In April of this year, Estonia suffered under a huge denial-of-service attack. Lest you think that Estonia is some little, underprepared country that doesn't follow basic computer security practices, you need to know that the same thing could happen to your country.
Today's Internet is so screwed up, security-wise, that there is absolutely nothing any country has that would stop a massive distributed DDoS (denial of service) attack. Think SQL Slammer worm, but using millions of bots designed to cause traffic floods. Bot nets under the control of one malicious hacker (or group) are often measured into the hundreds of thousands of nodes and, some analysts say, millions of compromised machines. If a very large bot net was used to attack a single country's Internet backbone, it would take that country -- even the most technology-savvy nation -- a few days to get legitimate traffic going again at previous levels.
Worrying about country-sized attacks isn't in most of our job descriptions, but mitigating smaller DDoS attacks against our organization are. To find out what most administrators could do to mitigate DDoS attacks against their company, I spoke to an administrator who has been there and done that: Paul Laudanski, founder and leader of CastleCops.
The effects of DDoS
Paul and his wife, Robin, lead the CastleCops site, which is the headquarters of a volunteer organization dedicated to fighting malware, spam, and phishing. They are very successful in getting malicious Web sites and compromised computers shut down. They also provide advice in Internet crime investigation and help others preserve evidence useful to law enforcement. CastleCops has been in business since 2002 and, by independent conservative calculations, prevented more than US$150 million in losses. This fact is not lost on the criminals who rule the Internet today. CastleCops has been the target of more than a dozen DDoS attacks. This year, it was subjected to two large gigabit-per-second DDoS attacks that caused connection problems for many days. CastleCops followed its own advice and Greg King has been charged in one of the attacks. You should read more details of the attack to understand how something similar could affect you.
I asked Paul what the average entity could do to mitigate the damage from a large DDoS attack. He said, "The first thing you need to do is decide whether you want to stay in business during the attack or not. If you want to stay in business, you'll need to absorb all the attack traffic along with your legitimate traffic. This means your broadband connection, routers, firewall, Web servers, and back-end databases have to be able to deal with the attack. Talk to your ISP: at many ISPs, traffic levels above 2Gbps will get you billed at the 95th percentile. If our ISP had committed us to that rate, CastleCops would have incurred a US$33,000 bill for a few days of DDoS traffic, which would have put our mostly volunteer organization out of business. Find out ahead of time how your ISP will handle DDoS events, and how you will be billed."
Paul continued, "I think many sites will need to scale to handle 10Gbps-to-30Gbps traffic loads." DDoS attackers will often start at lower traffic levels and attempt to increase the pain until your ISP, an upstream neighbor, or your servers fold. Although DDoS attacks above 10Gbps to 30Gbps occur, they are rare.
I asked Paul what administrators could do next to mitigate the attack. He offered, "Turn on your server and equipment logging to give you as much detail as possible. For example, Apache Web servers log connections by default, but not in enough detail. You'll want to get direct and forwarded IP addresses (to catch proxied connections), content details, user agents, and referral addresses." Then, using the information you collect, you can normally find a pattern to the DDoS traffic and place a filter on intervening devices to drop the malicious packets. Determined DDoS hackers will often change the pattern, so you will need to be on your feet and realize that implementing your first filter doesn't mean the DDoS is over.
Riding the DDoS storm
You can use an anti-DDoS mitigation service, such as Prolexic, to help out. Essentially, you change your Web server's public IP address (the DNS A record) to point to the mitigation service's IP address. They will scrub out the bad traffic and pass back the good traffic. You can also buy routers and network defense devices (such as Cisco or Juniper) built to take down DDoS attacks. Some of the devices will start working right away, putting down malicious traffic from the start, while others have to be plugged in a few weeks ahead of time to learn the difference between legitimate and anomalous traffic.