N10-009 Question 109
Single answerThree-tier hierarchical model: Core, Distribution, AccessA company is redesigning its campus network for three office floors. Users on each floor connect to local switches, inter-VLAN routing and policy enforcement must be centralized per floor, and traffic between floors must move with minimal latency. The network team wants the design to align with the three-tier hierarchical model and simplify troubleshooting. Which design best meets these requirements?
- A
Deploy access switches on each floor for end devices, use distribution switches to perform inter-VLAN routing and apply ACLs, and connect those distribution switches to a high-speed core layer that forwards traffic between floors
- B
Deploy a core switch on each floor for end devices, use access switches to route between VLANs, and place ACLs only at the core so all policies are handled centrally
- C
Use only distribution switches for user connections and connect them directly to the WAN router, eliminating the core layer to improve campus backbone performance
- D
Connect all end devices directly to the core layer, use the distribution layer only for Internet access, and configure the access layer as a backup path between buildings
Show answer and explanation
Correct answer: A
Explanation
The best answer is the design that assigns device connectivity to the access layer, routing and policy functions to the distribution layer, and high-speed transport to the core layer. This reflects the classic Cisco hierarchical campus model that CompTIA Network+ commonly tests at a conceptual level. Best practices for campus design emphasize modularity, predictable traffic flow, easier troubleshooting, and scalability: access for endpoint connectivity, distribution for aggregation and control, and core for fast, resilient forwarding. In practical deployments, the distribution layer is commonly where inter-VLAN routing, ACLs, and route summarization are applied, while the core layer is kept optimized for speed and availability rather than heavy policy processing. Although smaller networks may use a collapsed core, that is a different design choice and not the one requested in this scenario.
- A. Correct.
Correct. In the three-tier hierarchical model, the access layer connects end devices such as PCs, printers, and phones. The distribution layer aggregates access switches and commonly provides inter-VLAN routing, ACLs, QoS boundaries, and policy-based control. The core layer serves as the fast, resilient campus backbone and is designed to transport traffic efficiently between distribution blocks with minimal latency. This design matches the stated requirements for user connectivity, centralized policy enforcement, and high-speed traffic movement between floors.
- B. Incorrect.
Incorrect. This reverses the intended roles of the layers. End devices should connect at the access layer, not the core. Inter-VLAN routing is typically handled at the distribution layer in a classic three-tier design, not at the access layer. While some modern networks may use Layer 3 at the access layer in specific designs, that is not the standard three-tier role assignment being tested here. Placing all ACLs only at the core is also contrary to best practice because policy enforcement is usually applied closer to the source at the distribution layer.
- C. Incorrect.
Incorrect. Distribution switches can aggregate user traffic, but connecting users directly to distribution switches does not reflect the normal role of the access layer. Also, removing the core layer does not improve backbone performance in a multi-floor campus that needs a dedicated high-speed transport layer. In smaller environments, a collapsed core may be valid, but the scenario specifically asks for alignment with the three-tier hierarchical model, which includes a distinct core layer.
- D. Incorrect.
Incorrect. The core layer is not intended for direct end-user connectivity. Its role is to provide fast and reliable transport across the campus. The distribution layer is not limited to Internet access; it is the policy and routing boundary between access and core. The access layer is also not designed to act as an interbuilding backup backbone. This option misunderstands the purpose of all three layers.