I have this problem when my macbook air sometimes does not connect to free wifi hotspots. When the problem happens and I try to run the diagnostics, it normally gets to yellow network settings tab. It seems that it for some reason does not acquire automatically the router or dns address. Sometimes after I shut it down and restart it magically connects to the wifi hotspot but it is very inconsistent. Anyone knows a fix for this problem?
You may want to try changing the service order. What effect this actually has, I'm not positive, but it's worth a shot:
I've heard some claims that this is caused by TCP packet timestamps not agreeing, but I can't find the link (great). Maybe something related to this.
Free wifi hotspots are notoriously flakey. Does your machine ever exhibit this behavior with a reliable wireless network such as your home, a friend's, or your office?
First run Software Update to make sure you are up to date with all your Apple Software.
If that doesn't do it then make note of what your network and energy saver settings are by taking screen shots. Make note of locations, VPNs you have set up, timers for turning on comp, etc.
Navigate to the directory /Library/Preferences/SystemConfiguration
Note that this is the Library at the root of the drive, not in your user folder.
Copy that folder to your desktop as a backup. You will have to authenticate as an admin user.
Delete the entire SystemConfiguration folder. It will contain about 8 files. You will have to authenticate again.
Reboot the computer.
Set up your network and energy saver to your liking again and you should be good to go. You will have to manually join each wireless network again as you come across them, but this procedure does not remove any saved passwords for WiFi networks—they are still in your keychain.
Runing verify disk in Disk Utility (in your Utilities folder) and checking your drive with Disk Warrior (commercial app) could also help.
This isn't guaranteed to fix it, but is essentially starting you with fresh Network settings and will likely work. If the folder deletion, Disk Utility and Disk Warrior don't fix it I would reinstall the latest combo updater from apple on your machine. After that it sounds like an archive and install of the OS would be necessary, and if that doesn't do it there may be a hardware problem, possibly with the airport card.
10.6.1 Updater (there isn't a combo out yet until it hits .2) http://www.apple.com/downloads/macosx/apple/macosx%5Fupdates/macosxv1061update.html
You could try setting IPv6 to OFF :
You could also try disabling flow-control :
Try removing all any custom DNS settings (OpenDNS, Google DNS, etc.). I find that sometimes having those entries prevents the machine from getting an IP.