STP Lab 8: Per-VLAN Load Balancing Across Two Roots

Bundle lab · $29.99

Use Rapid-PVST+ to elect different root bridges per VLAN across two parallel trunks, spreading VLAN 80 and VLAN 81 across distinct physical links without modifying path cost or port priority. Validate independent per-VLAN trees and confirm hosts in VLAN 80 can communicate over the surviving path. Includes a drift-check to diagnose/restore trunk allow-lists.

Learning objectives

• Create VLANs 80, 81, and set a parking native VLAN 999; place users on VLAN 80 access ports only.
• Configure two parallel L2 trunks between SW1 and SW2 that carry VLANs 80 and 81 and use native VLAN 999 with negotiation disabled.
• Enable Rapid-PVST+ and elect deterministic per-VLAN roots: SW1 root for VLAN 80, SW2 root for VLAN 81 (bridge priority 4096 each).
• Harden host-facing access ports with PortFast and BPDU Guard only on access links.
• Verify per-VLAN tree independence: show different forwarding/blocked interfaces for VLAN 80 vs VLAN 81 on the same physical links.
• Diagnose a trunk allow-list drift and native VLAN mismatch, then restore symmetric trunk policy.

Troubleshooting focus

• If hosts in VLAN 80 cannot ping, confirm both trunks permit VLAN 80 on both ends and that access ports are in VLAN 80.
• If both VLANs ride the same trunk link, verify per-VLAN root election and confirm trunks are cross-connected and symmetric; then compare the per-VLAN root-port choice on each switch.
• If a trunk shows blocking for both VLANs on the same side, check for native VLAN mismatch (expect native 999) and ensure DTP is disabled with switchport nonegotiate.
• If PortFast/BPDU Guard triggers on host ports, ensure they are access ports that do not receive BPDUs and are not cabled to another switch.