Before some of you start rambling on about how I don't know that I'm talking about, which may possibly be the case, please hear me out. This information may be old, or new.
I, together with a friend, Matt, used to run an Australian Garry's Mod community named PubGamer, whom was popular throughout the last couple of years in Half Life 2 Roleplay, Dark Roleplay, TTT, as well PERP. Whilst running namely PERP, we were the victim of devnulls, day in, day out, hour after hour. After countless days researching on the issue, we found a program called Peerblock. What Peerblock effectively does is block IP's you tell it to block. Maybe the attacks on our server weren't as large as others, but we were still being hit with 30 thousand IP's simultaneously, with a total of 100 thousand being blocked ultimately.
Once blocking these IP's, which were indeed carrying COD4 data, the affect of the attack would happen for about 20-30 seconds, which was because Peerblock found it hard to block 30 thousand IP's all at once so it had to take a breather, then the overall affect of the attack would disappear. The packets were still being sent, they were just being blocked at a software level.
Here's all of our peerblock lists which contain, I believe, most of the offending IP's. Close to 100 thousand all up.
The only attack in which this did not withstand was a 15gb/s attack on Boxing day of 2010, which crashed Optus Queensland in Australia for 25 minutes.
I hope this information is useful to you all.