forked from extern/shorewall_code
1269 lines
56 KiB
XML
1269 lines
56 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
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"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
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<article id="three-interface">
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<!--$Id$-->
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<articleinfo>
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<title>Three-Interface Firewall</title>
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<authorgroup>
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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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</authorgroup>
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<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2002-2009</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>Permission is granted to copy, distribute and/or modify this
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document under the terms of the GNU Free Documentation License, Version
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1.2 or any later version published by the Free Software Foundation; with
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no Invariant Sections, with no Front-Cover, and with no Back-Cover
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Texts. A copy of the license is included in the section entitled
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<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
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License</ulink></quote>.</para>
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</legalnotice>
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</articleinfo>
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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.4 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.4.0 then please see the documentation for that
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release.</emphasis></para>
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</caution>
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<section id="Intro">
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<title>Introduction</title>
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<para>Setting up a Linux system as a firewall for a small network with DMZ
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is a fairly straight-forward task if you understand the basics and follow
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the documentation.</para>
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<para>This guide doesn't attempt to acquaint you with all of the features
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of Shorewall. It rather focuses on what is required to configure Shorewall
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in one of its more popular configurations:</para>
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<itemizedlist>
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<listitem>
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<para>Linux system used as a firewall/router for a small local
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network.</para>
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</listitem>
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<listitem>
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<para>Single public IP address.</para>
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<note>
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<para>If you have more than one public IP address, this is not the
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guide you want -- see the <ulink
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url="shorewall_setup_guide.htm">Shorewall Setup Guide</ulink>
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instead.</para>
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</note>
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</listitem>
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<listitem>
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<para>DMZ connected to a separate Ethernet interface. The purpose of a
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DMZ is to isolate those servers that are exposed to the Internet from
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your local systems so that if one of those servers is compromised
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there is still a firewall between the hacked server and your local
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systems.</para>
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</listitem>
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<listitem>
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<para>Connection through DSL, Cable Modem, 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>Here is a schematic of a typical installation.</para>
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<figure id="Figure1">
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<title>schematic of a typical installation</title>
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<mediaobject>
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<imageobject>
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<imagedata align="center" fileref="images/dmz1.png" format="PNG"/>
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</imageobject>
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</mediaobject>
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</figure>
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<section id="Reqs">
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<title>Requirements</title>
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<para>Shorewall requires that you have the
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<command>iproute</command>/<command>iproute2</command> package installed
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(on <trademark>RedHat</trademark>, the package is called
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<command>iproute</command>). You can tell if this package is installed
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by the presence of an <command>ip</command> program on your firewall
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system. As <systemitem class="username">root</systemitem>, you can use
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the <command>which</command> command to check for this program:</para>
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<programlisting>[root@gateway root]# <command>which ip</command>
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/sbin/ip
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[root@gateway root]#</programlisting>
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</section>
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<section id="Before">
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<title>Before you start</title>
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<para>I recommend that you first read through the guide to familiarize
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yourself with what's involved then go back through it again making your
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configuration changes.</para>
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<caution>
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<para>If you edit your configuration files on a
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<trademark>Windows</trademark> system, you must save them as
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<trademark>Unix</trademark> files if your editor supports that option
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or you must run them through <command>dos2unix</command> before trying
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to use them. Similarly, if you copy a configuration file from your
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<trademark>Windows</trademark> hard drive to a floppy disk, you must
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run <command>dos2unix</command> against the copy before using it with
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Shorewall.</para>
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<itemizedlist>
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<listitem>
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<para><ulink
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url="http://www.sourceforge.net/projects/dos2unix">Windows Version
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of dos2unix</ulink></para>
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</listitem>
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<listitem>
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<para><ulink
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url="http://www.megaloman.com/%7Ehany/software/hd2u/">Linux
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Version of dos2unix</ulink></para>
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</listitem>
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</itemizedlist>
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</caution>
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</section>
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<section id="Conventions">
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<title>Conventions</title>
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<para>Points at which configuration changes are recommended are flagged
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with <inlinegraphic fileref="images/BD21298_.gif" format="GIF"/>.</para>
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<para>Configuration notes that are unique to Debian and it's derivatives
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are marked with <inlinegraphic fileref="images/openlogo-nd-25.png"
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format="GIF"/>.</para>
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</section>
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</section>
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<section id="PPTP">
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<title>PPTP/ADSL</title>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
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<para>If you have an ADSL Modem and you use PPTP to communicate with a
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server in that modem, you must make the <ulink
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url="PPTP.htm#PPTP_ADSL">changes recommended here</ulink> in addition to
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those detailed below. ADSL with PPTP is most commonly found in Europe,
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notably in Austria.</para>
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</section>
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<section id="Concepts">
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<title>Shorewall Concepts</title>
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<para>The configuration files for Shorewall are contained in the directory
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<filename>/etc/shorewall</filename> -- for simple setups, you will only
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need to deal with a few of these as described in this guide.</para>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
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<para>After you have installed Shorewall, locate the three-interface
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Sample configuration:</para>
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<orderedlist>
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<listitem>
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<para>If you installed using an RPM, the samples will be in the
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Samples/three-interfaces/ subdirectory of the Shorewall documentation
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directory. If you don't know where the Shorewall documentation
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directory is, you can find the samples using this command:</para>
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<programlisting>~# rpm -ql shorewall | fgrep three-interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/masq
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/policy
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/rules
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/zones
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~#</programlisting>
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<para>When running Shorewall 5.0.14 or later:</para>
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<programlisting>~# rpm -ql shorewall | fgrep three-interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/interfaces
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/policy
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/rules
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/snat
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/usr/share/doc/packages/shorewall/Samples/three-interfaces/zones
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~#</programlisting>
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</listitem>
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<listitem>
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<para>If you installed using the tarball, the samples are in the
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Samples/three-interfaces directory in the tarball.</para>
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</listitem>
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<listitem>
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<para>If you installed using a Shorewall 3.x .deb, the samples are in
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/usr/share/doc/shorewall/examples/three-interfaces. You must install
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the shorewall-doc package.</para>
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</listitem>
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<listitem>
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<para><graphic align="left" fileref="images/openlogo-nd-25.png"/>If
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you installed using a Shorewall 4.x .deb, the samples are in <emphasis
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role="bold"><filename
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class="directory">/usr/share/doc/shorewall/examples/three-interfaces</filename></emphasis>.
