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

[Mark Tinka]

On 9/Jul/18 10:55, James Bensley wrote:

> 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.

An unstable IGP, generally, infers a physical link instability (hardware
resources and software bugs notwithstanding, of course).

I don't understand how having multiple RR's for redundant iBGP sessions
deals with an unstable IGP. If the IGP is unstable, it's unstable.

Perhaps the greater discussion to have is how to deal with an unstable
IGP. Is it a flapping link, and if so, do we take it out of operation if
it's bouncing rather going hard down?

Mark.
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