internal error: Network is already in use by interface virbr0

[Laine Stump]

On 9/17/21 7:11 AM, Michael Ströder wrote:
> HI!
> 
> I'm using libvirt 7.7.0 on openSUSE Tumbleweed.
> 
> Until recently everything just worked. But now my virtual NAT network is
> not usable anymore.
> 
> Starting a VM I get this error:
> 
> # virsh start ae-dir-suse-p1
> error: Failed to start domain 'ae-dir-suse-p1'
> error: Requested operation is not valid: network 'vnet1' is not active
> 
> Manually starting the network does not work either:
> 
> # virsh net-start vnet1
> error: Failed to start network vnet1
> error: internal error: Network is already in use by interface virbr0
> 
> In syslog I find:
> 
> libvirtd: 6325: error : networkCheckRouteCollision:296 : internal error:
> Network is already in use by interface virbr0
> 
> What does that mean? Where to look for a config error?


Someone else (probably libvirt itself, for libvirt's "default" network) 
has created a bridge device called virbr0, and has set it up on the same 
subnet that you are trying to use for your network, which is confusingly 
called "vnet1".

My first guess is would be that either:

1) you previously did not have the libvirt-daemon-config-network package 
(which adds the default network to the host and sets it to auto-start) 
and now it is installed, and being started before the "vnet1" network.

or

2) you *did* have libvirt-daemon-config-network (and thus the libvirt 
default network) installed, but for whatever reason your libvirtd was 
starting your "vnet1" network first, then failing to start the "default" 
network.

To fix this problem, change the subnet used by one or the other of the 
networks such that they don't conflict (e.g. if both have 
192.168.122.0/24, change one of them to 192.168.123.0/24) using "virsh 
net-edit $networkname", then virsh net-destroy and virsh net-start both 
networks.

Alternately, if you never use libvirt's default network, just 
net-destroy it and set it to not auto-start:

    virsh net-destroy default
    virsh net-autostart default --disable
    virsh net-start vnet1

Or, another alternate possibility - instead of using your own NAT 
network, just edit your guest config to use libvirt's default network 
and set net-autostart disable for your vnet1 network (if you have any 
extra config in that network, like static DHCP addresses, you'll want to 
move it into the default network, then net-destroy/net-start the default 
network so those changes take effect).

Once you've changed the config, it should persist through future reboots 
of your host.

> 
> When restarting libvirtd itself I see the following syslog warning message:
> 
> libvirtd: 5733: warning : netcfIfaceRegister:1287 : Failed to initialize
> libnetcontrol.  Management of interface devices is disabled

That's unrelated and unimportant. Most probably the libvirt APIs 
affected by that have *never* operated properly on openSUSE (it uses a 
"netcf-lookalike" that, AFAIU, accepts the same XML as netcf and has 
some of the same functions, but was never really "complete", and is 
probably just as much abandonware as netcf (which was abandoned, by me, 
last year)), and it's likely that you never had the libnetcontrol 
package installed at all, and have always had this warning but just 
didn't notice it until now.