Abstract: A method of controlling an SDN system, an SDN sub-controller, and an SDN system is provided. The SDN controller sends a keepalive notification to the SDN switch and the SDN sub-controller. The SDN switch sends a switching request to the SDN sub-controller on condition that the keepalive notification cannot be received during a predetermined specific period. The SDN sub-controller starts to control a communication setting of the SDN switch on condition that the keepalive notification cannot be received during the specific period and that the switching request has been received.

Abstract: A communication control system includes a memory and a processor coupled to the memory. The processor is configured to according to an instruction from an external device, perform processing related to changing a network setting on a communication device, after the processing has been executed, determine whether or not communication of the communication device matches a specific communication condition, and notify an error to the external device in a case in which determination has been made that the communication of the communication device does not match the specific communication condition.

Abstract: A communication control device includes a memory and a processor connected to the memory. The processor is configured to perform processing related to changing a network setting, on a communication device that is connected to the network and that is a setting change target, and perform processing to return the network setting to a prior state, on the communication device that is the setting change target, in a case in which a communication abnormality notification is received from a communication device that is connected to the network and that is not a setting change target.