The NetworkManager is the network renderer that allows switching the
network automatically when a system is moved or the network changes.
The NetworkManager is coming by default in Ubuntu 16.04 and 18.04 desktop installations. It also comes in RedHat 7, but is not enabled by default to manage
Very useful on laptops, especially with wifi settings.
NetworkManager is composed of two parts:
1. A running service, network-manager
2. A front-end, nmcli, nmtui, to modify the settings.
On Ubuntu 18.04, NetPlan needs to define NetworkManager as the service renderer to make NetworkManager effective. For example,
# renderer: networkd
The rest of the configuration is done through nmcli or nmtui or the GUI front ends.