[spring] Re: draft-decraene-spring-sr-mpls-aggregation-segment-00

[Robert Raszuk <[e-mail]>]

Hi,

Question (previously it was more of an observation :).

Draft says:

   If the same Aggregation segment is advertised by multiple nodes, it
   becomes an anycast segment.  Absent specific provisions (e.g.,
   context specific label) such anycast segment needs to advertise the
   same labels related parameters (first prefix, the absolute label
   associated with that first prefix) for all instances.

Well - I think this is expressed way too weakly.

Each area/level have at least two ABRs. So the proper procedure MUST be in
place to assure that all such ABRs aggregate in the same way and allocate
the same labels for the identical aggregates.

Otherwise this will lead to a situation of different labels (including
blocks) being advertised for the same aggregate prefix and then what do you
do on ingress ? Pick first and risk no redundancy ?

The crux of the matter here is how do you assure such strict symmetry ? Are
we back at the world of manual configuration (analogy to static routing in
large networks) ?

Cheers,
R.

On Mon, Mar 3, 2025 at 9:32 PM <[e-mail]> wrote:

> [obviously speaking as individual contributor]
>
> Hi all,
>
> We have just published a short draft.
> It introduces an Aggregation Segment for Segment Routing with MPLS data
> plane.
> This can be used to aggregate IP prefixes along with their SR Prefix
> Segments. Aggregation Segments enable aggregation of IP prefixes to be
> performed at border routers to improve scalability of MPLS networks.
>
> We would appreciate your review and comments.
>
> Thanks,
>
> --Shraddha, Ketan, Kamran, Bruno
>
> -----Original Message-----
> From: [e-mail] <[e-mail]>
> Sent: Monday, March 3, 2025 5:18 PM
> To: DECRAENE Bruno INNOV/NET <[e-mail]>; Kamran Raza <
> [e-mail]>; Ketan Talaulikar <[e-mail]>; Shraddha
> Hegde <[e-mail]>; Syed Raza <[e-mail]>
> Subject: New Version Notification for
> draft-decraene-spring-sr-mpls-aggregation-segment-00.txt
>
>
> A new version of Internet-Draft
> draft-decraene-spring-sr-mpls-aggregation-segment-00.txt has been
> successfully submitted by Bruno Decraene and posted to the IETF repository.
>
> Name:     draft-decraene-spring-sr-mpls-aggregation-segment
> Revision: 00
> Title:    SR-MPLS Aggregation Segment
> Date:     2025-03-03
> Group:    Individual Submission
> Pages:    9
>
>
> https://www.ietf.org/archive/id/draft-decraene-spring-sr-mpls-aggregation-segment-00.html
>
> Abstract:
>
>    One of the key features of IP that has helped IP Routing to scale is
>    aggregation of IP prefixes.  This is made possible with longest-match
>    lookup in IP forwarding.  Contrary to this, MPLS forwarding works on
>    exact match on MPLS labels.  This poses a challenge in aggregation of
>    IP prefixes when the forwarding is based on the MPLS labels
>    associated with those IP prefixes.
>
>    This document introduces an Aggregation Segment for Segment Routing
>    with MPLS data plane which can be used to aggregate IP prefixes along
>    with their SR Prefix Segments.  Aggregation Segments enable
>    aggregation of IP prefixes to be performed at border routers to
>    improve scalability of MPLS networks.
>
>
>
> The IETF Secretariat
>
>
>
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