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rfc:rfc4460

Network Working Group R. Stewart Request for Comments: 4460 Cisco Systems, Inc. Category: Informational I. Arias-Rodriguez

                                                 Nokia Research Center
                                                               K. Poon
                                                Sun Microsystems, Inc.
                                                               A. Caro
                                                      BBN Technologies
                                                             M. Tuexen
                                    Muenster Univ. of Applied Sciences
                                                            April 2006
     Stream Control Transmission Protocol (SCTP) Specification
                         Errata and Issues

Status of This Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2006).

Abstract

 This document is a compilation of issues found during six
 interoperability events and 5 years of experience with implementing,
 testing, and using Stream Control Transmission Protocol (SCTP) along
 with the suggested fixes.  This document provides deltas to RFC 2960
 and is organized in a time-based way.  The issues are listed in the
 order they were brought up.  Because some text is changed several
 times, the last delta in the text is the one that should be applied.
 In addition to the delta, a description of the problem and the
 details of the solution are also provided.

Table of Contents

 1. Introduction ....................................................6
    1.1. Conventions ................................................7
 2. Corrections to RFC 2960 .........................................7
    2.1. Incorrect Error Type During Chunk Processing. ..............7
         2.1.1. Description of the Problem ..........................7
         2.1.2. Text changes to the document ........................7
         2.1.3. Solution Description ................................7

Stewart, et al. Informational [Page 1] RFC 4460 SCTP Errata April 2006

    2.2. Parameter Processing Issue .................................7
         2.2.1. Description of the Problem ..........................7
         2.2.2. Text Changes to the Document ........................8
         2.2.3. Solution Description ................................8
    2.3. Padding Issues .............................................8
         2.3.1. Description of the Problem ..........................8
         2.3.2. Text Changes to the Document ........................9
         2.3.3. Solution Description ...............................10
    2.4. Parameter Types across All Chunk Types ....................10
         2.4.1. Description of the Problem .........................10
         2.4.2. Text Changes to the Document .......................10
         2.4.3. Solution Description ...............................12
    2.5. Stream Parameter Clarification ............................12
         2.5.1. Description of the problem .........................12
         2.5.2. Text Changes to the Document .......................12
         2.5.3. Solution Description ...............................13
    2.6. Restarting Association Security Issue .....................13
         2.6.1. Description of the Problem .........................13
         2.6.2. Text Changes to the Document .......................14
         2.6.3. Solution Description ...............................18
    2.7. Implicit Ability to Exceed cwnd by PMTU-1 Bytes ...........19
         2.7.1. Description of the Problem .........................19
         2.7.2. Text Changes to the Document .......................19
         2.7.3. Solution Description ...............................19
    2.8. Issues with Fast Retransmit ...............................19
         2.8.1. Description of the Problem .........................19
         2.8.2. Text Changes to the Document .......................20
         2.8.3. Solution Description ...............................23
    2.9. Missing Statement about partial_bytes_acked Update ........24
         2.9.1. Description of the Problem .........................24
         2.9.2. Text Changes to the Document .......................24
         2.9.3. Solution Description ...............................25
    2.10. Issues with Heartbeating and Failure Detection ...........25
         2.10.1. Description of the Problem ........................25
         2.10.2. Text Changes to the Document ......................26
         2.10.3. Solution Description ..............................28
    2.11. Security interactions with firewalls .....................29
         2.11.1. Description of the Problem ........................29
         2.11.2. Text Changes to the Document ......................29
         2.11.3. Solution Description ..............................31
    2.12. Shutdown Ambiguity .......................................31
         2.12.1. Description of the Problem ........................31
         2.12.2. Text Changes to the Document ......................31
         2.12.3. Solution Description ..............................32
    2.13. Inconsistency in ABORT Processing ........................32
         2.13.1. Description of the Problem ........................32
         2.13.2. Text changes to the document ......................33
         2.13.3. Solution Description ..............................33

Stewart, et al. Informational [Page 2] RFC 4460 SCTP Errata April 2006

    2.14. Cwnd Gated by Its Full Use ...............................34
         2.14.1. Description of the Problem ........................34
         2.14.2. Text Changes to the Document ......................34
         2.14.3. Solution Description ..............................36
    2.15. Window Probes in SCTP ....................................36
         2.15.1. Description of the Problem ........................36
         2.15.2. Text Changes to the Document ......................36
         2.15.3. Solution Description ..............................38
    2.16. Fragmentation and Path MTU Issues ........................39
         2.16.1. Description of the Problem ........................39
         2.16.2. Text Changes to the Document ......................39
         2.16.3. Solution Description ..............................40
    2.17. Initial Value of the Cumulative TSN Ack ..................40
         2.17.1. Description of the Problem ........................40
         2.17.2. Text Changes to the Document ......................40
         2.17.3. Solution Description ..............................41
    2.18. Handling of Address Parameters within the INIT or
          INIT-ACK .................................................41
         2.18.1. Description of the Problem ........................41
         2.18.2. Text Changes to the Document ......................41
         2.18.3. Solution description ..............................42
    2.19. Handling of Stream Shortages .............................42
         2.19.1. Description of the Problem ........................42
         2.19.2. Text Changes to the Document ......................42
         2.19.3. Solution Description ..............................43
    2.20. Indefinite Postponement ..................................43
         2.20.1. Description of the Problem ........................43
         2.20.2. Text Changes to the Document ......................43
         2.20.3. Solution Description ..............................44
    2.21. User-Initiated Abort of an Association ...................44
         2.21.1. Description of the Problem ........................44
         2.21.2. Text changes to the document ......................44
         2.21.3. Solution Description ..............................50
    2.22. Handling of Invalid Initiate Tag of INIT-ACK .............50
         2.22.1. Description of the Problem ........................50
         2.22.2. Text Changes to the Document ......................50
         2.22.3. Solution Description ..............................51
    2.23. Sending an ABORT in Response to an INIT ..................51
         2.23.1. Description of the Problem ........................51
         2.23.2. Text Changes to the Document ......................51
         2.23.3. Solution Description ..............................52
    2.24. Stream Sequence Number (SSN) Initialization ..............52
         2.24.1. Description of the Problem ........................52
         2.24.2. Text Changes to the Document ......................52
         2.24.3. Solution Description ..............................53
    2.25. SACK Packet Format .......................................53
         2.25.1. Description of the Problem ........................53
         2.25.2. Text Changes to the Document ......................53

Stewart, et al. Informational [Page 3] RFC 4460 SCTP Errata April 2006

         2.25.3. Solution Description ..............................53
    2.26. Protocol Violation Error Cause ...........................53
         2.26.1. Description of the Problem ........................53
         2.26.2. Text Changes to the Document ......................54
         2.26.3. Solution Description ..............................56
    2.27. Reporting of Unrecognized Parameters .....................56
         2.27.1. Description of the Problem ........................56
         2.27.2. Text Changes to the Document ......................56
         2.27.3. Solution Description ..............................57
    2.28. Handling of IP Address Parameters ........................58
         2.28.1. Description of the Problem ........................58
         2.28.2. Text Changes to the Document ......................58
         2.28.3. Solution Description ..............................58
    2.29. Handling of COOKIE ECHO Chunks When a TCB Exists .........59
         2.29.1. Description of the Problem ........................59
         2.29.2. Text Changes to the Document ......................59
         2.29.3. Solution Description ..............................59
    2.30. The Initial Congestion Window Size .......................59
         2.30.1. Description of the Problem ........................59
         2.30.2. Text Changes to the Document ......................60
         2.30.3. Solution Description ..............................61
    2.31. Stream Sequence Numbers in Figures .......................62
         2.31.1. Description of the Problem ........................62
         2.31.2. Text Changes to the Document ......................63
         2.31.3. Solution description ..............................67
    2.32. Unrecognized Parameters ..................................67
         2.32.1. Description of the Problem ........................67
         2.32.2. Text Changes to the Document ......................67
         2.32.3. Solution Description ..............................68
    2.33. Handling of Unrecognized Parameters ......................68
         2.33.1. Description of the Problem ........................68
         2.33.2. Text Changes to the Document ......................68
         2.33.3. Solution Description ..............................70
    2.34. Tie Tags .................................................70
         2.34.1. Description of the Problem ........................70
         2.34.2. Text Changes to the Document ......................70
         2.34.3. Solution Description ..............................72
    2.35. Port Number Verification in the COOKIE-ECHO ..............72
         2.35.1. Description of the Problem ........................72
         2.35.2. Text Changes to the Document ......................72
         2.35.3. Solution Description ..............................73
    2.36. Path Initialization ......................................74
         2.36.1. Description of the Problem ........................74
         2.36.2. Text Changes to the Document ......................74
         2.36.3. Solution Description ..............................76
    2.37. ICMP Handling Procedures .................................76
         2.37.1. Description of the Problem ........................76
         2.37.2. Text Changes to the Document ......................77

Stewart, et al. Informational [Page 4] RFC 4460 SCTP Errata April 2006

         2.37.3. Solution Description ..............................79
    2.38. Checksum .................................................79
         2.38.1. Description of the problem ........................79
         2.38.2. Text Changes to the Document ......................79
         2.38.3. Solution Description ..............................86
    2.39. Retransmission Policy ....................................86
         2.39.1. Description of the Problem ........................86
         2.39.2. Text Changes to the Document ......................87
         2.39.3. Solution Description ..............................87
    2.40. Port Number 0 ............................................88
         2.40.1. Description of the Problem ........................88
         2.40.2. Text Changes to the Document ......................88
         2.40.3. Solution Description ..............................89
    2.41. T Bit ....................................................89
         2.41.1. Description of the Problem ........................89
         2.41.2. Text Changes to the Document ......................89
         2.41.3. Solution Description ..............................93
    2.42. Unknown Parameter Handling ...............................93
         2.42.1. Description of the Problem ........................93
         2.42.2. Text Changes to the Document ......................93
         2.42.3. Solution Description ..............................95
    2.43. Cookie Echo Chunk ........................................95
         2.43.1. Description of the Problem ........................95
         2.43.2. Text Changes to the Document ......................95
         2.43.3. Solution Description ..............................96
    2.44. Partial Chunks ...........................................96
         2.44.1. Description of the Problem ........................96
         2.44.2. Text Changes to the Document ......................96
         2.44.3. Solution Description ..............................97
    2.45. Non-unicast Addresses ....................................97
         2.45.1. Description of the Problem ........................97
         2.45.2. Text Changes to the Document ......................97
         2.45.3. Solution Description ..............................98
    2.46. Processing of ABORT Chunks ...............................98
         2.46.1. Description of the Problem ........................98
         2.46.2. Text Changes to the Document ......................98
         2.46.3. Solution Description ..............................98
    2.47. Sending of ABORT Chunks ..................................99
         2.47.1. Description of the Problem ........................99
         2.47.2. Text Changes to the Document ......................99
         2.47.3. Solution Description ..............................99
    2.48. Handling of Supported Address Types Parameter ............99
         2.48.1. Description of the Problem ........................99
         2.48.2. Text Changes to the Document .....................100
         2.48.3. Solution Description .............................100
    2.49. Handling of Unexpected Parameters .......................101
         2.49.1. Description of the Problem .......................101
         2.49.2. Text Changes to the Document .....................101

Stewart, et al. Informational [Page 5] RFC 4460 SCTP Errata April 2006

         2.49.3. Solution Description .............................102
    2.50. Payload Protocol Identifier .............................102
         2.50.1. Description of the Problem .......................102
         2.50.2. Text Changes to the Document .....................103
         2.50.3. Solution Description .............................103
    2.51. Karn's Algorithm ........................................104
         2.51.1. Description of the Problem .......................104
         2.51.2. Text Changes to the Document .....................104
         2.51.3. Solution Description .............................104
    2.52. Fast Retransmit Algorithm ...............................104
         2.52.1. Description of the Problem .......................104
         2.52.2. Text Changes to the Document .....................105
         2.52.3. Solution Description .............................105
 3. Security Considerations .......................................105
 4. Acknowledgements ..............................................106
 5. IANA Considerations ...........................................106
 6. Normative References ..........................................106

1. Introduction

 This document contains a compilation of all defects found up until
 the publishing of this document for the Stream Control Transmission
 Protocol (SCTP), RFC 2960 [5].  These defects may be of an editorial
 or technical nature.  This document may be thought of as a companion
 document to be used in the implementation of SCTP to clarify errors
 in the original SCTP document.
 This document provides a history of the changes that will be compiled
 into RFC 2960's [5] BIS document.  Each error will be detailed within
 this document in the form of
 o  the problem description,
 o  the text quoted from RFC 2960 [5],
 o  the replacement text that should be placed into the BIS document,
    and
 o  a description of the solution.
 This document is a historical record of sequential changes what have
 been found necessary at various interop events and through discussion
 on this list.
 Note that because some text is changed several times, the last delta
 for a text in the document is the erratum for that text in RFC 2960.

Stewart, et al. Informational [Page 6] RFC 4460 SCTP Errata April 2006

1.1. Conventions

 The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
 SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
 they appear in this document, are to be interpreted as described in
 RFC 2119 [2].

2. Corrections to RFC 2960

2.1. Incorrect Error Type During Chunk Processing.

2.1.1. Description of the Problem

 A typo was discovered in RFC 2960 [5] that incorrectly specifies an
 action to be taken when processing chunks of unknown identity.

2.1.2. Text changes to the document

  1. ——–

Old text: (Section 3.2)

  1. ——–
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      parameter in an 'Unrecognized Parameter Type' (in either an
      ERROR or in the INIT ACK).
  1. ——–

New text: (Section 3.2)

  1. ——–
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      chunk in an 'Unrecognized Chunk Type'.

2.1.3. Solution Description

 The receiver of an unrecognized chunk should not send a 'parameter'
 error but instead should send the appropriate chunk error as
 described above.

2.2. Parameter Processing Issue

2.2.1. Description of the Problem

 A typographical error was introduced through an improper cut and
 paste in the use of the upper two bits to describe proper handling of
 unknown parameters.

Stewart, et al. Informational [Page 7] RFC 4460 SCTP Errata April 2006

2.2.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP packet and discard it; do not process
      any further chunks within it.
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      parameter in an 'Unrecognized Parameter Type' (in either an
      ERROR or in the INIT ACK).
  1. ——–

New text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP chunk and discard it, do not process
      any further parameters within this chunk.
 01 - Stop processing this SCTP chunk and discard it, do not process
      any further parameters within this chunk, and report the
      unrecognized parameter in an 'Unrecognized Parameter Type' (in
      either an ERROR or in the INIT ACK).

2.2.3. Solution Description

 It was always the intent to stop processing at the level one was at
 in an unknown chunk or parameter with the upper bit set to 0.  Thus,
 if you are processing a chunk, you should drop the packet.  If you
 are processing a parameter, you should drop the chunk.

2.3. Padding Issues

2.3.1. Description of the Problem

 A problem was found when a Chunk terminated in a TLV parameter.  If
 this last TLV was not on a 32-bit boundary (as required), there was
 confusion as to whether the last padding was included in the chunk
 length.

Stewart, et al. Informational [Page 8] RFC 4460 SCTP Errata April 2006

2.3.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.2)

  1. ——–
 Chunk Length: 16 bits (unsigned integer)
    This value represents the size of the chunk in bytes including the
    Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields.
    Therefore, if the Chunk Value field is zero-length, the Length
    field will be set to 4.  The Chunk Length field does not count any
    padding.
 Chunk Value: variable length
    The Chunk Value field contains the actual information to be
    transferred in the chunk.  The usage and format of this field is
    dependent on the Chunk Type.
 The total length of a chunk (including Type, Length and Value fields)
 MUST be a multiple of 4 bytes.  If the length of the chunk is not a
 multiple of 4 bytes, the sender MUST pad the chunk with all zero
 bytes and this padding is not included in the chunk length field.
 The sender should never pad with more than 3 bytes.  The receiver
 MUST ignore the padding bytes.
  1. ——–

New text: (Section 3.2)

  1. ——–
 Chunk Length: 16 bits (unsigned integer)
    This value represents the size of the chunk in bytes, including
    the Chunk Type, Chunk Flags, Chunk Length, and Chunk Value fields.
    Therefore, if the Chunk Value field is zero-length, the Length
    field will be set to 4.  The Chunk Length field does not count any
    chunk padding.
    Chunks (including Type, Length, and Value fields) are padded out
    by the sender with all zero bytes to be a multiple of 4 bytes
    long.  This padding MUST NOT be more than 3 bytes in total.  The
    Chunk Length value does not include terminating padding of the
    chunk.  However, it does include padding of any variable-length
    parameter except the last parameter in the chunk.  The receiver
    MUST ignore the padding.

Stewart, et al. Informational [Page 9] RFC 4460 SCTP Errata April 2006

    Note: A robust implementation should accept the Chunk whether or
    not the final padding has been included in the Chunk Length.
 Chunk Value: variable length
    The Chunk Value field contains the actual information to be
    transferred in the chunk.  The usage and format of this field is
    dependent on the Chunk Type.
 The total length of a chunk (including Type, Length, and Value
 fields) MUST be a multiple of 4 bytes.  If the length of the chunk is
 not a multiple of 4 bytes, the sender MUST pad the chunk with all
 zero bytes, and this padding is not included in the chunk length
 field.  The sender should never pad with more than 3 bytes.  The
 receiver MUST ignore the padding bytes.

2.3.3. Solution Description

 The above text makes clear that the padding of the last parameter is
 not included in the Chunk Length field.  It also clarifies that the
 padding of parameters that are not the last one must be counted in
 the Chunk Length field.

2.4. Parameter Types across All Chunk Types

2.4.1. Description of the Problem

 A problem was noted when multiple errors are needed to be sent
 regarding unknown or unrecognized parameters.  Since often the error
 type does not hold the chunk type field, it may become difficult to
 tell which error was associated with which chunk.

2.4.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.2.1)

  1. ——–
 The actual SCTP parameters are defined in the specific SCTP chunk
 sections.  The rules for IETF-defined parameter extensions are
 defined in Section 13.2.
  1. ——–

New text: (Section 3.2.1)

  1. ——–
 The actual SCTP parameters are defined in the specific SCTP chunk
 sections.  The rules for IETF-defined parameter extensions are

Stewart, et al. Informational [Page 10] RFC 4460 SCTP Errata April 2006

 defined in Section 13.2.  Note that a parameter type MUST be unique
 across all chunks.  For example, the parameter type '5' is used to
 represent an IPv4 address (see Section 3.3.2).  The value '5' then is
 reserved across all chunks to represent an IPv4 address and MUST NOT
 be reused with a different meaning in any other chunk.
  1. ——–

Old text: (Section 13.2)

  1. ——–
 13.2 IETF-defined Chunk Parameter Extension
 The assignment of new chunk parameter type codes is done through an
 IETF Consensus action as defined in [RFC2434].  Documentation of the
 chunk parameter MUST contain the following information:
 a) Name of the parameter type.
 b) Detailed description of the structure of the parameter field.
    This structure MUST conform to the general type-length-value
    format described in Section 3.2.1.
 c) Detailed definition of each component of the parameter type.
 d) Detailed description of the intended use of this parameter type,
    and an indication of whether and under what circumstances multiple
    instances of this parameter type may be found within the same
    chunk.
  1. ——–

New text: (Section 13.2)

  1. ——–
 13.2.  IETF-defined Chunk Parameter Extension
 The assignment of new chunk parameter type codes is done through an
 IETF Consensus action, as defined in [RFC2434].  Documentation of the
 chunk parameter MUST contain the following information:
 a) Name of the parameter type.
 b) Detailed description of the structure of the parameter field.
    This structure MUST conform to the general type-length-value
    format described in Section 3.2.1.
 c) Detailed definition of each component of the parameter type.

Stewart, et al. Informational [Page 11] RFC 4460 SCTP Errata April 2006

 d) Detailed description of the intended use of this parameter type,
    and an indication of whether and under what circumstances multiple
    instances of this parameter type may be found within the same
    chunk.
 e) Each parameter type MUST be unique across all chunks.

2.4.3. Solution Description

 By having all parameters unique across all chunk assignments (the
 current assignment policy), no ambiguity exists as to what a
 parameter means in different contexts.  The trade-off for this is a
 smaller parameter space, i.e., 65,536 parameters versus 65,536 *
 Number-of- chunks.

2.5. Stream Parameter Clarification

2.5.1. Description of the problem

 A problem was found where the specification is unclear on the
 legality of an endpoint asking for more stream resources than were
 allowed in the MIS value of the INIT.  In particular, the value in
 the INIT ACK requested in its OS value was larger than the MIS value
 received in the INIT chunk.  This behavior is illegal, yet it was
 unspecified in RFC 2960 [5]

2.5.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.3)

  1. ——–
 Number of Outbound Streams (OS):  16 bits (unsigned integer)
    Defines the number of outbound streams the sender of this INIT ACK
    chunk wishes to create in this association.  The value of 0 MUST
    NOT be used.
    Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD
    destroy the association discarding its TCB.

Stewart, et al. Informational [Page 12] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.3.3)

  1. ——–
 Number of Outbound Streams (OS): 16 bits (unsigned integer)
    Defines the number of outbound streams the sender of this INIT ACK
    chunk wishes to create in this association.  The value of 0 MUST
    NOT be used, and the value MUST NOT be greater than the MIS value
    sent in the INIT chunk.
    Note: A receiver of an INIT ACK with the OS value set to 0 SHOULD
    destroy the association, discarding its TCB.

