Example communications systems, methods and network devices are described. One example method includes sending a first message by a first access network device to a core network device to enable the core network device to send a second message to a second access network device, where the first message includes an identity of the second network device. The first message is used to request for X2 transport network layer (TNL) configuration information of a third network device, and the third network device is a network device that has established an X2 connection to the second network device. The first network device receives the X2 TNL configuration information of the third access network device from the second access network device. Therefore, a network device connected to a control plane of a core network can obtain TNL addresses of more network devices that are not connected to the control plane of the core network.