[c-nsp] BFD expectations

[Pete Lumbis]

The forwarding on the 6k can be decentralized but as of today I believe that
BFD is still a centralized process. That is, it is punted to the CPU and
control plane issues can give false positives as Phil mentioned.

I think there are plans to make BFD distributed in the future but I have no
idea what that time line is.

-Pete

On Wed, Sep 22, 2010 at 7:19 PM, Chris Evans <chrisccnpspam2 at gmail.com>wrote:

> Phil you bring up a great point. Until sxi bfd code was crap on the 6500..
> We have done exstensive testing at the ECATS lab. We concluded that 450ms
> is
> a good number on this platform with its centralized architecture. We tested
> this with approx 35 peers and had no issues under heavy CPU load.
>
> As stated before bfd is a triggering mechanism it still doesn't fix overall
> protocol reconvergence issues.
> > On 09/22/2010 03:22 PM, Jason Lixfeld wrote:
> >> It's my understanding that BFD can provide failure detection and
> >> recovery similar to that found in POS. To that end, I'd like to use
> >> BFD with ISIS to design an L3 network that has failure detection and
> >> recovery mechanisms which rival L2 mechanisms like REP/G.8023/STP's
> >> various incarnations, etc.
> >
> > Wouldn't we all?
> >
> > AFAICT, you will have to try very, very hard to get <200msec failover
> > using available layer3 mechanisms. It can be done, but it's difficult
> > and the configurations are highly topology-specific. Certainly achieving
> > 50msec / layer2 failover times seems to be all but impossible in the
> > general case.
> >
> > If you search the archives, you'll get posts from the helpful Cisco guys
> > on the list saying "contact your account manager and we can help you
> > tune X to get 100msec failover".
> >
> > Have you tuned your IGP? There is a lot of stuff to tweak on this, and
> > without it, BFD will not help you overmuch.
> >
> >>
> >> I've labbed BFD+ISIS between a 7301 and an ME3600, run MTR between
> >> test hosts connected to each of the two devices and yanked one of the
> >> two links connecting the 7301 and the ME. I lose about 2-3 seconds
> >> worth of packets. Those results seem a little inconsistent with the
> >> claims of BFD's timing, unless there's something I'm missing and even
> >> with the BFD hooks, ISIS isn't able to react at near POS speeds.
> >>
> >> Anyone have any perspective from the real world?
> >
> > For us, BFD was useless. It triggered false positives all the time, then
> > Cisco removed SVI support under later 12.2SX IOS. It didn't seem to be
> > "distributed", so anything which loaded the sup RP/SP CPUs caused it to
> > crap out.
> >
> > We gained far more from simply:
> >
> > router ospf 1
> > timers throttle spf 10 100 5000
> > timers throttle lsa all 10 100 5000
> > timers lsa arrival 80
> >
> > ...on all our boxes.
> >
> > YMMV, but I would not believe the marketing hype around BFD.
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