What Is a DDoS Attack?

DoS attacks are also called flood attacks. They intend to exhaust the network or system resources on the target computer, causing service interruption or suspension. Consequently, legitimate users fail to access network services. A DDoS attack involves multiple compromised computers controlled by an attacker flooding the targeted server with superfluous requests. Table 1 describes the common DDoS attacks.

**Table 1** Common DDoS attacks
Attack Type	Description	Example
Network layer attack	Occupies the network bandwidth with volumetric traffic, causing your service to be unable to respond to legitimate access requests.	NTP flood attack
Transport layer DDoS attack	Occupies the connection resources of the server, resulting in denial of services.	SYN flood, ACK flood, and ICMP flood attacks.
Session layer attack	Occupies SSL session resources of the server, resulting in denial of services.	SSL slow connection attack
Application layer attack	Occupies the application processing resources of the server and consumes its processing performance, resulting in denial of services.	HTTP GET flood attack and HTTP POST flood attack