![]() ![]() The client then connects to the open port of the server through the N+1 port for data transmission. Open a port locally, and then tell the client the open port. ![]() After successful login, if you want to list or read data, send a PASV command to the FTP server. The working principle of the passive mode: the FTP client uses N to connect to port 21 of the FTP server, and sends a user name and password to log in. ![]() Send the PORT command to the FTP server, tell the server-client to adopt the active mode and open the port After receiving the PORT active mode command and port number, the FTP server connects through the server's 20 port and the client's open port to send data. The working principle of the active mode: FTP client uses N port to connect to port 21 of the FTP server, sends a user name and password to log in, and after successful login to list or read data, the client opens the N+1 port. When the concept of active/passive mode is mixed in, the data port may not be 20. Usually, port 21 is the command port and port 20 is the data port. FTP differs from other services in that it uses two ports and one data port. Many companies build FTP servers to provide file download services. FTP) is a common protocol in the file transfer process. ![]()
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