How do I set up the L2TP client on Nethserver, if on the router and other tools they only fill in the IP, User and Password then connect directly?
I am sorry, it seems the L2TP function has been dropped in Nethserver 7, it was supported in Nethserver 6:
http://docs.nethserver.org/en/v7/release_notes.html?highlight=l2tp
Here it seems like it’s not possible with CentOS 7 anymore:
https://raymii.org/s/tutorials/IPSEC_vpn_with_CentOS_7.html
But you may try to manually setup L2TP with some tutorial for CentOS 7/RHEL 7 from the net like this: