Board Thread:Questions and Answers/@comment-31857924-20170601145733/@comment-70.40.238.39-20170608150806

Pretty sure you have to forward a port. Risk of Rain uses port 11100 by default, so you'd have to either call up your ISP or log in to your router's settings page and set up port forwarding. Then you should be able to host it. Your friends should be able to join with your IP address. I haven't gotten around to doing this myself, but it should work.