Recent advances in information and communication technology have let not only a single node but also an entire network (mobile network) move across the Internet. Many schemes providing route optimization function for mobile networks have already been proposed in recent years. A scheme using Hierarchical Mobile IPv6 (traditional scheme) is one of them. The traditional scheme, however, suffers from a significant number of simultaneous signaling messages as the number of Mobile Network Nodes (MNNs) and/or the number of their Correspondent Nodes (CNs) increase. This paper proposes a scheme to overcome this problem. The simulation results show that our scheme reduces the mean handover delay of MNNs compared to the traditional scheme.