A method and an apparatus for topology discovery are disclosed. Link state information of each port of each device on a ring network is confirmed through neighbor negotiation between a first device and a neighbor device, and by broadcasting a link state information base of each device to other devices on the ring network, each device on the ring network can obtain the newest and synchronous link state information of each port on the ring network, so that each network device on the ring network implements topology discovery of the ring network where the network device is located.