2.5.3. Solution Description

 The change in wording, above, changes it so that a responder to an
 INIT chunk does not specify more streams in its OS value than were
 represented to it in the MIS value, i.e., its maximum.

2.6. Restarting Association Security Issue

2.6.1. Description of the Problem

 A security problem was found when a restart occurs.  It is possible
 for an intruder to send an INIT to an endpoint of an existing
 association.  In the INIT the intruder would list one or more of the
 current addresses of an association and its own.  The normal restart
 procedures would then occur, and the intruder would have hijacked an
 association.

Stewart, et al. Informational [Page 13] RFC 4460 SCTP Errata April 2006

2.6.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.10 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.

Stewart, et al. Informational [Page 14] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
    11              Restart of an Association with New Addresses
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields.
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.11 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.
  1. ——–

New text: (Note no old text, new error cause added in section 3.3.10)

  1. ——–
 3.3.10.11.  Restart of an Association with New Addresses (11)
  Cause of error
  --------------
  Restart of an association with new addresses: An INIT was received
  on an existing association.  But the INIT added addresses to the
  association that were previously NOT part of the association.  The
  new addresses are listed in the error code.  This ERROR is normally
  sent as part of an ABORT refusing the INIT (see Section 5.2).

Stewart, et al. Informational [Page 15] RFC 4460 SCTP Errata April 2006

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Cause Code=11         |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /                       New Address TLVs                        /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    Note: Each New Address TLV is an exact copy of the TLV
    that was found in the INIT chunk that was new, including the
    Parameter Type and the Parameter length.
  1. ——–

Old text: (Section 5.2.1)

  1. ——–
 Upon receipt of an INIT in the COOKIE-WAIT or COOKIE-ECHOED state, an
 endpoint MUST respond with an INIT ACK using the same parameters it
 sent in its original INIT chunk (including its Initiation Tag,
 unchanged).  These original parameters are combined with those from
 the newly received INIT chunk.  The endpoint shall also generate a
 State Cookie with the INIT ACK.  The endpoint uses the parameters
 sent in its INIT to calculate the State Cookie.
  1. ——–

New text: (Section 5.2.1)

  1. ——–
 Upon receipt of an INIT in the COOKIE-WAIT state, an endpoint MUST
 respond with an INIT ACK using the same parameters it sent in its
 original INIT chunk (including its Initiation Tag, unchanged).  When
 responding, the endpoint MUST send the INIT ACK back to the same
 address that the original INIT (sent by this endpoint) was sent to.
 Upon receipt of an INIT in the COOKIE-ECHOED state, an endpoint MUST
 respond with an INIT ACK using the same parameters it sent in its
 original INIT chunk (including its Initiation Tag, unchanged),
 provided that no NEW address has been added to the forming
 association.  If the INIT message indicates that a new address has
 been added to the association, then the entire INIT MUST be
 discarded, and NO changes should be made to the existing association.
 An ABORT SHOULD be sent in response that MAY include the error
 'Restart of an association with new addresses'.  The error SHOULD
 list the addresses that were added to the restarting association.

Stewart, et al. Informational [Page 16] RFC 4460 SCTP Errata April 2006

 When responding in either state (COOKIE-WAIT or COOKIE-ECHOED) with
 an INIT ACK, the original parameters are combined with those from the
 newly received INIT chunk.  The endpoint shall also generate a State
 Cookie with the INIT ACK.  The endpoint uses the parameters sent in
 its INIT to calculate the State Cookie.
  1. ——–

Old text: (Section 5.2.2)

  1. ——–
 5.2.2 Unexpected INIT in States Other than CLOSED, COOKIE-ECHOED,
       COOKIE-WAIT and SHUTDOWN-ACK-SENT
 Unless otherwise stated, upon reception of an unexpected INIT for
 this association, the endpoint shall generate an INIT ACK with a
 State Cookie.  In the outbound INIT ACK the endpoint MUST copy its
 current Verification Tag and peer's Verification Tag into a reserved
 place within the state cookie.  We shall refer to these locations as
 the Peer's-Tie-Tag and the Local-Tie-Tag.  The outbound SCTP packet
 containing this INIT ACK MUST carry a Verification Tag value equal to
 the Initiation Tag found in the unexpected INIT.  And the INIT ACK
 MUST contain a new Initiation Tag (randomly generated see Section
 5.3.1).  Other parameters for the endpoint SHOULD be copied from the
 existing parameters of the association (e.g., number of outbound
 streams) into the INIT ACK and cookie.
 After sending out the INIT ACK, the endpoint shall take no further
 actions, i.e., the existing association, including its current state,
 and the corresponding TCB MUST NOT be changed.
 Note: Only when a TCB exists and the association is not in a COOKIE-
 WAIT state are the Tie-Tags populated.  For a normal association INIT
 (i.e., the endpoint is in a COOKIE-WAIT state), the Tie-Tags MUST be
 set to 0 (indicating that no previous TCB existed).  The INIT ACK and
 State Cookie are populated as specified in section 5.2.1.
  1. ——–

New text: (Section 5.2.2)

  1. ——–
 5.2.2.  Unexpected INIT in States Other Than CLOSED, COOKIE-ECHOED,
         COOKIE-WAIT, and SHUTDOWN-ACK-SENT
 Unless otherwise stated, upon receipt of an unexpected INIT for this
 association, the endpoint shall generate an INIT ACK with a State
 Cookie.  Before responding, the endpoint MUST check to see if the
 unexpected INIT adds new addresses to the association.  If new
 addresses are added to the association, the endpoint MUST respond

Stewart, et al. Informational [Page 17] RFC 4460 SCTP Errata April 2006

 with an ABORT, copying the 'Initiation Tag' of the unexpected INIT
 into the 'Verification Tag' of the outbound packet carrying the
 ABORT.  In the ABORT response, the cause of error MAY be set to
 'restart of an association with new addresses'.  The error SHOULD
 list the addresses that were added to the restarting association.
 If no new addresses are added, when responding to the INIT in the
 outbound INIT ACK, the endpoint MUST copy its current Verification
 Tag and peer's Verification Tag into a reserved place within the
 state cookie.  We shall refer to these locations as the Peer's-Tie-
 Tag and the Local-Tie-Tag.  The outbound SCTP packet containing this
 INIT ACK MUST carry a Verification Tag value equal to the Initiation
 Tag found in the unexpected INIT.  And the INIT ACK MUST contain a
 new Initiation Tag (randomly generated; see Section 5.3.1).  Other
 parameters for the endpoint SHOULD be copied from the existing
 parameters of the association (e.g., number of outbound streams) into
 the INIT ACK and cookie.
 After sending out the INIT ACK or ABORT, the endpoint shall take no
 further actions; i.e., the existing association, including its
 current state, and the corresponding TCB MUST NOT be changed.
 Note: Only when a TCB exists and the association is not in a COOKIE-
 WAIT or SHUTDOWN-ACK-SENT state are the Tie-Tags populated with a
 value other than 0.  For a normal association INIT (i.e., the
 endpoint is in the CLOSED state), the Tie-Tags MUST be set to 0
 (indicating that no previous TCB existed).

2.6.3. Solution Description

 A new error code is being added, along with specific instructions to
 send back an ABORT to a new association in a restart case or
 collision case, where new addresses have been added.  The error code
 can be used by a legitimate restart to inform the endpoint that it
 has made a software error in adding a new address.  The endpoint then
 can choose to wait until the OOTB ABORT tears down the old
 association, or to restart without the new address.
 Also, the note at the end of Section 5.2.2 explaining the use of the
 Tie-Tags was modified to properly explain the states in which the
 Tie-Tags should be set to a value different than 0.

Stewart, et al. Informational [Page 18] RFC 4460 SCTP Errata April 2006

2.7. Implicit Ability to Exceed cwnd by PMTU-1 Bytes

2.7.1. Description of the Problem

 Some implementations were having difficulty growing their cwnd.  This
 was due to an improper enforcement of the congestion control rules.
 The rules, as written, provided for a slop over of the cwnd value.
 Without this slop over, the sender would appear NOT to be using its
 full cwnd value and thus would never increase it.

2.7.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.1)

  1. ——–
 B) At any given time, the sender MUST NOT transmit new data to a
    given transport address if it has cwnd or more bytes of data
    outstanding to that transport address.
  1. ——–

New text: (Section 6.1)

  1. ——–
 B) At any given time, the sender MUST NOT transmit new data to a
    given transport address if it has cwnd or more bytes of data
    outstanding to that transport address.  The sender may exceed cwnd
    by up to (PMTU-1) bytes on a new transmission if the cwnd is not
    currently exceeded.

2.7.3. Solution Description

 The text changes make clear the ability to go over the cwnd value by
 no more than (PMTU-1) bytes.

2.8. Issues with Fast Retransmit

2.8.1. Description of the Problem

 Several problems were found in the current specification of fast
 retransmit.  The current wording did not require GAP ACK blocks to be
 sent, even though they are essential to the workings of SCTP's
 congestion control.  The specification left unclear how to handle the
 fast retransmit cycle, having the implementation wait on the cwnd to
 retransmit a TSN that was marked for fast retransmit.  No limit was
 placed on how many times a TSN could be fast retransmitted.  Fast
 Recovery was not specified, causing the congestion window to be
 reduced drastically when there are multiple losses in a single RTT.

Stewart, et al. Informational [Page 19] RFC 4460 SCTP Errata April 2006

2.8.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.2)

  1. ——–
 Acknowledgements MUST be sent in SACK chunks unless shutdown was
 requested by the ULP in which case an endpoint MAY send an
 acknowledgement in the SHUTDOWN chunk.  A SACK chunk can acknowledge
 the reception of multiple DATA chunks.  See Section 3.3.4 for SACK
 chunk format.  In particular, the SCTP endpoint MUST fill in the
 Cumulative TSN Ack field to indicate the latest sequential TSN (of a
 valid DATA chunk) it has received.  Any received DATA chunks with TSN
 greater than the value in the Cumulative TSN Ack field SHOULD also be
 reported in the Gap Ack Block fields.
  1. ——–

New text: (Section 6.2)

  1. ——–
 Acknowledegments MUST be sent in SACK chunks unless shutdown was
 requested by the ULP, in which case an endpoint MAY send an
 acknowledgement in the SHUTDOWN chunk.  A SACK chunk can acknowledge
 the reception of multiple DATA chunks.  See Section 3.3.4 for SACK
 chunk format.  In particular, the SCTP endpoint MUST fill in the
 Cumulative TSN Ack field to indicate the latest sequential TSN (of a
 valid DATA chunk) it has received.  Any received DATA chunks with
 TSN greater than the value in the Cumulative TSN Ack field are
 reported in the Gap Ack Block fields.  The SCTP endpoint MUST
 report as many Gap Ack Blocks as can fit in a single SACK
 chunk limited by the current path MTU.
  1. ——–

Old text: (Section 6.2.1)

  1. ——–
    D) Any time a SACK arrives, the endpoint performs the following:
          i) If Cumulative TSN Ack is less than the Cumulative TSN Ack
          Point, then drop the SACK.  Since Cumulative TSN Ack is
          monotonically increasing, a SACK whose Cumulative TSN Ack is
          less than the Cumulative TSN Ack Point indicates an out-of-
          order SACK.
          ii) Set rwnd equal to the newly received a_rwnd minus the
          number of bytes still outstanding after processing the
          Cumulative TSN Ack and the Gap Ack Blocks.

Stewart, et al. Informational [Page 20] RFC 4460 SCTP Errata April 2006

          iii) If the SACK is missing a TSN that was previously
          acknowledged via a Gap Ack Block (e.g., the data receiver
          reneged on the data), then mark the corresponding DATA chunk
          as available for retransmit:  Mark it as missing for fast
          retransmit as described in Section 7.2.4 and if no
          retransmit timer is running for the destination address
          to which the DATA chunk was originally transmitted, then
          T3-rtx is started for that destination address.
  1. ——–

New text: (Section 6.2.1)

  1. ——–
    D) Any time a SACK arrives, the endpoint performs the following:
          i) If Cumulative TSN Ack is less than the Cumulative TSN Ack
          Point, then drop the SACK.  Since Cumulative TSN Ack is
          monotonically increasing, a SACK whose Cumulative TSN Ack is
          less than the Cumulative TSN Ack Point indicates an out-of-
          order SACK.
          ii) Set rwnd equal to the newly received a_rwnd minus the
          number of bytes still outstanding after processing the
          Cumulative TSN Ack and the Gap Ack Blocks.
          iii) If the SACK is missing a TSN that was previously
          acknowledged via a Gap Ack Block (e.g., the data receiver
          reneged on the data), then consider the corresponding DATA
          that might be possibly missing: Count one miss indication
          towards fast retransmit as described in Section 7.2.4, and
          if no retransmit timer is running for the destination
          address to which the DATA chunk was originally transmitted,
          then T3-rtx is started for that destination address.
          iv) If the Cumulative TSN Ack matches or exceeds the Fast
          Recovery exitpoint (Section 7.2.4), Fast Recovery is exited.
  1. ——–

Old text: (Section 7.2.4)

  1. ——–
 Whenever an endpoint receives a SACK that indicates some TSN(s)
 missing, it SHOULD wait for 3 further miss indications (via
 subsequent SACK's) on the same TSN(s) before taking action with
 regard to Fast Retransmit.
 When the TSN(s) is reported as missing in the fourth consecutive
 SACK, the data sender shall:

Stewart, et al. Informational [Page 21] RFC 4460 SCTP Errata April 2006

 1) Mark the missing DATA chunk(s) for retransmission,
 2) Adjust the ssthresh and cwnd of the destination address(es) to
    which the missing DATA chunks were last sent, according to the
    formula described in Section 7.2.3.
 3) Determine how many of the earliest (i.e., lowest TSN) DATA chunks
    marked for retransmission will fit into a single packet, subject
    to constraint of the path MTU of the destination transport address
    to which the packet is being sent.  Call this value K.  Retransmit
    those K DATA chunks in a single packet.
 4) Restart T3-rtx timer only if the last SACK acknowledged the lowest
    outstanding TSN number sent to that address, or the endpoint is
    retransmitting the first outstanding DATA chunk sent to that
    address.
 Note: Before the above adjustments, if the received SACK also
 acknowledges new DATA chunks and advances the Cumulative TSN Ack
 Point, the cwnd adjustment rules defined in Sections 7.2.1 and 7.2.2
 must be applied first.
 A straightforward implementation of the above keeps a counter for
 each TSN hole reported by a SACK.  The counter increments for each
 consecutive SACK reporting the TSN hole.  After reaching 4 and
 starting the fast retransmit procedure, the counter resets to 0.
 Because cwnd in SCTP indirectly bounds the number of outstanding
 TSN's, the effect of TCP fast-recovery is achieved automatically with
 no adjustment to the congestion control window size.
  1. ——–

New text: (Section 7.2.4)

  1. ——–
 Whenever an endpoint receives a SACK that indicates that some TSNs
 are missing, it SHOULD wait for 3 further miss indications (via
 subsequent SACKs) on the same TSN(s) before taking action with
 regard to Fast Retransmit.
 Miss indications SHOULD follow the HTNA (Highest TSN Newly
 Acknowledged) algorithm.  For each incoming SACK, miss
 indications are incremented only for missing TSNs prior to
 the highest TSN newly acknowledged in the SACK.  A newly
 acknowledged DATA chunk is one not previously acknowledged
 in a SACK.  If an endpoint is in Fast Recovery and a SACK
 arrives that advances the Cumulative TSN Ack Point, the
 miss indications are incremented for all TSNs reported
 missing in the SACK.

Stewart, et al. Informational [Page 22] RFC 4460 SCTP Errata April 2006

 When the fourth consecutive miss indication is received for a TSN(s),
 the data sender shall do the following:
 1) Mark the DATA chunk(s) with four miss indications for
    retransmission.
 2) If not in Fast Recovery, adjust the ssthresh and cwnd of the
    destination address(es) to which the missing DATA chunks were
    last sent, according to the formula described in Section 7.2.3.
 3) Determine how many of the earliest (i.e., lowest TSN) DATA chunks
    marked for retransmission will fit into a single packet, subject
    to constraint of the path MTU of the destination transport address
    to which the packet is being sent.  Call this value K.  Retransmit
    those K DATA chunks in a single packet.  When a Fast Retransmit is
    being performed, the sender SHOULD ignore the value of cwnd and
    SHOULD NOT delay retransmission for this single packet.
 4) Restart T3-rtx timer only if the last SACK acknowledged the lowest
    outstanding TSN number sent to that address, or the endpoint is
    retransmitting the first outstanding DATA chunk sent to that
    address.
 5) Mark the DATA chunk(s) as being fast retransmitted and thus
    ineligible for a subsequent fast retransmit.  Those TSNs marked
    for retransmission due to the Fast Retransmit algorithm that
    did not fit in the sent datagram carrying K other TSNs are also
    marked as ineligible for a subsequent fast retransmit.  However,
    as they are marked for retransmission they will be retransmitted
    later on as soon as cwnd allows.
 6) If not in Fast Recovery, enter Fast Recovery and mark the highest
    outstanding TSN as the Fast Recovery exit point.  When a SACK
    acknowledges all TSNs up to and including this exit point, Fast
    Recovery is exited.  While in Fast Recovery, the ssthresh and cwnd
    SHOULD NOT change for any destinations due to a subsequent Fast
    Recovery event (i.e., one SHOULD NOT reduce the cwnd further due
    to a subsequent fast retransmit).
 Note: Before the above adjustments, if the received SACK also
 acknowledges new DATA chunks and advances the Cumulative TSN Ack
 Point, the cwnd adjustment rules defined in Sections 7.2.1 and 7.2.2
 must be applied first.

2.8.3. Solution Description

 The effect of the above wording changes are as follows:

Stewart, et al. Informational [Page 23] RFC 4460 SCTP Errata April 2006

 o  It requires with a MUST the sending of GAP Ack blocks instead of
    the current RFC 2960 [5] SHOULD.
 o  It allows a TSN being Fast Retransmitted (FR) to be sent only once
    via FR.
 o  It ends the delay in waiting for the flight size to drop when a
    TSN is identified as being ready to FR.
 o  It changes the way chunks are marked during fast retransmit, so
    that only new reports are counted.
 o  It introduces a Fast Recovery period to avoid multiple congestion
    window reductions when there are multiple losses in a single RTT
    (as shown by Caro et al. [3]).
 These changes will effectively allow SCTP to follow a similar model
 as TCP+SACK in the handling of Fast Retransmit.

2.9. Missing Statement about partial_bytes_acked Update

2.9.1. Description of the Problem

 SCTP uses four control variables to regulate its transmission rate:
 rwnd, cwnd, ssthresh, and partial_bytes_acked.  Upon detection of
 packet losses from SACK, or when the T3-rtx timer expires on an
 address, cwnd and ssthresh should be updated as stated in Section
 7.2.3.  However, that section should also clarify that
 partial_bytes_acked must be updated as well; it has to be reset to 0.

2.9.2. Text Changes to the Document

  1. ——–

Old text: (Section 7.2.3)

  1. ——–
 7.2.3 Congestion Control
 Upon detection of packet losses from SACK  (see Section 7.2.4), An
 endpoint should do the following:
    ssthresh = max(cwnd/2, 2*MTU)
    cwnd = ssthresh
 Basically, a packet loss causes cwnd to be cut in half.
 When the T3-rtx timer expires on an address, SCTP should perform slow
 start by:

Stewart, et al. Informational [Page 24] RFC 4460 SCTP Errata April 2006

    ssthresh = max(cwnd/2, 2*MTU)
    cwnd = 1*MTU
  1. ——–

New text: (Section 7.2.3)

  1. ——–
 7.2.3.  Congestion Control
 Upon detection of packet losses from SACK (see Section 7.2.4), an
 endpoint should do the following if not in Fast Recovery:
    ssthresh = max(cwnd/2, 2*MTU)
    cwnd = ssthresh
    partial_bytes_acked = 0
 Basically, a packet loss causes cwnd to be cut in half.
 When the T3-rtx timer expires on an address, SCTP should perform slow
 start by
    ssthresh = max(cwnd/2, 2*MTU)
    cwnd = 1*MTU
    partial_bytes_acked = 0

2.9.3. Solution Description

 The missing text added solves the doubts about what to do with
 partial_bytes_acked in the situations stated in Section 7.2.3, making
 clear that, along with ssthresh and cwnd, partial_bytes_acked should
 also be updated by being reset to 0.

2.10. Issues with Heartbeating and Failure Detection

2.10.1. Description of the Problem

 Five basic problems have been discovered with the current heartbeat
 procedures:
 o  The current specification does not specify that you should count a
    failed heartbeat as an error against the overall association.
 o  The current specification is not specific as to when you start
    sending heartbeats and when you should stop.
 o  The current specification is not specific as to when you should
    respond to heartbeats.

Stewart, et al. Informational [Page 25] RFC 4460 SCTP Errata April 2006

 o  When responding to a Heartbeat, it is unclear what to do if more
    than a single TLV is present.
 o  The jitter applied to a heartbeat was meant to be a small variance
    of the RTO and is currently a wide variance, due to the default
    delay time and incorrect wording within the RFC.

