Ubuntu 3.13.0-24.46-generic 3.13.9 seems to be affected by the same bug as described here: http://patchwork.ozlabs.org/patch/326048/
The suggested workaround (echo 0 > /sys/class/net/br0/bridge/multicast_snooping) solves IPv6-problems for KVM guests.
Ubuntu 3.13.0- 24.46-generic 3.13.9 seems to be affected by the same bug as described here: http:// patchwork. ozlabs. org/patch/ 326048/
The suggested workaround (echo 0 > /sys/class/ net/br0/ bridge/ multicast_ snooping) solves IPv6-problems for KVM guests.