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RFC 8540

Stream Control Transmission Protocol: Errata and Issues in RFC 4960

Pages: 94
Informational
Part 1 of 7 – Pages 1 to 12
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Internet Engineering Task Force (IETF)                        R. Stewart
Request for Comments: 8540                                 Netflix, Inc.
Category: Informational                                        M. Tuexen
ISSN: 2070-1721                         Muenster Univ. of Appl. Sciences
                                                              M. Proshin
                                                                Ericsson
                                                           February 2019


                 Stream Control Transmission Protocol:
                     Errata and Issues in RFC 4960

Abstract

   This document is a compilation of issues found since the publication
   of RFC 4960 in September 2007, based on experience with implementing,
   testing, and using the Stream Control Transmission Protocol (SCTP)
   along with the suggested fixes.  This document provides deltas to RFC
   4960 and is organized in a time-ordered way.  The issues are listed
   in the order in which 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 deltas, a description of each
   problem and the details of the solution for each are also provided.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8540.
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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Corrections to RFC 4960 . . . . . . . . . . . . . . . . . . .   4
     3.1.  Path Error Counter Threshold Handling . . . . . . . . . .   4
     3.2.  Upper-Layer Protocol Shutdown Request Handling  . . . . .   5
     3.3.  Registration of New Chunk Types . . . . . . . . . . . . .   6
     3.4.  Variable Parameters for INIT Chunks . . . . . . . . . . .   7
     3.5.  CRC32c Sample Code on 64-Bit Platforms  . . . . . . . . .   8
     3.6.  Endpoint Failure Detection  . . . . . . . . . . . . . . .   9
     3.7.  Data Transmission Rules . . . . . . . . . . . . . . . . .  10
     3.8.  T1-Cookie Timer . . . . . . . . . . . . . . . . . . . . .  11
     3.9.  Miscellaneous Typos . . . . . . . . . . . . . . . . . . .  12
     3.10. CRC32c Sample Code  . . . . . . . . . . . . . . . . . . .  19
     3.11. partial_bytes_acked after T3-rtx Expiration . . . . . . .  19
     3.12. Order of Adjustments of partial_bytes_acked and cwnd  . .  20
     3.13. HEARTBEAT ACK and the Association Error Counter . . . . .  21
     3.14. Path for Fast Retransmission  . . . . . . . . . . . . . .  22
     3.15. Transmittal in Fast Recovery  . . . . . . . . . . . . . .  23
     3.16. Initial Value of ssthresh . . . . . . . . . . . . . . . .  24
     3.17. Automatically CONFIRMED Addresses . . . . . . . . . . . .  25
     3.18. Only One Packet after Retransmission Timeout  . . . . . .  26
     3.19. INIT ACK Path for INIT in COOKIE-WAIT State . . . . . . .  27
     3.20. Zero Window Probing and Unreachable Primary Path  . . . .  28
     3.21. Normative Language in Section 10 of RFC 4960  . . . . . .  29
     3.22. Increase of partial_bytes_acked in Congestion Avoidance .  32
     3.23. Inconsistent Handling of Notifications  . . . . . . . . .  33
     3.24. SACK.Delay Not Listed as a Protocol Parameter . . . . . .  37
     3.25. Processing of Chunks in an Incoming SCTP Packet . . . . .  39
     3.26. Increasing the cwnd in the Congestion Avoidance Phase . .  41
     3.27. Refresh of cwnd and ssthresh after Idle Period  . . . . .  43
     3.28. Window Updates after Receiver Window Opens Up . . . . . .  45
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     3.29. Path of DATA and Reply Chunks . . . . . . . . . . . . . .  46
     3.30. "Outstanding Data", "Flightsize", and "Data in Flight"
           Key Terms . . . . . . . . . . . . . . . . . . . . . . . .  47
     3.31. Degradation of cwnd due to Max.Burst  . . . . . . . . . .  49
     3.32. Reduction of RTO.Initial  . . . . . . . . . . . . . . . .  50
     3.33. Ordering of Bundled SACK and ERROR Chunks . . . . . . . .  51
     3.34. Undefined Parameter Returned by RECEIVE Primitive . . . .  52
     3.35. DSCP Changes  . . . . . . . . . . . . . . . . . . . . . .  53
     3.36. Inconsistent Handling of ICMPv4 and ICMPv6 Messages . . .  55
     3.37. Handling of Soft Errors . . . . . . . . . . . . . . . . .  56
     3.38. Honoring cwnd . . . . . . . . . . . . . . . . . . . . . .  57
     3.39. Zero Window Probing . . . . . . . . . . . . . . . . . . .  58
     3.40. Updating References regarding ECN . . . . . . . . . . . .  60
     3.41. Host Name Address Parameter Deprecated  . . . . . . . . .  62
     3.42. Conflicting Text regarding the 'Supported Address Types'
           Parameter . . . . . . . . . . . . . . . . . . . . . . . .  66
     3.43. Integration of RFC 6096 . . . . . . . . . . . . . . . . .  67
     3.44. Integration of RFC 6335 . . . . . . . . . . . . . . . . .  70
     3.45. Integration of RFC 7053 . . . . . . . . . . . . . . . . .  72
     3.46. CRC32c Code Improvements  . . . . . . . . . . . . . . . .  76
     3.47. Clarification of Gap Ack Blocks in SACK Chunks  . . . . .  87
     3.48. Handling of SSN Wraparounds . . . . . . . . . . . . . . .  89
     3.49. Update to RFC 2119 Boilerplate Text . . . . . . . . . . .  90
     3.50. Removal of Text (Previously Missed in RFC 4960) . . . . .  91
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  91
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  92
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  92
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  92
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  92
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  94
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  94

