In Chapter 2, “IPSec Overview,” and Chapter 3, “Enhanced IPSec Features,” you reviewed the fundamental concepts of IPSec VPNs. In this chapter, you will use those concepts to learn about IPSec VPN architectures. As you read in Chapter 1, “Introduction to VPNs,” VPNs have been around for many years. Conceptually, the process of designing an IPSec VPN network is no different from the one used to determine any other VPN architecture, such as Frame Relay; however, IPSec adds a few more constraints and capabilities. In this chapter, you will be presented with the aspects that differentiate IPSec VPN networks from traditional VPN architectures, and understand key considerations when designing such a network.