UDP floods are used frequently for larger bandwidth DDoS attacks because they are connectionless and it is easy to generate UDP packets using scripts.

DNS uses UDP primarily and under some circumstances uses TCP. Because, the usage of UDP/DNS protocol is extremely popular as a DDoS tool.

Since DNS is a critically important protocol upon which the Internet is based, its availability is of utmost importance. To deny the availability, a malicious attacker sends spoofed requests to open DNS resolvers that allow recursion. There are millions of open DNS resolvers on the Internet including many home gateways. The open DNS resolver processes these requests as valid and then returns the DNS replies to the spoofed recipient (i.e., the victim). When the number of requests is large, the resolvers could potentially generate a large flood of DNS replies. This is known as an amplification attack because this method takes advantage of misconfigured DNS resolvers to turn a small DNS query into a much larger payload directed at the target. In yet another type of attacks, unsolicted or anomalous queries may be sent to the DNS servers. Click Here To Continue Reading