Add network bridge with ubuntu 18.04

To create a network bridge with netplan you have to create a file

network:
  version: 2
  ethernets:
     enp6s0:
        dhcp4: true
  bridges:
     br0:
       interfaces: [enp6s0]
       dhcp4: true
       optional: false
       macaddress: <some mac>

Make sure to place a mac address in and replace the interface name enp6s0 with yours.

Then run sudo netplan apply.

The machine gets a new IP from dhcp so make sure you have it configured in your dhcp before or have a local console ;-)