Network mobility has attracted large attention to provide vehicles such as trains with Internet connectivity. NEMO Basic Support Protocol (NEMO-BS) supports network mobility. However, through our experiment using a train in service, NEMO-BS shows that the handover latency becomes very large if the signaling messages are lost due to instability of the wireless link during handover. This paper proposes PNEMO, a network-based localized mobility management protocol for mobile networks. In PNEMO, mobility management is basically handled in the wired network so that the signaling messages are not transmitted on the wireless link when handover occurs. This makes handover stable even if the wireless link is unstable during handover. PNEMO is implemented in Linux. The measured performance shows that the handover latency is almost constant even if the wireless link is unstable when handover occurs, and that the overhead of PNEMO is negligible in comparison with NEMO-BS.