A fiber link detection method is implemented by a first network device of an optical communications network. The fiber link detection method includes obtaining a forward delay value indicating a forward delay of transmitting a first Precision Time Protocol (PTP) packet by a second interface of a second network device to a first interface of the first network device over a fiber link. A reverse delay value indicating a reverse delay of transmitting a second PTP packet by the first interface to the second interface over the fiber link is obtained, and a determination is made, based on the forward delay value, the reverse delay value, and a first threshold, that the fiber link comprises a third network device, where the first network device and the second network device support a PTP, and where the third network device does not support the PTP.