2.10.2. Text Changes to the Document

  1. ——–

Old text: (Section 8.1)

  1. ——–
 8.1 Endpoint Failure Detection
 An endpoint shall keep a counter on the total number of consecutive
 retransmissions to its peer (including retransmissions to all the
 destination transport addresses of the peer if it is multi-homed).
 If the value of this counter exceeds the limit indicated in the
 protocol parameter 'Association.Max.Retrans', the endpoint shall
 consider the peer endpoint unreachable and shall stop transmitting
 any more data to it (and thus the association enters the CLOSED
 state).  In addition, the endpoint shall report the failure to the
 upper layer, and optionally report back all outstanding user data
 remaining in its outbound queue.  The association is automatically
 closed when the peer endpoint becomes unreachable.
 The counter shall be reset each time a DATA chunk sent to that peer
 endpoint is acknowledged (by the reception of a SACK), or a
 HEARTBEAT-ACK is received from the peer endpoint.

Stewart, et al. Informational [Page 26] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 8.1)

  1. ——–
 8.1.  Endpoint Failure Detection
 An endpoint shall keep a counter on the total number of consecutive
 retransmissions to its peer (this includes retransmissions to all the
 destination transport addresses of the peer if it is multi-homed),
 including unacknowledged HEARTBEAT Chunks.  If the value of this
 counter exceeds the limit indicated in the protocol parameter
 'Association.Max.Retrans', the endpoint shall consider the peer
 endpoint unreachable and shall stop transmitting any more data to it
 (and thus the association enters the CLOSED state).  In addition, the
 endpoint MAY report the failure to the upper layer and optionally
 report back all outstanding user data remaining in its outbound
 queue.  The association is automatically closed when the peer
 endpoint becomes unreachable.
 The counter shall be reset each time a DATA chunk sent to that peer
 endpoint is acknowledged (by the reception of a SACK), or a
 HEARTBEAT-ACK is received from the peer endpoint.
  1. ——–

Old text: (Section 8.3)

  1. ——–
 8.3 Path Heartbeat
 By default, an SCTP endpoint shall monitor the reachability of the
 idle destination transport address(es) of its peer by sending a
 HEARTBEAT chunk periodically to the destination transport
 address(es).
  1. ——–

New text: (Section 8.3)

  1. ——–
 8.3 Path Heartbeat
 By default, an SCTP endpoint SHOULD monitor the reachability of the
 idle destination transport address(es) of its peer by sending a
 HEARTBEAT chunk periodically to the destination transport
 address(es).  HEARTBEAT sending MAY begin upon reaching the
 ESTABLISHED state and is discontinued after sending either SHUTDOWN
 or SHUTDOWN-ACK.  A receiver of a HEARTBEAT MUST respond to a
 HEARTBEAT with a HEARTBEAT-ACK after entering the COOKIE-ECHOED state

Stewart, et al. Informational [Page 27] RFC 4460 SCTP Errata April 2006

 (INIT sender) or the ESTABLISHED state (INIT receiver), up until
 reaching the SHUTDOWN-SENT state (SHUTDOWN sender) or the SHUTDOWN-
 ACK-SENT state (SHUTDOWN receiver).
  1. ——–

Old text: (Section 8.3)

  1. ——–
 The receiver of the HEARTBEAT should immediately respond with a
 HEARTBEAT ACK that contains the Heartbeat Information field copied
 from the received HEARTBEAT chunk.
  1. ——–

New text: (Section 8.3)

  1. ——–
 The receiver of the HEARTBEAT should immediately respond with a
 HEARTBEAT ACK that contains the Heartbeat Information TLV, together
 with any other received TLVs, copied unchanged from the received
 HEARTBEAT chunk.
  1. ——–

Old text: (Section 8.3)

  1. ——–
 On an idle destination address that is allowed to heartbeat, a
 HEARTBEAT chunk is RECOMMENDED to be sent once per RTO of that
 destination address plus the protocol parameter 'HB.interval' , with
 jittering of +/- 50%, and exponential back-off of the RTO if the
 previous HEARTBEAT is unanswered.
  1. ——–

New text: (Section 8.3)

  1. ——–
 On an idle destination address that is allowed to heartbeat, it is
 recommended that a HEARTBEAT chunk is sent once per RTO of that
 destination address plus the protocol parameter 'HB.interval', with
 jittering of +/- 50% of the RTO value, and exponential back-off of
 the RTO if the previous HEARTBEAT is unanswered.

2.10.3. Solution Description

 The above text provides guidance as to how to respond to the five
 issues mentioned in Section 2.10.1.  In particular, the wording
 changes provide guidance as to when to start and stop heartbeating,

Stewart, et al. Informational [Page 28] RFC 4460 SCTP Errata April 2006

 how to respond to a heartbeat with extra parameters, and it clarifies
 the error counting procedures for the association.

2.11. Security interactions with firewalls

2.11.1. Description of the Problem

 When dealing with firewalls, it is advantageous for the firewall to
 be able to properly determine the initial startup sequence of a
 reliable transport protocol.  With this in mind, the following text
 is to be added to SCTP's security section.

2.11.2. Text Changes to the Document

  1. ——–

New text: (no old text, new section added)

  1. ——–
 11.4 SCTP Interactions with Firewalls
 It is helpful for some firewalls if they can inspect
 just the first fragment of a fragmented SCTP packet and unambiguously
 determine whether it corresponds to an INIT chunk (for further
 information, please refer to RFC1858).  Accordingly, we
 stress the requirements, stated in 3.1, that (1) an INIT chunk MUST
 NOT be bundled with any other chunk in a packet, and (2) a packet
 containing an INIT chunk MUST have a zero Verification Tag.
 Furthermore, we require that the receiver of an INIT chunk MUST
 enforce these rules by silently discarding an arriving packet with an
 INIT chunk that is bundled with other chunks.
  1. ——–

Old text: (Section 18)

  1. ——–
 18.  Bibliography
 [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End
            Network Path Properties", Proc. SIGCOMM'99, 1999.
 [FALL96]   Fall, K. and Floyd, S., Simulation-based Comparisons of
            Tahoe, Reno, and SACK TCP, Computer Communications Review,
            V. 26 N. 3, July 1996, pp. 5-21.
 [RFC1750]  Eastlake, D. (ed.), "Randomness Recommendations for
            Security", RFC 1750, December 1994.

Stewart, et al. Informational [Page 29] RFC 4460 SCTP Errata April 2006

 [RFC1950]  Deutsch P. and J. Gailly, "ZLIB Compressed Data Format
            Specification version 3.3", RFC 1950, May 1996.
 [RFC2104]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC: Keyed-
            Hashing for Message Authentication", RFC 2104, March 1997.
 [RFC2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
            September 1997.
 [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
            Protocol", RFC 2522, March 1999.
 [SAVAGE99] Savage, S., Cardwell, N., Wetherall, D., and Anderson, T.,
            "TCP Congestion Control with a Misbehaving Receiver", ACM
            Computer Communication Review, 29(5), October 1999.
  1. ——–

New text: (Section 18)

  1. ——–
 18.  Bibliography
 [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End
            Network Path Properties", Proc. SIGCOMM'99, 1999.
 [FALL96]   Fall, K. and Floyd, S., Simulation-based Comparisons of
            Tahoe, Reno, and SACK TCP, Computer Communications Review,
            V. 26 N. 3, July 1996, pp.  5-21.
 [RFC1750]  Eastlake, D. (ed.), "Randomness Recommendations for
            Security", RFC 1750, December 1994.
 [RFC1858]  Ziemba, G., Reed, D. and Traina P., "Security
            Considerations for IP Fragment Filtering", RFC 1858,
            October 1995.
 [RFC1950]  Deutsch P. and J. Gailly, "ZLIB Compressed Data Format
            Specification version 3.3", RFC 1950, May 1996.
 [RFC2104]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:  Keyed-
            Hashing for Message Authentication", RFC 2104, March 1997.
 [RFC2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
            September 1997.
 [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
            Protocol", RFC 2522, March 1999.

Stewart, et al. Informational [Page 30] RFC 4460 SCTP Errata April 2006

 [SAVAGE99] Savage, S., Cardwell, N., Wetherall, D., and Anderson, T.,
            "TCP Congestion Control with a Misbehaving Receiver", ACM
            Computer Communication Review, 29(5), October 1999.

2.11.3. Solution Description

 The above text, which adds a new subsection to the Security
 Considerations section of RFC 2960 [5] makes clear that, to make
 easier the interaction with firewalls, an INIT chunk must not be
 bundled in any case with any other chunk that will silently discard
 the packets that do not follow this rule (this rule is enforced by
 the packet receiver).

2.12. Shutdown Ambiguity

2.12.1. Description of the Problem

 Currently, there is an ambiguity between the statements in Sections
 6.2 and 9.2.  Section 6.2 allows the sending of a SHUTDOWN chunk in
 place of a SACK when the sender is in the process of shutting down,
 while section 9.2 requires that both a SHUTDOWN chunk and a SACK
 chunk be sent.
 Along with this ambiguity there is a problem wherein an errant
 SHUTDOWN receiver may fail to stop accepting user data.

2.12.2. Text Changes to the Document

  1. ——–

Old text: (Section 9.2)

  1. ——–
 If there are still outstanding DATA chunks left, the SHUTDOWN
 receiver shall continue to follow normal data transmission procedures
 defined in Section 6 until all outstanding DATA chunks are
 acknowledged; however, the SHUTDOWN receiver MUST NOT accept new data
 from its SCTP user.
 While in SHUTDOWN-SENT state, the SHUTDOWN sender MUST immediately
 respond to each received packet containing one or more DATA chunk(s)
 with a SACK, a SHUTDOWN chunk, and restart the T2-shutdown timer.  If
 it has no more outstanding DATA chunks, the SHUTDOWN receiver shall
 send a SHUTDOWN ACK and start a T2-shutdown timer of its own,
 entering the SHUTDOWN-ACK-SENT state.  If the timer expires, the
 endpoint must re-send the SHUTDOWN ACK.

Stewart, et al. Informational [Page 31] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 9.2)

  1. ——–
 If there are still outstanding DATA chunks left, the SHUTDOWN
 receiver MUST continue to follow normal data transmission procedures
 defined in Section 6, until all outstanding DATA chunks are
 acknowledged; however, the SHUTDOWN receiver MUST NOT accept new data
 from its SCTP user.
 While in SHUTDOWN-SENT state, the SHUTDOWN sender MUST immediately
 respond to each received packet containing one or more DATA chunks
 with a SHUTDOWN chunk and restart the T2-shutdown timer.  If a
 SHUTDOWN chunk by itself cannot acknowledge all of the received DATA
 chunks (i.e., there are TSNs that can be acknowledged that are larger
 than the cumulative TSN, and thus gaps exist in the TSN sequence), or
 if duplicate TSNs have been received, then a SACK chunk MUST also be
 sent.
 The sender of the SHUTDOWN MAY also start an overall guard timer
 'T5-shutdown-guard' to bound the overall time for shutdown sequence.
 At the expiration of this timer, the sender SHOULD abort the
 association by sending an ABORT chunk.  If the 'T5-shutdown-guard'
 timer is used, it SHOULD be set to the recommended value of 5 times
 'RTO.Max'.
 If the receiver of the SHUTDOWN has no more outstanding DATA chunks,
 the SHUTDOWN receiver MUST send a SHUTDOWN ACK and start a
 T2-shutdown timer of its own, entering the SHUTDOWN-ACK-SENT state.
 If the timer expires, the endpoint must re-send the SHUTDOWN ACK.

2.12.3. Solution Description

 The above text clarifies the use of a SACK in conjunction with a
 SHUTDOWN chunk.  It also adds a guard timer to the SCTP shutdown
 sequence to protect against errant receivers of SHUTDOWN chunks.

2.13. Inconsistency in ABORT Processing

2.13.1. Description of the Problem

 It was noted that the wording in Section 8.5.1 did not give proper
 directions in the use of the 'T bit' with the Verification Tags.

Stewart, et al. Informational [Page 32] RFC 4460 SCTP Errata April 2006

2.13.2. Text changes to the document

  1. ——–

Old text: (Section 8.5.1)

  1. ——–
 B) Rules for packet carrying ABORT:
  1. The endpoint shall always fill in the Verification Tag field

of the outbound packet with the destination endpoint's tag

       value if it is known.
  1. If the ABORT is sent in response to an OOTB packet, the

endpoint MUST follow the procedure described in Section 8.4.

  1. The receiver MUST accept the packet if the Verification Tag

matches either its own tag, OR the tag of its peer. Otherwise,

       the receiver MUST silently discard the packet and take no
       further action.
  1. ——–

New text: (Section 8.5.1)

  1. ——–
 B) Rules for packet carrying ABORT:
  1. The endpoint MUST always fill in the Verification Tag field of

the outbound packet with the destination endpoint's tag value,

       if it is known.
  1. If the ABORT is sent in response to an OOTB packet, the

endpoint MUST follow the procedure described in Section 8.4.

  1. The receiver of a ABORT MUST accept the packet if the

Verification Tag field of the packet matches its own tag OR if

       it is set to its peer's tag and the T bit is set in the Chunk
       Flags.  Otherwise, the receiver MUST silently discard the
       packet and take no further action.

2.13.3. Solution Description

 The above text change clarifies that the T bit must be set before an
 implementation looks for the peer's tag.

Stewart, et al. Informational [Page 33] RFC 4460 SCTP Errata April 2006

2.14. Cwnd Gated by Its Full Use

2.14.1. Description of the Problem

 A problem was found with the current specification of the growth and
 decay of cwnd.  The cwnd should only be increased if it is being
 fully utilized, and after periods of underutilization, the cwnd
 should be decreased.  In some sections, the current wording is weak
 and is not clearly defined.  Also, the current specification
 unnecessarily introduces the need for special case code to ensure
 cwnd degradation.  Plus, the cwnd should not be increased during Fast
 Recovery, since a full cwnd during Fast Recovery does not qualify the
 cwnd as being fully utilized.  Additionally, multiple loss scenarios
 in a single window may cause the cwnd to grow more rapidly as the
 number of losses in a window increases [3].

2.14.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.1)

  1. ——–
 D) Then, the sender can send out as many new DATA chunks as Rule A
    and Rule B above allow.
  1. ——–

New text: (Section 6.1)

  1. ——–
 D) When the time comes for the sender to transmit new DATA chunks,
    the protocol parameter Max.Burst SHOULD be used to limit the
    number of packets sent.  The limit MAY be applied by adjusting
    cwnd as follows:
    if((flightsize + Max.Burst*MTU) < cwnd)
       cwnd = flightsize + Max.Burst*MTU
    Or it MAY be applied by strictly limiting the number of packets
    emitted by the output routine.
 E) Then, the sender can send out as many new DATA chunks as Rule A
    and Rule B allow.

Stewart, et al. Informational [Page 34] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 7.2.1)

  1. ——–
 o  When cwnd is less than or equal to ssthresh an SCTP endpoint MUST
    use the slow start algorithm to increase cwnd (assuming the
    current congestion window is being fully utilized).  If an
    incoming SACK advances the Cumulative TSN Ack Point, cwnd MUST be
    increased by at most the lesser of 1) the total size of the
    previously outstanding DATA chunk(s) acknowledged, and 2) the
    destination's path MTU.  This protects against the ACK-Splitting
    attack outlined in [SAVAGE99].
  1. ——–

New text: (Section 7.2.1)

  1. ——–
 o  When cwnd is less than or equal to ssthresh, an SCTP endpoint MUST
    use the slow start algorithm to increase cwnd only if the current
    congestion window is being fully utilized, an incoming SACK
    advances the Cumulative TSN Ack Point, and the data sender is not
    in Fast Recovery.  Only when these three conditions are met can
    the cwnd be increased; otherwise, the cwnd MUST not be increased.
    If these conditions are met, then cwnd MUST be increased by, at
    most, the lesser of 1) the total size of the previously
    outstanding DATA chunk(s) acknowledged, and 2) the destination's
    path MTU.  This upper bound protects against the ACK-Splitting
    attack outlined in [SAVAGE99].
  1. ——–

Old text: (Section 14)

  1. ——–
 14.  Suggested SCTP Protocol Parameter Values
 The following protocol parameters are RECOMMENDED:
 RTO.Initial              - 3  seconds
 RTO.Min                  - 1  second
 RTO.Max                 -  60 seconds
 RTO.Alpha                - 1/8
 RTO.Beta                 - 1/4
 Valid.Cookie.Life        - 60  seconds
 Association.Max.Retrans  - 10 attempts
 Path.Max.Retrans         - 5  attempts (per destination address)
 Max.Init.Retransmits     - 8  attempts
 HB.interval              - 30 seconds

Stewart, et al. Informational [Page 35] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 14)

  1. ——–
 14.  Suggested SCTP Protocol Parameter Values
 The following protocol parameters are RECOMMENDED:
 RTO.Initial              - 3  seconds
 RTO.Min                  - 1  second
 RTO.Max                  - 60 seconds
 Max.Burst                - 4
 RTO.Alpha                - 1/8
 RTO.Beta                 - 1/4
 Valid.Cookie.Life        - 60 seconds
 Association.Max.Retrans  - 10 attempts
 Path.Max.Retrans         - 5  attempts (per destination address)
 Max.Init.Retransmits     - 8  attempts
 HB.Interval              - 30 seconds

2.14.3. Solution Description

 The above changes strengthen the rules and make it much more apparent
 as to the need to block cwnd growth when the full cwnd is not being
 utilized.  The changes also apply cwnd degradation without
 introducing the need for complex special case code.

2.15. Window Probes in SCTP

2.15.1. Description of the Problem

 When a receiver clamps its rwnd to 0 to flow control the peer, the
 specification implies that one must continue to accept data from the
 remote peer.  This is incorrect and needs clarification.

2.15.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.2)

  1. ——–
 The SCTP endpoint MUST always acknowledge the receipt of each valid
 DATA chunk.

Stewart, et al. Informational [Page 36] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 6.2)

  1. ——–
 The SCTP endpoint MUST always acknowledge the reception of each valid
 DATA chunk when the DATA chunk received is inside its receive window.
 When the receiver's advertised window is 0, the receiver MUST drop
 any new incoming DATA chunk with a TSN larger than the largest TSN
 received so far.  If the new incoming DATA chunk holds a TSN value
 less than the largest TSN received so far, then the receiver SHOULD
 drop the largest TSN held for reordering and accept the new incoming
 DATA chunk.  In either case, if such a DATA chunk is dropped, the
 receiver MUST immediately send back a SACK with the current receive
 window showing only DATA chunks received and accepted so far.  The
 dropped DATA chunk(s) MUST NOT be included in the SACK, as they were
 not accepted.  The receiver MUST also have an algorithm for
 advertising its receive window to avoid receiver silly window
 syndrome (SWS), as described in RFC 813.  The algorithm can be
 similar to the one described in Section 4.2.3.3 of RFC 1122.
  1. ——–

Old text: (Section 6.1)

  1. ——–
 A) At any given time, the data sender MUST NOT transmit new data to
    any destination transport address if its peer's rwnd indicates
    that the peer has no buffer space (i.e., rwnd is 0, see Section
    6.2.1).  However, regardless of the value of rwnd (including if it
    is 0), the data sender can always have one DATA chunk in flight to
    the receiver if allowed by cwnd (see rule B below).  This rule
    allows the sender to probe for a change in rwnd that the sender
    missed due to the SACK having been lost in transit from the data
    receiver to the data sender.

Stewart, et al. Informational [Page 37] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 6.1)

  1. ——–
 A) At any given time, the data sender MUST NOT transmit new data to
    any destination transport address if its peer's rwnd indicates
    that the peer has no buffer space (i.e., rwnd is 0; see Section
    6.2.1).  However, regardless of the value of rwnd (including if it
    is 0), the data sender can always have one DATA chunk in flight to
    the receiver if allowed by cwnd (see rule B, below).  This rule
    allows the sender to probe for a change in rwnd that the sender
    missed due to the SACK's having been lost in transit from the data
    receiver to the data sender.
    When the receiver's advertised window is zero, this probe is
    called a zero window probe.  Note that a zero window probe
    SHOULD only be sent when all outstanding DATA chunks have
    been cumulatively acknowledged and no DATA chunks are in
    flight.  Zero window probing MUST be supported.
    If the sender continues to receive new packets from the receiver
    while doing zero window probing, the unacknowledged window probes
    should not increment the error counter for the association or any
    destination transport address.This is because the receiver MAY
    keep its window closed for an indefinite time.  Refer to
    Section 6.2 on the receiver behavior when it advertises a zero
    window.  The sender SHOULD send the first zero window probe after
    1 RTO when it detects that the receiver has closed its window
    and SHOULD increase the probe interval exponentially afterwards.
    Also note that the cwnd SHOULD be adjusted according to
    Section 7.2.1.  Zero window probing does not affect the
    calculation of cwnd.
    The sender MUST also have an algorithm for sending new DATA chunks
    to avoid silly window syndrome (SWS) as described in RFC 813.  The
    algorithm can be similar to the one described in Section 4.2.3.4
    of RFC 1122.

