[rbridge] Can we ever have pt-to-pt links?

[Russ White]

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> I'm going to ask on the IS-IS list. Manual configuration is actually
> scarier (and harder) because different
> RBridges can be configured differently. With this proposal (the DRB

I'm pretty certain the worst that is going to have with two ends
configured differently is that the link won't be used for transit. One
end will be transmitting a pnode, but the other end won't be advertising
a connection to it--instead, it will be advertising a connection to the
other is on the link. This means the twcc won't work, and the tree won't
build through that link.

The only other possibility is that the link could be configured for
p-2-p, while there are actually three devices on it. A good
implementation would shut down all adj's on such a link, but that's
implementation specific, though perhaps we should have suggested in the
p-2-p draft.... Even if it tries to form, the twcc across the 0 cost
backlinks to the pnode are going to cause the tree to fail to build
through the link, I think. It might build for the pair that do build an
adjacency, but the third is on the link will just be left out in
everyone else's tree.....

Hence, I think the manual configuration option is pretty safe.... And,
the protocol can't tell if the link was intended to be a p-2-p or not.
If you have a link with three is', and one fails, auto detecting the
link has now become p-2-p makes everyone in the domain run SPF. If you
don't do the auto-detection, they can run a partial, just slicing off
the link that failed.

:-)

Russ

- --
riw at cisco.com CCIE <>< Grace Alone

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