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. …

Source: Mac OSX Hints