2.15.3. Solution Description

 The above allows a receiver to drop new data that arrives and yet
 still requires the receiver to send a SACK showing the conditions
 unchanged (with the possible exception of a new a_rwnd) and the
 dropped chunk as missing.  This will allow the association to
 continue until the rwnd condition clears.

Stewart, et al. Informational [Page 38] RFC 4460 SCTP Errata April 2006

2.16. Fragmentation and Path MTU Issues

2.16.1. Description of the Problem

 The current wording of the Fragmentation and Reassembly forces an
 implementation that supports fragmentation to always fragment.  This
 prohibits an implementation from offering its users an option to
 disable sends that exceed the SCTP fragmentation point.
 The restriction in RFC 2960 [5], Section 6.9, was never meant to
 restrict an implementations API from this behavior.

2.16.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.1)

  1. ——–
 6.9 Fragmentation and Reassembly
 An endpoint MAY support fragmentation when sending DATA chunks, but
 MUST support reassembly when receiving DATA chunks.  If an endpoint
 supports fragmentation, it MUST fragment a user message if the size
 of the user message to be sent causes the outbound SCTP packet size
 to exceed the current MTU.  If an implementation does not support
 fragmentation of outbound user messages, the endpoint must return an
 error to its upper layer and not attempt to send the user message.
 IMPLEMENTATION NOTE:  In this error case, the Send primitive
 discussed in Section 10.1 would need to return an error to the upper
 layer.
  1. ——–

New text: (Section 6.1)

  1. ——–
 6.9.  Fragmentation and Reassembly
 An endpoint MAY support fragmentation when sending DATA chunks, but
 it MUST support reassembly when receiving DATA chunks.  If an
 endpoint supports fragmentation, it MUST fragment a user message if
 the size of the user message to be sent causes the outbound SCTP
 packet size to exceed the current MTU.  If an implementation does not
 support fragmentation of outbound user messages, the endpoint MUST
 return an error to its upper layer and not attempt to send the user
 message.

Stewart, et al. Informational [Page 39] RFC 4460 SCTP Errata April 2006

 Note: If an implementation that supports fragmentation makes
 available to its upper layer a mechanism to turn off fragmentation it
 may do so.  However, in so doing, it MUST react just like an
 implementation that does NOT support fragmentation, i.e., it MUST
 reject sends that exceed the current P-MTU.
 IMPLEMENTATION NOTE:  In this error case, the Send primitive
 discussed in Section 10.1 would need to return an error to the upper
 layer.

2.16.3. Solution Description

 The above wording will allow an implementation to offer the option of
 rejecting sends that exceed the P-MTU size even when the
 implementation supports fragmentation.

2.17. Initial Value of the Cumulative TSN Ack

2.17.1. Description of the Problem

 The current description of the SACK chunk within the RFC does not
 clearly state the value that would be put within a SACK when no DATA
 chunk has been received.

2.17.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.4)

  1. ——–
 Cumulative TSN Ack: 32 bits (unsigned integer)
    This parameter contains the TSN of the last DATA chunk received in
    sequence before a gap.
  1. ——–

New text: (Section 3.3.4)

  1. ——–
 Cumulative TSN Ack: 32 bits (unsigned integer)
    This parameter contains the TSN of the last DATA chunk received in
    sequence before a gap.  In the case where no DATA chunk has
    been received, this value is set to the peer's Initial TSN minus
    one.

Stewart, et al. Informational [Page 40] RFC 4460 SCTP Errata April 2006

2.17.3. Solution Description

 This change clearly states what the initial value will be for a SACK
 sender.

2.18. Handling of Address Parameters within the INIT or INIT-ACK

2.18.1. Description of the Problem

 The current description on handling address parameters contained
 within the INIT and INIT-ACK does not fully describe a requirement
 for their handling.

2.18.2. Text Changes to the Document

  1. ——–

Old text: (Section 5.1.2)

  1. ——–
 C) If there are only IPv4/IPv6 addresses present in the received INIT
    or INIT ACK chunk, the receiver shall derive and record all the
    transport address(es) from the received chunk AND the source IP
    address that sent the INIT or INIT ACK.  The transport address(es)
    are derived by the combination of SCTP source port (from the
    common header) and the IP address parameter(s) carried in the INIT
    or INIT ACK chunk and the source IP address of the IP datagram.
    The receiver should use only these transport addresses as
    destination transport addresses when sending subsequent packets to
    its peer.
  1. ——–

New text: (Section 5.1.2)

  1. ——–
 C) If there are only IPv4/IPv6 addresses present in the received INIT
    or INIT ACK chunk, the receiver MUST derive and record all the
    transport addresses from the received chunk AND the source IP
    address that sent the INIT or INIT ACK.  The transport addresses
    are derived by the combination of SCTP source port (from the
    common header) and the IP address parameter(s) carried in the INIT
    or INIT ACK chunk and the source IP address of the IP datagram.
    The receiver should use only these transport addresses as
    destination transport addresses when sending subsequent packets to
    its peer.

Stewart, et al. Informational [Page 41] RFC 4460 SCTP Errata April 2006

 D) An INIT or INIT ACK chunk MUST be treated as belonging
    to an already established association (or one in the
    process of being established) if the use of any of the
    valid address parameters contained within the chunk
    would identify an existing TCB.

2.18.3. Solution description

 This new text clearly specifies to an implementor the need to look
 within the INIT or INIT ACK.  Any implementation that does not do
 this may (for example) not be able to recognize an INIT chunk coming
 from an already established association that adds new addresses (see
 Section 2.6) or an incoming INIT ACK chunk sent from a source address
 different from the destination address used to send the INIT chunk.

2.19. Handling of Stream Shortages

2.19.1. Description of the Problem

 The current wording in the RFC places the choice of sending an ABORT
 upon the SCTP stack when a stream shortage occurs.  This decision
 should really be made by the upper layer, not the SCTP stack.

2.19.2. Text Changes to the Document

  1. ——–

Old text:

  1. ——–
 5.1.1 Handle Stream Parameters
 In the INIT and INIT ACK chunks, the sender of the chunk shall
 indicate the number of outbound streams (OS) it wishes to have in
 the association, as well as the maximum inbound streams (MIS) it
 will accept from the other endpoint.
 After receiving the stream configuration information from the other
 side, each endpoint shall perform the following check:  If the peer's
 MIS is less than the endpoint's OS, meaning that the peer is
 incapable of supporting all the outbound streams the endpoint wants
 to configure, the endpoint MUST either use MIS outbound streams, or
 abort the association and report to its upper layer the resources
 shortage at its peer.

Stewart, et al. Informational [Page 42] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 5.1.2)

  1. ——–
 5.1.1.  Handle Stream Parameters
 In the INIT and INIT ACK chunks, the sender of the chunk MUST
 indicate the number of outbound streams (OS) it wishes to have in
 the association, as well as the maximum inbound streams (MIS) it will
 accept from the other endpoint.
 After receiving the stream configuration information from the other
 side, each endpoint MUST perform the following check:  If the peer's
 MIS is less than the endpoint's OS, meaning that the peer is
 incapable of supporting all the outbound streams the endpoint wants
 to configure, the endpoint MUST use MIS outbound streams and MAY
 report any shortage to the upper layer.  The upper layer can then
 choose to abort the association if the resource shortage
 is unacceptable.

2.19.3. Solution Description

 The above changes take the decision to ABORT out of the realm of the
 SCTP stack and place it into the user's hands.

2.20. Indefinite Postponement

2.20.1. Description of the Problem

 The current RFC does not provide any guidance on the assignment of
 TSN sequence numbers to outbound messages nor reception of these
 messages.  This could lead to a possible indefinite postponement.

2.20.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.1)

  1. ——–
 Note: The data sender SHOULD NOT use a TSN that is more than 2**31 -
 1 above the beginning TSN of the current send window.
 6.2  Acknowledgement on Reception of DATA Chunks

Stewart, et al. Informational [Page 43] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 6.1)

  1. ——–
 Note: The data sender SHOULD NOT use a TSN that is more than 2**31 -
 1 above the beginning TSN of the current send window.
 The algorithm by which an implementation assigns sequential TSNs to
 messages on a particular association MUST ensure that no user
 message that has been accepted by SCTP is indefinitely postponed
 from being assigned a TSN.  Acceptable algorithms for assigning TSNs
 include
 (a) assigning TSNs in round-robin order over all streams with
     pending data; and
 (b) preserving the linear order in which the user messages were
     submitted to the SCTP association.
 When an upper layer requests to read data on an SCTP association,
 the SCTP receiver SHOULD choose the message with the lowest TSN from
 among all deliverable messages.  In SCTP implementations that allow a
 user to request data on a specific stream, this operation SHOULD NOT
 block if data is not available, since this can lead to a deadlock
 under certain conditions.
 6.2.  Acknowledgement on Receipt of DATA Chunks

2.20.3. Solution Description

 The above wording clarifies how TSNs SHOULD be assigned by the
 sender.

2.21. User-Initiated Abort of an Association

2.21.1. Description of the Problem

 It is not possible for an upper layer to abort the association and
 provide the peer with an indication of why the association is
 aborted.

2.21.2. Text changes to the document

 Some of the changes given here already include changes suggested in
 Section 2.6 of this document.

Stewart, et al. Informational [Page 44] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.10 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.

Stewart, et al. Informational [Page 45] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
    11              Restart of an Association with New Addresses
    12              User-Initiated Abort
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.12 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.
  1. ——–

New text: (Note: no old text, new error added in Section 3.3.10)

  1. ——–
 3.3.10.12.  User-Initiated Abort (12)
  Cause of error
  --------------
  This error cause MAY be included in ABORT chunks that are sent
  because of an upper layer request.  The upper layer can specify
  an Upper Layer Abort Reason that is transported by SCTP
  transparently and MAY be delivered to the upper layer protocol
  at the peer.

Stewart, et al. Informational [Page 46] RFC 4460 SCTP Errata April 2006

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Cause Code=12         |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /                    Upper Layer Abort Reason                   /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
  1. ——–

Old text: (Section 9.1)

  1. ——–
 9.1 Abort of an Association
    When an endpoint decides to abort an existing association, it
    shall send an ABORT chunk to its peer endpoint.  The sender MUST
    fill in the peer's Verification Tag in the outbound packet and
    MUST NOT bundle any DATA chunk with the ABORT.
    An endpoint MUST NOT respond to any received packet that contains
    an ABORT chunk (also see Section 8.4).
    An endpoint receiving an ABORT shall apply the special
    Verification Tag check rules described in Section 8.5.1.
    After checking the Verification Tag, the receiving endpoint shall
    remove the association from its record and shall report the
    termination to its upper layer.
  1. ——–

New text: (Section 9.1)

  1. ——–
    9.1.  Abort of an Association
    When an endpoint decides to abort an existing association, it MUST
    send an ABORT chunk to its peer endpoint.  The sender MUST fill in
    the peer's Verification Tag in the outbound packet and MUST NOT
    bundle any DATA chunk with the ABORT.  If the association is
    aborted on request of the upper layer, a User-Initiated Abort
    error cause (see 3.3.10.12) SHOULD be present in the ABORT chunk.
    An endpoint MUST NOT respond to any received packet that contains
    an ABORT chunk (also see Section 8.4).
    An endpoint receiving an ABORT MUST apply the special Verification
    Tag check rules described in Section 8.5.1.
    After checking the Verification Tag, the receiving endpoint MUST

Stewart, et al. Informational [Page 47] RFC 4460 SCTP Errata April 2006

    remove the association from its record and SHOULD report the
    termination to its upper layer.  If a User-Initiated Abort error
    cause is present in the ABORT chunk, the Upper Layer Abort Reason
    SHOULD be made available to the upper layer.
  1. ——–

Old text: (Section 10.1)

  1. ——–
    D) Abort
    Format: ABORT(association id [, cause code])
    -> result
    Ungracefully closes an association.  Any locally queued user
    data will be discarded and an ABORT chunk is sent to the peer.
    A success code will be returned on successful abortion of the
    association.  If attempting to abort the association results
    in a failure, an error code shall be returned.
    Mandatory attributes:
    o  association id - local handle to the SCTP association
    Optional attributes:
    o  cause code - reason of the abort to be passed to the peer.
  1. ——–

New text: (Section 10.1)

  1. ——–
    D) Abort
    Format: ABORT(association id [, Upper Layer Abort Reason])
    -> result
    Ungracefully closes an association.  Any locally queued user
    data will be discarded, and an ABORT chunk is sent to the peer.
    A success code will be returned on successful abortion of the
    association.  If attempting to abort the association results
    in a failure, an error code shall be returned.
    Mandatory attributes:
    o  association id - Local handle to the SCTP association.

Stewart, et al. Informational [Page 48] RFC 4460 SCTP Errata April 2006

    Optional attributes:
    o  Upper Layer Abort Reason - Reason of the abort to be passed
       to the peer.
    None.
  1. ——–

Old text: (Section 10.2)

  1. ——–
    E) COMMUNICATION LOST notification
    When SCTP loses communication to an endpoint completely (e.g., via
    Heartbeats) or detects that the endpoint has performed an abort
    operation, it shall invoke this notification on the ULP.
    The following shall be passed with the notification:
    o  association id - local handle to the SCTP association
    o status - This indicates what type of event has occurred; The
               status may indicate a failure OR a normal termination
               event occurred in response to a shutdown or abort
               request.
    The following may be passed with the notification:
    o  data retrieval id - an identification used to retrieve
       unsent and unacknowledged data.
    o  last-acked - the TSN last acked by that peer endpoint;
    o  last-sent - the TSN last sent to that peer endpoint;
  1. ——–

New text: (Section 10.2)

  1. ——–
    E) COMMUNICATION LOST notification
    When SCTP loses communication to an endpoint completely (e.g., via
    Heartbeats) or detects that the endpoint has performed an abort
    operation, it shall invoke this notification on the ULP.
    The following shall be passed with the notification:
    o  association id - Local handle to the SCTP association.

Stewart, et al. Informational [Page 49] RFC 4460 SCTP Errata April 2006

    o  status - This indicates what type of event has occurred; The
                status may indicate that a failure OR a normal
                termination event occurred in response to a shutdown
                or abort request.
    The following may be passed with the notification:
    o  data retrieval id - An identification used to retrieve unsent
       and unacknowledged data.
    o  last-acked - The TSN last acked by that peer endpoint.
    o  last-sent - The TSN last sent to that peer endpoint.
    o  Upper Layer Abort Reason - The abort reason specified in
                                  case of a user-initiated abort.

2.21.3. Solution Description

 The above allows an upper layer to provide its peer with an
 indication of why the association was aborted.  Therefore, an
 addition error cause was introduced.

2.22. Handling of Invalid Initiate Tag of INIT-ACK

2.22.1. Description of the Problem

 RFC 2960 requires that the receiver of an INIT-ACK with the Initiate
 Tag set to zero handles this as an error and sends back an ABORT.
 But the sender of the INIT-ACK normally has no TCB, and thus the
 ABORT is useless.

2.22.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.3)

  1. ——–
    Initiate Tag: 32 bits (unsigned integer)
       The receiver of the INIT ACK records the value of the
       Initiate Tag parameter.  This value MUST be placed into
       the Verification Tag field of every SCTP packet that the
       INIT ACK receiver transmits within this association.
       The Initiate Tag MUST NOT take the value 0.  See Section 5.3.1
       for more on the selection of the Initiate Tag value.

Stewart, et al. Informational [Page 50] RFC 4460 SCTP Errata April 2006

       If the value of the Initiate Tag in a received INIT ACK chunk
       is found to be 0, the receiver MUST treat it as an error and
       close the association by transmitting an ABORT.
  1. ——–

New text: (Section 3.3.3)

  1. ——–
    Initiate Tag: 32 bits (unsigned integer)
       The receiver of the INIT ACK records the value of the
       Initiate Tag parameter.  This value MUST be placed into
       the Verification Tag field of every SCTP packet that the
       INIT ACK receiver transmits within this association.
       The Initiate Tag MUST NOT take the value 0.  See Section 5.3.1
       for more on the selection of the Initiate Tag value.
       If the value of the Initiate Tag in a received INIT ACK
       chunk is found to be 0, the receiver MUST destroy the
       association discarding its TCB.  The receiver MAY send an
       ABORT for debugging purpose.

2.22.3. Solution Description

 The new text does not require that the receiver of the invalid INIT-
 ACK send the ABORT.  This behavior is in tune with the error case of
 invalid stream numbers in the INIT-ACK.  However, sending an ABORT
 for debugging purposes is allowed.

2.23. Sending an ABORT in Response to an INIT

2.23.1. Description of the Problem

 Whenever the receiver of an INIT chunk has to send an ABORT chunk in
 response, for whatever reason, it is not stated clearly which
 Verification Tag and value of the T-bit should be used.

2.23.2. Text Changes to the Document

  1. ——–

Old text: (Section 8.4)

  1. ——–
    3) If the packet contains an INIT chunk with a Verification Tag
       set to '0', process it as described in Section 5.1.
       Otherwise,

Stewart, et al. Informational [Page 51] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 8.4)

  1. ——–
    3) If the packet contains an INIT chunk with a Verification Tag
       set to '0', process it as described in Section 5.1.  If, for
       whatever reason, the INIT cannot be processed normally and
       an ABORT has to be sent in response, the Verification Tag
       of the packet containing the ABORT chunk MUST be the
       Initiate tag of the received INIT chunk, and the T-Bit of
       the ABORT chunk has to be set to 0, indicating that
       a TCB was destroyed.  Otherwise,

2.23.3. Solution Description

 The new text stated clearly which value of the Verification Tag and
 T-bit have to be used.

2.24. Stream Sequence Number (SSN) Initialization

2.24.1. Description of the Problem

 RFC 2960 does not describe the fact that the SSN has to be
 initialized to 0, as required by RFC 2119.

2.24.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.5)

  1. ——–
    The stream sequence number in all the streams shall start from 0
    when the association is established.  Also, when the stream
    sequence number reaches the value 65535 the next stream sequence
    number shall be set to 0.
  1. ——–

New text: (Section 6.5)

  1. ——–
    The stream sequence number in all the streams MUST start from 0
    when the association is established.  Also, when the stream
    sequence number reaches the value 65535 the next stream sequence
    number MUST be set to 0.

Stewart, et al. Informational [Page 52] RFC 4460 SCTP Errata April 2006

2.24.3. Solution Description

 The 'shall' in the text is replaced by a 'MUST' to clearly state the
 required behavior.

2.25. SACK Packet Format

2.25.1. Description of the Problem

 It is not clear in RFC 2960 whether a SACK must contain the fields
 Number of Gap Ack Blocks and Number of Duplicate TSNs.

2.25.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.4)

  1. ——–
    The SACK MUST contain the Cumulative TSN Ack and
    Advertised Receiver Window Credit (a_rwnd) parameters.
  1. ——–

New text: (Section 3.3.4)

  1. ——–
    The SACK MUST contain the Cumulative TSN Ack,
    Advertised Receiver Window Credit (a_rwnd), Number
    of Gap Ack Blocks, and Number of Duplicate TSNs fields.

2.25.3. Solution Description

 The text has been modified.  It is now clear that a SACK always
 contains the fields Number of Gap Ack Blocks and Number of Duplicate
 TSNs.

2.26. Protocol Violation Error Cause

2.26.1. Description of the Problem

 There are many situations where an SCTP endpoint may detect that its
 peer violates the protocol.  The result of such detection often
 results in the association being destroyed by the sending of an
 ABORT.  Currently, there are only some error causes that could be
 used to indicate the reason for the abort, but these do not cover all
 cases.

Stewart, et al. Informational [Page 53] RFC 4460 SCTP Errata April 2006

2.26.2. Text Changes to the Document

 Some of the changes given here already include changes suggested in
 Section 2.6 and 2.21 of this document.
  1. ——–

Old text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.10 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.

Stewart, et al. Informational [Page 54] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.3.10)

  1. ——–
    Cause Code
    Value           Cause Code
    ---------      ----------------
     1              Invalid Stream Identifier
     2              Missing Mandatory Parameter
     3              Stale Cookie Error
     4              Out of Resource
     5              Unresolvable Address
     6              Unrecognized Chunk Type
     7              Invalid Mandatory Parameter
     8              Unrecognized Parameters
     9              No User Data
    10              Cookie Received While Shutting Down
    11              Restart of an Association with New Addresses
    12              User Initiated Abort
    13              Protocol Violation
 Cause Length: 16 bits (unsigned integer)
    Set to the size of the parameter in bytes, including the Cause
    Code, Cause Length, and Cause-Specific Information fields
 Cause-specific Information: variable length
    This field carries the details of the error condition.
 Sections 3.3.10.1 - 3.3.10.13 define error causes for SCTP.
 Guidelines for the IETF to define new error cause values are
 discussed in Section 13.3.
  1. ——–

New text: (Note: no old text; new error added in section 3.3.10)

  1. ——–
 3.3.10.13.  Protocol Violation (13)
  Cause of error
  --------------
  This error cause MAY be included in ABORT chunks that are sent
  because an SCTP endpoint detects a protocol violation of the peer
  that is not covered by the error causes described in 3.3.10.1 to
  3.3.10.12.  An implementation MAY provide additional information
  specifying what kind of protocol violation has been detected.

