Maybe my question is not enought clear so i will try to explian it more.

Ok i have a computer plug in a router. My router is a dhcp server . When im starting it give me an ip adress like 192.168.0.2. My router is connected to the internet and he have the ip adress that my isp gave me ex: 207.207.207.207. So i want to make a program that will retrieve this ip (207.207.207.207).