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605 lines
18 KiB
XML
605 lines
18 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="OPENVPN">
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<!--Id$-->
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<articleinfo>
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<title>OpenVPN Tunnels and Bridges</title>
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<authorgroup>
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<author>
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<firstname>Simon</firstname>
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<surname>Matter</surname>
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</author>
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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</year>
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<year>2004</year>
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<year>2005</year>
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<year>2006</year>
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<holder>Simon Mater</holder>
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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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<caution>
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<para><emphasis role="bold">This article applies to Shorewall 3.0 and
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later and to OpenVPN 2.0 and later. If you are running a version of
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Shorewall earlier than Shorewall 3.0.0 then please see the documentation
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for that release.</emphasis></para>
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</caution>
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<para>OpenVPN is a robust and highly configurable VPN (Virtual Private
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Network) daemon which can be used to securely link two or more private
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networks using an encrypted tunnel over the Internet. OpenVPN is an Open
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Source project and is <ulink
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url="http://openvpn.sourceforge.net/license.html">licensed under the
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GPL</ulink>. OpenVPN can be downloaded from <ulink
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url="http://openvpn.net/">http://openvpn.net/</ulink>.</para>
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<para>Unless there are interoperability issues (the remote systems do not
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support OpenVPN), OpenVPN is my choice any time that I need a VPN.</para>
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<orderedlist>
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<listitem>
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<para>It is widely supported -- I run it on both Linux and Windows
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XP.</para>
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</listitem>
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<listitem>
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<para>It requires no kernel patching.</para>
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</listitem>
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<listitem>
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<para>It is very easy to configure.</para>
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</listitem>
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<listitem>
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<para>It just works!</para>
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</listitem>
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</orderedlist>
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<section id="Prelim">
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<title>Preliminary Reading</title>
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<para>I recommend reading the <ulink url="VPNBasics.html">VPN
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Basics</ulink> article if you plan to implement any type of VPN.</para>
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</section>
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<section id="Routed">
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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
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<filename>/etc/shorewall/tunnels</filename> file and the
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<filename>/etc/shorewall/policy file</filename> and OpenVPN.</para>
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<para>While it was possible to use the Shorewall start and stop script to
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start and stop OpenVPN, I decided to use the init script of OpenVPN to
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start and stop it.</para>
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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 <filename>/etc/shorewall/zones</filename> on both
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systems as follows.</para>
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<blockquote>
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<para><filename>/etc/shorewall/zones</filename> — Systems A &
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B</para>
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<programlisting>#ZONE TYPE OPTIONS IN OUT
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# OPTIONS OPTIONS
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vpn ipv4</programlisting>
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</blockquote>
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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.</para>
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<blockquote>
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<para>In <filename>/etc/shorewall/interfaces</filename> on system
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A:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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vpn tun0</programlisting>
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</blockquote>
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<para>In <filename>/etc/shorewall/tunnels</filename> on system A, we need
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the following:</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn net 134.28.54.2</programlisting>
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</blockquote>
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<para>This entry in <filename>/etc/shorewall/tunnels</filename> opens the
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firewall so that OpenVPN traffic on the default port 1194/udp will be
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accepted to/from the remote gateway. If you change the port used by
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OpenVPN to 7777, you can define /etc/shorewall/tunnels like this:</para>
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<blockquote>
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<para>/etc/shorewall/tunnels with port 7777:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn:7777 net 134.28.54.2</programlisting>
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</blockquote>
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<para>Similarly, if you want to use TCP for your tunnel rather than UDP
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(the default), then you can define /etc/shorewall/tunnels like
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this:</para>
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<blockquote>
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<para>/etc/shorewall/tunnels using TCP:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn:tcp net 134.28.54.2</programlisting>
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</blockquote>
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<para>Finally, if you want to use TCP and port 7777:</para>
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<blockquote>
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<para>/etc/shorewall/tunnels using TCP port 7777:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn:tcp:7777 net 134.28.54.2</programlisting>
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</blockquote>
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<para>This is the OpenVPN config on system A:</para>
