Detecting Distributed Denial of Service Attacks: Methods, Tools and Future Directions

The minimal processing and best-e↵ort forwarding of any packet, malicious or not, was the prime concern when the Internet was designed. This architecture creates an unregulated network path, which can be exploited by any cyber attacker motivated by revenge, prestige, politics or money. Denial-of-service (DoS) attacks exploit this to target critical Web services [1, 2, 3, 4, 5]. This type of attack is intended to make a computer resource unavailable to its legitimate users. Denial of service attack programs have been around for many years. Old single source attacks are now countered easily by many defense mechanisms and the source of these attacks can be easily rebu↵ed or shut down with improved tracking capabilities. However, with the astounding growth of the Internet during the last decade, an increasingly large number of vulnerable systems are now available to attackers. Attackers can now employ a large number of these vulnerable hosts to launch an attack instead of using a single server, an approach which is not very e↵ective and detected easily. A distributed denial of service (DDoS) attack [1, 6] is a large-scale, coordinated attack on the availability of services of a victim system or network resources, launched indirectly through many compromised computers on the Internet. The first well-documented DDoS attack appears to have occurred in August 1999, when a DDoS tool called Trinoo was deployed in at least 227 systems, to flood a single University of Minnesota computer, which was knocked down for more than two days1. The first largescale DDoS attack took place on February 20001. On February 7, Yahoo! was the victim of a DDoS attack during which its Internet portal was inaccessible for three hours. On February 8, Amazon, Buy.com, CNN and eBay were all hit by DDoS attacks that caused them to either stop functioning completely or slowed them down significantly1. DDoS attack networks follow two types of architectures: the Agent-Handler architecture and the Internet Relay Chat (IRC)-based architecture as discussed by [7]. The Agent-Handler architecture for DDoS attacks is comprised of clients, handlers, and agents (see Figure 6). The attacker communicates with the rest of the DDoS attack system at the client systems. The handlers are often software packages located throughout the Internet that are used by the client to communicate with the agents. Instances of the agent software are placed in the compromised systems that finally carry out the attack. The owners and users of the agent systems are generally unaware of the situation. In the IRC-based DDoS attack architecture, an IRC communication channel is used to connect the client(s) to the agents. IRC