Install Libvirt/KVM on Ubuntu 18.04 LTS and setup a bridge (br0) using NetPlan
Add your user to the libvirt and libvirt-qemu groups so you can connect to libvirt using virt-manager without being root
Configure the ethernet adapter and setup a bridge using netplan
The Ethernet adapter will be joined to a bridge device named br0
When setting up a bridge, the bridge (br0) gets the IP address.
All of our virtual machines will use the bridge (br0) as their network interface.
OPTIONAL: Remove the NAT network
Libvirt comes with a default network (192.168.122.0/24) which provides a NAT gateway.
However, it may be decided that the NAT network is unwanted overhead and that all of the VM’s should have direct network access using the bridge (br0), in which case the default NAT network is unwanted.
Restore the default NAT network
If you decide that you made a huge mistake by removing that default NAT network, it can easily be restored from the previously created backup.
OPTIONAL: Create a host-only network
Many virtualization systems create host-only networks.
If you are looking to setup a trust-zone, you will need a host-only network.