DNS Query Flood is a type of DDoS attack that belongs to the application attacks family. During the attack, the attacker sends a succession of UDP packets to a DNS server in an attempt to exhaust server-side assets such as CPU or memory. By that. the attack prevents the server from directing legitimate requests to zone resources.
The usage of the UDP protocol makes it easy to spoof packet information (IP, data size ect.). Therefore, it is difficult to distinguish the traffic of this attack from legitimate traffic, making it more difficult to mitigate.