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…
Source: 10 Simple Ways to Mitigate DNS Based DDoS Attacks” target=”_blank”>Fortinet Blog

Firewall deployments can be characterised by episodes of intense activity interspersed with long periods of “I assume it’s working ok”. However, between the cutover and Business as Usual (BAU) transition the long term feed and water…
Source: Centralised vs Distributed FortiGuard Updates” target=”_blank”>Fortinet Blog