After updating to Mac OS X 10.6.8, many users have experienced DHCP networking problems, where the Mac won’t pick up a valid IP address and instead gets a self-assigned IP address (169.254.x.x). In a few cases this was resolved using traditional troubleshooting techniques (reapplying 10.6.8 combo updater, running Applejack…), but the more common fix that has surfaced is deleting the Firewall preference file named com.apple.alf.plist located in /Library/Preferences and rebooting. Apparently, updating to Mac OS X 10.6.8 sometimes corrupts this file, and prevents the Mac from communicating with the DHCP server.