Is it possible to get your router's external ip address without using a website?

• Sometime the device will provide a web interface (common with small home devices like Cable Modems) where this kind of information can be found and/or configured.
• You may be able to make a command-line connection to the device using telnet or ssh, then use /sbin/ifconfig or the local equivalent.

You want to know how are you being seen from outside, so to do this you need to use some outside service.

Note, that it does not have to be just your router WAN address. If you are using http proxy for example the result can by an IP of host many hoops away from your router.

There are several sites with such service. Most is HTTP based, for convenience.

If you need to do it from terminal, you can:

wget -q -O - whatismyip.org