1.  Introduction

   This document contains a compilation of all defects for [RFC4960]
   ("Stream Control Transmission Protocol") that were found up until the
   publication of this document.  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 the Stream Control
   Transmission Protocol (SCTP) to clarify errors in the original SCTP
   document.

   This document provides a history of the changes that will be compiled
   into a bis document for [RFC4960].  It is structured similarly to
   [RFC4460].
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   Each error will be detailed within this document in the form of:

   o  The problem description,

   o  The text quoted from [RFC4960],

   o  The replacement text that should be placed into an upcoming bis
      document, and

   o  A description of the solution.

   Note that when reading this document one must use care to ensure that
   a field or item is not updated later on within the document.  Since
   this document is a historical record of the sequential changes that
   have been found necessary at various interop events and through
   discussion on the Transport Area Working Group mailing list, the last
   delta in the text is the one that should be applied.

2.  Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Corrections to RFC 4960

3.1.  Path Error Counter Threshold Handling

3.1.1.  Description of the Problem

   The handling of the 'Path.Max.Retrans' parameter is described in
   Sections 8.2 and 8.3 of [RFC4960] in an inconsistent way.  Whereas
   Section 8.2 of [RFC4960] says that a path is marked inactive when the
   path error counter exceeds the threshold, Section 8.3 of [RFC4960]
   says that the path is marked inactive when the path error counter
   reaches the threshold.

   This issue was reported as an errata for [RFC4960] with
   Errata ID 1440.
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3.1.2.  Text Changes to the Document

   ---------
   Old text: (Section 8.3)
   ---------

   When the value of this counter reaches the protocol parameter
   'Path.Max.Retrans', the endpoint should mark the corresponding
   destination address as inactive if it is not so marked, and may also
   optionally report to the upper layer the change of reachability of
   this destination address.  After this, the endpoint should continue
   HEARTBEAT on this destination address but should stop increasing the
   counter.

   ---------
   New text: (Section 8.3)
   ---------

   When the value of this counter exceeds the protocol parameter
   'Path.Max.Retrans', the endpoint SHOULD mark the corresponding
   destination address as inactive if it is not so marked and MAY also
   optionally report to the upper layer the change in reachability of
   this destination address.  After this, the endpoint SHOULD continue
   HEARTBEAT on this destination address but SHOULD stop increasing the
   counter.

   This text has been modified by multiple errata.  It is further
   updated in Section 3.23.

