netdev - Re: Rate Limitation of Router Reachability Probing for possible dead routers (is Re: ipv6: Do not depend on rt->n in rt6

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Date:	Mon, 21 Jan 2013 15:44:25 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	yoshfuji@...ux-ipv6.org
Cc:	netdev@...r.kernel.org
Subject: Re: Rate Limitation of Router Reachability Probing for possible
 dead routers (is Re: ipv6: Do not depend on rt->n in rt6_probe().)

From: YOSHIFUJI Hideaki <yoshfuji@...ux-ipv6.org>
Date: Tue, 22 Jan 2013 04:28:36 +0900

> Ok, fix is easy, but in fact, we have broken router reachability
> probing.
> 
> Here rt->n was neighbour entry for (unreachable) router.
> The specification says, we SHOUDLD probe such router, but we
> should  have some rate limit (once per minute, or so).
> 
> We used "rt->n->updated" for this purpose, but now, if NS failed,
> we may immediately removes neighbour entry for it.  So,
> we might continue sending NS to dead router every 1 second.
> 
> Any ideas?

I don't see exactly how looking up the neigh on demand is different
from using a cached one in this context.

In both cases there should be a neigh entry in nd_tbl, why would
there not be one?

If necessary, you can decide to mark entries in such a way that
they would have a lower priority for neigh GC purging if that
is the issue.
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