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You do not need the shorewall-doc package to have access to the
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samples.</para>
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<warning>
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<para><emphasis role="bold">Note to Debian Users</emphasis></para>
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<para>If you install using the .deb, you will find that your
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<filename class="directory">/etc/shorewall</filename> directory is
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empty. This is intentional. The released configuration file
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skeletons may be found on your system in the directory <filename
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class="directory">/usr/share/doc/shorewall/default-config</filename>.
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Simply copy the files you need from that directory to <filename
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class="directory">/etc/shorewall</filename> and modify the
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copies.</para>
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</warning>
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</listitem>
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</orderedlist>
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<para>As each file is introduced, I suggest that you look at the actual
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file on your system and that you look at the <ulink
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url="configuration_file_basics.htm#Manpages">man page</ulink> for that
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file. For example, to look at the man page for the
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<filename>/etc/shorewall/zones</filename> file, type <command>man
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shorewall-zones</command> at a shell prompt.</para>
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<para>Note: Beginning with Shorewall 4.4.20.1, there are versions of the
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sample files that are annotated with the corresponding manpage contents.
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These files have names ending in '.annotated'. You might choose to look at
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those files instead.</para>
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<para>Shorewall views the network where it is running as being composed of
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a set of zones. In the three-interface sample configuration, the following
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zone names are used:</para>
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<para><programlisting>#ZONE TYPE OPTIONS IN_OPTIONS OUT_OPTIONS
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fw firewall
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net ipv4
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loc ipv4
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dmz ipv4</programlisting>Zone names are defined in
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<filename>/etc/shorewall/zones</filename>.</para>
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<para>Note that Shorewall recognizes the firewall system as its own zone.
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When the /etc/shorewall/zones file is processed, he name of the firewall
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zone is stored in the shell variable <firstterm>$FW</firstterm> which may
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be used throughout the Shorewall configuration to refer to the firewall
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zone.</para>
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<para>Rules about what traffic to allow and what traffic to deny are
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expressed in terms of zones.</para>
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<itemizedlist>
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<listitem>
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<para>You express your default policy for connections from one zone to
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another zone in the <filename>/etc/shorewall/policy</filename>
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file.</para>
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</listitem>
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<listitem>
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<para>You define exceptions to those default policies in the
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<filename>/etc/shorewall/rules</filename> file.</para>
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</listitem>
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</itemizedlist>
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<para>For each connection request entering the firewall, the request is
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first checked against the <filename>/etc/shorewall/rules</filename> file.
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If no rule in that file matches the connection request then the first
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policy in <filename>/etc/shorewall/policy</filename> that matches the
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request is applied. If there is a <ulink
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url="shorewall_extension_scripts.htm">common action</ulink> defined for
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the policy in <filename>/etc/shorewall/actions</filename> or
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<filename>/usr/share/shorewall/actions.std</filename> then that action is
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performed before the action is applied. The purpose of the common action
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is two-fold:</para>
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<itemizedlist>
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<listitem>
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<para>It silently drops or rejects harmless common traffic that would
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otherwise clutter up your log — Broadcasts for example.</para>
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</listitem>
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<listitem>
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<para>If ensures that traffic critical to correct operation is allowed
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through the firewall — ICMP <emphasis>fragmentation-needed</emphasis>
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for example.</para>
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</listitem>
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</itemizedlist>
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<para>The <filename>/etc/shorewall/policy</filename> file included with
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the three-interface sample has the following policies:</para>
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<programlisting>#SOURCE DEST POLICY LOGLEVEL LIMIT
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loc net ACCEPT
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net all DROP info
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all all REJECT info</programlisting>
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<important>
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<para>In the three-interface sample, the line below is included but
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commented out. If you want your firewall system to have full access to
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servers on the Internet, uncomment that line.</para>
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<programlisting>#SOURCE DEST POLICY LOGLEVEL LIMIT
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$FW net ACCEPT</programlisting>
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</important>
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<para>The above policy will:</para>
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<orderedlist>
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<listitem>
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<para>allow all connection requests from your local network to the
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Internet</para>
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</listitem>
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<listitem>
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<para>drop (ignore) all connection requests from the Internet to your
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firewall or local network</para>
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</listitem>
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<listitem>
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<para>optionally accept all connection requests from the firewall to
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the Internet (if you uncomment the additional policy)</para>
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</listitem>
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<listitem>
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<para>reject all other connection requests.</para>
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</listitem>
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</orderedlist>
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<para>The word <firstterm>info</firstterm> in the LOG LEVEL column for the
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DROP and REJECT policies indicates that packets dropped or rejected under
