The default netplan configuration files in Ubuntu Core leave management of Ethernet devices to networkd. Therefore, to avoid conflicts, the network-manager snap does not manage Ethernet devices by default. The user has to take care to enable it after installation if desired.
Before following the instructions below, backup the contents of /etc/netplan to be able to restore it at a later point.
Also, note that this change might lead to a system without properly configured network connections, which would lead to problems accessing the device, so be careful when doing this.
To enable ethernet support, you have to set the
ethernet.enable property to
true. See how to do this here.
When this is done, configuration files for netplan are created so
network-manager is the default netplan renderer. When set to
default), the NM snap explicitly disables the management of ethernet devices to
avoid conflicts with networkd.
Rebooting the system will be needed for the changes to take effect.
After the reboot, NetworkManager should automatically set up attached Ethernet ports or use existing netplan configuration files to setup connections.
Once logged into the system you may check the current connection status by
$ nmcli c show