Internet Protocol (IP) traceback is the technology to give security to internet and secure from the internet crime. IP traceback system is also called as Flexible Deterministic Packet Marking (FDPM) which builds such a defense mechanism which has ability to find out real source of attacks on packets that traverse through the network. While a number of other trace back schemes exist, FDPM provides innovative features to trace the source of IP attack and can obtain better tracing capability than others. In this paper, the authors are concentrating on how packet marking is done and how they trace the source of attack so, firstly the whole message is splits into number of packets.