Cisco has refined a hierarchical approach to network design that enables network designers to organize the network into distinct layers of devices. The resulting network is
Three Layer of Network Design is Access Layer, Distribution Layer, Core Layer.
The access layer exists where the end users are connected to the network. Access switches usually provide Layer 2 (VLAN) connectivity between users. Devices in this layer sometimes called building access switches, should have the following capabilities:
■ Low cost per switch port
■ High port density
■ Scalable uplinks to higher layers
■ High availability
■ Ability to converge network services (that is, data, voice, video)
■ Security features and quality of service (QoS)
The distribution layer provides interconnection between the campus network’s access and core layers. Devices in this layer, sometimes called building distribution switches should have the following capabilities:
■ Aggregation of multiple access layer switches
■ High Layer 3 routing throughput for packet handling
■ Security and policy-based connectivity functions
■ QoS features
■ Scalable and redundant high-speed links to the core and access layers
The distribution layer usually is a Layer 3 boundary, where routing meets the
VLANs of the access layer.
A campus network’s core layer provides connectivity between all distribution layer devices. The core, sometimes referred to as the backbone, must be capable of switching traffic as efficiently as possible. Core switches should have the following attributes:
■ Very high Layer 3 routing throughput
■ No costly or unnecessary packet manipulations (access lists, packet filtering)
■ Redundancy and resilience for high availability
■ Advanced QoS functions
** But small or medium-size campus networks might not have the size or volume requirements that would require the functions of all three layers.