Router on a Stick Configuration Lab

In this lab, you will configure Inter-VLAN Routing using the Router-on-a-Stick method.

A single physical link between the switch and the router will carry multiple VLANs using 802.1Q encapsulation.
This allows devices in different VLANs to communicate through the router.

Figure 1 - Router on a Stick Topology

Imagine a company where different departments, such as Sales and Tech need to be able to communicate with each other.

So far in this course, you’ve learned:

• How VLANs segment broadcast domains

• How trunking carries multiple VLANs over a single link

• How default gateways allow traffic to leave a subnet

• How routers use subinterfaces to route between VLANs

In this lab, you will put all these concepts together.
We’ll walk through each step to configure Router-on-a-Stick, verify the subinterfaces, set gateways, and test inter-VLAN communication.

Lab Overview

Here’s the structure we will follow throughout this lab:

• Step 1 – Set Up VLANs and Switch Ports

• Step 2 – Configure Router Subinterfaces

• Step 3 – Set Default Gateways on PCs

• Step 4 – Test Inter-VLAN Routing

In the next sections, we’ll walk through each configuration step together and verify that Router-on-a-Stick is working properly.

In this first step, you will prepare the switch so that each department is placed in the right VLAN.

Figure 2 - Router on a Stick Topology

Your goal here is simple:

• create VLANs

• assign the PCs to those VLANs

• configure the trunk toward the router

This prepares the entire Layer 2 side before the router can route between VLANs.

Create VLAN 10 and VLAN 20

Start by creating the two VLANs used in this lab.
VLAN 10 will group the Sales PCs, and VLAN 20 will group the Tech PCs.

Enter the following commands on SW1:

SW1# conf t
Enter configuration commands, one per line.  End with CNTL/Z.
SW1(config)# vlan 10
SW1(config-vlan)# name Sales
SW1(config-vlan)# exit

SW1(config)# vlan 20
SW1(config-vlan)# name Tech
SW1(config-vlan)# exit

At this stage, the switch knows both VLANs exist, but no ports belong to them yet.

Assign Access Ports

Now, you need to place the correct switch ports into the right VLANs.

• Ports F0/1–2 → VLAN 10

• Ports F0/3–4 → VLAN 20

This ensures each PC belongs to the correct department.

SW1(config)# int range f0/1-2
SW1(config-if-range)# switchport mode access 
SW1(config-if-range)# switchport access vlan 10
SW1(config-if-range)# no shut
SW1(config-if-range)# exit

SW1(config)# int range f0/3-4
SW1(config-if-range)# switchport mode access 
SW1(config-if-range)# switchport access vlan 20
SW1(config-if-range)# no shut
SW1(config-if-range)# exit

You’ve now created two isolated Layer 2 networks.

Configure the Trunk Toward the Router

Next, you must connect SW1 to the router using a trunk.
This trunk is essential: it allows both VLANs to travel over a single physical link (G0/1) using 802.1Q tags.

Without this trunk, the router would never see VLAN 10 or VLAN 20.

SW1(config)# int g0/1
SW1(config-if)# switchport mode trunk 
SW1(config-if)# switchport trunk allowed vlan 10,20
SW1(config-if)# end

Your switch is now ready for Router-on-a-Stick.

In the next step, you’ll configure the router so it can route traffic between your VLANs.

Now that your switch is ready and the trunk is carrying VLAN 10 and VLAN 20, it’s time to prepare the router.
This is the crucial part of Router-on-a-Stick: you will create one logical interface per VLAN, each with its own encapsulation and IP address.