When bridged and direct connections are used, the network interface definition of guests managed by libvirt can have host-specific information embedded in the guest config; for example in direct mode, the name of the physical device being used, or in bridge mode the name of the bridge device. In order to make migrations between non-identical hosts possible, this RFE provides a method of removing the host-specific items in the guest's network interface config, placing it in a libvirt virtual network definition instead. The guest can then simply reference the network to use by name, avoiding the necessity to put host-specific info in the guest config. At run-time libvirt will look up the guest definition for the current host, and use that information (which may be different for each host) to setup the guest's network connectivity.
Note that, in addition to making migration possible, this RFE allows setting up "pools" of physical interfaces for use in direct mode - rather than the config for each guest needing to specify a particular device (which must then be reserved for that guest even when it's not running), the guest just references a network - libvirt will then locate an unused (or the least used, depending on which is appropriate) interface, and use that interface instead.