Connection abruptly closed

Question

Hello,

we are experiencing connection problems with CompleteFTP 8.2.0 on a Windows 2008 R2 production system. The server is being accessed daily by multiple clients. Some portion of these clients - some days 10%, other days 80% - cannot complete their transfers for unknown reasons.

The clients use Renci.SshNet SFTPClient to connect to the server.

The only clue I could gather from the logs is "WARN SFTPConnection [..] Connection abruptly closed: <closed by remote host (this part is in German)>". This looks like http://enterprisedt.com/questions/index.php/2919/sftp-exception-forcibly-closed-by-the-remote-host , but unfortunately there has never been any final answer/statement on the result.

Any hints on how to isolate the problem?

Thanks in advance, Tobias

Answer 1

Hi Tobias

If the message says the remote host closed the connection, there's basically two options - either a firewall somewhere in between has severed the connection, or the client closed the connection. If you have the client logs, they should tell you more about what is happening as far as the client is concerned. If you have a network administrator it is worthwhile examining the firewall logs to see if the firewall is terminating connections after they have been open for more than a certain amount of time.

Bruce

Comments

Hi Bruce,

thank you for your quick response. I checked with our hosting provider and the firewall shouldn't be the problem.

Right now our best theory is some weird hacking/DoS attempt: We are seeing lots of connection attempts, followed by immediately closed connections (see above) from the same client (234 attempts in one minute). To be clear, this happens even before authentication.

Does CompleteFTP has any built-in functionality or plug-ins available to auto-ban these kinds of "attacks"? The auto-ban feature doesn't seem fitting, as it only bans failed authentication attemps.

Cheers
Tobias