Adding a Red lan

Hi,

It's a problem of routes.
Your station is connected on a green side, and probably have an internet access. When you create a red nic in the Nethserver instance, this one lost its routes during the modification.

One way to not lost the connection could be to create a second green nic, like this, The Ns will not change its routes. Only after, you could creates the routes and change the zone of the Nic.