I. Introduction
With the growth of vehicular network, accessing the Internet during movement becomes a trend and is gradually being familiar by everyone [1]. Network mobility inquries and resovles how to manage the location transition of a group of devices or users [2], [3]. Through the use of the network mobility technique, not only a mobile device but also a device which has no mobility support can still move with a transport vechicle and keep the Internet connection all the time. Two kinds of solutions have been proposed at different layers. The Internet Engineering Task Force (IETF) has defined an extension from Mobile IPv6 called Network Mobility (NEMO) Basic Support Protocol (BSP) at the network layer [4]. According to the IETF document, a mobile router (MR) would establish a bidirectional tunnel with its corresponding home agent (HA). All traffic to and from a mobile network must pass through the tunnel without any exception. Thus, the bi-directional tunnel results in sub-optimal routing.