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722 lines
22 KiB
XML
722 lines
22 KiB
XML
<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<article id="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>2006-03-21</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>
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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>
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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>
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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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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 in 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; and</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="Documentation.htm#Interfaces">/etc/shorewall/interfaces</ulink>.</para>
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</listitem>
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</orderedlist>
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<para>If you want to selectively allow communication between the clients,
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then see <ulink
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url="http://www.iut-lannion.fr/ZONZON/memos_index.php?part=Network&section=WRTMemo&subsec=vpnwithshorewall">this
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article</ulink> by Marc Zonzon</para>
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</section>
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<section id="Bridge">
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<title>Securing a Home Wireless Network with OpenVPN (OpenVPN
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Bridge)</title>
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<para>This section will describe how we once secured our home wireless
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network using OpenVPN. Our network as it was then<footnote>
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<para>Our current network uses a similar technique -- see the <ulink
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url="XenMyWay.html">Xen My Way</ulink> article.</para>
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</footnote> is as shown in the following diagram.</para>
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<graphic fileref="images/network3.png" />
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<para>The Wireless network is in the lower right of the diagram and
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consists of two laptops: Eastepnc6000 (Dual Boot Windows XP - SP1, SUSE
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10.0) and Tipper (SUSE 10.0). We used OpenVPN to bridge those two laptops
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with the local LAN shown in the lower left hand corner. The laptops were
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configured with addresses in the 192.168.3.0/24 network connected to the
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firewall's <filename class="devicefile">eth0</filename> interface which
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places them in the firewall's <emphasis role="bold">Wifi</emphasis> zone.
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OpenVPN bridging allowed them to be assigned an additional IP address from
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the 192.168.1.0/24 network and to be securely bridged to the LAN on the
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lower left.</para>
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<note>
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<para>Eastepnc6000 is shown in both the local LAN and in the Wifi zone
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with IP address 192.168.1.6 -- clearly, the computer could only be in
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one place or the other. Tipper could also be in either place and would
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have the IP address 192.168.1.8 regardless.</para>
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</note>
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<section>
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<title>Configuring the Bridge</title>
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|
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<para>The firewall ran Debian Sarge so the bridge was defined in
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<filename>/etc/network/interfaces</filename>.</para>
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<programlisting># LAN interface
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auto br0
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iface br0 inet static
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address 192.168.1.254
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netmask 255.255.255.0
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pre-up /usr/sbin/openvpn --mktun --dev tap0
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pre-up /sbin/ip link set tap0 up
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pre-up /sbin/ip link set eth3 up
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pre-up /usr/sbin/brctl addbr br0
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pre-up /usr/sbin/brctl addif br0 eth3
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pre-up /usr/sbin/brctl addif br0 tap0
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post-down /usr/sbin/brctl delif br0 eth3
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post-down /usr/sbin/brctl delif br0 tap0
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post-down /usr/sbin/brctl delbr br0
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post-down /usr/sbin/openvpn --rmtun --dev tap0</programlisting>
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<para>Note that the IP address assigned to the bridge is 192.168.1.254
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-- that was the default gateway address for hosts in the local
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zone.</para>
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</section>
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<section>
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<title>Configuring OpenVPN</title>
