AirPort Utility 5.6 could show you all the devices connected to your AirPort base station—wired and wireless alike. AirPort Utility 6.x, however, only lists devices connected to your base station over Wi-Fi. There’s no way to use the app to list off the IP addresses and names of devices plugged directly into the base station.
You can stil grab the old version of the utility from Apple, though you need a little help to install the app on Mountain Lion, since the installer (falsely) reports that AirPort Utility 5.6 is incompatible with Mac OS X 10.8.
But while you can force AirPort Utility 5.6 to install on Mountain Lion, there’s no guarantee that the app will continue to work on OS X 10.9 Mavericks or beyond. So if you want to find the IP addresses of other devices connected directly to your base station, you might prefer another option.
There are several.
In Terminal, you can use the
arp -na command, which will list out devices it finds using the address resolution protocol. You won’t necessarily see friendly names for the devices it finds, but you’ll at least get a list of all the local IP addresses in use that it discovers.
You can also turn to multiple third-party apps. One such app, iNet, is available on the Mac App Store. There are iOS apps for the same purpose, like the free Fing and the $3 LAN Scan.
Those apps will, if possible, list off friendlier device names (in addition to IP addresses) than
arp -na offers.
Mac OS X Hints