How To set up an OpenVPN Server on Windows

Network diagram

Server configuration

• OpenVPN Server:
  • OS: Windows Server 2019
  • Role: OpenVPN Server
  • IP: 192.168.0.254

Prerequisites

In order to create the connection certificates, we need to install OpenSSL library. I personaly use the slproweb.com packages.

Download OpenSSL

Download the latest version of OpenSSL Light.

Install OpenSSL

• Accept the license agreement:

• Select destination location:

• Select start menu folder:

• Select the OpenSSL binaries directory:

• Click on install:

• Click on Finish to exit (and donate if you can, it helps the project! 🥰)

Add OpenSSL in Environment Variables

We'll add OpenSSL to the environment variables.

• Run SystemPropertiesAdvanced to open the System Properties:

• Click on Environment Variables…:

• Select Path and click on Edit…:

• Click on New and add the line %ProgramFiles%\OpenSSL-Win64\bin:

• Open a new Windows command prompt and check that you can run this openssl command:

Installing OpenVPN

Go to the official OpenVPN website: https://openvpn.net/ to download the lastest installer.

• As we want to install OpenVPN as a server, we will choose Customize:

• We enable the OpenVPN Service to run on startup:

• We install EasyRsa to create certificates for the server and clients:

• Finally, click on Close:

Set up a Certificate Authority (CA) and generate certificates and keys for server and clients

Here we're going to set up a pki to create our server and client certificates.

• Open a Command Prompt:

• Type the following commands to enter the EasyRSA command interpreter:

• Delete the existing configuration, just in case:

• Initialize pki, and type yes to confirm:

• Create the certificate authority:

• Generate server certificate and key:

• Generate Diffie Hellman parameters:

Create clients certificates

• If it has been closed previously or to add new clients, open an EasyRSA shell:

• Generate client certificates:

Certificates

• Move these files (from C:\Program Files\OpenVPN\easy-rsa\pki, C:\Program Files\OpenVPN\easy-rsa\pki\issued and C:\Program Files\OpenVPN\easy-rsa\pki\private):
  • ca.crt
  • dh.pem
  • server.crt
  • server.key
• In the folders C:\Program Files\OpenVPN\config-auto and C:\Program Files\OpenVPN\config.

Add a Windows Firewall Rule

• We need to create two firewall rules:
  • One to open port 1194 in udp to allow OpenVPN clients connections
  • Another to authorize the 10.50.8.0/24 network, so that clients can communique with the services present on the server (ping, file sharing etc…).

To do this, use the Windows Firewall Management Console or these two commands in an administrator's PowerShell console.

• Create the rule to allow incoming connections on port 1194 udp:

• Create the rule to allow all incoming connections from the 10.50.8.0/24 network:

The server.ovpn configuration file

As administrator, create the file C:\Program Files\OpenVPN\config-auto\server.ovpn:

Restart the OpenVPN service

Then, restart the OpenVPN service:

• From the service management console:

• Right-click on the OpenVPNService and select Restart:

• Or from an administrator's command prompt:

• Or from a PowerShell console:

Client configuration

• OpenVPN Client:
  • OS: Windows 11
  • Role: OpenVPN Client

Installing OpenVPN

We're going to download the same package as for the server, and install it with the default settings.

Copy certificates from the Server

• From the server, retrieve the following files (from C:\Program Files\OpenVPN\easy-rsa\pki, C:\Program Files\OpenVPN\easy-rsa\pki\issued and C:\Program Files\OpenVPN\easy-rsa\pki\private):
  • ca.crt
  • client01.crt
  • client01.key
• And paste them into C:\Program Files\OpenVPN\config.

• Edit C:\Program Files\OpenVPN\config\client.ovpn file with administrator rights:

Establishing the connection

• Right-click on the OpenVPN desktop icon and select Run as administrator:

• Right-click on the OpenVPN icon next to the Windows clock and click on Connect:

• A pop-up window confims that we are connected:

Server Access

To reach the server, we'll use the IP address 10.50.8.1.

⚠️ Troubleshooting: After a Windows Update, I no longer had access to the server share (OpenVPN could connect, however). For this to work again, I had to repair (available by re-running the installer) the OpenVPN program on the server.