Comment 9 for bug 1640635

Additional nuance:

On a netplan enabled system also using cloud-init (+ curtin), the same assertion is made regarding how to disable network functionality tied to cloud-init is mentioned in /etc/netplan/50-cloud-init.yaml ("… disable via stanza in /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg …") and /etc/cloud/cloud.cfg.d/50-curtin-networking.cfg files.

… however …

If /etc/netplan/50-cloud-init.yaml is not deleted, that stanza is ignored.

Ubuntu 18.04.0 Server (via Bionic Live-Server 2018.03.19 daily)

No network related arguments included in kernel command line.

Initial install configuration was first-ethernet dhcp IPv4.

Neither ifupdown nor ifupdown2 not installed.

At the end of the installation phase + first reboot, both /etc/netplan/50-cloud-init.yaml and /etc/cloud/cloud.cfg.d/50-curtin-networking.cfg contain the minimal definition (first-ethernet dhcp IPv4).