Assume that a TCP connection works properly, and the peer AS number configured for a BGP router is different from the AS number of its BGP peer. During the
establishment of a BGP session, the BGP router exchanges routing information with its peer, and finds that its peer AS number is different from the AS number of
the peer. Therefore, the BGP router sends a Notification message to the peer, indicating that the establishment of a BGP session fails. Which message can be
identified by the Error Code field in the Notification message?