A single physical NIC can be carved into multiple VNICs, which can be assigned to different Solaris xVM instances running on the same system. VNICs are managed using the dladm command line utility described in the dladm(1M) man page. You can use virsh dumpxml output to correlate the domain's network interface with the assigned VNIC.
The dladm show-vnic command can be used to display VNIC information. In the following output, 1 is the domain ID, and 0 is the NIC number for that guest.
# dladm show-vnic LINK OVER SPEED MACADDRESS MACADDRTYPE VID xvm1_0 e1000g0 1000 0:16:3e:64:99:4d fixed 0
For more information, see OpenSolaris Project: Crossbow: Network Virtualization and Resource Control. Crossbow provides network virtualization and resource control by virtualizing the stack and NIC around any service, protocol, or virtual machine.