Recently, Distributed Denial of Service (DDoS) attacks have been threatening the Internet severely. Tracing IP packets back to their origins is an efficient and important part of the defense against those attacks. Currently two major kinds of IP traceback methods have been used for IP traceback in IPv6: packet marking and packet logging. IP traceback based on packet marking requires routers to write their identifiable information into the forwarded packets. It incurs little overhead on routers but needs a large number of packets to construct the complete attack path. IP traceback based on packet logging requires routers to store the digests of the forwarded packets.