Three-way handshake is implemented on P2P interfaces of IS-IS devices. Why is the local switch Up and the peer switch down

Q: Three-way handshake is implemented on P2P interfaces of IS-IS switches. Why is the local switch Up and the peer switch down?
A: To be compatible with the peer switch supporting only two-way handshake rather than three-way handshake, the local switch also works in two-way handshake mode. As a result, there is a possibility that the local switch is Up and the remote switch is Down.

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