CCNA: Pruning the Allowed VLAN List on Trunks

Bundle lab · $29.99

Hands-on CCNA lab focusing on 802.1Q trunk allow-lists. Build a realistic three-switch campus with two user hosts in VLAN 10. First bring up trunks carrying all VLANs by default, then implement an explicit allowed VLAN list and prune a non-used VLAN. Intentionally remove VLAN 10 from one trunk to observe an outage, verify with Linux pings and IOS show commands, and restore service by fixing the allow-list. Reinforce native VLAN alignment and compare default vs explicit trunk policy.

Learning objectives

• Create VLANs and map access ports correctly for end hosts
• Build 802.1Q trunks and compare default all-VLAN behavior to an explicit allow-list
• Curate each trunk's VLAN allow-list (adding, removing, or excepting VLANs as needed) to control trunk transport
• Align native VLAN on both ends and harden trunks with nonegotiate
• Verify trunk/allowed sets and diagnose an allow-list outage with show interfaces trunk and end-host pings

Troubleshooting focus

• Detect a missing VLAN on a trunk allow-list causing inter-switch isolation of that VLAN
• Identify native VLAN mismatches and their symptoms
• Catch host ports placed in the wrong access VLAN during onboarding