The Cisco three-layer model is simply a blueprint, just like the OSI model. This model creates a hierarchy that helps us to understand where our internet-working devices should be placed and what responsibilities they have at each one of the layers:
The Cisco three-layer model
Core layer
This layer is responsible for sending large quantities of data that will generate lots of traffic, but it will be reliable and fast. Its only purpose in life is to route or switch traffic to its destination as quickly as possible. If something were to fail at the core layer, everyone below it will feel the impact and your network will be down.
Because of this, the core devices should steer away by performing the following at this layer:
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