Using xenial lxd container, migrating to networkd using netplan, and updating generated .network file to include RequiredForOnline=false, i can see that it is correctly ignored.
# dpkg-query -W systemd
systemd 229-4ubuntu21.2
# /lib/systemd/systemd-networkd-wait-online --timeout=5
ignoring: lo
ignoring: eth0
Event loop failed: Connection timed out
Using xenial lxd container, migrating to networkd using netplan, and updating generated .network file to include RequiredForOnli ne=false, i can see that it is correctly ignored.
# dpkg-query -W systemd
systemd 229-4ubuntu21.2
# /lib/systemd/ systemd- networkd- wait-online --timeout=5
ignoring: lo
ignoring: eth0
Event loop failed: Connection timed out