In a nutshell: Apple’s latest Airport update limits the MacBook’s ability to scan for wireless networks who’s base channel is higher than 11. The fix: Change your wireless router’s base channel to 11 or lower.

The Long Story:

I have recently stumbled upon a horrible problem – my iBook G4 could no longer see our wireless access point!

By instinct I blamed the hardware (Cisco have their occasional weirdness factor) but then remembered that it used to work, and that nothing has changed with our hardware.

The problem was difficult to trace because of the following:

1. My iBook could see other networks just fine! It did not list mine among the available networks, even though mine is the closest.
2. I could enter it manually, and attempt to connect, but instead of telling me the network does not exist, the iBook said there was an error connecting.
3. It was not clear at first if the other networks were WAP / WEP, or standard open networks. I assumed at first that the problem was related to WPA2, which is what the latest Airport update intends to fix. But then, I tried it at home on my WPA network and it connected just fine!
4. I used MacStumbler at first, which does not give you enough information about the networks it lists. It indicated that some of the networks are WEP, but it seemed like MacStumbler never heard about WPA or WPA2!

The tool that helped me get the job done, eventually, was KisMac. It really is an amazing tool, and it seems like it really knows how to deal with the Airport on a low level. KisMac immediately found my network, and I was then able to analyze why my iBook can not list it or connect to it. A few minutes of poking around, and I found a possible discrepancy. My Cisco hotspot’s base channel was 13. I remembered that some older wireless hardware could not go above channel 11, but my iBook did connect to this hotspot before. Nevertheless I call my ISP (who control our network equipment) and ask them to change the base channel to 7.

So they make the change, call me to notify me it was done, I tell my iBook to connect, and IT WORKS!

The conclusion is that the latest Airport update breaks the ability to connect to channels above 13, so beware!