Upgrade CentOS 7 to 8, error: network is already in use by interface

[Filip Hruska]

Hi,

I've been trying to migrate some of my CentOS 7 KVM hypervisors to 
CentOS 8, and I have encountered the following issue while trying to 
load my network config:

virsh:
     error: Failed to start network test1
     error: internal error: Network is already in use by interface virbr2
journalctl:
     error : networkCheckRouteCollision:123 : internal error: Network is 
already in use by interface virbr2

I use the following network definitions, which are a bit non-standard, 
however they work perfectly on CentOS 7:

<network>
   <name>test1</name>
   <forward mode='open'/>
   <bridge name='virbr1' stp='off' delay='0'/>
   <mac address='52:54:00:c1:a7:7c'/>
   <dns enable='no'/>
   <ip address='10.0.0.1' netmask='255.255.255.255'></ip>
   <route address='192.168.1.22' prefix='32' gateway='10.0.0.1'/>
</network>
<network>
   <name>test2</name>
   <forward mode='open'/>
   <bridge name='virbr2' stp='off' delay='0'/>
   <mac address='52:54:00:54:09:3c'/>
   <dns enable='no'/>
   <ip address='10.0.0.1' netmask='255.255.255.255'></ip>
   <route address='192.168.1.33' prefix='32' gateway='10.0.0.1'/>
</network>

My question is, why is the behaviour different across CentOS releases, 
despite the libvirt versions apparently matching? Output from both 
systems is the same:

# virsh version
Compiled against library: libvirt 4.5.0
Using library: libvirt 4.5.0
Using API: QEMU 4.5.0
Running hypervisor: QEMU 2.12.0

What would be the best approach on patching out this check, so I can 
continue using my network config?

Just to summarize the expected output:
- virbr1 and virbr2 get created, each one with an address 10.0.0.1/32.
- Two routes get created:
192.168.1.22 via 10.0.0.1 dev virbr1
192.168.1.33 via 10.0.0.1 dev virbr2

Thanks,
Filip Hruska