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The Cisco Three-Layer Hierarchical Model
Most of us were exposed to hierarchy early in life. Anyone with older siblings learned what it
was like to be at the bottom of the hierarchy. Regardless of where you first discovered hierarchy,
today most of us experience it in many aspects of our lives. It is hierarchy that helps us
understand where things belong, how things fit together, and what functions go where. It
brings order and understandability to otherwise complex models. If you want a pay raise, for
instance, hierarchy dictates that you ask your boss, not your subordinate. That is the person
whose role it is to grant (or deny) your request. So basically, understanding hierarchy helps us
discern where we should go to get what we need.
Hierarchy has many of the same benefits in network design that it does in other areas of life.
When used properly, it makes networks more predictable. It helps us define which areas should
perform certain functions. Likewise, you can use tools such as access lists at certain levels in hierarchical
networks and avoid them at others.
Large networks can be extremely complicated, with multiple protocols, detailed
configurations, and diverse technologies. Hierarchy helps us summarize a complex collection
of details into an understandable model. Then, as specific configurations are needed, the model
dictates the appropriate manner in which to apply them.
The Cisco hierarchical model can help you design, implement, and maintain a scalable,
reliable, cost-effective hierarchical internetwork.
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