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those policies should be <ulink url="shorewall_logging.html">logged at
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that level</ulink>.</para>
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<para>Some people want to consider their firewall to be part of their
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local network from a security perspective. If you want to do this, add
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these two policies:</para>
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<programlisting>#SOURCE DEST POLICY LOGLEVEL LIMIT
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loc $FW ACCEPT
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$FW loc ACCEPT</programlisting>
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<para>It is important to note that Shorewall policies (and rules) refer to
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<emphasis role="bold">connections</emphasis> and not packet flow. With the
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policies defined in the <filename
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class="directory">/etc/shorewall/policy</filename> file shown above,
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connections are allowed from the <emphasis>loc</emphasis> zone to the
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<emphasis>net</emphasis> zone even though connections are not allowed from
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the <emphasis>loc</emphasis> zone to the firewall itself.</para>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
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<para>At this point, edit your <filename>/etc/shorewall/policy</filename>
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file and make any changes that you wish.</para>
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</section>
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<section id="Interfaces">
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<title>Network Interfaces</title>
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<figure id="Figure2">
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<title>DMZ</title>
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<mediaobject>
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<imageobject>
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<imagedata align="center" fileref="images/dmz1.png" format="PNG"/>
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</imageobject>
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</mediaobject>
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</figure>
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<para>The firewall has three network interfaces. Where Internet
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connectivity is through a cable or DSL <quote>Modem</quote>, the External
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Interface will be the Ethernet adapter that is connected to that
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<quote>Modem</quote> (e.g., <filename class="devicefile">eth0</filename>)
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unless you connect via <emphasis>Point-to-Point Protocol</emphasis> over
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Ethernet (PPPoE) or <emphasis>Point-to-Point Tunneling Protocol</emphasis>
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(PPTP) in which case the External Interface will be a
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<literal>ppp</literal> interface (e.g., <filename
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class="devicefile">ppp0</filename>). If you connect via a regular modem,
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your External Interface will also be <filename
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class="devicefile">ppp0</filename>. If you connect using ISDN, you
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external interface will be <filename
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class="devicefile">ippp0</filename>.</para>
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<caution>
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<para>Be sure you know which interface is your external interface. Many
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hours have been spent floundering by users who have configured the wrong
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interface. If you are unsure, then as root type <command>ip route
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ls</command> at the command line. The device listed in the last
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(default) route should be your external interface.</para>
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<para>Example:</para>
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<programlisting>root@lists:~# ip route ls
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192.168.1.1 dev eth0 scope link
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192.168.2.2 dev tun0 proto kernel scope link src 192.168.2.1
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192.168.3.0/24 dev br0 proto kernel scope link src 192.168.3.254
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10.13.10.0/24 dev tun1 scope link
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192.168.2.0/24 via 192.168.2.2 dev tun0
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192.168.1.0/24 dev br0 proto kernel scope link src 192.168.1.254
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206.124.146.0/24 dev eth0 proto kernel scope link src 206.124.146.176
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10.10.10.0/24 dev tun1 scope link
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default via 206.124.146.254 dev <emphasis role="bold">eth0</emphasis>
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root@lists:~# </programlisting>
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<para>In that example, <filename class="devicefile">eth0</filename> is
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the external interface.</para>
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</caution>
|
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
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<para>I<emphasis role="bold">f your external interface is <filename
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class="devicefile">ppp0</filename> or <filename
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class="devicefile">ippp0</filename> then you will want to set
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<varname>CLAMPMSS=yes</varname> in
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<filename>/etc/shorewall/shorewall.conf</filename>.</emphasis></para>
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<para>Your Local Interface will be an Ethernet adapter (<filename
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class="devicefile">eth0</filename>, <filename
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class="devicefile">eth1</filename> or <filename
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class="devicefile">eth2</filename>) and will be connected to a hub or
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switch. Your local computers will be connected to the same switch (note:
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If you have only a single local system, you can connect the firewall
|
|
directly to the computer using a cross-over cable).</para>
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<para>Your DMZ Interface will also be an Ethernet adapter (<filename
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class="devicefile">eth0</filename>, <filename
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class="devicefile">eth1</filename> or <filename
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class="devicefile">eth2</filename>) and will be connected to a hub or
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switch. Your DMZ computers will be connected to the same switch (note: If
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you have only a single DMZ system, you can connect the firewall directly
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to the computer using a cross-over cable).</para>
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|
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<caution>
|
|
<para><emphasis role="bold">Do NOT connect multiple interfaces to the
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same hub or switch except for testing</emphasis>. You can test using
|
|
this kind of configuration if you specify the <emphasis
|
|
role="bold">arp_filter</emphasis> option or the <emphasis
|
|
role="bold">arp_ignore</emphasis> option in
|
|
<filename>/etc/shorewall/interfaces</filename> for all interfaces
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|
connected to the common hub/switch. <emphasis role="bold">Using such a
|
|
setup with a production firewall is strongly recommended
|
|
against</emphasis>.</para>
|
|
</caution>
|
|
|
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<caution>
|
|
<para><emphasis role="bold">Do not configure a default route on your
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internal and DMZ interfaces.</emphasis> Your firewall should have
|
|
exactly one default route via your ISP's Router.</para>
|
|
</caution>
|
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|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>The Shorewall three-interface sample configuration assumes that the
|
|
external interface is <filename class="devicefile">eth0</filename>, the
|
|
local interface is <filename class="devicefile">eth1</filename> and the
|
|
DMZ interface is <filename class="devicefile">eth2</filename>. If your
|
|
configuration is different, you will have to modify the sample
|
|