3.1.3.  Solution Description

   The intended state change should happen when the threshold is
   exceeded.

3.2.  Upper-Layer Protocol Shutdown Request Handling

3.2.1.  Description of the Problem

   Section 9.2 of [RFC4960] describes the handling of received SHUTDOWN
   chunks in the SHUTDOWN-RECEIVED state instead of the handling of
   shutdown requests from its upper layer in this state.

   This issue was reported as an errata for [RFC4960] with
   Errata ID 1574.
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3.2.2.  Text Changes to the Document

   ---------
   Old text: (Section 9.2)
   ---------

   Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST NOT
   send a SHUTDOWN in response to a ULP request, and should discard
   subsequent SHUTDOWN chunks.

   ---------
   New text: (Section 9.2)
   ---------

   Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST
   ignore ULP shutdown requests but MUST continue responding to SHUTDOWN
   chunks from its peer.

   This text is in final form and is not further updated in this
   document.

3.2.3.  Solution Description

   The text never intended that the SCTP endpoint ignore SHUTDOWN chunks
   from its peer.  If it did, the endpoints could never gracefully
   terminate associations in some cases.

3.3.  Registration of New Chunk Types

3.3.1.  Description of the Problem

   Section 14.1 of [RFC4960] should deal with new chunk types; however,
   the text only refers to parameter types.

   This issue was reported as an errata for [RFC4960] with
   Errata ID 2592.

3.3.2.  Text Changes to the Document

   ---------
   Old text: (Section 14.1)
   ---------

   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:
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   ---------
   New text: (Section 14.1)
   ---------

   The assignment of new chunk type codes is done through an IETF
   Consensus action, as defined in [RFC8126].  Documentation for the
   chunk type MUST contain the following information:

   This text has been modified by multiple errata.  It is further
   updated in Section 3.43.

3.3.3.  Solution Description

   The new text refers to chunk types as intended and changes the
   reference to [RFC8126].

3.4.  Variable Parameters for INIT Chunks

3.4.1.  Description of the Problem

   In Section 3.3.2 of [RFC4960], newlines in wrong places break the
   layout of the table of variable parameters for the INIT chunk.

   This issue was reported as an errata for [RFC4960] with
   Errata ID 3291 and Errata ID 3804.

3.4.2.  Text Changes to the Document

   ---------
   Old text: (Section 3.3.2)
   ---------

   Variable Parameters                  Status     Type Value
   -------------------------------------------------------------
   IPv4 Address (Note 1)               Optional    5 IPv6 Address
   (Note 1)               Optional    6 Cookie Preservative
   Optional    9 Reserved for ECN Capable (Note 2)   Optional
   32768 (0x8000) Host Name Address (Note 3)          Optional
   11 Supported Address Types (Note 4)    Optional    12
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   ---------
   New text: (Section 3.3.2)
   ---------

   Variable Parameters                  Status     Type Value
   -------------------------------------------------------------
   IPv4 Address (Note 1)               Optional    5
   IPv6 Address (Note 1)               Optional    6
   Cookie Preservative                 Optional    9
   Reserved for ECN Capable (Note 2)   Optional    32768 (0x8000)
   Host Name Address (Note 3)          Optional    11
   Supported Address Types (Note 4)    Optional    12

   This text is in final form and is not further updated in this
   document.

3.4.3.  Solution Description

   The formatting of the table is corrected.

3.5.  CRC32c Sample Code on 64-Bit Platforms

3.5.1.  Description of the Problem

   The sample code for CRC32c computation, as provided in [RFC4960],
   assumes that a variable of type unsigned long uses 32 bits.  This is
   not true on some 64-bit platforms (for example, platforms that
   use LP64).

   This issue was reported as an errata for [RFC4960] with
   Errata ID 3423.

