1. Both ends are set to self-negotiation mode
Both sides send/C/code stream to each other. If three identical/C/codes are received in succession and the received code stream matches the local working mode, they return to the other side a/C/code with Ack response. After receiving Ack information from the other side, they think that they can communicate with each other and set the port to UP state.
2. One end is set to self-negotiation and the other end is set to compulsion.
Since the negotiation end sends / C / stream and the compulsory end sends / I / stream, the compulsory end can not provide the negotiation information to the other end, nor can it return Ack response to the other end, so the DOWN of the negotiation end is self-negotiating. But the mandatory end itself can recognize / C / code, and think that the opposite end is the port that matches itself, so set the local port to UP state directly.
3. Both ends are set to compulsory mode
Both sides send/I/bit stream to each other. When one end receives/I/bit stream, it considers that the other end is the port matching itself, and sets the port of this end to UP state directly.