The Hierarchical Design Model
Core
Access
Distribution
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The hierarchical design model divides a network into three layers:
■ Access—End stations attach to VLANs.
— Clients attach to switch ports.
—VLAN assigned/broadcast domains established.
— Built using low-cost ports.
■ Distribution—Intermediate devices route and apply policies.
—VLANs terminated, routing between.
— Policies applied, such as route selection.
—Access-lists.
— Quality of Service (QoS).
■ Core—The backbone that provides a high-speed path between
distribution elements.
— Distribution devices are interconnected.
— High speed (there is a lot of traffic).
— No policies (it is tough enough to keep up).
Later versions of this model include redundant distribution and core devices,
and connections that make the model more fault-tolerant. A set of distribution
devices and their accompanying access layer switches are called a switch
block.