A method for automatic topology discovery implemented in a wavelength division multiplexing (WDM) network is disclosed. The WDM network contains a number of wavelength switching devices, and the method starts with selecting an unassigned wavelength between a pair of wavelength switching devices. For a first port of a first wavelength switching device, a pass through state is configured between the first port and a coupling port of the first wavelength switching device, and a first probing signal is sent at the unassigned wavelength to the first wavelength switching device. The method continues with detecting iteratively the first probing signal at the unassigned wavelength through each of a set of ports of a second wavelength switching device during a time period, and recording a connection between the first port of the first wavelength switching device and a port of the second wavelength switching devices when the first probing signal is detected.