[libvirt] libvirt: use existing network bridge

[Cole Robinson]

On 10/19/2009 03:18 AM, Daniel Berteaud wrote:
> Le lundi 19 octobre 2009 à 09:14 +0200, Chris Lalancette a écrit :
>> 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.
> 
> Existing bridge shows up in virt-manager when run on the local machine.
> If you use a remote connection (at least qemu+ssh), you don't see it,
> you need to manually edit the guest XML.
>
> (btw, is this a known "problem" or a bug ?)
>

For a while, libvirt didn't support a way to enumerate bridge devices on
a remote machine. That support now exists, but virt-manager needs to be
updated to use it (nontrivial). Known issue.

- Cole