1. A communication system, comprising: a node(s) that processes a packet received in accordance with a processing rule that stipulates a matching rule and processing for a packet matching to the matching rule; and a controller; the controller including: a removal request history management unit that retains record(s) of past request(s) to the node(s) to remove a processing rule; a processing rule search unit that, in setting a new processing rule for the node(s), references the removal request history management unit to search a processing rule having a matching rule competing with the new processing rule; and a processing rule setting unit that, in case a processing rule having the matching rule competing with the new processing rule exists, re-requests the node(s) to remove the processing rule having the matching rule competing with the new processing rule.