Complete site-to-site setup

In this recipe, we set up a complete site-to-site network, using most of the built-in security features that OpenVPN offers. It is intended as a "one-stop-shop" example of how to set up a point-to-point network.

Getting ready

We use the following network layout:

Install OpenVPN 2.0 or higher on two computers. Make sure that the computers are connected over a network. For this recipe, the server computer was running CentOS 5 Linux and OpenVPN 2.1.1 and the client was running Fedora 13 Linux and OpenVPN 2.1.1. We'll use the secret.key file from the OpenVPN Secret keys recipe here.

Make sure routing (IP forwarding) is configured on both the server and client.

How to do it...

1. Create the server configuration file:

   dev tun
   proto udp
   local  openvpnserver.example.com
   lport  1194
   remote openvpnclient.example.com
   rport  1194
   
   secret secret.key 0
   ifconfig 10.200.0.1 10.200.0.2
   route 192.168.4.0 255.255.255.0
   
   user  nobody
   group nobody
   persist-tun
   persist-key
   keepalive 10 60
   ping-timer-rem
   
   verb 3
   daemon
   log-append /tmp/openvpn.log

   Save it as example1-7-server.conf.

2. On the client side, we create the configuration file:

   dev tun
   proto udp
   local  openvpnclient.example.com
   lport  1194
   remote openvpnserver.example.com
   rport  1194
   
   secret secret.key 1
   ifconfig 10.200.0.2 10.200.0.1
   route 172.31.32.0 255.255.255.0
   
   user  nobody
   group nobody
   persist-tun
   persist-key
   keepalive 10 60
   ping-timer-rem
   
   verb 3
   daemon
   log-append /tmp/openvpn.log

   Save it as example1-7-client.conf.

3. We start the tunnel on both ends:

       [root@server]# openvpn --config example1-7-server.conf
   

   And:

       [root@client]# openvpn --config client.conf
   

   Now our site-to-site tunnel is established.

4. Check the log files on both the client and server, to verify that the connection has been established.

   After the connection comes up, the machines on the LANs behind both end points can be reached over the OpenVPN tunnel.

5. For example, when we ping a machine on the client-side LAN from the server, we see the following:

   

How it works...

The client and server configuration files are very similar:

• The server listens only on one interface and one UDP port

• The server accepts connections only from a single IP address and port

• The client has these options mirrored

Here is the set of configuration options:

user  nobody
group nobody
persist-tun
persist-key
keepalive 10 60
ping-timer-rem

They are used to make the connection more robust and secure, as follows:

• The OpenVPN process runs as user nobody, group nobody, after the initial connection is established. Even if somebody is able to take control of the OpenVPN process itself he would still only be user nobody and not root. Note that on some Linux distributions the group nogroup is used instead.

• The persist-tun and persist-key options are used to ensure that the connection comes back up automatically if the underlying network is disrupted. These options are necessary when using user nobody and group nobody (or group nogroup).

• The keepalive and ping-timer-rem options cause OpenVPN to send a periodic 'ping' message over the tunnel to ensure that both ends of the tunnel remain up and running.

There's more...

This point-to-point setup can also be used to evade restrictive firewalls. The data stream between the two endpoints is not recognizable and very hard to decipher. When OpenVPN is run in client/server (see Chapter 2, Multi-client TUN-style Networks), the traffic is recognizable as OpenVPN traffic due to the initial TLS handshake.

See also

• Chapter 8, Troubleshooting OpenVPN: Routing Issues, in which the most common routing issues are explained.