Volume Based Attacks
Includes UDP floods, ICMP floods, and other spoofed-packet floods. The attacker's goal is to saturate the bandwidth of the attacked site/service, and magnitude is measured in bits per second (Bps).
Includes SYN floods, fragmented packet attacks, Ping of Death, Smurf DDoS and more. This type of attack consumes actual server resources, or those of intermediate communication devices, such as firewalls and load balancers, and is measured in packets per second (Pps).
Application Layer Attacks
Includes low-and-slow attacks, GET/POST floods, attacks that target Apache, Windows or OpenBSD vulnerabilities and even more. Comprised of seemingly legitimate and innocent requests, the goal of these attacks is to crash the web server down, and the magnitude is measured in Requests per second (Rps).