That, and you'll have to put your computer in front of the routers firewall, otherwise even if you have your wan ip, the firewall will block anyone from joining. Two ways to do this is to go into your router properties and either forward your lan ip outside the firewall or set your computer up as the DMZ host. Either way will put you in front of the firewall. And you don't hafta open port 27015, it is open automatically by default when you create a server.