cho0b: Only blocks can be null-routed (minimum a /5 but depends). All 4chan has is 3 IPs.

You're right about the rules.. /b/ has ZOMG NO RULES!

Anyway, if this is really a DDoS, and 4chan manages to intermittently come back during the attack, then it's very weak. Counting with 0.5 mbit as an average upload speed, one only needs 200 zombies to saturate 100 mbit. Small botnets start at 10000..