Lisp sockets for communication over the Internet

I'm trying to set up a game to run in Lisp on two computers on different internet connections. Thus, there is a need for TCP communication. I've tried some toy examples with a server/client program and they work just fine on localhost, but no guides I found actually go on to use different machines. Trying that causes a "cannot connect" error. Is there some additional step for a distant connection versus localhost testing that I may be missing?