Cisco IOS Access Lists

Chapter 7. Case Studies

In this chapter, I present three case studies that use access lists in common scenarios. These case studies show how different types of access lists can be used together in situations you may encounter. They also illustrate how the three key concerns we talked about—security, robustness, and business policy—are implemented in realistic situations. The first example deals with a single organization’s intranet connected by a wide area network (WAN). I show how to use access lists to implement a secure and stable WAN. The second example goes over a common firewall configuration called the screened subnet architecture. Here, I use access lists to secure an organization’s perimeter. The final case study covers how an organization connects to the Internet. This example shows how to use access lists to implement route preferences while still maintaining security.

A WAN case study

In this case study, we’ll see how to use access lists in routers that make up a wide area network in the network shown in Figure 7.1. Like many large organizations, different departments control and manage different parts of this network. Site 1’s network is run by a different organization from Site 2, neither of which run Site 3’s network. Each of these three sites have separate address spaces, and each site runs a different routing protocol. The routers that connect the three sites, Routers A through F, are run by a separate organization, which uses yet another routing protocol. For our ...