A method, a device, and a system for implementing a multiplexer (mux) machine, where the method includes setting a mux machine on a first aggregation port to be in a PROTECT_WAITING state, when the mux machine is in the PROTECT_WAITING state, determining that the first aggregation port is not in a collecting and distributing state, and sending, to a second network device, a first Link Aggregation Control Protocol Data Unit (LACPDU) packet that is used to notify that the first aggregation port is in the collecting and distributing state, and when a second LACPDU packet that is from the second network device and indicating that a second aggregation port is in the collecting and distributing state is received, switching a status of the mux machine from the PROTECT_WAITING state to a COLLECTING_DISTRIBUTING state, and setting the first aggregation port to be in the collecting and distributing state.