[alligator]

I forgot to forward a port on my Airport Extreme which is sitting at another house. Is there any way to remotely tap into the Airport from my current location and set up the port forwarding? I'm hoping to avoid a 2 hour drive to the other location.

[Sherman Homan]

Short answer: maybe.
Is the Airport WAN port on a public IP address or is it behind another router? If it is on a public address and you know that address then you could remotely admin it. If it is behind a router then all bets are off.

[rjt1000]

Airport admin utility-->Click on "Other"--> Enter public ip address and password-->administer as usual

[alligator]

Another problem: how do I figure out the IP address? I'll have to call my cable provider because they use dynamic addresses. Also, it is not behind another router.

[Sherman Homan]

Too late to help today, but you can't find that address remotely and your ISP probably has no idea. When you get back, go to:
WhatIsMyIP.com - 207.58.150.186
Most IP addresses don't change that often.

[ghporter]

And make darn sure you have a REALLY GOOD password on your Extreme. By exposing it to the Internet AND allowing remote admin, you are opening yourself up to any number of port scans and attempts at intrusion. Be VERY careful.

As Sherman points out, WhatIsMyIP.com (among others) provides your Internet IP without any trouble. There are also helper apps that allow you to keep something like a web page running behind a dynamic IP (assuming your cable provider allows you to use port 80, etc.). But you'll just want the manual check unless your provider expires dynamic addresses frequently.