![]() All settings for passive mode are on a single page making the whole set-up process easier. ![]() The above is intended to explain why you need to twiddle certain settings and how to choose options for your installation. Reason for this, active FTP will not work behind a NAT device. If you have ever set-up an FTP client behind a NAT (Network Address Translation) router you will have been forced to changed mode from active to passive. ![]() The FileZilla team neatly resolves this issue by providing a dynamic IP address resolution service. It needs to be set during FTP server configuration, not a problem if you have a fixed IP address however a dynamic IP is problematic. Because of address translation through a NAT device the FTP servers has no way of determining this IP address. In reality unprivileged ports are restricted to a small range for example 50000 to 50100.ĭuring a data transfer the FTP server needs to send its visible IP address back to a client. What’s important when using a NAT device is the need to forward ports 20, 21, 990 and all unprivileged ports. The client then initiates the connection from it’s second port to transfer data.Ī secure FTP server follows the above procedure with one minor difference the command port used is reserved port 990. In response the server opens a random unprivileged port and sends the “ PORT P” command back to the client. The first port contacts the server on port 21, and issues the “ PASV” command. A client first opens two consecutive random unprivileged ports (ports above 1023). In passive mode a client initiates both connections to the server. Most browsers use passive mode for connection this mode changes the data port as follows. ![]() Depending on the operating mode, the data port is not always on port 20. The following covers this mode and the added complication of running a FTP server behind a wireless router with NAT.įTP uses two ports, a ' command' (control) port and ' data' port traditionally these are assigned ports 21 and 20 respectively. Everything is geared to make it easier for the client hence your server must support passive mode. On a local network FTP works just fine however when connecting to the Internet you need to consider a user (FTP client) more importantly the mode of transfer, active or passive. ![]()
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