[Tutorial] CentOS 6 OpenVPN Client - Connecting to Existing Site to Site VPN (TomatoUSB)

In this tutorial, I'm going to show you how to add a CentOS 6 server as a OpenVPN client to your existing Site to Site VPN.

This is an extension of my [Tutorial - 30 Minutes or Less] Site to Site VPN with TomatoUSB and OpenVPN and assumes you already have your Site to Site VPN operational. However, you should be able to follow this tutorial and connect to any existing OpenVPN Server.

At the end of this tutorial, your CentOS server will be able to securely access your LAN resources (i.e, computers, printers) on both sites and vice versa (you will also be able to seamlessly access your CentOS server).

Overview of the Steps:

1) Generate Certs and Keys

2) Copy/Transfer over Certs and Keys to Client VPS

3) Install OpenVPN (client)

4) Configure OpenVPN Client

5) Connect

Generate cert/keys for VPS (CentOS 6 32-bit OpenVPN Client)

SSH into your TomatoUSB OpenVPN Server.

#Setup and initialize environment
cd /opt/openvpn-easy-rsa
source ./vars

#myvps_client is the Common Name
./build-key myvps_client

Copy/Transfer over Certs and Keys to Client VPS

Since my CentOS server is running SSH, I'm going to use SSH and SCP (secure copy) to transfer over the certificates and key. You can also transfer over the keys via SFTP or a USB drive.

#create the /etc/openvpn/keys folder on my centos server
ssh root@myvps.qnology.com mkdir -p /etc/openvpn/keys 

#copy over the certificates and keys
#all one line
cd /opt/openvpn-easy-rsa
scp keys/ca.crt keys/myvps_client.crt keys/myvps_client.key root@myvps.qnology.com:/etc/openvpn/keys

Install OpenVPN on CentOS 6

#Bring everything up to date
yum -y update
#Add EPEL (Extra Packages for Enterprise Linux) Repo
# RHEL/CentOS 6 32-Bit ##
cd /tmp 

wget http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm rpm -ivh epel-release-6-8.noarch.rpm

yum --enablerepo=epel install openvpn.i686

Configure OpenVPN Client

#copy sample client.conf to /etc/openvpn
cp /usr/share/doc/openvpn-2.2.2/sample-config-files/client.conf /etc/openvpn

#edit openvpn client.conf

nano /etc/openvpn/client.conf

Update the following lines
#remote OpenVPNServer.ADynamicDNSAddress.com 1194
#ca /etc/openvpn/keys/ca.crt
#cert /etc/openvpn/keys/myvps_client.crt
#key /etc/openvpn/keys/myvps_client.key

#start VPN manually to test
openvpn --config /etc/openvpn/client.conf

#test starting VPN as a service
service openvpn start

#autostart at OpenvPN client on reboot
chkconfig openvpn on