The correct answer is 'SSH on port 22' because SSH provides a secure channel over an unsecured network by using a secure encryption protocol, which ensures confidentiality, integrity, and authentication. Remote administration often relies on command-line access, which SSH supports securely. Telnet, on the other hand, is unsuitable for secure operations because it transmits data, including passwords, in plaintext without encryption. HTTP on port 80 is also not secure as it does not encrypt the traffic. While RDP on port 3389 does offer encryption, it is typically used for Windows remote desktop services, not command-line access.