N10-009 Question 111
Single answerCollapsed coreA company is moving into a new three-floor office with about 120 employees. The network administrator wants a design that reduces hardware costs and management overhead while still providing high-speed switching between floors. The environment does not have the scale of a large campus, but it does require VLANs, inter-VLAN routing, and redundant uplinks from access switches. Which design best fits these requirements?
- A
Deploy a collapsed core design by combining the core and distribution layers into a pair of multilayer switches, with access switches on each floor uplinking to them
- B
Deploy separate access, distribution, and core layers on each floor so local traffic never reaches a central switching point
- C
Use a router-on-a-stick design as the primary backbone so all floor switches trunk to a single router interface for inter-VLAN routing
- D
Replace all floor access switches with unmanaged switches and handle VLAN separation through host-based firewall rules
Show answer and explanation
Correct answer: A
Explanation
A collapsed core is a design in which the core and distribution layers are merged, usually into one redundant switching block. In hierarchical campus design guidance, this approach is recommended for smaller environments where a dedicated core layer would add unnecessary cost and complexity. It still supports important enterprise features such as high-speed Layer 2 switching, Layer 3 inter-VLAN routing, policy enforcement, and redundant uplinks from access switches. By contrast, a traditional three-tier architecture is better suited to larger campuses, while router-on-a-stick is usually reserved for smaller or less performance-sensitive deployments. This aligns with common campus design best practices from enterprise networking vendors such as Cisco, which describe collapsed core architectures as appropriate for small to medium campus networks.
- A. Correct.
Correct. A collapsed core design combines the core and distribution functions, typically into a redundant pair of multilayer switches. This is a common best-practice design for small to medium-sized organizations that need high-speed switching, inter-VLAN routing, policy control, and simpler management without the cost and complexity of maintaining a separate core layer. Access switches on each floor can uplink redundantly to the collapsed core switches.
- B. Incorrect.
Incorrect. A full three-tier design with separate access, distribution, and core layers is more appropriate for larger campus environments that need greater scalability and traffic aggregation. For a 120-user office, building separate core and distribution layers on each floor would increase cost and complexity without providing proportional benefit. The idea that each floor should have its own complete hierarchy is a common overdesign mistake.
- C. Incorrect.
Incorrect. Router-on-a-stick can provide inter-VLAN routing for small environments, but it is generally a bottleneck compared with multilayer switching because all inter-VLAN traffic traverses a trunk to a router interface. It does not align well with the requirement for high-speed switching between floors and would not be the preferred backbone design for this office. Candidates may pick this if they remember inter-VLAN routing but overlook performance and scalability concerns.
- D. Incorrect.
Incorrect. Unmanaged switches do not support enterprise features such as VLAN configuration, trunking, spanning tree controls, or link aggregation in the way this scenario requires. Host-based firewall rules also do not replace network-layer segmentation. This option reflects the misconception that endpoint controls can substitute for proper switching architecture.