A method for constructing a multipath forwarding rule, comprising: invoking, by a controller, a multipath algorithm to generate multiple paths for a data stream; and whereby the method comprises the steps of: generating, by the controller, a multiport rule of each forwarding device according to the multiple paths, wherein the multiport rule of each forwarding device indicates that the forwarding device corresponds to at least one forwarding port of the multiple paths; generating, by the controller, metadata according to the multiport rule of each forwarding device, wherein the metadata comprises information for indicating the at least one forwarding port of the forwarding device; generating, by the controller, a flow entry establishment indication, wherein the flow entry establishment indication comprises a write-metadata indication, an indication of going to a multipath table, and the metadata that corresponds to the write-metadata indication; and sending, by the controller, the flow entry establishment indication to each forwarding device, so that each forwarding device selects the at least one forwarding port of the forwarding device according to the metadata and according to the flow entry establishment indication, to forward the data stream. invoking, by a controller, a multipath algorithm to generate multiple paths for a data stream; and whereby the method comprises the steps of: generating, by the controller, a multiport rule of each forwarding device according to the multiple paths, wherein the multiport rule of each forwarding device indicates that the forwarding device corresponds to at least one forwarding port of the multiple paths; generating, by the controller, metadata according to the multiport rule of each forwarding device, wherein the metadata comprises information for indicating the at least one forwarding port of the forwarding device; generating, by the controller, a flow entry establishment indication, wherein the flow entry establishment indication comprises a write-metadata indication, an indication of going to a multipath table, and the metadata that corresponds to the write-metadata indication; and sending, by the controller, the flow entry establishment indication to each forwarding device, so that each forwarding device selects the at least one forwarding port of the forwarding device according to the metadata and according to the flow entry establishment indication, to forward the data stream. generating, by the controller, a multiport rule of each forwarding device according to the multiple paths, wherein the multiport rule of each forwarding device indicates that the forwarding device corresponds to at least one forwarding port of the multiple paths; generating, by the controller, metadata according to the multiport rule of each forwarding device, wherein the metadata comprises information for indicating the at least one forwarding port of the forwarding device; generating, by the controller, a flow entry establishment indication, wherein the flow entry establishment indication comprises a write-metadata indication, an indication of going to a multipath table, and the metadata that corresponds to the write-metadata indication; and sending, by the controller, the flow entry establishment indication to each forwarding device, so that each forwarding device selects the at least one forwarding port of the forwarding device according to the metadata and according to the flow entry establishment indication, to forward the data stream.