The Three-Tier Network Architecture
Most commercial buildings use the classic Cisco three-tier (or collapsed two-tier) network architecture: Core, Distribution, and Access layers. Each layer has a specific function:
- Access layer: Where end devices connect — workstations, IP phones, printers, wireless APs, IP cameras. Access switches provide 1 Gbps copper ports, PoE, and port security. Located in each IDF (Intermediate Distribution Frame) closet.
- Distribution layer: Aggregates access switches, enforces inter-VLAN routing policies, applies QoS and ACL policies, and provides uplinks to the core. Distribution switches are typically multilayer (Layer 3) and located in the main equipment room.
- Core layer: The high-speed backbone that interconnects distribution switches and provides connectivity to the internet edge and data center. Core switches must never be the bottleneck — high-capacity (40/100 Gbps) switches with redundant paths and sub-second failover.
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