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426 lines
16 KiB
XML
426 lines
16 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="Shorewall_Squid_Usage">
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<!--$Id$-->
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<articleinfo>
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<title>Using Shorewall with Squid</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>2005-05-19</pubdate>
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<copyright>
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<year>2003-2005</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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<para>This page covers Shorewall configuration to use with <ulink
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url="http://www.squid-cache.org">Squid</ulink> running as a Transparent
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Proxy or as a Manual Proxy.</para>
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<warning>
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<para>This documentation assumes that you are running Shorewall 2.0.0 or
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later.</para>
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</warning>
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<section>
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<title>Squid as a Transparent Proxy</title>
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<important>
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<para>This section gives instructions for transparent proxying of HTTP.
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HTTPS (normally TCP port 443) <emphasis role="bold">cannot</emphasis> be
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proxied transparently (stop and think about it for a minute; if HTTPS
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could be transparently proxied, then how secure would it be?).</para>
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</important>
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<caution>
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<para>Please observe the following general requirements:</para>
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<itemizedlist>
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<listitem>
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<para>In all cases, Squid should be configured to run as a transrent
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proxy as described at <ulink
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url="http://www.tldp.org/HOWTO/mini/TransparentProxy.html">http://www.tldp.org/HOWTO/mini/TransparentProxy.html</ulink>.</para>
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</listitem>
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<listitem>
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<para>Depending on your distribution, other Squid configuration
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changes may be required. These changes typically consist of:</para>
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<orderedlist>
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<listitem>
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<para>Adding an ACL that represents the clients on your local
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network.</para>
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<para>Example:</para>
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<programlisting>ACL my_networks src 192.168.1.0/24 192.168.2.0/24</programlisting>
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</listitem>
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<listitem>
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<para>Allowing HTTP access to that ACL.</para>
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<para>Example:</para>
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<programlisting>http_access allow my_networks</programlisting>
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</listitem>
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</orderedlist>
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<para>See your distribution's Squid documenation and <ulink
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url="http://www.squid-cache.org/">http://www.squid-cache.org/</ulink>
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for details.</para>
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<para>It is a good idea to get Squid working as a <link
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linkend="Manual">manual proxy</link> first before you try
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transparent proxying.</para>
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</listitem>
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<listitem>
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<para>The following instructions mention the files
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/etc/shorewall/start and /etc/shorewall/init -- if you don't have
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those files, siimply create them.</para>
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</listitem>
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<listitem>
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<para>When the Squid server is in the DMZ zone or in the local zone,
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that zone must be defined ONLY by its interface -- no
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/etc/shorewall/hosts file entries. That is because the packets being
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routed to the Squid server still have their original destination IP
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addresses.</para>
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</listitem>
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<listitem>
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<para>You must have iptables installed on your Squid server.</para>
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</listitem>
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</itemizedlist>
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</caution>
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<caution>
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<para>In the instructions below, only TCP Port 80 is opened from the
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system running Squid to the internet. If your users require browsing
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sites that use a port other than 80 (e.g.,
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http://www.domain.tld:<emphasis role="bold">8080</emphasis>) then you
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must open those ports as well.</para>
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</caution>
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</section>
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<section>
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<title>Configurations</title>
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<para>Three different configurations are covered:</para>
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<simplelist>
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<member>Squid (transparent) Running on the Firewall</member>
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<member>Squid (transparent) Running in the local Network</member>
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<member>Squid (transparent) Running in a DMZ</member>
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</simplelist>
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<section id="Firewall">
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<title>Squid (transparent) Running on the Firewall</title>
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<para>You want to redirect all local www connection requests EXCEPT
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those to your own http server (206.124.146.177) to a Squid transparent
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proxy running on the firewall and listening on port 3128. Squid will of
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course require access to remote web servers.</para>
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<para>In <filename>/etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL
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# PORT(S) DEST
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REDIRECT loc 3128 tcp www - !206.124.146.177
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ACCEPT fw net tcp www</programlisting>
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<para>There may be a requirement to exclude additional destination hosts
