authentication with steam/Friends can't join my local gmod/ttt Server

Hey i want to play ttt with a few friends. The Problem is that they are not able to join the server. We have 5 PC’s in a Local Network but anytime they try to join on the local server they get a progress bar which says “authentication with steam” and then stopps moving. What is the Problem? I already tried turning off the firewall and changed a few things with my IP. I also used Commands like “sv_lan 0” but nothing worked. Please Help me!

If your friends are on your Local Network, you shouldn’t need to portforward or anything. Sv_lan should be to set to 1, if they are on your local network.