A DoS attack is an attack designed to make a computer or network incapable of providing normal services.
This attack can be classified into five categories based on the targeted protocol lev-el (element of the victim’s infrastructure). Attacks at the network device level try to exploit software bugs or to exhaust the hardware in order to crash the device. Operating system level attacks take advantage of the way protocols function and try to crash machines by sending non-standard messages with, for example, greater than normal sizes. Application-based attacks take advantage of specific bugs of applications that are running on the target host in order to block these applications or to drain resources. Data flooding attacks try to saturate the victim’s net-work by sending massive quantities of data; this forces the host to process meaningless packets instead of legitimate requests. Finally, there are attacks based on protocol features. These take advantage of certain standard protocol features and can, for example, make a DNS server cache false records or saturate a server’s memory with uncompleted handshakes.