[c-nsp] MPLS best practices question

[Oliver Boehmer (oboehmer)]

> On Tue, 2010-06-22 at 09:49 -0500, cisconsp at secureobscure.com wrote:
> > 2) OSPF timers or BFD? Currently my approach has been ospf timers of
> > 1/4, its fast and seems pretty compatible with everything I have
tried
> > it on. All of my links are direct between routed ports so there are
no
> > intermediate devices that would keep a link lit after equipment
> > failure. I know BFD makes sense but some of my code is old and
> > linecards are flakey so I'm curious to know who has ditched low
timers
> > for BFD or vice versa.
> 
> We ditched BFD in favour of low (IS-IS) timers, since 6500/Sup720 SXF
> couldn't handle low BFD timers well. We're running SXI now, but
haven't
> changed back. We would actually like to, since some of our (leased)
> amplified/DWDM links are very slow to see link down.
> 
> Question: Is fast BFD timers a good idea on Sup720/SXI?

I would give it another try. SXF's BFD implementation was not really
optimized and led to false positives..

> Another question: Is adjusting IGP timers (or using BFD) enough in an
> MPLS network? How does the network invalidate allocated labels and
> choosing a new LSP, disregarding FRR? Does it make sense to adjust the
> holdtime or backoff timers in LDP for faster convergence?

LDP's liberal retention mode basically ensures that once IGP switches to
a new path, there is already a label to use. So core convergence really
only depends on IGP (and failure detection). The link-up issue (where
IGP/LDP sync or LDP session protection come into play) is really the
only thing you need to look at when it comes to LDP in an IGP-tuned
core.

	oli