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OpenVPN Cookbook
OpenVPN Cookbook

OpenVPN Cookbook: Get the most out of OpenVPN by exploring it's advanced features. , Second Edition

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OpenVPN Cookbook

Chapter 2.  Client-server IP-only Networks

In this chapter, we will cover the following topics:

  • Setting up the public and private keys
  • A simple configuration
  • Server-side routing
  • Adding IPv6 support
  • Using client-config-dir files
  • Routing - subnets on both sides
  • Redirecting the default gateway
  • Redirecting the IPv6 default gateway
  • Using an ifconfig-pool block
  • Using the status file
  • The management interface
  • Proxy-arp

Introduction

The recipes in this chapter will cover the most commonly used deployment model for OpenVPN: a single server with multiple remote clients capable of routing IP traffic.

We will also look at several common routing configurations in addition to the use of the management interface at both the client and server side.

The last recipe of this chapter will show how it is possible to avoid the use of network bridges for most practical use cases.

As a routed TUN-style setup is the most commonly used deployment model, some of the sample configuration files presented in this chapter will be reused throughout the rest of the book. In particular, the configuration files such as basic-udp-server.confbasic-udp-client.confbasic-tcp-server.conf, and basic-tcp-client.conf from the Server-side routing recipe will be reused often, as well as the Windows client configuration files basic-udp-client.ovpn and basic-tcp-client.ovpn from the Using an ifconfig-pool block...

Setting up the public and private keys

Before we can set up a client/server VPN, we need to set up the public key infrastructure (PKI). The PKI comprises the certificate authority, the private keys, and the certificates (public keys) for both the client and server. We also need to generate a Diffie-Hellman parameter file, which is required for perfect forward secrecy.

To set up PKI, we make use of the easy-rsa scripts. These scripts were originally supplied with the OpenVPN distribution itself, but nowadays, they can also be downloaded and installed separately.

Getting ready

The PKI needs to be set up on a trusted computer. This can be the same as the computer on which the OpenVPN server is run, but from a security point of view, it is best if the PKI is kept completely separate from the rest of the OpenVPN services. One option is to keep the PKI certificate authority (CA) key located on a separate external disk, which is attached only when required. Another option would be to keep the CA...

A simple configuration

This recipe will demonstrate how to set up a connection in the client or server mode using certificates.

Getting ready

Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 22 Linux and OpenVPN 2.3.10.

How to do it...

  1. Create the server configuration file:
            proto udp 
            port 1194 
            dev tun 
            server 10.200.0.0 255.255.255.0 
     
            ca   /etc/openvpn/cookbook/ca.crt 
            cert /etc/openvpn/cookbook/server.crt 
            key  /etc/openvpn/cookbook/server.key 
            dh   /etc/openvpn/cookbook/dh2048.pem 
    

    Then save it as example2-2-server.conf.

  2. Copy over...

Server-side routing

This recipe will demonstrate how to set up server-side routing in client or server mode. With this setup, the OpenVPN client will be able to reach all the machines behind the OpenVPN server.

Compared to the previous recipe, this recipe contains extra settings that are often used in production environments including the use of linear addresses (topology subnet).

The configuration files used in this recipe are useful building blocks for other recipes throughout this book; therefore, they are named basic-udp-server.confbasic-udp-client.conf, and so on.

Getting ready

Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9.

We use the following network layout here:

Getting ready

How to do it...

  1. Create the server configuration file...

Introduction


The recipes in this chapter will cover the most commonly used deployment model for OpenVPN: a single server with multiple remote clients capable of routing IP traffic.

We will also look at several common routing configurations in addition to the use of the management interface at both the client and server side.

The last recipe of this chapter will show how it is possible to avoid the use of network bridges for most practical use cases.

As a routed TUN-style setup is the most commonly used deployment model, some of the sample configuration files presented in this chapter will be reused throughout the rest of the book. In particular, the configuration files such as basic-udp-server.confbasic-udp-client.confbasic-tcp-server.conf, and basic-tcp-client.conf from the Server-side routing recipe will be reused often, as well as the Windows client configuration files basic-udp-client.ovpn and basic-tcp-client.ovpn from the Using an ifconfig-pool block recipe.

