The first straightforward account of DDoS - a serious issue that impacts revenue in the board room and production in the server room.

Sven Dietrich is a member of the technical staff at the CERT Coordination Center, part of the Software Engineering Institute at Carnegie Mellon University.

It is Monday night and you are still in the office, when you suddenly become aware of the whirring of the disks and network lights blinking on the Web server. It seems like your company's Web site is quite well visited tonight, which is good because you are in e-business, selling products over the Internet, and more visits mean more earnings. You decide to check it out too, but the Web page will not load. Something is wrong. A few minutes later, network operations confirm your worst fears. Your company's Web site is under a denial-of-service attack. It is receiving so many requests for a Web page that it cannot serve them all--50 times your regular load. Just like you cannot access the Web site,none of your customers can.Your business has come to a halt. You all work hard through the night trying to devise filtering rules to weed out bogus Web page requests from the real ones. Unfortunately, the traffic you are receiving is very diverse and you cannot find a common feature that would make the attack packets stand out. You next try to identify the sources that send you a lot of traffic and blacklist them in your firewall. But there seem to be hundreds of thousands of them and they keep changing. You spend the next day bringing up backup servers and watching them overload as your earnings settle around zero. You contact the FBI and they explain that they are willing to help you, but it will take them a few days to get started. They also inform you that many perpetrators of denial-of-service attacks are never caught, since they do not leave enough traces behind them. All you are left with are questions: Why are you being attacked? Is it for competitive advantage? Is an ex-employee trying to get back at you? Is this a very upset customer? How long can your business be offline and remain viable? How did you get into this situation, and how will you get out of it? Or is this just a bug in your own Web applications, swamping your servers accidentally? This is a book aboutDenial-of-Service attacks,orDoSfor short. These attacks aim at crippling applications, servers, and whole networks, disrupting legitimate users' communication. They are performed intentionally, easy to perpetrate, and very, very hard to handle. The popular form of these attacks, Distributed Denial-of-Service (DDoS) attacks, employs dozens, hundreds, or even well over 100,000 compromised computers, to perform a coordinated and widely distributed attack. It is immensely hard to defend yourself against a coordinated action by so many machines. This book describes DoS and DDoS attacks and helps you understand this new threat. It also teaches you how to prepare for these attacks, preventing them when possible, dealing with them when they do occur, and learning how to live with them, how to quickly recover and how to take legal action against the attackers. 1.1 DoS and DDoS The goal of a DoS attack is to disrupt some legitimate activity, such as browsing Web pages, listening to an online radio, transferring money from your bank account, or even docking ships communicating with a naval port. Thisdenial-of-serviceeffect is achieved by sending messages to the target that interfere with its operation, and make it hang, crash, reboot, or do useless work. One way to interfere with a legitimate operation is to exploit a vulnerability present on the target machine or inside the target application. The attacker sends a few messages crafted in a specific manner that take advantage of the given vulnerability. Another way is to send a vast number of messages that consume some key resource at the target such as bandwidth, CPU time, memory, etc. The target application, machine, or network spends all of its critical resources on handling the attack traffic and cannot attend to its legitimate clients. Of course, to generate such a vast number of messages the attacker must control a very powerful machi