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Thread: FTP port 20 vs port 21

  1. #1
    Join Date
    May 2008
    Posts
    976

    FTP port 20 vs port 21

    I am looking for the ftp connection. I came across the term port 20 and port 21. Can you help to know what is the relation between port 20 and port 21 in ftp? I mean what is port 20 and port 21 used and what are their differences?

  2. #2
    Join Date
    Nov 2008
    Posts
    1,001

    Re: FTP port 20 vs port 21

    FTP is a TCP based service exclusively. FTP utilizes two ports a 'data' port (port 20) and a 'command' port (port 21). FTP client initiating a connection on port 20 with the FTP server on its port 21. Port 21 is where the server is listening for commands issued to it, and in turn, which it will respond to.

  3. #3
    Join Date
    Jan 2006
    Posts
    3,792

    Re: FTP port 20 vs port 21

    Basically FTP is a protocol that uses two ports namely port 21 for commands and port 20 for data. In Active FTP, the client initiates a connection on the server’s command port. The server then initiates a connection with the client from its data port. In Passive FTP, the client initiates both connections with the server, which remains “passive”.

  4. #4
    Join Date
    May 2008
    Posts
    2,945

    Re: FTP port 20 vs port 21

    FTP port 20 is the default data transfer port which is required for inbound if internal users are allowed access to external FTP sites, yet open port poses a threat (hole for network mapping, etc). Modern firewalls solve this by keeping it closed until a valid FTP session exists, then only opening it between those hosts. Control via a stateful-tracking firewall, do not simply open at perimeter.

    FTP port 21 is an Invisible FTP port. It is used by server.

    Source: auditmypc

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