NAME
    Net::DNAT - Psuedo Layer7 Packet Processer

SYNOPSIS
      use Net::DNAT;

      run Net::DNAT <settings...>;

DESCRIPTION
    This module is intended to be used for testing applications designed for
    load balancing systems. It listens on specified ports and forwards the
    incoming connections to the appropriate remote applications. The remote
    application can be on a separate machine or on the same machine
    listening on a different port and/or address.

PEER SOCKET SPOOF
    This implementation does not actually translate the destination address
    in the packet headers and resend the packet, like true DNAT does. It is
    implemented like a port forwarding proxy. When a client connects, a new
    socket is made to the remote application and the connection is tunnelled
    to/from the client. This causes the peer side of the socket to appear to
    the remote application like it is coming from the Net::DNAT box instead
    of the real client. This peer modification side effect is usually fine
    for testing and developmental purposes, though.

HTTP
    If you do not care about where the hits on your web server are coming
    from, then you do not need to worry about this section. If the remote
    application is the Apache 1.3.x web server, ( see
    http://httpd.apache.org/ ), then the Apache::DNAT module can be used to
    correctly and seemlessly UnDNATify this peer munging described above. If
    mod_perl is enabled for Apache, then add this line to its httpd.conf:

      PerlModule Apache::DNAT
      PerlInitHandler Apache::DNAT

    If you cannot do this, (because it is a web server other than Apache, or
    you do not have mod_perl enabled, or you do not have access to the web
    server, or you just do not want the CPU overhead to fix the peer back to
    normal, or for whatever reason), then it will still function fine. Just
    the server logs will be inaccurate and the CGI programs will run with
    the wrong environment variables pertaining to the peer (i.e.,
    REMOTE_ADDR and REMOTE_PORT).

EXAMPLE CONFIGURATION
    HARDWARE:

      \  |     |  /
       \_|_____|_/
       /         \
      |           |
      | INTERNET  |
      |           |
       \_________/
            |
            |
      ======|========= Firewall ================
            |
       _____|_____ Public Interface  (x.x.x.x)
      |           |
      | Net::DNAT |
      |___________|
         |         Private Interface (10.0.0.1)
         |
         |   _________________________
         \__| Apache::DNAT (10.0.0.2) |
         |  |_________________________|
         |
         |   _________________________
      H  \__| Apache::DNAT (10.0.0.3) |
      U  |  |_________________________|
      B  |
         |   _________________________
         \__| Apache::DNAT (10.0.0.4) |
         |  |_________________________|
         |
         |   _________________________
         \__| Apache::DNAT (10.0.0.5) |
            |_________________________|

    SOFTWARE:

      #!/usr/bin/perl
      # Program: dnat.pl
      # Run this at startup on the box with both
      # the public and the private interfaces.

      use strict;
      use Net::DNAT;

      my $pools = {
        main => [ "10.0.0.2", "10.0.0.3" ],
        banner => "10.0.0.4",
        devel =>  "10.0.0.5:8080",
      };

      my $site2pool = {
        "site.com"     => "main",
        "www.site.com" => "main",
        "banner.site.com" => "banner",
        "dev.site.com" => "devel",
      };

      run Net::DNAT
        port => 80,
        pools => $pools,
        default_pool => "main",
        host_switch_table => $site2pool,
        ;

EXAMPLES
    See demo/* from the distribution for some more examples.

TODO
      Support for HTTP/1.1 protocol conversion to 1.0 protocol and back again.
      Support for HTTP/1.1 KeepAlive timeout and KeepAliveRequests.
      Support for SSL protocol conversion to plain text.
      Support for html error pages for internal errors like Server outages.
      Support for error logs.
      Support for access logs.
      Support for CVS protocol.
      Support for FTP protocol.
      Support for OOB channel data correctly.
      Support for DNS protocol.
      Support for periodic service checks (Net::Ping)
        to disable and enable forwarding.

LAYER
      More information on network layers:

      http://uwsg.iu.edu/usail/network/nfs/network_layers.html

COPYRIGHT
      Copyright (C) 2002,
      Rob Brown, rob@roobik.com

      This package may be distributed under the same terms as Perl itself.

      All rights reserved.

SEE ALSO
     L<Apache::DNAT>,
     L<Net::Server>,
     L<IO::Multiplex>