A communication system comprising a communication terminal (MN1; MN2) and a router (AR1; AR2), wherein the communication terminal (MN1; MN2) comprises: a receiver configured to receive a first router advertisement received through an access point of a destination for handover and a second router advertisement received through an access point under current wireless communication; a judgment unit configured to generate an activation message upon receiving a router advertisement; and a notification unit configured to transmit the activation message generated by the judgement unit to the router (AR1; AR2) connected to the access point of a destination for handover when the first router advertisement is received through the access point of the destination for handover; the router (AR1; AR2) comprises: a routing information updating unit configured to assign a routing host address to the communication terminal (MN1; MN2) by establishing correspondence between a unique host address which is unique to the communication terminal (MN1; MN2) and a routing host address used in the router (AR1; AR2), and when the activation message is received from the communication terminal (MN1; MN2), to update a routing information which establishes correspondence between the unique host address and an output port for output of a packet addressed to the communication terminal (MN1; MN2), and to update the correspondence between the unique host address and the routing host address; characterized in that the judgement unit is further configured to judge, based on the router advertisements, whether the first router advertisement and the second router advertisement are transmitted from a same router (AR1; AR2); and when it is judged that the first router advertisement and the second router advertisement are transmitted from the same access router, to generate a link moving notification, which indicates that handover is executed between the access points connected to the same router (AR1; AR2) the notification unit is further configured to, transmit the link moving notification to the router (AR1; AR2); and and wherein when the link moving notification is received, the routing information updating unit is adapted to update only the routing information while maintaining the routing host address to the communication terminal (MN1; MN2) and the correspondence between the unique host address and the routing host address unchanged. a receiver configured to receive a first router advertisement received through an access point of a destination for handover and a second router advertisement received through an access point under current wireless communication; a judgment unit configured to generate an activation message upon receiving a router advertisement; and a notification unit configured to transmit the activation message generated by the judgement unit to the router (AR1; AR2) connected to the access point of a destination for handover when the first router advertisement is received through the access point of the destination for handover; a routing information updating unit configured to assign a routing host address to the communication terminal (MN1; MN2) by establishing correspondence between a unique host address which is unique to the communication terminal (MN1; MN2) and a routing host address used in the router (AR1; AR2), and when the activation message is received from the communication terminal (MN1; MN2), to update a routing information which establishes correspondence between the unique host address and an output port for output of a packet addressed to the communication terminal (MN1; MN2), and to update the correspondence between the unique host address and the routing host address; the judgement unit is further configured to judge, based on the router advertisements, whether the first router advertisement and the second router advertisement are transmitted from a same router (AR1; AR2); and when it is judged that the first router advertisement and the second router advertisement are transmitted from the same access router, to generate a link moving notification, which indicates that handover is executed between the access points connected to the same router (AR1; AR2) the notification unit is further configured to, transmit the link moving notification to the router (AR1; AR2); and and wherein when the link moving notification is received, the routing information updating unit is adapted to update only the routing information while maintaining the routing host address to the communication terminal (MN1; MN2) and the correspondence between the unique host address and the routing host address unchanged.