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<blockquote>
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<programlisting>dev tun
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local 206.162.148.9
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remote 134.28.54.2
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ifconfig 192.168.99.1 192.168.99.2
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route 10.0.0.0 255.0.0.0 192.168.99.2
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tls-server
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dh dh1024.pem
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ca ca.crt
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cert my-a.crt
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key my-a.key
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comp-lzo
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verb 5</programlisting>
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</blockquote>
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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</para>
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<blockquote>
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<para>In <filename>/etc/shorewall/interfaces</filename> on system
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B:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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vpn tun0 </programlisting>
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</blockquote>
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<para>In <filename>/etc/shorewall/tunnels</filename> on system B, we
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have:</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn net 206.191.148.9</programlisting>
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</blockquote>
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<para>And in the OpenVPN config on system B:</para>
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<blockquote>
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<programlisting>dev tun
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local 134.28.54.2
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remote 206.162.148.9
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ifconfig 192.168.99.2 192.168.99.1
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route 192.168.1.0 255.255.255.0 192.168.99.1
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tls-client
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ca ca.crt
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cert my-b.crt
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key my-b.key
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comp-lzo
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verb 5</programlisting>
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</blockquote>
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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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<blockquote>
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<para><filename>/etc/shorewall/policy </filename>on systems A &
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B</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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</blockquote>
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<para>On both systems, restart Shorewall and start OpenVPN. The systems in
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the two masqueraded subnetworks can now talk to each other.</para>
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</section>
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<section id="RoadWarrior">
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<title>Roadwarrior</title>
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<para>OpenVPN 2.0 provides excellent support for roadwarriors. Consider
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the setup in the following diagram:</para>
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<graphic fileref="images/Mobile.png" />
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<para>On the gateway system (System A), we need a zone to represent the
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remote clients — we'll call that zone <quote>road</quote>.</para>
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<blockquote>
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<para><filename>/etc/shorewall/zones</filename> — System A:</para>
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<programlisting>#ZONE TYPE OPTIONS IN OUT
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# OPTIONS OPTIONS
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road ipv4</programlisting>
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</blockquote>
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<para>On system A, the remote clients will comprise the <emphasis
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role="bold">road</emphasis> zone.</para>
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<blockquote>
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<para>In <filename>/etc/shorewall/interfaces</filename> on system
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A:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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road tun+</programlisting>
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</blockquote>
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<para>In <filename>/etc/shorewall/tunnels</filename> on system A, we need
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the following:</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn:1194 net 0.0.0.0/0</programlisting>
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</blockquote>
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<para>If you are running Shorewall 2.4.3 or later, you might prefer the
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following in <filename>/etc/shorewall/tunnels</filename> on system A.
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Specifying the tunnel type as openvpnserver has the advantage that the VPN
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connection will still work if the client is behind a gateway/firewall that
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uses NAT.</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpnserver:1194 net 0.0.0.0/0</programlisting>
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</blockquote>
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<para>We want the remote systems to have access to the local LAN — we do
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that with an entry in <filename>/etc/shorewall/policy</filename> (assume
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that the local LAN comprises the zone <quote>loc</quote>).</para>
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<blockquote>
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<programlisting>#SOURCE DESTINATION POLICY
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road loc ACCEPT</programlisting>
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</blockquote>
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<para>The OpenVPN configuration file on system A is something like the
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following:</para>
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<blockquote>
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<programlisting>dev tun
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server 192.168.2.0 255.255.255.0
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dh dh1024.pem
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ca /etc/certs/cacert.pem
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crl-verify /etc/certs/crl.pem
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cert /etc/certs/SystemA.pem
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key /etc/certs/SystemA_key.pem
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port 1194
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comp-lzo
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user nobody
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group nogroup
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ping 15
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ping-restart 45
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ping-timer-rem
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persist-tun
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persist-key
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push "route 192.168.1.0 255.255.255.0"
