The multilayer campus design consists of a number of building blocks connected across a campus backbone. Several alternative backbone

designs are discussed in the next section. See Figure 2 to view the generic campus design. Note the three characteristic layers: access,

distribution, and core. In the most general model, Layer 2 switching is used in the access layer, Layer 3 switching in the distribution layer,

and Layer 3 switching in the core.

One advantage of the multilayer campus design is scalability. New buildings and server farms can be easily added without changing the

design. The redundancy of the building block is extended with redundancy in the backbone. If a separate backbone layer is configured, it

should always consist of at least two separate switches. Ideally, these switches should be located in different buildings to maximize the

redundancy benefits.

Two versions of the multilayer design model are discussed. Both versions are based on the building blocks shown in Figure 1. The building

design is appropriate for a building-sized network with up to several thousand networked devices. The campus design is appropriate for a large

campus consisting of many buildings. Both are based on a simple building block or module, which is the foundation of the modular design.

The building design is described first because it is also used for each building within the campus design. To scale from the building model to

the campus model, a campus backbone is added. Each building block or module connects to the campus backbone. Five different campus

backbone designs are presented in the following section.