A multicast group is set up to represent a virtual network. Any guest virtual machines whose network devices are in the same multicast group can talk to each other even across host physical machines. This mode is also available to unprivileged users. There is no default DNS or DHCP support and no outgoing network access. To provide outgoing network access, one of the guest virtual machines should have a second NIC which is connected to one of the first four network types, thus providing appropriate routing. The multicast protocol is compatible with the guest virtual machine user mode. Note that the source address that you provide must be from the address used for the multicast address block.

To create a multicast tunnel, specify the following XML details into the <devices> element:

      
  ...
  <devices>
    <interface type='mcast'>
      <mac address='52:54:00:6d:90:01'>
      <source address='230.0.0.1' port='5558'/>
    </interface>
  </devices>
  ...