A method of transmitting a packet, comprising: receiving , by a controller , a packet from a virtual switch ; obtaining , by the controller , a forwarding priority corresponding to the packet, wherein the forwarding priority is determined based on a tenant type and a service type associated with the packet; generating , by the controller , a flow entry corresponding to the packet, wherein the flow entry is used to perform encapsulation of a specified type on a packet matching the flow entry and add the forwarding priority into a DSCP field of an out-layer IP header of the encapsulated packet, wherein the encapsulation of the specified type comprises VXLAN encapsulation; distributing , by the controller , the flow entry to the virtual switch , the flow entry being used by the virtual switch to send the packet; and distributing, by the controller, a configuration command to an edge network device connected, through a port, with a physical server containing the virtual switch, the configuration command is to instruct the edge network device to trust the DSCP field of the outer-layer of the encapsulated packet received via the port; wherein, obtaining the forwarding priority corresponding to the packet comprises: sending , by the controller , a query request message to a cloud management platform , wherein the query request message carries information in the packet; and receiving , by the controller , a query response message from the cloud management platform , wherein the query response message carries the forwarding priority corresponding to the information. receiving , by a controller , a packet from a virtual switch ; obtaining , by the controller , a forwarding priority corresponding to the packet, wherein the forwarding priority is determined based on a tenant type and a service type associated with the packet; generating , by the controller , a flow entry corresponding to the packet, wherein the flow entry is used to perform encapsulation of a specified type on a packet matching the flow entry and add the forwarding priority into a DSCP field of an out-layer IP header of the encapsulated packet, wherein the encapsulation of the specified type comprises VXLAN encapsulation; distributing , by the controller , the flow entry to the virtual switch , the flow entry being used by the virtual switch to send the packet; and distributing, by the controller, a configuration command to an edge network device connected, through a port, with a physical server containing the virtual switch, the configuration command is to instruct the edge network device to trust the DSCP field of the outer-layer of the encapsulated packet received via the port; wherein, obtaining the forwarding priority corresponding to the packet comprises: sending , by the controller , a query request message to a cloud management platform , wherein the query request message carries information in the packet; and receiving , by the controller , a query response message from the cloud management platform , wherein the query response message carries the forwarding priority corresponding to the information. sending , by the controller , a query request message to a cloud management platform , wherein the query request message carries information in the packet; and receiving , by the controller , a query response message from the cloud management platform , wherein the query response message carries the forwarding priority corresponding to the information. <EOS>