Wi-Fi has stopped working around the time 10.7.3 update. Might they be related? I have a MacBook Air which was working fine. Now I have awful network issues since the 10.7.3 update.

My home router is a D-Link DIR-615. I was securing the Wi-Fi network using WEP which worked great on Windows 7/XP/Vista, Ubuntu, iOS, and Mac OS X Lion. 

Then I installed the 10.7.3 update on my MacBook Air and the Wi-FI stopped functioning on it. I started to receiving error messages saying, "Select a certificate and enter username and password". I googled this and decided to switch to WPA security since is more secure and though this issue would be resolved. Easily done. No more error messages, internet is working fine everywhere...except on the MacBook Air. 

Now when I attempt to connect to Wi-Fi on my MacBook Air, it attempts to connect to my network and connects but gives the error message "Alert: No Internet connection". I checked and it is not getting an IP address. After two minutes or so, it receives a proper IP address, but the internet is not working. Sites simply won't load. When I try to ping my router, I get timeout messages. I have verified that my DNS settings are correct.

Here's what I've already tried:


Turning firewall on/off/on again
Removed Wi-Fi configuration from System Preferences > Network, and added them again
Rebooted my router (several times)
Cleared /Library/Preferences/SystemConfiguration folder
Installed 10.7.3 combo update


All other Wi-FI devices on my network work with no issues. It's just the MacBook Air that is having this problem.
From what I've seen - this seems to be more a network routing issue than a hardware / link level problem. The first step is to narrow down if it's a network issue or a hardware issue.

In Finder, Shift+Command+G Go to the folder /System/Library/CoreServices and run the two Lion diagnostic tools to assist in narrowing down your problems.


Wi-Fi Diagnostics
Network Diagnostics


Once you have narrowed down the issue, you can ask a second, more detailed question on how to solve a failing step X in diagnostic Y if you still need help in getting this sorted.



This process was used (as described in the comments) to determine that Little Snitch and the existing firewall were causing the network issues.