3. A controller, that is connected to a node(s) configured for processing a packet received in accordance with a processing rule that stipulates a matching rule and processing for a packet matching to the matching rule, the controller comprising: a removal request history management unit that retains record(s) of past request(s) to the node(s) to remove the 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 that competes with the new processing rule; a processing rule setting unit that, in case a processing rule having a matching rule competing with the new processing rule exists in the removal request history management unit, re-requests the node(s) to remove the processing rule having the matching rule competing with the new processing rule; and a processing rule removal re-request policy management unit that removes the record(s) from the removal request history management unit based on a pre-set policy, wherein, when a number of times of re-requests for removal of the processing rule competing with the new processing rule as formed by the processing rule setting unit has reached a pre-set threshold value, the processing rule removal re-request policy management unit removes the record(s) from the removal request history management unit.
3. A controller, that is connected to a node(s) configured for processing a packet received in accordance with a processing rule that stipulates a matching rule and processing for a packet matching to the matching rule, the controller comprising: a removal request history management unit that retains record(s) of past request(s) to the node(s) to remove the 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 that competes with the new processing rule; a processing rule setting unit that, in case a processing rule having a matching rule competing with the new processing rule exists in the removal request history management unit, re-requests the node(s) to remove the processing rule having the matching rule competing with the new processing rule; and a processing rule removal re-request policy management unit that removes the record(s) from the removal request history management unit based on a pre-set policy, wherein, when a number of times of re-requests for removal of the processing rule competing with the new processing rule as formed by the processing rule setting unit has reached a pre-set threshold value, the processing rule removal re-request policy management unit removes the record(s) from the removal request history management unit. 4. The controller according to claim 3 , wherein, a threshold value, as set from one node to another, is used as the pre-set threshold value.