MESSAGE TRANSMISSION METHOD, APPARATUS, AND SYSTEM

Embodiments of this application provide a packet transmission method, apparatus, and system, and relate to the computer field, to increase a probability that a transmitting end device of a probe packet receives a response packet of the probe packet, and improve tunnel detection accuracy when the probe packet is used to detect a tunnel status. A specific solution is as follows: A first network device sends a probe packet to a second network device, where the probe packet includes an identifier of the first network device, and the identifier of the first network device is used to indicate the second network device to add the identifier of the first network device to a destination address in a response packet of the probe packet; and receives the response packet from the second network device, where the destination address in the response packet is the identifier of the first network device; or receives an updated response packet from a third network device, where a destination address in the updated response packet is the identifier of the first network device, and both the third network device and the first network device are connected to a same user-side network device.