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Core Principles of Virtual Private Networks (VPNs) for CompTIA Network+

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One of the most exciting and predominant technology areas in modern networking has been the Virtual Private Network. Thanks to these technologies, companies can save vast sums of money using the public Internet to safely and securely replace the need for a dedicated WAN. This article teaches readers about the core principles that make VPNs such an important and growing area of networking.
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Virtual Private Networks (VPNs) are tools that allow network users to connect through the public internet to an organization’s internal network. Where many companies rely on dedicated leased lines to connect remote physical sites, it simply is not feasible to rely on the same technology to allow dozens or even hundreds of remote workers to connect from home or from temporary field locations. VPNs offer a secure method of connectivity that encrypts data, and they are perfect solutions for individual remote users or very small remote sites. In addition to the technological advantage, VPNs help reduce costs. In a nutshell, VPNs when properly implemented, can provide wide area security, reduce the costs associated with traditional leased lines, and provide effective support of telecommuters, and road warriors. Additionally, both the organization and the remote users can save money. The company can forgo the cost of leased lines, and the remote users escape long distances costs by using a local service provider to communicate with their headquarters office. All these advantages are made possible by the concept of a Virtual Tunnel that re-encapsulates a data packet inside another data packet and transmits it over the public internet.

Types of VPNs


In a site to site VPN, data is encrypted from one VPN gateway to the other, providing a secure link between two sites over the internet. This would enable both sites to share resources such as documents and other types of data over the VPN link.

Remote Access VPN

In a Remote Access VPN deployment which is also known as a mobile VPN a secure connection is made from an individual computer to a VPN router. This enables a user to access their e-mail, files and other resources at work from outside the network, provided they have an internet connection. There are a number of common forms of technology used in remote access VPNs and VPN Tunnels.

VPN Networking Protocols

VPN tunnels rely on one of four major networking protocols, all of which can provide different levels of security.

PPTP (Point-to-Point Tunneling Protocol)

PPTP supports the use of VPNs. Using PPTP allows remote users to access their business networks in a secure fashion while using Microsoft Windows Systems and other PPP (Point to Point tunneling Protocol) capable platforms. Remote users leverage their local internet providers to connect securely to their networks via the internet.

PPTP brings with it its own problems and is a weak security protocol compared to other options; however, it should be pointed out that Microsoft has enhanced the operation of PPTP to correct protocol instabilities. This protocol is easier to deploy than a solution like IPSec which we will discuss later.

L2TP (Layer 2 Tunneling Protocol)

L2TP is an enhancement of PPTP (Point to point tunneling protocol) and it is widely used by internet service providers to offer VPN services over the internet. L2TP is actually a hybrid of two protocol types: PPTP (Point-to-Point Tunneling Protocol) and L2F (Layer 2 Forwarding Protocol), with some other functionality stolen from IPSec. It should be noted that L2TP can be deployed in unison with IPSec to satisfy virtually any encryption, authentication, or data integrity requirements.

IPSec (IP Security)

IPSec works at the third layer of the OSI model and as such can it can protect any protocol that runs on the IP stack. IPSec is actually a suite of protocols and associated algorithms that can be expanded on in a modular fashion. IPSec is a strong, flexible, and scalable security protocol and virtually perfect for securing VPNs. IPSec requires significant amounts of setup on a network as well as on the client. This makes the protocol a complicated solution to work with, not to mention it is much more of a processor strain for all devices that run it than its lighter weight counterparts. The added bonus is that IPSec can be used for both site-to-site and Remote Access VPNs.

SSL VPN (Secure Socket Layer)

SSL VPN provides the best of both worlds when it comes to protection and ease of use. Another benefit is that it has been a tried and true solution that has been used heavily on the internet for years. Most commonly this protocol is employed by online stores and online banking. When you see https: in your browser URL bar, you know immediately that you are being protected by SSL.

The reduction in complication offered by SSL VPNs comes when you consider that the client no longer requires client software to be installed and running. This single fact lessens the burden of the protocol as well as reduces the overhead needed to maintain and troubleshoot it in a working environment. The absence of client software means that a user needs to rely on a secure portal. A secure portal is a graphical interface served up to a web browser that provides tools and access to applications running on the network. Today one of the most common applications served up in this fashion are email and thin clients tools like RDP. SSL can also approximate the way IPSec works with additional lightweight software that can be installed with very little effort via the browser. This fact can simplify the processes involved in securely accessing the corporate network.

SSL VPNS can literally support thousands of end users that need access to the headquarters network without requiring the support of an administrator or even a single hour of configuring or troubleshooting unlike IPSec protocol.

VPNs on a Linksys Router

If you have a Linksys router, you can set it up so that you can form a VPN through the router itself, giving you a way to securely access a computer on your network. Emphasizing both the value of VPNs and their popularity the majority of Cisco’s Linksys devices allow these protocols to pass through the router’s firewall by default. This behavior can be changed on a Linksys router via the web-based setup page where we can find the Security tab. Once this tab has been selected, we will be presented with the VPN Passthrough sub-tab. After clicking the sub-tab we will see three categories of VPN Passthrough options and radio buttons that allow us to disable or enable pass-through behavior:

  • IPSec Passthrough—IPSec Pass-Through is enabled by default. To disable IPSec Passthrough, select Disabled.
  • L2TP Passthrough—L2TP Pass-Through is enabled by default. To disable L2TP Passthrough, select Disabled.
  • PPTP Passthrough —PPTP Pass-Through is enabled by default. To disable PPTP Passthrough, select Disabled.

Any changes can be made permanent by clicking Save Settings and the Continue button on the next page.


VPNs are renowned for eliminating the need for expensive leased connectivity. T1 lines or frame circuits have traditionally been employed to connect multiple office locations in a secure fashion. If the office locations are very far apart, the cost of renting leased lines can be exorbitant. A VPN, however, only requires a broadband internet connection. Plus they eliminate the monthly cost of dedicated lines. This means that VPNs offer an excellent and cost effective solution for companies with several branch offices, partners, and/or remote users to share data and connect to a corporate network in a secure and private manner.

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