The FTP Connection Issue

Trying to connect to an FTP server can sometimes result in a 500 Illegal PORT command error. This issue often occurs when the FTP program or client is not correctly configured for Passive Mode.

When the client attempts to tell the server which port to use for the data connection (using the PORT command), the server may reject it if it expects a Passive (PASV) connection or if the port is blocked.

The Error Log Snippet

You may encounter an error snippet in your logs that looks something like this:

                COMMAND:> [3/11/2015 1:17:05 PM] PORT 192,168,0,101,196,215
                [3/11/2015 1:17:05 PM] 500 Illegal PORT command.
                ERROR:> [3/11/2015 1:17:05 PM] Syntax error: command unrecognized.
                ERROR:> [3/11/2015 1:17:05 PM] Failed to establish data socket.
            

The Solution: Passive Mode Configuration

To resolve this issue, you need to configure your FTP server to handle Passive Mode connections correctly. This involves defining the specific ports for passive connections and specifying the server's IP address in the configuration file.

Configuration Settings

Check your FTP server's configuration file (e.g., vsftpd.conf or similar depending on your software) and add or modify the following settings:

                pasv_enable=YES
                pasv_promiscuous=YES
                pasv_max_port=[Enter max port range allowed]
                pasv_min_port=[Enter min port range allowed]
                pasv_address=[Ip Address of your server]
            

pasv_enable: Enables passive mode.
pasv_max_port / pasv_min_port: Defines the range of ports the server will use for data connections. Ensure these are open in your firewall.
pasv_address: The public IP address of your server.

After making these changes, restart the FTP service and check the FTP connection again.

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