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

TCP protocol and different ports

The default protocol that OpenVPN uses is UDP, as it is generally more suitable for VPN connections. However, if the TCP protocol is required, then the preceding example needs to be modified only slightly:

On the listening end, start the OpenVPN server instance:

[root@server] # openvpn \
    --ifconfig \
    --dev tun \
    --proto tcp-server

On the client side, the code is as follows:

[root@client] # openvpn \
    --ifconfig \
     --dev tun \
    --proto tcp-client \

OpenVPN will now connect over TCP port 1194. It is also possible to override the port number using the --port parameter, for example, --port 5000.

The TAP mode

If non-TCP/IP traffic needs to be passed over the VPN tunnel (for example, legacy AppleTalk or IPX traffic), then a tap device is required. The tap device provides an interface to pass full Ethernet frames over the VPN tunnel. The overhead when passing full...