[libvirt-users] multicast traffic no longer working after reboot

[Dennis Jacobfeuerborn]

On 31.07.2014 15:14, Dennis Jacobfeuerborn wrote:
> Hi,
> today a couple of Hypervisors got restarted due to a power outage. While
> the systems and the VMs on the are running fine multicast traffic
> between the guests is no longer working.
> 
> I generate multicast udp packet using iperf in the guest and check on
> the host using tcpdump:
> 
> tcpdump vnet0 => multicast packets are visible
> tcpdump vlanbr8 => multicast packets are visible
> tcpdump em1.8 => no multicast packets visible
> 
> vlanbr8 is the bridge, vnet0 the interface of the guest and em1.8 the
> physical interface for vlan 8.
> 
> I compared the settings in /sys/class/net/vlanbr8/bridge/multicast_*
> with a system where multicast works fine and see no differences. brctl
> showstp also shows "mc router" to be 1 for both interfaces and the
> bridge. All settings in /proc/sys/net/bridge/* are 0.
> 
> Any ideas why the bridge doesn't seem to forward multicast packets?
> iperf with unicast udp also works fine so it's just multicast that is
> the problem.

I did some further testing and strangely enough after booting the HV and
the guest things work as expected but after 2-3 minutes I suddenly don't
see the the packets anymore on em1.8. This is really bizarre behavior.

Regards,
  Dennis