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verb 3</programlisting>
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</blockquote>
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<para>Configuration on the remote clients follows a similar line. We
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define a zone to represent the remote LAN:</para>
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<blockquote>
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<para><filename>/etc/shorewall/zones</filename> — System B:</para>
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<programlisting>#ZONE TYPE OPTIONS IN OUT
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# OPTIONS OPTIONS
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home ipv4</programlisting>
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</blockquote>
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<para>On system A, the hosts accessible through the tunnel will comprise
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the <emphasis role="bold">home</emphasis> zone.</para>
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<blockquote>
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<para>In <filename>/etc/shorewall/interfaces</filename> on system
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B:</para>
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<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
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home tun0</programlisting>
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</blockquote>
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<para>In <filename>/etc/shorewall/tunnels</filename> on system B, we need
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the following:</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpn:1194 net 206.162.148.9</programlisting>
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</blockquote>
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<para>Again, if you are running Shorewall 2.4.3 or later, in
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<filename>/etc/shorewall/tunnels</filename> on system B you might
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prefer:</para>
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<blockquote>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpnclient:1194 net 206.162.148.9</programlisting>
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</blockquote>
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<para>We want the remote client to have access to the local LAN — we do
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that with an entry in <filename>/etc/shorewall/policy</filename>.</para>
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<blockquote>
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<programlisting>#SOURCE DESTINATION POLICY
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$FW home ACCEPT</programlisting>
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</blockquote>
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<para>The OpenVPN configuration on the remote clients is along the
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following line:</para>
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<blockquote>
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<programlisting>dev tun
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remote 206.162.148.9
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up /etc/openvpn/home.up
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tls-client
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pull
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ca /etc/certs/cacert.pem
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cert /etc/certs/SystemB.pem
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key /etc/certs/SystemB_key.pem
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port 1194
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user nobody
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group nogroup
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comp-lzo
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ping 15
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ping-restart 45
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ping-timer-rem
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persist-tun
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persist-key
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verb 3</programlisting>
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</blockquote>
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<para>If you want multiple remote clients to be able to communicate openly
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with each other then you must:</para>
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<orderedlist>
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<listitem>
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<para>Include the <emphasis role="bold">client-to-client</emphasis>
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directive in the server's OpenVPN configuration; or</para>
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</listitem>
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<listitem>
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<para>Specify the <emphasis role="bold">routeback</emphasis> option on
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the <filename class="devicefile">tun+</filename> device in <ulink
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url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>.</para>
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</listitem>
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</orderedlist>
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</section>
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<section id="Dupnet">
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<title>Roadwarrior with Duplicate Network Issue</title>
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<para>The information in this section was contributed by Nicola
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Moretti.</para>
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<para>If your local lan uses a popular RFC 1918 network like
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192.168.1.0/24, there will be times when your roadwarriors need to access
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your lan from a remote location that uses that same network.</para>
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<graphic align="center" fileref="images/Mobile1.png" />
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<para>This may be accomplished by configuring a second server on your
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firewall that uses a different port and by using <ulink
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url="netmap.html">NETMAP</ulink> in your Shorewall configuration. The
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server configuration in the above diagram is modified as shown
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here:</para>
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<blockquote>
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<programlisting>dev tun
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<emphasis role="bold">server 192.168.3.0 255.255.255.0</emphasis>
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dh dh1024.pem
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ca /etc/certs/cacert.pem
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crl-verify /etc/certs/crl.pem
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cert /etc/certs/SystemA.pem
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key /etc/certs/SystemA_key.pem
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<emphasis role="bold">port 1195</emphasis>
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comp-lzo
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user nobody
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group nogroup
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ping 15
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ping-restart 45
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ping-timer-rem
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persist-tun
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persist-key
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<emphasis role="bold">push "route 172.20.1.0 255.255.255.0"</emphasis>
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verb 3</programlisting>
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</blockquote>
