forked from extern/shorewall_code
472 lines
20 KiB
XML
472 lines
20 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="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><?dbtimestamp format="Y/m/d"?></pubdate>
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<copyright>
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<year>2003-2008</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 <quote>
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<ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink>
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</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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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 4.0 and
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later. If you are running a version of Shorewall earlier than Shorewall
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4.0.0 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="Transparent">
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<title>Squid as a Transparent (Interception) 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
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transparent proxy as described at <ulink
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url="http://wiki.squid-cache.org/SquidFaq/InterceptionProxy">http://wiki.squid-cache.org/SquidFaq/InterceptionProxy</ulink>.</para>
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<para>The bottom line of that article is that if you are running
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<emphasis role="bold">Squid 2.6 or later</emphasis>, then you simply
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need to add the word <firstterm>transparent</firstterm> to your
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http_port specification:</para>
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<programlisting>http_port 3128 transparent</programlisting>
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<para>In <emphasis role="bold">earlier Squid versions</emphasis>,
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you need to set several options:</para>
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<programlisting>http_port 3128
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httpd_accel_host virtual
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httpd_accel_port 80
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httpd_accel_with_proxy on
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httpd_accel_uses_host_header on</programlisting>
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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 documentation 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 file
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/etc/shorewall/start - if you don't have that file, simply create
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it.</para>
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</listitem>
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<listitem>
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<para>When the Squid server is in the local zone, that zone must be
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defined ONLY by its interface -- no /etc/shorewall/hosts file
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entries. That is because the packets being routed to the Squid
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server still have their original destination IP 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 id="Configurations">
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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
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of 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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ACCEPT $FW net tcp www
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REDIRECT loc 3128 tcp www - !206.124.146.177
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</programlisting>
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<para>There may be a requirement to exclude additional destination
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hosts or networks from being redirected. For example, you might also
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want requests destined for 130.252.100.0/24 to not be routed to
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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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<para>People frequently ask <emphasis>How can I exclude certain
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internal systems from using the proxy? I want to allow those systems
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to go directly to the net</emphasis>.</para>
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<para>Suppose that you want to exclude 192.168.1.5 and 192.168.1.33
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from the proxy. Your rules would then be:</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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ACCEPT $FW net tcp www
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REDIRECT loc:!192.168.1.5,192.168.1.33\
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3128 tcp www - !206.124.146.177,130.252.100.0/24
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ACCEPT loc net tcp www</programlisting>
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<para>The last rule may be omitted if your loc->net policy is
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ACCEPT.</para>
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<para>In some cases (when running an LTSP server on the Shorewall
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system), you might want to transparently proxy web connections that
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originate on the firewall itself. This requires care to ensure that
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Squid's own web connections are not proxied.</para>
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<para>First, determine the user id that Squid is running under:</para>
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<programlisting>gateway:/etc/shorewall# <emphasis role="bold">ps aux | fgrep -i squid | fgrep -v fgrep</emphasis>
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root 10085 0.0 0.0 23864 700 ? Ss Apr22 0:00 /usr/sbin/squid -D -YC
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<emphasis role="bold">proxy</emphasis> 10088 0.0 0.9 40512 19192 ? S Apr22 10:58 <emphasis
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role="bold">(squid)</emphasis> -D -YC
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gateway:/etc/shorewall# </programlisting>
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<para>In this case, the proxy process <emphasis
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role="bold">(squid)</emphasis> is running under the <emphasis
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role="bold">proxy</emphasis> user Id. We add these rules:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S) SOURCE ORIGINAL RATE USER/
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# PORT(S) DEST LIMIT GROUP
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ACCEPT $FW net tcp www
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REDIRECT $FW 3128 tcp www - - - <emphasis
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role="bold"> !proxy</emphasis></programlisting>
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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
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Squid 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
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be a web server running on 192.168.1.3. It is assumed that web access
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is already enabled from the local zone to the Internet.</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 loose,notrack</programlisting>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/mangle</filename> add:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST
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# PORT(S)
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MARK(202):P eth1:!192.168.1.3 0.0.0.0/0 tcp 80</programlisting>
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<para>Corresponding /etc/shorewall/tcrules entries are:</para>
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<programlisting>#MARK SOURCE DEST PROTO DEST
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# PORT(S)
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202:P eth1:!192.168.1.3 0.0.0.0/0 tcp 80</programlisting>
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</listitem>
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<listitem>
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<para>In <filename> <filename>/etc/shorewall/interfaces</filename>
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</filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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loc eth1 detect <emphasis role="bold">routeback,routefilter=0,logmartians=0</emphasis> </programlisting>
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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 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
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system.</para>
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</section>
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<section>
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<title>Simple Configuration</title>
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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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DNAT loc dmz:192.0.2.177:3128 tcp 80 - !192.0.2.177</programlisting>
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</section>
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<section>
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<title>More Complex configuration</title>
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<para>Assume that the dmz is connected through eth2 and that your
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local lan interfaces through eth1</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 - eth2 192.0.2.177 loose,notrack</programlisting>
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</listitem>
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<listitem>
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<para>In <filename>/etc/shorewall/mangle</filename> add:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST
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# PORT(S)
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MARK(202):P eth1 0.0.0.0/0 tcp 80</programlisting>
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<para>Corresponding /etc/shorewall/tcrules entries are:</para>
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<programlisting>#MARK SOURCE DEST PROTO DEST
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# PORT(S)
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202:P eth1 0.0.0.0/0 tcp 80</programlisting>
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</listitem>
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<listitem>
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<para>In <filename> <filename>/etc/shorewall/interfaces</filename>
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</filename>:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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loc eth2 detect <emphasis role="bold">routefilter=0,logmartians=0</emphasis> </programlisting>
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</listitem>
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<listitem>
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<para>On 172.0.2.177, 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 192.0.2.177 -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>
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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 id="Example1">
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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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<section id="TPROXY">
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<title>Squid3 as a Transparent Proxy with TPROXY</title>
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<para>Shorewall 4.5.4 contains support for TPROXY. TPROXY differs from
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REDIRECT in that it does not modify the IP header and requires Squid 3 or
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later. Because the IP header stays intact, TPROXY requires policy routing
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to direct the packets to the proxy server running on the firewall. This
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approach requires TPROXY support in your kernel and iptables and Squid 3.
