A mobile network is disclosed in which there exists a Mobile Node (MN), the MN is managed by a first Access Router (AR), and there exists a second AR with a subnet different from the first AR. A method is provided for the MN performing a fast handoff from the first AR to the second AR, which includes receiving a Routing Advertisement (RA) message of the second AR from the first AR, generating an IP address to be used in the second AR using the RA message of the second AR if the MN recognizes that it should perform a handoff from the first AR to the second AR, performing a trigger for using the generated IP address if the movement to the second AR is completed, and transmitting/receiving a Correspondent Node (CN) and data using the IP address.