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or networks from being redirected. For example, you might also want
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requests destined for 130.252.100.0/24 to not be routed to Squid.</para>
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<para>If needed, you may just add the additional hosts/networks to the
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ORIGINAL DEST column in your REDIRECT rule.</para>
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<para><filename>/etc/shorewall/rules</filename>:<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL
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# PORT(S) DEST
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REDIRECT loc 3128 tcp www - !206.124.146.177,130.252.100.0/24</programlisting></para>
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</section>
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<section id="Local">
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<title>Squid (transparent) Running in the local network</title>
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<para>You want to redirect all local www connection requests to a Squid
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transparent proxy running in your local zone at 192.168.1.3 and
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listening on port 3128. Your local interface is eth1. There may also be
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a web server running on 192.168.1.3. It is assumed that web access is
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already enabled from the local zone to the internet.</para>
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<para>If you are running a Shorewall version earlier than 2.3.2 OR your
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kernel and/or iptables do not have <ulink
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url="Shorewall_and_Routing.html#RouteTarget">ROUTE target
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support</ulink> then:</para>
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<orderedlist>
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<listitem>
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<para>On your firewall system, issue the following command</para>
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<programlisting><command>echo 202 www.out >> /etc/iproute2/rt_tables</command></programlisting>
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</listitem>
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<listitem>
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<para>Create <filename>/etc/shorewall/addroutes</filename> as
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follows:</para>
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<programlisting><command>#!/bin/sh
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if [ -z "`ip rule list | grep www.out`" ] ; then
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ip rule add fwmark 0xCA table www.out # Note 0xCA = 202
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ip route add default via 192.168.1.3 dev eth1 table www.out
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ip route flush cache
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echo 0 > /proc/sys/net/ipv4/conf/eth1/send_redirects
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fi</command></programlisting>
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</listitem>
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<listitem>
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<para>Make <filename>/etc/shorewall/addroutes </filename>executable
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via:</para>
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<programlisting><command>chmod +x /etc/shorewall/addroutes</command></programlisting>
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</listitem>
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<listitem>
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<para>In /etc/shorewall/init, put:</para>
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<programlisting><command>run_and_save_command "/etc/shorewall/addroutes"</command></programlisting>
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</listitem>
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</orderedlist>
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<para>If you are running Shorewall 2.3.2 or later:</para>
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<orderedlist>
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<listitem>
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<para>Add this entry to your /etc/shorewall/providers file.</para>
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<programlisting>#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS
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Squid 1 202 - eth1 192.168.1.3 -</programlisting>
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</listitem>
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</orderedlist>
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<para>Regardless of your Shorewall version, you need the
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following:</para>
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<orderedlist>
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<listitem>
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<para>In <filename>/etc/shorewall/start</filename> add:</para>
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<programlisting><command>iptables -t mangle -A PREROUTING -i eth1 -s ! 192.168.1.3 -p tcp --dport 80 -j MARK --set-mark 202</command></programlisting>
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</listitem>
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<listitem>
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<para>In
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<filename><filename>/etc/shorewall/interfaces</filename></filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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loc eth1 detect <emphasis role="bold">routeback</emphasis> </programlisting>
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</listitem>
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<listitem>
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<para>In /etc/shorewall/rules:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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ACCEPT loc loc tcp www</programlisting>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>Alternativfely, you can have the following policy in place
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of the above rule.</para>
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<para><filename>/etc/shorewall/policy</filename></para>
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<programlisting>#SOURCE DESTINATION POLICY
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loc loc ACCEPT</programlisting>
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</listitem>
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</orderedlist>
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</listitem>
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<listitem>
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<para>On 192.168.1.3, arrange for the following command to be
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executed after networking has come up</para>
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<programlisting><command>iptables -t nat -A PREROUTING -i eth0 -d ! 192.168.1.3 -p tcp --dport 80 -j REDIRECT --to-ports 3128</command></programlisting>
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<para>If you are running RedHat on the server, you can simply
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execute the following commands after you have typed the iptables
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command above:</para>
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<programlisting><command>iptables-save > /etc/sysconfig/iptables
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chkconfig --level 35 iptables on</command></programlisting>
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</listitem>
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</orderedlist>
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</section>
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<section id="DMZ">
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<title>Squid (transparent) Running in the DMZ</title>
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<para>You have a single Linux system in your DMZ with IP address
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192.0.2.177. You want to run both a web server and Squid on that system.