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<para>In <filename>/etc/shorewall/netmap</filename>, put these
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entries:</para>
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<blockquote>
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<programlisting>#TYPE NET1 INTERFACE NET2
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SNAT 192.168.1.0/24 tun1 172.20.1.0/24
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DNAT 172.20.1.0/24 tun1 192.168.1.0/24
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</programlisting>
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</blockquote>
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<para>The roadwarrior can now connect to port 1195 and access the lan on
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the right as 172.20.1.0/24.</para>
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</section>
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<section>
|
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<title>Bridged Roadwarrior</title>
|
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|
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<para>If you want to use a bridged OpenVPN configuration rather than a
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routed configuration, then follow any of the available HOWTOs to set up
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the bridged configuration. Then:</para>
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|
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<orderedlist>
|
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<listitem>
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<para>In your current Shorewall two-interface configuration, replace
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references to your internal interface with the name of the bridge;
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and</para>
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</listitem>
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|
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<listitem>
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<para>Set the <emphasis role="bold">routeback</emphasis> option in the
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bridge's entry in <ulink
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url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>;
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end</para>
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</listitem>
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<listitem>
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<para>Add this entry to <ulink
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url="manpages/shorewall-tunnels.html">/etc/shorewall/tunnels</ulink>:</para>
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<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
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openvpnserver:1194 net 0.0.0.0/0</programlisting>
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</listitem>
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</orderedlist>
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|
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<para>This will make the roadwarrior part of your local zone.</para>
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</section>
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<section>
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<title>Bridging Two Networks</title>
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<para>Occasionally, the need arises to have a single LAN span two
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different geographical locations. OpenVPN allows that to be done
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easily.</para>
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<para>Consider the following case:</para>
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<graphic align="center" fileref="images/bridge4.png" />
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<para>Part of the 192.168.1.0/24 network is in one location and part in
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another. The two LANs can be bridged with OpenVPN as described in this
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section. This example uses a fixed shared key for encryption.</para>
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<para>OpenVPN configuration on left-hand firewall:</para>
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<programlisting>remote 130.252.100.109
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dev tap0
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secret /etc/openvpn/bridgekey</programlisting>
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<para>OpenVPN configuration on right-hand firewall:</para>
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<programlisting>remote 206.124.146.176
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dev tap0
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secret /etc/openvpn/bridgekey</programlisting>
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<para>The bridges can be created by manually making the tap device tap0
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and bridgeing it with the local ethernet interface. Assuming that the
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local interface on both sides is eth1, the following stanzas in
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/etc/network/interfaces (Debian and derivatives) will create the bridged
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interfaces.</para>
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<para>/etc/network/interfaces on the left-hand firewall:</para>
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<programlisting>iface br0 inet static
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pre-up /usr/sbin/openvpn --mktun --dev tap0
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pre-up /usr/sbin/brctl addbr br1
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address 192.168.1.254
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network 192.168.1.0
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broadcast 192.168.1.255
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netmask 255.255.255.0
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post-up /sbin/ip link set tap0 up
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post-up /usr/sbin/brctl addif br0 tap0
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post-up /sbin/ip link set eth1 up
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post-up /usr/sbin/brctl addif br0 eth1
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post-down /usr/sbin/brctl delbr br0
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post-down /usr/sbin/tunctl -d tap0
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post-down /sbin/ip link set eth1 down </programlisting>
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<para>/etc/network/interfaces on the right-hand firewall:</para>
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<programlisting>iface br0 inet static
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pre-up /usr/sbin/openvpn --mktun --dev tap0
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pre-up /usr/sbin/brctl addbr br1
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address 192.168.1.253
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network 192.168.1.0
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broadcast 192.168.1.255
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netmask 255.255.255.0
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post-up /sbin/ip link set tap0 up
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post-up /usr/sbin/brctl addif br0 tap0
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post-up /sbin/ip link set eth1 up
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post-up /usr/sbin/brctl addif br0 eth1
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post-down /usr/sbin/brctl delbr br0
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post-down /usr/sbin/tunctl -d tap0
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post-down /sbin/ip link set eth1 down </programlisting>
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<para>The Shorewall configuration is just a <ulink
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url="SimpleBridge.html">Simple Bridge</ulink>.</para>
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</section>
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</article>
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