/

   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 a
   destination being deleted.

<span class="h4"><a class="selflink" id="section-5.3.2" href="#section-5.3.2">5.3.2</a>.  A Special Case for Changing an Address</span>

   In some instances, the sender may only have one IP address in an
   association that is being renumbered.  When this occurs, the sender
   may not be able to send the appropriate ADD/DELETE pair to the peer,
   and may use the old address as a source in the IP header.  For this
   reason, the sender MUST fill in the Address Parameter field with an
   address that is part of the association (in this case, the one being
   deleted).  This will allow the receiver to locate the association
   without using the source address found in the IP header.

   The receiver of such a chunk MUST always first use the source address
   found in the IP header in looking up the association.  The receiver
   should attempt to use the address found in the Address Parameter
   field only if the lookup using the source address from the IP header
   fails.  The receiver MUST reply to the source address of the packet
   in this case, which is the new address that was added by the ASCONF
   (since the old address is no longer part of the association after
   processing).

<span class="h3"><a class="selflink" id="section-5.4" href="#section-5.4">5.4</a>.  Setting of the Primary Address</span>

   A sender of the set primary parameter MAY elect to send this combined
   with an add or delete of an address.  A sender MUST 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



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   an add new IP address request, the set primary will be discarded
   unless the add request is to be processed BEFORE the set primary
   (i.e., it precedes the set primary).

   A request to set primary MAY also appear in an INIT or INIT-ACK
   chunk, which can give advice to the peer endpoint as to which of its
   addresses the sender of the INIT or INIT-ACK would prefer as the
   primary address.

   The request to set an address as the primary path is an option the
   receiver SHOULD perform.  It is considered advice to the receiver of
   the best-destination address to use in sending SCTP packets (in the
   requester's view).  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.

<span class="h3"><a class="selflink" id="section-5.5" href="#section-5.5">5.5</a>.  Bundling of Multiple ASCONFs</span>

   In the normal case, a single ASCONF is sent in a packet and a single
   reply ASCONF-ACK is received.  However, in the event of the loss of
   an SCTP packet containing either an ASCONF or ASCONF-ACK, it is
   allowable for a sender to bundle additional ASCONFs in the
   retransmission.  In bundling multiple ASCONFs, the following rules
   MUST be followed:

   1.  Previously transmitted ASCONF Chunks MUST be left unchanged.

   2.  Each SCTP packet containing ASCONF Chunks MUST be bundled
       starting with the smallest ASCONF Sequence Number first in the
       packet (closest to the Chunk header) and preceding in sequential
       order from the lowest to highest ASCONF Sequence Number.

   3.  All ASCONFs within the packet MUST be adjacent to each other,
       i.e., no other chunk type must separate the ASCONFs.

   4.  Each new ASCONF lookup address MUST be populated as if the
       previous ASCONFs had been processed and accepted.

<span class="h2"><a class="selflink" id="section-6" href="#section-6">6</a>.  Security Considerations</span>

   The addition and or deletion of an IP address to an existing
   association does provide an additional mechanism by which existing
   associations can be hijacked.  Therefore, this document requires the
   use of the authentication mechanism defined in [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>] to limit the
   ability of an attacker to hijack an association.





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   Hijacking an association by using the addition and deletion of an IP
   address is only possible for an attacker who is able to intercept the
   initial two packets of the association setup when the SCTP-AUTH
   extension is used without pre-shared keys.  If such a threat is
   considered a possibility, then the [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>] extension MUST be used
   with a preconfigured shared endpoint pair key to mitigate this
   threat.  For a more detailed analysis, see [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>].

   When the address parameter in ASCONF chunks with Add, IP Delete IP,
   or Set Primary IP parameters is a wildcard, the source address of the
   packet is used.  This address is not protected by SCTP-AUTH [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>]
   and an attacker can therefore intercept such a packet and modify the
   source address.  Even if the source address is not one presently an
   alternate for the association, the identification of the association
   may rely on the other information in the packet (perhaps the
   verification tag, for example).  An on-path attacker can therefore
   modify the source address to its liking.

   If the ASCONF includes an Add IP with a wildcard address, the
   attacker can add an address of its liking, which provides little
   immediate damage but can set up later attacks.

