FTP Servers support PORT and PASV mode. By default the FTP Server publishing rule in ISA 2004 does not support PASV mode, but we can change this!

I have an FTP server set up to transfer files around between my laptop, work PC and between my virtual network and the real network (Virtual Server 2005 NEEDS the Shared Folders feature from VMWare). I have my FTP server set up to use ports 50666 to 50777 for PASV connections and ISA is configured with a typical FTP Server publishing rule. FTP access is working in PORT mode. Open up the ISA Manager MMC and locate your FTP Server publsihing rule, right-click the rule and select properties. Click on the Traffic tab, then click the Properties button to edit the protocol properties.

On the FTP Server Properties page, click the Parameters tab, then click Add next to Primary Connections.

Here is where we can define the ports to use for PASV mode connections. Ensure TCP is selected, as well as Inbound, then enter the port range you set on your FTP server for PASV connections.

Click OK, and verify the ports, then click OK again to close the properties page. Apply the rule and you will be able to connect to your FTP server via a PASV mode connection.

PASV mode is becoming more and more prevalent with the adoption of broadband routers in the home enviroment.

For more information see:

Active FTP vs. Passive FTP, a Definitive Explanation