Telnet Application Port

B.

Telnet is a network protocol that allows a user to connect to a remote device and interact with it using a command line interface. Telnet uses TCP/IP (Transmission Control Protocol/Internet Protocol) as its underlying network protocol, and it typically runs on port 23.

Therefore, the correct answer to the question is B. 23.

To clarify the other options provided in the question:

• Port 21 is used by the FTP (File Transfer Protocol) to transfer files between devices.
• Port 80 is used by HTTP (Hypertext Transfer Protocol) to serve web pages over the internet.
• Port 443 is used by HTTPS (HTTP Secure) to serve secure web pages over the internet.

It's important to note that telnet is an insecure protocol because all the communication between the devices is transmitted in clear text, including usernames, passwords, and other sensitive information. For this reason, it's recommended to use a more secure protocol, such as SSH (Secure Shell), which also provides encryption and authentication features.