One of my clients has a standalone storage box that is capable of acting as a FTP server for file sharing. He wanted to set it up so that his clients can upload files to him using FTP. His storage box is plugged behind a wireless router that is connecting all the workstations in the office. However, he is not able to setup his FTP server so that people outside his office can connect. He has tried many settings, such as opening all the required ports, putting the storage box in DMZ, and enabling/disabling passive mode. However, the closest outcome is that the FTP client is able to login but can not list any remote directories.
The problem is that internal IP addresses are being forwarded in the FTP connection. Therefore, the FTP client can not establish the connection correctly. To resolve this problem, some FTP client has the option to ignore the FTP server’s Passive IP address (ie. the internal IP). This will allow the FTP client to establish the connection with the FTP server correctly. Unfortunately, not every FTP client has this feature so you will have to look for one that supports it. The gFTP program in Linux has it and its pop-up tip explains the problem clearly.
If you know which other FTP clients can ignore the internal IP, then please share the info with us.
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