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Your DMZ interface is eth1 and your local interface is eth2.</para>
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<para>If you are running a Shorewall version earlier than 2.3.2 OR your
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kernel and/or iptables do not have <ulink
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url="Shorewall_and_Routing.html#RouteTarget">ROUTE target
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support</ulink> then:</para>
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<orderedlist>
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<listitem>
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<para>On your firewall system, issue the following command</para>
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<programlisting><command>echo 202 www.out >> /etc/iproute2/rt_tables</command></programlisting>
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</listitem>
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<listitem>
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<para>Create <filename>/etc/shorewall/addroutes</filename> as
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follows:</para>
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<programlisting><command>#!/bin/sh
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if [ -z "`ip rule list | grep www.out`" ] ; then
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ip rule add fwmark 0xCA table www.out # Note 0xCA = 202
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ip route add default via 192.168.1.3 dev eth1 table www.out
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ip route flush cache
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echo 0 > /proc/sys/net/ipv4/conf/eth1/send_redirects
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fi</command></programlisting>
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</listitem>
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<listitem>
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<para>Make <filename>/etc/shorewall/addroutes</filename> executable
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via:</para>
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<programlisting><command>chmod +x /etc/shorewall/addroutes</command></programlisting>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/init</filename>, put:</para>
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<programlisting><command>run_and_save_command "/etc/shorewall/addroutes"</command></programlisting>
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</listitem>
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</orderedlist>
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<para>If you are running Shorewall 2.3.2 or later:</para>
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<orderedlist>
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<listitem>
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<para>Add this entry in
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<filename>/etc/shorewall/providers</filename>:</para>
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</listitem>
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</orderedlist>
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<blockquote>
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<programlisting>#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS
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Squid 1 202 - eth1 192.0.2.177 -
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</programlisting>
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</blockquote>
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<para>Regardless of your Shorewall version, you need the
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following:</para>
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<orderedlist>
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<listitem>
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<para>Do <emphasis role="bold">one</emphasis> of the
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following:</para>
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<orderedlist numeration="loweralpha">
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<listitem>
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<para>In <filename>/etc/shorewall/start</filename> add</para>
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<programlisting><command>iptables -t mangle -A PREROUTING -i eth2 -p tcp --dport 80 -j MARK --set-mark 202</command></programlisting>
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</listitem>
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<listitem>
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<para>Set MARK_IN_FORWARD_CHAIN=No in
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<filename>/etc/shorewall/shorewall.conf</filename> and add the
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following entry in
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<filename>/etc/shorewall/tcrules</filename>:</para>
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<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT
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202 eth2 0.0.0.0/0 tcp 80</programlisting>
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</listitem>
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<listitem>
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<para>Add the following entry in
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<filename>/etc/shorewall/tcrules</filename>:</para>
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<programlisting>#MARK SOURCE DESTINATION PROTOCOL PORT
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202:P eth2 0.0.0.0/0 tcp 80</programlisting>
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</listitem>
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</orderedlist>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/rules</filename>, you will
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need:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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ACCEPT loc dmz tcp 80
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ACCEPT dmz net tcp 80</programlisting>
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</listitem>
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<listitem>
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<para>On 192.0.2.177 (your Web/Squid server), arrange for the
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following command to be executed after networking has come up</para>
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<programlisting><command>iptables -t nat -A PREROUTING -i eth0 -d ! 192.0.2.177 -p tcp --dport 80 -j REDIRECT --to-ports 3128</command></programlisting>
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<para>If you are running RedHat/Fedora on the server, you can simply
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execute the following commands after you have typed the iptables
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command above:</para>
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<programlisting><command>iptables-save > /etc/sysconfig/iptables
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chkconfig --level 35 iptables on</command></programlisting>
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</listitem>
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</orderedlist>
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</section>
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</section>
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<section id="Manual">
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<title>Squid as a Manual Proxy</title>
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<para>Assume that Squid is running in zone SZ and listening on port SP;
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all web sites that are to be accessed through Squid are in the
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<quote>net</quote> zone. Then for each zone Z that needs access to the
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Squid server.</para>
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<para><filename>/etc/shorewall/rules</filename>:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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ACCEPT Z SZ tcp SP
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ACCEPT SZ net tcp 80,443</programlisting>
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<example>
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<title>Squid on the firewall listening on port 8080 with access from the
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<quote>loc</quote> zone:</title>
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<para><filename>/etc/shorewall/rules:</filename><programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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ACCEPT loc fw tcp 8080
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ACCEPT fw net tcp 80,443</programlisting></para>
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</example>
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</section>
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</article> |