[c-nsp] BFD expectations

[Phil Mayers]

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.