Re: [pim] BSR update

["Christopher Thomas Brown" <ctbrown at nexthop.com>]

Stig Venaas wrote:
> 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.

I'd say this kills the idea. I'd much rather have the partition with the
stale data converge more slowly than risk having stale data propagate
once the partition begins to heal.

> This is the worst case scenario I can think of. This might be bad enough 
> to go for no forwarding (with some flag bit whatever) I suppose,

I still want to know which bit people have in mind. The only spare bits
are in the encoded group address and I would not like having to parse
that far into the BSM in order to determine if it should be accepted
or rejected.

Chris

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