<filename>/etc/shorewall/interfaces</filename> file accordingly. While you
|
|
are there, you may wish to review the list of options that are specified
|
|
for the interfaces. Some hints:</para>
|
|
|
|
<tip>
|
|
<para>If your external interface is <filename
|
|
class="devicefile">ppp0</filename> or <filename
|
|
class="devicefile">ippp0</filename>, you can replace the
|
|
<quote>detect</quote> in the second column with <quote>-</quote>
|
|
(without the quotes).</para>
|
|
</tip>
|
|
|
|
<tip>
|
|
<para>If your external interface is <filename
|
|
class="devicefile">ppp0</filename> or <filename
|
|
class="devicefile">ippp0</filename> or if you have a static IP address,
|
|
you can remove <quote>dhcp</quote> from the option list.</para>
|
|
</tip>
|
|
</section>
|
|
|
|
<section id="Addresses">
|
|
<title>IP Addresses</title>
|
|
|
|
<para>Before going further, we should say a few words about Internet
|
|
Protocol (IP) addresses. Normally, your ISP will assign you a single
|
|
Public IP address. This address may be assigned via the Dynamic Host
|
|
Configuration Protocol (DHCP) or as part of establishing your connection
|
|
when you dial in (standard modem) or establish your PPP connection. In
|
|
rare cases, your ISP may assign you a static IP address; that means that
|
|
you configure your firewall's external interface to use that address
|
|
permanently. Regardless of how the address is assigned, it will be shared
|
|
by all of your systems when you access the Internet. You will have to
|
|
assign your own addresses for your internal network (the local and DMZ
|
|
Interfaces on your firewall plus your other computers). RFC 1918 reserves
|
|
several Private IP address ranges for this purpose:</para>
|
|
|
|
<programlisting>10.0.0.0 - 10.255.255.255
|
|
172.16.0.0 - 172.31.255.255
|
|
192.168.0.0 - 192.168.255.255</programlisting>
|
|
|
|
<para>You will want to assign your local addresses from one sub-network or
|
|
subnet and your DMZ addresses from another subnet. For our purposes, we
|
|
can consider a subnet to consists of a range of addresses <systemitem
|
|
class="ipaddress">x.y.z.0</systemitem> - <systemitem
|
|
class="ipaddress">x.y.z.255</systemitem>. Such a subnet will have a Subnet
|
|
Mask of <systemitem class="netmask">255.255.255.0</systemitem>. The
|
|
address <systemitem class="ipaddress">x.y.z.0</systemitem> is reserved as
|
|
the Subnet Address and <systemitem class="netmask">x.y.z.255</systemitem>
|
|
is reserved as the Subnet Broadcast Address. In Shorewall, a subnet is
|
|
described using Classless InterDomain Routing (CIDR) notation with
|
|
consists of the subnet address followed by <varname>/24</varname>. The
|
|
<varname>24</varname> refers to the number of consecutive <quote>1</quote>
|
|
bits from the left of the subnet mask.</para>
|
|
|
|
<table id="Table1">
|
|
<title>Example sub-network</title>
|
|
|
|
<tgroup cols="2">
|
|
<colspec align="left"/>
|
|
|
|
<tbody>
|
|
<row>
|
|
<entry>Range:</entry>
|
|
|
|
<entry><systemitem class="ipaddress">10.10.10.0</systemitem> -
|
|
<systemitem class="ipaddress">10.10.10.255</systemitem></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>Subnet Address:</entry>
|
|
|
|
<entry><systemitem
|
|
class="ipaddress">10.10.10.0</systemitem></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>Broadcast Address:</entry>
|
|
|
|
<entry><systemitem
|
|
class="ipaddress">10.10.10.255</systemitem></entry>
|
|
</row>
|
|
|
|
<row>
|
|
<entry>CIDR Notation:</entry>
|
|
|
|
<entry><systemitem
|
|
class="ipaddress">10.10.10.0/24</systemitem></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<para>It is conventional to assign the internal interface either the first
|
|
usable address in the subnet (<systemitem
|
|
class="ipaddress">10.10.10.1</systemitem> in the above example) or the
|
|
last usable address (<systemitem
|
|
class="ipaddress">10.10.10.254</systemitem>).</para>
|
|
|
|
<para>One of the purposes of subnetting is to allow all computers in the
|
|
subnet to understand which other computers can be communicated with
|
|
directly. To communicate with systems outside of the subnetwork, systems
|
|
send packets through a gateway (router).</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>Your local computers (Local Computers 1 & 2) should be
|
|
configured with their default gateway set to the IP address of the
|
|
firewall's internal interface and your DMZ computers (DMZ Computers 1
|
|
& 2) should be configured with their default gateway set to the IP
|
|
address of the firewall's DMZ interface.</para>
|
|
|
|
<para>The foregoing short discussion barely scratches the surface
|
|
regarding subnetting and routing. If you are interested in learning more
|
|
about IP addressing and routing, I highly recommend <quote>IP
|
|
Fundamentals: What Everyone Needs to Know about Addressing &
|
|
Routing</quote>, Thomas A. Maufer, Prentice-Hall, 1999, ISBN
|
|
0-13-975483-0.</para>
|
|
|
|
<para>The remainder of this guide will assume that you have configured
|
|
your network as shown here:</para>
|
|
|
|
<figure id="Figure3">
|
|
<title>DMZ</title>
|
|
|
|
<mediaobject>
|
|
<imageobject>
|
|
<imagedata fileref="images/dmz2.png"/>
|
|
</imageobject>
|
|
|
|
<caption><para>The default gateway for the DMZ computers would be
|
|
<systemitem class="ipaddress">10.10.11.254</systemitem> and the
|
|
default gateway for the Local computers would be <systemitem
|
|
class="ipaddress">10.10.10.254</systemitem>.</para> <warning>
|
|
<para>Your ISP might assign your external interface an RFC 1918
|
|
address. If that address is in the <systemitem
|
|
class="ipaddress">10.10.10.0/24</systemitem> subnet then you will
|
|
need to select a DIFFERENT RFC 1918 subnet for your local network
|
|
and if it is in the <systemitem
|
|
class="ipaddress">10.10.11.0/24</systemitem> subnet then you will
|
|
need to select a different RFC 1918 subnet for your DMZ.</para>
|
|
</warning></caption>
|
|
</mediaobject>
|
|
</figure>
|
|
</section>
|
|
|
|
<section id="SNAT">
|
|
<title>IP Masquerading (SNAT)</title>
|
|
|
|
<para>The addresses reserved by RFC 1918 are sometimes referred to as
|
|
non-routable because the Internet backbone routers don't forward packets
|
|
which have an RFC-1918 destination address. When one of your local systems
|
|
(let's assume local computer 1) sends a connection request to an Internet
|
|
host, the firewall must perform Network Address Translation (NAT). The
|
|
firewall rewrites the source address in the packet to be the address of
|
|
the firewall's external interface; in other words, the firewall makes it
|
|
look as if the firewall itself is initiating the connection. This is
|
|
necessary so that the destination host will be able to route return
|
|
packets back to the firewall (remember that packets whose destination
|
|
address is reserved by RFC 1918 can't be routed across the Internet). When
|
|
the firewall receives a return packet, it rewrites the destination address
|
|
back to 10.10.10.1 and forwards the packet on to local computer 1.</para>
|
|
|
|
<para>On Linux systems, the above process is often referred to as IP
|
|
Masquerading and you will also see the term Source Network Address
|
|
Translation (SNAT) used. Shorewall follows the convention used with
|
|
Netfilter: <itemizedlist>
|
|
<listitem>
|
|
<para><emphasis>Masquerade</emphasis> describes the case where you
|
|
let your firewall system automatically detect the external interface
|
|
address.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis>SNAT</emphasis> refers to the case when you
|
|
explicitly specify the source address that you want outbound packets
|
|
from your local network to use.</para>
|
|
</listitem>
|
|
</itemizedlist> In Shorewall, both Masquerading and SNAT are configured
|
|
with entries in the <filename
|
|
class="directory">/etc/shorewall/</filename><filename>masq</filename> file
|
|
(<filename>/etc/shorewall/snat</filename> when running Shorewall 5.0.14 or
|
|
later).</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>If your external firewall interface is <filename
|
|
class="devicefile">eth0</filename> then you do not need to modify the file
|
|
provided with the sample. Otherwise, edit <filename
|
|
class="directory">/etc/shorewall/</filename><filename>masq</filename> or
|
|
<filename>/etc/shorewall/snat</filename> and change it to match your
|
|
configuration.</para>
|
|
|
|
<para>If, in spite of all advice to the contrary, you are using this guide
|
|
and want to use one-to-one NAT or Proxy ARP for your DMZ, you will need to
|
|
modify the SOURCE column to list just your local interface (10.10.10.0/24
|
|
in the above example).</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>If your external <acronym>IP</acronym> is static then, if you are
|
|
running Shorewall 5.0.13 or earlier, you can enter our static IP in the
|
|
third column in the <filename
|
|
class="directory">/etc/shorewall/</filename><filename>masq</filename>
|
|
entry if you like although your firewall will work fine if you leave that
|
|
column empty (Masquerade). Entering your static <acronym>IP</acronym> in
|
|
column 3 (SNAT) makes the processing of outgoing packets a little more
|
|
efficient.</para>
|
|
|
|
<para>When running Shorewall 5.0.14 or later, the rule in
|
|
/etc/shorewall/snat must be change from a MASQUERADE rule to an SNAT
|
|
rule.</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO PORT
|
|
<emphasis role="bold">SNAT(<replaceable>static-ip</replaceable>)</emphasis> ...</programlisting>
|
|
|
|
<graphic align="left" fileref="images/openlogo-nd-25.png"/>
|
|
|
|
<para><emphasis role="bold">If you are using the Debian package, please
|
|
check your <filename>shorewall.conf</filename> file to ensure that the
|
|
following is set correctly; if it is not, change it appropriately:
|
|
</emphasis><itemizedlist>
|
|
<listitem>
|
|
<para><varname>IP_FORWARDING=On</varname></para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
</section>
|
|
|
|
<section id="Logging">
|
|
<title>Logging</title>
|
|
|
|
<para>Shorewall does not maintain a log itself but rather relies on your
|
|
<ulink url="shorewall_logging.htm">system's logging configuration</ulink>.
