Creating java FTP client; problem with firewall and PASV mode

Discussion in 'Java' started by Jimmy Schmoe, Dec 10, 2003.

  1. Jimmy Schmoe

    Jimmy Schmoe Guest

    I've successfully created a nice little java FTP client (actual FTP
    <RFC959>, not the URL version Java supports by default <RFC1738>). I
    wrote it to support both PORT and PASV modes, and it works
    successfully as long as no firewall is between the client and server.
    The firewall blocks PORT communication, which is standard and
    expected. For some reason, though, all firewalls this has been tested
    with block the port assigned by the FTP server through the PASV
    command, even though the same setup works fine from MS command line
    FTP using PASV as well as other clients (tested with CuteFTP). Does
    anyone have any ideas why the socket opened with Java would be blocked
    while sockets opened with other programs aren't blocked? The firewall
    is reporting that the expected port is being blocked, even though it
    should be picking up the port to open when it sends the response to
    the PASV command through -- the java client does get the PASV response
    successfully, and seems to be attempting to open a socket on the
    correct port, as shown by the firewall. Is there any reason this
    should be happening, and what can I do to fix it?

    Thanks for any help given,

    Jimmy
     
    Jimmy Schmoe, Dec 10, 2003
    #1
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