Stewart, et al. Informational [Page 55] RFC 4460 SCTP Errata April 2006

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |         Cause Code=13         |      Cause Length=Variable    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /                    Additional Information                     /
    \                                                               \
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

2.26.3. Solution Description

 An additional error cause has been defined that can be used by an
 endpoint to indicate a protocol violation of the peer.

2.27. Reporting of Unrecognized Parameters

2.27.1. Description of the Problem

 It is not stated clearly in RFC 2960 [5] how unrecognized parameters
 should be reported.  Unrecognized parameters in an INIT chunk could
 be reported in the INIT-ACK chunk or in a separate ERROR chunk, which
 can get lost.  Unrecognized parameters in an INIT-ACK chunk have to
 be reported in an ERROR-chunk.  This can be bundled with the COOKIE-
 ERROR chunk or sent separately.  If it is sent separately and
 received before the COOKIE-ECHO, it will be handled as an OOTB
 packet, resulting in sending out an ABORT chunk.  Therefore, the
 association would not be established.

2.27.2. Text Changes to the Document

 Some of the changes given here already include changes suggested in
 Section 2.2 of this document.
  1. ——–

Old text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it.
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      parameter in an 'Unrecognized Parameter Type' (in either an
      ERROR or in the INIT ACK).
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter Type' (in
      either an ERROR or in the INIT ACK).

Stewart, et al. Informational [Page 56] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP chunk and discard it; do not process
      any further parameters within this chunk.
 01 - Stop processing this SCTP chunk and discard it, do not process
      any further parameters within this chunk, and report the
      unrecognized parameter in an 'Unrecognized Parameter Type', as
      described in 3.2.2.
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter Type', as
      described in 3.2.2.
  1. ——–

New text: (Note: no old text; clarification added in Section 3.2)

  1. ——–
 3.2.2.  Reporting of Unrecognized Parameters
    If the receiver of an INIT chunk detects unrecognized parameters
    and has to report them according to Section 3.2.1, it MUST put
    the 'Unrecognized Parameter' parameter(s) in the INIT-ACK chunk
    sent in response to the INIT-chunk.  Note that if the receiver
    of the INIT chunk is NOT going to establish an association (e.g.,
    due to lack of resources), then no report would be sent back.
    If the receiver of an INIT-ACK chunk detects unrecognized
    parameters and has to report them according to Section 3.2.1,
    it SHOULD bundle the ERROR chunk containing the
    'Unrecognized Parameter' error cause with the COOKIE-ECHO
    chunk sent in response to the INIT-ACK chunk.  If the
    receiver of the INIT-ACK cannot bundle the COOKIE-ECHO chunk
    with the ERROR chunk, the ERROR chunk MAY be sent separately
    but not before the COOKIE-ACK has been received.
    Note: Any time a COOKIE-ECHO is sent in a packet, it MUST be the
    first chunk.

2.27.3. Solution Description

 The procedure of reporting unrecognized parameters has been described
 clearly.

Stewart, et al. Informational [Page 57] RFC 4460 SCTP Errata April 2006

2.28. Handling of IP Address Parameters

2.28.1. Description of the Problem

 It is not stated clearly in RFC 2960 [5] how an SCTP endpoint that
 supports either IPv4 addresses or IPv6 addresses should respond if
 IPv4 and IPv6 addresses are presented by the peer in the INIT or
 INIT-ACK chunk.

2.28.2. Text Changes to the Document

  1. ——–

Old text: (Section 5.1.2)

  1. ——–
    IMPLEMENTATION NOTE: In the case that the receiver of an INIT ACK
    fails to resolve the address parameter due to an unsupported type,
    it can abort the initiation process and then attempt a
    re-initiation by using a 'Supported Address Types' parameter in
    the new INIT to indicate what types of address it prefers.
  1. ——–

New text: (Section 5.1.2)

  1. ——–
    IMPLEMENTATION NOTE: In the case that the receiver of an INIT ACK
    fails to resolve the address parameter due to an unsupported type,
    it can abort the initiation process and then attempt a re-
    initiation by using a 'Supported Address Types' parameter in the
    new INIT to indicate what types of address it prefers.
    IMPLEMENTATION NOTE: If an SCTP endpoint that only supports either
    IPv4 or IPv6 receives IPv4 and IPv6 addresses in an INIT or INIT-
    ACK chunk from its peer, it MUST use all the addresses belonging
    to the supported address family.  The other addresses MAY be
    ignored.  The endpoint SHOULD NOT respond with any kind of error
    indication.

2.28.3. Solution Description

 The procedure of handling IP address parameters has been described
 clearly.

Stewart, et al. Informational [Page 58] RFC 4460 SCTP Errata April 2006

2.29. Handling of COOKIE ECHO Chunks When a TCB Exists

2.29.1. Description of the Problem

 The description of the behavior in RFC 2960 [5] when a COOKIE ECHO
 chunk and a TCB exist could be misunderstood.  When a COOKIE ECHO is
 received, a TCB exists and the local tag and peer's tag match, it is
 stated that the endpoint should enter the ESTABLISHED state if it has
 not already done so and send a COOKIE ACK.  It was not clear that, in
 the case the endpoint has already left the ESTABLISHED state again,
 then it should not go back to established.  In case D, the endpoint
 can only enter state ESTABLISHED from COOKIE-ECHOED because in state
 CLOSED it has no TCB and in state COOKIE-WAIT it has a TCB but knows
 nothing about the peer's tag, which is requested to match in this
 case.

2.29.2. Text Changes to the Document

  1. ——–

Old text: (Section 5.2.4)

  1. ——–

D) When both local and remote tags match the endpoint should

       always enter the ESTABLISHED state, if it has not already
       done so.  It should stop any init or cookie timers that may
       be running and send a COOKIE ACK.
  1. ——–

New text: (Section 5.2.4)

  1. ——–

D) When both local and remote tags match, the endpoint should

       enter the ESTABLISHED state, if it is in the COOKIE-ECHOED
       state.  It should stop any cookie timer that may
       be running and send a COOKIE ACK.

2.29.3. Solution Description

 The procedure of handling of COOKIE-ECHO chunks when a TCB exists has
 been described clearly.

2.30. The Initial Congestion Window Size

2.30.1. Description of the Problem

 RFC 2960 was published with the intention of having the same
 congestion control properties as TCP.  Since the publication of RFC
 2960, TCP's initial congestion window size has been increased via RFC
 3390.  This same update will be needed for SCTP to keep SCTP's
 congestion control properties equivalent to that of TCP.

Stewart, et al. Informational [Page 59] RFC 4460 SCTP Errata April 2006

2.30.2. Text Changes to the Document

  1. ——–

Old text: (Section 7.2.1)

  1. ——–

o The initial cwnd before DATA transmission or after a

       sufficiently long idle period MUST be <= 2*MTU.
  1. ——–

New text: (Section 7.2.1)

  1. ——–

o The initial cwnd before DATA transmission or after a

       sufficiently long idle period MUST be set to
       min(4*MTU, max (2*MTU, 4380 bytes)).
  1. ——–

Old text: (Section 7.2.1)

  1. ——–

o When the endpoint does not transmit data on a given transport

       address, the cwnd of the transport address should be adjusted
       to max(cwnd/2, 2*MTU) per RTO.
  1. ——–

New text: (Section 7.2.1)

  1. ——–

o When the endpoint does not transmit data on a given transport

       address, the cwnd of the transport address should be adjusted
       to max(cwnd/2, 4*MTU) per RTO.
  1. ——–

Old text: (Section 7.2.2)

  1. ——–

o Same as in the slow start, when the sender does not transmit

       DATA on a given transport address, the cwnd of the transport
       address should be adjusted to max(cwnd / 2, 2*MTU) per RTO.
  1. ——–

New text: (Section 7.2.2)

  1. ——–

o Same as in the slow start, when the sender does not transmit

       DATA on a given transport address, the cwnd of the transport
       address should be adjusted to max(cwnd / 2, 4*MTU) per RTO.

Stewart, et al. Informational [Page 60] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 7.2.3)

  1. ——–
 7.2.3.  Congestion Control
    Upon detection of packet losses from SACK  (see Section 7.2.4), an
    endpoint should do the following:
       ssthresh = max(cwnd/2, 2*MTU)
       cwnd = ssthresh
    Basically, a packet loss causes cwnd to be cut in half.
    When the T3-rtx timer expires on an address, SCTP should perform
    slow start by
       ssthresh = max(cwnd/2, 2*MTU)
       cwnd = 1*MTU
  1. ——–

New text: (Section 7.2.3)

  1. ——–
 7.2.3 Congestion Control
    Upon detection of packet losses from SACK  (see Section 7.2.4), An
    endpoint should do the following:
       ssthresh = max(cwnd/2, 4*MTU)
       cwnd = ssthresh
    Basically, a packet loss causes cwnd to be cut in half.
    When the T3-rtx timer expires on an address, SCTP should perform
    slow start by:
       ssthresh = max(cwnd/2, 4*MTU)
       cwnd = 1*MTU

2.30.3. Solution Description

 The change to SCTP's initial congestion window will allow it to
 continue to maintain the same congestion control properties as TCP.

Stewart, et al. Informational [Page 61] RFC 4460 SCTP Errata April 2006

2.31. Stream Sequence Numbers in Figures

2.31.1. Description of the Problem

 In Section 2.24 of this document, it is clarified that the SSN are
 initialized with 0.  Two figures in RFC 2960 [5] illustrate that they
 start with 1.

Stewart, et al. Informational [Page 62] RFC 4460 SCTP Errata April 2006

2.31.2. Text Changes to the Document

  1. ——–

Old text: (Section 7.2.1)

  1. ——–
  Endpoint A                                          Endpoint Z
  {app sets association with Z}
  (build TCB)
  INIT [I-Tag=Tag_A
        & other info]  ------\
  (Start T1-init timer)       \
  (Enter COOKIE-WAIT state)    \---> (compose temp TCB and Cookie_Z)
                                 /-- INIT ACK [Veri Tag=Tag_A,
                                /             I-Tag=Tag_Z,
  (Cancel T1-init timer) <-----/               Cookie_Z, & other info]
                                         (destroy temp TCB)
  COOKIE ECHO [Cookie_Z] ------\
  (Start T1-init timer)         \
  (Enter COOKIE-ECHOED state)    \---> (build TCB enter ESTABLISHED
                                        state)
                                 /---- COOKIE-ACK
                                /
  (Cancel T1-init timer, <-----/
   Enter ESTABLISHED state)
  {app sends 1st user data; strm 0}
   DATA [TSN=initial TSN_A
       Strm=0,Seq=1 & user data]--\
   (Start T3-rtx timer)            \
                                    \->
                                /----- SACK [TSN Ack=init
                               /              TSN_A,Block=0]
 (Cancel T3-rtx timer) <------/
                                        ...
                                        {app sends 2 messages;strm 0}
                                  /---- DATA
                                 /        [TSN=init TSN_Z
                             <--/          Strm=0,Seq=1 & user data 1]
 SACK [TSN Ack=init TSN_Z,     /    ---- DATA
          Block=0]     --------\  /        [TSN=init TSN_Z +1,
                                \/         Strm=0,Seq=2 & user data 2]
                         <------/\
                                  \
                                   \------>
                      Figure 4: INITiation Example

Stewart, et al. Informational [Page 63] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 7.2.1)

  1. ——–
  Endpoint A                                          Endpoint Z
  {app sets association with Z}
  (build TCB)
  INIT [I-Tag=Tag_A
        & other info]  ------\
  (Start T1-init timer)       \
  (Enter COOKIE-WAIT state)    \---> (compose temp TCB and Cookie_Z)
                                  /-- INIT ACK [Veri Tag=Tag_A,
                                 /             I-Tag=Tag_Z,
  (Cancel T1-init timer) <------/              Cookie_Z, & other info]
                                       (destroy temp TCB)
  COOKIE ECHO [Cookie_Z] ------\
  (Start T1-init timer)         \
  (Enter COOKIE-ECHOED state)    \---> (build TCB enter ESTABLISHED
                                        state)
                                 /---- COOKIE-ACK
                                /
  (Cancel T1-init timer, <-----/
   Enter ESTABLISHED state)
  {app sends 1st user data; strm 0}
  DATA [TSN=initial TSN_A
      Strm=0,Seq=0 & user data]--\
  (Start T3-rtx timer)            \
                                   \->
                                 /----- SACK [TSN Ack=init
                                /           TSN_A,Block=0]
  (Cancel T3-rtx timer) <------/
                                        ...
                                       {app sends 2 messages;strm 0}
                                 /---- DATA
                                /        [TSN=init TSN_Z
                            <--/          Strm=0,Seq=0 & user data 1]
  SACK [TSN Ack=init TSN_Z,      /---- DATA
        Block=0]     --------\  /        [TSN=init TSN_Z +1,
                              \/          Strm=0,Seq=1 & user data 2]
                       <------/\
                                \
                                 \------>
                     Figure 4: INITiation Example

Stewart, et al. Informational [Page 64] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 5.2.4.1)

  1. ——–
 Endpoint A                                          Endpoint Z
 <------------ Association is established---------------------->
 Tag=Tag_A                                             Tag=Tag_Z
 <------------------------------------------------------------->
 {A crashes and restarts}
 {app sets up a association with Z}
 (build TCB)
 INIT [I-Tag=Tag_A'
       & other info]  --------\
 (Start T1-init timer)         \
 (Enter COOKIE-WAIT state)      \---> (find a existing TCB
                                       compose temp TCB and Cookie_Z
                                       with Tie-Tags to previous
                                       association)
                                 /--- INIT ACK [Veri Tag=Tag_A',
                                /               I-Tag=Tag_Z',
 (Cancel T1-init timer) <------/                Cookie_Z[TieTags=
                                                Tag_A,Tag_Z
                                                 & other info]
                                      (destroy temp TCB,leave original
                                       in place)
 COOKIE ECHO [Veri=Tag_Z',
              Cookie_Z
              Tie=Tag_A,
              Tag_Z]----------\
 (Start T1-init timer)         \
 (Enter COOKIE-ECHOED state)    \---> (Find existing association,
                                       Tie-Tags match old tags,
                                       Tags do not match i.e.,
                                       case X X M M above,
                                       Announce Restart to ULP
                                       and reset association).
                                /---- COOKIE-ACK
 (Cancel T1-init timer, <------/
  Enter ESTABLISHED state)
 {app sends 1st user data; strm 0}
 DATA [TSN=initial TSN_A
     Strm=0,Seq=1 & user data]--\
 (Start T3-rtx timer)            \
                                  \->
                               /--- SACK [TSN Ack=init TSN_A,Block=0]
 (Cancel T3-rtx timer) <------/
                   Figure 5: A Restart Example

Stewart, et al. Informational [Page 65] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 5.2.4.1)

  1. ——–
 Endpoint A                                          Endpoint Z
 <-------------- Association is established---------------------->
 Tag=Tag_A                                             Tag=Tag_Z
 <--------------------------------------------------------------->
 {A crashes and restarts}
 {app sets up a association with Z}
 (build TCB)
 INIT [I-Tag=Tag_A'
       & other info]  --------\
 (Start T1-init timer)         \
 (Enter COOKIE-WAIT state)      \---> (find a existing TCB
                                       compose temp TCB and Cookie_Z
                                       with Tie-Tags to previous
                                       association)
                                 /--- INIT ACK [Veri Tag=Tag_A',
                                /               I-Tag=Tag_Z',
 (Cancel T1-init timer) <------/                Cookie_Z[TieTags=
                                                Tag_A,Tag_Z
                                                 & other info]
                                      (destroy temp TCB,leave original
                                       in place)
 COOKIE ECHO [Veri=Tag_Z',
              Cookie_Z
              Tie=Tag_A,
              Tag_Z]----------\
 (Start T1-init timer)         \
 (Enter COOKIE-ECHOED state)    \---> (Find existing association,
                                       Tie-Tags match old tags,
                                       Tags do not match i.e.,
                                       case X X M M above,
                                       Announce Restart to ULP
                                       and reset association).
                                /---- COOKIE-ACK
 (Cancel T1-init timer, <------/
  Enter ESTABLISHED state)
 {app sends 1st user data; strm 0}
 DATA [TSN=initial TSN_A
     Strm=0,Seq=0 & user data]--\
 (Start T3-rtx timer)            \
                                  \->
                               /--- SACK [TSN Ack=init TSN_A,Block=0]
 (Cancel T3-rtx timer) <------/
                   Figure 5: A Restart Example

Stewart, et al. Informational [Page 66] RFC 4460 SCTP Errata April 2006

2.31.3. Solution description

 Figure 4 and 5 were changed so that the SSN starts with 0 instead of
 1.

2.32. Unrecognized Parameters

2.32.1. Description of the Problem

 The RFC does not state clearly in Section 3.3.3.1 whether one or
 multiple unrecognized parameters are included in the 'Unrecognized
 Parameter' parameter.

2.32.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.3)

  1. ——–

Variable Parameters Status Type Value

  1. ————————————————————

State Cookie Mandatory 7

       IPv4 Address (Note 1)               Optional    5
       IPv6 Address (Note 1)               Optional    6
       Unrecognized Parameters             Optional    8
       Reserved for ECN Capable (Note 2)   Optional    32768 (0x8000)
       Host Name Address (Note 3)          Optional    11
  1. ——–

New text: (Section 3.3.3)

  1. ——–

Variable Parameters Status Type Value

  1. ————————————————————

State Cookie Mandatory 7

       IPv4 Address (Note 1)               Optional    5
       IPv6 Address (Note 1)               Optional    6
       Unrecognized Parameter              Optional    8
       Reserved for ECN Capable (Note 2)   Optional    32768 (0x8000)
       Host Name Address (Note 3)          Optional    11
  1. ——–

Old text: (Section 3.3.3.1)

  1. ——–

Unrecognized Parameters:

       Parameter Type Value: 8
       Parameter Length:  Variable Size.

Stewart, et al. Informational [Page 67] RFC 4460 SCTP Errata April 2006

       Parameter Value:
          This parameter is returned to the originator of the INIT
          chunk when the INIT contains an unrecognized parameter
          which has a value that indicates that it should be reported
          to the sender.  This parameter value field will contain
          unrecognized parameters copied from the INIT chunk complete
          with Parameter Type, Length and Value fields.
  1. ——–

New text: (Section 3.3.3.1)

  1. ——–

Unrecognized Parameter:

       Parameter Type Value: 8
       Parameter Length:  Variable Size.
       Parameter Value:
          This parameter is returned to the originator of the INIT
          chunk when the INIT contains an unrecognized parameter
          that has a value that indicates that it should be reported
          to the sender.  This parameter value field will contain the
          unrecognized parameter copied from the INIT chunk complete
          with Parameter Type, Length, and Value fields.

2.32.3. Solution Description

 The new text states clearly that only one unrecognized parameter is
 reported per parameter.

2.33. Handling of Unrecognized Parameters

2.33.1. Description of the Problem

 It is not stated clearly in RFC 2960 [5] how unrecognized parameters
 should be handled.  The problem comes up when an INIT contains an
 unrecognized parameter with highest bits 00.  It was not clear
 whether an INIT-ACK should be sent.

2.33.2. Text Changes to the Document

 Some of the changes given here already include changes suggested in
 Section 2.27 of this document.

Stewart, et al. Informational [Page 68] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it.
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      parameter in an 'Unrecognized Parameter Type' (in either an
      ERROR or in the INIT ACK).
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter Type' (in
      either an ERROR or in the INIT ACK).
  1. ——–

New text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this parameter; do not process
      any further parameters within this chunk.
 01 - Stop processing this parameter, do not process
      any further parameters within this chunk, and report the
      unrecognized parameter in an 'Unrecognized Parameter Type', as
      described in 3.2.2.
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter Type', as
      described in 3.2.2.
  1. ——–

New text: (Note: no old text; clarification added in section 3.2)

  1. ——–
 3.2.2.  Reporting of Unrecognized Parameters
 If the receiver of an INIT chunk detects unrecognized parameters and
 has to report them according to Section 3.2.1, it MUST put the
 'Unrecognized Parameter' parameter(s) in the INIT-ACK chunk sent in
 response to the INIT-chunk.  Note that if the receiver of the INIT
 chunk is NOT going to establish an association (e.g., due to lack of

Stewart, et al. Informational [Page 69] RFC 4460 SCTP Errata April 2006

 resources), an 'Unrecognized Parameter' would NOT be included with
 any ABORT being sent to the sender of the INIT.
 If the receiver of an INIT-ACK chunk detects unrecognized parameters
 and has to report them according to Section 3.2.1, it SHOULD bundle
 the ERROR chunk containing the 'Unrecognized Parameter' error cause
 with the COOKIE-ECHO chunk sent in response to the INIT-ACK chunk.
 If the receiver of the INIT-ACK cannot bundle the COOKIE-ECHO chunk
 with the ERROR chunk, the ERROR chunk MAY be sent separately but not
 before the COOKIE-ACK has been received.
 Note: Any time a COOKIE-ECHO is sent in a packet, it MUST be the
 first chunk.

2.33.3. Solution Description

 The procedure of handling unrecognized parameters has been described
 clearly.

2.34. Tie Tags

2.34.1. Description of the Problem

 RFC 2960 requires that Tie-Tags be included in the COOKIE.  The
 cookie may not be encrypted.  An attacker could discover the value of
 the Verification Tags by analyzing cookies received after sending an
 INIT.

