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rfc:rfc5061

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
            Stream Control Transmission Protocol (SCTP)
                  Dynamic Address Reconfiguration

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) (RFC 4960) 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.

Stewart, et al. Standards Track [Page 1] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

Table of Contents

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

Stewart, et al. Standards Track [Page 2] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

1. Introduction

 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.

2. Conventions

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

Stewart, et al. Standards Track [Page 3] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

3. Serial Number Arithmetic

 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 "=<"
 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 [RFC1982]
 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 [RFC1982]) where SERIAL_BITS = 16.
 All other arithmetic and comparisons in this document use normal
 arithmetic.

4. Additional Chunks and Parameters

 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.

4.1. New Chunk Types

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

Stewart, et al. Standards Track [Page 4] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      Chunk Type  Chunk Name
      --------------------------------------------------------------
      0xC1    Address Configuration Change Chunk        (ASCONF)
      0x80    Address Configuration Acknowledgment      (ASCONF-ACK)
            Table 1: Address Configuration Chunks

4.1.1. Address Configuration Change Chunk (ASCONF)

 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 [RFC4960] for all variable parameters.  This
 chunk MUST be sent in an authenticated way by using the mechanism
 defined in [RFC4895].  If this chunk is received unauthenticated it
 MUST be silently discarded as described in [RFC4895].
      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
 [RFC4960].  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

Stewart, et al. Standards Track [Page 5] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC4960], Section 3.2.  Note that the upper two bits in
 the ASCONF Chunk are set to one.  As defined in [RFC4960], Section
 3.2, 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 Section 4.2.  One or more requests may be present in an
 ASCONF Chunk.

4.1.2. Address Configuration Acknowledgment Chunk (ASCONF-ACK)

 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
 [RFC4895].  If this chunk is received unauthenticated it MUST be
 silently discarded as described in [RFC4895].

Stewart, et al. Standards Track [Page 6] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      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.

4.2. New Parameter Types

 The seven new parameters added follow the format defined in Section
 3.2.1 of [RFC4960].  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

Stewart, et al. Standards Track [Page 7] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      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.

4.2.1. Add IP Address

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type = 0xC001          |    Length = Variable          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               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.

Stewart, et al. Standards Track [Page 8] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 Address Parameter: TLV
 This field contains an IPv4 or IPv6 address parameter as described in
 Section 3.3.2.1 of [RFC4960].  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.

4.2.2. Delete IP Address

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type =0xC002           |    Length = Variable          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               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.

Stewart, et al. Standards Track [Page 9] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 Address Parameter: TLV
 This field contains an IPv4 or IPv6 address parameter, as described
 in Section 3.3.2.1 of [RFC4960].  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.

4.2.3. Error Cause Indication

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Type = 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.

Stewart, et al. Standards Track [Page 10] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC4960]).  The Error
 Cause(s) follow the format defined in Section 3.3.10 of [RFC4960].
 Valid Chunk Appearance
 The Error Cause Indication parameter may only appear in the ASCONF-
 ACK Chunk Type.

4.2.4. Set Primary IP Address

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type =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
 Section 3.3.2.1 of [RFC4960].  The complete TLV is wrapped within
 this parameter.  It requests the receiver to mark the specified
 address as the primary address to send data to (see Section 5.1.2 of
 [RFC4960]).  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:

Stewart, et al. Standards Track [Page 11] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

         +--------------------------------+
         |  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.

4.2.5. Success Indication

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type = 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.

Stewart, et al. Standards Track [Page 12] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

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

4.2.6. Adaptation Layer Indication

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |        Type =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.

4.2.7. Supported Extensions Parameter

 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.

Stewart, et al. Standards Track [Page 13] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

    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.

4.3. New Error Causes

 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

Stewart, et al. Standards Track [Page 14] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

4.3.1. Error Cause: Request to Delete Last Remaining IP Address

 Cause of error
 Request to Delete Last Remaining IP Address: The receiver of this
 error sent a request to delete the last IP address from its
 association with its peer.  This error indicates that the request is
 rejected.
      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |     Cause Code=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         |
         +----------------+---------------+

4.3.2. Error Cause: Operation Refused Due to Resource Shortage

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

Stewart, et al. Standards Track [Page 15] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      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         |
         +----------------+---------------+

4.3.3. Error Cause: Request to Delete Source IP Address

 Cause of error
 Request to Delete Source IP Address: The receiver of this error sent
 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                     /
     /                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Stewart, et al. Standards Track [Page 16] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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.

