On 04/14/2013 09:56 PM, yue wrote:

in my case each ethernet must in UP status even it is a NAT network where is the point i can start its virt-ethernet when i start a NAT-network?

I've discussed this with (who I *think* is) the author of this email on irc, but just in case anyone in the future does a search for "virbr0-nic", the short answer is this: ignore the virbr*-nic interfaces, pretend they don't exist; they are an implementation detail whose purpose is only to provide the libvirt network's bridge device with a stable MAC address. They never pass any traffic and they don't have any useful information that isn't available elsewhere. If you're really interested in the "why" of this, look at the first bug report for a description of the problem caused by *not* setting a stable MAC address on the bridge, and the 2nd for all the followup (including pointers to the upstream patches that added the -nic tap devices): https://bugzilla.redhat.com/show_bug.cgi?id=560994 https://bugzilla.redhat.com/show_bug.cgi?id=609463