Hierarchical internetworking model
- Hierarchical internetworking model
The Hierarchical internetworking model, or "three-layer model", is a network design model first proposed by Cisco. Thethree-layer model divides enterprise networks into three layers: core, distribution, and access layer. Each layer provides differentservices to end-stations and servers.
Access layer
End-stations and servers connect to the enterprise at the "access layer". Access layer devices are usually commodity switchingplatforms, and may or may not provide layer 3 switching services. The traditional focus at the access layer is minimizing"cost-per-port": the amount of investment the enterprise must make for each provisioned Ethernet port.
Distribution layer
The distribution layer is the "smart" layer in the three-layer model. Routing, filtering, and QoS policies are managed at thedistribution layer. Distribution layer devices also often manage individual branch-office WAN connections.
Core layer
The core network provides high-speed, highly-redundant forwarding services to move packets between distribution-layer devices indifferent regions of the network. Core switches and routers are usually the most powerful, in terms of raw forwarding power, in theenterprise; core network devices manage the highest-speed connections, such as 10 Gigabit Ethernet.
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