4.3.4. Error Cause: Association Aborted Due to Illegal ASCONF-ACK

 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 Section 5.3, 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           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.3.5. Error Cause: Request Refused - No Authorization.

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

Stewart, et al. Standards Track [Page 17] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      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                    /
     /                                                               \
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5. Procedures

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

5.1. ASCONF Chunk Procedures

 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 Section 4.1.1.  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 [RFC4960], Section 6.4 for
      details).

Stewart, et al. Standards Track [Page 18] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC4960], Sections 8.1 and 8.2.
 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 [RFC4960],
      Sections 8.1 and 8.2.
 B2)  Increment the association error counters and perform endpoint
      failure detection on the association as defined in [RFC4960],
      Sections 8.1 and 8.2.
 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.

Stewart, et al. Standards Track [Page 19] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 B4)  Re-transmit the ASCONF Chunk last sent and if possible choose an
      alternate destination address (please refer to [RFC4960],
      Section 6.4.1).  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 Section 5.5.
 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 [RFC4960], Section 6.4.1 for details).

5.1.1. Congestion Control of ASCONF Chunks

 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 Section 5.5.
 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.

Stewart, et al. Standards Track [Page 20] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC1122] and 1280 octets for
      IPv6 [RFC2460].
 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.

5.2. Upon Reception of an ASCONF Chunk

 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 [RFC4960] 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.

Stewart, et al. Standards Track [Page 21] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 D3)  If neither D1, D2, nor D2-ext locates the association, treat the
      chunk as an Out Of The Blue packet as defined in [RFC4960].
 D4)  Follow the normal rules to validate the SCTP verification tag
      found in [RFC4960].
 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 [RFC4895].
      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).

Stewart, et al. Standards Track [Page 22] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 Section 3.3.10.8, [RFC4960].  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.

Stewart, et al. Standards Track [Page 23] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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.

5.3. General Rules for Address Manipulation

 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

Stewart, et al. Standards Track [Page 24] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

      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 Section 5.3.1 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.

Stewart, et al. Standards Track [Page 25] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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.

Stewart, et al. Standards Track [Page 26] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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
      [RFC4960], Section 5.4.
     Endpoint-A                                     Endpoint-Z
     ----------                                     ----------
     ASCONF[Add-IP:X]------------------------------>
                                             /--ASCONF-ACK
                                            /
                                  /--------/---New DATA:
                                 /        /    Destination
            <-------------------/        /     IP:X
                                        /
            <--------------------------/
 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.

Stewart, et al. Standards Track [Page 27] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 A similar problem exists with the deletion of an IP address as
 follows:
     Endpoint-A                                     Endpoint-Z
     ----------                                     ----------
                                  /------------New DATA:
                                 /             Destination
                                /              IP:X
     ASCONF [DEL-IP:X]---------/---------------->
            <-----------------/------------------ASCONF-ACK
                             /
                            /
             <-------------/
 In this example, we see a DATA chunk destined to the IP:X (which is
 about to be deleted) arriving after the deletion is complete.  For
 the ADD case, an endpoint SHOULD consider the newly 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 [RFC4960] section 8.4).  It MAY drop the data
 silently or it MAY consider it part of the association, but it MUST
 NOT respond with an ABORT.
 For the DELETE case, an endpoint MAY respond to the late-arriving
 DATA packet as an OOTB datagram or it MAY hold the deleting IP
 address for a small period of time as still valid.  If it treats the
 DATA packet as 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.

Stewart, et al. Standards Track [Page 28] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

5.3.1. A Special Case for OOTB ABORT Chunks

 Another case worth mentioning is illustrated below:
     Endpoint-A                                     Endpoint-Z
     ----------                                     ----------
     New DATA:------------\
     Source IP:X           \
                            \
     ASCONF-REQ[DEL-IP:X]----\------------------>
                              \        /---------ASCONF-ACK
                               \      /
                                \----/-----------> OOTB
     (Ignored <---------------------/-------------ABORT
      by rule F4)                  /
            <---------------------/
 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.

