I have a standard network setup where all my network devices, both WIFI and ethernet, are connected to the same router. Lately, however, I've been experiencing some very strange behavior.

It started as a simple connecting error, when I tried to reach an FTP server using the external IP. Of course I went right into one of those CheckMyIP sites, to double check the IP and it turned out to be correct.

Then I went into my router setup, which is through a tool called aiport-tool, because I have an Apple Aiport Extreme router. Turns out the router displays a different external IP, and for some reason that external IP works when I try to access the FTP server.

Can anyone explain what is going on? Why are the devices connected to the router displaying an incorrect external IP?

BTW i have no VPN/proxy setups on any of my devices.