Hierarchical versus Flat Designs

The CCDA should understand that there is a limit on the number of nodes in flat network designs. Network broadcasts can overcome slow serial links. Build the network in a hierarchical manner with subnetting to reduce the amount of traffic on WAN links.

The CCDA must understand the three layers of the hierarchical model for network design: the core, distribution, and access layers. Figure 1-4 provides an example of these three layers.

At the core layer, high-speed switching is used with high availability and redundancy. Apply access and distribution lists at the distribution layer, which is where the security policies are applied. Address summarization and media translations are applied in the distribution layer as well. The access layer consists of the remote office sites using ISDN, Frame Relay, and DDR, and private lines accessing the corporate network. Local-area networks end segments are also part of the access layer.

Figure 1-4 Hierarchical Design Model

Core

Distribution

(Route Policies, — Access Lists)

Access

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