A client packet is received by a server with a destination port number of 21. What service is the client requesting?

A client packet is received by a server with a destination port number of 21. What service is the client requesting?

• A. SFTP
• B. FTP
• C. Telnet
• D. DNS

Answer: (B)

When a packet is received by a server with a destination port number of 21, it is indicative of a client requesting the File Transfer Protocol (FTP) service. Port 21 is the default port designated for control commands in FTP. This protocol is widely used for transferring files over the Internet, where the client establishes a connection to a server to send or retrieve files. The FTP protocol operates in two modes: active and passive. Regardless of the mode used, the control connection typically utilizes port 21 for commands, making it essential knowledge for understanding how file transfers are managed in network communications. This distinguishes FTP from other services, such as SFTP (Secure File Transfer Protocol), which operates on port 22, or Telnet, which uses port 23 for remote command-line interface access. DNS (Domain Name System) operates over port 53 and is used for resolving domain names to IP addresses. Understanding these port associations enhances one's knowledge of networking protocols and their specific uses.

When a packet is received by a server with a destination port number of 21, it is indicative of a client requesting the File Transfer Protocol (FTP) service. Port 21 is the default port designated for control commands in FTP. This protocol is widely used for transferring files over the Internet, where the client establishes a connection to a server to send or retrieve files.

The FTP protocol operates in two modes: active and passive. Regardless of the mode used, the control connection typically utilizes port 21 for commands, making it essential knowledge for understanding how file transfers are managed in network communications. This distinguishes FTP from other services, such as SFTP (Secure File Transfer Protocol), which operates on port 22, or Telnet, which uses port 23 for remote command-line interface access. DNS (Domain Name System) operates over port 53 and is used for resolving domain names to IP addresses. Understanding these port associations enhances one's knowledge of networking protocols and their specific uses.