======Remove Netplan On Ubuntu 18.04======

With Canonical's addition of [[https://netplan.io|netplan]] in Ubuntu 18.04 as the de-facto networking replacement, certain configurations can be quite cumbersome and time-consuming to sort-out on this new ''YAML'' fed system.

This guide will demonstrate how to revert back to the industry standard ''ifupdown'' system, implemented exactly as it was in Ubuntu 16.04.

=====Installing ifupdown=====

Reinstall the **ifupdown** package:

<code>$ sudo apt-get update
$ sudo apt-get install ifupdown</code>

=====Configuration=====

Configure your **/etc/network/interfaces** file with configuration stanzas such as:

<code>source /etc/network/interfaces.d/*

# The loopback network interface
auto lo
iface lo inet loopback

allow-hotplug enp0s3
auto enp0s3
iface enp0s3 inet static
  address 192.168.1.133
  netmask 255.255.255.0
  broadcast 192.168.1.255
  gateway 192.168.1.1
  # Only relevant if you make use of RESOLVCONF(8)
  # or similar...
  dns-nameservers 1.1.1.1 1.0.0.1
</code>

=====Apply Configuration=====

Make the configuration effective (no reboot needed):

<code>$ sudo ifdown --force enp0s3 lo && ifup -a
$ sudo systemctl unmask networking
$ sudo systemctl enable networking
$ sudo systemctl restart networking</code>

=====Remove Netplan Services=====

Disable and remove the unwanted services:

<code>$ sudo systemctl stop systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online
$ sudo systemctl disable systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online
$ sudo systemctl mask systemd-networkd.socket systemd-networkd networkd-dispatcher systemd-networkd-wait-online
$ sudo apt-get --assume-yes purge nplan netplan.io
</code>

Then you're done.

**Note:** You **MUST**, of course, adapt the values according to your system (network, interface name...).

=====DNS Resolver=====

Because Ubuntu Bionic Beaver (18.04) make use of the DNS stub resolver as provided by SYSTEMD-RESOLVED.SERVICE(8), you **SHOULD** also add the DNS to contact into the /etc/systemd/resolved.conf file. For instance:

<code>
....
DNS=1.1.1.1
DNS=1.0.0.1
....
</code>

and then restart the systemd-resolved service once done:

<code>
$ sudo systemctl restart systemd-resolved
</code>

The DNS entries in the ifupdown INTERFACES(5) file, as shown above, are only relevant if you make use of RESOLVCONF(8) or similar.