More Accurate Explicit Congestion Notification (AccECN) Feedback in TCP
draft-ietf-tcpm-accurate-ecn-34

[Ballot comment]
Thanks for the work in this document, I only briefly browsed through it as it is really outside of my expertise even if the text is clear (BTW, I hope that this complex specification and re-use of one flag have been heavily tested in real networks).

Nevertheless some comments:

Should "AccECN" be part of the title and in the abstract ? This could help searches.

The term `middlebox` is often used without a proper definition or reference and it seems to cover a lot of different roles from TCP offload to TCP normalizers (cfr section 3.3)

Section 1, any chance to get some explanations without reading RFC 7560 about `DCTCP [RFC8257] or L4S [RFC9330] need to know when more than one marking is received` ?

In the same section `So its applicability is intended to include all public and private IP networks`, the use of public/private is unusual, but I hope that everyone understands the same concept.

Section 1.4, s/two bit field/two-bit field/

Section 7, I wonder why there is a note to remove the IANA request. It is also unclear who is instructed to remove the text (I guess RFC Editor).

[Ballot comment]
Thank you to Elwyn B. Davies for the GENART review.  Please review the feedback as there a number of suggestions for improved clarity.

** Section 7.  Explicitly name the registries that are going to be updated

OLD
The flag will now be defined as:
NEW
The flag will now be defined as the following in the “TCP Header Flags” registry in the “Transmission Control Protocol (TCP) Parameters” registry group:

OLD
These values are defined as:
NEW
These values are defined as the following in the “TCP Option Kind Numbers” registry in the “Transmission Control Protocol (TCP) Parameters” registry group:

[Ballot comment]
# Internet AD comments for draft-ietf-tcpm-accurate-ecn-32
CC @ekline

* comment syntax:
  - https://github.com/mnot/ietf-comments/blob/main/format.md

* "Handling Ballot Positions":
  - https://ietf.org/about/groups/iesg/statements/handling-ballot-positions/

## Nits

### S1.4

* "expirience" -> "experience"

* "Remote Direct Access Memory" -> "Remote Direct Memory Access"

IESG/Authors/WG Chairs:

IANA has completed its review of draft-ietf-tcpm-accurate-ecn-31. If any part of this review is inaccurate, please let us know.

IANA understands that, upon approval of this document, there are three actions which we must complete.

First, in the TCP Header Flag registry in the Transmission Control Protocol (TCP) Parameters registry group located at:

https://www.iana.org/assignments/tcp-parameters/

the existing bit offset 7 is to be renamed as follows:

Bit Offset: 7
Name: AE (Accurate ECN)
Reference: [ RFC-to-be ]
Assignment Notes: Previously used as NS (Nonce Sum) by [RFC3540], which is now historic [RFC8311]

Second, in the TCP Option Kind Numbers registry also in the Transmission Control Protocol (TCP) Parameters registry group located at:

https://www.iana.org/assignments/tcp-parameters/

two TEMPORARY registrations will be made permanent and their references changed to [ RFC-to-be ] as follows:

Kind: 172
Length: N
Meaning: Accurate ECN Order 0 (AccECN0)
Reference: [ RFC-to-be ]

Kind: 174
Length: N
Meaning: Accurate ECN Order 1 (AccECN1)
Reference: [ RFC-to-be ]

Third, in the TCP Experimental Option Experiment Identifiers (TCP ExIDs) registry also in the Transmission Control Protocol (TCP) Parameters registry group located at:

https://www.iana.org/assignments/tcp-parameters/

the existing early registrations for two ExIDs will have their references changed to [ RFC-to-be ]:

Value: 0xACC0
Description: AccECN Experimental Option - Order 0
Reference: [ RFC-to-be ]

Value: 0xACC1
Description: AccECN Experimental Option - Order 1
Reference: [ RFC-to-be ]

We understand that these are the only actions required to be completed upon approval of this document.

NOTE: The actions requested in this document will not be completed until the document has been approved for publication as an RFC. This message is meant only to confirm the list of actions that will be performed.

