Network Design Fundamentals
What the exam tests
Network Design Fundamentals covers the disciplined process of turning business requirements into a repeatable, documented Juniper-based design. Expect questions on requirements gathering, hierarchical models, availability, capacity planning, modularity, and lifecycle governance rather than product speeds alone.
Core rules
- Work top-down: business drivers → technical requirements → logical topology → physical topology → validation.
- Use an access/distribution/core hierarchy; collapse tiers only when scale, failure domain, and policy justify it.
- Design redundancy as independent failure domains, not merely duplicate links. N+1 is a starting point; calculate availability.
- Summarize addressing at boundaries, reserve growth blocks, and document VLAN, routing, and policy intent.
- Include operations: out-of-band management, telemetry, configuration backup, and change control.
Worked example
A three-building campus has 600 users, 20% three-year growth, and a 99.9% uptime target. A full three-tier core is hard to justify: 600 users fit a collapsed core. Put a pair of distribution switches in the MDF, dual-home each building’s access switches over fiber, and route between VLANs at distribution. Size uplinks for 1 Gbps access with 4:1 oversubscription: 24 access ports at 1 Gbps = 24 Gbps peak; two 10 Gbps uplinks give 20 Gbps, about 1.2:1, so use four 10 Gbps members or accept monitored oversubscription. The reasoning is failure domain and growth, not port count alone.
Traps
Designing for today’s user count; calling two links redundant when they share a conduit or power feed; ignoring east-west traffic; and omitting assumptions, constraints, and acceptance tests from the design document.