First sticking a common: Pasv Mode "Is it a matter of" Passive Mode "? So what is" passive mode ", what is it taken?
============================================================================================================================================================================================================= ============= ftp is the abbreviation of the English File Transfer Protocol, meaning the file transfer protocol. It is the same as HTTP is a widely used protocol on both computers to transfer files between two computers. Compared to HTTP, the FTP protocol is much more complicated. Complex reasons because the FTP protocol is used to use two TCP connections, one is a command link to deliver commands between FTP clients and servers; the other is a data link, used to upload or download data. The FTP protocol has two ways of working: Port mode and PASV mode, meaning in Chinese means active and passive. The connection process of the Port is: the client is sent to the server's FTP port (default is 21) Send a connection request, the server accepts the connection, and establish a command link. When you need to transfer data, the client uses the port command on the command link to tell the server: "I opened the *** X port, and you came over to connect me." The server is then transmitted from the 20-port *** X port to the client, and a data link is created to transmit data. The connection process of the PASV (passive) method is: the client sends a connection request to the server's FTP port (default is 21), the server accepts the connection, and establish a command link. When you need to transfer data, the server uses the PASV command on the command link to tell the client: "I opened the *** X port, and you came over to connect me." The client sends a connection request to the server's *** X port to create a data link to transmit data. As can be seen from the above, the command link connection method of two ways is the same, and the establishment method of the data link is completely different. The complexity of FTP is here.
