Tracing IP packets to their sources, known as IP traceback, is an important task in defending against IP spoofing and DoS attacks. Log-based IP traceback technique is to log packets at routers in the network and then determine the network paths which packets traversed using data extraction techniques. The biggest advantage of log-based IP traceback is the potential to trace a single packet. Tracing a single packet in the Internet using log-based IP traceback involves cooperation among all Autonomous Systems (AS) traversed by the packet. The single packet traceback process may not reach the packet origin if some AS on the forwarding path does not support IP traceback. IP traceback mechanisms are deployed within each AS independently. It is not reasonable to assume all ASes begin to support the same IP traceback mechanism in a short period of time. In this paper, we study the effectiveness of log-based IP traceback in tracing a single packet under the environment where not every AS sup...