Hi,
I'm having an issue with WinSCP GUI FTP downloads only from a Windows 2019 Server.
The same portable WinSCP folder copied from that server to my laptop works perfectly fine, so the executable itself seems fine.
What works on the server:
- Authentication to the remote FTP server
- Directory listing (LIST) always works
- PASV commands succeed
- Server responds with **150** and then **226 Transfer complete**
What Fails:
When downloading any file (RETR), we get:
Timeout detected. (data connection)
Copying files from remote side failed.
Timeout happens **\~15 seconds after** the server sends
`226 Transfer complete`
No data is actually received
What works on a different machine:
Using the same WinSCP executable, copied from the server to my laptop:
- Connects successfully
- Lists successfully
- Downloads all files normally
- Same network tunnel path (My Firewall team have confirmed that servers and clients use the same network tunnel.
So the issue is specific to the server environment, not WinSCP, not the FTP server, and not the firewall.
Script being used (credentials masked):
option batch on
option confirm off
option reconnecttime 60
option transfer binary
option timeout 30
open "ftp://<username>:<password>@x.x.x.x" -passive=on -rawsettings FtpForcePasvIp=1
cd /fdc-ftp/Outgoing
lcd "E:\temp\SomeFolder1"
get someFile.txt
get someFile.txt
get someFile.txt
lcd "E:\temp\SomeFolder2"
get someFile.txt
get someFile.txt
get someFile.txt
close
exit
Environment (server):
Windows Server 2019
Hyper‑V virtual machine
WinSCP 5.9.1 portable (same folder works on a laptop)
What’s been ruled out:
- Firewall: network team confirmed the passive ports are allowed; laptops use the same tunnel
- FTP server: downloads work from multiple machines and can also upload to the server
- WinSCP version/exe: same folder works on another machine
- Script issues: same script works on laptop
- GUI WinSCP: also fails on the server, so not a scripting issue
Summary:
The server opens the passive port, receives `150`, then `226` from the FTP server, but never receives the actual data packets before timing out. Another machine using the same WinSCP folder works fine.
This suggests something environmental on the server (NIC offloading, Hyper‑V, antivirus inspection, etc.).
Are there any known issues in older WinSCP builds (or with the Windows networking stack) on Server 2019 + Hyper‑V NIC offloading that can cause passive FTP data connections to stall after `226`?
Happy to provide full level‑2 logs if needed.
Thanks,
Mo