WiFi Network Dropping Packets on a Mac

A MacBookPro running 10.9.4 was experiencing a problem where it would suffer constant connection drops on some WiFi networks with upwards of 70% packet loss.  Cable connections were fine and not all WiFi connections displayed this problem.

The WiFi router was replaced and a separate WiFi access point was tried and still the drops continued.  Other computers connected to the same WiFi network did not have this problem.

We resolved the issue by following these steps:

• Turn on WiFi on the Mac
• Open System Preferences/Network
• Highlight the WiFi connection and click on the "Advanced" tab
• Click on the "Wi-Fi" tab
• Remove the problematic network.  It might be a good idea to remove ALL the saved networks as long as the user knows the passwords for them!
• Click "OK" and then "Apply" to apply the changes
• Open Keychain Access
• Highlight the "Login" keychain
• Search for "Airport"
• Find the "AirPort network password(s)" that are associated with the problem network and delete them.  Note: there are normally two per network, "System" and "Local Items" Keychains
• Restart
• Log into the WiFi network and enter the authentication details when prompted

After removing the shared networks and deleting the items from the Keychain the packet loss stopped and normal WiFi connectivity was restored.