Subject: [mpls] draft-dai-mpls-rsvp-te-mbb-label-reuse

From: "Nobo Akiya" <[email-masked]>
Date: Fri, 27 Mar 2015 13:24:26 -0500

Hi Authors,

I have couple of comments from OAM perspective.
(using email instead of mic since we are very short on time)

Section 2

   The
   best case scenario is complete overlap of the two paths end to end;
   in which case there is no need for any label changes and LFIB
   updates, both in the transit as well as in the ingress routers.  In
   this scenario there is also no need to perform data plane
   verification for the new tunnel instance.

Being a paranoid OAM person, the statement "no need to perform data plane
verification" makes me a bit nervous. There's a big difference between
"there should be no data plane impact" to "there is no data plane impact",
particularly because code changes required are to not change existing data
plane via label sharing by multiple LSPs. That implies that any
bugs/timing-issues/etc in that specific code space can cause existing data
plane to actually purged [accidently]. I would feel more comfortable if the
document did not imply that everything about the new LSP is perfectly happy
w/o any OAM to verify it.

   For the case where the two
   paths overlaps only from a certain transit router (rather than from
   the ingress), label reuse starts at that router and continues all the
   way to the egress router.  In this case the existing data plane
   verification method can still be used to verify new tunnel instance
   as before.

I'm fairly sure that you did not imply "existing data plane verification
_instance_ can still be used ...". But to doubly make sure ... if we take
BFD [RFC5884] as an existing data plane verification method, you cannot
reuse an existing BFD instance (i.e., BFD session for the old LSP cannot be
used for the new LSP), since the BFD session on the egress is tied to the
FEC for the old LSP. If you attempt to do this w/o any further BFD
procedures, the BFD session at the egress for the old LSP will be removed
when the old LSP is removed from the egress.

Thanks!

-Nobo