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

Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 22 Linux and OpenVPN 2.3.10. We'll use the secret.key file from the OpenVPN secret keys recipe here.

We will use the following network layout:

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  # use "group nogroup" on some distros 
           persist-tun 
           persist-key 
           keepalive 10 60 
           ping-timer-rem 
    
           verb 3 
           daemon 
           log-append /tmp/openvpn.log 
   

2. Save it as example1-7-server.conf.
3. On the client side, 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  # use "group nogroup" on some distros 
           persist-tun 
           persist-key 
           keepalive 10 60 
           ping-timer-rem 
    
           verb 3 
           daemon 
           log-append /tmp/openvpn.log 
   

4. Save it as example1-7-client.conf.
5. Then start the tunnel on both ends. The following is for the server end:

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

   Here's the code for the client end:

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

   Now our site-to-site tunnel is established.

6. Check the log files on both the client and server to verify that the connection has been established.
7. After the connection comes up, the machines on the LANs behind both the end points can be reached over the OpenVPN tunnel. For example, when we ping a machine on the client-side LAN from the server, we will 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 

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

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

The persist-tun and persist-key options are used to ensure that the connection comes back 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, Client-server IP-only Networks), the traffic is recognizable as OpenVPN traffic due to the initial TLS handshake.

See also

• The last recipe in this chapter, Using IPv6, which builds upon this recipe by adding support for IPv6 traffic
• Chapter 7, Troubleshooting OpenVPN - Routing, in which the most common routing issues are explained