netdev - Re: [PATCH] ipv6: Fix default route failover when CONFIG_IPV6_ROUTER

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Message-Id: <20121203.135923.1359930693250099951.davem@davemloft.net>
Date:	Mon, 03 Dec 2012 13:59:23 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	pmarks@...gle.com
Cc:	yoshfuji@...ux-ipv6.org, netdev@...r.kernel.org
Subject: Re: [PATCH] ipv6: Fix default route failover when
 CONFIG_IPV6_ROUTER_PREF=n

From: Paul Marks <pmarks@...gle.com>
Date: Sun,  2 Dec 2012 02:00:21 -0800

> I believe this commit from 2008 was incorrect:
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=398bcbebb6f721ac308df1e3d658c0029bb74503
> 
> When CONFIG_IPV6_ROUTER_PREF is disabled, the kernel should follow
> RFC4861 section 6.3.6: if no route is NUD_VALID, then traffic should be
> sprayed across all routers (indirectly triggering NUD) until one of them
> becomes NUD_VALID.
> 
> However, the following experiment demonstrates that this does not work:
> 
> 1) Connect to an IPv6 network.
> 2) Change the router's MAC (and link-local) address.
> 
> The kernel will lock onto the first router and never try the new one, even
> if the first becomes unreachable.  This patch fixes the problem by
> allowing rt6_check_neigh() to return 0; if all routers return 0, then
> rt6_select() will fall back to round-robin behavior.
> 
> This patch should have no effect when CONFIG_IPV6_ROUTER_PREF=y.
> 
> Note that rt6_check_neigh() is only used in a boolean context, so the
> presence of both "m = 1" and "m = 2" was irrelevant and confusing.
> 
> Signed-off-by: Paul Marks <pmarks@...gle.com>

The values '1' and '2' used to influence rt6_score_route() in different
ways.

Please change rt6_check_neigh() to return a "bool" if you are going to
do this.

Thanks.
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