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FTPS Data Connection Problems (FileZilla works but Chilkat does not?)

Nov 09 '16 at 09:20

Our customer reports a problem with FTPS. He has a server in Passive mode and FTPS. Our client can connect the server from within internal network, but cannot connect from outside network (outside of a company). But he claims that the FileZilla client can connect the server without any problems.


This is a common question because often there are many barriers to overcome in order to establish the data connection for an FTP upload or download.

The quick answer is this: If you can do it in FileZilla, then there are Chilkat FTP2 properties that provide the flexibility to do the same with Chilkat. There are no features lacking in Chilkat that cannot handle a particular situation (where FileZilla works, but Chilkat does not).

Here's a checklist of things to try, in the order of most common / quickest to test.

  1. Make sure you're using the same mode (Passive vs. Active).
  2. If using passive, set the ftp2.PassiveUseHostAddr property to true. See if that solves the problem.
  3. (If on Windows) It could be the Windows Firewall. The FileZilla application likely added an exception to the Windows Firewall during install so that the Firewall allows all communications to/from the program. Your application however, is unknown to the Firewall. Try adding an exception to the Firewall, or if it makes sense, do a quick test with the Windows Firewall temporarily turned off.
  4. The above three items are the most common solutions. See for more details about other settings that affect data connection establishment.