RE: [pim] BSR update

["Venu Hemige" <venu.hemige at alcatel.com>]

> -----Original Message-----
> From: Stig Venaas [mailto:stig.venaas at uninett.no]
> Sent: Monday, April 10, 2006 1:55 PM
> Cc: John Zwiebel; venu.hemige at alcatel.com; 'Christopher Thomas Brown';
> pim at ietf.org
> Subject: Re: [pim] BSR update

[...]
> 
> I believe I see one problem now. If we have the following scenario:
> 
>            _________________ long non-preferred backup path
>           /                  \
> BSR -- A -- R1 -- B -- R2 -- C1 -- C2 -- C3
> 
> With BSR being the only C-BSR (and elected). Assume now that routers
R1
> and R2 restart, and are gone for say 1.5 * BS Period. Assume that
while
> they are restarting, the BSR changes the RP set and A and C routers
> learn the new set. B will however still have the old set. When R1 and
R2
> comes up, R2 might accept stale BSM from B. Now if R2 forwards this
> towards C routers and the IGP by then has gone back to prefer tha main
> path (not using the backup path), then C routers will accept and use
the
> stale data.
> 

No, I would think the C routers will discard the BSM from B since the
BSM has lower bsr-priority than what they know about (from router BSR).

Also if you are saying the long non-preferred backup path is not used,
then it means that both R1 and R2 are up. Which means R1 should start
forwarding the BSM received from BSR since that BSM has a better weight
than what it learnt from B. And hence R1, B and R2 should soon start
using BSR as the elected BSR. The RP-SETs on routers BSR, A and C1, C2,
C3 should all be unaffected.

Forwarding triggered BSMs is a good thing. And I don't think anything
wrong will happen in the example you pointed out.

Regards,
-Venu


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