I have several network interfaces and am setting them up via NetworkManager. When setting method to
IPv4 tab the save Button is greyed out as soon as I enter a Gateway into the
Gateway row. This only occurs for certain interfaces.
Check if the
never-default option is set. This option is not mirrored in the GUI afaik although NetworkManager is intended for graphical desktop environments.
You can try adding the gateway via command line tool:
~$ nmcli connection edit nameOfConnection > goto ipv4 > set gateway enter 'gateway' value: 192.0.2.1 > save
Now nmcli should complain after validating the entry.
[…] gateway not compatible to »never-default«
Set this option to false and save should work
> set never-default enter 'never-default' value: false > save