|
|
The following <ulink url="manpages/shorewall.html">commands</ulink> rely
|
|
on knowing where Netfilter messages are logged:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><command>shorewall show log</command> (Displays the last 20
|
|
Netfilter log messages)</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><command>shorewall logwatch</command> (Polls the log at a
|
|
settable interval</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><command>shorewall dump</command> (Produces an extensive report
|
|
for inclusion in Shorewall problem reports)</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para>It is important that these commands work properly because when you
|
|
encounter connection problems when Shorewall is running, the first thing
|
|
that you should do is to look at the Netfilter log; with the help of
|
|
<ulink url="FAQ.htm#faq17">Shorewall FAQ 17</ulink>, you can usually
|
|
resolve the problem quickly.</para>
|
|
|
|
<para>The Netfilter log location is distribution-dependent:</para>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Debian and its derivatives log Netfilter messages to
|
|
<filename>/var/log/kern.log</filename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Recent <trademark>SuSE/OpenSuSE</trademark> releases come
|
|
preconfigured with syslog-ng and log netfilter messages to
|
|
<filename>/var/log/firewall</filename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>For other distributions, Netfilter messages are most commonly
|
|
logged to <filename>/var/log/messages</filename>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>If you are running a distribution that logs netfilter messages to a
|
|
log other than <filename>/var/log/messages</filename>, then modify the
|
|
LOGFILE setting in <filename>/etc/shorewall/shorewall.conf</filename> to
|
|
specify the name of your log.</para>
|
|
|
|
<important>
|
|
<para>The LOGFILE setting does not control where the Netfilter log is
|
|
maintained -- it simply tells the /sbin/<filename>shorewall</filename>
|
|
utility where to find the log.</para>
|
|
</important>
|
|
</section>
|
|
|
|
<section id="Modules">
|
|
<title>Kernel Module Loading</title>
|
|
|
|
<para>Beginning in Shorewall 4.4.7,
|
|
<filename>/etc/shorewall/shorewall.conf</filename> contains a
|
|
LOAD_HELPERS_ONLY option which is set to <option>Yes</option> in the
|
|
samples. This causes Shorewall to attempt to load the modules listed in
|
|
<filename>/usr/share/shorewall/helpers</filename>. In addition, it sets
|
|
<emphasis role="bold">sip_direct_media=0</emphasis> when loading the
|
|
nf_conntrack_sip module. That setting is somewhat less secure than
|
|
<emphasis role="bold">sip_direct_media=1</emphasis>, but it generally
|
|
makes VOIP through the firewall work much better.</para>
|
|
|
|
<para>The modules in <filename>/usr/share/shorewall/helpers</filename> are
|
|
those that are not autoloaded. If your kernel does not support module
|
|
autoloading and you want Shorewall to attempt to load all netfilter
|
|
modules that it might require, then set LOAD_HELPERS_ONLY=No. That will
|
|
cause Shorewall to try to load the modules listed in
|
|
<filename>/usr/share/shorewall/modules</filename>. That file does not set
|
|
<emphasis role="bold">sip_direct_media=0</emphasis>.</para>
|
|
|
|
<para>If you need to modify either
|
|
<filename>/usr/share/shorewall/helpers</filename> or
|
|
<filename>/usr/share/shorewall/modules</filename> then copy the file to
|
|
<filename>/etc/shorewall</filename> and modify the copy.</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>Modify the setting of LOAD_HELPER_ONLY as necessary.</para>
|
|
</section>
|
|
|
|
<section id="DNAT">
|
|
<title>Port Forwarding (DNAT)</title>
|
|
|
|
<para>One of your goals will be to run one or more servers on your DMZ
|
|
computers. Because these computers have RFC-1918 addresses, it is not
|
|
possible for clients on the Internet to connect directly to them. It is
|
|
rather necessary for those clients to address their connection requests to
|
|
your firewall who rewrites the destination address to the address of your
|
|
server and forwards the packet to that server. When your server responds,
|
|
the firewall automatically performs SNAT to rewrite the source address in
|
|
the response.</para>
|
|
|
|
<para>The above process is called <emphasis>Port Forwarding</emphasis> or
|
|
<emphasis>Destination Network Address Translation</emphasis> (DNAT). You
|
|
configure port forwarding using DNAT rules in the <filename
|
|
class="directory">/etc/shorewall/</filename><filename>rules</filename>
|
|
file.</para>
|
|
|
|
<para>The general form of a simple port forwarding rule in <filename
|
|
class="directory">/etc/shorewall/</filename><filename>rules</filename> is:
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
DNAT net dmz:<emphasis><server local IP address></emphasis>[:<emphasis><server port></emphasis>] <emphasis><protocol></emphasis> <emphasis><port></emphasis></programlisting>
|
|
If you don't specify the <emphasis><varname><server
|
|
port></varname></emphasis>, it is assumed to be the same as
|
|
<emphasis><varname><port></varname></emphasis>.</para>
|
|
|
|
<important>
|
|
<para>Be sure to add your rules after the line that reads <emphasis
|
|
role="bold">SECTION NEW.</emphasis></para>
|
|
</important>
|
|
|
|
<example id="Example1">
|
|
<title>You run a Web Server on DMZ Computer 2 and you want to forward
|
|
incoming TCP port 80 to that system</title>
|
|
|
|
<para><programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
Web(DNAT) net dmz:10.10.11.2
|
|
Web(ACCEPT) loc dmz:10.10.11.2</programlisting><itemizedlist>
|
|
<listitem>
|
|
