Ssh exchange identification: Connection closed by remote host

문제 상황

아래와 같은 메시지가 나오면서 SSH 접속이 되지 않는다.

Looking up host 'example.com'...
Host 'example.com' resolved to 111.222.33.44.
Connecting to 111.222.33.44:22...
Connection established.
Escape character is '^@]'.

Connection closed by foreign host.

다른 서버에서 접속한 후 거기서 시도해 봐도 되지 않는다.

[root@localhost ~]# ssh example.com
ssh_exchange_identification: Connection closed by remote host