Cisco uses a three−tier hierarchical network model, that consists of three layers: the Core layer, the Distribution layer, and the Access layer.

Core Layer

Core Layer consists of biggest, fastest, and most expensive routers with the highest model numbers and Core Layer is considered as the back bone of networks. Core Layer routers are used to merge geographically separated networks. The Core Layer routers move information on the network as fast as possible.

Distribution layer:

Distribution Layer includes LAN-based routers and layer 3 switches. Distribution Layer ensures that packets are properly routed between subnets and VLANs in your enterprise.

Access layer

Access layer includes hubs, switches and routers to segment LAN. Access layer ensures that packets are delivered to end user computers.