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

Using an external DHCP server

In a bridged setup, it is possible to integrate the clients into the server-side network even further. In most networks, a DHCP server is used to assign IP addresses. Normally, OpenVPN assigns IP addresses to its clients using either the following command:


Or, using the following command:


It is also possible to use an external DHCP server to assign addresses to the OpenVPN clients. To achieve this, simply remove the specification of any IP address ranges after the server-bridge option, as shown in the following (Linux-oriented) configuration file:

proto udp
port 1194

dev tap0 ## the '0' is extremely important


remote-cert-tls client
tls-auth /etc/openvpn/movpn/ta.key 0
dh       /etc/openvpn/movpn/dh2048.pem
ca       /etc/openvpn/movpn/movpn-ca.crt
cert     /etc/openvpn/movpn/server.crt
key      /etc/openvpn/movpn/server.key