20/TCP is commonly used for which data transfer service?

20/TCP is commonly used for which data transfer service?

• A. Telnet
• B. SSH
• C. FTP Data
• D. FTP Control

Answer: (C)

FTP uses two separate connections: a control channel for commands and a data channel for transferring files. The data channel that the server uses traditionally originates from port 20, which is why 20/TCP is associated with FTP data transfers. The control channel operates on port 21. In contrast, Telnet uses port 23 and SSH uses port 22, so those don’t match the data transfer role. Note that in passive FTP the data connection uses a port chosen by the server rather than the fixed 20, but the classic data transfer port for FTP is 20.

FTP uses two separate connections: a control channel for commands and a data channel for transferring files. The data channel that the server uses traditionally originates from port 20, which is why 20/TCP is associated with FTP data transfers. The control channel operates on port 21. In contrast, Telnet uses port 23 and SSH uses port 22, so those don’t match the data transfer role. Note that in passive FTP the data connection uses a port chosen by the server rather than the fixed 20, but the classic data transfer port for FTP is 20.