Which protocol provides secure remote command-line access to network devices and typically uses port 22?

• A. Virtual Private Network (VPN)
• B. Secure Copy (SCP)
• C. Simple Mail Transfer Protocol (SMTP)
• D. Secure Shell (SSH)

Answer: (D)

Secure remote command-line access to network devices is provided by a protocol that encrypts the session and authenticates users, typically using port 22. This protocol is Secure Shell, commonly called SSH. It replaces plaintext protocols like Telnet by offering encryption for all data in transit, strong authentication (passwords or public keys), and integrity verification, so commands you issue and responses from devices are protected from eavesdropping and tampering. Because network devices such as routers and switches are managed remotely, SSH enables you to log in securely and run commands as if you were at the console. A related tool, Secure Copy, uses SSH as its transport to securely transfer files but does not itself provide a remote command-line interface. A VPN creates a secure tunnel for network traffic but isn’t the specific remote shell protocol used for device management, and SMTP is an email protocol unrelated to remote management. SSH uses port 22 by default, though it can be configured to listen on different ports.