A network system includes one controller and a plurality of forwarding devices, where the forwarding devices form a plurality of virtual network topologies; the controller is configured to allocate a global label to each of the plurality of virtual network topologies, and send a binding relationship between the global labels and the virtual network topologies to the forwarding devices, where global labels allocated to different virtual network topologies are different; the forwarding devices are configured to receiving the binding relationship, and generate label forwarding entries including a mapping relationship between the global labels and forwarding information bases; and when a packet received by the forwarding device carries a global label, the forwarding device searches according to the global label, a forwarding information base of a virtual network topology corresponding to the global label, and determines that the packet is to be forwarded by using the forwarding information base.