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104 lines
5.5 KiB
XML
104 lines
5.5 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- $Id$ -->
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<article id="two-interface">
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<articleinfo>
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<title>Basic Two-Interface Firewall</title>
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<author>
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<firstname>Tom</firstname>
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<surname>Eastep</surname>
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</author>
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<pubdate>2003/12/24</pubdate>
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<copyright>
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<year>2003</year>
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<holder>Thomas M. Eastep</holder>
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</copyright>
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<legalnotice>
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<para>
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Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled <quote><ulink url="copyright.htm" type="">GNU Free Documentation License</ulink></quote>.
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</para>
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</legalnotice>
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</articleinfo>
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<section>
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<title>Introduction</title>
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<para>
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Setting up a Linux system as a firewall for a small network is a fairly straight-forward task if you understand the basics and follow the documentation.
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</para>
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<para>
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This guide doesn't attempt to acquaint you with all of the features of Shorewall. It rather focuses on what is required to configure Shorewall in its most common configuration:
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</para>
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<itemizedlist mark="bullet" spacing="compact">
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<listitem>
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<para>
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Linux system used as a firewall/router for a small local network.
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</para>
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</listitem>
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<listitem>
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<para>
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<emphasis role="bold">Single public IP address.</emphasis> If you have more than one public IP address, this is not the guide you want -- see the <ulink url="shorewall_setup_guide.htm">Shorewall Setup Guide</ulink> instead.
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</para>
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</listitem>
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<listitem>
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<para>
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Internet connection through cable modem, DSL, ISDN, Frame Relay, dial-up ...
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</para>
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</listitem>
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</itemizedlist>
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<para>
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Here is a schematic of a typical installation:
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</para>
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<figure label="1">
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<title>Common two interface firewall configuration</title>
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<mediaobject>
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<imageobject>
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<imagedata fileref="images/basics.png" format="PNG" align="center" width="4in" />
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</imageobject>
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</mediaobject>
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</figure>
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<note>
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<title>Shorewall and <trademark>Mandrake</trademark> 9.0+</title>
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<para>
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If you are running Shorewall under <trademark>Mandrake</trademark> 9.0 or later, you can easily configure the above setup using the <trademark>Mandrake</trademark> <quote>Internet Connection Sharing</quote> applet. From the <emphasis><interface>Mandrake Control Center</interface></emphasis>, select <quote><guimenuitem>Network</guimenuitem> & <guisubmenu>Internet</guisubmenu></quote> then <quote><interface>Connection Sharing</interface></quote>.
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</para>
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<para>
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Note however, that the Shorewall configuration produced by <emphasis>Mandrake Internet Connection Sharing</emphasis> is strange and is apt to confuse you if you use the rest of this documentation (it has two local zones; <varname>loc</varname> and <varname>masq</varname> where <varname>loc</varname> is empty; this conflicts with this documentation which assumes a single local zone <varname>loc</varname>). We therefore recommend that once you have set up this sharing that you uninstall the <trademark>Mandrake</trademark> Shorewall RPM and install the one from the <ulink url="download.htm">download</ulink> page then follow the instructions in this Guide.
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</para>
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</note>
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<para>
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Shorewall requires that you have the <command>iproute</command>/<command>iproute2</command> package installed (on <trademark>RedHat</trademark>, the package is called <command>iproute</command>). You can tell if this package is installed by the presence of an <command>ip</command> program on your firewall system. As <literal>root</literal>, you can use the <command>which</command> command to check for this program:
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<programlisting>
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[root@gateway root]# which ip
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/sbin/ip
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[root@gateway root]#
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</programlisting>
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I recommend that you first read through the guide to familiarize yourself with what's involved then go back through it again making your configuration changes.
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</para>
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<caution>
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<para>
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If you edit your configuration files on a <trademark>Windows</trademark> system, you must save them as <trademark>Unix</trademark> files if your editor supports that option or you must run them through <command>dos2unix</command> before trying to use them. Similarly, if you copy a configuration file from your <trademark>Windows</trademark> hard drive to a floppy disk, you must run <command>dos2unix</command> against the copy before using it with Shorewall.
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<itemizedlist>
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<listitem>
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<para>
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<ulink url="http://www.simtel.net/pub/pd/51438.html"><trademark>Windows</trademark> Version of <command>dos2unix</command></ulink>
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</para>
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</listitem>
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<listitem>
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<para>
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<ulink url="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version of <command>dos2unix</command></ulink>
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</para>
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</listitem>
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</itemizedlist>
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</para>
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</caution>
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</section>
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<section>
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<title>PPTP/ADSL</title>
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<important>
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<para>
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If you have an <acronym>ADSL</acronym> Modem and you use <acronym>PPTP</acronym> to communicate with a server in that modem, you must make the changes recommended here in addition to those detailed below. <acronym>ADSL</acronym> with <acronym>PPTP</acronym> is most commonly found in Europe, notably in Austria.
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</para>
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</important>
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</section>
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</article>
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