583 lines
18 KiB
HTML
583 lines
18 KiB
HTML
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</head>
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<body>
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<div class="document" id="openvpn-examples">
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<h1 class="title">openvpn examples</h1>
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<h2 class="subtitle" id="secure-ip-tunnel-daemon">Secure IP tunnel daemon</h2>
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<table class="docinfo" frame="void" rules="none">
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<col class="docinfo-name" />
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<col class="docinfo-content" />
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<tbody valign="top">
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<tr class="manual-section field"><th class="docinfo-name">Manual section:</th><td class="field-body">5</td>
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</tr>
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<tr class="manual-group field"><th class="docinfo-name">Manual group:</th><td class="field-body">Configuration files</td>
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</tr>
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</tbody>
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</table>
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<div class="section" id="introduction">
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<h1>INTRODUCTION</h1>
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<p>This man page gives a few simple examples to create OpenVPN setups and configuration files.</p>
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</div>
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<div class="section" id="examples">
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<h1>EXAMPLES</h1>
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<p>Prior to running these examples, you should have OpenVPN installed on
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two machines with network connectivity between them. If you have not yet
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installed OpenVPN, consult the INSTALL file included in the OpenVPN
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distribution.</p>
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<div class="section" id="firewall-setup">
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<h2>Firewall Setup:</h2>
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<p>If firewalls exist between the two machines, they should be set to
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forward the port OpenVPN is configured to use, in both directions.
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The default for OpenVPN is 1194/udp. If you do not have control
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over the firewalls between the two machines, you may still be able to
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use OpenVPN by adding <tt class="docutils literal"><span class="pre">--ping</span> 15</tt> to each of the <tt class="docutils literal">openvpn</tt> commands
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used below in the examples (this will cause each peer to send out a UDP
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ping to its remote peer once every 15 seconds which will cause many
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stateful firewalls to forward packets in both directions without an
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explicit firewall rule).</p>
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<p>Please see your operating system guides for how to configure the firewall
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on your systems.</p>
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</div>
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<div class="section" id="vpn-address-setup">
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<h2>VPN Address Setup:</h2>
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<p>For purposes of our example, our two machines will be called
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<tt class="docutils literal">bob.example.com</tt> and <tt class="docutils literal">alice.example.com</tt>. If you are constructing a
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VPN over the internet, then replace <tt class="docutils literal">bob.example.com</tt> and
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<tt class="docutils literal">alice.example.com</tt> with the internet hostname or IP address that each
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machine will use to contact the other over the internet.</p>
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<p>Now we will choose the tunnel endpoints. Tunnel endpoints are private IP
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addresses that only have meaning in the context of the VPN. Each machine
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will use the tunnel endpoint of the other machine to access it over the
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VPN. In our example, the tunnel endpoint for bob.example.com will be
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10.4.0.1 and for alice.example.com, 10.4.0.2.</p>
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<p>Once the VPN is established, you have essentially created a secure
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alternate path between the two hosts which is addressed by using the
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tunnel endpoints. You can control which network traffic passes between
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the hosts (a) over the VPN or (b) independently of the VPN, by choosing
