|  | 3.3 | How to Identify and Select Networking Capabilities
| 3.3.9 | Two-layer network designs
In a two-layer design, a WAN link is used to interconnect separate sites, as shown in the figure. Inside the site, multiple LANs may be implemented, with each LAN segment being its own broadcast domain. The router at Site F becomes a concentration point from WAN links.
| Threaded Case Study
Washington Project: The Two-Layer Hierarchical Model

The Washington School District WAN should be based on a two-layer hierarchical model. Three regional Hubs should be established-one each at the District Office/Data Center, the Service Center, and Shaw Butte Elementary School-in order to form a fast WAN core network.