3.5.2.  Text Changes to the Document

   ---------
   Old text: (Appendix C)
   ---------

   unsigned long
   generate_crc32c(unsigned char *buffer, unsigned int length)
   {
     unsigned int i;
     unsigned long crc32 = ~0L;
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   ---------
   New text: (Appendix C)
   ---------

   unsigned long
   generate_crc32c(unsigned char *buffer, unsigned int length)
   {
     unsigned int i;
     unsigned long crc32 = 0xffffffffL;

   This text has been modified by multiple errata.  It is further
   updated in Section 3.10 and again in Section 3.46.

3.5.3.  Solution Description

   The new text uses 0xffffffffL instead of ~0L; this gives the same
   value on platforms using 32 bits or 64 bits for variables of type
   unsigned long.

3.6.  Endpoint Failure Detection

3.6.1.  Description of the Problem

   The handling of the association error counter defined in Section 8.1
   of [RFC4960] can result in an association failure even if the path
   used for data transmission is available (but idle).

   This issue was reported as an errata for [RFC4960] with
   Errata ID 3788.

3.6.2.  Text Changes to the Document

   ---------
   Old text: (Section 8.1)
   ---------

   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.

   ---------
   New text: (Section 8.1)
   ---------

   An endpoint SHOULD keep a counter on the total number of consecutive
   retransmissions to its peer (this includes data retransmissions to
   all the destination transport addresses of the peer if it is
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   multi-homed), including the number of unacknowledged HEARTBEAT chunks
   observed on the path that is currently used for data transfer.
   Unacknowledged HEARTBEAT chunks observed on paths different from the
   path currently used for data transfer SHOULD NOT increment the
   association error counter, as this could lead to association closure
   even if the path that is currently used for data transfer is
   available (but idle).

   This text has been modified by multiple errata.  It is further
   updated in Section 3.23.

3.6.3.  Solution Description

   A more refined handling of the association error counter is defined.

3.7.  Data Transmission Rules

3.7.1.  Description of the Problem

   When integrating the changes to Section 6.1 A) of [RFC2960] as
   described in Section 2.15.2 of [RFC4460], some text was duplicated
   and became the final paragraph of Section 6.1 A) of [RFC4960].

   This issue was reported as an errata for [RFC4960] with
   Errata ID 4071.

3.7.2.  Text Changes to the Document

   ---------
   Old text: (Section 6.1 A))
   ---------

   The sender MUST also have an algorithm for sending new DATA chunks to
   avoid silly window syndrome (SWS) as described in [RFC0813].  The
   algorithm can be similar to the one described in Section 4.2.3.4 of
   [RFC1122].

   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.
Top   ToC   Page 11
   ---------
   New text: (Section 6.1 A))
   ---------

   The sender MUST also have an algorithm for sending new DATA chunks to
   avoid silly window syndrome (SWS) as described in [RFC1122].  The
   algorithm can be similar to the algorithm described in
   Section 4.2.3.4 of [RFC1122].

   This text is in final form and is not further updated in this
   document.

3.7.3.  Solution Description

   The last paragraph of Section 6.1 A) is removed, as had been intended
   in Section 2.15.2 of [RFC4460].

3.8.  T1-Cookie Timer

3.8.1.  Description of the Problem

   Figure 4 of [RFC4960] illustrates the SCTP association setup.
   However, it incorrectly shows that the T1-init timer is used in the
   COOKIE-ECHOED state, whereas the T1-cookie timer should have been
   used instead.

   This issue was reported as an errata for [RFC4960] with
   Errata ID 4400.

3.8.2.  Text Changes to the Document

   ---------
   Old text: (Section 5.1.6, Figure 4)
   ---------

   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)
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   ---------
   New text: (Section 5.1.6, Figure 4)
   ---------

   COOKIE ECHO [Cookie_Z] ------\
   (Start T1-cookie timer)       \
   (Enter COOKIE-ECHOED state)    \---> (build TCB, enter ESTABLISHED
                                         state)
                                  /---- COOKIE-ACK
                                 /
   (Cancel T1-cookie timer, <---/
    enter ESTABLISHED state)

   This text has been modified by multiple errata.  It is further
   updated in Section 3.9.

3.8.3.  Solution Description

   The figure is changed such that the T1-cookie timer is used instead
   of the T1-init timer.



(page 12 continued on part 2)

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