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IntermediatePublished 2026-06-30

A Policy-Correct Multi-VLAN Trunk

Bundle lab

Build a single 802.1Q trunk between two Layer-2 switches that correctly carries three VLANs with an explicit allow-list and a dedicated non-default native VLAN. Place hosts in Users (VLAN 10) across both switches and a server in Servers (VLAN 20). Verify that the trunk allows VLANs 10, 20, and 99, that the native VLAN matches on both ends, and that same-VLAN hosts communicate across the trunk. Then intentionally break and restore the configuration to practice troubleshooting trunk allow-lists, native VLAN alignment, and host VLAN placement.

Track
Est. time
47 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Create VLANs and map access ports to the correct VLANs on Layer-2 switches
  • Configure a static 802.1Q trunk with an explicit allowed VLAN list and a non-default native VLAN
  • Verify trunk status, allowed VLANs, and native VLAN symmetry using show interfaces trunk
  • Validate end-host placement and intra-VLAN connectivity across a trunk
  • Troubleshoot common trunk issues: omitted VLANs on allow-lists, native VLAN mismatches, and wrong access VLANs

Troubleshooting focus

  • A native VLAN mismatch causes unexpected untagged/Native traffic behavior and warnings
  • A required VLAN omitted from the trunk allow-list breaks cross-switch reachability for that VLAN
  • An access port assigned to the wrong VLAN strands a host in the wrong broadcast domain

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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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