Active and passive FTP mode

FTP can work both in the active mode and in the passive mode.

In active mode, the client performs a control connection with the server, and the server makes a connection to the client for data transfer.
The passive control connection and data connection are made by the client himself.

Under the control connection is meant authentication and command transmission.
The control connection is executed by the client in both cases equally, from the client side from the dynamic TCP port 1024-65535 to the server port 21.

In the active mode after the control connection from the client, the FTP server connects to the client’s dynamic port 1024-65535 from its TCP port 20 for data transfer.
In the passive mode after the control connection from the client, the FTP server tells the client the number of the dynamic TCP port 1024-65535 to which it can be connected to the client for data transmission.

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