[spring] Comments on draft-ietf-spring-segment-routing-policy (ver 03)

[Vishnu Pavan Beeram <[e-mail]>]

Authors, Hi!

There are some use-cases where the candidate-path (multipath) needs to be
constructed in such a way that a part of the multipath (a set of
segment-lists) uses one set of constraints, while the other part (another
set of segment-lists) uses another set of constraints. Consider the
scenario where the traffic needs to be steered onto a policy in such a way
that a specified portion of it uses paths that traverse only blue links
while the rest uses paths that traverse only red links.

The current semantics of a candidate-path as defined in Section 2.2 of
version 3 preclude such use-cases. It should be possible to let the
semantics be a tad more flexible than they currently are and cater to the
above scenario (and the likes of it).

There are a few different ways of addressing this, but I would like to
propose one that seems least disruptive.

In addition to the currently specified semantics:
-- A candidate path may comprise of a set of sub-candidate paths where each
each sub-candidate path is either dynamic or explicit. The sub-candidate
path is the unit of signaling of an SR policy between a headend and a
controller.

Regards,
-Pavan