Virtual Private Networks, Second Edition

Creating a VPN with PPP and SSH

It’s possible to create a routed secure network over the Internet by creating a PPP connection within an SSH connection. In this scenario, you would have a Linux server connected to each network you would like to include in the VPN. These servers could either be acting as routers/firewalls, or simply be routers sitting behind another firewall. For simplicity’s sake, we’re just going to use an example where Linux systems are routers behind another firewall. There are a number of firewalls that can be used and we don’t want to muddle the description of how to set up the VPN with setting up a firewall.

Figure 8-1 shows our sample setup, which we’ll use throughout the rest of this chapter. In this scenario, there’s a “master” and a “slave” VPN system. Each of these systems is a Unix system with SSH, PPP, and other needed applications. The designation of master and slave is actually arbitrary. The terms are just used to differentiate between the system that initiates the SSH connection (the master) and the one that accepts it (the slave). Either machine could be both a master and a slave that makes and accepts multiple VPN connections. It’s easy to picture this situation as being a branch office that has a master server, making a VPN connection to a central office’s slave server. Other branch offices could also call into that same slave server for their own VPNs.

Figure 8-1. A VPN setup between a master and server in the ora-vpn.com domain

In our example, ...