The most convenient way of doing this is with IP2. [8kb] (no install needed)

Your WAN address (from the perspective of an 'outsider' on the Internet) and your LAN address (the one for your local environment) may be the same if you directly access the Internet with something like a dial-up modem or a cable modem without a hardware NAT router. However, if you use some kind of hardware router or firewall as your gateway to the Internet, your computer will most likely have a so-called 'non-routable' IP address such as 10.x.x.x or 192.168.x.x. In this situation, there is no easy way to find out what your true Internet IP address is. That's when you can use IP2.