212.5 OpenVPN (weight: 2)

Tech Tutorial: 212.5 OpenVPN #

Introduction #

OpenVPN is a robust and highly flexible VPN daemon. It supports SSL/TLS for key exchange and is capable of traversing network address translators (NATs) and firewalls. This tutorial will guide you through the setup and configuration of an OpenVPN server on Linux, and provide detailed code examples to illustrate each step.

Exam Objective: #

The candidate should be able to manage and maintain a secure OpenVPN server.

Key Knowledge Areas: #

  • Installation of OpenVPN on various Linux distributions
  • Configuration of OpenVPN server and clients
  • Management of server-side and client-side certificates
  • Troubleshooting OpenVPN setups

Utilities: #

  • openvpn
  • easy-rsa

Step-by-Step Guide #

Step 1: Installation of OpenVPN #

Depending on your Linux distribution, use one of the following commands to install OpenVPN:

On Debian/Ubuntu systems: #

sudo apt update
sudo apt install openvpn easy-rsa

On Red Hat-based systems: #

sudo yum install epel-release
sudo yum install openvpn easy-rsa

On Arch Linux: #

sudo pacman -Sy openvpn easy-rsa

Step 2: Certificate Management with easy-rsa #

  1. Set up the environment:
make-cadir ~/openvpn-ca
cd ~/openvpn-ca
  1. Customize the vars file: Edit the vars file in the easy-rsa directory to adjust the certificate options.
nano vars

Example configuration:

export KEY_COUNTRY="US"
export KEY_PROVINCE="CA"
export KEY_CITY="SanFrancisco"
export KEY_ORG="MyOrg"
export KEY_EMAIL="me@example.com"
export KEY_OU="MyOrganizationalUnit"
  1. Source the vars file:
source vars
  1. Clean up the environment and build the CA:
./clean-all
./build-ca
  1. Generate server certificate and key:
./build-key-server server
  1. Generate client certificate and key:
./build-key client1

Step 3: Configure the OpenVPN Server #

  1. Copy the server configuration template:
gunzip -c /usr/share/doc/openvpn/examples/sample-config-files/server.conf.gz > /etc/openvpn/server.conf
  1. Edit the server configuration:
nano /etc/openvpn/server.conf

Include the paths to the certificates and keys you created:

ca ca.crt
cert server.crt
key server.key  # This file should be kept secret
dh dh2048.pem
  1. Enable IP forwarding:
echo "net.ipv4.ip_forward = 1" >> /etc/sysctl.conf
sysctl -p
  1. Start the OpenVPN service:
systemctl start openvpn@server
systemctl enable openvpn@server

Step 4: Setting up OpenVPN Client #

  1. Transfer the client certificates and keys: Securely transfer ca.crt, client1.crt, and client1.key to the client machine.

  2. Create client configuration file: Use a template or create a new configuration file:

nano client.conf

Example client configuration:

client
dev tun
proto udp
remote my-server-1 1194
resolv-retry infinite
nobind
user nobody
group nogroup
persist-key
persist-tun
ca ca.crt
cert client1.crt
key client1.key
remote-cert-tls server
cipher AES-256-CBC
verb 3
  1. Start the OpenVPN client:
sudo openvpn --config client.conf

Conclusion #

In this tutorial, we have covered the installation, configuration, and management of an OpenVPN server and client setup on Linux. We also went through the process of creating and managing certificates using easy-rsa. This setup ensures a secure connection between the client and the server using strong encryption standards.

For further customization and detailed troubleshooting, refer to the OpenVPN manual and your distribution’s specific guidelines on OpenVPN.