<para>Entry 1 forwards port 80 from the Internet.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Entry 2 allows connections from the local network.</para>
|
|
</listitem>
|
|
</itemizedlist> Several important points to keep in mind:<itemizedlist>
|
|
<listitem>
|
|
<para>When you are connecting to your server from your local
|
|
systems, you must use the server's internal IP address
|
|
(<systemitem class="ipaddress">10.10.11.2</systemitem>) or you
|
|
must use DNAT from the loc zone as well (see below).</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT ORIGDEST
|
|
Web(DNAT) loc dmz:10.10.11.2 - - - <replaceable>external-ip-address</replaceable></programlisting>
|
|
|
|
<para>where <replaceable>external-ip-address</replaceable> is the
|
|
IP address of the firewall's external interface.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Many ISPs block incoming connection requests to port 80. If
|
|
you have problems connecting to your web server, try the following
|
|
rule and try connecting to port 5000 (e.g., connect to
|
|
<literal>http://w.x.y.z:5000 where w.x.y.z</literal> is your
|
|
external IP).<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT ORIGDEST
|
|
DNAT net dmz:10.10.11.2:80 tcp 5000</programlisting></para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you want to be able to access your server from the local
|
|
network using your external address, then if you have a static
|
|
external IP you can replace the loc->dmz rule above
|
|
with:<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT ORIGDEST
|
|
DNAT loc dmz:10.10.11.2 tcp 80 - <emphasis><external IP></emphasis></programlisting>If
|
|
you have a dynamic IP then you must ensure that your external
|
|
interface is up before starting Shorewall and you must code the
|
|
rule as follows (assume that your external interface is <filename
|
|
class="devicefile">eth0</filename>):</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT SPORT ORIGDEST
|
|
DNAT loc dmz:10.10.11.2 tcp 80 - &eth0</programlisting>
|
|
|
|
<para>'&eth0' expands to the IP address of eth0 (see <ulink
|
|
url="configuration_file_basics.htm#AddressVariables">this
|
|
article</ulink>).</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>If you want to access your server from the DMZ using your
|
|
external IP address, see <ulink url="FAQ.htm#faq2a">FAQ
|
|
2a</ulink>.</para>
|
|
</listitem>
|
|
</itemizedlist></para>
|
|
</example>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>At this point, add the DNAT and ACCEPT rules for your
|
|
servers.</para>
|
|
|
|
<important>
|
|
<para>When testing DNAT rules like those shown above, you must test from
|
|
a client OUTSIDE YOUR FIREWALL (in the 'net' zone). You cannot test
|
|
these rules from inside the firewall!</para>
|
|
|
|
<para>For DNAT troubleshooting tips, <ulink url="FAQ.htm#faq1a">see FAQs
|
|
1a and 1b</ulink>.</para>
|
|
</important>
|
|
</section>
|
|
|
|
<section id="DNS">
|
|
<title>Domain Name Server (DNS)</title>
|
|
|
|
<para>Normally, when you connect to your ISP, as part of getting an IP
|
|
address your firewall's <emphasis>Domain Name Service</emphasis> (DNS)
|
|
resolver will be automatically configured (e.g., the
|
|
<filename>/etc/resolv.conf</filename> file will be written).
|
|
Alternatively, your ISP may have given you the IP address of a pair of DNS
|
|
name servers for you to manually configure as your primary and secondary
|
|
name servers. It is your responsibility to configure the resolver in your
|
|
internal systems. You can take one of two approaches: <itemizedlist>
|
|
<listitem>
|
|
<para>You can configure your internal systems to use your ISP's name
|
|
servers. If your ISP gave you the addresses of their servers or if
|
|
those addresses are available on their web site, you can configure
|
|
your internal systems to use those addresses. If that information
|
|
isn't available, look in <filename>/etc/resolv.conf</filename> on
|
|
your firewall system -- the name servers are given in
|
|
<quote>nameserver</quote> records in that file.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><inlinegraphic fileref="images/BD21298_.gif"
|
|
format="GIF"/></para>
|
|
|
|
<para>You can configure a <emphasis>Caching Name Server</emphasis>
|
|
on your firewall or in your DMZ. <trademark>Red Hat</trademark> has
|
|
an RPM for a caching name server (which also requires the
|
|
'<command>bind</command>' RPM) and for Bering users, there is
|
|
<filename>dnscache.lrp</filename>. If you take this approach, you
|
|
configure your internal systems to use the caching name server as
|
|
their primary (and only) name server. You use the internal IP
|
|
address of the firewall (<systemitem
|
|
class="ipaddress">10.10.10.254</systemitem> in the example above)
|
|
for the name server address if you choose to run the name server on
|
|
your firewall. To allow your local systems to talk to your caching
|
|
name server, you must open port 53 (both UDP and TCP) from the local
|
|
network to the server; you do that by adding the rules in
|
|
<filename>/etc/shorewall/rules</filename>.</para>
|
|
</listitem>
|
|
</itemizedlist> If you run the name server on the firewall:
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
DNS(ACCEPT) loc $FW
|
|
DNS(ACCEPT) dmz $FW </programlisting> Run name server on DMZ
|
|
computer 1: <programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
DNS(ACCEPT) loc dmz:10.10.11.1
|
|
DNS(ACCEPT) $FW dmz:10.10.11.1 </programlisting></para>
|
|
|
|
<para>In the rules shown above, <quote>DNS</quote>(ACCEPT)is an example of
|
|
a <emphasis>defined macro</emphasis>. Shorewall includes a number of
|
|
defined macros and <ulink url="Macros.html">you can add your own</ulink>.
