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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN"
"http://www.oasis-open.org/docbook/xml/4.4/docbookx.dtd">
<article id="OPENVPN">
<!--$Id$-->
<articleinfo>
<title>OpenVPN Tunnels and Bridges</title>
<authorgroup>
<author>
<firstname>Simon</firstname>
<surname>Matter</surname>
</author>
<author>
<firstname>Tom</firstname>
<surname>Eastep</surname>
</author>
</authorgroup>
<pubdate><?dbtimestamp format="Y/m/d"?></pubdate>
<copyright>
<year>2003</year>
<year>2004</year>
<year>2005</year>
<year>2006</year>
<holder>Simon Mater</holder>
<holder>Thomas M. Eastep</holder>
</copyright>
<legalnotice>
<para>Permission is granted to copy, distribute and/or modify this
document under the terms of the GNU Free Documentation License, Version
1.2 or any later version published by the Free Software Foundation; with
no Invariant Sections, with no Front-Cover, and with no Back-Cover
Texts. A copy of the license is included in the section entitled
<quote><ulink url="GnuCopyright.htm">GNU Free Documentation
License</ulink></quote>.</para>
</legalnotice>
</articleinfo>
<caution>
<para><emphasis role="bold">This article applies to Shorewall 3.0 and
later and to OpenVPN 2.0 and later. If you are running a version of
Shorewall earlier than Shorewall 3.0.0 then please see the documentation
for that release.</emphasis></para>
</caution>
<para>OpenVPN is a robust and highly configurable VPN (Virtual Private
Network) daemon which can be used to securely link two or more private
networks using an encrypted tunnel over the Internet. OpenVPN is an Open
Source project and is <ulink
url="http://openvpn.sourceforge.net/license.html">licensed under the
GPL</ulink>. OpenVPN can be downloaded from <ulink
url="http://openvpn.net/">http://openvpn.net/</ulink>.</para>
<para>Unless there are interoperability issues (the remote systems do not
support OpenVPN), OpenVPN is my choice any time that I need a VPN.</para>
<orderedlist>
<listitem>
<para>It is widely supported -- I run it on both Linux and Windows
XP.</para>
</listitem>
<listitem>
<para>It requires no kernel patching.</para>
</listitem>
<listitem>
<para>It is very easy to configure.</para>
</listitem>
<listitem>
<para>It just works!</para>
</listitem>
</orderedlist>
<section id="Prelim">
<title>Preliminary Reading</title>
<para>I recommend reading the <ulink url="VPNBasics.html">VPN
Basics</ulink> article if you plan to implement any type of VPN.</para>
</section>
<section id="Routed">
<title>Bridging two Masqueraded Networks</title>
<para>Suppose that we have the following situation:</para>
<graphic fileref="images/TwoNets1.png" />
<para>We want systems in the 192.168.1.0/24 subnetwork to be able to
communicate with the systems in the 10.0.0.0/8 network. This is
accomplished through use of the
<filename>/etc/shorewall/tunnels</filename> file and the
<filename>/etc/shorewall/policy file</filename> and OpenVPN.</para>
<para>While it was possible to use the Shorewall start and stop script to
start and stop OpenVPN, I decided to use the init script of OpenVPN to
start and stop it.</para>
<para>On each firewall, you will need to declare a zone to represent the
remote subnet. We'll assume that this zone is called <quote>vpn</quote>
and declare it in <filename>/etc/shorewall/zones</filename> on both
systems as follows.</para>
<blockquote>
<para><filename>/etc/shorewall/zones</filename> — Systems A &amp;
B</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
vpn ipv4</programlisting>
</blockquote>
<para>On system A, the 10.0.0.0/8 will comprise the <emphasis
role="bold">vpn</emphasis> zone.</para>
<blockquote>
<para>In <filename>/etc/shorewall/interfaces</filename> on system
A:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
vpn tun0</programlisting>
</blockquote>
<para>In <filename>/etc/shorewall/tunnels</filename> on system A, we need
