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BeginnerPublished 2026-06-30

Router-on-a-Stick Fundamentals: Two VLANs, One Trunk

Free preview — the first lab of Inter-VLAN Routing

Configure inter-VLAN routing using router-on-a-stick with one router, one Layer-2 switch, and two hosts. Build VLAN 10 and VLAN 20, trunk the router uplink, create subinterfaces for each VLAN, and verify that hosts can now reach each other across VLANs.

Track
Est. time
45 minutes
Difficulty
Beginner
Topics

Learning objectives

  • Translate a two-VLAN addressing plan into router-on-a-stick subinterfaces
  • Configure an 802.1Q trunk between a router and a Layer-2 switch
  • Create VLANs on a Layer-2 switch and assign access ports correctly
  • Verify inter-VLAN reachability from end hosts and with IOS show commands
  • Recognize and correct trunk allow-list and access-port misconfiguration issues

Troubleshooting focus

  • Detect a missing VLAN gateway (absent router subinterface)
  • Identify a trunk that is not in 802.1Q mode or is pruned to the wrong allow-list
  • Spot a host connected to the wrong access VLAN
  • Confirm that the router physical interface carries no IP address and is up

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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