Denial of Service (DoS) attacks pose a serious threat to the Internet. Mobile networks, which are expected to develop rapidly over a few years, are also vulnerable to DoS attacks. Although IP traceback is one of the promising countermeasures for DoS attacks, the fact that attackers have the mobility privilege makes the traceback difficult in mobile networks. In this paper we propose the basic concept of the modification technique for the previously proposed enhanced ITrace-CP scheme in order to trace the attack route before the attacker enters another network. The proposed scheme uses Time To Live (TTL) values of packets and is capable of tracing the attacker in a short time. Simulation experiments show that the proposed scheme is more efficient in tracing attackers in a mobile environment than conventional approaches.