NEtwork MObility (NEMO) handles mobility of multiple nodes in an aggregate manner as a mobile network. The standard NEMO suffers from a number of limitations, such as inefficient routing and increased handoff latency. Most previous studies attempting to solve such problems have imposed an extra signaling load and/or modified the functionalities of the main entities. In this paper, the authors propose a more secure and lightweight Route Optimization (RO) mechanism based on exploiting the firewall in performing the RO services on behalf of the Correspondent Nodes (CNs). The proposed mechanism provides secure communications by making an authorized decision about the Mobile Router (MR) home of address, MR care of address, and the complete mobile network prefixes underneath the MR.