By internal network, I mean a network that does not correspond to a physical NIC. It exists purely to allow VMs to communicate with each other.
On the oVirt Node
With that said, let’s begin. oVirt requires that all networks, even internal ones, correspond to a NIC. So step one is to make the host think that it has an extra NIC. We can do this with a dummy interface:
install /sbin/modprobe --ignore-install dummy; ip link add dummy0 type dummy
To have this automatically happen, those lines should also be added to /etc/modprobe.d/dummy.conf.
Also, run the following to make sure the dummy module is added on reboot:
echo "dummy" > /etc/modules-load.d/dummy.conf
Finally, make the network script for the interface. This should be in /etc/sysconfig/network-scripts/ifcfg-dummy0:
DEVICE=dummy0 BRIDGE=$Internal-network-name ONBOOT=yes MTU=1500 DEFROUTE=no NM_CONTROLLED=no IPV6INIT=no
Replacing $Internal-network-name with the name of the network you made on the oVirt web interface.
With all that done, when assigning networks to NICs in oVirt, you should now see dummy_1 as an option. Do be warned that this network will only exist on this host.