N10-009 Question 108
Single answerThree-tier hierarchical model: Core, Distribution, AccessA company is redesigning its campus network for a three-story office building using the three-tier hierarchical model. Users on each floor connect to edge switches in nearby wiring closets. The network team wants to improve performance, simplify troubleshooting, and keep policy enforcement separate from high-speed backbone forwarding. Which design best fits the core, distribution, and access layers in this environment?
- A
Use the access layer switches to enforce inter-VLAN routing and ACLs, connect them directly to the ISP, and reserve the distribution layer for end-user device connections.
- B
Use the core layer as a fast, resilient backbone between distribution switches, use the distribution layer for inter-VLAN routing and policy controls such as ACLs, and use the access layer to connect end devices such as PCs, phones, and printers.
- C
Use the core layer to provide PoE and port security to end devices, use the distribution layer only for WAN termination, and use the access layer only for server-to-server traffic in the data center.
- D
Collapse all user devices, routing policies, and backbone links into the core layer so that traffic takes the fewest number of hops and can be managed from a single place.
Show answer and explanation
Correct answer: B
Explanation
In the three-tier hierarchical campus model, the access layer provides connectivity for end devices, the distribution layer aggregates access-layer switches and applies policies, and the core layer serves as the high-speed, resilient backbone. This separation improves scalability, performance, and troubleshooting by keeping endpoint access, policy enforcement, and transport functions logically distinct. Common best-practice guidance from enterprise campus design references, including Cisco hierarchical network design principles widely reflected in Network+ objectives, places features such as port security and PoE at the access layer, inter-VLAN routing and ACLs at the distribution layer, and fast redundant forwarding at the core layer. Option 2 is the only answer that correctly aligns those functions with the proper tiers.
- A. Incorrect.
Incorrect. This reverses the normal roles of the access and distribution layers. In a standard three-tier design, the access layer connects end devices and provides edge connectivity features, while the distribution layer commonly handles inter-VLAN routing, ACLs, and other policy-based functions. Direct ISP connectivity is also not a defining role of access switches in a campus hierarchical model.
- B. Correct.
Correct. This matches the accepted three-tier hierarchical model used in campus networks. The core layer is designed for high-speed, highly available transport between distribution blocks. The distribution layer aggregates access switches and commonly applies routing, ACLs, QoS boundaries, and route summarization where appropriate. The access layer connects endpoints such as workstations, IP phones, printers, and wireless access points.
- C. Incorrect.
Incorrect. PoE and port security are typically access-layer functions because they are applied at the edge where endpoints connect. The core layer should generally remain optimized for fast forwarding and resiliency rather than endpoint-facing services. Limiting the distribution layer to WAN termination is also inaccurate in a campus three-tier design.
- D. Incorrect.
Incorrect. This ignores the purpose of hierarchical design, which is modularity, scalability, fault isolation, and separation of functions. Placing everything in the core creates a design that is harder to scale and troubleshoot and can turn the backbone into a policy bottleneck. Best practice is to keep the core focused on rapid transport and place policy enforcement at the distribution layer.