Another Distributed Denial of Service question (and this one) floated into the review queue. Is there any interest in creating a canonical question and answer for all of D/DOS questions that we see?
I'm of the opinion that for 90% of the audience here (myself included) the appropriate answer to "Help! I'm being D/DOS-ed" questions is for them to contact their upstream provider, be it their ISP's security team, their co-location facility's network team or their shared hosting / VPS provider and ask them to intervene. The proliferation and the ease of use of tools like Low Orbit Ion Cannon, not to mention the ubiquity of botnets, has created a threat environment where pretty significant D/DOS attacks are a relatively simple affair and defending against them often takes specialized knowledge and infrastructure that is beyond most administrators. No amount of gyrations performed on the host can truly mitigate one of these attack (i.e., Fail2Ban and iptables rate-limit just doesn't cut the mustard).