Thanks , Hahn! I think I get your point ,libvirt or the host machine is independent from the guest OS. but ,as I know ,on the VMware ESX server , they supply an extra tool called vmware-tools which can get more information about the Guest OS,including the network info. How did they do this? Now I had to write a tool to get more information about the active Guest OS using KVM hypervisor , have no idea how to who can help me ? Sincerely wade