Mobile IP and SIP give solutions to wireless applications to maintain the connectivity while handover is occurred. However, many existing services need further modification in order to perform advanced mobile behaviours. This study presents a software agent, which performs the undercover maintenance of connectivity at the application layer for handling the mobility in all-IP networks. It gives an end-to-end handover solution via proxy-based component using API hooking technology. There is no equipment added, no change of protocol stack and no modification on existing services. While a peer node performs handover, services will not be aware of packets re-directing to the new destination address. An experimental testbed is presented for performance measurement.