   If the ASCONF includes a Delete IP with a wildcard address, the
   attacker can cause all addresses but one of its choosing to be
   deleted from an association.  The address supplied by the attacker
   must already belong to the association, which makes this more
   difficult for the attacker.  However, the sole remaining address
   might be one that the attacker controls, for example, or can monitor,
   etc.  In the least, the sender and the deceived receiver would have
   different ideas of what that sole remaining address would be.  This
   will eventually cause the association to fail, but in the meantime,
   the deceived receiver could be transmitting packets to an address the
   sender did not intend.

   If the ASCONF includes a Set Primary IP with a wildcard address, then
   the attacker can cause an address to be used as a primary address.
   This is limited to an address that already belongs to the
   association, so the damage is limited.  At least, the result would be
   that the recipient is using a primary address that the sender did not
   intend.  However, if both a wildcard Add IP and a wildcard Set
   Primary IP are used, then the attacker can modify the source address
   to both add an address to its liking to the association and make it
   the primary address.  Such a combination would present the attacker
   with an opportunity for more damage.







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   Note that all these attacks are from an on-path attacker.  Endpoints
   that believe they face a threat from on-path attackers SHOULD NOT use
   wildcard addresses in ASCONF Add IP, Delete IP, or Set Primary IP
   parameters.

   If an SCTP endpoint that supports this extension receives an INIT
   that indicates that the peer supports the ASCONF extension but does
   NOT support the [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>] extension, the receiver of such an INIT
   MUST send an ABORT in response.  Note that an implementation is
   allowed to silently discard such an INIT as an option as well, but
   under NO circumstance is an implementation allowed to proceed with
   the association setup by sending an INIT-ACK in response.

   An implementation that receives an INIT-ACK that indicates that the
   peer does not support the [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>] extension MUST NOT send the
   COOKIE-ECHO to establish the association.  Instead, the
   implementation MUST discard the INIT-ACK and report to the upper-
   layer user that an association cannot be established destroying the
   Transmission Control Block (TCB).

   Other types of attacks, e.g., bombing, are discussed in detail in
   [<a href="./rfc5062" title="&quot;Security Attacks Found Against SCTP and Current Countermeasures&quot;">RFC5062</a>].  The bombing attack, in particular, is countered by the
   use of a random nonce and is required by [<a href="./rfc4960" title="&quot;Stream Control Transmission Protocol&quot;">RFC4960</a>].

   An on-path attacker can modify the INIT and INIT-ACK Supported
   Extensions parameter (and authentication-related parameters) to
   produce a denial of service.  If the on-path attacker removes the
   [<a href="./rfc4895" title="&quot;Authenticated Chunks for the Stream Control Transmission Protocol (SCTP)&quot;">RFC4895</a>]-related parameters from an INIT that indicates it supports
   the ASCONF extension, the association will not be established.  If
   the on-path attacker adds a Supported Extensions parameter mentioning
   the ASCONF type to an INIT or INIT-ACK that does not carry any AUTH-
   related parameters, the association will not be established.  If the
   on-path attacker removes the Supported Extensions parameter (or
   removes the ASCONF type from that parameter) from the INIT or the
   INIT-ACK, then the association will not be able to use the ADD-IP
   feature.  If the on-path attacker adds the Supported Extensions
   parameter listing the ASCONF type to an INIT-ACK that did not carry
   one (but did carry AUTH-related parameters), then the INIT sender may
   use ASCONF where the INIT-ACK sender does not support it.  This would
   be discovered later if the INIT sender transmitted an ASCONF, but the
   INIT sender could have made configuration choices at that point.  As
   the INIT and INIT-ACK are not protected by the AUTH feature, there is
   no way to counter such attacks.  Note however that an on-path
   attacker capable of modifying the INIT and INIT-ACK would almost
   certainly also be able to prevent the INIT and INIT-ACK from being
   delivered or modify the verification tags or checksum to cause the
   packet to be discarded, so the Supported Extensions adds little
   additional vulnerability (with respect to preventing association



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   formation) to the SCTP protocol.  The ability to prevent the use of
   this new feature is an additional vulnerability to SCTP but only for
   this new feature.

   The Adaptation Layer Indication is subject to corruption, insertion,
   or deletion from the INIT and INIT-ACK chunks by an on-path attacker.
   This parameter SHOULD be opaque to the SCTP protocol (see <a href="#section-4.2.6">Section</a>
   <a href="#section-4.2.6">4.2.6</a>), and so changes to the parameter will likely not affect the
   SCTP protocol.  However, any adaptation layer that is defined SHOULD
   consider its own vulnerabilities in the Security Considerations
   section of the RFC that defines its adaptation code point.

