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From: Ata@RADC-MULTICS.ARPA ("John G. Ata")
Newsgroups: comp.protocols.tcp-ip
Subject: Re: FTP client program
Message-ID: <870413134830.986995@RADC-MULTICS.ARPA>
Date: Mon, 13-Apr-87 08:48:00 EST
Article-I.D.: RADC-MUL.870413134830.986995
Posted: Mon Apr 13 08:48:00 1987
Date-Received: Sat, 18-Apr-87 17:52:59 EST
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    Date:  12 April 1987 13:33 edt
    From:  Joe I. Herman <dzoey at TERMINUS.UMD.EDU>
    Subject:  Re: FTP client program

                    .
                    .
                    .
    The well know data port for FTP is port 20.  You can change this by
    issuing the PORT command to the host before you issue a STOR or
    RETR.  I forget the exact syntax for the PORT command, but it's in
    the RFC.

Port 20 is the well known data port for the FTP Server.  It cannot be
changed by having the client FTP send the port command to the Server.
This only changes the port that the client FTP uses which is usually NOT
port 20.  The server may change from port 20 by issuing the PORT command
to the client.

    example

    user wants to stor data:

    client: PORT x
    server: {200,250} PORT command okay
    client: listen on x
    client: STOR foo
    server: {150,125} Establishing connection {opens a tcp connection to port x}

    If you want more info, I'll be glad to help.
                                            Joe Herman

    dzoey@umd5.umd.edu

Again, this changes the port that the client listens on, not the
server's use of port 20.  I didn't get a copy of the original message
that started this, but hope that it helps.

                    John G.  Ata