CompTIA Network+ (N10-009)Network ImplementationHard
A network administrator wants VLAN 10 traffic to use SwitchA as the spanning tree root bridge while VLAN 20 traffic uses SwitchB as the root bridge, allowing traffic load to be balanced across both uplinks. Which switching technology natively supports this per-VLAN root bridge assignment?
- APer-VLAN Spanning Tree Plus (PVST+)
- BCommon Spanning Tree (802.1D)
- CVLAN Trunking Protocol (VTP)
- DLink Aggregation Control Protocol (LACP)
Show answer & explanationAnswer & explanation
Correct answer: A. Per-VLAN Spanning Tree Plus (PVST+)
PVST+ (and Rapid PVST+) runs a separate spanning tree instance per VLAN, allowing administrators to assign different root bridges to different VLANs for load balancing across redundant uplinks, unlike Common Spanning Tree which uses one instance for all VLANs.
Why the other options are wrong
- B. Common Spanning Tree (802.1D) runs a single instance for all VLANs, so all VLANs share the same root bridge.
- C. VTP synchronizes VLAN database information across switches, not spanning tree topology.
- D. LACP aggregates links into one logical interface and has nothing to do with spanning tree root election.
PVST+ (Per-VLAN Spanning Tree)
A Cisco enhancement to STP that runs a separate spanning tree instance for each VLAN, allowing different root bridges per VLAN for load balancing.
- Contrasts with Common Spanning Tree (single instance for all VLANs)
- Enables per-VLAN load balancing across redundant links
- Rapid PVST+ combines this with 802.1w's faster convergence
Memory trick: PVST+ = 'Personalized VLAN Spanning Trees' — each VLAN picks its own root.