[j-nsp] Segment Routing Real World Deployment (was: VPC mc-lag)

[James Bensley]

On 8 July 2018 21:35:36 BST, adamv0025 at netconsultings.com wrote:
>Hold on gents,
>You are still talking about multi-hop TCP sessions, right? Sessions
>that
>carry information that is ephemeral to the underlying transport network
>-why
>would you want those session ever go down as a result of anything going
>on
>in the underlying transport network -that's a leaky abstraction , not
>good
>in my opinion.
>You just reroute the multi-hop control-plane TCP session around the
>failed
>link and move on, failed/flapping link should remain solely a
>data-plane
>problem right?
>So in this particular case the VC label remains the same no matter that
>transport labels change in reaction to failed link.
>The PW should go down only in case any of the entities it's bound to
>goes
>down be it a interface or a bridge-domain at either end (or a whole PE
>for
>that matter) -and not because there's a problem somewhere in the core.

I was having the exact same thoughts. LDP or BGP signaled - it should
be independent of IGP link flaps. Saku raises a good point that with
BGP signaled we can have multiple RR's meaning that loosing one
doesn't mean that the server state is lost from the network (so the
service stays up) however, if there is one ingress PE that SPoF
undermines multiple RR's. With LDP we can signal backup pseudowires
(haven't tried with BGP?) - there is a service disruption whilst the
LDP session is detected as dead - but it does work if you have two
ingress PEs and two egress PEs and set up a crisscross topology of
pseudowires/backup-pseudowires.

Cheers,
James.