Re: [Idr] SRv6 Transposition for SAFI 76

["Rabadan, Jorge (Nokia - US/Sunnyvale)" <[e-mail]>]

Hi Gyan,

My question was not about RFC9252, but rather about the statement about BGP CT and the intend to not use transposition for SRv6. It is up to the authors and the WG, but I think transposition is important in SRv6 to have a better BGP update packing, and since BGP CT uses a new SAFI, transposition can be defined in a way that can be used without any issues.

About your comment, I think RFC9252 is perfectly ok and allows deployment in brown field scenarios, since the transposition procedures are completely optional. An operator can choose to not transpose functions into the label fields if that may cause issues in non-upgraded routers.

Thanks.
Jorge

From: Gyan Mishra <[e-mail]>
Date: Thursday, July 28, 2022 at 10:32 PM
To: Rabadan, Jorge (Nokia - US/Sunnyvale) <[e-mail]>
Cc: idr wg <[e-mail]>
Subject: Re: [Idr] SRv6 Transposition for SAFI 76
Hi Jorge

I just responded to Kaliraj on this issue and here is an excerpt below of the problem and possible solution.

Excerpt below:

The RFC 9252 BGP Service Overlay for SRv6 reuse of the existing VPN SAFI 128 caused mis routing for any/all  Brown field deployments.

In RFC 9252 a new SAFI would have been the best approach for VPN, then reusing the same VPN SAFI 128 to disambiguate SRv6 VPN overlay from MPLS VPN overlay.  This is the 2nd time this issue has cropped up with the first with extending MPLS EVPN RFC 7432 with RFC 8365 EVPN for NVO IP DC underlay, which also reuses  the MPLS1 MPLS2 label field to carry the L2 VNI / L3 VNI in the presence of BGP Tunnel Encapsulation extended community RFC 9012.

As a result of the SRV6 reuse of SAFI 128,  the VPN SAFI 128 traffic is mis routed going to SRv6 or MPLS as the NLRI appears to be the same due missing error handling for BGP prefix SID NLRI and transposition scheme.

Thank you for pointing this out as most operators would be migrating from brown field and so this is a major issue for anyone trying to deploy SRv6.

We should pick this mis route issue with RFC 9252 up on IDR / BESS and discuss if we need to do a BIS or new updated draft for this problem as it’s a very serious issue for any operators deploying SRv6.

***possible solution game plan***

I will start a separate thread on BESS and include IDR on the thread on how best to resolve this issue.

This draft proposes a new capability, however I think the best approach would be to define a new SAFI for VPN used with SRv6.

Just a thought here, what we could do is an errata or BIS update to RFC 9252 stating the problem clearly and that RFC 9252 should not be used for brownfield deployments.

Write a new draft and quickly get it progressed so we can fix existing deployments and any operators looking to deploy SRV6 soon - this draft would allocate a new SAFI for VPN used for SRv6.

Alternative SRv6 capability draft - I don’t think we should use this approach

https://datatracker.ietf.org/doc/html/draft-lz-bess-srv6-service-capability-03


Kind Regards

Gyan

On Wed, Jul 27, 2022 at 4:18 PM Rabadan, Jorge (Nokia - US/Sunnyvale) <[e-mail]<mailto:[e-mail]>> wrote:
Hi everyone,

During the IDR meeting, the CT authors mentioned that they wanted the WG to help with “clarification for disallowing SRv6 transposition for SAFI 76”.

Authors, could you please elaborate on that and why SRv6 transposition cannot be used with SAFI 76?

Thanks!
Jorge



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