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20.16.9.8. Multicast tunnel

A multicast group may be used to represent a virtual network. Any guest virtual machine whose network devices are within the same multicast group will talk to each other, even if they reside across multiple physical host physical machines. This mode may be used as an unprivileged user. 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 4 network types in order to provide appropriate routing. The multicast protocol is compatible with protocols used by user mode linux guest virtual machines as well. Note that the source address used must be from the multicast address block. A multicast tunnel is created by manipulating the interface type using a management tool and setting/changing it to mcast, and providing a mac and source address. The result is shown in changes made to the domain XML:

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

Figure 20.45. Devices - network interfaces- multicast tunnel