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Types of VPNs
By Erik Rodriguez
This article describes the use of VPN technology. VPNs are used to connect users and networks securely to share data. VPNs are commonly used to allow remote users and offices to access an intranet, server, or other network resources.
What is a VPN?
A VPN (Virtual Private Network) is a way of creating a secure connection to and from a network or computer. VPNs have been used for years, but the technology that powers them has greatly increased in the last few years. They have become more affordable and also much faster. There are many different types of VPNs available today. The most common ones are shown below.
Leased Line VPN
One of the first types of VPN technology was the leased line. Simply put, two or more networks were connected using a dedicated line from the telephone company. These took the form of ISDN, T1, or frame relay lines. These type of connections are still used today, although they are rare because they are expensive, and other alteratives work just as well. The main strength of using a leased line is that is a circuit-based point-to-point connection. It does not use a public Internet link, so there is no latency caused by router hops, collisions, etc. See the diagram below:
As I mentioned before these types of connection are expensive. This is because a physical "loop" of wire must be used to connect the destinations. Sometimes laying the loop is charged by the mile, or even by the foot. But because these are true point-to-point connections the maximum throughput is realistic. Meaning, a 128k ISDN line actually passes data at the rate all the time.
PPTP VPN
A commonly used method for VPN is PPTP. It is a software based VPN system that uses your existing Internet connection. By using your Internet connection, a secure "tunnel" is created between two points allowing remote users to connect to corporate offices and vice versa. You can setup this type of connection with various types of software, and you won't have to pay the teleco company any loop fees. See the diagram below:
As you can see, data must travel through the Internet. This means there is more room for collisions, latency, and packet loss. While PPTP is a cheap an easy solution, it does not work well for large networks, or bandwidth hungry applications. Another form of this is a L2TP VPN. L2TP performs the same functionality of PPTP, but is used to connect two or more networks and not just individual users.
ISP Managed VPN (MPLS)
The most popular type of VPNs today are managed by an ISP or other service provider. These VPNs operate on the same standards as the others, but the data is routed a little differently. See the diagram below:
As you can see some of the routers are yellow. These means that data is passed through these specific routers. These routers are controlled by the service provider and are part of a "private network." This means that normal Internet traffic will not pass through these routers making them less susceptible to collisions, latency and packet loss. This type of VPN is powered by a frame relay or MPLS technology. Frame relay is an older technology that is basically being phased out. It has several strengths, but MPLS is taking the VPN world by storm. MPLS (Multi-Protocol Label Switching) was originally designed to improve the store-and-forward speed of routers. MPLS was created as a team effort on the part of Ipsilon, Cisco, IBM, and Toshiba. These companies worked together as part of the IETF (Internet Engineering Task Force) and MPLS was born.
Conclusion
VPNs are becoming more common among organizations and wide area networks. The technology powering these VPNs is becoming more efficient and more cost effective. The creation of new protocols and topologies keeps network engineers and hardware vendors on their toes. When deciding on a VPN you should take several things into consideration:
- Number of users/bandwidth
- Security
- Topology
- Cost
Remember that cheaper is not always better! Un-managed PPTP VPNs usually have a high latency because of the amount of hops each data packet travels as well as the naming (WINS) resolution inside your network.
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