I have both FTP client and server behind different routers (doing NAT). The router in the server side has opened the proper port to work. My FTP client is configured to use active mode and it sends the following command when I try to upload a file to the server:

PORT 192,168,1,42,184,89

It is ok, my client with internal IP is trying to setup a data connection with the server in the port specified by the PORT command. The problem is that the server is capable of responding me. As I am behind a router, how it is possible? from where the TCP server gets the public IP to reach my router through the Internet?



The NAT probably translates the IP address in PORT command. That's possible if the traffic is not encrypted. Try enabling TLS/SSL encryption. The data connection should fail then.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.