1. Introduction
Researches of DDoS attacks started since its birth. These researches provide methods to detect DDoS attacks used by firewall or network-based intrusion detection systems (NIDS), so simulating the flow of DDoS attack is essentially needed for studying or testing network devices in real environment. Developing the specific software [1] or using the existing simulation software like OPNET [2], NS2 [3] can help to build a virtual environment. Although high speed rate of data flow can be simulated in such way, it is possible that the simulation situation may be different from the real circumstance. While using large-scale network test equipment, such as SmartBits, is able to generate real attack flow. However, there are some inherent defects of these devices: highly specialized, complexly configured, unfriendly using, what's more important, most researchers cannot afford the high expense.