Network Infrastructure Design and Topologies
Design questions test whether you can translate requirements into a physical topology. Start with the logical models: star, hierarchical three-tier (core, distribution, access), collapsed core, spine-leaf for data centers, and ring for resilience. Then map them to physical constraints such as distance, pathway capacity, redundancy, and growth. Candidates should explain why a star dominates LAN access, why spine-leaf reduces latency and oversubscription, and when redundancy requires dual homing, diverse pathways, or redundant power.
Understand the role of telecommunications rooms and equipment rooms, backbone versus horizontal distribution, and how media selection follows distance and bandwidth needs. Design also covers addressing adjacency, port density planning, and spare capacity. Expect questions about single points of failure, pathway diversity, and separating power and data routes.
Traps: assuming a redundant switch removes all single points of failure when both feed one pathway or one power strip; confusing logical topology with physical layout; and overbuilding category or fiber where distance and budget do not justify it. Another trap is treating wireless as a replacement for structured cabling rather than a complement requiring backhaul.
Rule of thumb: design for at least 20 to 30 percent spare port and pathway capacity, and trace every critical service for a single point of failure before approving the plan.
Worked example: a 200-desk floor needs access switching. At 48 ports per switch with 25 percent spare, you need about six switches (200 divided by 36 usable ports rounds up), plus uplinks and redundant power per closet.
Key concepts
- Hierarchical and spine-leaf topologies
- Redundancy and single points of failure
- Capacity and growth planning
- Logical versus physical design