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Ask Slashdot: Experience Handling DDoS Attacks On a Mid-Tier Site?
New submitter caboosesw writes "A customer of mine recently was hit by a quick and massive DDoS attack. As we were in the middle of things, we learned that there are proxy services of varying maturity to deal with these kinds of outbreaks from the small and mysterious (DOSArrest, ServerOrigin, BlackLotus, DDOSProtection, CloudFlare, etc.) to the large and mature (Prolexic, Verisign, etc.) Have you guys used any of these services? Especially on the lower price point that a small e-commerce (not pr0n or gambling) company could afford? Is a DDoS service really mandatory as Gartner now puts this type of service in the same tier as SEIM, firewalls, IPS, etc?"
There's two key strategies to avoid being DDoSed... first, have more processor, network speed, and disk I/O resources than you need for normal load so that the attacker can't fill one of your computers pipes. Then, host your server or servers at multi-connected datacenters which can cut off large users of your server before it reaches your NIC card. Firewalls at the server can't get back the bandwidth lost to needless connections, but firewalls at the datacenter entry points can. Basically, make sure none of your time-sensitive loads reach 100% and you're fine.
Having been the target of an HTTP-DDOS attack, I can tell you that manually blacklisting IP ranges is really ineffective. A DDOS botnet is comprised of thousands of machines that have been randomly infected by whatever vector the botnet operator used: Emails, web drive-by, etc. The result is that the source addresses are scattered widely with little relation between most participating addresses.
To defend against the attack, I wrote up an automatic firewall blacklisting program that detected and blocked each participating IP address individually in near-realtime. I was blocking more than 31,000 separate addresses before the DDOSers finally gave up trying to down the attacked website. Wierdly, there appears to have been no motive at all for the attack, yet they spent weeks attacking the target machine and actively trying to tune their attack to get past my filtering.