ServerArk
Linux game server UDP flood analyzer and protector
... packets from being processed by the game server at all. It essentially lifts the game server "above the flood" and allows the game to still be playable, even under very heavy attacks.
It can be run interactively with a high level of verbosity (to watch its logic in action), or it can be run unobtrusively as a daemon with output to daily log files (typical usage).