2.34.2. Text Changes to the Document

  1. ——–

Old text: (Section 1.4)

  1. ——–

o Tie-Tags: Verification Tags from a previous association. These

       Tags are used within a State Cookie so that the newly
       restarting association can be linked to the original
       association within the endpoint that did not restart.
  1. ——–

New text: (Section 1.4)

  1. ——–
    o  Tie-Tags: Two 32-bit random numbers that together make a 64-
       bit nonce.  These Tags are used within a State Cookie and TCB
       so that a newly restarting association can be linked to the
       original association within the endpoint that did not restart
       and yet not reveal the true Verification Tags of an existing
       association.

Stewart, et al. Informational [Page 70] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 5.2.1)

  1. ——–
    For an endpoint that is in the COOKIE-ECHOED state it MUST
    populate its Tie-Tags with the Tag information of itself and
    its peer (see Section 5.2.2 for a description of the Tie-Tags).
  1. ——–

New text: (Section 5.2.1)

  1. ——–

For an endpoint that is in the COOKIE-ECHOED state it MUST

    populate its Tie-Tags within both the association TCB and
    inside the State Cookie (see section 5.2.2 for a description
    of the Tie-Tags).
  1. ——–

Old text: (Section 5.2.2)

  1. ——–

Unless otherwise stated, upon reception of an unexpected INIT for

    this association, the endpoint shall generate an INIT ACK with a
    State Cookie.  In the outbound INIT ACK the endpoint MUST copy its
    current Verification Tag and peer's Verification Tag into a
    reserved place within the state cookie.  We shall refer to these
    locations as the Peer's-Tie-Tag and the Local-Tie-Tag.  The
    outbound SCTP packet containing this INIT ACK MUST carry a
    Verification Tag value equal to the Initiation Tag found in the
    unexpected INIT.  And the INIT ACK MUST contain a new Initiation
    Tag (randomly generated see Section 5.3.1).  Other parameters
    for the endpoint SHOULD be copied from the existing parameters
    of the association (e.g., number of outbound streams) into the
    INIT ACK and cookie.
  1. ——–

New text: (Section 5.2.2)

  1. ——–
    Unless otherwise stated, upon receipt of an unexpected INIT for
    this association, the endpoint MUST generate an INIT ACK with a
    State Cookie.  In the outbound INIT ACK, the endpoint MUST copy
    its current Tie-Tags to a reserved place within the State Cookie
    and the association's TCB.  We shall refer to these locations
    inside the cookie as the Peer's-Tie-Tag and the Local-Tie-Tag.  We
    will refer to the copy within an association's TCB as the Local
    Tag and Peer's Tag.  The outbound SCTP packet containing this INIT
    ACK MUST carry a Verification Tag value equal to the Initiation
    Tag found in the unexpected INIT.  And the INIT ACK MUST contain a

Stewart, et al. Informational [Page 71] RFC 4460 SCTP Errata April 2006

    new Initiation Tag (randomly generated; see Section 5.3.1).  Other
    parameters for the endpoint SHOULD be copied from the existing
    parameters of the association (e.g., number of outbound streams)
    into the INIT ACK and cookie.

2.34.3. Solution Description

 The solution to this problem is not to use the real Verification Tags
 within the State Cookie as tie-tags.  Instead, two 32-bit random
 numbers are created to form one 64-bit nonce and stored both in the
 State Cookie and the existing association TCB.  This prevents
 exposing the Verification Tags inadvertently.

2.35. Port Number Verification in the COOKIE-ECHO

2.35.1. Description of the Problem

 The State Cookie sent by a listening SCTP endpoint may not contain
 the original port numbers or the local Verification Tag.  It is then
 possible that the endpoint, on receipt of the COOKIE-ECHO, will not
 be able to verify that these values match the original values found
 in the INIT and INIT-ACK that began the association setup.

2.35.2. Text Changes to the Document

  1. ——–

Old text: (Section 5.1.5)

  1. ——–

3) Compare the creation timestamp in the State Cookie to the

       current local time.  If the elapsed time is longer than the
       lifespan carried in the State Cookie, then the packet,
       including the COOKIE ECHO and any attached DATA chunks,
       SHOULD be discarded and the endpoint MUST transmit an ERROR
       chunk with a "Stale Cookie" error cause to the peer endpoint,
    4) If the State Cookie is valid, create an association to the
       sender of the COOKIE ECHO chunk with the information in the
       TCB data carried in the COOKIE ECHO, and enter the
       ESTABLISHED state,
    5) Send a COOKIE ACK chunk to the peer acknowledging reception
       of the COOKIE ECHO.  The COOKIE ACK MAY be bundled with an
       outbound DATA chunk or SACK chunk; however, the COOKIE ACK
       MUST be the first chunk in the SCTP packet.
    6) Immediately acknowledge any DATA chunk bundled with the COOKIE
       ECHO with a SACK (subsequent DATA chunk acknowledgement should
       follow the rules defined in Section 6.2).  As mentioned in step

Stewart, et al. Informational [Page 72] RFC 4460 SCTP Errata April 2006

       5), if the SACK is bundled with the COOKIE ACK, the COOKIE ACK
       MUST appear first in the SCTP packet.
  1. ——–

New text: (Section 5.1.5)

  1. ——–
    3) Compare the port numbers and the Verification Tag contained
       within the COOKIE ECHO chunk to the actual port numbers and the
       Verification Tag within the SCTP common header of the received
       packet.  If these values do not match, the packet MUST be
       silently discarded.
    4) Compare the creation timestamp in the State Cookie to the
       current local time.  If the elapsed time is longer than the
       lifespan carried in the State Cookie, then the packet,
       including the COOKIE ECHO and any attached DATA chunks,
       SHOULD be discarded, and the endpoint MUST transmit an
       ERROR chunk with a "Stale Cookie" error cause to the peer
       endpoint.
    5) If the State Cookie is valid, create an association to the
       sender of the COOKIE ECHO chunk with the information in the
       TCB data carried in the COOKIE ECHO and enter the
       ESTABLISHED state.
    6) Send a COOKIE ACK chunk to the peer acknowledging receipt of
       the COOKIE ECHO.  The COOKIE ACK MAY be bundled with an
       outbound DATA chunk or SACK chunk; however, the COOKIE ACK
       MUST be the first chunk in the SCTP packet.
    7) Immediately acknowledge any DATA chunk bundled with the COOKIE
       ECHO with a SACK (subsequent DATA chunk acknowledgement should
       follow the rules defined in Section 6.2).  As mentioned in step
       5, if the SACK is bundled with the COOKIE ACK, the COOKIE ACK
       MUST appear first in the SCTP packet.

2.35.3. Solution Description

 By including both port numbers and the local Verification Tag within
 the State Cookie and verifying these during COOKIE-ECHO processing,
 this issue is resolved.

Stewart, et al. Informational [Page 73] RFC 4460 SCTP Errata April 2006

2.36. Path Initialization

2.36.1. Description of the Problem

 When an association enters the ESTABLISHED state, the endpoint has no
 verification that all of the addresses presented by the peer do in
 fact belong to the peer.  This could cause various forms of denial of
 service attacks.

2.36.2. Text Changes to the Document

  1. ——–

Old text: None

  1. ——–
  1. ——–

New text: (Section 5.4)

  1. ——–

5.4. Path Verification

 During association establishment, the two peers exchange a list of
 addresses.  In the predominant case, these lists accurately represent
 the addresses owned by each peer.  However, it is possible that a
 misbehaving peer may supply addresses that it does not own.  To
 prevent this, the following rules are applied to all addresses of the
 new association:
 1) Any address passed to the sender of the INIT by its upper layer is
    automatically considered to be CONFIRMED.
 2) For the receiver of the COOKIE-ECHO the only CONFIRMED address is
    the one that the INIT-ACK was sent to.
 3) All other addresses not covered by rules 1 and 2 are considered
    UNCONFIRMED and are subject to probing for verification.
 To probe an address for verification, an endpoint will send
 HEARTBEATs including a 64-bit random nonce and a path indicator (to
 identify the address that the HEARTBEAT is sent to) within the
 HEARTBEAT parameter.
 Upon receipt of the HEARTBEAT-ACK, a verification is made that the
 nonce included in the HEARTBEAT parameter is the one sent to the
 address indicated inside the HEARTBEAT parameter.  When this match
 occurs, the address that the original HEARTBEAT was sent to is now
 considered CONFIRMED and available for normal data transfer.

Stewart, et al. Informational [Page 74] RFC 4460 SCTP Errata April 2006

 These probing procedures are started when an association moves to the
 ESTABLISHED state and are ended when all paths are confirmed.
 Each RTO a probe may be sent on an active UNCONFIRMED path in an
 attempt to move it to the CONFIRMED state.  If during this probing
 the path becomes inactive, this rate is lowered to the normal
 HEARTBEAT rate.  At the expiration of the RTO timer, the error
 counter of any path that was probed but not CONFIRMED is incremented
 by one and subjected to path failure detection, as defined in section
 8.2.  When probing UNCONFIRMED addresses, however, the association
 overall error count is NOT incremented.
 The number of HEARTBEATS sent at each RTO SHOULD be limited by the
 HB.Max.Burst parameter.  It is an implementation decision as to how
 to distribute HEARTBEATS to the peer's addresses for path
 verification.
 Whenever a path is confirmed, an indication MAY be given to the upper
 layer.
 An endpoint MUST NOT send any chunks to an UNCONFIRMED address, with
 the following exceptions:
  1. A HEARTBEAT including a nonce MAY be sent to an UNCONFIRMED

address.

  1. A HEARTBEAT-ACK MAY be sent to an UNCONFIRMED address.
  1. A COOKIE-ACK MAY be sent to an UNCONFIRMED address, but it MUST be

bundled with a HEARTBEAT including a nonce. An implementation that

   does NOT support bundling MUST NOT send a COOKIE-ACK to an
   UNCONFIRMED address.
  1. A COOKE-ECHO MAY be sent to an UNCONFIRMED address, but it MUST be

bundled with a HEARTBEAT including a nonce, and the packet MUST NOT

   exceed the path MTU.  If the implementation does NOT support
   bundling or if the bundled COOKIE-ECHO plus HEARTBEAT (including
   nonce) would exceed the path MTU, then the implementation MUST NOT
   send a COOKIE-ECHO to an UNCONFIRMED address.
  1. ——–

Old text: (Section 14)

  1. ——–
 14.  Suggested SCTP Protocol Parameter Values
 The following protocol parameters are RECOMMENDED:

Stewart, et al. Informational [Page 75] RFC 4460 SCTP Errata April 2006

 RTO.Initial              - 3  seconds
 RTO.Min                  - 1  second
 RTO.Max                 -  60 seconds
 RTO.Alpha                - 1/8
 RTO.Beta                 - 1/4
 Valid.Cookie.Life        - 60  seconds
 Association.Max.Retrans  - 10 attempts
 Path.Max.Retrans         - 5  attempts (per destination address)
 Max.Init.Retransmits     - 8  attempts
 HB.interval              - 30 seconds
  1. ——–

New text: (Section 14)

  1. ——–
 14.  Suggested SCTP Protocol Parameter Values
 The following protocol parameters are RECOMMENDED:
 RTO.Initial              - 3 seconds
 RTO.Min                  - 1 second
 RTO.Max                  - 60 seconds
 Max.Burst                - 4
 RTO.Alpha                - 1/8
 RTO.Beta                 - 1/4
 Valid.Cookie.Life        - 60 seconds
 Association.Max.Retrans  - 10 attempts
 Path.Max.Retrans         - 5 attempts (per destination address)
 Max.Init.Retransmits     - 8 attempts
 HB.Interval              - 30 seconds
 HB.Max.Burst             - 1

2.36.3. Solution Description

 By properly setting up initial path state and accelerated probing via
 HEARTBEAT's, a new association can verify that all addresses
 presented by a peer belong to that peer.

2.37. ICMP Handling Procedures

2.37.1. Description of the Problem

 RFC 2960 does not describe how ICMP messages should be processed by
 an SCTP endpoint.

Stewart, et al. Informational [Page 76] RFC 4460 SCTP Errata April 2006

2.37.2. Text Changes to the Document

  1. ——-

Old text: None

  1. ——-
  1. ——–

New text

  1. ——–
 11.5.  Protection of Non-SCTP Capable Hosts.
 To provide a non-SCTP capable host with the same level of protection
 against attacks as for SCTP-capable ones, all SCTP stacks MUST
 implement the ICMP handling described in Appendix C.
 When an SCTP stack receives a packet containing multiple control or
 DATA chunks and the processing of the packet requires the sending of
 multiple chunks in response, the sender of the response chunk(s) MUST
 NOT send more than one packet.  If bundling is supported, multiple
 response chunks that fit into a single packet MAY be bundled together
 into one single response packet.  If bundling is not supported, then
 the sender MUST NOT send more than one response chunk and MUST
 discard all other responses.  Note that this rule does NOT apply to a
 SACK chunk, since a SACK chunk is, in itself, a response to DATA and
 a SACK does not require a response of more DATA.
 An SCTP implementation SHOULD abort the association if it receives a
 SACK acknowledging a TSN that has not been sent.
 An SCTP implementation that receives an INIT that would require a
 large packet in response, due to the inclusion of multiple ERROR
 parameters, MAY (at its discretion) elect to omit some or all of the
 ERROR parameters to reduce the size of the INIT-ACK.  Due to a
 combination of the size of the COOKIE parameter and the number of
 addresses a receiver of an INIT may be indicating to a peer, it is
 always possible that the INIT-ACK will be larger than the original
 INIT.  An SCTP implementation SHOULD attempt to make the INIT-ACK as
 small as possible to reduce the possibility of byte amplification
 attacks.
  1. ——–

Old text: None

  1. ——–

Stewart, et al. Informational [Page 77] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Appendix C)

  1. ——–
 Appendix C ICMP Handling
 Whenever an ICMP message is received by an SCTP endpoint the
 following procedures MUST be followed to ensure proper utilization of
 the information being provided by layer 3.
 ICMP1) An implementation MAY ignore all ICMPv4 messages where the
        type field is not set to "Destination Unreachable".
 ICMP2) An implementation MAY ignore all ICMPv6 messages where the
        type field is not "Destination Unreachable, "Parameter
        Problem" or "Packet Too Big".
 ICMP3) An implementation MAY ignore any ICMPv4 messages where the
        code does not indicate "Protocol Unreachable" or
        "Fragmentation Needed".
 ICMP4) An implementation MAY ignore all ICMPv6 messages of type
        "Parameter Problem" if the code is not "Unrecognized next
        header type encountered".
 ICMP5) An implementation MUST use the payload of the ICMP message (V4
        or V6) to locate the association that sent the message that
        ICMP is responding to.  If the association cannot be found, an
        implementation SHOULD ignore the ICMP message.
 ICMP6) An implementation MUST validate that the Verification Tag
        contained in the ICMP message matches the verification tag of
        the peer.  If the Verification Tag is not 0 and does NOT
        match, discard the ICMP message.  If it is 0 and the ICMP
        message contains enough bytes to verify that the chunk type is
        an INIT chunk and that the initiate tag matches the tag of the
        peer, continue with ICMP7.  If the ICMP message is too short
        or the chunk type or the initiate tag does not match, silently
        discard the packet.
 ICMP7) If the ICMP message is either a V6 "Packet Too Big" or a V4
        "Fragmentation Needed", an implementation MAY process this
        information as defined for PATH MTU discovery.
 ICMP8) If the ICMP code is a "Unrecognized next header type
        encountered" or a "Protocol Unreachable", an implementation
        MUST treat this message as an abort with the T bit set if it
        does not contain an INIT chunk.  If it does contain an INIT

Stewart, et al. Informational [Page 78] RFC 4460 SCTP Errata April 2006

        chunk and the association is in COOKIE-WAIT state, handle the
        ICMP message like an ABORT.
 ICMP9) If the ICMPv6 code is "Destination Unreachable", the
        implementation MAY mark the destination into the unreachable
        state or alternatively increment the path error counter.
 Note that these procedures differ from RFC 1122 [1] and from its
 requirements for processing of port-unreachable messages and the
 requirements that an implementation MUST abort associations in
 response to a "protocol unreachable" message.  Port unreachable
 messages are not processed, since an implementation will send an
 ABORT, not a port unreachable.  The stricter handling of the
 "protocol unreachable" message is due to security concerns for hosts
 that do NOT support SCTP.

2.37.3. Solution Description

 The new appendix now describes proper handling of ICMP messages in
 conjunction with SCTP.

2.38. Checksum

2.38.1. Description of the problem

 RFC 3309 [6] changes the SCTP checksum due to weaknesses in the
 original Adler 32 checksum for small messages.  This document, being
 used as a guide for a cut and paste replacement to update RFC 2960,
 thus also needs to incorporate the checksum changes.  The idea is
 that one could apply all changes found in this guide to a copy of RFC
 2960 and have a "new" document that has ALL changes (including RFC
 3309).

2.38.2. Text Changes to the Document

  1. ——–

Old text:

  1. ——–
 6.8 Adler-32 Checksum Calculation
    When sending an SCTP packet, the endpoint MUST strengthen the data
    integrity of the transmission by including the Adler-32 checksum
    value calculated on the packet, as described below.
    After the packet is constructed (containing the SCTP common header
    and one or more control or DATA chunks), the transmitter shall:

Stewart, et al. Informational [Page 79] RFC 4460 SCTP Errata April 2006

    1) Fill in the proper Verification Tag in the SCTP common header
       and initialize the checksum field to 0's.
    2) Calculate the Adler-32 checksum of the whole packet, including
       the SCTP common header and all the chunks.  Refer to
       appendix B for details of the Adler-32 algorithm.  And,
    3) Put the resultant value into the checksum field in the common
       header, and leave the rest of the bits unchanged.
    When an SCTP packet is received, the receiver MUST first check the
    Adler-32 checksum:
    1) Store the received Adler-32 checksum value aside,
    2) Replace the 32 bits of the checksum field in the received SCTP
       packet with all '0's and calculate an Adler-32 checksum value
       of the whole received packet.  And,
    3) Verify that the calculated Adler-32 checksum is the same as the
       received Adler-32 checksum.  If not, the receiver MUST treat
       the packet as an invalid SCTP packet.
    The default procedure for handling invalid SCTP packets is to
    silently discard them.
  1. ——–

New text:

  1. ——–
 6.8 CRC-32c Checksum Calculation
    When sending an SCTP packet, the endpoint MUST strengthen the data
    integrity of the transmission by including the CRC32c checksum
    value calculated on the packet, as described below.
    After the packet is constructed (containing the SCTP common header
    and one or more control or DATA chunks), the transmitter MUST
    1) fill in the proper Verification Tag in the SCTP common header
       and initialize the checksum field to '0's,
    2) calculate the CRC32c checksum of the whole packet, including
       the SCTP common header and all the chunks (refer to
       appendix B for details of the CRC32c algorithm); and
    3) put the resultant value into the checksum field in the common
       header, and leave the rest of the bits unchanged.

Stewart, et al. Informational [Page 80] RFC 4460 SCTP Errata April 2006

    When an SCTP packet is received, the receiver MUST first check the
    CRC32c checksum as follows:
    1) Store the received CRC32c checksum value aside.
    2) Replace the 32 bits of the checksum field in the received SCTP
       packet with all '0's and calculate a CRC32c checksum value of
       the whole received packet.
    3) Verify that the calculated CRC32c checksum is the same as the
       received CRC32c checksum.  If it is not, the receiver MUST
       treat the packet as an invalid SCTP packet.
    The default procedure for handling invalid SCTP packets is to
    silently discard them.
    Any hardware implementation SHOULD be done in a way that is
    verifiable by the software.
  1. ——–

Old text:

  1. ——–
 Appendix B Alder 32 bit checksum calculation
    The Adler-32 checksum calculation given in this appendix is
    copied from [RFC1950].
    Adler-32 is composed of two sums accumulated per byte: s1 is the
    sum of all bytes, s2 is the sum of all s1 values.  Both sums are
    done modulo 65521.  s1 is initialized to 1, s2 to zero.  The
    Adler-32 checksum is stored as s2*65536 + s1 in network byte
    order.
    The following C code computes the Adler-32 checksum of a data
    buffer.  It is written for clarity, not for speed.  The sample
    code is in the ANSI C programming language.  Non C users may
    find it easier to read with these hints:
    &      Bitwise AND operator.
    >>     Bitwise right shift operator.  When applied to an
           unsigned quantity, as here, right shift inserts zero bit(s)
           at the left.
    <<     Bitwise left shift operator.  Left shift inserts zero
           bit(s) at the right.
    ++     "n++" increments the variable n.
    %      modulo operator: a % b is the remainder of a divided by b.

