SFTP connection from a specific external IP cannot connect.

Question

We have an associate that tries to connect on our SFTP server with no success. All other associates are able to connect normally. From our tests we can see that the problem has to do with their public IP address and our SFTP. We tried one of their other IP addresses temporarily and during the time they had the different IP, they were able to connect normally. They cannot change their public IP though. This was done only for testing.

We have a correct listing of "Allowed IP addresses" on the SFTP server. We also created another user for them and they still could not access the server when connected from that public IP. During the tests we had no firewall enabled. On the server's CompleteFTP monitoring there is no listing of the specific public IP in the logs.

Can you please advise on what could be causing the issue and how we can troubleshoot this case?

Thank you.

Comments

Turn on debug logging on the server and get them to connect. You'll see a connection attempt in the logs even if it denied. If there is no connection attempt in the logs, then there is another firewall preventing access (it could be at their end).

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I turned on debug logging and I cannot find an entry from the specific IP in the logs. I am selecting the Server logging level: Debug and then I click on the Diagnostics.log but i cannot find any entry for the specific IP.
I have also enabled the Real-time Logging and again I cannot see any connection when they try to connect.
On the server's endpoint firewall I can see an "allow" entry for the specific IP in the endpoint's log when the associate tries to connect.

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You might want to do a quick search of the actual log files - they can be found in C:\ProgramData\Enterprise Distributed Technologies\Complete FTP\Logs

If there is no evidence in the CompleteFTP logs then they are being blocked by an intermediate firewall (perhaps one on the server itself).