For definitions of IANA review states, please see:

https://datatracker.ietf.org/help/state/draft/iana-review

Thank you,

David Dong
IANA Services Sr. Specialist

The following Last Call announcement was sent out (ends 2025-02-10):

From: The IESG
To: IETF-Announce
CC: draft-ietf-tcpm-accurate-ecn@ietf.org, tcpm-chairs@ietf.org, tcpm@ietf.org, tuexen@fh-muenster.de, zahed.sarker.ietf@gmail.com
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (More Accurate Explicit Congestion Notification (ECN) Feedback in TCP) to Proposed Standard


The IESG has received a request from the TCP Maintenance and Minor Extensions
WG (tcpm) to consider the following document: - 'More Accurate Explicit
Congestion Notification (ECN) Feedback in TCP'
  as Proposed Standard

The IESG plans to make a decision in the next few weeks, and solicits final
comments on this action. Please send substantive comments to the
last-call@ietf.org mailing lists by 2025-02-10. Exceptionally, comments may
be sent to iesg@ietf.org instead. In either case, please retain the beginning
of the Subject line to allow automated sorting.

Abstract


  Explicit Congestion Notification (ECN) is a mechanism where network
  nodes can mark IP packets instead of dropping them to indicate
  incipient congestion to the endpoints.  Receivers with an ECN-capable
  transport protocol feed back this information to the sender.  ECN was
  originally specified for TCP in such a way that only one feedback
  signal can be transmitted per Round-Trip Time (RTT).  Recent new TCP
  mechanisms like Congestion Exposure (ConEx), Data Center TCP (DCTCP)
  or Low Latency, Low Loss, and Scalable Throughput (L4S) need more
  accurate ECN feedback information whenever more than one marking is
  received in one RTT.  This document updates the original ECN
  specification in RFC 3168 to specify a scheme that provides more than
  one feedback signal per RTT in the TCP header.  Given TCP header
  space is scarce, it allocates a reserved header bit previously
  assigned to the ECN-Nonce.  It also overloads the two existing ECN
  flags in the TCP header.  The resulting extra space is exploited to
  feed back the IP-ECN field received during the 3-way handshake as
  well.  Supplementary feedback information can optionally be provided
  in two new TCP option alternatives, which are never used on the TCP
  SYN.  The document also specifies the treatment of this updated TCP
  wire protocol by middleboxes.




The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-tcpm-accurate-ecn/


The following IPR Declarations may be related to this I-D:

  https://datatracker.ietf.org/ipr/1881/

# Document Shepherd Write-Up for Group Documents

*This version is dated 4 July 2022.*

Thank you for your service as a document shepherd. Among the responsibilities is
answering the questions in this write-up to give helpful context to Last Call
and Internet Engineering Steering Group ([IESG][1]) reviewers, and your
diligence in completing it is appreciated. The full role of the shepherd is
further described in [RFC 4858][2]. You will need the cooperation of the authors
and editors to complete these checks.

Note that some numbered items contain multiple related questions; please be sure
to answer all of them.

## Document History

1. Does the working group (WG) consensus represent the strong concurrence of a
  few individuals, with others being silent, or did it reach broad agreement?

  There is strong consensus in the WG, except for one individual.

2. Was there controversy about particular points, or were there decisions where
  the consensus was particularly rough?

  The only area of controversy (argued by one individual) is related to
  sending of ACKs in response to ACKs. This does not happen with TCP stacks
  which are not supporting the extension defined in this document.
  The problem described happens when the sender of an ACK receives an ACK for
  its ACK, because it might trigger undesired reactions due to incorrectly
  interpreting the received ACK as a duplicate ACK. In particular, this
  misinterpretation could happen if the SACK extension is not used.
  To mitigate this problem, the use of the SACK extension is recommended,
  and if the SACK extension is supported, support for the DSACK extension
  is required.
  However, to trigger the sending of ACKs of ACKs requires the sender of
  the initial ACKs to set the ECN code point to ECT. Doing so, is not
  described in this document, but in another document
  (draft-ietf-tcpm-generalized-ecn), which also requires the use of the SACK
  extension.
  In general, the view of the rest of the WG is that a TCP endpoint not being
  able to deal with the ACKs of ACKs in an appropriate manner just should not
  mark the pure ACKs it is sending with ECT.

