This application relates to message sending and receiving methods and apparatuses, and a communication system. A control plane CP device in a communication system in which a CP and a user plane UP are separated generates a first message, where the first message includes route information and a control indication for the route information, and the route information is associated with a UP device. The CP device sends the first message to the UP device, so that the UP device updates the route information based on the control indication, where the first message is a packet forwarding control protocol PFCP message. Based on the technical solutions provided herein, interaction on routing control between the CP device and the UP device in a communication system architecture in which a CP and a UP are separated may be implemented.