Introduction

As you progress through this chapter, you will understand the concepts of virtual private networks (VPNs), how VPNs operate, and how to implement VPN tunnels using IPSec (Internet Protocol Security) on Netscreen appliances. At this time you may be thinking, "What is a VPN and why would I need to use one?" There are several good reasons to implement VPN technology in your infrastructure, starting with security. A VPN is a means of creating secure communications over a public network infrastructure. VPNs use encryption and authentication to ensure that information is kept private and confidential. This means that you can share data and resources among several locations without the worry of data integrity being compromised.

Alone, the ability to make use of a public network to transmit data is also an advantage of VPN technology. Without using the Internet as a transport mechanism you would have to purchase point-to-point T1s or some other form of leased line to connect multiple locations. Leased lines are traditionally expensive to operate, especially if the two points being connected are across a large geographic region. Using VPNs instead of leased lines reduces the operating cost for your company.

VPNs are also cost effective for traveling users. Without VPNs, a traveling salesperson working outside the office might have to dial into a modem bank at the office and incur long distance charges for the call. A dialup VPN is much more cost effective, allowing the salesperson to connect to a local ISP (Internet service...