The Evolving Network Model

Hierarchical Design Model

Three-Layer Network Design
The layers break a network in the following way:
Access layer—End stations attach to the network using low-cost devices.
Distribution layer—Intermediate devices apply policies.
Route summarization
Policies applied, such as:
Route selection
Access lists
Quality of Service (QoS)

Core layer—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).

Problems with the Hierarchical Design Model:
Where do wireless devices fit in?
How should Internet access and security be provisioned?
How do you account for remote access, such as dial-up or VPN?
Where should workgroup and enterprise services be located?