FTP error: '425 Can't open data connection.'

The FTP server returns this error: "425 Can't open data connection." when trying to list a directory or transfer data.

Date Entered: 03/23/1998    Last Updated: 01/24/2008

This can be caused when a firewall is not allowing connections to be completed. Since FTP uses two connections (the main connection, and then another for the data transfers), this is a problem with firewalls.

By default, the FTP component Passive property is true, meaning the component is in passive mode (this is not true in older versions, in which passive was fault by default, which is called active mode). In this case, the TCP connection for data transfers is opened to the server from the client. In this case, if the server is behind a firewall that has not been configured correctly, the server may not be able to make a connection. Try changing the value of the passive property.

When an FTP server is setup correctly - the port range that it uses for passive data connections will be coordinated with the firewall - so that the firewall will allow TCP connections to come in on that port range. Some firewalls are smart enough to see the port specified in the server reply and will let the connection through - but that won't work for secure FTPS connections.


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