The controller sets control information in a switch over a control channel to control the switch. The switch includes a packet processing unit that processes a packet received based on control information as set from the controller, and a Layer-2 forwarding unit that learns an input port of a control packet between the controller and a neighboring switch or switches and that forwards the control packet on the basis of learned results. The switch also includes an alternative control channel construction unit that, on detecting a disconnection of the control channel, sends a packet requesting a resolution of a Layer-2 address of the controller to the neighboring switch or switches. The alternative control channel construction unit acquires the Layer-2 address from the controller via the neighboring switch or switches and transmits the control packet to the controller using the Layer-2 address acquired to construct a second control channel between the switch and the controller.