Your capture shows that the 40.69.0.11 does not attempt to talk to the FTP server at control level, so its attempt to open a TCP session to port 50044 is not triggered by previous FTP control communication. (To make the picture complete: some clients can detect server side NAT by difference between the IP to which they have opened the control session and the IP indicated in the 227). Normally, the NAT device would have to modify the IP address indicated inside the 227 Entering Passive Mode before forwarding the packet so that the client could initiate the TCP session for ftp-data properly, but in your case, it seems the server is configured to send the public IP in the 227 so the NAT doesn't have to modify it. there is no need to analyse FTP messages, create dynamic public_ip:port_y to private_ip:port_x mappings, and modifying the port number in the FTP messages. Which means that FTP-awareness is not necessary, as any packet arriving at public_ip:port_n is forwarded to private_ip:port_n, i.e. Or some timeout issue may play a role.ĭo you know if an Azure LoadBalancer is FTP-Aware?

If the ftpd has indicated the same port to both clients, it's its own fault if it hasn't, one of the clients may have chosen that port by mistake - in such case, it would be that client's fault. In general, there is nothing wrong if two TCP sessions share a IP:port tuple at the local side if their remote IP:port tuples differ, but the ftp daemon you use may think otherwise.Ī complete capture should reveal more information on what made 40.69.0.11 start setting up a TCP session to the same port like 77.243.43.254 did. The point is that at the screenshot you can see two different clients are attempting to open a TCP session to server's port 50044, and the question is whether the server doesn't have a problem with that. Screenshots are almost useless for any analysis, so please publish the capture at Cloudshark (which is preferred at this site) or at any file sharing service and edit your Question with a login-free link to it. Sure it could, the question is why the RST itself happens, and that seems to be related to the ftp daemon's behaviour. Could the TCP reset have anything to do with the error I'm experiencing?

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