We are attempting to set up a VC connection to a client's (external) secure FTP site, and encountering the following issue.

When we use Ipswitch WS-FTP Pro (an FTP client) to manually test our login to the site, we use the following checkbox to get it to work: "Force passive connections to use host address."

Then, when we attempt to connect to the FTP server and transfer the file, we see the following output:

PASV Entering passive mode (<their private IP address - not their public IP address we established the connection with>
connecting data channel to <private IP address>
Substituting connection address <public IP address that we established the connection with> for private address <private IP address> from PASV
...and we are able to upload a file to the FTP server.

When we use VC to attempt upload the file, we get the following output:

PASV Entering passive mode (<private IP address).
LIST
Opening data connection.
QUIT

I think what is happening is that the client's FTP server is behind something that provides natting; when the FTP session enters passive mode, their FTP server responds with their private address, rather than the public IP address that we started the session with. When we use WS-FTP Pro, the before-mentioned checkbox option forces the FTP client to switch back to the public IP address, and we can continue the FTP session and transfer the file. When we use VC to attempt to transfer the file, the FTP client attempts to respond back to their server with their private IP address, and the session is then rejected, and we can't transfer a file.

I think what we need to do is to identify the command equivalent to that checkbox in WS-FTP Pro, and use that as a custom command. I did find a command, that as best as I can tell, seems to be what should be required - "EPSV". However, when I use that as a custom command, in conjunction with the FTP upload, I get the response back from their FTP server "EPSV command not understood", so it seems that their server does not support that command.

The simple solution would be to ask our client what command their FTP server might support for this. The problem is, that they want us to use their FTP client - we, of course, would much, much, much prefer to use VC.

Does anyone have any idea what might be a command equivalent to the "Force passive connections to use host address" option in WS-FTP Pro, or have any other ideas on what might allow this to work? (While my research turned up "EPSV", I'm not entirely certain that is correct, or at least the not the only option. For one thing, if that were the underlying command for that option in WS-FTP Pro, then I would think that WS-FTP Pro wouldn't work, either, if their server doesn't support it. Also, I don't see that command ever used in the output from the WS-FTP Pro connection - I can't identify a command in the output that might correspond to the checkbox.

You could ask for the ftp server log of your session. If they log all the commands you can macth a working and a not working ftp session and see the missing command.

Regards
Erik

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Thank you for your response.

We regularly need to set up connections to customer FTP servers, and this is likely to prove very helpful at some point in working out how we need to set up our VC FTP connection, sometimes we see what needs to be done with the WS-FTP Pro test connection, but it can take a while to translate it to a command for VC to use.

In this specific case, we can't get any support from their side in figuring it out since they want to make us use their FTP client, so we're reduced to trying to figure out what it might be, if we want to use VC.

You could ask for a ftp test account and ask visualcron support to test with this ftp server using this test account. The test environment should be the same as your production environment. Good luck.

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Thanks for the suggestion.

We ended up using WS-FTP Pro, in conjunction with VC, to be able to use that option. I'm not sure anymore that there was a missing command - as best as I can tell it may be more of a configuration option that controls the behavior of the client, rather than something entered at the server.

Not sure if this would be a candidate for an addition to VC's FTP options?

Which is the actual request?

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I wondered if it would be feasible to add to the VC FTP client the particular option, that in WS-FTP Pro is called "Force passive connections to use host address." The effect that the option has, is that if an FTP server responds back with a private IP address, it forces the FTP client to respond back on the orginally configured host IP address, instead of the private IP address (if the FTP client responds back on the private IP address that the FTP server responded with, the communication will fail.)

At first, I thought that there may be a command that could be used in custom commands that would work. Now, I'm thinking that it may simply be a configuration option that controls the behavior of the client, rather than a command that is entered at the server.

We are able to work with this by using VC to run WS-FTP Pro; it's just nice to be able to standardize as much as possible on VC, rather than needing another client for this particular case.