![]() ![]() 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 server 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. FTP uses two ports, a command (control) port and data port traditionally these are assigned ports 21 and 20 respectively. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |