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IntermediatePublished 2026-06-30

Native VLAN on a Router-on-a-Stick Trunk

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Build and verify inter-VLAN routing using router-on-a-stick with a native (untagged) VLAN on the trunk. Configure one router (subinterfaces only), one Layer-2 access switch (VLANs, access ports, and a single 802.1Q trunk), and two end hosts in different VLANs. The management VLAN 99 rides untagged as the trunk's native VLAN, so the router subinterface must use 'encapsulation dot1Q 99 native' and the switch trunk must match 'switchport trunk native vlan 99'. Verify from Linux hosts and IOS 'show' commands, then practice troubleshooting common native-VLAN faults.

Track
Est. time
50 minutes
Difficulty
Intermediate
Topics

Learning objectives

  • Configure router-on-a-stick subinterfaces with correct 802.1Q VLAN tags and the native keyword for the management VLAN.
  • Create VLANs on a Layer-2 switch, assign access ports, and build a matching 802.1Q trunk with the correct native VLAN.
  • Validate end-to-end reachability from hosts, including cross-VLAN ping and traceroute via the router subinterface.
  • Identify and correct native VLAN mismatches and missing VLANs on trunks.

Troubleshooting focus

  • PC-M cannot reach 10.0.99.1 while PC-A works: native VLAN mismatch. SW-LAB-ACC1 shows native VLAN 99, so RTR-LAB-EDGE1 Ethernet0/0.99 must also treat VLAN 99 as native. Align both ends.
  • Hosts in one VLAN cannot cross the trunk: that VLAN is off the trunk's allowed-VLAN list. Check show interfaces trunk and add the missing VLAN.
  • A host never sees its gateway: its access port is likely still in the default VLAN 1. Reassign the port to the intended VLAN — Ethernet0/1 to 10, Ethernet0/2 to 99.
  • Both subinterfaces are down: the parent Ethernet0/0 on RTR-LAB-EDGE1 is shut, which takes every subinterface with it. Put the parent in no shutdown.

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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.
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