The network mobility basic support protocol is an extension of mobile IP that enables an entire network to change its attachment point to the Internet. However, it incurs high overhead on the network if a mobile router moves frequently. In this paper, therefore, we propose a paging extensions for network mobility in nested mobile networks. To minimize signaling overhead, in our proposal, an idle mobile router does not register when moving within a paging area in the nested mobile networks. The cost analysis presented in this paper shows that our proposal offers considerable performance advantages to existing network mobility scheme.