Re: [Idr] I-D Action: draft-ietf-idr-entropy-label-03.txt

[John Scudder <[e-mail]>]

Hi All,

It recently came up that according to the “letter of the law” of RFC 7447, we are supposed to propagate attribute 28 no matter what it contains, and that seems like not a great idea considering that for some implementations now in the field, the attribute 28 produced by other implementations is a breaking error. The “right thing” for the Internet is to drop attribute 28 (unless it’s being specifically enabled in configuration for purposes of transition), and not to do what RFC 7447 requires. (The strategy specified by RFC 7447 seemed like a good idea at the time, but was too optimistic, alas.)

With that in mind, we added a new Section 4 to the draft, now published as version 03. You can see it in the iddiff of course, but the new section in its entirety is:

4.  Legacy ELC

   The ELCv3 functionality introduced in this document replaces the "BGP
   Entropy Label Capability Attribute" (ELC attribute) that was
   introduced by [RFC6790], and deprecated by [RFC7447].  The latter RFC
   specifies that the ELC attribute, BGP path attribute 28, "MUST be
   treated as any other unrecognized optional, transitive attribute".
   This specification revises that requirement.

   As the current specification was developed, it became clear that due
   to incompatibilities between how the ELC attribute is processed by
   different fielded implementations, the most prudent handling of
   attribute 28 is not to propagate it as an unrecognized optional,
   transitive attribute, but to discard it.  Therefore, this
   specification updates [RFC7447], by instead requiring that an
   implementation that receives the ELC attribute MUST discard any
   received ELC attribute.

Thanks,

—John

> On Feb 20, 2023, at 3:46 PM, [e-mail] wrote:
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> This Internet-Draft is a work item of the Inter-Domain Routing WG of the IETF.
> 
>        Title           : BGP Router Capabilities Attribute
>        Authors         : Bruno Decraene
>                          John G. Scudder
>                          Wim Henderickx
>                          Kireeti Kompella
>                          Satya Mohanty
>                          James Uttaro
>                          Bin Wen
>  Filename        : draft-ietf-idr-entropy-label-03.txt
>  Pages           : 14
>  Date            : 2023-02-20
> 
> Abstract:
>   RFC 5492 allows a BGP speaker to advertise its capabilities to its
>   peer.  When a route is propagated beyond the immediate peer, it is
>   useful to allow certain capabilities to be conveyed further.  In
>   particular, it may be useful to advertise forwarding plane features.
> 
>   This specification defines a new BGP transitive attribute to carry
>   such capability information, the "Router Capabilities Attribute," or
>   RCA.
> 
>   This specification also defines an RCA capability that can be used to
>   advertise the ability to process the MPLS Entropy Label as an egress
>   LSR for all NLRI advertised in the BGP UPDATE.  It updates RFC 6790
>   and RFC 7447 concerning this BGP signaling.
> 
...