Virtual Private Network

Common Protocols for Virtual Private Networks (VPNs)

Maintaining the security of internal data as well as the data of clients or customers is an important part of any organization’s operations. In the last few years, many organizations that didn’t take information security seriously have been hacked, with the stolen data openly released—or sold to opposing parties. These incidents have been happening for years; the only difference is that lately they have been more visible, and they have affected the information of many more people.

One way of protecting data as it passes between internal and remote locations is by implementing a virtual private network (VPN).VPNs have been around for a long time (over 20 years) and have been used in two primary ways: protecting the data from a host machine to a central location (client to network),

or protecting the data from one organizational network to another (network to network). Both types of VPN have been implemented over the public Internet. This article reviews some of the most common VPN types and discusses how they are typically implemented.

Generic Routing Encapsulation (GRE)

The concept of Generic Routing Encapsulation (GRE) has been around for more than 20 years. GRE is a common solution to transport the information from one network to another. The idea behind GRE is to offer a method of transporting information over an Internet Protocol (IP) medium. The protocol that is passed over the GRE tunnel can be one of several supported protocols, including the ability to transport IP inside a GRE/IP tunnel. It can also transport a number of protocols, including IPv4, IPv6, or AppleTalk, among others, with IP and IPv6 being the most common.

IP Security (IPSec)

IP Security (IPSec) has been around as a concept for about as long as GRE and is used to provide a secure communications channel through an existing IP network. IPSec itself is not a single protocol but rather a group of protocols that can be implemented in a number of ways, depending on the specific requirements of the situation.

Point-to-Point Tunneling Protocol (PPTP)

The Point-to-Point Tunneling Protocol (PPTP) has been around since the late 1990s and was initially implemented heavily in Microsoft Windows products (from Windows 95 Update 1.3 forward). PPTP takes advantage of a few other protocols to provide a complete solution, including the Point-to-Point Protocol (PPP) and an enhanced version of GRE.

Secure Sockets Layer (SSL) VPN

One of the most talked-about VPN technologies recently has been SSL VPN; this is mainly due to a number of different evolutions in its implementation that make it easier to deploy and use. In the past, SSL VPN was mainly used to provide support via a centralized portal, which offered limited support for a specific set of protocols. Modern implementations offer the ability to support both client-based and clientless SSL VPN options; clientless deployments are more limited than their client-based alternatives, but much thinner to implement (nothing permanently loaded on the client).


The use of VPNs has continued to expand as Internet connections have become faster, more reliable, and more widely available. Many companies are moving their remote office connections from expensive leased-line connections to Internet-based VPN connections. This trend will most likely continue as speeds and connections continue to expand.