PASV and port modes of Serv-U FTP

FTP connections generally have two connections: one is the client and the server transmission command, and the other is the data transmission connection. FTP service programs generally support two different modes: Port mode and PASV mode ), let me first talk about the two different connection modes.
Assume that the client is C and the server is S.
Port mode:
After client C connects to server s, the port mode is used, then client C will send a command to inform server s (client C opens a local port n waiting for you to connect to the data ), when the server s receives the PORT command, it connects to the port n opened by the client, which is generated.
PASV mode:
After client C connects to server s, server s will send a message to client C. The message is (server s opens a local port M, So connect to me now ), after receiving this information, client C can connect to the M Port of server S. After the connection is successful, the data connection is established.
From the above explanation, we can see that the main difference between the two modes is that the data connection is established differently. For the port mode, in PASV mode, server s opens a port locally and waits for client C to establish a data connection.

FTP requires two ports. One port serves as the control connection port, that is, port 21, which is used to send commands to the server and wait for the server to respond. The other port is the data transmission port, the port number is 20 (only in Port mode). It is used to establish a data transmission channel and has three main functions.
Sends a file from the client to the server.
The slave server sends a file to the client.
The slave server sends a file or directory list to the client.

If you want to enable PASV in IE, open IE and choose tools> Internet Options> advanced from the menu, hook up before "use Passive FTP" (supported only by ie6.0 or above ).

All FTP server software supports port mode. Most FTP server software supports port and PASV. Serv-U is supported in both modes by default. If you want to disable the PASV mode, enable Serv-U to go to domains-> user.dns0755.net-> Settings-> advanced-> remove the hooks before "allow passive mode data transfers.
In the local server-> Settings-> advanced-> PASV port range of Serv-U, enter the local port range used in PASV mode, for example, 60000-60020. Limit the port range to 20. Then open the port range in the firewall.

PASV and port modes of Serv-U FTP