Chapter 14. Campus Design Models

This chapter covers the following key topics:

• Changing Traffic Patterns The rise of client/server computing, server farms, and Internet-based technology has dramatically changed most campus traffic patterns. This chapter looks at some of the challenging issues that this has created for campus network designers.

• Campus Design Terminology Explains IDF/MDF and access/distribution/core terminology, the two most common ways of explaining and discussing campus designs.

• Key Requirements of Campus Designs Looks at the attributes of the ideal campus design.

• Advantages of Routing The recommended approach to campus design makes extensive use of Layer 3 switching (routing) technology. The important benefits of this approach are discussed.

• Campus Design Models Three of the most common campus design models are discussed: the router and hub model, the campus-wide VLANs model, and the multilayer model.

• General Recommendation: Multilayer Model Some specific considerations and issues associated with the multilayer model, the recommended approach to campus design, are discussed.

• Distribution Blocks Discusses issues related to distribution blocks (usually a set of switches contained within a single building) for the multilayer design model.

• Core Explains issues related to designing a core for a multilayer network.

This chapter looks at several important models that can be used for campus designs. The discussion begins with a look at two sets of terminology used to describe and discuss network designs. Then, the three main approaches to campus design are presented:

• First, the traditional router and hub model is covered. Although this design is not suitable for use in modern campus networks, the proven advantages of this design are highlighted.

• Second, the chapter discusses the campus-wide VLANs or "flat earth" design. This is the design most people think of when the subject of a switched campus network comes up. Although it can be very useful for certain requirements, in general, it has many drawbacks and downsides.

• Third, the multilayer model is presented. This model is designed to blend Layer 2 and Layer 3 processing into a cohesive whole. The last half of the chapter elaborates on some issues that are specific to the multilayer architecture.

Whereas this chapter focuses on overall design architectures and paradigms, Chapter 15, "Campus Design Implementation," looks at specific strategies associated with campus designs. For example, this chapter points out the advantages of the multilayer model for the Spanning-Tree Protocol (STP), and Chapter 15 discusses STP best practices and makes specific STP recommendations.

Finally, please note that the intent of this chapter is not to create a survey of every campus design ever conceived. Instead, this text is oriented toward the design process. It explores several of the more popular and widely applicable designs in an attempt to discuss good design practices, as well as the pros and cons of various approaches to campus design.