A campus LAN serves local users across a site ranging from one switch to multiple buildings. Cisco designs it with modular access, distribution, and core layers. section 15.2
The hierarchical layers divide operational responsibilities:
- Access layer connects end hosts and commonly implements QoS, security services, and PoE. section 15.5
- Distribution layer aggregates access connections and provides connectivity toward the WAN or internet. section 15.2
- Core layer aggregates connections between distribution layers in larger LANs. section 15.2
Three-building campus
A three-tier design connects end hosts to access blocks, access blocks to distribution blocks, and distribution blocks through the core. A smaller campus may omit one or more layers; a two-tier design combines distribution and core functions. section 15.5