3. Has anyone threatened an appeal or otherwise indicated extreme discontent? If
  so, please summarize the areas of conflict in separate email messages to the
  responsible Area Director. (It should be in a separate email because this
  questionnaire is publicly available.)

  One individual has raised the issue described above.

4. For protocol documents, are there existing implementations of the contents of
  the document? Have a significant number of potential implementers indicated
  plans to implement? Are any existing implementations reported somewhere,
  either in the document itself (as [RFC 7942][3] recommends) or elsewhere
  (where)?

  * Apple has an implementation in its latest released version of their
    operating systems. Disabled by default.
  * There is an implementation for FreeBSD, which will be committed to the
    source tree, as soon as the document is finished.
  * There is also an implementation for Linux where people are working on getting
    it into the main tree.
  * Tooling support is also there. Wireshark support is there and also support
    in packetdrill.
  All this support was possible, since the TCP option kind numbers where early
  assigned.

## Additional Reviews

5. Do the contents of this document closely interact with technologies in other
  IETF working groups or external organizations, and would it therefore benefit
  from their review? Have those reviews occurred? If yes, describe which
  reviews took place.

  The document deals with ECN markings, which are, for example, discussed in
  TSVWG. It was made sure to involve people from TSVWG in the discussion and
  review of this document.

6. Describe how the document meets any required formal expert review criteria,
  such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.

  No part of the document needs such formal review.

7. If the document contains a YANG module, has the final version of the module
  been checked with any of the [recommended validation tools][4] for syntax and
  formatting validation? If there are any resulting errors or warnings, what is
  the justification for not fixing them at this time? Does the YANG module
  comply with the Network Management Datastore Architecture (NMDA) as specified
  in [RFC 8342][5]?

  The document does not contain a YANG module.
 
8. Describe reviews and automated checks performed to validate sections of the
  final version of the document written in a formal language, such as XML code,
  BNF rules, MIB definitions, CBOR's CDDL, etc.

  The document does not contain such sections.

## Document Shepherd Checks

9. Based on the shepherd's review of the document, is it their opinion that this
  document is needed, clearly written, complete, correctly designed, and ready
  to be handed off to the responsible Area Director?

  Yes to all questions above.

10. Several IETF Areas have assembled [lists of common issues that their
    reviewers encounter][6]. For which areas have such issues been identified
    and addressed? For which does this still need to happen in subsequent
    reviews?

    No issues have been identified.

11. What type of RFC publication is being requested on the IETF stream ([Best
    Current Practice][12], [Proposed Standard, Internet Standard][13],
    [Informational, Experimental or Historic][14])? Why is this the proper type
    of RFC? Do all Datatracker state attributes correctly reflect this intent?

    The intended status is Proposed Standard. It was extensively discussed in
    the WG that this is the correct state. The alternative would have been
    Experimental. But there is no need for an experiment.

12. Have reasonable efforts been made to remind all authors of the intellectual
    property rights (IPR) disclosure obligations described in [BCP 79][7]? To
    the best of your knowledge, have all required disclosures been filed? If
    not, explain why. If yes, summarize any relevant discussion, including links
    to publicly-available messages when applicable.

    Yes, all authors where directly contaced and stated that to their knowledge
    all IPRs have been disclosed.
    There is one IPR declaration (https://datatracker.ietf.org/ipr/1881/) from
    NetApp. Please note that one of the co-authors (Richard Scheffenegger from
    NetApp) said, that the IPR was declared for an older version of the
    document and the current documents is not affected by the IPR anymore.

13. Has each author, editor, and contributor shown their willingness to be
    listed as such? If the total number of authors and editors on the front page
    is greater than five, please provide a justification.

    Yes.

14. Document any remaining I-D nits in this document. Simply running the [idnits
    tool][8] is not enough; please review the ["Content Guidelines" on
    authors.ietf.org][15]. (Also note that the current idnits tool generates
    some incorrect warnings; a rewrite is underway.)

    No.

15. Should any informative references be normative or vice-versa? See the [IESG
    Statement on Normative and Informative References][16].

    No.

16. List any normative references that are not freely available to anyone. Did
    the community have sufficient access to review any such normative
    references?

