[c-nsp] BFD expectations

[Chris Evans]

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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