Subject: RE: BSR convergency time

From: Brian Edwards <[email-masked]>
Date: Thu, 22 Feb 2001 15:13:12 -0800

Mark,
Unicast routing convergence is not an issue for most routers in the domain.
Only routers that had shortest IGP route to the router that is now in the
other partition. Most routers will have shortest IGP route stay the same (to
the router in their own partition).

I don't think BSR timeout is a huge deal. I'm just commenting on the
differences.

-Brian

-----Original Message-----
From: Mark Handley [mailto:[email-masked]]
Sent: Thursday, February 22, 2001 2:13 PM
To: Brian Edwards
Cc: 'Pavlin Ivanov Radoslavov'; [email-masked]
Subject: Re: BSR convergency time 

>> 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.

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

---

From: Mark Handley <[email-masked]>
Date: Thu, 22 Feb 2001 15:22:33 -0800

>the router in their own partition).

So the real difference is not with RP failure, but with total network
partitioning.

If we were just talking about RP failure, it seems like there's not
much to choose between the two (all groups in one anycast RP's region
affected vs some of the groups in the whole domain affected).

>I don't think BSR timeout is a huge deal. I'm just commenting on the

Agreed - I'm just trying to understand the tradeoff.

Cheers,	
	Mark