A method of transmitting a packet, comprising: receiving, by a controller, a packet from a virtual switch (11, 22, 33); 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 (11, 22, 33), the flow entry being used by the virtual switch (11, 22, 33) 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 (11, 22, 33); 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 (11, 22, 33), the flow entry being used by the virtual switch (11, 22, 33) 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.