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whether to use (a) the VPN endpoint address or (b) the public internet
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address, to access the remote host. For example if you are on
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bob.example.com and you wish to connect to <tt class="docutils literal">alice.example.com</tt> via
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<tt class="docutils literal">ssh</tt> without using the VPN (since <strong>ssh</strong> has its own built-in security)
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you would use the command <tt class="docutils literal">ssh alice.example.com</tt>. However in the same
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scenario, you could also use the command <tt class="docutils literal">telnet 10.4.0.2</tt> to create a
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telnet session with alice.example.com over the VPN, that would use the
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VPN to secure the session rather than <tt class="docutils literal">ssh</tt>.</p>
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<p>You can use any address you wish for the tunnel endpoints but make sure
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that they are private addresses (such as those that begin with 10 or
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192.168) and that they are not part of any existing subnet on the
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networks of either peer, unless you are bridging. If you use an address
|
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that is part of your local subnet for either of the tunnel endpoints,
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you will get a weird feedback loop.</p>
|
|
</div>
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|
<div class="section" id="example-1-a-simple-tunnel-without-security">
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|
<h2>Example 1: A simple tunnel without security</h2>
|
|
<p>On bob:</p>
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|
<pre class="literal-block">
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|
openvpn --remote alice.example.com --dev tun1 \
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|
--ifconfig 10.4.0.1 10.4.0.2 --verb 9
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|
</pre>
|
|
<p>On alice:</p>
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|
<pre class="literal-block">
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|
openvpn --remote bob.example.com --dev tun1 \
|
|
--ifconfig 10.4.0.2 10.4.0.1 --verb 9
|
|
</pre>
|
|
<p>Now verify the tunnel is working by pinging across the tunnel.</p>
|
|
<p>On bob:</p>
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|
<pre class="literal-block">
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|
ping 10.4.0.2
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|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
ping 10.4.0.1
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|
</pre>
|
|
<p>The <tt class="docutils literal"><span class="pre">--verb</span> 9</tt> option will produce verbose output, similar to the
|
|
<tt class="docutils literal">tcpdump</tt>(8) program. Omit the <tt class="docutils literal"><span class="pre">--verb</span> 9</tt> option to have OpenVPN run
|
|
quietly.</p>
|
|
</div>
|
|
<div class="section" id="example-2-a-tunnel-with-static-key-security-i-e-using-a-pre-shared-secret">
|
|
<h2>Example 2: A tunnel with static-key security (i.e. using a pre-shared secret)</h2>
|
|
<p>First build a static key on bob.</p>
|
|
<pre class="literal-block">
|
|
openvpn --genkey --secret key
|
|
</pre>
|
|
<p>This command will build a key file called <tt class="docutils literal">key</tt> (in ascii format). Now
|
|
copy <tt class="docutils literal">key</tt> to <tt class="docutils literal">alice.example.com</tt> over a secure medium such as by using
|
|
the <tt class="docutils literal">scp</tt>(1) program.</p>
|
|
<p>On bob:</p>
|
|
<pre class="literal-block">
|
|
openvpn --remote alice.example.com --dev tun1 \
|
|
--ifconfig 10.4.0.1 10.4.0.2 --verb 5 \
|
|
--secret key
|
|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
openvpn --remote bob.example.com --dev tun1 \
|
|
--ifconfig 10.4.0.2 10.4.0.1 --verb 5 \
|
|
--secret key
|
|
</pre>
|
|
<p>Now verify the tunnel is working by pinging across the tunnel.</p>
|
|
<p>On bob:</p>
|
|
<pre class="literal-block">
|
|
ping 10.4.0.2
|
|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
ping 10.4.0.1
|
|
</pre>
|
|
</div>
|
|
<div class="section" id="example-3-a-tunnel-with-full-tls-based-security">
|
|
<h2>Example 3: A tunnel with full TLS-based security</h2>
|
|
<p>For this test, we will designate <tt class="docutils literal">bob</tt> as the TLS client and <tt class="docutils literal">alice</tt>
|
|
as the TLS server.</p>
|
|
<dl class="docutils">
|
|
<dt><em>Note:</em></dt>
|
|
<dd>The client or server designation only has
|
|
meaning for the TLS subsystem. It has no bearing on OpenVPN's
|
|
peer-to-peer, UDP-based communication model.*</dd>
|
|
</dl>
|
|
<p>First, build a separate certificate/key pair for both bob and alice (see
|
|
above where <tt class="docutils literal"><span class="pre">--cert</span></tt> is discussed for more info). Then construct
|
|
Diffie Hellman parameters (see above where <tt class="docutils literal"><span class="pre">--dh</span></tt> is discussed for
|
|
more info). You can also use the included test files <code>client.crt</code>,
|
|
<code>client.key</code>, <code>server.crt</code>, <code>server.key</code> and
|
|
<code>ca.crt</code>. The <tt class="docutils literal">.crt</tt> files are certificates/public-keys, the
|
|
<tt class="docutils literal">.key</tt> files are private keys, and <code>ca.crt</code> is a certification
|
|
authority who has signed both <code>client.crt</code> and <code>server.crt</code>.
