[Idr] Re: Éric Vyncke's Discuss on draft-ietf-idr-link-bandwidth-19: (with DISCUSS and COMMENT)

[Reshma Das <[e-mail]>]

Hi Éric Vyncke ,

Thanks for reviewing the document. Please find my reply inline as RD>

Thanks & Regards,
Reshma Das



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From: Éric Vyncke via Datatracker <[e-mail]>
Date: Friday, October 10, 2025 at 2:09 AM
To: The IESG <[e-mail]>
Cc: [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>, [e-mail] <[e-mail]>
Subject: Éric Vyncke's Discuss on draft-ietf-idr-link-bandwidth-19: (with DISCUSS and COMMENT)
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DISCUSS:
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# Éric Vyncke, INT AD, comments for draft-ietf-idr-link-bandwidth-19
CC @evyncke

Thank you for the work put into this document.

Please find below one blocking DISCUSS points (easy to address I think), some
non-blocking COMMENT points/nits (replies would be appreciated even if only for
my own education).

Special thanks to Jeffrey Haas for the shepherd's detailed write-up including
the WG consensus and the justification of the intended status and about having
6 authors rather than the recommended max of 5 authors.

I hope that this review helps to improve the document,

Regards,

-éric

## DISCUSS (blocking)

As noted in
https://urldefense.com/v3/__https://datatracker.ietf.org/doc/statement-iesg-handling-ballot-positions-20220121/__;!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5QJnDX1Q$<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/statement-iesg-handling-ballot-positions-20220121/__;!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5QJnDX1Q$> ,
a DISCUSS ballot is a request to have a discussion on the points below; I
really think that the document would be improved with a change here, but can be
convinced otherwise.

### Section 2

(see also non-blocking comments about this section)

As the section text is about *router* bandwidth, what is a *router* bandwidth
as opposed to a *link* bandwidth ? Is it the max forwarding rate ? or the sum
of all link bandwidth ?

This must be specified (or a reference be added to its definition)
RD> The draft has been updated, and the following has been added to the Introduction. Please let me know this addresses your concern.
“The Link Bandwidth Extended Community carries the bandwidth information of a directly connected link or multi-hop/multipath nexthop as advertised by a router.”



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COMMENT:
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## COMMENTS (non-blocking)

### BCP 14

I second Mohamed Boucadair's DISCUSS about the use of the wrong BCP14 template
at the common location.

RD>  ACK, this has been updated.

### Abstract

Abstract gains to be short and concise but this one is really short as it does
not even mention 'bandwidth'... Please consider giving a more descriptive
abstract.

The abstract should also mention that only 16-bit ASN are fully supported per
section 2.

RD> Please find suggested text for new Abstract:
“This document defines a BGP Extended Community, the Link Bandwidth Extended Community, which carries link bandwidth information to enable weighted load-balancing in multipath scenarios. It specifies the format and processing rules for this community type””

Per section 4, this I-D also specifies forwarding behaviour in addition to
defining a BGP community, let's mention this in the abstract *and* introduction.

### Section 1

Should there be some text about *how* this metric can be used ? Obviously not
for ECMP as the costs are no more equal.
RD> This has been mentioned in receiver section.
https://www.ietf.org/archive/id/draft-ietf-idr-link-bandwidth-19.html#name-receiver-receiving-link-ban


### Section 2

The section title is about *link* bandwidth while the text is about *router*
bandwidth? Which one is the correct one ? Please ensure that section title and
section content are aligned.

RD>  The document defines:
“The Link Bandwidth Extended Community provides a mechanism for routers to advertise the bandwidth of their downstream path that may either be a directly connected link or multi-hop/multipath nexthop. “
Hence rewording this section as below, please review:
“The Link Bandwidth Extended Community is defined as a BGP extended community that carries the bandwidth information, represented by BGP Next Hop, connecting to a remote network”

I am not a BGP expert but processing only 16-bit ASN in 2025 seems quite
limitative per `The encoding of 4-octet ASN is out of scope of this document.`
Did the IDR WG try to explore other techniques to support 32-bit ASN ?
RD> I would like to point you to Jeffs reply<https://urldefense.com/v3/__https:/mailarchive.ietf.org/arch/msg/idr/inJK_mowTUP-JlY7gDwyPmPVkmk/__;!!NEt6yMaO-gk!E3eFCzM3qCIf9qoqIcqWNtDgCVTRRL38kvsM9BZ2qBzn1chSnIcGR5rM-bTWrlqpgAO4--I5rEY2e_al3ualFYq0KO-GB6M$> to a similar comment that details the format of extended community.
Based on various review comments we have reworded this section, please check the new text GitHub-ASNUM<https://urldefense.com/v3/__https:/github.com/ietf-wg-idr/draft-ietf-idr-link-bandwidth/pull/21/commits/4461d3def20e589987be61e38e7b88ac2f08ffbd*diff-483d4c38615bf145bb86c3b6a77bdae817e0b0f15c616c5df65039377016e59a__;Iw!!NEt6yMaO-gk!E3eFCzM3qCIf9qoqIcqWNtDgCVTRRL38kvsM9BZ2qBzn1chSnIcGR5rM-bTWrlqpgAO4--I5rEY2e_al3ualFYq0CJp-aKo$>.



### Section 3.1

This section contains several "SHOULD" but nothing is specified about when
these "SHOULD" can be bypassed or what are the consequences of bypassing them.
See the IESG statement
https://urldefense.com/v3/__https://datatracker.ietf.org/doc/statement-iesg-statement-on-clarifying-the-use-of-bcp-14-key-words/__;!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5fCIUpxI$<https://urldefense.com/v3/__https:/datatracker.ietf.org/doc/statement-iesg-statement-on-clarifying-the-use-of-bcp-14-key-words/__;!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5fCIUpxI$>
RD>  As noted in Appendix-A<https://www.ietf.org/archive/id/draft-ietf-idr-link-bandwidth-19.html#appendix-A>, The previous versions of the draft supported only non-transitive, while current version supports both transitive and non-transitive LBWC. Any implementation that supports this current draft should be able to process both these versions. Please note that the main goal of this effort is to record all implementation behaviors observed in the field today, allowing them to be used as the default behavior. The intent is that no existing implementation should be considered non-compliant following publication of this specification as an RFC. Also making sure all implementations interoperate. Hence SHOULD has been used




### Section 4

The section title is about "Error" but except for paragraph 4 and 5, the
content is not about error handling. Consider splitting this section in 2.

### Section 5

Suggest adding a reference to the registry URI, e.g.,
https://urldefense.com/v3/__https://www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml*trans-two-octet-as__;Iw!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5NJ2duuo$<https://urldefense.com/v3/__https:/www.iana.org/assignments/bgp-extended-communities/bgp-extended-communities.xhtml*trans-two-octet-as__;Iw!!NEt6yMaO-gk!F6g9-SE4iwzK_9_Nl403nfwaTxkQrHiXCtLOQuqFDoZxy548EM2e6WHD71BOUxBpO7KSLmS5NJ2duuo$>

### Section 7

As this section contains only another section without any lead text, consider
removing the section 7.1 title.
RD> This section has been expanded to add another section.
https://github.com/ietf-wg-idr/draft-ietf-idr-link-bandwidth/blob/main/draft-ietf-idr-link-bandwidth.txt


This section mentions "previous implementations", was there a RFC for it ?
RD> This is covered in the Appendix. This document has a long history as it was introduced in 2009.
https://www.ietf.org/archive/id/draft-ietf-idr-link-bandwidth-19.html#appendix-A