A communication system includes a communication control apparatus, and one or more communication processing apparatuses, which reside on a network. The communication control apparatus includes a memory configured to store instructions which, when executed by one or more processors, causes the one or more processors to: in response to detection of unauthorized communication in the network, instruct a particular communication processing apparatus corresponding to an IP address of a source terminal of the unauthorized communication to transmit a packet-in message; determine whether the packet-in message transmitted from the particular communication processing apparatus is the unauthorized communication; when the packet-in message is the unauthorized communication, generate a first communication control rule that causes the particular communication processing apparatus to execute processing of blocking communication with an IP address of a terminal provided for the particular communication processing apparatus; and transmit the first communication control rule to the particular communication processing apparatus.