A system for identifying a test packet during evaluation of transmission performance related to a network node, wherein the system comprises the network node and a control node coupled to the network node, and the network node belongs to a path; and the network node is configured to obtain a test packet, wherein the test packet comprises a 5-tuple corresponding to the path, and process the test packet by using a virtual switch, to generate a mirrored packet corresponding to the test packet, wherein the mirrored packet carries a generation timestamp and generation location information, the generation timestamp is used to indicate a timestamp of a time for generating the mirrored packet, and the generation location information is used to indicate a location at which the mirrored packet is generated; and the control node is configured to receive the mirrored packet from the network node, to evaluate, based on the mirrored packet, transmission performance of at least a part of link that is related to the network node and that is in the path, wherein the test packet comprises a first identifier field having a first value and a second identifier field having a second value, the first value and the second value jointly indicate that a packet is a test packet, and a bit length of the second identifier field is greater than a bit length of the first identifier field; and wherein the network node is specifically configured to: determine at least one pre-matched packet from a plurality of received packets based on the first identifier field having the first value; and determine the test packet from the at least one pre-matched packet based on the second identifier field having the second value. the network node is configured to obtain a test packet, wherein the test packet comprises a 5-tuple corresponding to the path, and process the test packet by using a virtual switch, to generate a mirrored packet corresponding to the test packet, wherein the mirrored packet carries a generation timestamp and generation location information, the generation timestamp is used to indicate a timestamp of a time for generating the mirrored packet, and the generation location information is used to indicate a location at which the mirrored packet is generated; and the control node is configured to receive the mirrored packet from the network node, to evaluate, based on the mirrored packet, transmission performance of at least a part of link that is related to the network node and that is in the path, wherein the test packet comprises a first identifier field having a first value and a second identifier field having a second value, the first value and the second value jointly indicate that a packet is a test packet, and a bit length of the second identifier field is greater than a bit length of the first identifier field; and wherein the network node is specifically configured to: determine at least one pre-matched packet from a plurality of received packets based on the first identifier field having the first value; and determine the test packet from the at least one pre-matched packet based on the second identifier field having the second value. determine at least one pre-matched packet from a plurality of received packets based on the first identifier field having the first value; and determine the test packet from the at least one pre-matched packet based on the second identifier field having the second value.