Posted 23 April 2010 - 06:33 PM
Your WAN IP is the address you got from Whatismyip, and is the WAN IP address of your router. The IP address of your computer is the 192.168.x.x that shows in an ipconfig /all command. It is called a private address because it does not show up on the Internet and so can be re-used by many private networks. Your router translates from the private inside 192.168.x.x addresses of all computers on the "inside" to the single WAN IP address on the "outside" of the router. In order for your friend to access your computer directly you need to specifically tell your router what to send to your computer and how. This is called port mapping. The process is slightly different depending on the type of router, but involves defining a "port" and "protocol" on the outside that is mapped to a specific IP address, port, and protocol on the inside. By default, the router drops any traffic originating from outside your network. The process of translating is called NAT, for Network Address Translation, although in this case it is more properly known as PAT, or Port Address Translation. The Port you are translating are specific to the application, like HTML Web services use port 80, and the protocol is usually one of the two major IP protocols, TCP or UDP. If you are trying to set up a game or similar look on the developer's support page on what the required ports are and how to map them. You may also have to open those ports on your computer's firewall.
Be aware that mapping ports makes that port available to everyone on the Internet, including some folks that think its fun to mess with your computer. Be very careful. Many routers have a function called a DMZ machine. This allows all incoming traffic to be forwarded to one internal IP address. It's an easy way to do what you want to do, but it also means a lot of things, like your local file and printer shares and a lot of other stuff that really shouldn't be exposed to the Internet will be. Only fully hardened machines should be mapped as DMZ hosts, and then with great caution. I've had more than a couple of clients that have discovered that their computer was no longer theirs but had been hijacked by spammers and worse and a lot of very personal info had been stolen because of mapping them to the DMZ. Consider yourself strongly warned, don't do that unless you are really sure of what you are doing.