the following:</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn net 134.28.54.2</programlisting>
</blockquote>
<para>This entry in <filename>/etc/shorewall/tunnels</filename> opens the
firewall so that OpenVPN traffic on the default port 1194/udp will be
accepted to/from the remote gateway. If you change the port used by
OpenVPN to 7777, you can define /etc/shorewall/tunnels like this:</para>
<blockquote>
<para>/etc/shorewall/tunnels with port 7777:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn:7777 net 134.28.54.2</programlisting>
</blockquote>
<para>Similarly, if you want to use TCP for your tunnel rather than UDP
(the default), then you can define /etc/shorewall/tunnels like
this:</para>
<blockquote>
<para>/etc/shorewall/tunnels using TCP:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn:tcp net 134.28.54.2</programlisting>
</blockquote>
<para>Finally, if you want to use TCP and port 7777:</para>
<blockquote>
<para>/etc/shorewall/tunnels using TCP port 7777:</para>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn:tcp:7777 net 134.28.54.2</programlisting>
</blockquote>
<para>This is the OpenVPN config on system A:</para>
<blockquote>
<programlisting>dev tun
local 206.162.148.9
remote 134.28.54.2
ifconfig 192.168.99.1 192.168.99.2
route 10.0.0.0 255.0.0.0 192.168.99.2
tls-server
dh dh1024.pem
ca ca.crt
cert my-a.crt
key my-a.key
comp-lzo
verb 5</programlisting>
</blockquote>
<para>Similarly, On system B the 192.168.1.0/24 subnet will comprise the
<emphasis role="bold">vpn</emphasis> zone</para>
<blockquote>
<para>In <filename>/etc/shorewall/interfaces</filename> on system
B:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
vpn tun0 </programlisting>
</blockquote>
<para>In <filename>/etc/shorewall/tunnels</filename> on system B, we
have:</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn net 206.191.148.9</programlisting>
</blockquote>
<para>And in the OpenVPN config on system B:</para>
<blockquote>
<programlisting>dev tun
local 134.28.54.2
remote 206.162.148.9
ifconfig 192.168.99.2 192.168.99.1
route 192.168.1.0 255.255.255.0 192.168.99.1
tls-client
ca ca.crt
cert my-b.crt
key my-b.key
comp-lzo
verb 5</programlisting>
</blockquote>
<para>You will need to allow traffic between the <quote>vpn</quote> zone
and the <quote>loc</quote> zone on both systems -- if you simply want to
admit all traffic in both directions, you can use the policy file:</para>
<blockquote>
<para><filename>/etc/shorewall/policy </filename>on systems A &amp;
B</para>
<programlisting>#SOURCE DEST POLICY LOG LEVEL
loc vpn ACCEPT
vpn loc ACCEPT</programlisting>
</blockquote>
<para>On both systems, restart Shorewall and start OpenVPN. The systems in
the two masqueraded subnetworks can now talk to each other.</para>
</section>
<section id="RoadWarrior">
<title>Roadwarrior</title>
<para>OpenVPN 2.0 provides excellent support for roadwarriors. Consider
the setup in the following diagram:</para>
<graphic fileref="images/Mobile.png" />
<para>On the gateway system (System A), we need a zone to represent the
remote clients — we'll call that zone <quote>road</quote>.</para>
<blockquote>
<para><filename>/etc/shorewall/zones</filename> — System A:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
road ipv4</programlisting>
</blockquote>
<para>On system A, the remote clients will comprise the <emphasis
role="bold">road</emphasis> zone.</para>
<blockquote>
<para>In <filename>/etc/shorewall/interfaces</filename> on system
A:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
road tun+</programlisting>
</blockquote>
<para>In <filename>/etc/shorewall/tunnels</filename> on system A, we need
the following:</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn:1194 net 0.0.0.0/0</programlisting>
</blockquote>
<para>If you are running Shorewall 2.4.3 or later, you might prefer the
following in <filename>/etc/shorewall/tunnels</filename> on system A.
