There are many methods to fight DDoS attacks, the best ones are the proactive and reactive methods. Proactive mode would use in-line tool that has 100 percent visibility through packet analysis, thereby checking every single piece of the received traffic using pre-determined information and behavioral indicators. In the case of the reactive mode, the system would always be on and would require 1:1 capabilities. The reactive mode takes slightly longer time to identify an attack and also to react. The proactive mode tends to be expensive, since it does the analysis using flow thats already built into the network.”]
Source: https://hackercombat.com/proactive-or-reactive-which-is-the-better-method-for-ddos-defence/