But before you go to check out your firewall, be sure you're using the Assistant and Admin applications included with your AirPort Express, or a later version. Earlier versions don't work with AirPort Express.
When using the built-in Mac OS X Firewall (located in Sharing preferences) or a third-party firewall, the simplest test is to temporarily turn it off and try again. If the applications can find AirPort Express with your firewall off, you simply need to turn your firewall back on, and open these ports in the firewall: 192, 5009, and 5353.
For the Mac OS X Firewall, you'd follow these steps
- From the Apple menu, choose System Preferences.
- From the View, choose Sharing.
- Click the Firewall tab.
- Click New.
- From the Port Name pop-up menu, choose Other.
- In the Port Number, Range or Series field, type in:
192, 5009, 5353
- In the Description field type in: AirPort Admin
- Click OK.