   The Set Primary IP Address parameter is subject to corruption,
   insertion, or deletion by an on-path attacker when included in the
   INIT and INIT-ACK chunks.  The attacker could use this to influence
   the receiver to choose an address to its own purposes (one over which
   it has control, one that would be less desirable for the sender,
   etc.).  An on-path attacker would also have the ability to include or
   remove addresses for the association from the INIT or INIT-ACK, so it
   is not limited in the address it can specify in the Set Primary IP
   Address.  Endpoints that wish to avoid this possible threat MAY defer
   sending the initial Set Primary request and wait until the
   association is fully established before sending a fully protected
   ASCONF with the Set Primary as its single parameter.

<span class="h2"><a class="selflink" id="section-7" href="#section-7">7</a>.  IANA Considerations</span>

   This document defines the following new SCTP parameters, chunks, and
   errors (<a href="http://www.iana.org/assignments/sctp-parameters">http://www.iana.org/assignments/sctp-parameters</a>):

   o  two new chunk types,

   o  six parameter types, and

   o  five new SCTP error causes.

   The chunk types with their assigned values are shown below.

        Chunk Type  Chunk Name
        --------------------------------------------------------------
        0xC1    Address Configuration Change Chunk        (ASCONF)
        0x80    Address Configuration Acknowledgment      (ASCONF-ACK)









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   The parameter types are listed below:

        Parameter Type     Parameter Name
        -------------------------------------------------
        0x8008             Supported Extensions
        0xC001             Add IP Address
        0xC002             Delete IP Address
        0xC003             Error Cause Indication
        0xC004             Set Primary Address
        0xC005             Success Indication
        0xC006             Adaptation Layer Indication

   The Error Causes are listed below:

       Cause Code
       Value          Cause Code
       ---------      ----------------
       0x00A0          Request to Delete Last Remaining IP Address
       0x00A1          Operation Refused Due to Resource Shortage
       0x00A2          Request to Delete Source IP Address
       0x00A3          Association Aborted Due to Illegal ASCONF-ACK
       0x00A4          Request Refused - No Authorization

   This document also defines an adaptation code point.  The adaptation
   code point is a 32-bit integer that is assigned by IANA through an
   IETF Consensus action as defined in [<a href="./rfc2434" title="">RFC2434</a>].  For this new
   registry, no initial values are being added by this document;
   however, [<a href="#ref-RDDP" title="&quot;Stream Control Transmission Protocol (SCTP) Direct Data Placement (DDP) Adaptation&quot;">RDDP</a>] will add the first entry.

<span class="h2"><a class="selflink" id="section-8" href="#section-8">8</a>.  Acknowledgments</span>

   The authors would like to express a special note of thanks to Michael
   Ramahlo and Phillip Conrad for their extreme efforts in the early
   formation of this draft.

   The authors wish to thank Jon Berger, Mark Butler, Lars Eggert,
   Janardhan Iyengar, Greg Kendall, Seok Koh, Salvatore Loreto, Peter
   Lei, John Loughney, Sandy Murphy, Ivan Arias Rodriguez, Renee Revis,
   Marshall Rose, Ronnie Sellars, Chip Sharp, and Irene Ruengeler for
   their invaluable comments.

   The authors would also like to give special mention to Maria-Carmen
   Belinchon and Ian Rytina for their early contributions to this
   document and their thoughtful comments.

   And a special thanks to James Polk, abstract writer to the few but
   lucky.




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<span class="h2"><a class="selflink" id="section-9" href="#section-9">9</a>.  References</span>

<span class="h3"><a class="selflink" id="section-9.1" href="#section-9.1">9.1</a>.  Normative References</span>

   [<a id="ref-RFC1122">RFC1122</a>]  Braden, R., "Requirements for Internet Hosts -
              Communication Layers", STD 3, <a href="./rfc1122">RFC 1122</a>, October 1989.

   [<a id="ref-RFC1982">RFC1982</a>]  Elz, R. and R. Bush, "Serial Number Arithmetic", <a href="./rfc1982">RFC 1982</a>,
              August 1996.

   [<a id="ref-RFC2119">RFC2119</a>]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", <a href="https://www.rfc-editor.org/bcp/bcp14">BCP 14</a>, <a href="./rfc2119">RFC 2119</a>, March 1997.

