[libvirt] libvirt: use existing network bridge

[Chris Lalancette]

Sascha Frey wrote:
> Hi,
> 
> I met a problem setting up virt-manager and libvirt:
> 
> I want to use an existing customized network bridge with libvirt
> (I need special iptables rules and a custom DHCP setup).
> 
> So I created a network definition file like this:
> <network>
>   <name>NAT</name>
>   <bridge name='br-nat' />
> </network>
> 
> Unfortunately, I'm unable to activate this network, because libvirt
> tries to create the bridge `br-nat' and fails, because it already
> exists:
> 
> # virsh net-start NAT
> error: Failed to start network NAT
> error: cannot create bridge 'br-nat': File exists
> 
> 
> I just want libvirt to attach the guest's tap devices to this existing 
> bridge. I don't want libvirt to manage the network.
> 
> Is there any chance to realize this set-up?
> It should work with virt-manager using the graphical wizard.

Yes, just don't define a new network.  To use existing bridges, you just need to
edit your guest XML files to use something like:

    <interface type='bridge'>
      <mac address='00:16:3e:4a:f6:89'/>
      <source bridge='br0'/>
    </interface>

Note that configured bridges should also show up in virt-manager, I believe.

-- 
Chris Lalancette