I'm posting this here in the hopes of saving some folk the trouble of running this down.
If you are trying to use
macvtaponto an existing adapter for a libvirt guest and you're having odd problems with dropped IPv6 traffic, you'll need to add
<interface>stanza in your XML.
<interface type='direct' trustGuestRxFilters='yes'> <mac address='52:54:00:0d:42:ce'/> <source dev='eth0' mode='bridge'/> <model type='virtio'/> <address type='pci' domain='0x0000' bus='0x02' slot='0x01' function='0x0'/> </interface>
The problem is caused by the
macvtapnot updating its multicast tables correctly. This is considered correct by design for security reasons. I hope with increased deployment of IPv6 this decision will be revisited.
Some of the reading that led me here: