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IntermediatePublished 2026-06-30

CCNA: Pruning the Allowed VLAN List on Trunks

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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.

Track
Est. time
48 minutes
Difficulty
Intermediate
Topics

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

Topology

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Learn VLANs, Trunking & Inter-VLAN RoutingWhat Is a VLAN? VLANs Explained for Beginners

Grade your work

How this lab is graded
  • Build it your way. Where a lab lets you choose a value — a VLAN name, an interface description — grading checks that you configured it, not which name you picked. Names that another line has to reference, like an ACL applied with access-class, are stated in the guide and do have to match.
  • Addresses, modes and protocol keywords are exact. An IP address, a subnet mask, switchport mode trunk, an encapsulation — these carry the meaning of the lab, so they are graded as written in the guide.
  • Grading reads your saved configuration. Export the lab from CML after you have configured it, and make sure anything you set is in the running-config — a change that only exists in a terminal session never reaches the grader.
  • You can submit as many times as you like. Your best score stands, and each attempt tells you which checks passed so you can work the gaps.
  • Scored something you believe is correct? Use Report an issue on this page — that is exactly how the grading fixes in the changelog got found.

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