Setting up the public and private keys


Before we can set up a client/server VPN, we need to set up the public key infrastructure (PKI). The PKI comprises the certificate authority, the private keys, and the certificates (public keys) for both the client and server. We also need to generate a Diffie-Hellman parameter file, which is required for perfect forward secrecy.

To set up PKI, we make use of the easy-rsa scripts. These scripts were originally supplied with the OpenVPN distribution itself, but nowadays, they can also be downloaded and installed separately.

Getting ready

The PKI needs to be set up on a trusted computer. This can be the same as the computer on which the OpenVPN server is run, but from a security point of view, it is best if the PKI is kept completely separate from the rest of the OpenVPN services. One option is to keep the PKI certificate authority (CA) key located on a separate external disk, which is attached only when required. Another option would be to keep the CA private...

A simple configuration


This recipe will demonstrate how to set up a connection in the client or server mode using certificates.

Getting ready

Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 22 Linux and OpenVPN 2.3.10.

How to do it...

  1. Create the server configuration file:

            proto udp 
            port 1194 
            dev tun 
            server 10.200.0.0 255.255.255.0 
     
            ca   /etc/openvpn/cookbook/ca.crt 
            cert /etc/openvpn/cookbook/server.crt 
            key  /etc/openvpn/cookbook/server.key 
            dh   /etc/openvpn/cookbook/dh2048.pem 
    

    Then save it as example2-2-server.conf.

  2. Copy over the public certificates and the server private key from the /etc/openvpn/cookbook/keys directory:

          [server]$ cd /etc/openvpn/cookbook
          [server]$ cp keys...

Server-side routing


This recipe will demonstrate how to set up server-side routing in client or server mode. With this setup, the OpenVPN client will be able to reach all the machines behind the OpenVPN server.

Compared to the previous recipe, this recipe contains extra settings that are often used in production environments including the use of linear addresses (topology subnet).

The configuration files used in this recipe are useful building blocks for other recipes throughout this book; therefore, they are named basic-udp-server.confbasic-udp-client.conf, and so on.

Getting ready

Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9.

We use the following network layout here:

How to do it...

  1. Create the server configuration file:

        ...

Adding IPv6 support


Support for IPv6 addresses is relatively new in OpenVPN. As IPv6 addresses are now being used more and more by companies and Internet Service Providers, this recipe provides a setup for using IPv6 for tunnel endpoints as well as using it inside the tunnel.

Getting ready

This recipe is a continuation of the previous one. Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9. Keep the configuration file, basic-udp-server.conf, from the previous recipe at hand as well as the client configuration file, basic-udp-client.conf.

How to do it...

  1. Modify the server configuration file, basic-udp-server.conf, by adding a line:

        server-ipv6 2001:db8:100::0/112
    

    Then save it as example2-4-server.conf.

  2. Start the server:

          [root...

Using client-config-dir files


In a setup where a single server can handle many clients, it is sometimes necessary to set per-client options that overrule the global options. The client-config-dir option is very useful for this. It allows the administrator to assign a specific IP address to a client; to push specific options, such as compression and DNS server, to a client; or to temporarily disable a client altogether.

Getting ready

This recipe is a continuation of the previous one. Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. Set up the client and server certificates using the previous recipe. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9. Keep the server configuration file, basic-udp-server.conf, at hand along with the client configuration file, basic-udp-client.conf, from the Server-side routing recipe.

How to do it...

  1. Modify the server...

Routing - subnets on both sides


This recipe will demonstrate how to set up server-side and client-side routing in client/server mode. With this setup, the OpenVPN client will be able to reach all the machines behind the OpenVPN server, and the server will be able to reach all the machines behind the client.

Getting ready

This recipe uses the PKI files created in the first recipe of this chapter. Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9. Keep the server configuration file, basic-udp-server.conf, handy along with the client configuration file, basic-udp-client.conf, from the Server-side routing recipe.

We use the following network layout:

How to do it...

  1. Modify the server configuration file, basic-udp-server.conf, by adding these lines:

            client-config-dir /etc/openvpn/cookbook/clients ...

Redirecting the default gateway


A very common use of a VPN is to route all of the traffic over a secure tunnel. This allows one to safely access a network or even the Internet itself from within a hostile environment (for example, a poorly protected, but properly trojaned Internet caféteria).

