This chapter focused on techniques for developing a topology for a network design. Designing a network topology is the first step in the logical design phase of the top-down network design methodology. By designing a logical topology before a physical implementation, you can increase the likelihood of meeting a customer's goals for scalability, adaptability, and performance.
This chapter discussed four characteristics of network topologies: hierarchy, modularity, redundancy, and security. All of these characteristics can be applied to both campus and enterprise WAN design. The characteristics are not mutually exclusive. Your goal should be to design hierarchical, modular, redundant, and secure network architectures based on your customer's goals.
Hierarchy and modularity let you develop a network consisting of many interrelated components in a layered and structured fashion. Using a hierarchical model can help you maximize network performance, reduce the time to implement and troubleshoot a design, and minimize costs.
Redundant network designs let you meet requirements for network availability by duplicating network components. Redundancy eliminates single points of failure on the network. Redundancy also facilitates load sharing which increases network performance. Redundancy adds complexity and cost to the network, however, and should be designed with care.
Depending on your particular network design, you should plan a secure topology that protects core routers, demarcation points, cabling, switches, servers, and so on. Adding one or more firewalls to your topology can help you protect enterprise networks from outside attackers.
After completing a logical topology for a customer, you should continue in the logical design phase by designing network addressing and naming models, selecting switching and routing protocols, and developing network security and management strategies. These topics are covered in the next few chapters. Doing a thorough job in the logical design phase can ease your transition into the design of the physical implementation of the network. It can also prepare you for the job of selecting the right products and technologies for your customer.
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