File transfer protocol (FTP) is one of the prominent protocol which is used to transfer files between two computers in the internet. Standard ports range from 0 to 1024 and FTP uses port 21 for the signalling. In FTP there are two things, first to have connection between client and server and the other one is transferring the files between both the computers.
Port at which server listen for incoming connections is known as "command port" and the one which is used for data is known as "data port". Port 21 is also known as "command port". Port number higher than 1024 values are used for data transmission from both side client and server both.
There are two modes of data transmission. When client listen on a port for data connection and server makes connection with client is known as "Active mode" while reverse order is known as "Passive Mode". Passive mode of FTP is widely used approach.