re: http://tools.ietf.org/html/draft-nordmark-6man-impatient-nud-00
I'm afraid have more questions than answers.
Are there any implications for different nodes having different NUD
timeout behavior on a link, and this no longer being symmetrical?
If I can think of two examples......
e.g. 1. Say Node A (router) declares node C (end node) unreachable but
Node B (alternate back up router) has not yet timed out node C?
I'm guessing this case is just like a split-brain segment, so is not
significant compared to existing failures.
Now the case of router failover....
e.g. 2. Say Node A (end host) declares node B (router) unreachable
locally, but node B (router) is still up and running but has not yet
timed out Node A.
Is that significant? I suspect so. After all if the raison d'etre of
changing NUD timers is to quicken / slow down router failover, surely
Node B (the router) also has to time out at the same speed as the end
host (Node A) otherwise the router will continue to advertise valid
routes to node A, and packets will black hole/queue anyway until NUD on
node B also notices the failure.
Vice versa is also true, if the router notices the failure first, but
the end node does not react to the failure and hangs around retrying
NUD, packets may queue/black hole in the other direction.
In the good old days we had things like gratuitous ARP for such events
to attempt to wake up end nodes to refresh their cache, but if they got
lost in some layer 2 STP thrashing it didn't help much anyway.
Is there thus a need for any over-ridden NUD parameters to be
synchronized across all nodes on a link e.g. via RA messages?
Is there a minimum and maximum timeout needed? To prevent danger of an
update storm [as specified in RFC2461 that all Neighbor Solicitations
are rate-limited on a per-neighbor basis] or "stuck in stale".
regards,
RayH
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