(This seems more appropriate for the libvirt-users mailing list) On 09/08/2011 10:16 PM, Wayne Xia wrote: <virtualport> is used only when configuring guests that connect directly to a VEPA or VNLINK (i.e. 802.1Q) capable switch. Unless you have one of these switches, you will not use it. If you do have one of these switches, you will also have information included with them that explains the meaning of the virtualport parameters and how they are used (they're opaque to libvirt - it just passes them on to the switch without assigning any meaning to them). portgroup is a tag used to select certain bits of config out of <portgroup> sections in the <network> definition being used for the interface. Currently the things that can be configured in the <portgroup> sections are 1) <bandwidth> info, and 2) <virtualport> parameters. Again, it has nothing to do with VLAN groups. <portgroup> is very new, btw - it has only been in libvirt since 0.9.4, so if you're using an older version don't expect it to do anything. Down to the real basic question of which VLAN a particular guest is using - that can either be determined by the guest itself, or if the guest has no VLAN id setting, it could be determined by the switch/bridge the guest is connected to; in other words, wherever it is done, it's outside of libvirt (well, I guess if your platform has support for the iface-* commands, you could define a bridge that uses a vlan interface as its connection to the physical network - then traffic from any guest connected to that bridge would end up going onto the physical network with the given vlan id).