Stewart, et al. Informational [Page 81] RFC 4460 SCTP Errata April 2006

     #define BASE 65521 /* largest prime smaller than 65536 */
     /*
       Update a running Adler-32 checksum with the bytes buf[0..len-1]
       and return the updated checksum.  The Adler-32 checksum should
       be initialized to 1.
        Usage example:
          unsigned long adler = 1L;
          while (read_buffer(buffer, length) != EOF) {
            adler = update_adler32(adler, buffer, length);
           }
          if (adler != original_adler) error();
       */
       unsigned long update_adler32(unsigned long adler,
          unsigned char *buf, int len)
       {
         unsigned long s1 = adler & 0xffff;
         unsigned long s2 = (adler >> 16) & 0xffff;
         int n;
         for (n = 0; n < len; n++) {
           s1 = (s1 + buf[n]) % BASE;
           s2 = (s2 + s1)     % BASE;
         }
         return (s2 << 16) + s1;
       }
       /* Return the adler32 of the bytes buf[0..len-1] */
       unsigned long adler32(unsigned char *buf, int len)
       {
         return update_adler32(1L, buf, len);
       }
  1. ——–

New text:

  1. ——–
 Appendix B CRC32c Checksum Calculation
    We define a 'reflected value' as one that is the opposite of the
    normal bit order of the machine.  The 32-bit CRC is calculated as
    described for CRC-32c and uses the polynomial code 0x11EDC6F41
    (Castagnoli93) or x^32+x^28+x^27+x^26+x^25
    +x^23+x^22+x^20+x^19+x^18+x^14+x^13+x^11+x^10+x^9+x^8+x^6+x^0.
    The CRC is computed using a procedure similar to ETHERNET CRC
    [ITU32], modified to reflect transport level usage.

Stewart, et al. Informational [Page 82] RFC 4460 SCTP Errata April 2006

    CRC computation uses polynomial division.  A message
    bit-string M is transformed to a polynomial, M(X), and the CRC
    is calculated from M(X) using polynomial arithmetic [PETERSON 72].
    When CRCs are used at the link layer, the polynomial is derived
    from on-the-wire bit ordering: the first bit 'on the wire' is the
    high-order coefficient.  Since SCTP is a transport-level protocol,
    it cannot know the actual serial-media bit ordering.  Moreover,
    different links in the path between SCTP endpoints may use
    different link-level bit orders.
    A convention must therefore be established for mapping SCTP
    transport messages to polynomials for purposes of CRC computation.
    The bit-ordering for mapping SCTP messages to polynomials is that
    bytes are taken most-significant first; but within each byte, bits
    are taken least-significant first.  The first byte of the message
    provides the eight highest coefficients.  Within each byte,
    the least-significant SCTP bit gives the most significant
    polynomial coefficient within that byte, and the most-significant
    SCTP bit is the least significant polynomial coefficient in that
    byte.  (This bit ordering is sometimes called 'mirrored' or
    'reflected' [WILLIAMS93].)  CRC polynomials are to be transformed
    back into SCTP transport-level byte values, using a consistent
    mapping.
    The SCTP transport-level CRC value should be calculated as
    follows:
  1. CRC input data are assigned to a byte stream, numbered from

0 to N-1.

  1. The transport-level byte-stream is mapped to a polynomial

value. An N-byte PDU with j bytes numbered 0 to N-1 is

          considered as coefficients of a polynomial M(x) of order
          8N-1, with bit 0 of byte j being coefficient x^(8(N-j)-8),
          and bit 7 of byte j being coefficient x^(8(N-j)-1).
  1. The CRC remainder register is initialized with all 1s and

the CRC is computed with an algorithm that simultaneously

          multiplies by x^32 and divides by the CRC polynomial.
  1. The polynomial is multiplied by x^32 and divided by G(x),

the generator polynomial, producing a remainder R(x) of

          degree less than or equal to 31.
  1. The coefficients of R(x) are considered a 32-bit sequence.

Stewart, et al. Informational [Page 83] RFC 4460 SCTP Errata April 2006

  1. The bit sequence is complemented. The result is the CRC

polynomial.

  1. The CRC polynomial is mapped back into SCTP transport-level

bytes. The coefficient of x^31 gives the value of bit 7 of

          SCTP byte 0, and the coefficient of x^24 gives the value of
          bit 0 of byte 0.  The coefficient of x^7 gives bit 7 of
          byte 3, and the coefficient of x^0 gives bit 0 of byte 3.
          The resulting four-byte transport-level sequence is the
          32-bit SCTP checksum value.
    IMPLEMENTATION NOTE: Standards documents, textbooks, and vendor
    literature on CRCs often follow an alternative formulation, in
    which the register used to hold the remainder of the
    long-division algorithm is initialized to zero rather than
    all-1s, and instead the first 32 bits of the message are
    complemented.  The long-division algorithm used in our
    formulation is specified such that the initial
    multiplication by 2^32 and the long-division are combined into
    one simultaneous operation.  For such algorithms, and for
    messages longer than 64 bits, the two specifications are
    precisely equivalent.  That equivalence is the intent of
    this document.
    Implementors of SCTP are warned that both specifications are to be
    found in the literature, sometimes with no restriction on the
    long-division algorithm.  The choice of formulation in this
    document is to permit non-SCTP usage, where the same CRC
    algorithm may be used to protect messages shorter than 64 bits.
    There may be a computational advantage in validating the
    Association against the Verification Tag, prior to performing a
    checksum, as invalid tags will result in the same action as a bad
    checksum in most cases.  The exceptions for this technique would
    be INIT and some SHUTDOWN-COMPLETE exchanges, as well as a stale
    COOKIE-ECHO.  These special case exchanges must represent small
    packets and will minimize the effect of the checksum calculation.
  1. ——–

Old text: (Section 18)

  1. ——–
 18.  Bibliography
 [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End
            Network Path Properties", Proc. SIGCOMM'99, 1999.

Stewart, et al. Informational [Page 84] RFC 4460 SCTP Errata April 2006

 [FALL96]   Fall, K. and Floyd, S., Simulation-based Comparisons of
            Tahoe, Reno, and SACK TCP, Computer Communications Review,
            V. 26 N. 3, July 1996, pp.  5-21.
 [RFC1750]  Eastlake, D. (ed.), "Randomness Recommendations for
            Security", RFC 1750, December 1994.
 [RFC1950]  Deutsch P. and J. Gailly, "ZLIB Compressed Data Format
            Specification version 3.3", RFC 1950, May 1996.
 [RFC2104]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:  Keyed-
            Hashing for Message Authentication", RFC 2104, March 1997.
 [RFC2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
            September 1997.
 [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
            Protocol", RFC 2522, March 1999.
 [SAVAGE99] Savage, S., Cardwell, N., Wetherall, D., and Anderson, T.,
            "TCP Congestion Control with a Misbehaving Receiver",  ACM
            Computer Communication Review, 29(5), October 1999.
  1. ——–

New text: (Section 18, including changes from 2.11)

  1. ——–
 18.  Bibliography
 [ALLMAN99] Allman, M. and Paxson, V., "On Estimating End-to-End
            Network Path Properties", Proc. SIGCOMM'99, 1999.
 [FALL96]   Fall, K. and Floyd, S., Simulation-based Comparisons of
            Tahoe, Reno, and SACK TCP, Computer Communications Review,
            V. 26 N. 3, July 1996, pp.  5-21.
 [ITU32]         ITU-T Recommendation V.42, "Error-correcting
                 procedures for DCEs using asynchronous-to-synchronous
                 conversion", Section 8.1.1.6.2, October 1996.
 [PETERSON 1972] W. W. Peterson and E.J Weldon, Error Correcting
                 Codes, 2nd Edition, MIT Press, Cambridge,
                 Massachusetts.
 [RFC1750]  Eastlake, D., Ed., "Randomness Recommendations for
            Security", RFC 1750, December 1994.

Stewart, et al. Informational [Page 85] RFC 4460 SCTP Errata April 2006

 [RFC1858]  Ziemba, G., Reed, D. and Traina P., "Security
            Considerations for IP Fragment Filtering", RFC 1858,
            October 1995.
 [RFC1950]  Deutsch P. and J. Gailly, "ZLIB Compressed Data Format
            Specification version 3.3", RFC 1950, May 1996.
 [RFC2104]  Krawczyk, H., Bellare, M. and R. Canetti, "HMAC:  Keyed-
            Hashing for Message Authentication", RFC 2104, March 1997.
 [RFC2196]  Fraser, B., "Site Security Handbook", FYI 8, RFC 2196,
            September 1997.
 [RFC2522]  Karn, P. and W. Simpson, "Photuris: Session-Key Management
            Protocol", RFC 2522, March 1999.
 [SAVAGE99] Savage, S., Cardwell, N., Wetherall, D., and Anderson, T.,
            "TCP Congestion Control with a Misbehaving Receiver", ACM
            Computer Communication Review, 29(5), October 1999.
 [WILLIAMS93]    Williams, R., "A PAINLESS GUIDE TO CRC ERROR
                 DETECTION ALGORITHMS" - Internet publication, August
                 1993,
                 http://www.geocities.com/SiliconValley/Pines/
                 8659/crc.htm.

2.38.3. Solution Description

 This change adds to the implementor's guide the complete set of
 changes that, when combined with RFC 2960 [5], encompasses the
 changes from RFC 3309 [6].

2.39. Retransmission Policy

2.39.1. Description of the Problem

 The current retransmission policy (send all retransmissions an
 alternate destination) in the specification has performance issues
 under certain loss conditions with multihomed endpoints.  Instead,
 fast retransmissions should be sent to the same destination, and only
 timeout retransmissions should be sent to an alternate destination
 [4].

Stewart, et al. Informational [Page 86] RFC 4460 SCTP Errata April 2006

2.39.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.4)

  1. ——–
 Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
 retransmit a chunk to an active destination transport address that is
 different from the last destination address to which the DATA chunk
 was sent.
  1. ——–

New text: (Section 6.4)

  1. ——–
 Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
 retransmit a chunk that timed out to an active destination transport
 address that is different from the last destination address to which
 the DATA chunk was sent.
  1. ——–

Old text: (Section 6.4.1)

  1. ——–
 When retransmitting data, if the endpoint is multi-homed, it should
 consider each source-destination address pair in its retransmission
 selection policy.  When retransmitting the endpoint should attempt to
 pick the most divergent source-destination pair from the original
 source-destination pair to which the packet was transmitted.
  1. ——–

New text: (Section 6.4.1)

  1. ——–
 When retransmitting data that timed out, if the endpoint is
 multi-homed, it should consider each source-destination address
 pair in its retransmission selection policy.  When retransmitting
 timed out data, the endpoint should attempt to pick the most
 divergent source-destination pair from the original
 source-destination pair to which the packet was transmitted.

2.39.3. Solution Description

 The above wording changes clarify that only timeout retransmissions
 should be sent to an alternate active destination.

Stewart, et al. Informational [Page 87] RFC 4460 SCTP Errata April 2006

2.40. Port Number 0

2.40.1. Description of the Problem

 The port number 0 has a special semantic in various APIs.  For
 example, in the socket API, if the user specifies 0, the SCTP
 implementation chooses an appropriate port number for the user.
 Therefore, the port number 0 should not be used on the wire.

2.40.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.1)

  1. ——–
    Source Port Number: 16 bits (unsigned integer)
       This is the SCTP sender's port number.  It can be used by the
       receiver in combination with the source IP address, the SCTP
       destination port, and possibly the destination IP address to
       identify the association to which this packet belongs.
    Destination Port Number: 16 bits (unsigned integer)
       This is the SCTP port number to which this packet is destined.
       The receiving host will use this port number to de-multiplex
       the SCTP packet to the correct receiving endpoint/application.
  1. ——–

New text: (Section 3.1)

  1. ——–
    Source Port Number: 16 bits (unsigned integer)
       This is the SCTP sender's port number.  It can be used by the
       receiver in combination with the source IP address, the SCTP
       destination port and possibly the destination IP address to
       identify the association to which this packet belongs.
       The port number 0 MUST NOT be used.
    Destination Port Number: 16 bits (unsigned integer)
       This is the SCTP port number to which this packet is destined.
       The receiving host will use this port number to de-multiplex
       the SCTP packet to the correct receiving endpoint/application.
       The port number 0 MUST NOT be used.

Stewart, et al. Informational [Page 88] RFC 4460 SCTP Errata April 2006

2.40.3. Solution Description

 It is clearly stated that the port number 0 is an invalid value on
 the wire.

2.41. T Bit

2.41.1. Description of the Problem

 The description of the T bit as the bit describing whether a TCB has
 been destroyed is misleading.  In addition, the procedure described
 in Section 2.13 is not as precise as needed.

2.41.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.7)

  1. ——–
    T bit:  1 bit
       The T bit is set to 0 if the sender had a TCB that it
       destroyed.  If the sender did not have a TCB it should set
       this bit to 1.
  1. ——–

New text: (Section 3.3.7)

  1. ——–
    T bit:  1 bit
       The T bit is set to 0 if the sender filled in the
       Verification Tag expected by the peer.  If the Verification
       Tag is reflected, the T bit MUST be set to 1.  Reflecting means
       that the sent Verification Tag is the same as the received
       one.
  1. ——–

Old text: (Section 3.3.13)

  1. ——–
    T bit:  1 bit
       The T bit is set to 0 if the sender had a TCB that it
       destroyed.  If the sender did not have a TCB it should set
       this bit to 1.

Stewart, et al. Informational [Page 89] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 3.3.13)

  1. ——–
    T bit:  1 bit
       The T bit is set to 0 if the sender filled in the
       Verification Tag expected by the peer.  If the Verification
       Tag is reflected, the T bit MUST be set to 1.  Reflecting means
       that the sent Verification Tag is the same as the received
       one.
  1. ——–

Old text: (Section 8.4)

  1. ——–
     3) If the packet contains an INIT chunk with a Verification Tag
        set to '0', process it as described in Section 5.1.
        Otherwise,
  1. ——–

New text: (Section 8.4)

  1. ——–

3) If the packet contains an INIT chunk with a Verification Tag

       set to '0', process it as described in Section 5.1.  If, for
       whatever reason, the INIT cannot be processed normally and
       an ABORT has to be sent in response, the Verification Tag of
       the packet containing the ABORT chunk MUST be the Initiate
       tag of the received INIT chunk, and the T-Bit of the ABORT
       chunk has to be set to 0, indicating that the Verification
       Tag is NOT reflected.
  1. ——–

Old text: (Section 8.4)

  1. ——–

5) If the packet contains a SHUTDOWN ACK chunk, the receiver

       should respond to the sender of the OOTB packet with a
       SHUTDOWN COMPLETE.  When sending the SHUTDOWN COMPLETE, the
       receiver of the OOTB packet must fill in the Verification
       Tag field of the outbound packet with the Verification Tag
       received in the SHUTDOWN ACK and set the T-bit in the Chunk
       Flags to indicate that no TCB was found.  Otherwise,

Stewart, et al. Informational [Page 90] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Section 8.4)

  1. ——–
    5) If the packet contains a SHUTDOWN ACK chunk, the receiver
       should respond to the sender of the OOTB packet with a
       SHUTDOWN COMPLETE.  When sending the SHUTDOWN COMPLETE, the
       receiver of the OOTB packet must fill in the Verification
       Tag field of the outbound packet with the Verification Tag
       received in the SHUTDOWN ACK and set the T-bit in the
       Chunk Flags to indicate that the Verification Tag is
       reflected.  Otherwise,
  1. ——–

Old text: (Section 8.4)

  1. ——–
    8) The receiver should respond to the sender of the OOTB packet
       with an ABORT.  When sending the ABORT, the receiver of the
       OOTB packet MUST fill in the Verification Tag field of the
       outbound packet with the value found in the Verification
       Tag field of the OOTB packet and set the T-bit in the Chunk
       Flags to indicate that no TCB was found.  After sending this
       ABORT, the receiver of the OOTB packet shall discard the
       OOTB packet and take no further action.
  1. ——–

New text: (Section 8.4)

  1. ——–
    8) The receiver should respond to the sender of the OOTB packet
       with an ABORT.  When sending the ABORT, the receiver of the
       OOTB packet MUST fill in the Verification Tag field of the
       outbound packet with the value found in the Verification Tag
       field of the OOTB packet and set the T-bit in the Chunk Flags
       to indicate that the Verification Tag is reflected.  After
       sending this ABORT, the receiver of the OOTB packet shall
       discard the OOTB packet and take no further action.
  1. ——–

Old text: (Section 8.5.1)

  1. ——–
    B) Rules for packet carrying ABORT:

Stewart, et al. Informational [Page 91] RFC 4460 SCTP Errata April 2006

  1. The endpoint shall always fill in the Verification Tag

field of the outbound packet with the destination

          endpoint's tag value if it is known.
  1. If the ABORT is sent in response to an OOTB packet, the

endpoint MUST follow the procedure described in

          Section 8.4.
  1. The receiver MUST accept the packet if the Verification

Tag matches either its own tag, OR the tag of its peer.

          Otherwise, the receiver MUST silently discard the packet
          and take no further action.
  1. ——–

New text: (Section 8.5.1)

  1. ——–
   B) Rules for packet carrying ABORT:
  1. The endpoint MUST always fill in the Verification Tag

field of the outbound packet with the destination

          endpoint's tag value, if it is known.
  1. If the ABORT is sent in response to an OOTB packet, the

endpoint MUST follow the procedure described in

          Section 8.4.
  1. The receiver of an ABORT MUST accept the packet

if the Verification Tag field of the packet matches its

          own tag and the T bit is not set
          OR
          if it is set to its peer's tag and the T bit is set in
          the Chunk Flags.
          Otherwise, the receiver MUST silently discard the packet
          and take no further action.
  1. ——–

Old text: (Section 8.5.1)

  1. ——–
    C) Rules for packet carrying SHUTDOWN COMPLETE:
  1. When sending a SHUTDOWN COMPLETE, if the receiver of the

SHUTDOWN ACK has a TCB then the destination endpoint's

          tag MUST be used.  Only where no TCB exists should the
          sender use the Verification Tag from the SHUTDOWN ACK.

Stewart, et al. Informational [Page 92] RFC 4460 SCTP Errata April 2006

  1. The receiver of a SHUTDOWN COMPLETE shall accept the

packet if the Verification Tag field of the packet matches

          its own tag OR it is set to its peer's tag and the T bit
          is set in the Chunk Flags.  Otherwise, the receiver MUST
          silently discard the packet and take no further action.
          An endpoint MUST ignore the SHUTDOWN COMPLETE if it is
          not in the SHUTDOWN-ACK-SENT state.
  1. ——–

New text: (Section 8.5.1)

  1. ——–
    C) Rules for packet carrying SHUTDOWN COMPLETE:
  1. When sending a SHUTDOWN COMPLETE, if the receiver of the

SHUTDOWN ACK has a TCB, then the destination endpoint's tag

          MUST be used, and the T-bit MUST NOT be set.  Only where no
          TCB exists should the sender use the Verification Tag from
          the SHUTDOWN ACK, and MUST set the T-bit.
  1. The receiver of a SHUTDOWN COMPLETE shall accept the packet

if the Verification Tag field of the packet matches its own

          tag and the T bit is not set
          OR
          if it is set to its peer's tag and the T bit is set in the
          Chunk Flags.
          Otherwise, the receiver MUST silently discard the packet
          and take no further action.  An endpoint MUST ignore the
          SHUTDOWN COMPLETE if it is not in the SHUTDOWN-ACK-SENT
          state.

2.41.3. Solution Description

 The description of the T bit now clearly describes the semantic of
 the bit.  The procedures for receiving the T bit have been clarified.

2.42. Unknown Parameter Handling

2.42.1. Description of the Problem

 The description given in Section 2.33 does not state clearly whether
 an INIT-ACK or COOKIE-ECHO is sent.

2.42.2. Text Changes to the Document

 The changes given here already include changes suggested in Section
 2.2, 2.27, and 2.33 of this document.

Stewart, et al. Informational [Page 93] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this SCTP packet and discard it do not process
      any further chunks within it.
 01 - Stop processing this SCTP packet and discard it, do not process
      any further chunks within it, and report the unrecognized
      parameter in an 'Unrecognized Parameter Type' (in either an
      ERROR or in the INIT ACK).
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter Type' (in
      either an ERROR or in the INIT ACK).
  1. ——–

New text: (Section 3.2.1)

  1. ——–
 00 - Stop processing this parameter; do not process
      any further parameters within this chunk.
 01 - Stop processing this parameter, do not process
      any further parameters within this chunk, and report the
      unrecognized parameter in an 'Unrecognized Parameter', as
      described in 3.2.2.
 10 - Skip this parameter and continue processing.
 11 - Skip this parameter and continue processing but report the
      unrecognized parameter in an 'Unrecognized Parameter', as
      described in 3.2.2.
 Please note that in all four cases an INIT-ACK or COOKIE-ECHO
 chunk is sent.  In the 00 or 01 case the processing of the
 parameters after the unknown parameter is canceled, but no
 processing already done is rolled back.

Stewart, et al. Informational [Page 94] RFC 4460 SCTP Errata April 2006

  1. ——–

New text: (Note: no old text; clarification added in Section 3.2)

  1. ——–
 3.2.2.  Reporting of Unrecognized Parameters
    If the receiver of an INIT chunk detects unrecognized parameters
    and has to report them according to Section 3.2.1, it MUST put
    the 'Unrecognized Parameter' parameter(s) in the INIT-ACK chunk
    sent in response to the INIT-chunk.  Note that if the receiver
    of the INIT chunk is NOT going to establish an association (e.g.,
    due to lack of resources), an 'Unrecognized Parameter' would NOT
    be included with any ABORT being sent to the sender of the INIT.
    If the receiver of an INIT-ACK chunk detects unrecognized
    parameters and has to report them according to Section 3.2.1, it
    SHOULD bundle the ERROR chunk containing the 'Unrecognized
    Parameters' error cause with the COOKIE-ECHO chunk sent in
    response to the INIT-ACK chunk.  If the receiver of the INIT-ACK
    cannot bundle the COOKIE-ECHO chunk with the ERROR chunk, the
    ERROR chunk MAY be sent separately but not before the COOKIE-ACK
    has been received.
    Note: Any time a COOKIE-ECHO is sent in a packet, it MUST be the
    first chunk.

