To optimize bandwidth on an enterprise network, the network must be organized so that traffic stays local and is not propagated unnecessarily onto other portions of the network. Using the three-layer hierarchical design model helps organize the network.

This model divides the network functionality into three distinct layers, as shown in Figure 1:

Each layer is designed to meet specific functions.

The access layer provides connectivity for the users. The distribution layer is used to forward traffic from one local network to another. Finally, the core layer represents a high-speed backbone layer between dispersed networks. User traffic is initiated at the access layer and passes through the other layers if the functionality of those layers is required.

Even though the hierarchical model has three layers, some smaller enterprise networks may implement a two-tier hierarchical design. In a two-tier hierarchical design, the core and distribution layers are collapsed into one layer, reducing cost and complexity, as shown in Figure 2.