A method for probing a packet forwarding path, comprising: determining, by a controller, a source device and a destination device, wherein there is at least one intermediate device between the source device and the destination device, the source device belongs to a first network segment, and the destination device belongs to a second network segment; sending, by the controller, an Internet Protocol, IP, packet that comprises a probe identifier to the source device so that the source device sends the IP packet to the destination device, wherein the probe identifier is located in an acknowledgment, ACK, number field of a TCP header of the IP packet; receiving, by the controller, a first message sent by the destination device and a second message sent by the intermediate device, wherein the first message comprises the IP packet that is captured by the destination device according to the probe identifier, and a first inbound interface identifier of the IP packet, the first inbound interface identifier is used to indicate an interface used by the destination device to receive the IP packet, the second message comprises the IP packet that is captured by the intermediate device according to the probe identifier, and a second inbound interface identifier of the IP packet, and the second inbound interface identifier is used to indicate an interface used by the intermediate device to receive the IP packet; and determining, by the controller, a forwarding path of the IP packet according to the IP packet and the first inbound interface identifier that are sent by the destination device, the IP packet and the second inbound interface identifier that are sent by the intermediate device, and a network topology. determining, by a controller, a source device and a destination device, wherein there is at least one intermediate device between the source device and the destination device, the source device belongs to a first network segment, and the destination device belongs to a second network segment; sending, by the controller, an Internet Protocol, IP, packet that comprises a probe identifier to the source device so that the source device sends the IP packet to the destination device, wherein the probe identifier is located in an acknowledgment, ACK, number field of a TCP header of the IP packet; receiving, by the controller, a first message sent by the destination device and a second message sent by the intermediate device, wherein the first message comprises the IP packet that is captured by the destination device according to the probe identifier, and a first inbound interface identifier of the IP packet, the first inbound interface identifier is used to indicate an interface used by the destination device to receive the IP packet, the second message comprises the IP packet that is captured by the intermediate device according to the probe identifier, and a second inbound interface identifier of the IP packet, and the second inbound interface identifier is used to indicate an interface used by the intermediate device to receive the IP packet; and determining, by the controller, a forwarding path of the IP packet according to the IP packet and the first inbound interface identifier that are sent by the destination device, the IP packet and the second inbound interface identifier that are sent by the intermediate device, and a network topology.