Before classification of DDoS attacks, we describe a typical DDoS attack scenario. Then we
introduce why it is so prevalent, and its intrinsic reasons why it is so easy to launch. Figure (1)
shows a hierarchical model of a DDoS attack. DDoS attack divide into 2 types. One is
bandwidth depletion. This method is to congest the network, massive use of the bandwidth then
lead the network breakdown. The other type is resource depletion. Attacker depletes the key
resources such as CPU, memory and so on. Then break the server [1]. The attack usually starts
from numerous sources to aim at a single target. Multiple target attacks are less common;
however, there is the possibility for attackers to launch such type of attack Spoofed, altered, or
replayed routing information