Abstract
Denial-of-Service (DoS) attack has been a great threat to network security. Although tremendous efforts have been made to counteract DoS attacks, DoS attacks still succeed now and again due to the aggressive development of attacking techniques. Unlike other researches that focus on illegitimate flow identification and tracing back suspects, this paper proposes to view DoS as Quality-of-Service (QoS) deterioration and treat it within the framework of the Internet Differentiated Service Model (DiffServ). We describe a two-stage defense strategy, preventing servers from shut down and choking attack sources from entering the Internet. Our simulation with Network Simulator-2 (NS-2) shows encouraging results for the effectiveness of our strategy.