   [<a id="ref-RFC2434">RFC2434</a>]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", <a href="https://www.rfc-editor.org/bcp/bcp26">BCP 26</a>, <a href="./rfc2434">RFC 2434</a>,
              October 1998.

   [<a id="ref-RFC2460">RFC2460</a>]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", <a href="./rfc2460">RFC 2460</a>, December 1998.

   [<a id="ref-RFC4960">RFC4960</a>]  Stewart, R., Ed., "Stream Control Transmission Protocol",
              <a href="./rfc4960">RFC 4960</a>, September 2007.

   [<a id="ref-RFC4895">RFC4895</a>]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
              "Authenticated Chunks for the Stream Control Transmission
              Protocol (SCTP)", <a href="./rfc4895">RFC 4895</a>, August 2007.

<span class="h3"><a class="selflink" id="section-9.2" href="#section-9.2">9.2</a>.  Informative References</span>

   [<a id="ref-RFC5062">RFC5062</a>]  Stewart, R., Tuexen, M., and G. Camarillo, "Security
              Attacks Found Against SCTP and Current Countermeasures",
              <a href="./rfc5062">RFC 5062</a>, September 2007.

   [<a id="ref-RDDP">RDDP</a>]     Bestler, C. and R. Stewart, "Stream Control Transmission
              Protocol (SCTP) Direct Data Placement (DDP) Adaptation",
              Work in Progress, September 2006.















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<span class="h2"><a class="selflink" id="appendix-A" href="#appendix-A">Appendix A</a>.  Abstract Address Handling</span>

<span class="h3"><a class="selflink" id="appendix-A.1" href="#appendix-A.1">A.1</a>.  General Remarks</span>

   This appendix is non-normative.  It is present to give the reader a
   concise mathematical definition of an SCTP endpoint.  The following
   text provides a working definition of the endpoint notion to discuss
   address reconfiguration.  It is not intended to restrict
   implementations in any way; its goal is to provide a set of
   definitions only.  Using these definitions should make a discussion
   about address issues easier.

<span class="h3"><a class="selflink" id="appendix-A.2" href="#appendix-A.2">A.2</a>.  Generalized Endpoints</span>

   A generalized endpoint is a pair of a set of IP addresses and a port
   number at any given point of time.  The precise definition is as
   follows:

   A generalized endpoint gE at time t is given by

                  gE(t) = ({IP1, ..., IPn}, Port)

   where {IP1, ..., IPn} is a non-empty set of IP addresses.

   Please note that the dynamic addition and deletion of IP addresses
   described in this document allows the set of IP addresses of a
   generalized endpoint to be changed at some point of time.  The port
   number can never be changed.

   The set of IP addresses of a generalized endpoint gE at a time t is
   defined as

               Addr(gE)(t) = {IP1, ..., IPn}

   if gE(t) = ({IP1, ..., IPn}, Port) holds at time t.

   The port number of a generalized endpoint gE is defined as

               Port(gE) = Port

   if gE(t) = ({IP1, ..., IPn}, Port) holds at time t.

   There is one fundamental rule that restricts all generalized
   endpoints:

   For two different generalized endpoints gE' and gE'' with the same
   port number Port(gE') = Port(gE''), the address sets Addr(gE')(t) and
   Addr(gE'')(t) must be disjoint at every point in time.



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<span class="h3"><a class="selflink" id="appendix-A.3" href="#appendix-A.3">A.3</a>.  Associations</span>

   Associations consist of two generalized endpoints and the two address
   sets known by the peer at any time.  The precise definition is as
   follows:

   An association A between two different generalized endpoints gE' and
   gE'' is given by

                  A = (gE', S', gE'', S'')

   where S'(t) and S''(t) are a set of addresses at any time t such that
   S'(t) is a non-empty subset of Addr(gE')(t) and S''(t) is a non-empty
   subset of Addr(gE'')(t).

   If A = (gE', S', gE'', S'') is an association between the generalized
   endpoints gE' and gE'', the following notion is used:

                  Addr(A, gE') = S'   and  Addr(A, gE'') = S''.

   If the dependency on time is important the notion Addr(A, gE')(t) =
   S'(t) will be used.

   If A is an association between gE' and gE'', then Addr(A, gE') is the
   subset of IP addresses of gE', which is known by gE'' and used by
   gE'.

