Which port is used for FTP control (command channel)?

Which port is used for FTP control (command channel)?

• A. 989
• B. 21
• C. 20
• D. 990

Answer: (B)

FTP uses two separate channels: a control channel for commands and a data channel for file transfers. The control channel is the well-known port 21, which is where clients send commands like USER, PASS, LIST, and RETR and receive responses. The data channel behavior varies by mode: in active mode the server uses port 20 as the source when connecting to the client, while in passive mode the server opens a random high port and the client connects to it. The other ports listed are related to FTPS (FTP over TLS) in implicit mode, not the standard FTP control channel. So, the port used for the FTP control channel is 21.

FTP uses two separate channels: a control channel for commands and a data channel for file transfers. The control channel is the well-known port 21, which is where clients send commands like USER, PASS, LIST, and RETR and receive responses. The data channel behavior varies by mode: in active mode the server uses port 20 as the source when connecting to the client, while in passive mode the server opens a random high port and the client connects to it. The other ports listed are related to FTPS (FTP over TLS) in implicit mode, not the standard FTP control channel. So, the port used for the FTP control channel is 21.