In recent years, DoS attacks are becoming more serious in security of the Internet. They are rather easy to implement, but difficult to prevent. Therefore, tracing to the attackers and punishing them is considered to be an effective means against the attacks. Several tracing mechanisms have been proposed and analyzed for simplified models.

This paper describes a simulation method for two network models, ICMP traceback (iTrace) and IP marking traceback (IP marking). This method modifies the OPNET to add the tracing codes. Also described is the results of simulation experiments, which indicate the effectiveness of the method.