|
|
To see the list of macros included with your version of Shorewall, run the
|
|
command <command>shorewall show
|
|
<filename>macros</filename></command>.</para>
|
|
|
|
<para>You don't have to use defined macros when coding a rule in
|
|
<filename>/etc/shorewall/rules</filename>. The first example above (name
|
|
server on the firewall) could also have been coded as follows:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
ACCEPT loc $FW tcp 53
|
|
ACCEPT loc $FW udp 53
|
|
ACCEPT dmz $FW tcp 53
|
|
ACCEPT dmz $FW udp 53 </programlisting>
|
|
|
|
<para>In cases where Shorewall doesn't include a defined macro to meet
|
|
your needs, you can either define the macro yourself or you can simply
|
|
code the appropriate rules directly. <ulink url="ports.html">This
|
|
page</ulink> can be of help if you don't know the protocol and port
|
|
involved.</para>
|
|
|
|
<caution>
|
|
<para>The Shorewall-provided macros assume that the service is using its
|
|
standard port and will not work with a service listening on a
|
|
non-standard port.</para>
|
|
</caution>
|
|
</section>
|
|
|
|
<section id="Open">
|
|
<title>Other Connections</title>
|
|
|
|
<para>The three-interface sample includes the following rule:
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
DNS(ACCEPT) $FW net </programlisting>That rule allow DNS access
|
|
from your firewall and may be removed if you commented out the line in
|
|
<filename>/etc/shorewall/policy</filename> allowing all connections from
|
|
the firewall to the Internet.</para>
|
|
|
|
<para>The sample also includes: <programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
SSH(ACCEPT) loc $FW
|
|
SSH(ACCEPT) loc dmz </programlisting>Those rules allow you to run
|
|
an SSH server on your firewall and in each of your DMZ systems and to
|
|
connect to those servers from your local systems.</para>
|
|
|
|
<para>If you wish to enable other connections between your systems, the
|
|
general format for using a defined macro is: <programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
<<emphasis>macro</emphasis>>(ACCEPT) <emphasis><source zone> <destination zone></emphasis></programlisting></para>
|
|
|
|
<para>The general format when not using a defined macro
|
|
is:<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
ACCEPT <emphasis><source zone> <destination zone> <protocol> <port> </emphasis></programlisting></para>
|
|
|
|
<example id="Example2">
|
|
<title>You want to run a publicly-available DNS server on your firewall
|
|
system</title>
|
|
|
|
<para>Using defined macros:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
DNS(ACCEPT) net $FW</programlisting>
|
|
|
|
<para>Not using defined macros:</para>
|
|
|
|
<programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
ACCEPT net $FW tcp 53
|
|
ACCEPT net $FW udp 53 </programlisting>
|
|
|
|
<para>Those rules would of course be in addition to the rules listed
|
|
above under "If you run the name server on your firewall".</para>
|
|
</example>
|
|
|
|
<para>If you don't know what port and protocol a particular application
|
|
uses, <ulink url="ports.htm">look here</ulink>.</para>
|
|
|
|
<important>
|
|
<para>I don't recommend enabling telnet to/from the Internet because it
|
|
uses clear text (even for login!). If you want shell access to your
|
|
firewall from the Internet, use SSH: <programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
SSH(ACCEPT) net $FW</programlisting></para>
|
|
</important>
|
|
|
|
<para><inlinegraphic fileref="images/leaflogo.gif" format="GIF"/> Bering
|
|
users will want to add the following two rules to be compatible with
|
|
Jacques's Shorewall configuration: <programlisting>#ACTION SOURCE DEST PROTO DPORT
|
|
ACCEPT loc $FW udp 53
|
|
ACCEPT net $FW tcp 80 </programlisting><itemizedlist>
|
|
<listitem>
|
|
<para>Entry 1 allows the DNS Cache to be used.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Entry 2 allows the <quote>weblet</quote> to work.</para>
|
|
</listitem>
|
|
</itemizedlist><inlinegraphic fileref="images/BD21298_.gif"
|
|
format="GIF"/></para>
|
|
|
|
<para>Now modify <filename>/etc/shorewall/rules</filename> to add or
|
|
remove other connections as required.</para>
|
|
</section>
|
|
|
|
<section id="Other">
|
|
<title>Some Things to Keep in Mind</title>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para><emphasis role="bold">You cannot test your firewall from the
|
|
inside</emphasis>. Just because you send requests to your firewall
|
|
external IP address does not mean that the request will be associated
|
|
with the external interface or the <quote>net</quote> zone. Any
|
|
traffic that you generate from the local network will be associated
|
|
with your local interface and will be treated as loc->fw
|
|
traffic.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">IP addresses are properties of systems,
|
|
not of interfaces</emphasis>. It is a mistake to believe that your
|
|
firewall is able to forward packets just because you can ping the IP
|
|
address of all of the firewall's interfaces from the local network.
|
|
The only conclusion you can draw from such pinging success is that the
|
|
link between the local system and the firewall works and that you
|
|
probably have the local system's default gateway set correctly.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">All IP addresses configured on firewall
|
|
interfaces are in the $FW (fw) zone</emphasis>. If 192.168.1.254 is
|
|
the IP address of your internal interface then you can write
|
|
<quote><emphasis role="bold">$FW:192.168.1.254</emphasis></quote> in a
|
|
rule but you may not write <quote><emphasis
|
|
role="bold">loc:192.168.1.254</emphasis></quote>. Similarly, it is
|
|
nonsensical to add 192.168.1.254 to the <emphasis
|
|
role="bold">loc</emphasis> zone using an entry in
|
|
<filename>/etc/shorewall/hosts</filename>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Reply packets do NOT automatically follow
|
|
the reverse path of the one taken by the original request</emphasis>.
