Serv-U FTP PASV and PORT mode

                  FTP connections generally have two connections, one for client and server transfer commands, and one for data transfer. FTP service programs generally support two different modes, one is Port mode and the other is Passive mode (Pasv Mode). Let me first talk about the difference between the two different modes of connection.
First assume that the client is C, the server is S.
Port mode:
When client C connects to server S, it uses Port mode, then client C will send a command to tell Server S (Client C opens a port N locally waiting for you to connect to the data). When the server S receives the Port command, it will connect to the port N opened by the client. This data connection It is generated.
Pasv mode:
When client C connects to server S, server S will send a message to client C. This information is (server S opens a port M locally, you are now connected I), when the client C receives this information, it can connect to the M port of the server S. After the connection is successful, the data connection is also established.
From the above explanation, you can see that the main difference between the two modes is the difference in the establishment of the data connection. For the Port mode, the client C opens a port and other server S to connect to establish a data connection; Pasv mode is that server S opens a port and waits for client C to establish a data connection.

FTP requires two ports, one port is connected to a control port, the port 21 is configured to send instructions to the server and wait for the server response; other port is a data transfer port, the port number is 20 ( Only PORT mode) is used to establish a data transmission channel. There are mainly three functions
to send a file from the client to the server.
Send a file from the server to the client.
Send a list of files or directories from the server to the client.

If you want to enable PASV way ie, the open ie, in the menu select: Tools - & gt; Internet Options - & gt; Advanced, the "use passive ftp" in front of a hook (need more than IE6.0 Only support).

FTP server software supports all PORT way. Most FTP server software PORT mode and PASV mode are supported. Both modes are supported by the Serv-U default configuration. To turn off the PASV mode, open Serv-U and go to Domains -> user.dns0755.net -> Settings -> Advanced -> Remove the hook in front of "Allow passive mode data transfers".
In the Serv-U Local Server -> Settings -> Advanced -> PASV port range, fill in the local port range used for PASV mode, such as 60000-60020. Please limit the port range to less than 20. After that, open the port of this range in the firewall.