We used Apple’s Migration Assistant Application to migrate my brother’s files and user account and stuff over to a new machine. The new machine has airport.
After the migration (and a few changes to our simple local home network), the Airport interface in System Preferences simply wasn’t there. Instead all we had was Ethernet 2. The new machine (an iMac G5) only has one ethernet interface, so Ethernet 2 made no sense at all!
I renamed the Ethernet 2 interface to Airport, turned it off and back on again. AFter this, Airport wouldn’t connect to the wireless signal, and the machine automatically renamed it back to Ethernet 2. Frustrating. Tried this about 5 times, and still all I had was Ethernet 2.
So, a bit of research led us to attempt to reset the network settings back to factory default. It was pretty easy to do this. All we had to do was to remove/rename a preference file and restart the machine. On boot the system will recreate the preference file from its default sources.
To do this, I renamed the file:
/Library/Preferences/SystemConfiguration/preferences.plist
to:
/Library/Preferences/SystemConfiguration/preferences.plist.bak
and restarted the machine. It worked!
The reason I choose to rename it instead of deleting it is just in case it didn’t work, I could at least put the old back. It’s always best to keep a backup before removing files, especially if you’re not really sure what the hell the file even does in the first place! 
Kay Morgan-Gurr
2009.08.24
Thankyou – this fix fixed this – and more!
Majonex
2009.10.14
I just deleted everything in the SystemConfiguration folder and restarted. Voila, OS X fixed up all my network settings. I could not see my own Airport. After this operation everything was back to normal! Thanks!
Elko
2009.10.21
tried this, says “You do not have sufficient access privileges to rename the item”
Steve
2009.10.21
Elko, you gotta be an admin user to remove the file. OSX should prompt for your password. Could also try using sudo from Terminal, but you’ll still need to be an admin.
lala
2010.02.17
i fucking love you man i almost threw myself out of my window
mads
2010.03.03
THANK YOU for this help! It fixed my “server denies connection” problem! Thank you!
Rulexo
2010.07.16
Can you help with the sudo command? i am an admin and it is not letting me, i had to make some changes to my host file and i aldo had to do it with sudo, someone else was kind enough like you to help with that.
Thanks.
Steve
2010.07.18
Just type sudo before your command, and you’ll be prompted to type your admin password. If it doesn’t work, then the account you’re using isn’t an admin.
Rulexo
2010.07.18
So i actually renamed the file and it did nothing, there was some heavy thunder the day before and the only cable attached to the grid was the ethernet, so i was thinkinf of physical damage. And today i started installing win7 with bootcamp and the light in the network switch instantly turned itself on, i guess my only option will be reinstalling osx…
Thank you for your help.