When you connect to a File Transfer Protocol (FTP) server using a Windows command-line FTP client and you then issue a quote list
command (or another quote command), the next command you use may return the following error message:
425 Can't open data connection.
When an FTP client passes a command to an FTP server and the client is in active mode, the client also passes a port on which it listens for the response from the server. If the client is sending a command that does not require a data port (such as the syst
command), the client does not set up a data port. The ls
command, also called the list command, requires a data port to return the data. If the server is expecting a data port from the client, and the server does not receive a data port, the server generates the 425 error.
FTP clients can pass commands that they do not interpret to the server. These commands are passed using the following syntax:
Because the client does not interpret the command it is sending, the client sends the command to the server without generating a listen port for the data, and therefore the server cannot open the data port.
The FTP clients that ship with Windows do not support passive mode. Therefore, they always need to negotiate a data port when issuing a command that returns data.
To see a list of the commands that the client successfully supports, type help
at the FTP prompt.