Subject: RE: BSR convergency time

From: Brian Edwards <[email-masked]>
Date: Thu, 22 Feb 2001 11:34:25 -0800

> Before describing this solution, could someone enlighten me
> what exactly is the problem with the BSR convergency time.
> E.g, how slow it is in practice, is it slow because of configuration
> issues, or simply because the way it works, or both.
> Also, how exactly MSDP helps here in the picture.

Slow convergence is caused because the BSR has to wait for a timeout when it
stops receiving Candidate-RP messages. MSDP/Anycast doesn't require the BSR
to redo the RP-group mapping, because both RPs are using the same address.
One of the partions will have to elect a new BSR, but this isn't a problem
because it will generate the same RP-group mapping info, and the RP-group
mapping on each router throughout the partion will remain stable.

---

From: Mark Handley <[email-masked]>
Date: Thu, 22 Feb 2001 14:12:34 -0800

>mapping on each router throughout the partion will remain stable.

It seems though that the convergence time of unicast routing for the
anycast failover, and the timeout for the C-RP are probably not too
different, assuming that C-RPs that are in the BSR's reported RP-Set
use a fairly short holdtime and periodic interval for their C-RP-Advs.
[The defaults are for the holdtime to be 150 seconds, which is
relatively high.]

If you care about this, you can certainly crank the holdtime down to
(say) 45 seconds, and the C-RP-Adv interval down to (say) 15 seconds
for any C-RP that is selected by the BSR as an active RP.  The
aggregate C-RP-Adv rate is still likely to be pretty low.

So is this really such a big deal?

Cheers,
	Mark