More information about "Transfer channel can't be opened" error:
https://winscp.net/eng/docs/message_transfer_channel_cant_be_opened

Hi,

Sent you direct email reply on this :-)

martin wrote:

Not sure if you understand me.

What IP address do you get when you do ping ftp_server_hostname?

What is 10.152.1.166?

. 2014-06-02 16:37:42.614 Connected with ********************, negotiating TLS connection...
< 2014-06-02 16:37:42.658 220 NASFTPD Turbo station 1.3.2e Server (ProFTPD) [10.152.1.166]

Not sure if you understand me.

What IP address do you get when you do ping ftp_server_hostname?

What is 10.152.1.166?

. 2014-06-02 16:37:42.614 Connected with ********************, negotiating TLS connection...
< 2014-06-02 16:37:42.658 220 NASFTPD Turbo station 1.3.2e Server (ProFTPD) [10.152.1.166]

martin wrote:

Thanks for the log. Is the IP address attempted for passive mode transfer (109.231.208.149) what the FTP server hostname (obfuscated in the log) resolves to?

Yes. In both passive and non passive attempts the same things occurs.
Thanks for looking into this by the way (and I'd also like to say that we use this application for SFTP a lot, and it is fantastic!!)

Thanks for the log. Is the IP address attempted for passive mode transfer (109.231.208.149) what the FTP server hostname (obfuscated in the log) resolves to?

OK, strangely enough I have been unable to reproduce the original working scenario of using an old version of WinSCP and be able to successfully connect to an FTPS server with only a static route and no default gateway.

But, just to hopefully get this moving I am posting my logs using the current version of WinSCP (slightly redacted to move private information).

Attached is the connection attempts in both Passive and non-Passive modes. Both of them succesfully connect but then have issues as originally described afterwards.

no worries, working my way through them...

dsimpson wrote:

Or should we try slightly newer versions until I find where it stops working, and then give you the logs from that one?

That would be great, obviously :)

We were using version 4.27. So, that's pretty old! Do you still want the logs from that version? Or should we try slightly newer versions until I find where it stops working, and then give you the logs from that one?

What version did you use before? Can you attach a complete log file both using the old version and the latest one?

Hi there,

We have upgraded to WinSCP 5.5.3 and are now unable to connect to remote servers where the connecting client does not have a default gateway (but does have a static route to the destination server).

When connecting, it does request authentication - which works fine, but when that is finished it seems to "loose" connectivity with the remote server and gives an error message: "Transfer channel can't be opened. Reason: A socket operation was attempted to an unreachable host. Could not retrieve directory listing." Clicking Ok loads the main WinSCP folder screen but immediately "Timeout detected" is presented.

This seems to work fine with SFTP but with FTP or FTPS this does not appear to work correctly as above.
The server in question we are using is FTPS with Explicit TLS enabled.

To put things into context, we are a financial company and lock connectivity on our network down as much a possible, which is why we do not have default gateways on our PCs and only use static routes.