[mpls] Anycast segments and context-specific label spaces

[Alexander Vainshtein <[e-mail]>]

Hi all,
I have read the draft<https://tools.ietf.org/html/draft-ietf-spring-mpls-anycast-segments-01> in question, and, from my POV, it defines, under the name of Virtual LFIB,  a dedicated context-specific label space (see RFC 5331<https://tools.ietf.org/html/rfc5331>)  in the devices that are assigned with one or more anycast segments, and uses the labels such devices allocate for these segments as the context labels identifying this space.

If my understanding is correct:

*         Explicit mapping of the definitions of the draft to already defined and well-understood MPLS architectural mechanisms would greatly improve its readability. It would also greatly help the implementers, especially if they have already implemented (or consider implementation of) context-specific label spaces in their devices

*         Adding the relevant references (including a normative reference to RFC 5331) seems necessary

Using context-specific label spaces and context labels in conjunction with anycast (or anycast-like) functionality  in MPLS is not new. One example (as indicated in Eric Rosen's email<https://www.ietf.org/mail-archive/web/mpls/current/msg12659.html>)  is the PW Endpoint Fast Failure Protection mechanism defined in RFC 8104<https://tools.ietf.org/html/rfc8104>. The analogy looks important to me since anycast groups are commonly considered as a protection mechanism (and not just as a load-balancing one). I also think that relationships between this draft and the egress protection framework<https://datatracker.ietf.org/doc/draft-shen-mpls-egress-protection-framework/?include_text=1> one are worth looking at carefully.

My 2c,
Sasha

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