    None.

17. Are there any normative downward references (see [RFC 3967][9] and [BCP
    97][10]) that are not already listed in the [DOWNREF registry][17]? If so,
    list them.

    No.

18. Are there normative references to documents that are not ready to be
    submitted to the IESG for publication or are otherwise in an unclear state?
    If so, what is the plan for their completion?

    No, all normative references are to already published RFCs.

19. Will publication of this document change the status of any existing RFCs? If
    so, does the Datatracker metadata correctly reflect this and are those RFCs
    listed on the title page, in the abstract, and discussed in the
    introduction? If not, explain why and point to the part of the document
    where the relationship of this document to these other RFCs is discussed.

    This document updates RFC 3168, but both documents are PS. The relation to
    RFC 3168 is listed on the title page and discussed on the abstract and in
    the introduction.
    However, this is NOT mentioned in the Datatracker metadata. To be honest,
    I don't know where it should be in the Datatracker metadata.

20. Describe the document shepherd's review of the IANA considerations section,
    especially with regard to its consistency with the body of the document.
    Confirm that all aspects of the document requiring IANA assignments are
    associated with the appropriate reservations in IANA registries. Confirm
    that any referenced IANA registries have been clearly identified. Confirm
    that each newly created IANA registry specifies its initial contents,
    allocations procedures, and a reasonable name (see [RFC 8126][11]).

    The document defines one bit of the TCP flags (bit number 7) and
    specifies two TCP options. The TCP option kinds have been early allocated
    and they can already used in existing implementations.
    The registries are clearly identified.
    There are no new IANA registries.

21. List any new IANA registries that require Designated Expert Review for
    future allocations. Are the instructions to the Designated Expert clear?
    Please include suggestions of designated experts, if appropriate.

    This document does not define any new IANA registries.

[1]: https://www.ietf.org/about/groups/iesg/
[2]: https://www.rfc-editor.org/rfc/rfc4858.html
[3]: https://www.rfc-editor.org/rfc/rfc7942.html
[4]: https://wiki.ietf.org/group/ops/yang-review-tools
[5]: https://www.rfc-editor.org/rfc/rfc8342.html
[6]: https://wiki.ietf.org/group/iesg/ExpertTopics
[7]: https://www.rfc-editor.org/info/bcp79
[8]: https://www.ietf.org/tools/idnits/
[9]: https://www.rfc-editor.org/rfc/rfc3967.html
[10]: https://www.rfc-editor.org/info/bcp97
[11]: https://www.rfc-editor.org/rfc/rfc8126.html
[12]: https://www.rfc-editor.org/rfc/rfc2026.html#section-5
[13]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.1
[14]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.2
[15]: https://authors.ietf.org/en/content-guidelines-overview
[16]: https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/
[17]: https://datatracker.ietf.org/doc/downref/

# Document Shepherd Write-Up for Group Documents

*This version is dated 4 July 2022.*

Thank you for your service as a document shepherd. Among the responsibilities is
answering the questions in this write-up to give helpful context to Last Call
and Internet Engineering Steering Group ([IESG][1]) reviewers, and your
diligence in completing it is appreciated. The full role of the shepherd is
further described in [RFC 4858][2]. You will need the cooperation of the authors
and editors to complete these checks.

Note that some numbered items contain multiple related questions; please be sure
to answer all of them.

## Document History

1. Does the working group (WG) consensus represent the strong concurrence of a
  few individuals, with others being silent, or did it reach broad agreement?

  There is strong consensus in the WG, except for one individual.

2. Was there controversy about particular points, or were there decisions where
  the consensus was particularly rough?

  The only area of controversy (argued by one individual) is related to
  sending of ACKs in response to ACKs. This does not happen with TCP stacks
  which are not supporting the extension defined in this document.
  The problem described happens when the sender of an ACK receives an ACK for
  its ACK, because it might trigger undesired reactions due to incorrectly
  interpreting the received ACK as a duplicate ACK. In particular, this
  misinterpretation could happen if the SACK extension is not used.
  To mitigate this problem, the use of the SACK extension is recommended,
  and if the SACK extension is supported, support for the DSACK extension
  is required.
  However, to trigger the sending of ACKs of ACKs requires the sender of
  the initial ACKs to set the ECN code point to ECT. Doing so, is not
  described in this document, but in another document
  (draft-ietf-tcpm-generalized-ecn), which also requires the use of the SACK
  extension.
  In general, the view of the rest of the WG is that a TCP endpoint not being
  able to deal with the ACKs of ACKs in an appropriate manner just should not
  mark the pure ACKs it is sending with ECT.

