Book Image

Mastering OpenVPN

By : Jan Just Keijser, Eric F Crist
Book Image

Mastering OpenVPN

By: Jan Just Keijser, Eric F Crist

Overview of this book

Security on the internet is increasingly vital to both businesses and individuals. Encrypting network traffic using Virtual Private Networks is one method to enhance security. The internet, corporate, and “free internet” networks grow more hostile every day. OpenVPN, the most widely used open source VPN package, allows you to create a secure network across these systems, keeping your private data secure. The main advantage of using OpenVPN is its portability, which allows it to be embedded into several systems. This book is an advanced guide that will help you build secure Virtual Private Networks using OpenVPN. You will begin your journey with an exploration of OpenVPN, while discussing its modes of operation, its clients, its secret keys, and their format types. You will explore PKI: its setting up and working, PAM authentication, and MTU troubleshooting. Next, client-server mode is discussed, the most commonly used deployment model, and you will learn about the two modes of operation using "tun" and "tap" devices. The book then progresses to more advanced concepts, such as deployment scenarios in tun devices which will include integration with back-end authentication, and securing your OpenVPN server using iptables, scripting, plugins, and using OpenVPN on mobile devices and networks. Finally, you will discover the strengths and weaknesses of the current OpenVPN implementation, understand the future directions of OpenVPN, and delve into the troubleshooting techniques for OpenVPN. By the end of the book, you will be able to build secure private networks across the internet and hostile networks with confidence.
Table of Contents (17 chapters)
Mastering OpenVPN
About the Authors
About the Reviewers


Scripting is likely one of the best tools available to an OpenVPN administrator. With the ability to designate both client-side and server-side scripts, OpenVPN can initiate other system responses by opening firewalls, running applications, or even sending a message to an administrator.

One important caveat when writing scripts is the time it takes for a script to complete. OpenVPN is a single-threaded process, which means that while a script is running the entire VPN is blocked to all connected or connecting clients. A slow authentication script can cripple a well-functioning VPN. Plugins are less affected by this, as they do run in a separate thread.

As of Version 2.3.6, OpenVPN supports 13 server-side scripting options and 10 client-side options. The commands with asterisks are setup options, and allow the options that follow to do specific things. The server-side scripts are as follows (in the order of execution):

  • --setenv*

  • --setenv-safe*

  • --script-security*

  • --up-restart*

  • ...