Setup Inter-VLAN Communication via “Router on a Stick”

This lab demonstrates inter-VLAN communication via the “Router on a Stick” method. To enable inter-VLAN communication, a trunk link is created between a router and switch. Trunk links can carry traffic for multiple VLANS. Trunk links can also be used to span VLANs across multiple switches and allow them to communicate with each other. In general, communication between VLANs must go through a layer 3 device.

In this lab, I use an old school Cisco 2611 router [IOS 12.3(18)] with a more modern Cisco WS-C3560G-24TS switch [IOS 12.2(40)SE]. Of course, in reality, it would not make much sense to use a router with only FastEthernet ports with a switch that uses GigabitEthernet ports – but this is the equipment I had on hand, so this is what I used. The “Router on a Stick” method does create a bottleneck and a single point of failure, but for someone who has a limited number of router ports available, it could be worth it. The number of VLANs the trunk link will support is only limited by the bandwidth available and the amount of traffic being passed. Since the Cisco 2611 router only has 2 FastEthernet ports, it actually is a good candidate for setting up a trunk link with a switch. Below is a diagram of the setup I created in the lab; I have included the respective IOS commands. Once you have setup your lab, you can perform a test by plugging a laptop into a port on one VLAN and pinging the IP of another VLAN.