5.3.2. A Special Case for Changing an Address

 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).

5.4. Setting of the Primary Address

 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

Stewart, et al. Standards Track [Page 29] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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.

5.5. Bundling of Multiple ASCONFs

 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.

6. Security Considerations

 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 [RFC4895] to limit the
 ability of an attacker to hijack an association.

Stewart, et al. Standards Track [Page 30] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC4895] extension MUST be used
 with a preconfigured shared endpoint pair key to mitigate this
 threat.  For a more detailed analysis, see [RFC4895].
 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 [RFC4895]
 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.

Stewart, et al. Standards Track [Page 31] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC4895] 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 [RFC4895] 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
 [RFC5062].  The bombing attack, in particular, is countered by the
 use of a random nonce and is required by [RFC4960].
 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
 [RFC4895]-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

Stewart, et al. Standards Track [Page 32] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 Section
 4.2.6), 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.

7. IANA Considerations

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

Stewart, et al. Standards Track [Page 33] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 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 [RFC2434].  For this new
 registry, no initial values are being added by this document;
 however, [RDDP] will add the first entry.

8. Acknowledgments

 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.

Stewart, et al. Standards Track [Page 34] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

9. References

9.1. Normative References

 [RFC1122]  Braden, R., "Requirements for Internet Hosts -
            Communication Layers", STD 3, RFC 1122, October 1989.
 [RFC1982]  Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
            August 1996.
 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
            IANA Considerations Section in RFCs", BCP 26, RFC 2434,
            October 1998.
 [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
            (IPv6) Specification", RFC 2460, December 1998.
 [RFC4960]  Stewart, R., Ed., "Stream Control Transmission Protocol",
            RFC 4960, September 2007.
 [RFC4895]  Tuexen, M., Stewart, R., Lei, P., and E. Rescorla,
            "Authenticated Chunks for the Stream Control Transmission
            Protocol (SCTP)", RFC 4895, August 2007.

9.2. Informative References

 [RFC5062]  Stewart, R., Tuexen, M., and G. Camarillo, "Security
            Attacks Found Against SCTP and Current Countermeasures",
            RFC 5062, September 2007.
 [RDDP]     Bestler, C. and R. Stewart, "Stream Control Transmission
            Protocol (SCTP) Direct Data Placement (DDP) Adaptation",
            Work in Progress, September 2006.

Stewart, et al. Standards Track [Page 35] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

Appendix A. Abstract Address Handling

A.1. General Remarks

 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.

A.2. Generalized Endpoints

 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.

Stewart, et al. Standards Track [Page 36] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

A.3. Associations

 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.

Stewart, et al. Standards Track [Page 37] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

A.4. Relationship with RFC 4960

 [RFC4960] defines the notion of an endpoint.  This subsection will
 show that these endpoints are also (special) generalized endpoints.
 [RFC4960] 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'').

A.5. Rules for Address Manipulation

 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.

Stewart, et al. Standards Track [Page 38] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

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

Stewart, et al. Standards Track [Page 39] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

 Masahiro Kozuka
 Kyoto University
 Yoshida-Honmachi
 Sakyo-ku
 Kyoto, Kyoto  606-8501
 JAPAN
 Phone: +81-75-753-7417
 EMail: ma-kun@kozuka.jp

Stewart, et al. Standards Track [Page 40] RFC 5061 SCTP Dynamic Address Reconfiguration September 2007

Full Copyright Statement

 Copyright (C) The IETF Trust (2007).
 This document is subject to the rights, licenses and restrictions
 contained in BCP 78, 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
 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Intellectual Property

 The IETF takes no position regarding the validity or scope of any
 Intellectual Property Rights or other rights that might be claimed to
 pertain to the implementation or use of the technology described in
 this document or the extent to which any license under such rights
 might or might not be available; nor does it represent that it has
 made any independent effort to identify any such rights.  Information
 on the procedures with respect to rights in RFC documents can be
 found in BCP 78 and BCP 79.
 Copies of IPR disclosures made to the IETF Secretariat and any
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 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
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 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.

Stewart, et al. Standards Track [Page 41]

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