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173 lines
5.9 KiB
XML
173 lines
5.9 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="IPIP">
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<!--$Id$-->
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<articleinfo>
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<title>GRE and IPIP Tunnels</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>2001</year>
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<year>2002</year>
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<year>2003</year>
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<year>2004</year>
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<year>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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<warning>
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<para>GRE and IPIP Tunnels are insecure when used over the Internet; use
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them at your own risk</para>
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</warning>
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<para>GRE and IPIP tunneling with Shorewall can be used to bridge two
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masqueraded networks.</para>
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<para>The simple scripts described in the <citetitle><ulink
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url="http://ds9a.nl/lartc">Linux Advanced Routing and Shaping
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HOWTO</ulink></citetitle> work fine with Shorewall. Shorewall also includes
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a tunnel script for automating tunnel configuration. If you have installed
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the RPM, the tunnel script may be found in the Shorewall documentation
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directory (usually /usr/share/doc/shorewall-<version>/).</para>
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<section id="Bridged">
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<title>Bridging two Masqueraded Networks</title>
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<para>Suppose that we have the following situation:</para>
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<graphic fileref="images/TwoNets1.png"/>
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<para>We want systems in the 192.168.1.0/24 subnetwork to be able to
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communicate with the systems in the 10.0.0.0/8 network. This is
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accomplished through use of the /etc/shorewall/tunnels file, the
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/etc/shorewall/policy file and the /etc/shorewall/tunnel script that is
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included with Shorewall.</para>
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<para>The <quote>tunnel</quote> script is not installed in /etc/shorewall
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by default -- If you install using the tarball, the script is included in
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the tarball; if you install using the RPM, the file is in your Shorewall
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documentation directory (normally
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/usr/share/doc/shorewall-<version>).</para>
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<para>In the /etc/shorewall/tunnel script, set the
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<quote>tunnel_type</quote> parameter to the type of tunnel that you want
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to create.</para>
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<example id="Tunnel">
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<title>/etc/shorewall/tunnel</title>
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<programlisting>tunnel_type=gre</programlisting>
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</example>
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<warning>
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<para>If you use the PPTP connection tracking modules from Netfilter
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Patch-O-Matic (ip_conntrack_proto_gre ip_conntrack_pptp,
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ip_nat_proto_gre and ip_nat_pptp) then you cannot use GRE
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tunnels.</para>
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</warning>
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<para>On each firewall, you will need to declare a zone to represent the
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remote subnet. We'll assume that this zone is called <quote>vpn</quote>
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and declare it in /etc/shorewall/zones on both systems as follows.</para>
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<programlisting>#ZONE TYPE OPTIONS
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vpn ipv4</programlisting>
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<para>On system A, the 10.0.0.0/8 will comprise the <emphasis
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role="bold">vpn</emphasis> zone. In /etc/shorewall/interfaces:</para>
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<programlisting>#ZONE INTERFACE OPTIONS
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vpn tosysb</programlisting>
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<para>In /etc/shorewall/tunnels on system A, we need the following:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY_ZONE
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ipip net 134.28.54.2</programlisting>
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<para>This entry in /etc/shorewall/tunnels, opens the firewall so that the
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IP encapsulation protocol (4) will be accepted to/from the remote
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gateway.</para>
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<para>In the tunnel script on system A:</para>
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<example id="TunnelA">
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<title>tunnel script on system A</title>
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<programlisting>tunnel=tosysb
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myrealip=206.161.148.9 (for GRE tunnel only)
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myip=192.168.1.1
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hisip=10.0.0.1
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gateway=134.28.54.2
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subnet=10.0.0.0/8
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</programlisting>
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</example>
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<para>Similarly, On system B the 192.168.1.0/24 subnet will comprise the
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<emphasis role="bold">vpn</emphasis> zone. In
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/etc/shorewall/interfaces:</para>
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<programlisting>#ZONE INTERFACE
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vpn tosysa</programlisting>
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<para>In /etc/shorewall/tunnels on system B, we have:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY_ZONE
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ipip net 206.191.148.9</programlisting>
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<para>And in the tunnel script on system B:</para>
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<example id="TunnelB">
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<title>tunnel script on system B</title>
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<programlisting>tunnel=tosysa
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myrealip=134.28.54.2 (for GRE tunnel only)
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myip=10.0.0.1
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hisip=192.168.1.1
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gateway=206.191.148.9
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subnet=192.168.1.0/24</programlisting>
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</example>
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<para>You can rename the modified tunnel scripts if you like; be sure that
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they are secured so that root can execute them.</para>
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<para>You will need to allow traffic between the <quote>vpn</quote> zone
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and the <quote>loc</quote> zone on both systems -- if you simply want to
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admit all traffic in both directions, you can use the policy file:</para>
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<programlisting>#SOURCE DEST POLICY LOG LEVEL
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loc vpn ACCEPT
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vpn loc ACCEPT</programlisting>
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<para>On both systems, restart Shorewall and run the modified tunnel
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script with the <quote>start</quote> argument on each system. The systems
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in the two masqueraded subnetworks can now talk to each other</para>
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</section>
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</article>
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