forked from extern/shorewall_code
8e93d3b6ec
git-svn-id: https://shorewall.svn.sourceforge.net/svnroot/shorewall/trunk@2380 fbd18981-670d-0410-9b5c-8dc0c1a9a2bb
518 lines
19 KiB
XML
518 lines
19 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id="standalone">
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<!--$Id$-->
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<articleinfo>
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<title>Standalone 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>2005-07-12</pubdate>
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<copyright>
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<year>2002-2005</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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<section>
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<title>Introduction</title>
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<para>Setting up Shorewall on a standalone Linux system is very easy if
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you understand the basics and follow 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 most common configurations:</para>
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<itemizedlist>
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<listitem>
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<para>Linux system</para>
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</listitem>
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<listitem>
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<para>Single external IP address</para>
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</listitem>
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<listitem>
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<para>Connection through Cable Modem, DSL, ISDN, Frame Relay,
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dial-up... or connected to a LAN and you simply wish to protect your
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Linux system from other systems on that LAN.</para>
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</listitem>
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</itemizedlist>
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<section>
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<title>Requirements</title>
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<para>Shorewall requires that you have the iproute/iproute2 package
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installed (on RedHat, the package is called
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<emphasis>iproute</emphasis>). You can tell if this package is installed
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by the presence of an <emphasis role="bold">ip</emphasis> program on
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your firewall system. As root, you can use the <quote>which</quote>
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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>
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<title>Before you start</title>
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<para>I recommend that you read through the guide first 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 Windows system, you
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must save them as Unix files if your editor supports that option or
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you must run them through dos2unix before trying to use them.
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Similarly, if you copy a configuration file from your Windows hard
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drive to a floppy disk, you must run dos2unix against the copy before
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using it with Shorewall.</para>
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<simplelist>
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<member><ulink url="http://www.simtel.net/pub/pd/51438.html">Windows
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Version of dos2unix</ulink></member>
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<member><ulink
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url="http://www.megaloman.com/~hany/software/hd2u/">Linux Version of
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dos2unix</ulink></member>
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</simplelist>
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</caution>
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</section>
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<section>
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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"
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format="GIF" />.</para>
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</section>
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</section>
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<section>
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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> <emphasis
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role="underline">in addition to those described in the steps
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below</emphasis>. ADSL with PPTP is most commonly found in Europe, notably
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in Austria.</para>
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</section>
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<section>
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<title>Shorewall Concepts</title>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
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<para>The configuration files for Shorewall are contained in the directory
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<filename class="directory">/etc/shorewall</filename> -- for simple
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setups, you only need to deal with a few of these as described in this
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guide. After you have <ulink url="Install.htm">installed
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Shorewall</ulink>, <emphasis role="bold">download the <ulink
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url="http://www1.shorewall.net/pub/shorewall/Samples/">one-interface
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sample</ulink>, un-tar it (tar -zxvf one-interface.tgz) and and copy the
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files to /etc/shorewall (they will replace files with the same names that
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were placed in /etc/shorewall during Shorewall
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installation)</emphasis>.</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 <filename
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class="directory">/etc/shorewall</filename> directory is empty. This is
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intentional. The released configuration file skeletons may be found on
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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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<para>Note that you must copy <filename
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class="directory">/usr/share/doc/shorewall/default-config/shorewall.conf</filename>
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and /usr/share/doc/shorewall/default-config/modules to <filename
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class="directory">/etc/shorewall</filename> even if you do not modify
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those files.</para>
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</warning>
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<para>As each file is introduced, I suggest that you look through the
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actual file on your system -- each file contains detailed configuration
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instructions and default entries.</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 <emphasis>zones</emphasis>. In the one-interface sample
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configuration, only one zone is defined:</para>
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<informaltable>
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<tgroup cols="2">
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<thead>
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<row>
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<entry align="center">Name</entry>
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<entry align="center">Description</entry>
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</row>
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</thead>
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<tbody>
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<row>
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<entry>net</entry>
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<entry>The Internet</entry>
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</row>
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</tbody>
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</tgroup>
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</informaltable>
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<para>Shorewall zones are defined in <ulink
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url="Documentation.htm#Zones"><filename>/etc/shorewall/zones</filename></ulink>.</para>
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<para>Shorewall also recognizes the firewall system as its own zone - by
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default, the firewall itself is known as <emphasis
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role="bold">fw</emphasis>.</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 <ulink
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url="Documentation.htm#Policy"><filename>/etc/shorewall/policy</filename></ulink>
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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 <ulink
