A quick calculation of the amplification with a Wireshark test is approximately 1:700 over 200 seconds as per below. According my steam servers list there are 2536 killing floor 2 servers online. If the attacker sends 15000 packets to each server we get 2536x15000=38 040 000. Assuming 90% loss for things like servers not responding, network loss,etc,etc we get 3 804 000 packets per second and this will go on for 200 seconds minimum. This number of packets will ddos most firewalls and most servers.