Re: [pim] BSR update

[Stig Venaas <stig.venaas at uninett.no>]

Stig Venaas wrote:
[...]
> So, it might be safer to not forward it, but it adds complexity due to 
> this bit. So I would like to see if there are any problems with doing 
> the forwarding. As I noted above, there might be some unnecessary 
> messages forwarded but there are also some benefits. Do you see more 
> serious problems?

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.

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,

Stig


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