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See <ulink
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url="http://wiki.squid-cache.org/Features/Tproxy4">http://wiki.squid-cache.org/Features/Tproxy4</ulink>.</para>
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<note>
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<para>Support for the TPROXY action in shorewall-tcrules(5) and the
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<option>local</option> option in shorewall-providers(5) has been
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available since Shoreall 4.4.7. That support required additional rules
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to be added in the 'start' extention script to make it work reliably.
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Beginning with Shorewall 4.6.0, TPROXY in <ulink
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url="manpages/shorewall-tcrules.html">shorewall-tcrules</ulink>(5) and
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in <ulink
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url="manpages/shorewall-mangle.html">shorewall-mangle</ulink>(5) work as
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described here.</para>
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</note>
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<para>The following configuration works with Squid running on the firewall
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itself (assume that Squid is listening on port 3129 for TPROXY
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connections).</para>
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<para><filename>/etc/shorewall/interfaces:</filename></para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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- lo - -</programlisting>
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<para><filename>/etc/shorewall/providers</filename>:</para>
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<programlisting>#NAME NUMBER MARK DUPLICATE INTERFACE GATEWAY OPTIONS COPY
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Tproxy 1 - - lo - tproxy</programlisting>
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<note>
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<para>Notice that the MARK, DUPLICATE and GATEWAY columns are empty and
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that the only option is <option>tproxy</option>.</para>
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</note>
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<para><filename>/etc/shorewall/mangle</filename> (assume loc interface is
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eth1 and net interface is eth0):</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST SOURCE
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# PORT(S) PORT(S)
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DIVERT eth0 0.0.0.0/0 tcp - 80
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TPROXY(3129) eth1 0.0.0.0/0 tcp 80</programlisting>
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<para>Corresponding <filename>/etc/shorewall/tcrules</filename>
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are:</para>
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<programlisting><emphasis role="bold">FORMAT 2</emphasis>
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#MARK SOURCE DEST PROTO DEST SOURCE
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# PORT(S) PORT(S)
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DIVERT eth0 0.0.0.0/0 tcp - 80
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TPROXY(3129) eth1 0.0.0.0/0 tcp 80</programlisting>
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<para>The DIVERT rules are used to avoid unnecessary invocation of TPROXY
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for request packets after the connection is established and to direct
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response packets back to Squid3.</para>
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<note>
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<para>If you run a web server on the Shorewall system that also listens
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on port 80, then you need to exclude it from TPROXY. Suppose that your
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web server listens on 192.0.2.144; then:</para>
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<programlisting><emphasis role="bold">FORMAT 2</emphasis>
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#MARK SOURCE DEST PROTO DEST SOURCE
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# PORT(S) PORT(S)
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DIVERT eth0 0.0.0.0/0 tcp - 80
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TPROXY(3129) eth1 !192.0.2.144 tcp 80 -</programlisting>
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</note>
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<para>/etc/shorewall/rules:</para>
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<programlisting>#ACTION SOURCE DEST PROTO DEST PORT(S)
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ACCEPT loc $FW tcp 80
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ACCEPT $FW net tcp 80</programlisting>
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<para><filename>/etc/squid3/squid.conf</filename>:</para>
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<programlisting>...
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http_port 3129 tproxy
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...</programlisting>
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<important>
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<para>If you use TPROXY with both IPv4 and IPv6, then both your local
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hosts and the gateway must have the same DNS view. If a client resolves
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a website URL to an IPv6 address and the server can only resolve to an
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IPv4 address, then Squid will attempt to connect to the IPv4 address
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using the local client's IPv6 address. That clearly doesn't work.</para>
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</important>
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</section>
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</article>
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