Because each layer (core,
distribution, and access) has a clearly defined function, each layer
demands a different set of features from routers, switches, and links.
Routers that operate in the same layer can be configured in a consistent
way because they all must perform similar tasks. In fact, the router is
the primary device that maintains logical and physical hierarchy in a
network, so proper and consistent configurations are imperative. Cisco
offers several router product lines, each with a particular set of
features tailored for one of the three layers:
- Core layer - 12000, 7500, 7200, and 7000 series
routers
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- Distribution layer - 4500, 4000, and 3600 series
routers
- 
- Access layer - 2600, 2500, 1700, and 1600 series
routers
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The following sections revisit each layer and examine
the specific routers and other devices used there.
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