What is FTP in operation for?

FTP: The File Transfer Protocol explained

One distinguishes active of passive FTP: In the active variant, the client establishes the connection as described via port 21 and thus tells the server which client-side port the server can use to transmit its responses. However, if the client is protected by a firewall, the server cannot send any responses because all external connections are blocked. The passive mode was developed for this. The server announces a port via which the client can set up the data channel. Since the client initiates the connection with this method, the firewall does not block the transfer.

The File Transfer Protocol knows various commands and status codes. With a total of 32 commands - not all of which are always implemented on the server - the client side instructs the server side to upload or download files, organize directories or delete files. The server responds with a status code that indicates whether the command could be implemented successfully.

Usually you need access data in order to be able to use FTP on a server. But there is also the possibility that a server Anonymous FTP offers. The operator of the server then enables each user to move files to the server via FTP or to download them from there - without having to use a password. Since such a public FTP server is associated with security risks, the options for users are usually limited.