Specifying the tunnel type as openvpnserver has the advantage that the VPN
connection will still work if the client is behind a gateway/firewall that
uses NAT.</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpnserver:1194 net 0.0.0.0/0</programlisting>
</blockquote>
<para>We want the remote systems to have access to the local LAN — we do
that with an entry in <filename>/etc/shorewall/policy</filename> (assume
that the local LAN comprises the zone <quote>loc</quote>).</para>
<blockquote>
<programlisting>#SOURCE DESTINATION POLICY
road loc ACCEPT</programlisting>
</blockquote>
<para>The OpenVPN configuration file on system A is something like the
following:</para>
<blockquote>
<programlisting>dev tun
server 192.168.2.0 255.255.255.0
dh dh1024.pem
ca /etc/certs/cacert.pem
crl-verify /etc/certs/crl.pem
cert /etc/certs/SystemA.pem
key /etc/certs/SystemA_key.pem
port 1194
comp-lzo
user nobody
group nogroup
ping 15
ping-restart 45
ping-timer-rem
persist-tun
persist-key
verb 3</programlisting>
</blockquote>
<para>Configuration on the remote clients follows a similar line. We
define a zone to represent the remote LAN:</para>
<blockquote>
<para><filename>/etc/shorewall/zones</filename> — System B:</para>
<programlisting>#ZONE TYPE OPTIONS IN OUT
# OPTIONS OPTIONS
home ipv4</programlisting>
</blockquote>
<para>On system A, the hosts accessible through the tunnel will comprise
the <emphasis role="bold">home</emphasis> zone.</para>
<blockquote>
<para>In <filename>/etc/shorewall/interfaces</filename> on system
B:</para>
<programlisting>#ZONE INTERFACE BROADCAST OPTIONS
home tun0</programlisting>
</blockquote>
<para>In <filename>/etc/shorewall/tunnels</filename> on system B, we need
the following:</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpn:1194 net 206.162.148.9</programlisting>
</blockquote>
<para>Again in you are running Shorewall 2.4.3 or later, in
<filename>/etc/shorewall/tunnels</filename> on system B you might
prefer:</para>
<blockquote>
<programlisting>#TYPE ZONE GATEWAY GATEWAY ZONE
openvpnclient:1194 net 206.162.148.9</programlisting>
</blockquote>
<para>We want the remote client to have access to the local LAN — we do
that with an entry in <filename>/etc/shorewall/policy</filename>.</para>
<blockquote>
<programlisting>#SOURCE DESTINATION POLICY
$FW home ACCEPT</programlisting>
</blockquote>
<para>The OpenVPN configuration on the remote clients is along the
following line:</para>
<blockquote>
<programlisting>dev tun
remote 206.162.148.9
up /etc/openvpn/home.up
tls-client
pull
ca /etc/certs/cacert.pem
cert /etc/certs/SystemB.pem
key /etc/certs/SystemB_key.pem
port 1194
user nobody
group nogroup
comp-lzo
ping 15
ping-restart 45
ping-timer-rem
persist-tun
persist-key
verb 3</programlisting>
</blockquote>
<para>If you want multiple remote clients to be able to communicate openly
with each other then you must:</para>
<orderedlist>
<listitem>
<para>Include the <emphasis role="bold">client-to-client</emphasis>
directive in the server's OpenVPN configuration; and</para>
</listitem>
<listitem>
<para>Specify the <emphasis role="bold">routeback</emphasis> option on
the <filename class="devicefile">tun+</filename> device in <ulink
url="manpages/shorewall-interfaces.html">/etc/shorewall/interfaces</ulink>.</para>
</listitem>
</orderedlist>
<para>If you want to selectively allow communication between the clients,
then see <ulink
url="http://marc.zonzon.free.fr/public_html/home.php?section=WRTMemo&amp;subsec=vpnwithshorewall">this
article</ulink> by Marc Zonzon</para>
</section>
<section id="Bridge">
<title>Securing a Home Wireless Network with OpenVPN (OpenVPN
Bridge)</title>
<para>This section will describe how we once secured our home wireless
network using OpenVPN. Our network as it was then<footnote>
<para>Our current network uses a similar technique -- see the <ulink
url="XenMyWay.html">Xen My Way</ulink> article.</para>
</footnote> is as shown in the following diagram.</para>
<graphic fileref="images/network3.png" />
<para>The Wireless network is in the lower right of the diagram and
consists of two laptops: Eastepnc6000 (Dual Boot Windows XP - SP1, SUSE
10.0) and Tipper (SUSE 10.0). We used OpenVPN to bridge those two laptops
with the local LAN shown in the lower left hand corner. The laptops were
configured with addresses in the 192.168.3.0/24 network connected to the
firewall's <filename class="devicefile">eth0</filename> interface which
places them in the firewall's <emphasis role="bold">Wifi</emphasis> zone.
