[Lsr] Entropy label for SR-MPLS

[<[e-mail]>]

Hi SPRING WG,

draft-ietf-isis-mpls-elc defines an IS-IS extension to allow the use of MPLS entropy labels in SR-MPLS networks.
https://tools.ietf.org/html/draft-ietf-isis-mpls-elc-05

As a reminder, entropy label has been defined in RFC 6790 by the MPLS WG. It improves load-balancing / allows the effective use of parallel paths. It requires a signaling and RFC 6790 defined it for LDP, RSVP-TE and BGP. As segment routing does not uses LDP nor RSVP-TE, an IGP extension is indeed required. https://tools.ietf.org/html/rfc6790

As of today (-05) the IGP encoding chosen by draft-ietf-isis-mpls-elc:
- may support inter-area/level deployments, albeit with additional complexity (currently not specified)
- does not support inter-AS and inter-protocol deployments. (Inter-protocol being the redistribution of prefixes/segments from a protocol (instance) to another IGP protocol (instance))

Following some discussions, this restriction is not an IGP technical issue as it would be easy to allow for this feature by using a different IGP encoding. It's a question of requirements so it would be better discussed in the SPRING WG.

I'd like to see a discussion on whether this restriction is a good or a bad thing from a SPRING requirement standpoint.
In other words, do we want to allow (or not) the use of entropy label in inter-AS and inter-protocol deployments or do we accept this regression compared to LDP and RSVP-TE?

Thanks,
Regards,
--Bruno

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