BIER Penultimate Hop Popping
draft-ietf-bier-php-16

[Ballot comment]
Thanks for the well-written document. I have just a couple of minor comments about the Introduction.

### Section 1, BFR

It seems relatively obvious that "BFR" must mean "BIER Forwarding Router" but please expand it on first use.

### Section 1, directly or indirectly?

  A potential solution to this issue is the use of Penultimate Hop
  Popping (PHP), whereby the upstream BFR pops the BIER header
  [RFC8296] and transmits the payload directly.  This transmission can
  occur either directly or indirectly through any type of tunnel to the
  PE.
 
The end of the first sentence ("transmits the payload directly") conflicts with the beginning of the next ("can occur [...] indirectly"). I think I get what you mean but it's still jarring. Maybe something like "... and transmits the payload without BIER encapsulation"?

[Ballot comment]
Thanks for the quick action to make the changes to allow me to clear my discuss.

I have no objection to publication of this draft.

[Ballot comment]
[ Was DISCUSS ]

Thank you for addressing my DISCUSS comment (based on Jen Linkova's OpsDir review (https://datatracker.ietf.org/doc/review-ietf-bier-php-12-opsdir-lc-linkova-2024-09-30/))

I've cleared my DISCUSS.

[Ballot discuss]
An easy discuss to resolve:

To quote Shawn Emery's secdir review comment: 

"The security considerations sections does exist and discloses that the protocol
does not introduce any additional security implications beyond that of "BIER
architecture and OSPF/IS-IS/BGP extensions for BIER signaling".  It would be
helpful to outline the relevant RFCs that each of these building blocks of this
draft is dependent upon on in this section."

Please include references in the security considerations for those documents.  The goal is to make it easier for an implementer to 'do the right thing'.  Including links to the references in the section helps.

[Ballot discuss]
Be ye not afraid -- see
https://www.ietf.org/about/groups/iesg/statements/handling-ballot-positions/ on handling ballots, especially DISCUSS ballots...

This should be an easy to address DISCUSS.

I did not see a response to Jen Linkova's OpsDir review (https://datatracker.ietf.org/doc/review-ietf-bier-php-12-opsdir-lc-linkova-2024-09-30/), nor do I see it answered in the document.

I think that this is a large enough issue that it should be noted in the document (or at least an explanation of why it's not needed).

[Ballot comment]
Other than my DISCUSS issue, I found this a good and clear document.

Also thanks to Jen for the OpsDir review - it's a good catch.

[Ballot comment]
Section 4, paragraph 1
>    BIER PHP can only be used when the conditions specified in Section 2
>    are met.  The BIER OAM functionality is not available on the BIER-
>    incapable flow overlay routers, but using PHP when the conditions are
>    met is simpler than the alternative of using BIER to send to some
>    whereas using non-BIER tunnels to send to other flow overlay routers.

Thanks to Jen Linkova for his OPSDIR review.

He had one minor comment in his review, that I would like to see a response to, if not consider an update to the draft based on the comment.

DOWNREF [I-D.ietf-bier-lsr-non-mpls-extensions] from this Proposed Standard to
draft-ietf-bier-lsr-non-mpls-extensions of unknown standards level. (For IESG
discussion. It seems this DOWNREF was not mentioned in the Last Call and also
seems to not appear in the DOWNREF registry.)

Found terminology that should be reviewed for inclusivity; see
https://www.rfc-editor.org/part2/#inclusive_language for background and more
guidance:

* Term "his"; alternatives might be "they", "them", "their"

[Ballot comment]

# Éric Vyncke, INT AD, comments for draft-ietf-bier-php-13

Thank you for the work put into this document.

Please find some non-blocking COMMENT points (but replies would be appreciated even if only for my own education).

Special thanks to Xiao Min for the shepherd's detailed write-up including the WG consensus and the justification of the intended status.

I hope that this review helps to improve the document,

Regards,

-éric

# COMMENTS (non-blocking)

## Section 1

I wonder why the MVPN/EVPN examples are given in this document, wouldn't be it enough to say (like in the abstract) "PHP enables the removal of the BIER header by the penultimate router, thereby reducing the processing burden on the final router in the delivery path" ? The text would then be easier to read.

## Section 2.1

What is `A BIER-incapable router` ? Does a router with the BIER code but without BIER configured qualified ? Is it per interface ?

(Via drafts-lastcall@iana.org): IESG/Authors/WG Chairs:

IANA has completed its review of draft-ietf-bier-php-12. If any part of this review is inaccurate, please let us know.

IANA understands that some of the actions requested in the IANA Considerations section of this document are dependent upon the approval of and completion of IANA Actions in another document:

[ID.ietf-bier-idr-extensions]

IANA has a question about one of the actions requested in the IANA Considerations section of this document.

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

First, in the BIER Info Sub-TLV registry in the IS-IS TLV Codepoints registry group located at:

https://www.iana.org/assignments/isis-tlv-codepoints/

a single new registration is to be made as follows:

Type: [ TBD-at-Registration ]
Name: BIER PHP Request
Reference: [ RFC-to-be ]

As this document requests a registration in an Expert Review or Specification Required (see RFC 8126) registry, we have completed the required Expert Review via a separate request.