In this recipe, we will set up OpenVPN to do exactly this. This recipe is very similar to the Server-side routing recipe, but there are some pitfalls when redirecting all of the traffic over a VPN tunnel.

Getting ready

The network layout used in this recipe is the same as in the Server-side routing recipe.

This recipe uses the PKI files created in the first recipe of this chapter. Install OpenVPN 2.3.9 or higher on two computers. Make sure the computers are connected over a network. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.3.9 and the client was running Fedora 20 Linux and OpenVPN 2.3.9. Keep the server configuration file, basic-udp-server.conf, at hand along with the...

Redirecting the IPv6 default gateway


With the advent of IPv6 networks, it is becoming increasingly important to be able to set up a VPN that will secure both IPv4 and IPv6 traffic. If only IPv4 traffic is secured over a VPN tunnel, then it is still possible for traffic to leak out over IPv6. In this recipe, we will set up OpenVPN to secure all IPv6 traffic as well. Support for this was added in OpenVPN 2.4.

Getting ready

The network layout used in this recipe is the same as in the Server-side routing recipe.

This recipe uses the PKI files created in the first recipe of this chapter. Install OpenVPN 2.4 or higher on two computers. Make sure the computers are connected over a network. For this recipe, the server computer was running CentOS 6 Linux and OpenVPN 2.4 and the client was running Fedora 20 Linux and OpenVPN 2.4. For the server, keep the IPv6 configuration file, example2-4-server.conf, from the Adding IPv6 support recipe at hand. For the client, keep the configuration file, basic-udp...

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Key benefits

  • Master the skills of configuring, managing, and securing your VPN using the latest OpenVPN
  • Gain expertise in establishing IPv6 connections and understand PolarSSL using the latest version of OpenVPN
  • This book contains enticing recipes about OpenVPN functionalities that cater to mission critical applications

Description

OpenVPN provides an extensible VPN framework that has been designed to ease site-specific customization, such as providing the capability to distribute a customized installation package to clients, and supporting alternative authentication methods via OpenVPN’s plugin module interface. This book provides you with many different recipes to help you set up, monitor, and troubleshoot an OpenVPN network. You will learn to configure a scalable, load-balanced VPN server farm that can handle thousands of dynamic connections from incoming VPN clients. You will also get to grips with the encryption, authentication, security, extensibility, and certifications features of OpenSSL. You will also get an understanding of IPv6 support and will get a demonstration of how to establish a connection via IPv64. This book will explore all the advanced features of OpenVPN and even some undocumented options, covering all the common network setups such as point-to-point networks and multi-client TUN-style and TAP-style networks. Finally, you will learn to manage, secure, and troubleshoot your virtual private networks using OpenVPN 2.4.

Who is this book for?

This book is for system administrators who have a basic knowledge of OpenVPN and are eagerly waiting to build, secure, and manage VPNs using the latest version. This book assumes some prior knowledge of TCP/IP networking and OpenVPN and you must have network administration skills to get the most out of this book.

What you will learn

  • Determine the best type of OpenVPN setup for your networking needs
  • Get to grips with the encryption, authentication, and certifications features of OpenSSL.
  • Integrate an OpenVPN server into the local IT infrastructure with the scripting features of OpenVPN
  • Ease the integration of Windows clients into the VPN using Windows-specific client-side configuration
  • Understand the authentication plugins for PAM and LDAP
  • Get to know the difference between TUN-style and TAP-style networks and when to use what
  • Troubleshoot your VPN setup
  • Establish a connection via IPv6 along with demonstrations

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Table of Contents

10 Chapters
1. Point-to-Point Networks Chevron down icon Chevron up icon
2. Client-server IP-only Networks Chevron down icon Chevron up icon
3. Client-server Ethernet-style Networks Chevron down icon Chevron up icon
4. PKI, Certificates, and OpenSSL Chevron down icon Chevron up icon
5. Scripting and Plugins Chevron down icon Chevron up icon
6. Troubleshooting OpenVPN - Configurations Chevron down icon Chevron up icon
7. Troubleshooting OpenVPN - Routing Chevron down icon Chevron up icon
8. Performance Tuning Chevron down icon Chevron up icon
9. OS Integration Chevron down icon Chevron up icon
10. Advanced Configuration Chevron down icon Chevron up icon

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