If you don't like or need the kdc process on Mac OS X, which opens TCP port 88 to the world, you can disable it with launchctl.
Disable:
sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.Kerberos.kdc.plist
Enable:
sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.Kerberos.kdc.plist