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url="Documentation.htm#Rules"><filename>/etc/shorewall/rules</filename></ulink>
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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
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<filename><filename>/etc/shorewall/rules</filename></filename> file. If no
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rule in that file matches the connection request then the first policy in
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<filename>/etc/shorewall/policy</filename> that matches the request is
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applied. If there is a <ulink url="shorewall_extension_scripts.htm">comon
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action</ulink> defined for the policy in
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<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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peformed before the action is applied.</para>
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<para>The <filename>/etc/shorewall/policy</filename> file included with
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the one-interface sample has the following policies:</para>
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<programlisting>#SOURCE ZONE DESTINATION ZONE POLICY LOG LEVEL LIMIT:BURST
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fw net ACCEPT
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net all DROP info
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all all REJECT info</programlisting>
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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 the firewall 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</para>
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</listitem>
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<listitem>
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<para>reject all other connection requests (Shorewall requires this
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catchall policy).</para>
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</listitem>
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</orderedlist>
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<para>At this point, edit your <filename>/etc/shorewall/policy</filename>
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and make any changes that you wish.</para>
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</section>
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<section>
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<title>External Interface</title>
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<para>The firewall has a single network interface. Where Internet
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connectivity is through a cable or DSL <quote>Modem</quote>, the
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<emphasis>External Interface</emphasis> will be the ethernet adapter
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(<emphasis role="bold">eth0</emphasis>) that is connected to that
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<quote>Modem</quote> <emphasis role="underline">unless</emphasis> you
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connect via <emphasis>Point-to-Point Protocol over Ethernet</emphasis>
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(PPPoE) or <emphasis>Point-to-Point Tunneling Protocol</emphasis> (PPTP)
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in which case the External Interface will be a <emphasis
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role="bold">ppp0</emphasis>. If you connect via a regular modem, your
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External Interface will also be <emphasis role="bold">ppp0</emphasis>. If
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you connect using ISDN, your external interface will be <emphasis
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role="bold">ippp0</emphasis>.</para>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
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<para>The Shorewall one-interface sample configuration assumes that the
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external interface is <emphasis role="bold">eth0</emphasis>. If your
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configuration is different, you will have to modify the sample
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/etc/shorewall/interfaces file accordingly. While you are there, you may
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wish to review the list of options that are specified for the interface.
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Some hints:</para>
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<tip>
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<para>If your external interface is <emphasis
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role="bold">ppp0</emphasis> or <emphasis role="bold">ippp0</emphasis>,
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you can replace the <quote>detect</quote> in the second column with
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<quote>-</quote>.</para>
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</tip>
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<tip>
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<para>If your external interface is <emphasis
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role="bold">ppp0</emphasis> or <emphasis role="bold">ippp0</emphasis> or
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if you have a static IP address, you can remove <quote>dhcp</quote> from
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the option list.</para>
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</tip>
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<tip>
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<para>If you specify <emphasis>nobogons</emphasis> for your external
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interface, you will want to check the <ulink url="errata.htm">Shorewall
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Errata</ulink> periodically for updates to the
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<filename>/usr/share/shorewall/bogons file</filename>.</para>
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</tip>
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</section>
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<section>
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<title>IP Addresses</title>
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<para>RFC 1918 reserves several <emphasis>Private</emphasis> IP address
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ranges for use in private networks:</para>
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<programlisting>10.0.0.0 - 10.255.255.255
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172.16.0.0 - 172.31.255.255
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192.168.0.0 - 192.168.255.255</programlisting>
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<para>These addresses are sometimes referred to as
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<emphasis>non-routable</emphasis> because the Internet backbone routers
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will not forward a packet whose destination address is reserved by RFC
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1918. In some cases though, ISPs are assigning these addresses then using
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<emphasis>Network Address Translation</emphasis> to rewrite packet headers
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when forwarding to/from the internet.</para>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
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<para>Before starting Shorewall, you should look at the IP address of your
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external interface and if it is one of the above ranges, you should remove
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the <quote>norfc1918</quote> option from the entry in
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<filename>/etc/shorewall/interfaces</filename>.</para>
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</section>
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<section>
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<title>Enabling other Connections</title>
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<para>Shorewall 2.0.0 and later include a collection of actions that can
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be used to quickly allow or deny services. You can find a list of the
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actions included in your version of Shorewall in the file
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<filename>/usr/share/shorewall/actions.std</filename>.</para>
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<para>Those actions that allow a connection begin with
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<quote>Allow</quote>.</para>
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<para>If you wish to enable connections from the internet to your firewall
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and you find an appropriate <quote>Allow</quote> action in
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<filename>/etc/shorewall/actions.std</filename>, the general format of a
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rule in <filename>/etc/shorewall/rules</filename> is:</para>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
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<<emphasis>action</emphasis>> net fw</programlisting>
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<example>
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<title>You want to run a Web Server and a POP3 Server on your firewall
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system:</title>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
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AllowWeb net fw
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AllowPOP3 net fw</programlisting>
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</example>
