shorewall_code/Shorewall-docs/GenericTunnels.xml
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<article id="GenericTunnels">
<!--$Id$-->
<articleinfo>
<title>Generic Tunnels</title>
<authorgroup>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate>2003-08-09</pubdate>
<copyright>
<year>2001</year>
<year>2002</year>
<year>2003</year>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<para>Shorewall includes built-in support for a wide range of VPN solutions.
If you have need for a tunnel type that does not have explicit support, you
can generally describe the tunneling software using <quote>generic tunnels</quote>.</para>
<section>
<title>Bridging two Masqueraded Networks</title>
<para>Suppose that we have the following situation:</para>
<graphic fileref="images/TwoNets1.png" />
<para>We want systems in the 192.168.1.0/24 subnetwork to be able to
communicate with the systems in the 10.0.0.0/8 network. This is
accomplished through use of the /etc/shorewall/tunnels file, the
/etc/shorewall/policy file and the /etc/shorewall/tunnel script that is
included with Shorewall.</para>
<para>Suppose that you have tunneling software that uses two different
protocols:</para>
<orderedlist numeration="loweralpha">
<listitem>
<para>TCP port 1071</para>
</listitem>
<listitem>
<para>GRE (Protocol 47)</para>
</listitem>
<listitem>
<para>The tunnel interface on system A is <quote>tun0</quote> and the
tunnel interface on system B is also <quote>tun0</quote>.</para>
</listitem>
</orderedlist>
<para>On each firewall, you will need to declare a zone to represent the
remote subnet. We&#39;ll assume that this zone is called <quote>vpn</quote>
and declare it in /etc/shorewall/zones on both systems as follows.</para>
<informaltable>
<tgroup cols="3">
<thead>
<row>
<entry align="center">ZONE</entry>
<entry align="center">DISPLAY</entry>
<entry align="center">COMMENTS</entry>
</row>
</thead>
<tbody>
<row>
<entry>vpn</entry>
<entry>VPN</entry>
<entry>Remote Subnet</entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>On system A, the 10.0.0.0/8 will comprise the <emphasis role="bold">vpn</emphasis>
zone. In /etc/shorewall/interfaces:</para>
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry align="center">ZONE</entry>
<entry align="center">INTERFACE</entry>
<entry align="center">BROADCAST</entry>
<entry align="center">OPTIONS</entry>
</row>
</thead>
<tbody>
<row>
<entry>vpn</entry>
<entry>tun0</entry>
<entry>10.255.255.255</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>In /etc/shorewall/tunnels on system A, we need the following:</para>
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry align="center">TYPE</entry>
<entry align="center">ZONE</entry>
<entry align="center">GATEWAY</entry>
<entry align="center">GATEWAY ZONE</entry>
</row>
</thead>
<tbody>
<row>
<entry>generic:tcp:1071</entry>
<entry>net</entry>
<entry>134.28.54.2</entry>
<entry></entry>
</row>
<row>
<entry>generic:47</entry>
<entry>net</entry>
<entry>134.28.54.2</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>These entries in /etc/shorewall/tunnels, opens the firewall so that
TCP port 1071 and the Generalized Routing Encapsulation Protocol (47) will
be accepted to/from the remote gateway.</para>
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry align="center">ZONE</entry>
<entry align="center">INTERFACE</entry>
<entry align="center">BROADCAST</entry>
<entry align="center">OPTIONS</entry>
</row>
</thead>
<tbody>
<row>
<entry>vpn</entry>
<entry>tun0</entry>
<entry>192.168.1.255</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>In /etc/shorewall/tunnels on system B, we have:</para>
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry align="center">TYPE</entry>
<entry align="center">ZONE</entry>
<entry align="center">GATEWAY</entry>
<entry align="center">GATEWAY ZONE</entry>
</row>
</thead>
<tbody>
<row>
<entry>generic:tcp:1071</entry>
<entry>net</entry>
<entry>206.191.148.9</entry>
<entry></entry>
</row>
<row>
<entry>generic:47</entry>
<entry>net</entry>
<entry>134.28.54.2</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>You will need to allow traffic between the <quote>vpn</quote> zone
and the <quote>loc</quote> zone on both systems -- if you simply want to
admit all traffic in both directions, you can use the policy file:</para>
<informaltable>
<tgroup cols="4">
<thead>
<row>
<entry align="center">SOURCE</entry>
<entry align="center">DEST</entry>
<entry align="center">POLICY</entry>
<entry align="center">LOG LEVEL</entry>
</row>
</thead>
<tbody>
<row>
<entry>loc</entry>
<entry>vpn</entry>
<entry>ACCEPT</entry>
<entry></entry>
</row>
<row>
<entry>vpn</entry>
<entry>loc</entry>
<entry>ACCEPT</entry>
<entry></entry>
</row>
</tbody>
</tgroup>
</informaltable>
<para>On both systems, restart Shorewall and start your VPN software on
each system. The systems in the two masqueraded subnetworks can now talk
to each other</para>
</section>
</article>