Problem Connecting to A private Server

OK so basically I'm having a problem connecting to my friends MangOS server or any server for that matter. I have the right version of WoW which his server uses (1.12.1) and I'm positive my realmlist is correct. What happens is when I try to connect it says "Connecting" then a few seconds later it says "Disconnected from server". I am behind a router so I unblocked a few ports in an attempt to fix the problem but nothing worked. If anyone can help me please give me some information.