OpenVPN server on Windows

Introduction

OpenVPN is an open-source software application that implements virtual private network (VPN) techniques for creating secure point-to-point or site-to-site connections in routed or bridged configurations and remote access facilities.

This article contains step-by-step instructions on how to create and run an OpenVPN server on a PC that runs on Windows OS. The information provided here is geared towards users of almost any knowledge level. The instructions apply to Windows 7 and newer systems.

Configuration overview and prerequisites

Before we begin, let's overview the configuration that we are attempting to achieve and the prerequisites that make it possible.

Prerequisites:

• A PC or Laptop running on Windows 7 or a later version
• The PC in question must have a Public IP address
• An active Internet connection

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Objective:

The purpose of this article is to provide the know-how needed to configure a working OpenVPN server on a Windows PC.

Step 1: installing OpenVPN software

• Download an OpenVPN installer file from here.
  Run the downloaded file.
• Before starting the installation process, click 'Customize':
  
• While in the 'Custom Installation' window, scroll down to find OpenSSL Utilities → EasyRSA 3 Certificate Management Scripts; make sure it is installed along with OpenVPN and click 'Install Now':
  

Step 2: preparing EasyRSA

• Now we can start preparing to generate certificates and keys. For this we'll be using the EasyRSA 3 application that was installed along with OpenVPN.
  EasyRSA commands have to be executed via the Windows Command Prompt. It can be opened by typing cmd in the Windows search bar (Windows button + S). When you launch it, make sure you run it as administrator:
  
• Change the current directory to the EasyRSA folder. To do so, execute this command:

  cd "C:\Program Files\OpenVPN\easy-rsa"

• Launch EasyRSA:

  EasyRSA-Start.bat

• Before you can generate files with EasyRSA, you must first initialize a directory for the Public Key Infrastructure (PKI). This can be done with the following command:

  ./easyrsa init-pki

• Open the vars.bat file with the Notepad text editor:

  notepad vars.bat

• This is the template file for generating certificates, i.e., the information stored here will be offered as default values during certificate generation. Locate and edit the following lines in accordance with your needs:

  set KEY_COUNTRY=US
  set KEY_PROVINCE=CA
  set KEY_CITY=SanFrancisco
  set KEY_ORG=OpenVPN
  set [email protected]

• You can also set the key size for the Diffie Hellman parameters:

  set DH_KEY_SIZE=2048

• Once you're done, save the file and close the editor; then run the following commands:

  vars.bat
  ./easyrsa clean-all

Step 3: generating certificates and keys

• Now we can start generating the certificates and keys. Begin with the certificate authority (CA) - the root certificate file that will be used to sign other certificates and keys:

  ./easyrsa build-ca nopass

• Next, build the server certificate and key:

  ./easyrsa build-server-full server nopass

• Next, build certificates and keys for the clients:

  ./easyrsa build-client-full Client1 nopass

  Note: replace Client1 with this client's Common Name (CN). Omit "nopass" and you will be prompted to choose the client's password.
  
  
• Lastly, generate Diffie Hellman parameters:

  ./easyrsa gen-dh

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The generated and signed files should appear in the following directories (by default):

File(s)		Location
CA certificate	→	C:\Program Files\OpenVPN\easy-rsa\pki
Diffie-Hellman parameters	→	C:\Program Files\OpenVPN\easy-rsa\pki
Client and Server keys	→	C:\Program Files\OpenVPN\easy-rsa\pki\private
Client and Server certificates	→	C:\Program Files\OpenVPN\easy-rsa\pki\issued