In this chapter, we define Virtual Private Networks (VPNs) and briefly revisit the VPNs from Chapter 4. In the rest of Part 2, we study several types of VPNs, see how they are used, and take note of their strengths and weaknesses. As we shall see, these VPNs can operate at any layer in the TCP/IP stack. As usual, we will be less concerned with the administrative details of configuring the VPNs than with developing an appreciation for the protocols themselves and the manifestation of those protocols on the wire.

This chapter is excerpted from the book titled: “VPNs Illustrated: Tunnels, VPNs, and IPsec”, authored by Jon C. Snader, Copyright © 2006 Pearson Education, Inc., ISBN 032124544X; Published: Oct 26, 2005. Reproduced by permission of Pearson Education, Inc. All rights reserved.