A communication control apparatus (1) is connected to a router (6) and a terminal device (4), and upon receiving prefix information transmitted from the router (6) by a router advertisement, stores the prefix information. In a case where prefix information of a transmission source address or a destination address, which is included in the received communication packet, is different from the stored prefix information, the communication control apparatus (1) blocks the communication packet, and in a case where the prefix information of the transmission source address or the destination address, which is included in the received communication packet, is the stored prefix information, the communication control apparatus (1) allows passing of the communication packet. In such a way, an unauthorized communication packet can be blocked appropriately under an IPv6 network environment.