Adam Williamson (adamw) has done a fine job at determining how to get
bridged networking working with NetworkManager:
https://www.happyassassin.net/2014/07/23/bridged-networking-for-libvirt-w...
According to Adam, he did the work on Fedora 21 whereas I did it on
Fedora 20. the undesirable features (problems) I found may be corrected
on F21 but I believe that they have not been fixed.
While Adam's procedure for creating a bridge definition for
NetworkManager using the Gnome or nm-connection-editor are basically
correct. However, The virt-manager & libvirt do not "like" the default
names. [*not a show stopper but it should be fixed*] Instead, the the
bridge definition, use "br0" for the connection name and the device
name. For the "slave" definition (the real physical NIC), use the
<physical_device_name> such as p33p1 or p4p1 or em0 or whatever. I then
rebooted the host to make sure everything was clean and the netowrk came
up fine on br0.
Then, using virt-manager, I took an existing VM, deleted the virtual
NIC, added a new virtual NIC using br0. After booting up the VM, you
need to edit its network configuration to delete the existing definition
and add a new one pointing to the new virtual NIC.
This works!!! And on Fedora 20 ... oops, not quite Fedora 20. This was
done on a Fedora 20 host which as the updates from fedora-virt-preview
applied. I still have a system without the preview updates so I will go
back and see if it works or it needs the preview updates.
Gene