Final answer:
Sarah has used the perimeter security model for her network design.
Step-by-step explanation:
Sarah has used the perimeter security model for her network design.
In this model, each network is protected by a separate firewall at the edge, or perimeter, of the network. The purpose of this approach is to provide different levels of security for each network depending on its sensitivity.
By having separate firewalls for the three networks and connecting them to a single router, Sarah ensures that each network is isolated and can be individually controlled and monitored.