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<para>You may also choose to code your rules directly without using the
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pre-defined actions. This will be necessary in the event that there is not
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a pre-defined action that meets your requirements. In that case the
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general format of a rule in <filename>/etc/shorewall/rules</filename>
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is:</para>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
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ACCEPT net fw <emphasis><protocol></emphasis> <emphasis><port></emphasis></programlisting>
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<example>
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<title>You want to run a Web Server and a POP3 Server on your firewall
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system:</title>
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<para><programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
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ACCEPT net fw tcp 80
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ACCEPT net fw tcp 110</programlisting></para>
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</example>
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<para>If you don't know what port and protocol a particular application
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uses, see <ulink url="ports.htm">here</ulink>.</para>
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<important>
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<para>I don't recommend enabling telnet to/from the internet because it
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uses clear text (even for login!). If you want shell access to your
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firewall from the internet, use SSH:</para>
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<programlisting>#ACTION SOURCE DESTINATION PROTO DEST PORT(S)
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AllowSSH net fw </programlisting>
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</important>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
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<para>At this point, edit <filename>/etc/shorewall/rules</filename> to add
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other connections as desired.</para>
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</section>
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<section>
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<title>Starting and Stopping Your Firewall</title>
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<para><inlinegraphic fileref="images/BD21298_.gif" format="GIF" /></para>
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<para>The <ulink url="Install.htm">installation procedure</ulink>
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configures your system to start Shorewall at system boot but beginning
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with Shorewall version 1.3.9 startup is disabled so that your system won't
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try to start Shorewall before configuration is complete. Once you have
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completed configuration of your firewall, you can enable Shorewall startup
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by removing the file
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<filename>/etc/shorewall/startup_disabled</filename>.</para>
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<important>
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<para><emphasis role="bold">Users of the .deb package must edit
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<filename>/etc/default/shorewall</filename> and set
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<quote>startup=1</quote>.</emphasis></para>
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</important>
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<important>
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<para><emphasis role="bold">If you are running Shorewall 2.1.3 or later,
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you must enable startup by editing /etc/shorewall/shorewall.conf and
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setting STARTUP_ENABLED=Yes.</emphasis></para>
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</important>
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<para>The firewall is started using the <quote><command>shorewall
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start</command></quote> command and stopped using
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<quote><command>shorewall stop</command></quote>. When the firewall is
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stopped, routing is enabled on those hosts that have an entry in
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<filename><ulink
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url="Documentation.htm#Routestopped">/etc/shorewall/routestopped</ulink></filename>.
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A running firewall may be restarted using the <quote><command>shorewall
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restart</command></quote> command. If you want to totally remove any trace
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of Shorewall from your Netfilter configuration, use
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<quote><command>shorewall clear</command></quote>.</para>
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<warning>
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<para>If you are connected to your firewall from the internet, do not
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issue a <quote><command>shorewall stop</command></quote> command unless
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you have added an entry for the IP address that you are connected from
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to <ulink
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url="Documentation.htm#Routestopped"><filename>/etc/shorewall/routestopped</filename></ulink>.
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Also, I don't recommend using <quote><command>shorewall
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restart</command></quote>; it is better to create an <emphasis><ulink
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url="configuration_file_basics.htm#Configs">alternate
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configuration</ulink></emphasis> and test it using the <ulink
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url="starting_and_stopping_shorewall.htm"><quote><command>shorewall
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try</command></quote> command</ulink>.</para>
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</warning>
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</section>
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<section>
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<title>Additional Recommended Reading</title>
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<para>I highly recommend that you review the <ulink
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url="configuration_file_basics.htm">Common Configuration File Features
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page</ulink> -- it contains helpful tips about Shorewall features than
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make administering your firewall easier.</para>
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</section>
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<appendix>
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<title>Revision History</title>
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<para><revhistory>
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<revision>
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<revnumber>1.8</revnumber>
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<date>2005-07-12</date>
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<authorinitials>TE</authorinitials>
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<revremark>Change reference to rfc1918 to bogons.</revremark>
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</revision>
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<revision>
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<revnumber>1.7</revnumber>
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<date>2004-02-16</date>
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<authorinitials>TE</authorinitials>
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<revremark>Move /etc/shorewall/rfc1918 to
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/usr/share/shorewall.</revremark>
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</revision>
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<revision>
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<revnumber>1.6</revnumber>
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<date>2004-02-05</date>
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<authorinitials>TE</authorinitials>
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<revremark>Update for Shorewall 2.0</revremark>
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</revision>
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<revision>
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<revnumber>1.5</revnumber>
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|
|
|
<date>2004-01-05</date>
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|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Standards Changes</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.4</revnumber>
|
|
|
|
<date>2003-12-30</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Add tip about /etc/shorewall/rfc1918 updates.</revremark>
|
|
</revision>
|
|
|
|
<revision>
|
|
<revnumber>1.3</revnumber>
|
|
|
|
<date>2003-11-15</date>
|
|
|
|
<authorinitials>TE</authorinitials>
|
|
|
|
<revremark>Initial Docbook Conversion</revremark>
|
|
</revision>
|
|
</revhistory></para>
|
|
</appendix>
|
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</article> |