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IntermediatePublished 2026-06-25

Voice & Data VLANs: Access + Trunk Allowed Lists

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Configure a two-switch access layer with data and voice VLANs on access ports and an 802.1Q trunk between switches. Add a router-on-a-stick gateway for VLAN 10/20. Verify VLAN placement, trunk status, and observe a connectivity failure caused by an allow-list misconfiguration on the inter-switch trunk—then correct it to restore intra-VLAN reachability.

Track
Est. time
65 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Create and name VLANs for data and voice segmentation
  • Configure access ports with both a data VLAN and a voice VLAN
  • Build and harden 802.1Q trunks (native VLAN and allowed VLANs)
  • Implement router-on-a-stick as the default gateway for user/voice VLANs
  • Verify VLAN membership and trunk status with show commands
  • Diagnose and fix trunk allow-list issues that break VLAN transport

Troubleshooting focus

  • Detect missing VLANs in a trunk’s allowed list when same-VLAN hosts can’t talk across switches
  • Spot access-port VLAN/voice-VLAN mismatches using show vlan / show interfaces switchport
  • Identify native VLAN mismatches on a trunk that trigger STP/l2 issues or control-plane leaks
  • Recognize when DTP negotiation is disabled but trunk mode wasn’t explicitly set on both ends
  • Use end-host pings to triangulate which trunk/path is failing

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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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