Re: [6man] New Version Notification for draft-nordmark-6man-impatient-nud-00.txt

[Philip Homburg <[e-mail]>]

In your letter dated Mon, 23 May 2011 23:10:09 +0200 you wrote:
>Who says that NUD can't also be used to declare an interface down/ 
>detect router neighbor loss?
>
>Maybe think of a BGP process running over TCP receiving ICMP 
>unreachables because the local NUD has declared the neighbor 
>unreachable. Meanwhile the other BGP partner router is still retrying at 
>TCP layer because NUD has not timed out on that node. Or am I seeing 
>non-existent links here?

Let's say router A declares router B unreachable because of some ND problem.
Meanwhile router B still considers router A reachable.

Now obviously, router A (and the routing system) will try to avoid routing
packets from A to B because that link is down.

B still assumes that A is reachable so it will continue to forward packets to
A. As long a A does not drop those packets, everything will be fine. I don't
think there is a reason to drop incoming packets when a neighbor on a link is
unreachable, but if an implementation does that, then that will break the
independence and will cause problems.

But for relatively stable links consisting of just BGP peers, it may make more
sense to just hardwire the ND entries and disable ND.