FTP active mode is defined as one connection initiated by the client to the server for the FTP control connection. Remember that FTP requires two port connections through TCP ports 20 (data) and 21 (control). The second connection is made for the FTP data connection (where data is transferred), which is initiated from the server back to the client.
Active FTP is less secure than passive mode because the FTP server, which, in theory, could be any host, initiates the data channel. Also, port 20 must be opened up to the outside world, which is inherently less secure than using just port 21.
Figure 2-2 displays the active FTP mode of operation between an FTP client and FTP server. Figure 2-2 FTP Active Mode
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