STP Lab 6: BPDU Guard — Protecting the Edge

Bundle lab · $29.99

Continue the STP series on a three-switch triangle with a real loop. SW1 is the deterministic root for VLAN 60, and access ports already use PortFast. In this lab you will harden the edge by enabling BPDU Guard on the two host-facing access ports on SW2 and SW3, while leaving the inter-switch trunks untouched. Verify with show commands that BPDU Guard is active only on the edge and that hosts still communicate normally.

Learning objectives

• Explain why PortFast needs BPDU Guard on access ports
• Enable BPDU Guard on PortFast-enabled access ports
• Verify BPDU Guard status on specific interfaces
• Confirm trunks do not have BPDU Guard enabled
• Validate root bridge election for VLAN 60 remains on SW1

Troubleshooting focus

• If a host port is err-disabled, check for unexpected BPDUs: show spanning-tree interface <if> detail and show errdisable recovery
• If inter-switch links go down unexpectedly, confirm BPDU Guard was not applied on trunks: show running-config interface <trunk-if>
• If hosts cannot ping each other, confirm both are in VLAN 60 on access ports and VLAN 60 is allowed across all trunks
• If STP does not block the expected loop link, verify root priority on SW1 and consistent Rapid-PVST operation on all switches