Do you mean you reach the end of the map in single player? or multiplayer?
I don't quite understand, you mention ports(as in network ports) if you are in single player then you dont need internet connection (free roam, missions) in multiplayer the world will not end you just end up going off the map( your depth indication wont tell you the depth nomore)
are you on a LAN connection with friends?
If you want to test the server connection let me know.