A controller, wherein the controller is configured to manage a first autonomous system AS, and the controller comprises: a communications unit, configured to receive a first Border Gateway Protocol, BGP, routing message from a node of the first AS; and a processing unit, configured to determine a destination node according to the first BGP routing message, wherein the destination node belongs to the first AS, wherein the processing unit is further configured to determine, according to the node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control; if determining to perform incoming-traffic adjustment and control, the processing unit is further configured to allocate a source node from a second AS, wherein the second AS is at least one AS that is directly connected to the first AS; the processing unit is further configured to obtain a preferred path between the source node and the destination node by using a network topology, wherein the network topology comprises an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS; the processing unit is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, wherein the first BR belongs to the first AS and belongs to the inter-domain topology, and the second BR belongs to the second AS and belongs to the inter-domain topology; and the communications unit is further configured to send a routing control message to a specified BR, wherein the specified BR belongs to the first AS, and wherein the routing control message comprises a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, the routing control message is used to instruct the specified BR to advertise a second BGP routing message to the second AS according to the neighbor pair, or wherein the routing control message comprises at least one neighbor pair that does not comprise a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, the routing control message is used to instruct the specified BR to advertise a second BGP routing message to the second AS according to the at least one neighbor pair. a communications unit, configured to receive a first Border Gateway Protocol, BGP, routing message from a node of the first AS; and a processing unit, configured to determine a destination node according to the first BGP routing message, wherein the destination node belongs to the first AS, wherein the processing unit is further configured to determine, according to the node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control; if determining to perform incoming-traffic adjustment and control, the processing unit is further configured to allocate a source node from a second AS, wherein the second AS is at least one AS that is directly connected to the first AS; the processing unit is further configured to obtain a preferred path between the source node and the destination node by using a network topology, wherein the network topology comprises an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS; the processing unit is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, wherein the first BR belongs to the first AS and belongs to the inter-domain topology, and the second BR belongs to the second AS and belongs to the inter-domain topology; and the communications unit is further configured to send a routing control message to a specified BR, wherein the specified BR belongs to the first AS, and wherein the routing control message comprises a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, the routing control message is used to instruct the specified BR to advertise a second BGP routing message to the second AS according to the neighbor pair, or wherein the routing control message comprises at least one neighbor pair that does not comprise a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, the routing control message is used to instruct the specified BR to advertise a second BGP routing message to the second AS according to the at least one neighbor pair.