2.42.3. Solution Description

 The new text clearly states that an INIT-ACK or COOKIE-ECHO has to be
 sent.

2.43. Cookie Echo Chunk

2.43.1. Description of the Problem

 The description given in Section 3.3.11 of RFC 2960 [5] is unclear as
 to how the COOKIE-ECHO is composed.

2.43.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.11)

  1. ——–

Cookie: variable size

       This field must contain the exact cookie received in the State
       Cookie parameter from the previous INIT ACK.

Stewart, et al. Informational [Page 95] RFC 4460 SCTP Errata April 2006

       An implementation SHOULD make the cookie as small as possible
       to insure interoperability.
  1. ——–

New text: (Section 3.3.11)

  1. ——–

Cookie: variable size

       This field must contain the exact cookie received in the State
       Cookie parameter from the previous INIT ACK.
       An implementation SHOULD make the cookie as small as possible
       to ensure interoperability.
       Note: A Cookie Echo does NOT contain a State Cookie
       Parameter; instead, the data within the State Cookie's
       Parameter Value becomes the data within the Cookie Echo's
       Chunk Value.  This allows an implementation to change only
       the first two bytes of the State Cookie parameter to become
       a Cookie Echo Chunk.

2.43.3. Solution Description

 The new text adds a note that helps clarify that a Cookie Echo chunk
 is nothing more than the State Cookie parameter with only two bytes
 modified.

2.44. Partial Chunks

2.44.1. Description of the Problem

 Section 6.10 of RFC 2960 [5] uses the notion of 'partial chunks'
 without defining it.

2.44.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.10)

  1. ——–

Partial chunks MUST NOT be placed in an SCTP packet.

  1. ——–

New text: (Section 6.10)

  1. ——–

Partial chunks MUST NOT be placed in an SCTP packet. A partial

 chunk is a chunk that is not completely contained in the SCTP
 packet; i.e., the SCTP packet is too short to contain all the bytes
 of the chunk as indicated by the chunk length.

Stewart, et al. Informational [Page 96] RFC 4460 SCTP Errata April 2006

2.44.3. Solution Description

 The new text adds a definition of 'partial chunks'.

2.45. Non-unicast Addresses

2.45.1. Description of the Problem

 Section 8.4 of RFC 2960 [5] forces the OOTB handling to discard all
 non-unicast addresses.  This leaves future use of anycast addresses
 in question.  With the addition of the add-ip feature, SCTP should be
 able to easily handle anycast INIT s that can be followed, after
 association setup, with a delete of the anycast address from the
 association.

2.45.2. Text Changes to the Document

  1. ——–

Old text: (Section 8.4)

  1. ——–

8.4 Handle "Out of the blue" Packets

    An SCTP packet is called an "out of the blue" (OOTB) packet if
    it is correctly formed, i.e., passed the receiver's Adler-32
    check (see Section 6.8), but the receiver is not able to
    identify the association to which this packet belongs.
    The receiver of an OOTB packet MUST do the following:
    1) If the OOTB packet is to or from a non-unicast address,
       silently discard the packet.  Otherwise,
  1. ——–

New text: (Section 8.4)

  1. ——–
 8.4.  Handle "Out of the Blue" Packets
    An SCTP packet is called an "out of the blue" (OOTB) packet if
    it is correctly formed (i.e., passed the receiver's CRC32c
    check; see Section 6.8), but the receiver is not able to identify
    the association to which this packet belongs.
    The receiver of an OOTB packet MUST do the following:
    1) If the OOTB packet is to or from a non-unicast address, a
       receiver SHOULD silently discard the packet.  Otherwise,

Stewart, et al. Informational [Page 97] RFC 4460 SCTP Errata April 2006

2.45.3. Solution Description

 The loosening of the wording to a SHOULD will now allow future use of
 anycast addresses.  Note that no changes are made to Section
 11.2.4.1, since responding to broadcast addresses could lead to
 flooding attacks and implementors should pay careful attention to
 these words.

2.46. Processing of ABORT Chunks

2.46.1. Description of the Problem

 Section 3.3.7 of RFC 2960 [5] requires an SCTP endpoint to silently
 discard ABORT chunks received for associations that do not exist.  It
 is not clear what this means in the COOKIE-WAIT state, for example.
 Therefore, it was not clear whether an ABORT sent in response to an
 INIT should be processed or silently discarded.

2.46.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.7)

  1. ——–
    If an endpoint receives an ABORT with a format error or for an
    association that doesn't exist, it MUST silently discard it.
  1. ——–

New text: (Section 3.3.7)

  1. ——–
    If an endpoint receives an ABORT with a format error or no
    TCB is found, it MUST silently discard it.

2.46.3. Solution Description

 It is now clearly stated that an ABORT chunk should be processed
 whenever a TCB is found.

Stewart, et al. Informational [Page 98] RFC 4460 SCTP Errata April 2006

2.47. Sending of ABORT Chunks

2.47.1. Description of the Problem

 Section 5.1 of RFC 2960 [5] requires that an ABORT chunk be sent in
 response to an INIT chunk when there is no listening end point.  To
 make port scanning harder, someone might not want these ABORTs to be
 received by the sender of the INIT chunks.  Currently, the only way
 to enforce this is by using a firewall that discards the packets
 containing the INIT chunks or the packets containing the ABORT
 chunks.  It is desirable that the same can be done without a middle
 box.

2.47.2. Text Changes to the Document

  1. ——–

Old text: (Section 5.1)

  1. ——–
    If an endpoint receives an INIT, INIT ACK, or COOKIE ECHO chunk
    but decides not to establish the new association due to missing
    mandatory parameters in the received INIT or INIT ACK, invalid
    parameter values, or lack of local resources, it MUST respond with
    an ABORT chunk.
  1. ——–

New text: (Section 5.1)

  1. ——–
    If an endpoint receives an INIT, INIT ACK, or COOKIE ECHO chunk
    but decides not to establish the new association due to missing
    mandatory parameters in the received INIT or INIT ACK, invalid
    parameter values, or lack of local resources, it SHOULD respond
    with an ABORT chunk.

2.47.3. Solution Description

 The requirement of sending ABORT chunks is relaxed such that an
 implementation can decide not to send ABORT chunks.

2.48. Handling of Supported Address Types Parameter

2.48.1. Description of the Problem

 The sender of the INIT chunk can include a 'Supported Address Types'
 parameter to indicate which address families are supported.  It is
 unclear how an INIT chunk should be processed where the source
 address of the packet containing the INIT chunk or listed addresses

Stewart, et al. Informational [Page 99] RFC 4460 SCTP Errata April 2006

 within the INIT chunk indicate that more address types are supported
 than those listed in the 'Supported Address Types' parameter.

2.48.2. Text Changes to the Document

 The changes given here already include changes suggested in Section
 2.28 of this document.
  1. ——–

Old text: (Section 5.1.2)

  1. ——–
    IMPLEMENTATION NOTE: In the case that the receiver of an INIT ACK
    fails to resolve the address parameter due to an unsupported type,
    it can abort the initiation process and then attempt a
    re-initiation by using a 'Supported Address Types' parameter in
    the new INIT to indicate what types of address it prefers.
  1. ——–

New text: (Section 5.1.2)

  1. ——–
    IMPLEMENTATION NOTE: In the case that the receiver of an INIT ACK
    fails to resolve the address parameter due to an unsupported type,
    it can abort the initiation process and then attempt a re-
    initiation by using a 'Supported Address Types' parameter in the
    new INIT to indicate what types of address it prefers.
    IMPLEMENTATION NOTE: If an SCTP endpoint that only supports either
    IPv4 or IPv6 receives IPv4 and IPv6 addresses in an INIT or INIT-
    ACK chunk from its peer, it MUST use all the addresses belonging
    to the supported address family.  The other addresses MAY be
    ignored.  The endpoint SHOULD NOT respond with any kind of error
    indication.
    IMPLEMENTATION NOTE: If an SCTP endpoint lists in the 'Supported
    Address Types' parameter either IPv4 or IPv6, but uses the other
    family for sending the packet containing the INIT chunk, or if it
    also lists addresses of the other family in the INIT chunk, then
    the address family that is not listed in the 'Supported Address
    Types' parameter SHOULD also be considered as supported by the
    receiver of the INIT chunk.  The receiver of the INIT chunk SHOULD
    NOT respond with any kind of error indication.

2.48.3. Solution Description

 It is now clearly described how these Supported Address Types
 parameters with incorrect data should be handled.

Stewart, et al. Informational [Page 100] RFC 4460 SCTP Errata April 2006

2.49. Handling of Unexpected Parameters

2.49.1. Description of the Problem

 RFC 2960 [5] clearly describes how unknown parameters in the INIT and
 INIT-ACK chunk should be processed.  But it is not described how
 unexpected parameters should be processed.  A parameter is unexpected
 if it is known and is an optional parameter in either the INIT or
 INIT-ACK chunk but is received in the chunk for which it is not an
 optional parameter.  For example, the 'Supported Address Types'
 parameter would be an unexpected parameter if contained in an INIT-
 ACK chunk.

2.49.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.2)

  1. ——–
    Note 4: This parameter, when present, specifies all the address
    types the sending endpoint can support.  The absence of this
    parameter indicates that the sending endpoint can support any
    address type.
  1. ——–

New text: (Section 3.3.2)

  1. ——–
    Note 4: This parameter, when present, specifies all the address
    types the sending endpoint can support.  The absence of this
    parameter indicates that the sending endpoint can support any
    address type.
    IMPLEMENTATION NOTE: If an INIT chunk is received with known
    parameters that are not optional parameters of the INIT chunk
    then the receiver SHOULD process the INIT chunk and send back
    an INIT-ACK.  The receiver of the INIT chunk MAY bundle an ERROR
    chunk with the COOKIE-ACK chunk later.  However, restrictive
    implementations MAY send back an ABORT chunk in response to
    the INIT chunk.

Stewart, et al. Informational [Page 101] RFC 4460 SCTP Errata April 2006

  1. ——–

Old text: (Section 3.3.3)

  1. ——–
    IMPLEMENTATION NOTE: An implementation MUST be prepared to receive
    a INIT ACK that is quite large (more than 1500 bytes) due to the
    variable size of the state cookie AND the variable address list.
    For example if a responder to the INIT has 1000 IPv4 addresses
    it wishes to send, it would need at least 8,000 bytes to encode
    this in the INIT ACK.
  1. ——–

New text: (Section 3.3.3)

  1. ——–
    IMPLEMENTATION NOTE: An implementation MUST be prepared to receive
    a INIT ACK that is quite large (more than 1500 bytes) due to the
    variable size of the state cookie AND the variable address list.
    For example, if a responder to the INIT has 1000 IPv4 addresses
    it wishes to send, it would need at least 8,000 bytes to encode
    this in the INIT ACK.
    IMPLEMENTATION NOTE: If an INIT-ACK chunk is received with known
    parameters that are not optional parameters of the INIT-ACK
    chunk, then the receiver SHOULD process the INIT-ACK chunk and
    send back a COOKIE-ECHO.  The receiver of the INIT-ACK chunk
    MAY bundle an ERROR chunk with the COOKIE-ECHO chunk.  However,
    restrictive implementations MAY send back an ABORT chunk in
    response to the INIT-ACK chunk.

2.49.3. Solution Description

 It is now stated how unexpected parameters should be processed.

2.50. Payload Protocol Identifier

2.50.1. Description of the Problem

 The current description of the payload protocol identifier does NOT
 highlight the fact that the field is NOT necessarily in network byte
 order.

Stewart, et al. Informational [Page 102] RFC 4460 SCTP Errata April 2006

2.50.2. Text Changes to the Document

  1. ——–

Old text: (Section 3.3.1)

  1. ——–

Payload Protocol Identifier: 32 bits (unsigned integer)

       This value represents an application (or upper layer) specified
       protocol identifier.  This value is passed to SCTP by its upper
       layer and sent to its peer.  This identifier is not used by
       SCTP but can be used by certain network entities as well as
       the peer application to identify the type of information being
       carried in this DATA chunk.  This field must be sent even in
       fragmented DATA chunks (to make sure it is available for agents
       in the middle of the network).
       The value 0 indicates no application identifier is specified by
       the upper layer for this payload data.
  1. ——–

New text: (Section 3.3.1)

  1. ——–

Payload Protocol Identifier: 32 bits (unsigned integer)

       This value represents an application (or upper layer) specified
       protocol identifier.  This value is passed to SCTP by its upper
       layer and sent to its peer.  This identifier is not used by
       SCTP but can be used by certain network entities, as well as by
       the peer application, to identify the type of information being
       carried in this DATA chunk.  This field must be sent even in
       fragmented DATA chunks (to make sure it is available for agents
       in the middle of the network).  Note that this field is NOT
       touched by an SCTP implementation, therefore its byte order is
       NOT necessarily Big Endian.  The upper layer is responsible
       for any byte order conversions to this field.
       The value 0 indicates that no application identifier is
       specified by the upper layer for this payload data.

2.50.3. Solution Description

 It is now explicitly stated that the upper layer is responsible for
 the byte order of this field.

Stewart, et al. Informational [Page 103] RFC 4460 SCTP Errata April 2006

2.51. Karn's Algorithm

2.51.1. Description of the Problem

 The current wording of the use of Karn's algorithm is not descriptive
 enough to ensure that an implementation in a multi-homed association
 does not incorrectly mismeasure the RTT.

2.51.2. Text Changes to the Document

  1. ——–

Old text: (Section 6.3.1)

  1. ——–
    C5) Karn's algorithm: RTT measurements MUST NOT be made using
        packets that were retransmitted (and thus for which it is
        ambiguous whether the reply was for the first instance of the
        packet or a later instance)
 ---------
 New text: (Section 6.3.1)
 ---------
    C5) Karn's algorithm: RTT measurements MUST NOT be made using
        chunks that were retransmitted (and thus for which it is
        ambiguous whether the reply was for the first instance of
        the chunk or for a later instance)
        IMPLEMENTATION NOTE: RTT measurements should only be
        made using a chunk with TSN r if no chunk
        with TSN less than or equal to r is retransmitted
        since r is first sent.

2.51.3. Solution Description

 The above clarification adds an implementation note that will provide
 additional guidance in the application of Karn's algorithm.

2.52. Fast Retransmit Algorithm

2.52.1. Description of the Problem

 The original SCTP specification is overly conservative in requiring 4
 missing reports before fast retransmitting a segment.  TCP uses 3
 missing reports or 4 acknowledgements indicating that the same
 segment was received.

Stewart, et al. Informational [Page 104] RFC 4460 SCTP Errata April 2006

2.52.2. Text Changes to the Document

  1. ——–

Old text:

  1. ——–
 7.2.4 Fast Retransmit on Gap Reports
    In the absence of data loss, an endpoint performs delayed
    acknowledgement.  However, whenever an endpoint notices a hole in
    the arriving TSN sequence, it SHOULD start sending a SACK back
    every time a packet arrives carrying data until the
    hole is filled.
    Whenever an endpoint receives a SACK that indicates some TSN(s)
    missing, it SHOULD wait for 3 further miss indications (via
    subsequent SACK's) on the same TSN(s) before taking action with
    regard to Fast Retransmit.
  1. ——–

New text:

  1. ——–
 7.2.4.  Fast Retransmit on Gap Reports
    In the absence of data loss, an endpoint performs delayed
    acknowledgement.  However, whenever an endpoint notices a hole in
    the arriving TSN sequence, it SHOULD start sending a SACK back
    every time a packet arrives carrying data until the
    hole is filled.
    Whenever an endpoint receives a SACK that indicates that some
    TSNs are missing, it SHOULD wait for 2 further miss indications
    (via subsequent SACKs for a total of 3 missing reports) on the
    same TSNs before taking action with regard to Fast Retransmit.

2.52.3. Solution Description

 The above changes will make SCTP and TCP behave similarly in terms of
 how fast they engage the Fast Retransmission algorithm upon receiving
 missing reports.

3. Security Considerations

 This document should add no additional security risks to SCTP and in
 fact SHOULD correct some original security flaws within the original
 document once it is incorporated into a RFC 2960 [5] BIS document.

Stewart, et al. Informational [Page 105] RFC 4460 SCTP Errata April 2006

4. Acknowledgements

 The authors would like to thank the following people who have
 provided comments and input for this document:
 Barry Zuckerman, La Monte Yarroll, Qiaobing Xie, Wang Xiaopeng,
 Jonathan Wood, Jeff Waskow, Mike Turner, John Townsend, Sabina
 Torrente, Cliff Thomas, Yuji Suzuki, Manoj Solanki, Sverre Slotte,
 Keyur Shah, Jan Rovins, Ben Robinson, Renee Revis, Ian Periam, RC
 Monee, Sanjay Rao, Sujith Radhakrishnan, Heinz Prantner, Biren Patel,
 Nathalie Mouellic, Mitch Miers, Bernward Meyknecht, Stan McClellan,
 Oliver Mayor, Tomas Orti Martin, Sandeep Mahajan, David Lehmann,
 Jonathan Lee, Philippe Langlois, Karl Knutson, Joe Keller, Gareth
 Keily, Andreas Jungmaier, Janardhan Iyengar, Mutsuya Irie, John
 Hebert, Kausar Hassan, Fred Hasle, Dan Harrison, Jon Grim, Laurent
 Glaude, Steven Furniss, Atsushi Fukumoto, Ken Fujita, Steve Dimig,
 Thomas Curran, Serkan Cil, Melissa Campbell, Peter Butler, Rob
 Brennan, Harsh Bhondwe, Brian Bidulock, Caitlin Bestler, Jon Berger,
 Robby Benedyk, Stephen Baucke, Sandeep Balani, and Ronnie Sellar.
 A special thanks to Mark Allman, who should actually be a co-author
 for his work on the max-burst, but managed to wiggle out due to a
 technicality.  Also, we would like to acknowledge Lyndon Ong and Phil
 Conrad for their valuable input and many contributions.

5. IANA Considerations

 This document recommends changes for the RFC 2960 [5] BIS document.
 As such, even though it lists new error cause code, this document in
 itself does NOT define those new codes.  Instead, the BIS document
 will make the needed changes to RFC 2960 [5] and thus its IANA
 section will require changes to be made.

6. Normative References

 [1]  Braden, R., "Requirements for Internet Hosts - Communication
      Layers", STD 3, RFC 1122, October 1989.
 [2]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [3]  Caro, A., Shah, K., Iyengar, J., Amer, P., and R. Stewart, "SCTP
      and TCP Variants: Congestion Control Under Multiple Losses",
      Technical Report TR2003-04, Computer and Information Sciences
      Department, University of Delaware, February 2003,
      <http://www.armandocaro.net/papers>.

Stewart, et al. Informational [Page 106] RFC 4460 SCTP Errata April 2006

 [4]  Caro, A., Amer, P., and R. Stewart, "Retransmission Schemes for
      End-to-end Failover with Transport Layer Multihoming", GLOBECOM,
      November 2004., <http://www.armandocaro.net/papers>.
 [5]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
      H., Taylor, T., Rytina, I., Kalla, M., Zhang, L., and V.
      Paxson, "Stream Control Transmission Protocol", RFC 2960,
      October 2000.
 [6]  Stone, J., Stewart, R., and D. Otis, "Stream Control
      Transmission Protocol (SCTP) Checksum Change", RFC 3309,
      September 2002.

Stewart, et al. Informational [Page 107] RFC 4460 SCTP Errata April 2006

Authors' Addresses

 Randall R. Stewart
 Cisco Systems, Inc.
 4875 Forest Drive
 Suite 200
 Columbia, SC  29206
 USA
 EMail: rrs@cisco.com
 Ivan Arias-Rodriguez
 Nokia Research Center
 PO Box 407
 FIN-00045 Nokia Group
 Finland
 EMail: ivan.arias-rodriguez@nokia.com
 Kacheong Poon
 Sun Microsystems, Inc.
 3571 N. First St.
 San Jose, CA  95134
 USA
 EMail: kacheong.poon@sun.com
 Armando L. Caro Jr.
 BBN Technologies
 10 Moulton St.
 Cambridge, MA 02138
 EMail: acaro@bbn.com
 URI:   http://www.armandocaro.net
 Michael Tuexen
 Muenster Univ. of Applied Sciences
 Stegerwaldstr. 39
 48565 Steinfurt
 Germany
 EMail: tuexen@fh-muenster.de

Stewart, et al. Informational [Page 108] RFC 4460 SCTP Errata April 2006

Full Copyright Statement

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 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
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 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
 ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
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 Copies of IPR disclosures made to the IETF Secretariat and any
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Acknowledgement

 Funding for the RFC Editor function is provided by the IETF
 Administrative Support Activity (IASA).

Stewart, et al. Informational [Page 109]

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