From: Halfix NB on
What is the best way to find out the external IP address of a computer that
is behind a router, modem, firewall, hub, etc... ?

I know there are websites such as whatismyip.com, but is there some way to
do this without hitting a website that I have no control over and don't know
who runs it... etc. ?

Do ISPs offer a service for finding out one's external ISP? If not, they
should...