|
|
All packets are routed according to the routing table of the host at
|
|
each step of the way. This issue commonly comes up when people install
|
|
a Shorewall firewall parallel to an existing gateway and try to use
|
|
DNAT through Shorewall without changing the default gateway of the
|
|
system receiving the forwarded requests. Requests come in through the
|
|
Shorewall firewall where the destination IP address gets rewritten but
|
|
replies go out unmodified through the old gateway.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para><emphasis role="bold">Shorewall itself has no notion of inside
|
|
or outside</emphasis>. These concepts are embodied in how Shorewall is
|
|
configured.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section id="Starting">
|
|
<title>Starting and Stopping Your Firewall</title>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>The <ulink url="Install.htm">installation procedure</ulink>
|
|
configures your system to start Shorewall at system boot but startup is
|
|
disabled so that your system won't try to start Shorewall before
|
|
configuration is complete. Once you have completed configuration of your
|
|
firewall, you can enable Shorewall startup by editing
|
|
<filename>/etc/shorewall/shorewall.conf</filename> and setting
|
|
STARTUP_ENABLED=Yes.<graphic align="left"
|
|
fileref="images/openlogo-nd-25.png"/><important>
|
|
<para>Users of the <filename>.deb</filename> package must edit
|
|
<filename>/etc/default/shorewall</filename> and set
|
|
<varname>startup=1</varname>.</para>
|
|
</important></para>
|
|
|
|
<para>While you are editing <filename>shorewall.conf</filename>, it is a
|
|
good idea to check the value of the SUBSYSLOCK option. You can find a
|
|
description of this option by typing 'man shorewall.conf' at a shell
|
|
prompt and searching for SUBSYSLOCK</para>
|
|
|
|
<para>The firewall is started using the <command>shorewall start</command>
|
|
command and stopped using <command>shorewall stop</command>. When the
|
|
firewall is stopped, routing is enabled on those hosts that have an entry
|
|
in <filename><ulink
|
|
url="manpages/shorewall-stoppedrules.html">/etc/shorewall/stoppedrules</ulink></filename>
|
|
(<ulink
|
|
url="manpages/shorewall-routestopped.html"><filename>/etc/shorewall/routestopped</filename></ulink>
|
|
on Shorewall 4.5.7 and earlier). A running firewall may be restarted using
|
|
the <command>shorewall reload</command> command. If you want to totally
|
|
remove any trace of Shorewall from your Netfilter configuration, use
|
|
<command>shorewall clear</command>.</para>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF"/></para>
|
|
|
|
<para>The three-interface sample assumes that you want to enable routing
|
|
to/from <filename class="devicefile">eth1</filename> (your local network)
|
|
and <filename class="devicefile">eth2</filename> (DMZ) when Shorewall is
|
|
stopped. If these two interfaces don't connect to your local network and
|
|
DMZ or if you want to enable a different set of hosts, modify
|
|
<filename>/etc/shorewall/routestopped</filename> accordingly. <warning>
|
|
<para>If you are connected to your firewall from the Internet, do not
|
|
issue a <quote><command>shorewall stop</command></quote> command
|
|
unless you have either:</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>Used ADMINISABSENTMINDED=Yes in
|
|
<filename>/etc/shorewall/shorewall.conf</filename>; or</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>added an entry for the <acronym>IP</acronym> address that
|
|
you are connected from to <filename
|
|
class="directory">/etc/shorewall/</filename><filename>routestopped</filename>.</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>Also, I don't recommend using <quote><command>shorewall
|
|
reload</command></quote>; it is better to create an alternate
|
|
configuration and test it using the <quote><command>shorewall
|
|
try</command></quote> command.</para>
|
|
</warning></para>
|
|
|
|
<para>The firewall will start after your network interfaces have been
|
|
brought up. This leaves a small window between the time that the network
|
|
interface are working and when the firewall is controlling connections
|
|
through those interfaces. If this is a concern, you can close that window
|
|
by installing the <ulink url="Shorewall-init.html">Shorewall Init
|
|
Package</ulink>.</para>
|
|
</section>
|
|
|
|
<section id="Trouble">
|
|
<title>If it Doesn't Work</title>
|
|
|
|
<itemizedlist>
|
|
<listitem>
|
|
<para>Re-check each of the items flagged with a red arrow
|
|
above.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Check your <ulink
|
|
url="shorewall_logging.html">log</ulink>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Check the <ulink url="troubleshoot.htm">Troubleshooting
|
|
Guide</ulink>.</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>Check the <ulink url="FAQ.htm">FAQ</ulink>.</para>
|
|
</listitem>
|
|
</itemizedlist>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Disabling your existing Firewall</title>
|
|
|
|
<para>Before starting Shorewall for the first time, it's a good idea to
|
|
stop your existing firewall. On older Redhat/CentOS/Fedora:</para>
|
|
|
|
<programlisting><command>service iptables stop</command></programlisting>
|
|
|
|
<para>On recent Fedora systems that run systemd, the command is:</para>
|
|
|
|
<programlisting><command>systemctl stop iptables.service</command></programlisting>
|
|
|
|
<para>If you are running SuSE, use Yast or Yast2 to stop
|
|
SuSEFirewall.</para>
|
|
|
|
<para>On other systems that use a classic SysV init system:</para>
|
|
|
|
<programlisting><command>/etc/init.d/iptables stop</command></programlisting>
|
|
|
|
<para>Once you have Shorewall running to your satisfaction, you should
|
|
totally disable your existing firewall. On older
|
|
Redhat/CentOS/Fedora:</para>
|
|
|
|
<programlisting><command>chkconfig --del iptables</command></programlisting>
|
|
|
|
<para>On Debian systems:</para>
|
|
|
|
<programlisting><command>update-rc.d iptables disable</command></programlisting>
|
|
|
|
<para>On recent Fedora system running systemd:</para>
|
|
|
|
<programlisting><command>systemctl disable iptables.service</command></programlisting>
|
|
|
|
<para><inlinegraphic fileref="images/BD21298_.gif"/></para>
|
|
|
|
<para>At this point, disable your existing firewall service.</para>
|
|
</section>
|
|
|
|
<section id="Reading">
|
|
<title>Additional Recommended Reading</title>
|
|
|
|
<para>I highly recommend that you review the <ulink
|
|
url="configuration_file_basics.htm">Common Configuration File
|
|
Features</ulink> page -- it contains helpful tips about Shorewall features
|
|
than make administering your firewall easier. Also, <ulink
|
|
url="starting_and_stopping_shorewall.htm">Operating Shorewall and
|
|
Shorewall Lite</ulink> contains a lot of useful operational hints.</para>
|
|
</section>
|
|
</article>
|