Ftp has two data transmission modes: active mode and passive mode. Each mode has a control port and a data transmission port. Unless otherwise specified, the default control port of both modes is 2 1. That is, all control commands are carried out through the 2 1 port of the server. Data transmission port, 20 ports of the server are used in active mode, and the server and the client negotiate and randomly specify ports in passive mode. This is true whether it is uploaded or downloaded.