What Are Dos and DDos Attacks?

Denial of service (DoS) attacks can range from single packet attacks that can crash applications and servers to streaming packet floods from the same attacker.

In single packet attacks, a carefully crafted packet is formed that exploits a known operating system flaw or application vulnerability. Malformed packet attacks are covered in more detail in Chapter 11.

In a DoS flood attack, server or network resources are exhausted by a flood of packets. Because a single attacker sending a flood of packets can be identified and isolated fairly easily, the approach of choice for attackers has evolved to distributed denial of service (DDoS) attacks. In a DDoS flood attack, an attacker uses multiple machines that he controls to flood a target (see the "Botnets" sidebar).