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|
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<para>We used X.509 certificates for authentication.</para>
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<section>
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<title>Firewall (Server) configuration.</title>
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<para>/etc/openvpn/server-bridge.conf defined a bridge and reserved IP
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addresses 192.168.1.64-192.168.1.71 for VPN clients. Note that the
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bridge server only used local IP address 192.168.3.254. We ran two
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instances of OpenVPN; this one and a second tunnel-mode instance for
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remote access (see <ulink url="myfiles.htm">this
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article</ulink>).</para>
|
|
|
|
<para></para>
|
|
|
|
<programlisting>dev tap0
|
|
|
|
local 192.168.3.254
|
|
|
|
server-bridge 192.168.1.254 255.255.255.0 192.168.1.64 192.168.1.71
|
|
|
|
client-to-client
|
|
|
|
dh dh1024.pem
|
|
|
|
ca /etc/certs/cacert.pem
|
|
|
|
crl-verify /etc/certs/crl.pem
|
|
|
|
cert /etc/certs/gateway.pem
|
|
key /etc/certs/gateway_key.pem
|
|
|
|
port 1194
|
|
|
|
comp-lzo
|
|
|
|
user nobody
|
|
group nogroup
|
|
|
|
keepalive 15 45
|
|
ping-timer-rem
|
|
persist-tun
|
|
persist-key
|
|
|
|
client-config-dir /etc/openvpn/bridge-clients
|
|
ccd-exclusive
|
|
|
|
verb 3</programlisting>
|
|
|
|
<para>The files in <filename>/etc/openvpn/bridge-clients</filename>
|
|
were used to assign a fixed IP address to each laptop. For example,
|
|
tipper.shorewall.net:</para>
|
|
|
|
<programlisting>ifconfig-push 192.168.1.8 255.255.255.0</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Tipper Configuration</title>
|
|
|
|
<para>/etc/openvpn/wireless.conf:</para>
|
|
|
|
<programlisting>dev tap
|
|
|
|
remote 192.168.3.254
|
|
tls-remote gateway.shorewall.net
|
|
|
|
client
|
|
|
|
redirect-gateway
|
|
|
|
ca /etc/certs/cacert.pem
|
|
|
|
cert /etc/certs/tipper.pem
|
|
key /etc/certs/tipper_key.pem
|
|
|
|
port 1194
|
|
|
|
comp-lzo
|
|
|
|
ping 15
|
|
ping-restart 45
|
|
ping-timer-rem
|
|
persist-tun
|
|
persist-key
|
|
|
|
mute-replay-warnings
|
|
|
|
verb 3</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Eastepnc6000 (Windows XP) Configuration</title>
|
|
|
|
<para>C:\Program Files\Openvpn\config\homewireless.ovpn:</para>
|
|
|
|
<programlisting>dev tap
|
|
remote 192.168.3.254
|
|
tls-remote gateway.shorewall.net
|
|
|
|
tls-client
|
|
pull
|
|
|
|
ca "/Program Files/OpenVPN/certs/cacert.pem"
|
|
|
|
cert "/Program Files/OpenVPN/certs/eastepnc6000.pem"
|
|
key "/Program Files/OpenVPN/certs/eastepnc6000_key.pem"
|
|
|
|
redirect-gateway
|
|
|
|
port 1194
|
|
|
|
comp-lzo
|
|
|
|
ping 15
|
|
ping-restart 45
|
|
ping-timer-rem
|
|
persist-tun
|
|
persist-key
|
|
|
|
verb 3</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Eastepnc6000 (SUSE10.0) Configuration</title>
|
|
|
|
<para>The configuration was the same as shown above only with
|
|
"/Program Files/OpenVPN" replaced with "/etc/openvpn" (I love
|
|
OpenVPN).</para>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Configuring Shorewall</title>
|
|
|
|
<para>In this configuration, we didn't need any firewalling between the
|
|
laptops and the local LAN so we set BRIDGING=No in shorewall.conf. The
|
|
configuration of the bridge then became as described in the <ulink
|
|
url="SimpleBridge.html">Simple Bridge documentation</ulink>. If you need
|
|
to control the traffic allowed through the VPN bridge then you will want
|
|
to configure Shorewall as shown in the <ulink
|
|
url="bridge.html">Bridge/Firewall documentation</ulink>.</para>
|
|
|
|
<section>
|
|
<title>Firewall</title>
|
|
|
|
<section>
|
|
<title>/etc/shorewall/interfaces</title>
|
|
|
|
<para>Note that the bridge (br0) is defined as the interface to the
|
|
local zone and has the <emphasis role="bold">routeback</emphasis>
|
|
option.</para>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
net eth2 206.124.146.255 dhcp,norfc1918,logmartians,blacklist,tcpflags,nosmurfs
|
|
loc br0 192.168.1.255 dhcp,<emphasis role="bold">routeback</emphasis>
|
|
dmz eth1 - logmartians
|
|
Wifi eth0 192.168.3.255 dhcp,maclist
|
|
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>/etc/shorewall/tunnels</title>
|
|
|
|
<programlisting>#TYPE ZONE GATEWAY GATEWAY
|
|
# ZONE
|
|
openvpnserver:1194 Wifi 192.168.3.0/24
|
|
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE</programlisting>
|
|
</section>
|
|
</section>
|
|
|
|
<section>
|
|
<title>Tipper</title>
|
|
|
|
<para>Wireless networks pose a threat to all systems that are
|
|
connected to them and we therefore ran Firewalls on the two Laptops.
|
|
Eastepnc6000 ran <trademark>Sygate</trademark> Security Agent and
|
|
Tipper ran a Shorewall-based Netfilter firewall.</para>
|
|
|
|
<section>
|
|
<title>/etc/shorewall/zones</title>
|
|
|
|
<programlisting>#ZONE TYPE OPTIONS IN OUT
|
|
# OPTIONS OPTIONS
|
|
<emphasis role="bold">lan ipv4</emphasis> #Wired LAN at our home
|
|
net ipv4
|
|
#LAST LINE - ADD YOUR ENTRIES ABOVE THIS ONE - DO NOT REMOVE
|
|
</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>/etc/shorewall/interfaces</title>
|
|
|
|
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
|
|
#
|
|
net eth0 detect routefilter,dhcp,tcpflags
|
|
<emphasis role="bold">lan tap0 192.168.1.255</emphasis>
|
|
#LAST LINE -- ADD YOUR ENTRIES BEFORE THIS ONE -- DO NOT REMOVE
|
|
</programlisting>
|
|
</section>
|
|
|
|
<section>
|
|
<title>/etc/shorewall/policy</title>
|
|
|
|
<para>Since we didn't expect any traffic between the <emphasis
|
|
role="bold">net</emphasis> zone and the <emphasis
|
|
role="bold">lan</emphasis> zone, we used NONE policies for that
|
|
traffic. If any such traffic would have occurred, it would have been
|
|
handled according to the all->all policy.</para>
|
|
|
|
<programlisting>#SOURCE DEST POLICY LOG LIMIT:BURST
|
|
# LEVEL
|
|
fw net ACCEPT
|
|
<emphasis role="bold">fw lan ACCEPT
|
|
lan fw ACCEPT
|
|
net lan NONE
|
|
lan net NONE</emphasis>
|
|
net all DROP info
|
|
# The FOLLOWING POLICY MUST BE LAST
|
|
all all REJECT info
|
|
#LAST LINE -- DO NOT REMOVE</programlisting>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
</section>
|
|
</article> |