|
|
For Diffie Hellman parameters you can use the included file
|
|
<code>dh2048.pem</code>.</p>
|
|
<dl class="docutils">
|
|
<dt><em>WARNING:</em></dt>
|
|
<dd>All client, server, and certificate authority certificates
|
|
and keys included in the OpenVPN distribution are totally
|
|
insecure and should be used for testing only.</dd>
|
|
</dl>
|
|
<p>On bob:</p>
|
|
<pre class="literal-block">
|
|
openvpn --remote alice.example.com --dev tun1 \
|
|
--ifconfig 10.4.0.1 10.4.0.2 \
|
|
--tls-client --ca ca.crt \
|
|
--cert client.crt --key client.key \
|
|
--reneg-sec 60 --verb 5
|
|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
openvpn --remote bob.example.com --dev tun1 \
|
|
--ifconfig 10.4.0.2 10.4.0.1 \
|
|
--tls-server --dh dh1024.pem --ca ca.crt \
|
|
--cert server.crt --key server.key \
|
|
--reneg-sec 60 --verb 5
|
|
</pre>
|
|
<p>Now verify the tunnel is working by pinging across the tunnel.</p>
|
|
<p>On bob:</p>
|
|
<pre class="literal-block">
|
|
ping 10.4.0.2
|
|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
ping 10.4.0.1
|
|
</pre>
|
|
<p>Notice the <tt class="docutils literal"><span class="pre">--reneg-sec</span> 60</tt> option we used above. That tells OpenVPN
|
|
to renegotiate the data channel keys every minute. Since we used
|
|
<tt class="docutils literal"><span class="pre">--verb</span> 5</tt> above, you will see status information on each new key
|
|
negotiation.</p>
|
|
<p>For production operations, a key renegotiation interval of 60 seconds is
|
|
probably too frequent. Omit the <tt class="docutils literal"><span class="pre">--reneg-sec</span> 60</tt> option to use
|
|
OpenVPN's default key renegotiation interval of one hour.</p>
|
|
</div>
|
|
<div class="section" id="routing">
|
|
<h2>Routing:</h2>
|
|
<p>Assuming you can ping across the tunnel, the next step is to route a
|
|
real subnet over the secure tunnel. Suppose that bob and alice have two
|
|
network interfaces each, one connected to the internet, and the other to
|
|
a private network. Our goal is to securely connect both private
|
|
networks. We will assume that bob's private subnet is <em>10.0.0.0/24</em> and
|
|
alice's is <em>10.0.1.0/24</em>.</p>
|
|
<p>First, ensure that IP forwarding is enabled on both peers. On Linux,
|
|
enable routing:</p>
|
|
<pre class="literal-block">
|
|
echo 1 > /proc/sys/net/ipv4/ip_forward
|
|
</pre>
|
|
<p>This setting is not persistent. Please see your operating systems
|
|
documentation how to properly configure IP forwarding, which is also
|
|
persistent through system boots.</p>
|
|
<p>If your system is configured with a firewall. Please see your operating
|
|
systems guide on how to configure the firewall. You typically want to
|
|
allow traffic coming from and going to the tun/tap adapter OpenVPN is
|
|
configured to use.</p>
|
|
<p>On bob:</p>
|
|
<pre class="literal-block">
|
|
route add -net 10.0.1.0 netmask 255.255.255.0 gw 10.4.0.2
|
|
</pre>
|
|
<p>On alice:</p>
|
|
<pre class="literal-block">
|
|
route add -net 10.0.0.0 netmask 255.255.255.0 gw 10.4.0.1
|
|
</pre>
|
|
<p>Now any machine on the <em>10.0.0.0/24</em> subnet can access any machine on the
|
|
<em>10.0.1.0/24</em> subnet over the secure tunnel (or vice versa).</p>
|
|
<p>In a production environment, you could put the route command(s) in a
|
|
script and execute with the <tt class="docutils literal"><span class="pre">--up</span></tt> option.</p>
|
|
</div>
|
|
</div>
|
|
</div>
|
|
</body>
|
|
</html>
|