SFTP connection issue

[littlebunny]

We are experiencing an issue where one external customer cannot connect to our SFTP server. It works for all other customers and is only affecting this one site when they're connecting from their internal network. They've tested connecting to an SFTP server in a different location (one of ours) which is running the same FTP server and that one works. They have tested from the same machine on an external network and it works fine. A wireshark capture on the Windows FTP server is showing that the traffic arrives but then sends a FIN packet back to the client. Looking at the Application logs, we're not seeing any traffic coming in. On a successful SFTP connection, we normally would see the traffic on the Application logs.

They're currently using CoreFTP and have tested with other FTP clients but no difference is seen. We've tried issuing new credentials but still no change.

Any ideas or suggestions on what could be the issue? Let me know if you need more information.

Thanks
LB

[ForumAdmin]

if the client log is available (or the error message), please post it.

[ForumAdmin]

The two most common issues will be:

1) If using Core FTP, the wrong "connection" type is selected (needs to be SSH/SFTP)

2) They have reconnected too quickly too many times and auto-banned themselves (which eventually is released after a period of not trying to connect)

[littlebunny]

After some more troubleshooting, a restart of the "Ipswitch SSH Server" service on our FTP server fixed the problem. Any ideas why that might have fixed it and why it was only affecting one source IP address?