Active FTP - Failed Connection for data Socket

[BruZilla]

Another difference might be in the operating systems' TCP/IP stack itself, maybe newer Windows versions send flags, scaling factors, or option headers in the SYN packet the IoT devices don't understand?

sounds good. how can i check this?

[botg]

A packet sniffer, ideally one that sits somewhere in the middle (if needed, put VPN into "none" encryption for testing), so that it can truly see what is going over the wire, without being influenced by either peer.

[BruZilla]

The only bigger change in this regard is Windows Defender, which was not in the old 2008R2, at least not in this format.

hi boco, thanks for your help solving this problem. windows defender is uninstalled, also no other antivirus is running. Windows firewall is deactivated.

@botg

A packet sniffer, ideally one that sits somewhere in the middle (if needed, put VPN into "none" encryption for testing), so that it can truly see what is going over the wire, without being influenced by either peer.

i can install wireshark on the ftp server itself? vpn "none encryption" is not possible. the vpn tunnel is without server/client software. the vpn tunnel is from the mobile phone provider. all data which are send over these 3g simcards are automatically routed over vpn in our network. my english is not so good, hope you understand my explanation

[BruZilla]

in case TCP/IP stack is the problem. what can i do then?

[BruZilla]

Mhh for what exactly im searching for?
Error: Timeout

FTPWireShark1.png (41.45 KiB) Viewed 6929 times

FTPWireShark2.png (36.6 KiB) Viewed 6929 times

Error Connection refused by Server:

FTPWireShark3.png (42.02 KiB) Viewed 6929 times

FTPWireShark4.png (36.22 KiB) Viewed 6929 times

sometimes he can starting the data transfer, but the files stay empty. i think hes kidding me, give me some hope to destroy it seconds later ...

FTPWireShark7.png (24.28 KiB) Viewed 6926 times

FTPWireShark5.png (41.54 KiB) Viewed 6928 times

FTPWireShark6.png (38.07 KiB) Viewed 6928 times

[botg]

The screenshots are useless.

Take a dump from Window Server 2008 R2, and a dump from Windows Server 2012R2. Now compare everything that happens after the PORT command, see if there is any difference.

[BruZilla]

Installed a ubuntu 22.04lts server with the newest verysecureftp (vsftp) version.
my iot devices can send data successfully over activeftp to this server.