3. Has anyone threatened an appeal or otherwise indicated extreme discontent? If
  so, please summarize the areas of conflict in separate email messages to the
  responsible Area Director. (It should be in a separate email because this
  questionnaire is publicly available.)

  One individual has raised the issue described above.

4. For protocol documents, are there existing implementations of the contents of
  the document? Have a significant number of potential implementers indicated
  plans to implement? Are any existing implementations reported somewhere,
  either in the document itself (as [RFC 7942][3] recommends) or elsewhere
  (where)?

  * Apple has an implementation in its latest released version of their
    operating systems. Disabled by default.
  * There is an implementation for FreeBSD, which will be committed to the
    source tree, as soon as the document is finished.
  * There is also an implementation for Linux where people are working on getting
    it into the main tree.
  * Tooling support is also there. Wireshark support is there and also support
    in packetdrill.
  All this support was possible, since the TCP option kind numbers where early
  assigned.

## Additional Reviews

5. Do the contents of this document closely interact with technologies in other
  IETF working groups or external organizations, and would it therefore benefit
  from their review? Have those reviews occurred? If yes, describe which
  reviews took place.

  The document deals with ECN markings, which are, for example, discussed in
  TSVWG. It was made sure to involve people from TSVWG in the discussion and
  review of this document.

6. Describe how the document meets any required formal expert review criteria,
  such as the MIB Doctor, YANG Doctor, media type, and URI type reviews.

  No part of the document needs such formal review.

7. If the document contains a YANG module, has the final version of the module
  been checked with any of the [recommended validation tools][4] for syntax and
  formatting validation? If there are any resulting errors or warnings, what is
  the justification for not fixing them at this time? Does the YANG module
  comply with the Network Management Datastore Architecture (NMDA) as specified
  in [RFC 8342][5]?

  The document does not contain a YANG module.
 
8. Describe reviews and automated checks performed to validate sections of the
  final version of the document written in a formal language, such as XML code,
  BNF rules, MIB definitions, CBOR's CDDL, etc.

  The document does not contain such sections.

## Document Shepherd Checks

9. Based on the shepherd's review of the document, is it their opinion that this
  document is needed, clearly written, complete, correctly designed, and ready
  to be handed off to the responsible Area Director?

  Yes to all questions above.

10. Several IETF Areas have assembled [lists of common issues that their
    reviewers encounter][6]. For which areas have such issues been identified
    and addressed? For which does this still need to happen in subsequent
    reviews?

    No issues have been identified.

11. What type of RFC publication is being requested on the IETF stream ([Best
    Current Practice][12], [Proposed Standard, Internet Standard][13],
    [Informational, Experimental or Historic][14])? Why is this the proper type
    of RFC? Do all Datatracker state attributes correctly reflect this intent?

    The intended status is Proposed Standard. It was extensively discussed in
    the WG that this is the correct state. The alternative would have been
    Experimental. But there is no need for an experiment.

12. Have reasonable efforts been made to remind all authors of the intellectual
    property rights (IPR) disclosure obligations described in [BCP 79][7]? To
    the best of your knowledge, have all required disclosures been filed? If
    not, explain why. If yes, summarize any relevant discussion, including links
    to publicly-available messages when applicable.

    Yes, all authors where directly contaced and stated that to their knowledge
    all IPRs have been disclosed.
    There is one IPR declaration (https://datatracker.ietf.org/ipr/1881/) from
    NetApp. Please note that one of the co-authors (Richard Scheffenegger from
    NetApp) said, that the IPR was declared for an older version of the
    document and the current documents is not affected by the IPR anymore.

