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BeginnerPublished 2026-06-30

802.1Q Trunk Fundamentals: Static Trunk and VLANs

Free preview — the first lab of VLAN Trunking (802.1Q)

Build a static 802.1Q trunk between two Layer-2 switches to carry VLANs 10 and 20. Map hosts to access ports, verify trunk encapsulation and allowed VLANs, demonstrate same-VLAN reachability across the trunk, and confirm inter-VLAN isolation. Then simulate an allow-list drift fault, diagnose with show commands, and restore service.

Track
Est. time
45 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Create VLANs and assign correct access ports on Layer-2 switches.
  • Configure a static 802.1Q trunk that explicitly forces 802.1Q tagging, hardens the native VLAN, and restricts the allowed VLAN list precisely.
  • Verify trunks and transported VLANs using show interfaces trunk and show vlan brief.
  • Validate same-VLAN reachability across the trunk and confirm isolation between different VLANs.
  • Diagnose and fix trunk allow-list drift and native VLAN mismatches.

Troubleshooting focus

  • Trunk forms but does not carry a required VLAN due to an incomplete allowed list.
  • Native VLAN mismatch detected; traffic may be misclassified/untagged inconsistently.
  • Endpoint plugged into an access port assigned to the wrong VLAN.
  • Trunk left dependent on DTP negotiation instead of forced static trunking, so it may not form deterministically on both ends.
  • VLAN missing from the local VLAN database on one switch.

Topology

Lab topology diagram

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Study this topic

Free guides, a command cheat sheet, and graded practice for this lab's topic.

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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