A communication system, comprising: a control device configured to control the communication system; a plurality of first forwarding nodes for which is set a processing rule(s) for forwarding a received packet in accordance with a route set in advance, with a processing rule being selected based on a path identifier, corresponding to the route, included in said received packet, to perform packet forwarding; and a second forwarding node positioned at a start point of said route configured to: perform packet processing according to said processing rule(s); and send a new flow detection notification to said control device; a third forwarding node positioned at an end point of said route configured to perform packet processing according to said processing rule(s), wherein said control device is configured to: set said processing rule in said first forwarding node(s) in said route in advance; cause said second forwarding node to add a path identifier in accordance with said route to a received packet, when a new flow detection notification is received at the control device from said second forwarding node, said new flow detection being sent when said processing rule(s) corresponding to said received packet is not set; and cause a third forwarding node to delete said path identifier from a received packet, at an occasion when the new flow detection notification is received at the control node from said second forwarding node. a control device configured to control the communication system; a plurality of first forwarding nodes for which is set a processing rule(s) for forwarding a received packet in accordance with a route set in advance, with a processing rule being selected based on a path identifier, corresponding to the route, included in said received packet, to perform packet forwarding; and a second forwarding node positioned at a start point of said route configured to: perform packet processing according to said processing rule(s); and send a new flow detection notification to said control device; a third forwarding node positioned at an end point of said route configured to perform packet processing according to said processing rule(s), wherein said control device is configured to: set said processing rule in said first forwarding node(s) in said route in advance; cause said second forwarding node to add a path identifier in accordance with said route to a received packet, when a new flow detection notification is received at the control device from said second forwarding node, said new flow detection being sent when said processing rule(s) corresponding to said received packet is not set; and cause a third forwarding node to delete said path identifier from a received packet, at an occasion when the new flow detection notification is received at the control node from said second forwarding node. perform packet processing according to said processing rule(s); and send a new flow detection notification to said control device; a third forwarding node positioned at an end point of said route configured to perform packet processing according to said processing rule(s), wherein said control device is configured to: set said processing rule in said first forwarding node(s) in said route in advance; cause said second forwarding node to add a path identifier in accordance with said route to a received packet, when a new flow detection notification is received at the control device from said second forwarding node, said new flow detection being sent when said processing rule(s) corresponding to said received packet is not set; and cause a third forwarding node to delete said path identifier from a received packet, at an occasion when the new flow detection notification is received at the control node from said second forwarding node. set said processing rule in said first forwarding node(s) in said route in advance; cause said second forwarding node to add a path identifier in accordance with said route to a received packet, when a new flow detection notification is received at the control device from said second forwarding node, said new flow detection being sent when said processing rule(s) corresponding to said received packet is not set; and cause a third forwarding node to delete said path identifier from a received packet, at an occasion when the new flow detection notification is received at the control node from said second forwarding node.