Chapter 3. EIGRP Network Design

The previous two chapters described many of the important network design techniques used to meet the design goals of high resiliency, manageability, and scalability. Now it is time to put these techniques into practice using the Cisco advanced distance vector routing protocol, Enhanced Interior Gateway Routing Protocol (EIGRP). These techniques will be applied to the networks shown in Figure 3-1.

Figure 3-1. Large-Scale Three-Layer Hierarchical Network

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For more information on how EIGRP functions, refer to Appendix A, "EIGRP for IP Basics of Operation." EIGRP has numerous advantages over its link-state routing protocol counterparts, but it also has limitations and behaviors that a network designer must understand to successfully implement a scalable EIGRP network. This chapter describes some of these behaviors and provides techniques that network designers can use to improve the performance and scalability of EIGRP networks.

This chapter helps you to do the following for both two-layer and three-layer hierarchical networks:

• Analyze summarization at each layer of the EIGRP network.

• Analyze the use of the stub feature for access routers.

• Analyze the best way to deal with external connections, common services, and dial-in clients.

• Explore case studies on summarization methods, query propagation, excessive redundancy, troubleshooting common problems, and redistribution issues.