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From: Axel Scheepers (ascheepesurf.iae.nl)
Date: Sat Jul 07 2001 - 08:32:47 CDT

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    Hi everybody,
    I hope I'm not being really off topic with this one but
    it's been troubling me for a while now.
    I'm looking for a way to provide acces to an ftpserver, my current
    network layout looks like this:

    Cable Modem ------> Gateway ---------> http/ftp server
                                                    |
                                                    |
                                                    +------------> private http/ftp/sql server
                                                    |
                                                    |
                                                    +------------> my workstation

    The gateway does natd and ipf since the other servers have private
    adresses. The problem now is that whenever I connect to my
    ftp servers from the outside, the server is unable to set up a
    data connection, because it wants to connect on a port > 1024, which
    is blocked by my firewall(and I want to leave it that way).
    Natd does the following:
    natd -redirect_port tcp 192.168.0.5:20 20 -redirect_port 192.168.0.5:21 21
    which redirects the traffic to my public ftp server.

    As I see it there can be 2 problems with this setup;
    1) The server wants to initiate the data connection at a port > 1024 and/or
    2) The server still somehow reports 192.168.0.5 as its address to the clients.

    I have tried to connect with the option passive is off, which I thought
    should force the server to stay on port 21 for tha data connection, but
    it didn't work. :(
    Can/will somebody help on getting this done the proper way ?
    I just want to use ipfilter, if possible, and I don't like to install
    a ftp proxy for this.

    Greetings,
    Axel Scheepers

    Unix System Administrator
    VIA NET.WORKS Nederland
    http://www.vianetworks.nl
    ascheepersvianetworks.nl

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