IBM i QuickTip: When You Can’t FTP from a Windows Desktop to an IBM i

ftpHere’s a common fix for when you can’t perform a Windows FTP transfer with your IBM i partition.

It’s common for a Windows-to-IBM i FTP transfer to get blocked when the Windows desktop firewall blocks port 20 traffic to the Windows desktop (port 20 is used in the FTP data transfer).

You may even see your FTP session connect to your IBM i partition but fail when it tries to transfer data. Sometimes the desktop will display an FTP 425 error–Unable to open data connection. This recently happened to a client of mine who was having trouble performing an FTP upload from a FedEx server on their warehouse floor.

The best way to take care of this is to turn off the Windows firewall on the blocked machine. That should allow you to complete the transfer.

(originally posted on May 1, 2013. Reposted on November 18, 2013)

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4 Responses to IBM i QuickTip: When You Can’t FTP from a Windows Desktop to an IBM i

  1. The standard port for an FTP service is 21 😉

    • Joe Hertvik says:

      While port 21 may be the standard FTP port, it appears that in some situations port 20 also needs to be open. This worked for the FedEx situation I described in my post. IBM even references it in their tech support Web site labeled IBM FTP 425 Error–Unable to Open Data Connections, which deals with this same topic of FTPing to an IBM i box from Windows.

      So it probably would be wise to insure that your Windows desktop isn’t denying both ports 20 and 21 when FTPing to the IBM i or OS/400 operating system. Anyone care to weigh in on what ports 20 and 21 do for FTP transfers from Windows to IBM i boxes?

      • Joe Hertvik says:

        Just did a little more research on this and it looks like port 21 is traditionally the FTP command port, while port 20 is used as the data port (though FTP can use another port besides 20 for this function). Which would explain why in my FedEx example, the Windows FTP client would be able to start a session with my IBM i server, but then die when it was time to transfer the data.

        So as a precaution, ports 21 and 20 should be open for most Windows to IBM i Data Transfers.

        To find more info on ports 21 and 20 in an FTP transfer, google ‘Port 20 21 FTP’ in Google.

  2. Doug Bridwell says:

    I was wondering if you or anyone else has had success with a graphical Windows FTP client? I have no problem using the DOS command prompt to FTP to or from my IBM i system. However, I have not found a graphical client that works with both IFS and non-IFS files. I can use FileZilla but it only works using namefmt 1 and only with IFS files.

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