The establishment of an SSH connection includes multiple mandatory phases that ensure both secure communication and authenticated access. First, the SSH client and server perform version negotiation to determine a mutually supported SSH protocol version. Then they carry out algorithm negotiation, during which they agree on the encryption algorithm, key exchange algorithm, integrity algorithm, and other security parameters to be used for the session.
After that, the peers perform key exchange, which is used to derive shared session keys securely over an insecure network. This stage is essential because it enables subsequent communication to be encrypted and protected against interception. Finally, once the secure channel has been established, user authentication is performed so that the server can verify the identity of the client user. This can be done using a password, public key, or other supported authentication method.
Therefore, all four options are required phases in the SSH connection establishment process.
HCIA-Datacom emphasizes these steps because SSH is a core secure management protocol used to replace insecure protocols such as Telnet and FTP in modern network operation and maintenance.