Re: IPv6 flapping with kernel 3.3 (regression from 3.2.9)

From: Maciej Rutecki
Date: Sun Mar 25 2012 - 02:44:33 EST

On czwartek, 22 marca 2012 o 08:34:28 Marc Haber wrote:
> Hi,
> I have a host which has IPv6 misbehaving when running with Linux 3.3.
> It is flawlessly working with Linux 3.2.9.
> The host
> - is running Debian stable (x64_64) with a few locally built and/or
> backported packages, including the kernel.
> - has native IPv6 connectivity on eth0
> - is not doing SLAAC on eth0, both IP address (from 2a01/16) and
> default gateway (fe80::1) are statically configured
> - is running a handful of VMs using KVM/libvirt
> - has IPv6 forwarding enabled
> - does IPv4 NAT
> - has a handful of iptables rules, both for v4 and v6. ICMP and ICMPv6
> are fully open
> - the gateway is not under my control
> - the VMs are either bridged to br0 or to br1
> - both br0 and br1 have an IPv6 /64 and radvd running to provide IPv6
> to the VMs
> This setup is unique in my machine list, my other machines either are
> no KVM hosts or do only have IPv6 tunneled.
> When I run the box with kernel 3.3, it drops off the IPv6 network
> every few minutes and is not responding to pings any more. This state
> stays like 30 seconds to a minute and then IPv6 resumes. It looks to
> me that the box does not lose its default route though. Once in a
> while, I see "fe80::1 dev eth0 router FAILED" in the ip neigh output.
> Running a continuous ping in either direction doesn't seem to help.
> Booting the box back to 3.2.9 immediately fixes the issue.
> I have not yet re-tried going back to 3.3 since a few of the VMs are
> too important to reboot again today. I tried running tcpdump on eth0
> over night but hit br1 instead, so I don't have any packet dumps to
> show.
> I guess that something goes wrong with neighbor detection regarding
> the IPv6 gateway.
> Was there a relevant change between 3.2.9 and 3.3? Where do I look for
> the issue?
> Greetings
> Marc

I created a Bugzilla entry at
for your bug/regression report, please add your address to the CC list in
there, thanks!

Maciej Rutecki
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