On 7/25/12 3:38 AM, Andrew McGregor wrote:
This originally came in the context of VRRP v3. If you want to run
some dynamic routing protocol at the same time as VRRP on the same
VLAN, you need another link-local address to talk to your routing
peers with, since there's no way for the non-master routers to use
the VRRP address. So, you have two (or more) link locals on the same
VLAN. Ideally only the VRRP one should be used for sending RAs, of
course.
Agreed.
Sounds like that is a small implementation matter in the router software.
I totally agree that RAs should take care of this, and in fact I
think one way to resolve the conundrum is to craft an RA to
specifically tell the host it is onlink with that exact destination,
rather than a redirect, since as I read the RA processing rules, it
does not matter what source address the router uses in that case.
I guess I don't understand the problem you want to solve. Can you clarify?
I thought the problem was that the 1st hop was suboptimal, and the 1st
hop router wants to send a redirect to tell the host to use a different
1st hop router to get to the offlink destination.
You can't do that by faking an RA.
But above it sounds like the destination is on-link. Is that the problem
you want to solve?
While you can fake an RA for that, it runs into a issue with NUD should
the destination ever move off-link. That issue is that the prefix
information in the RAs time out based on the preferred/valid lifetime,
and NUD doesn't affect that. Thus if the destination is no longer
off-link, either the routers have to detect that and send a fake RA with
the prefix with onlink=0, or communication will be broken until the
valid lifetime of the prefix expires.
Redirects don't have that issue; NUD knows to ignore/discard the
redirects when it doesn't get responses to the probes.
Erik
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