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.
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.
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
example1-7-server.conf
.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
example1-7-client.conf
. [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.
The client and server configuration files are very similar:
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.
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.
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