13. Has each author, editor, and contributor shown their willingness to be
    listed as such? If the total number of authors and editors on the front page
    is greater than five, please provide a justification.

    Yes.

14. Document any remaining I-D nits in this document. Simply running the [idnits
    tool][8] is not enough; please review the ["Content Guidelines" on
    authors.ietf.org][15]. (Also note that the current idnits tool generates
    some incorrect warnings; a rewrite is underway.)

    No.

15. Should any informative references be normative or vice-versa? See the [IESG
    Statement on Normative and Informative References][16].

    No.

16. List any normative references that are not freely available to anyone. Did
    the community have sufficient access to review any such normative
    references?

    None.

17. Are there any normative downward references (see [RFC 3967][9] and [BCP
    97][10]) that are not already listed in the [DOWNREF registry][17]? If so,
    list them.

    No.

18. Are there normative references to documents that are not ready to be
    submitted to the IESG for publication or are otherwise in an unclear state?
    If so, what is the plan for their completion?

    No, all normative references are to already published RFCs.

19. Will publication of this document change the status of any existing RFCs? If
    so, does the Datatracker metadata correctly reflect this and are those RFCs
    listed on the title page, in the abstract, and discussed in the
    introduction? If not, explain why and point to the part of the document
    where the relationship of this document to these other RFCs is discussed.

    This document updates RFC 3168, but both documents are PS. The relation to
    RFC 3168 is listed on the title page and discussed on the abstract and in
    the introduction.
    However, this is NOT mentioned in the Datatracker metadata. To be honest,
    I don't know where it should be in the Datatracker metadata.

20. Describe the document shepherd's review of the IANA considerations section,
    especially with regard to its consistency with the body of the document.
    Confirm that all aspects of the document requiring IANA assignments are
    associated with the appropriate reservations in IANA registries. Confirm
    that any referenced IANA registries have been clearly identified. Confirm
    that each newly created IANA registry specifies its initial contents,
    allocations procedures, and a reasonable name (see [RFC 8126][11]).

    The document defines one bit of the TCP flags (bit number 7) and
    specifies two TCP options. The TCP option kinds have been early allocated
    and they can already used in existing implementations.
    The registries are clearly identified.
    There are no new IANA registries.

21. List any new IANA registries that require Designated Expert Review for
    future allocations. Are the instructions to the Designated Expert clear?
    Please include suggestions of designated experts, if appropriate.

    This document does not define any new IANA registries.

[1]: https://www.ietf.org/about/groups/iesg/
[2]: https://www.rfc-editor.org/rfc/rfc4858.html
[3]: https://www.rfc-editor.org/rfc/rfc7942.html
[4]: https://wiki.ietf.org/group/ops/yang-review-tools
[5]: https://www.rfc-editor.org/rfc/rfc8342.html
[6]: https://wiki.ietf.org/group/iesg/ExpertTopics
[7]: https://www.rfc-editor.org/info/bcp79
[8]: https://www.ietf.org/tools/idnits/
[9]: https://www.rfc-editor.org/rfc/rfc3967.html
[10]: https://www.rfc-editor.org/info/bcp97
[11]: https://www.rfc-editor.org/rfc/rfc8126.html
[12]: https://www.rfc-editor.org/rfc/rfc2026.html#section-5
[13]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.1
[14]: https://www.rfc-editor.org/rfc/rfc2026.html#section-4.2
[15]: https://authors.ietf.org/en/content-guidelines-overview
[16]: https://www.ietf.org/about/groups/iesg/statements/normative-informative-references/
[17]: https://datatracker.ietf.org/doc/downref/

Changed document external resources from:

github_repo https://github.com/L4STeam/linux (Linux implementation source)
github_repo https://github.com/bbriscoe/accecn (XML source of draft)
repo https://reviews.freebsd.org/D21011 (FreeBSD implementation source)

to:

github_repo https://github.com/L4STeam/linux/blob/testing/README.md (Linux implementation source)
github_repo https://github.com/bbriscoe/accecn (XML source of draft)
repo https://reviews.freebsd.org/D21011 (FreeBSD implementation source without AccECN TCP options)
repo https://reviews.freebsd.org/D36303 (FreeBSD implementation source with AccECN TCP options)