VPN (Virtual Private Network) is a technology that provides secure communication through an insecure and untrusted network (like the Internet). Usually, it achieves this by authentication, encryption, compression and tunneling. Tunneling is a technique that encapsulates the packet header and data of one protocol inside the payload field of another protocol. This way, an encapsulated packet can traverse through networks it otherwise would not be capable of traversing. Currently, the two most common techniques for creating VPNs are IPsec and SSL/TLS. In this article, I describe the features and characteristics of these two techniques and present two short examples of how to create IPsec and SSL/TLS tunnels in Linux and verify that the tunnels started correctly. I also provide a short comparison of these two techniques.
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