Campus and Enterprise LAN Design
What the exam tests
Campus and Enterprise LAN Design tests Layer 2 and Layer 3 campus topology, VLAN segmentation, loop prevention, first-hop redundancy, link aggregation, PoE, and wireless integration in Juniper EX/QFX environments.
Core rules
- Keep Layer 2 domains small; route at distribution where possible.
- Use RSTP/MSTP for safe L2 loops, but prefer L3 ECMP and MC-LAG or Virtual Chassis to remove blocked links.
- Bundle links with LACP; verify member speeds, LACP mode, and hashing.
- Provide first-hop redundancy with VRRP or a Virtual Chassis/ESI-LAG anycast design.
- Budget PoE per switch and per UPS; voice VLANs need QoS trust boundaries.
Worked example
An 800-user office has 12 access switches, data and voice VLANs, and dual distribution switches. Put the two distribution EX switches in a Virtual Chassis, dual-home each access switch with one link to each VC member, and form a LACP bundle per access switch. Route VLANs on IRB interfaces in the VC; because the VC has one control plane, VRRP is not needed for gateway redundancy. If the switches were independent, configure VRRP with a shared virtual IP and tuned priorities. Uplink math: each access switch has 48 x 1 Gbps ports; two 10 Gbps uplinks give 20 Gbps, a 2.4:1 oversubscription. That is acceptable for general office traffic if monitoring confirms no sustained congestion; add a third 10 Gbps member for voice-heavy floors.
Traps
Mixing native VLANs; leaving STP root priority default; using LACP active/passive incorrectly; forgetting PoE budget; and designing wireless AP uplinks at 1 Gbps when 802.11ax can exceed it.