Virtual private networks (VPNs) provide a means of accessing a private network over a shared public network such as the internet. Access to the private network is provided via an encrypted tunnel, and connecting to the network in such a way emulates a point-to-point link between the remote node and the network. Since the tunnel is encrypted, any packets that are intercepted are indecipherable without the encryption keys. Thus, VPNs provide a secure means of accessing a private network remotely.

Prior to the advent of VPNs, the only way of providing remote connections to a private network was through private WAN circuits. Private WAN circuits provide low latency, and in some cases, they may still be the best solution for connecting to a private network, but they also have high monthly costs. VPN solutions have grown in popularity, in spite of the fact that they often have somewhat higher latency than private WAN circuits, because they provide the same point-to-point connectivity at a much lower cost.

pfSense is one such means by which you can implement low-cost VPN connectivity. While establishing and maintaining a VPN tunnel is somewhat CPU-intensive—a computer that barely meets the minimum specifications for pfSense will be hard-pressed to maintain a VPN connection—with pfSense, you will be able to set up VPN connections much more cheaply than you would be able to with commercial equipment.

In this chapter, we will cover the following topics:

• VPN fundamentals
• Configuring a VPN tunnel in pfSense (IPsec, L2TP, and OpenVPN)
• Troubleshooting VPNs