As distributed denial-of-service (DDoS) attacks have caused serious economic and social problems. In this paper, we propose the Service-oriented DDoS Detection Mechanism using a Pseudo State (SDM-P), which runs on network devices to defend against DDoS attacks without sacrificing performance in terms of data forwarding. In addition, we verified the performance of the SDM-P mechanism by evaluating its performance using a DDoS attack similar to the one that occurred in Korea and the USA on July 7th, 2009.