Second, in the OSPFv2 Extended Prefix TLV Sub-TLVs registry in the Open Shortest Path First v2 (OSPFv2) Parameters registry group located at:

https://www.iana.org/assignments/ospfv2-parameters/

a single new registration will be made as follows:

Value: [ TBD-at-Registration ]
Description: BIER PHP Request
Reference: [ RFC-to-be ]

Third, in the OSPFv3 Extended-LSA Sub-TLVs registry in the Open Shortest Path First v3 (OSPFv3) Parameters registry group located at:

https://www.iana.org/assignments/ospfv3-parameters/

a single new registration will be made as follows:

Value: [ TBD-at-Registration ]
Description: BIER PHP Request
L2BM:
Reference: [ RFC-to-be ]

IANA Question --> What should be the value for L2BM for this new registration in the OSPFv3 Extended-LSA Sub-TLVs registry?

Fourth, in the BGP BIER TLV and SUB-TLV Types registry which is proposed to be created upon approval of the current Internet Draft:

[ID.ietf-bier-idr-extensions]

a single new registration will be made as follows:

Value: [ TBD-at-Registration ]
Description: BIER PHP Request
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 2024-10-10):

From: The IESG
To: IETF-Announce
CC: bier-chairs@ietf.org, bier@ietf.org, draft-ietf-bier-php@ietf.org, gunter@vandevelde.cc, xiao.min2@zte.com.cn
Reply-To: last-call@ietf.org
Sender:
Subject: Last Call:  (BIER Penultimate Hop Popping) to Proposed Standard


The IESG has received a request from the Bit Indexed Explicit Replication WG
(bier) to consider the following document: - 'BIER Penultimate Hop Popping'
  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 2024-10-10. 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


  This document specifies a mechanism for Penultimate Hop Popping (PHP)
  in the Bit Index Explicit Replication (BIER) architecture.  PHP
  enables the removal of the BIER header by the penultimate router,
  thereby reducing the processing burden on the final router in the
  delivery path.  This extension to BIER enhances operational
  efficiency by optimizing packet forwarding in scenarios where the
  final hop's capabilities or requirements necessitate such handling.
  The document details the necessary extensions to the BIER
  encapsulation and forwarding processes to support PHP, providing
  guidance for implementation and deployment within BIER-enabled
  networks.





The file can be obtained via
https://datatracker.ietf.org/doc/draft-ietf-bier-php/


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

  https://datatracker.ietf.org/ipr/3234/



The document contains these normative downward references.
See RFC 3967 for additional information:
    draft-ietf-bier-lsr-non-mpls-extensions: LSR Extensions for BIER non-MPLS Encapsulation (None - Internet Engineering Task Force (IETF) stream)

# 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 a broad agreement to adopt and progress this work in the working group.

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

None.

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.)

None.

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)?

There is no report for existing or planned implementation yet, due to slow
deployment of base BIER functionality itself.
The situation is changing as more vendor implementations for BIER are coming.
As this extension will further promote the BIER deployment, it is expected that
vendors will start planning to support it.

## 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.

BIER PHP described in this document follows similar principles and examples of
MPLS PHP, several MPLS experts have carefully reviewed this document and suggested
some improvements.

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 formal review is required other than the review required to perform the IANA
actions (i.e., new IGP/BGP sub-TLV/sub-sub-TLV assignments).

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]?

N/A.

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.

N/A.

## 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, the document is ready. I've performed my shepherd's review, and made
several technical/editorial comments, which have been addressed by the author.

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 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?

This document requests publication as a Proposed Standard RFC. That
is indicated on the header page. The intended status is justified
given that the document specifies new IGP/BGP sub-TLV/sub-sub-TLV
with a set of normative behavior to ensure interoperability.

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.

IPR has been disclosed for its predecessor draft-zzhang-bier-php.
https://datatracker.ietf.org/ipr/3234/
There is only one author, whose organization disclosed the IPR.

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.

I think so. There is only one author.

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.)

None to report for -10.

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.

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.

No.

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]).

No issues on IANA considerations section identified.

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.

None.

[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://trac.ietf.org/trac/ops/wiki/yang-review-tools
[5]: https://www.rfc-editor.org/rfc/rfc8342.html
[6]: https://trac.ietf.org/trac/iesg/wiki/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 a broad agreement to adopt and progress this work in the working group.

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

None.

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.)

None.

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)?

There is no report for existing or planned implementation yet, due to slow
deployment of base BIER functionality itself.
The situation is changing as more vendor implementations for BIER are coming.
As this extension will further promote the BIER deployment, it is expected that
vendors will start planning to support it.

## 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.

BIER PHP described in this document follows similar principles and examples of
MPLS PHP, several MPLS experts have carefully reviewed this document and suggested
some improvements.

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 formal review is required other than the review required to perform the IANA
actions (i.e., new IGP/BGP sub-TLV/sub-sub-TLV assignments).

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]?

N/A.

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.

N/A.

## 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, the document is ready. I've performed my shepherd's review, and made
several technical/editorial comments, which have been addressed by the author.

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 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?

This document requests publication as a Proposed Standard RFC. That
is indicated on the header page. The intended status is justified
given that the document specifies new IGP/BGP sub-TLV/sub-sub-TLV
with a set of normative behavior to ensure interoperability.

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.

IPR has been disclosed for its predecessor draft-zzhang-bier-php.
https://datatracker.ietf.org/ipr/3234/
There is only one author, whose organization disclosed the IPR.

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.

I think so. There is only one author.

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.)

None to report for -10.

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.

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.

No.

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]).

No issues on IANA considerations section identified.

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.

None.

[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://trac.ietf.org/trac/ops/wiki/yang-review-tools
[5]: https://www.rfc-editor.org/rfc/rfc8342.html
[6]: https://trac.ietf.org/trac/iesg/wiki/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/