The address to be used for listening for VNC connections to a libvirt guest was previously required to be an IP address. In cases where the guest migrates from one host to another, and the admin wants the guest to be listening on a publicly visible interface, this address must necessarily change during migration.
In order to make this change in listen address possible, this RFE adds the option of specifying a "listen network" by name. libvirt will then locate the virtual network definition of that name on the current host, and use the IP address associated with that network (either the IP address of the bridge used by the network, or of the physical ethernet device specified by the network). By using the same network name on each host for a network definition using the device that should be used for vnc connection on that host, the guest can be migrated between the hosts, and its VNC listen address will change automatically as it migrates.