[spring] Re: WG Adoption Call for draft-ali-spring-srv6-policy-sid-list-optimization-01

[Gyan Mishra <[e-mail]>]

Dear authors

I read through the draft again and I believe there should be alignment
across all vendors on compression as it pertains to overlay and underlay
merge of SIDs.

Below is an example on cisco platform where overlay and underlay merge is
disabled and the command has been deprecated so that overlay and underlay
is not merged for compression which can lead to other issues.

This is on Cisco XR platform and by default the overlay and underlay are
not merged.

As you can see the service endpoint part of the 2 tuple on SR policy
headend {color,endpoint} in this fast the endpoint uN next Sid CSID is 4
with service Sid for uDT4 or e035.

So now if you merged overly and underlay you would burn to node Sid entries
in the carrier for endpoint node Sid and service Sid.

So in this case the underlay only contains Sid up to the USP node or prior
as last hop and then LPM routes to egress PE endpoint of the Sid list.

There is absolutely no reason to merge overlay and underlay Sids as it
burns up valuable space in the carrier when using CSID compression and this
applies to next Sid without SRH can steer up to a full 6 node Sid hope and
replace Sid can also now steer more hops as well within a single carrier so
both endpoint behaviors can benefit from this draft.

This is a very valuable draft and concept optimization and should be
standardized and I think some of the input I have given here should be
reflected in the draft.

Not standardizing on this concept makes it very painful for operators if
the vendors implement this differently.

next hop fc00:0:1:e010:: via fc00:0:1:e010::/64
SRv6 H.Encaps.Red SID-list {fc00:0:4:e035::}-------------------> overlay
SRv6 H.Insert.Red SID-list {fc00:0:2:e026:6:e020:5:e010}---> underlay

I have tested this disable or overlay and underlay merge on both Nokia and
Juniper in interop between the three vendors and for intra domain and multi
domain with algo 0 and flex algo and the behavior is identical and as I
would like to see it and behaves per this drafts optimization strategy.


Thanks

Gyan

On Wed, Oct 29, 2025 at 10:45 PM Gyan Mishra <[e-mail]> wrote:

>
> I support WG adoption.
>
> I think it’s a valuable optimization for compression efficiency.
>
> Thanks
>
> Gyan
>
> On Wed, Oct 29, 2025 at 10:24 AM Zafar Ali (zali) <zali=
> [e-mail]> wrote:
>
>> Dear chairs and the WG,
>>
>>
>>
>> As an author, I support WG Adoption of this draft. It improves
>> compression efficiency and makes packet processing more efficient for the
>> SR policy endpoint node.
>>
>>
>>
>> Thanks
>>
>>
>>
>> Regards … Zafar
>>
>>
>>
>> *From: *[e-mail] <[e-mail]>
>> *Date: *Wednesday, October 29, 2025 at 9:32 AM
>> *To: *SPRING WG List <[e-mail]>
>> *Cc: *[e-mail] <
>> [e-mail]>
>> *Subject: *[spring] WG Adoption Call for
>> draft-ali-spring-srv6-policy-sid-list-optimization-01
>>
>> Dear WG:
>>
>>
>>
>> This message starts a three-week adoption call for
>> draft-ali-spring-srv6-policy-sid-list-optimization, ending on November/19.
>>
>>
>>
>> From the Abstract:
>>
>>
>>
>>    Segment Routing (SR) allows a node to steer a packet flow along any
>>
>>    path.  SR Policy is an ordered list of segments (i.e., instructions)
>>
>>    that represent a source-routed policy.  The packets steered into an
>>
>>    SR Policy carry an ordered list of segments associated with that SR
>>
>>    Policy.  An SR Policy can be instantiated SR-MPLS and SRv6 data
>>
>>    planes.
>>
>>
>>
>>    In some use cases, an SRv6 Policy's SID list ends with the policy
>>
>>    endpoint's node SID, and the traffic steered (over policy) already
>>
>>    ensures that it is taken to the policy endpoint.  In such cases, the
>>
>>    SID list can be optimized by excluding the endpoint Node SID when
>>
>>    installing the policy.  This draft specifies procedures to indicate
>>
>>    whether the endpoint's node SID needs to be included or excluded when
>>
>>    installing the SRv6 Policy.
>>
>>
>>
>>
>> https://datatracker.ietf.org/doc/html/draft-ali-spring-srv6-policy-sid-list-optimization
>>
>>
>>
>>
>>
>>
>>
>> Please review the draft and consider whether you support its adoption by
>>
>> the WG. Please share any thoughts with the list to indicate support or
>>
>> opposition -- this is not a vote.
>>
>>
>>
>> If you are willing to provide a more in-depth review, please state it
>>
>> explicitly to give the chairs an indication of the energy level in the
>>
>> working group willing to work on the document.
>>
>>
>>
>> WG adoption is the start of the process. The fundamental question is
>>
>> whether you agree the proposal is worth the WG's time to work on and
>>
>> whether this draft represents a good starting point. The chairs are
>>
>> particularly interested in hearing the opinions of people who are not
>>
>> authors of the document.
>>
>>
>>
>>
>>
>> Thanks!
>>
>>
>>
>> Bruno (for the Chairs)
>>
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