A communications system, comprising a forwarding plane apparatus and a gateway control plane apparatus that are located in a core network having an OpenFlow architecture, wherein: the gateway control plane apparatus is an OpenFlow controller in the OpenFlow architecture, the communications system is configured so that the gateway control plane apparatus receives a data packet sent by the forwarding plane apparatus and parses out a destination IP address of the data packet; and the forwarding plane apparatus is an OpenFlow switch in the OpenFlow architecture, the communications system is configured so that the forwarding plane apparatus receives a processing rule from the gateway control plane apparatus and processes the data packet according to the processing rule, characterized in that: the gateway control plane apparatus is further configured to: obtain a route selection policy form another apparatus according to the destination IP address or preconfigured in the gateway control plane apparatus, determine an external gateway which is located in an external network connected to the core network and to which the data packet needs to be sent, according to the route selection policy and the destination IP address, and request from the forwarding plane apparatus a MAC address of the external gateway, the request comprising an indication of the external gateway, and receive in response to the request the MAC address of the external gateway, wherein the processing rule comprises the MAC address and is an instruction to the forwarding plane apparatus to send the data packet to the external gateway. the gateway control plane apparatus is an OpenFlow controller in the OpenFlow architecture, the communications system is configured so that the gateway control plane apparatus receives a data packet sent by the forwarding plane apparatus and parses out a destination IP address of the data packet; and the forwarding plane apparatus is an OpenFlow switch in the OpenFlow architecture, the communications system is configured so that the forwarding plane apparatus receives a processing rule from the gateway control plane apparatus and processes the data packet according to the processing rule, characterized in that: the gateway control plane apparatus is further configured to: obtain a route selection policy form another apparatus according to the destination IP address or preconfigured in the gateway control plane apparatus, determine an external gateway which is located in an external network connected to the core network and to which the data packet needs to be sent, according to the route selection policy and the destination IP address, and request from the forwarding plane apparatus a MAC address of the external gateway, the request comprising an indication of the external gateway, and receive in response to the request the MAC address of the external gateway, wherein the processing rule comprises the MAC address and is an instruction to the forwarding plane apparatus to send the data packet to the external gateway. obtain a route selection policy form another apparatus according to the destination IP address or preconfigured in the gateway control plane apparatus, determine an external gateway which is located in an external network connected to the core network and to which the data packet needs to be sent, according to the route selection policy and the destination IP address, and request from the forwarding plane apparatus a MAC address of the external gateway, the request comprising an indication of the external gateway, and receive in response to the request the MAC address of the external gateway, wherein the processing rule comprises the MAC address and is an instruction to the forwarding plane apparatus to send the data packet to the external gateway.