shorewall_code/Shorewall-docs/two-interface.xml

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<article id="two-interface">
	<articleinfo>
		<title>Basic Two-Interface Firewall</title>
		<author>
      <firstname>Tom</firstname>
      <surname>Eastep</surname>
		</author>
    <pubdate>2003&#047;12&#047;24</pubdate>
		<copyright>
			<year>2003</year>
			<holder>Thomas M. Eastep</holder>
		</copyright>
		<legalnotice>
			<para>
			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>.
			</para>
		</legalnotice>
	</articleinfo>
	<section>
		<title>Introduction</title>
		<para>
		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.
		</para>
		<para>
		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:
		</para>
		<itemizedlist mark="bullet" spacing="compact">
			<listitem>
				<para>
				Linux system used as a firewall/router for a small local network.
				</para>
			</listitem>
			<listitem>
				<para>
				<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.
				</para>
			</listitem>
			<listitem>
				<para>
				Internet connection through cable modem, DSL, ISDN, Frame Relay, dial-up ...
				</para>
			</listitem>
		</itemizedlist>
		<para>
		Here is a schematic of a typical installation:
		</para>
		<figure label="1">
			<title>Common two interface firewall configuration</title>
			<mediaobject>
				<imageobject>
					<imagedata fileref="images/basics.png" format="PNG" align="center" width="4in" />
				</imageobject>
			</mediaobject>
		</figure>
		<note>
			<title>Shorewall and <trademark>Mandrake</trademark> 9.0&#043;</title>
			<para>
			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> &#038; <guisubmenu>Internet</guisubmenu></quote> then <quote><interface>Connection Sharing</interface></quote>.
			</para>
			<para>
			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.
			</para>
		</note>
		<para>
		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:
		<programlisting>
[root@gateway root]# which ip
/sbin/ip
[root@gateway root]#
		</programlisting>
		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.
		</para>
		<caution>
			<para>
			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.
			<itemizedlist>
				<listitem>
					<para>
						<ulink url="http://www.simtel.net/pub/pd/51438.html"><trademark>Windows</trademark> Version of <command>dos2unix</command></ulink>
					</para>
				</listitem>
				<listitem>
					<para>
						<ulink url="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux Version of <command>dos2unix</command></ulink>
					</para>
				</listitem>
			</itemizedlist>
			</para>
		</caution>
	</section>
	<section>
		<title>PPTP/ADSL</title>
		<important>
			<para>
			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.
			</para>
		</important>

	</section>
</article>