window size shrinks until it gets to 0 and session times out (wodSFTP / wodSFTP.NET / wodSFTPdll)

Large file transfers to an important customer are repeatedly failing. The trace shows SFTPLib.NET sending smaller and smaller window sizes until it gets to a window size of zero, which causes the session to eventually timeout. We were using version 3.4.9.132, but also tried the latest version 3.4.9.134. The transfers work with CoreFTP.

Hi.

Are you referring to downloads or uploads? Window size shrinks by each packet sent out, but when it comes near zero each side should increase it. It depends whether it's upload or download to determine why it's not increased.

Do you know type of server you're connecting to?

Jasmine.

We are doing an upload (Put) to an IBM Sterling B2b integrator (v5.2.1.0) server. The puts do not fail all the time, but it does seem that they fail when there is a high latency return path to us from the server. We are not having trouble with other customers and only recently with this customer as we have increased volume to their server. The solution may be some configuration change on our end or their end?

Hi.

wodSFTP.NET to speed up the transfer may send blindly many packets in advance, without waiting for confirmation. THis could confuse the server.

We could try to make a workaround on client side, but I need to know exactly what type of server is on remote side? Can you telnet to the server on port 22 and paste me first line it returns?

Jasmine.

This is the telnet response: SSH-2.0-Attempts to access <deleted>.com are being monitored

Hi.

Unfortunately this didn't help since it's not default greeting.

We can try to make blind workaround for this server and you will have to test it. If that doesn't help, then we'll need to duplicate this issue by connecting to the server.

Can you please send email to techsupport so we can send you version to test, assuming your updates subscription is valid.

Kind regards,
Jasmine.