[Disowned]

You shouldn't handle all DDOS on the source level. You can mitigate it on the source level, but you should have a proper IPTables configuration first.

https://forums.alliedmods.net/showthread.php?t=166037
https://forums.alliedmods.net/showthread.php?t=165560

You're not going to get enterprise anti-DDOS of course, because many server hosts have racks and expertly configured networks that greatly mitigate DDOS better than the OS can by itself.