Inter VLAN Routing

Overview

The ability to create VLANs and establish multiple networks on a switch is useless if you cannot allow the separate VLANs to communicate with each other. For separate VLANs to communicate you need to have routing, you accomplish this by adding a router or a layer 3 switch to the network. The Cisco CCNA curriculum expects you to know how to configure inter-vlan routing using a router connected to a switch through a trunked link. Configuring Layer 3 switching is a CCNP topic and not expected in the CCNA.

To configure a router for inter-vlan routing the router’s ethernet port needs to be converted to a trunked link. As a trunk, multiple VLANs (networks) can travel across the one ethernet port. To do this the ethernet port needs to use sub-interfaces in order to become the gateway for multiple networks. The sub-interfaces also need to have the 802.1Q trunking protocol enabled and the VLAN ID or number specified in the configuration. When multiple VLANs (networks) can communicate with the router over one trunked link the configuration is called “Router on a Stick.”

In the video tutorials, below I cover the entire process of configuring VLANs, switchports and a trunk on a switch, and inter-vlan routing on a router, using Cisco’s Packet Tracer program to simulate a real network environment.

Video Tutorials

In part 1, I discuss the need for VLANs and Inter-VLAN routing in a network

If you want to follow along in Packet Tracer with the parts 2 & 3. Click here to download the start file: inter-vlan-routing-start.zip

In part 2, I lay out the “Router on a Stick” topology and begin configuring the switch for VLANs

In part 3, I configure sub-interfaces, 802.1Q encapsulation with VLAN IDs, and the native VLAN on the router

Video Tutorials

In this video, I setup inter-VLAN routing by configuring the switch VLANs, switchports, and trunk, then I configure the router the subinterfaces on the router with IP addresses and the 802.1Q protocol.

In this video, I configure the router for inter-vlan routing

Author: Dan

Dan teaches computer networking and security classes at Central Oregon Community College.

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