OpenVPN bridging allowed them to be assigned an additional IP address from
the 192.168.1.0/24 network and to be securely bridged to the LAN on the
lower left.</para>
<note>
<para>Eastepnc6000 is shown in both the local LAN and in the Wifi zone
with IP address 192.168.1.6 -- clearly, the computer could only be in
one place or the other. Tipper could also be in either place and would
have the IP address 192.168.1.8 regardless.</para>
</note>
<section id="bridge">
<title>Configuring the Bridge</title>
<para>The firewall ran Debian Sarge so the bridge was defined in
<filename>/etc/network/interfaces</filename>.</para>
<programlisting># LAN interface
auto br0
iface br0 inet static
address 192.168.1.254
netmask 255.255.255.0
pre-up /usr/sbin/openvpn --mktun --dev tap0
pre-up /sbin/ip link set tap0 up
pre-up /sbin/ip link set eth3 up
pre-up /usr/sbin/brctl addbr br0
pre-up /usr/sbin/brctl addif br0 eth3
pre-up /usr/sbin/brctl addif br0 tap0
pre-down /usr/sbin/brctl delif br0 eth3
pre-down /sbin/ip link set eth3 down
pre-down /usr/sbin/brctl delif br0 tap0
pre-down /sbin/ip link set tap0 down
post-down /usr/sbin/brctl delbr br0
post-down /usr/sbin/openvpn --rmtun --dev tap0</programlisting>
<para>Note that the IP address assigned to the bridge is 192.168.1.254
-- that was the default gateway address for hosts in the local
zone.</para>
</section>
<section id="openvpn">
<title>Configuring OpenVPN</title>
<para>We used X.509 certificates for authentication.</para>
<section id="server">
<title>Firewall (Server) configuration.</title>
<para>/etc/openvpn/server-bridge.conf defined a bridge and reserved IP
addresses 192.168.1.64-192.168.1.71 for VPN clients. Note that the
bridge server only used local IP address 192.168.3.254. We ran two
instances of OpenVPN; this one and a second tunnel-mode instance for
remote access.</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 id="tipper">
<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 id="XP">
<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 id="Linux">
<title>Eastepnc6000 (SUSE 10.0) 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>
<title>Ursa (Windows Vista) Configuration</title>
<para>In December 2007, I acquired a new laptop that runs Windows
Vista. After a frustrating effort, I managed to get it working. The
keys to getting it working were:</para>
<orderedlist>
<listitem>
<para>You must run a version of OpenVPN that is "Vista Ready" -- I
used Matias Sundman's combined OpenVPN 2.1_rc4/OpenVPN GUI 1.0.3
installer (see <ulink
url="http://openvpn.se/">http://openvpn.se/</ulink>).</para>
</listitem>
<listitem>
<para>OpenVPN GUI must be run as the Administrator. In the
Explorer, right click on the OpenVPN GUI binary and select
Properties-&gt;Compatibility and select "Run this program as an
administrator".</para>
</listitem>
<listitem>
<para>If you encounter problems where everything looks correct but
it doesn't work, reboot and try it again.</para>
</listitem>
</orderedlist>
</section>
</section>
<section id="Shorewall">
<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-Shorewall-perl.html">Bridge/Firewall
documentation</ulink>.</para>
<section id="FW">
<title>Firewall</title>
<section id="interfaces">
<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 id="tunnels">
<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 id="Tipper">
<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 id="zones">
<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 id="interfaces1">
<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 id="policy">
<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-&gt;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>
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