[libvirt-users] Domain XML Multicast Tunnel

Hello I found under networking in the Domain XML 'Multcast tunnel'. My question is does anyone know what is the intended use of multicast tunnel networking?What are the potential pitfalls of using such a configuration other than what's highlighted in the domain xml. eg: can it suffer from throughput issues? Can the tunnel be accessed from outside Libvirt? I'm struggling to find any information about it. If anyone has any information about it, Or where I can obtain such information it would be appreciated. Regards Richard