The File Transfer Protocol (FTP), although an older technology, is still very popular and is used routinely by IT departments and businesses worldwide. Even so, many users of FTP do not fully understand the difference between two of its basic configuration options: Active mode and Passive mode. I, being one of those people until a few years ago when I took on an FTP related project, intend to explain the details behind them.
FTP uses two communication paths (also know as “channels”) in order to accomplish its goal of transferring files from one location to another. The first is the control channel which is used to send FTP commands back and forth from the client and server. This connection is commonly made to port 21 of the server. The other channel, known as the data channel, is used to transmit the raw data of the files being sent. The server port used for this channel depends largely on what communication mode is being used, Active or Passive. Continue reading