   Association establishment between gE' and gE'' can be seen as:

   1.  gE' and gE'' do exist before the association.

   2.  If an INIT has to be sent from gE' to gE'', address-scoping rules
       and other limitations are applied to calculate the subset S' from
       Addr(gE').  The addresses of S' are included in the INIT chunk.

   3.  If an INIT-ACK has to be sent from gE'' to gE', address-scoping
       rules and other limitations are applied to calculate the subset
       S'' from Addr(gE'').  The addresses of S'' are included in the
       INIT-ACK chunk.

   4.  After the handshake the association A = (gE', S', gE'', S'') has
       been established.

   5.  Right after the association establishment Addr(A, gE') and
       Addr(A, gE'') are the addresses that have been seen on the wire
       during the handshake.





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<span class="h3"><a class="selflink" id="appendix-A.4" href="#appendix-A.4">A.4</a>.  Relationship with <a href="./rfc4960">RFC 4960</a></span>

   [<a id="ref-RFC4960">RFC4960</a>] defines the notion of an endpoint.  This subsection will
   show that these endpoints are also (special) generalized endpoints.

   [<a id="ref-RFC4960">RFC4960</a>] has no notion of address-scoping or other address-handling
   limitations and provides no mechanism to change the addresses of an
   endpoint.

   This means that an endpoint is simply a generalized endpoint that
   does not depend on time.  Neither the port nor the address list
   changes.

   During association setup, no address-scoping rules or other
   limitations will be applied.  This means that for an association A
   between two endpoints gE' and gE'', the following is true:

   Addr(A, gE') = Addr(gE') and Addr(A, gE'') = Addr(gE'').

<span class="h3"><a class="selflink" id="appendix-A.5" href="#appendix-A.5">A.5</a>.  Rules for Address Manipulation</span>

   The rules for address manipulation can now be stated in a simple way:

   1.  An address can be added to a generalized endpoint gE only if this
       address is not an address of a different generalized endpoint
       with the same port number.

   2.  An address can be added to an association A with generalized
       endpoint gE if it has been added to the generalized endpoint gE
       first.  This means that the address must be an element of
       Addr(gE) first and then it can become an element of Addr(A, gE).
       But this is not necessary.  If the association does not allow the
       reconfiguration of the addresses only Addr(gE) can be modified.

   3.  An address can be deleted from an association A with generalized
       endpoint gE as long as Addr(A, gE) stays non-empty.

   4.  An address can be deleted from an generalized endpoint gE only if
       it has been removed from all associations having gE as a
       generalized endpoint.

   These rules simply make sure that the rules for the endpoints and
   associations given above are always fulfilled.








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Authors' Addresses

   Randall R. Stewart
   Cisco Systems, Inc.
   4875 Forest Drive
   Suite 200
   Columbia, SC  29206
   US

   Phone:
   EMail: rrs@cisco.com


   Qiaobing Xie
   Motorola, Inc.
   1501 W. Shure Drive, 2-3C
   Arlington Heights, IL  60004
   USA

   Phone: +1-847-632-3028
   EMail: Qiaobing.Xie@motorola.com


   Michael Tuexen
   Univ. of Applied Sciences Muenster
   Stegerwaldstr. 39
   48565 Steinfurt
   Germany

   EMail: tuexen@fh-muenster.de


   Shin Maruyama
   Kyoto University
   Yoshida-Honmachi
   Sakyo-ku
   Kyoto, Kyoto  606-8501
   JAPAN

   Phone: +81-75-753-7417
   EMail: mail@marushin.gr.jp










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   Masahiro Kozuka
   Kyoto University
   Yoshida-Honmachi
   Sakyo-ku
   Kyoto, Kyoto  606-8501
   JAPAN

   Phone: +81-75-753-7417
   EMail: ma-kun@kozuka.jp










































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Full Copyright Statement

   Copyright (C) The IETF Trust (2007).

   This document is subject to the rights, licenses and restrictions
   contained in <a href="https://www.rfc-editor.org/bcp/bcp78">BCP 78</a>, and except as set forth therein, the authors
   retain all their rights.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

   The IETF takes no position regarding the validity or scope of any
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   Copies of IPR disclosures made to the IETF Secretariat and any
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   <a href="http://www.ietf.org/ipr">http://www.ietf.org/ipr</a>.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at
   ietf-ipr@ietf.org.












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