A method for acquiring, by a software defined network, SDN, switch, an exact flow entry, applied to a second SDN switch, wherein the second SDN switch is connected to a first SDN switch and an SDN controller, to form an SDN network, the SDN controller communicates with each SDN switch in an inband communication manner, and the method comprises: receiving a first control message sent by the first SDN switch and used for collecting path information, wherein the first control message carries path information of the first SDN switch, and the first control message is carried in a packet corresponding to a protocol used by a reliable connection established between the first SDN switch and the SDN controller, adding path information of the second SDN switch to the first control message, to obtain an updated first control message; and forwarding, to the SDN controller, the updated first control message to which the path information of the second SDN switch is added, so that after receiving a finally updated first control message comprising the updated first control message, the SDN controller determines a routing path between the SDN controller and the first SDN switch according to path information added by each SDN switch to the finally updated first control message, and delivers an exact flow entry to the first SDN switch according to the routing path; wherein the SDN network is implemented based on the OpenFlow protocol, and characterized in that the first control message comprises an OFPT_HELLO control message in the OpenFlow protocol that is sent by the first SDN switch to the SDN controller; wherein a body field of the OFPT_HELLO message is used for carrying the path information after being extended; wherein the step of adding path information of the second SDN switch to the first control message, to obtain an updated first control message comprises: adding the path information of the second SDN switch to the extended body field, used for carrying the path information, in the OFPT_HELLO message, to obtain an updated OFPT_HELLO message; and wherein the step of forwarding, to the SDN controller, the updated first control message to which the path information of the second SDN switch is added, so that after receiving a finally updated first control message comprising the updated first control message, the SDN controller determines a routing path between the SDN controller and the first SDN switch according to path information added by each SDN switch to the finally updated first control message, and delivers an exact flow entry to the first SDN switch according to the routing path comprises: forwarding, to the SDN controller, the updated OFPT_HELLO message to which the path information of the second SDN switch is added. receiving a first control message sent by the first SDN switch and used for collecting path information, wherein the first control message carries path information of the first SDN switch, and the first control message is carried in a packet corresponding to a protocol used by a reliable connection established between the first SDN switch and the SDN controller, adding path information of the second SDN switch to the first control message, to obtain an updated first control message; and forwarding, to the SDN controller, the updated first control message to which the path information of the second SDN switch is added, so that after receiving a finally updated first control message comprising the updated first control message, the SDN controller determines a routing path between the SDN controller and the first SDN switch according to path information added by each SDN switch to the finally updated first control message, and delivers an exact flow entry to the first SDN switch according to the routing path; wherein the SDN network is implemented based on the OpenFlow protocol, and characterized in that the first control message comprises an OFPT_HELLO control message in the OpenFlow protocol that is sent by the first SDN switch to the SDN controller; wherein a body field of the OFPT_HELLO message is used for carrying the path information after being extended; wherein the step of adding path information of the second SDN switch to the first control message, to obtain an updated first control message comprises: adding the path information of the second SDN switch to the extended body field, used for carrying the path information, in the OFPT_HELLO message, to obtain an updated OFPT_HELLO message; and wherein the step of forwarding, to the SDN controller, the updated first control message to which the path information of the second SDN switch is added, so that after receiving a finally updated first control message comprising the updated first control message, the SDN controller determines a routing path between the SDN controller and the first SDN switch according to path information added by each SDN switch to the finally updated first control message, and delivers an exact flow entry to the first SDN switch according to the routing path comprises: forwarding, to the SDN controller, the updated OFPT_HELLO message to which the path information of the second SDN switch is added.