I'm struggling to come to grasp with why all FTP servers requires the use of a port range for passive mode data channels as opposed to only using one data port for all incoming data channel connections.
FTP servers handle many simultaneously connected clients on port 21. Web servers handle many simultaneously connected clients on port 80. Etc..
Then why can't an FTP server use only one data channel port for all incoming passive data connections (and still be able to handle many simultaneously connected clients on that port, say port 1024)?
Or can it?
I am interested in knowing the technical details for why this is not possible or not recommended.