Subject: Re: bridge is not forwaring ICMP6 neighbor solicitation to KVM guest

From: Linus Lüssing <[email-masked]>
Date: Tue, 4 Mar 2014 11:52:54 +0100

Hi Jan,

On Tue, Mar 04, 2014 at 03:02:36AM -0500, Jan Stancek wrote:
> > For the broken query, ok, it's your manually crafted query. But
> > did you see a query with such a bogus source address "in the
> > wild", too? (I'm curious how urgent this sanity check is)
> 
> It's real packet I managed to capture during one such occurrence.
> I'm sending it with small C program over raw socket, but it's byte
> by byte exact copy of what I captured with tcpdump previously.
> 
> I'm not sure how that packet came to existence. Based on IPv6 address
> it came from host B, but all host B was doing at the time
> was running RHEL6 with couple qemu-kvm instances. KVM guests were
> set up to use bridge, so I'm assuming if any of them crafted
> this packet, source IPv6 address would be different.
> 

Ah, okay. Can you check whether it maybe came from the querier
code in the Linux bridge on host B? Is
"cat /sys/class/net/br0/bridge/multicast_querier" 1? Can you
isolate host B and disable any multicast router daemon on it? Then
check again, if you still see these queries. What kernel version
is running on host B?

Cheers, Linus