FileZilla Server 1.8.1 - A command is already being processed

[peppeantonini]

I have devices that connect via FTP and save text files: as far as I know they open the connection (in active mode), create the file and go to append for each line to be written.
I currently connect to a FileZilla Server 0.9 on a Windows Server 2008r2 and I have no problems.
However, I need to move them to a new machine running Windows Server 2016 and on which I have installed FileZilla Server 1.8.1.
Unfortunately, however, it doesn't work correctly: the file is created, but empty and I get this error.

Can someone help me?
Thank you

[botg]

Your client is broken. It already sends a command without having received the reply to a previous command. This is in violation to the FTP specifications. You need to contact your client vendor for further assistance.

[oibaf]

Although the client has the issue that @botg mentioned, FileZilla Server simply informs about it and keeps the command in the queue.

The real issue seems to be the timeout the server encounters while trying to establish the active connection with the client: this is networking issue, usually induced by a Firewall on either end, or port forwarding not properly configured, but could be due to a number of other reasons as well.

Is there any firewall or NAT device that needs to be properly configured in the picture?

[peppeantonini]

Your client is broken. It already sends a command without having received the reply to a previous command. This is in violation to the FTP specifications. You need to contact your client vendor for further assistance.

The strange thing though is that with FileZilla 0.9, on Windows 2008r2, the same client works!
This is the behavior on the other server

(006144) 17/03/2024 04:01:07 - (not logged in) (2.43.186.241)> Connected, sending welcome message...
(006144) 17/03/2024 04:01:07 - (not logged in) (2.43.186.241)> 220 FileZilla Server version 0.9.40 beta
(006144) 17/03/2024 04:01:07 - (not logged in) (2.43.186.241)> USER user
(006144) 17/03/2024 04:01:07 - (not logged in) (2.43.186.241)> 331 Password required for user
(006144) 17/03/2024 04:01:08 - (not logged in) (2.43.186.241)> PASS *****
(006144) 17/03/2024 04:01:08 - user (2.43.186.241)> 230 Logged on
(006144) 17/03/2024 04:01:11 - user (2.43.186.241)> TYPE A
(006144) 17/03/2024 04:01:11 - user (2.43.186.241)> 200 Type set to A
(006144) 17/03/2024 04:01:14 - user (2.43.186.241)> PORT 2,43,186,241,4,184
(006144) 17/03/2024 04:01:14 - user (2.43.186.241)> 200 Port command successful
(006144) 17/03/2024 04:01:14 - user (2.43.186.241)> STOR d016403170401.txt
(006144) 17/03/2024 04:01:14 - user (2.43.186.241)> 150 Opening data channel for file transfer.
(006144) 17/03/2024 04:01:27 - user (2.43.186.241)> 226 Transfer OK
(006144) 17/03/2024 04:01:30 - user (2.43.186.241)> PORT 2,43,186,241,4,185
(006144) 17/03/2024 04:01:30 - user (2.43.186.241)> 200 Port command successful
(006144) 17/03/2024 04:01:30 - user (2.43.186.241)> RETR setup016.txt
(006144) 17/03/2024 04:01:30 - user (2.43.186.241)> 550 File not found
(006144) 17/03/2024 04:01:43 - user (2.43.186.241)> PORT 2,43,186,241,4,186
(006144) 17/03/2024 04:01:43 - user (2.43.186.241)> 200 Port command successful
(006144) 17/03/2024 04:01:44 - user (2.43.186.241)> RETR tabil016.txt
(006144) 17/03/2024 04:01:44 - user (2.43.186.241)> 550 File not found
(006144) 17/03/2024 04:01:57 - user (2.43.186.241)> QUIT
(006144) 17/03/2024 04:01:57 - user (2.43.186.241)> 221 Goodbye
(006144) 17/03/2024 04:01:57 - user (2.43.186.241)> disconnected.

[peppeantonini]

Although the client has the issue that @botg mentioned, FileZilla Server simply informs about it and keeps the command in the queue.

The real issue seems to be the timeout the server encounters while trying to establish the active connection with the client: this is networking issue, usually induced by a Firewall on either end, or port forwarding not properly configured, but could be due to a number of other reasons as well.

Is there any firewall or NAT device that needs to be properly configured in the picture?

The server is directly exposed to the internet and while running the tests, I disable the Windows firewall.
Furthermore, I also tried with my Windows PC, using FileZilla Client by forcing it into passive mode and I didn't encounter any problems.

[peppeantonini]

Although the client has the issue that @botg mentioned, FileZilla Server simply informs about it and keeps the command in the queue.

The real issue seems to be the timeout the server encounters while trying to establish the active connection with the client: this is networking issue, usually induced by a Firewall on either end, or port forwarding not properly configured, but could be due to a number of other reasons as well.

Is there any firewall or NAT device that needs to be properly configured in the picture?

I took a look at the traffic via WireShark - can that help?

[sbsmithjax]

Greetings peppeantonini, did you ever solve this problem? I am having the exact same issue with my install.

Regards,
sbsmithjax