425 Cannot Open Data Connection Using IIS FTP with Server Proxy

Article ID: Q191144

The information in this article applies to:

Microsoft Internet Information Server version 4.0
Microsoft Proxy Server version 2.0

SYMPTOMS

The following error may be displayed on FTP clients when you use an IIS 4.0 FTP server and Microsoft Proxy Server with the Server Proxy feature:

   425 Can't open data connection

CAUSE

This error occurs when two or more users, using a non-passive mode FTP client, are simultaneously accessing the same IIS 4.0 FTP server located behind the Proxy Server.

WORKAROUND

This problem does not occur when you use an IIS 3.0 FTP server. If you are using an IIS 4.0 FTP, use one of the following methods to work around this problem:

Web browsers such as Microsoft Internet Explorer generally use passive mode by default and are not affected. However, if Internet Explorer is configured to use a proxy server, it will use non-passive mode automatically and fail.
Use another third party FTP client that supports passive mode connections.
Move the IIS 4.0 FTP server to the proxy server computer.

STATUS

Microsoft has confirmed this to be a problem in Microsoft Proxy Server version 2.0.

Additional query words: cannot dir LS get put pasv firewall

Keywords          :  
Version           : WINNT:1.0,2.0,3.0,4.0
Platform          : winnt
Issue type        : kbbug
Solution Type     : kbpending