Virtual Local Area Networks or VLANs are one of the latest and coolest network technologies developed in the past few years, though have only recently started to gain recognition. The non-stop growth of Local Area Networks (LANs) and the need to minimize the cost for this expensive equipment, without sacrificing network performance and security, created the necessary soil for the VLAN seed to surface and grow into most modern networks.

This article covers VLAN theory extensively using modern and easy-to-understand examples accompanied by detailed diagrams to ensure the theory is understood. VLAN Design, Access and Trunk Links, VLAN Tagging (ISL, 802.1q, LANE, IEEE 802.10), InterSwitch Link (ISL), InterVLAN Routing, Virtual Trunk Protocol (VTP) and VTP Pruning are just a few of the topics covered over the next couple of pages.

The truth is that VLANs are not as simple as most people peceive it to be. Instead they cover extensive material to be a whole study in itself as they contain a mixture of protocols, rules, and guidelines that a network administrator should be well aware of. Unfortunately, most documentation provided by vendors and other sites is inadequate or very shallow. They lightly touch upon the VLAN topic and fail to give the reader a good understanding on how VLANs really work and the wonderful things one can do when implementing them.

Like most topics covered on our site, VLANs have been broken down into a number of pages, each one focusing on specific areas to help the reader build up their knowledge as preparation for designing and building their own VLAN network.

Since VLANs is a topic that requires strong background knowledge of certain areas, as they contain a lot of information at the techincal and protocol level, we believe that the reader should be familiar and comfortable with the following concepts:

• Switches and hubs
• Broadcast and collision domains
• Internet Protocol (IP)
• IP routing

As we cover all the theory behind VLANs and how they are implemented within various network topologies, we will finally demonstrate the configuration of a Cisco powered network utilising VLANs!

Protocols such as Spanning Tree Protocol (STP) are essential when implementing VLANs within a mid to large sized network, so we will briefly touch upon the topic, without thoroughly analysing it in great detail because STP will be covered as a separate topic.

So What's Covered?

Before we begin our journey into the VLAN world, let's take a look at what we will be covering:

Section 1: The VLAN Concept. This page explains what a VLAN is and how it differs from a normal switched environment. Be sure to find our well known diagrams along with illustrations to help cover your questions. In short, its a great introductory page for the topic.

Section 2: Designing VLANs. (Subcategory)

Section 2.1: Designing VLANs - A Comparison With Old Networks. This subsection will give you an insight to the different VLAN implemenations: Static and Dynamic VLANs. The subsection begins with an introduction page to help you 'see' the actual difference in the network infrastructure between the old boring networks and VLAN powered networks. This way, you will be able to appreciate the technology much better!

Section 2.2: Designing VLANs - Static VLANs. Definately the most wide spread VLAN implementation. The popular Static VLANs are analysed here. We won't be covering any configuration commands here as this page serves as an introduction to this VLAN implementation. As always, cool 3D diagrams and examples are included to help you understand and process the information.

Section 2.3: Designing VLANs -  Dynamic VLANs. Dynamic VLANs are less common to most networks but offer substantial advantages over Static VLANs for certain requirements. Again, this page serves as an introduction to the specific VLAN implementation.

Section 3: VLAN Links: Access Links & Trunk Links. Access links are used to connect hosts, while Trunk links connect to the network backbone. Learn how Access & Trunk links operate, the logic which dictates the type of link and interface used and much more.

Section 4: VLAN Tagging - ISL, 802.1q, LANE and IEEE 802.10. To tag or not to tag! Understand the VLAN tagging process and find out the different tagging methods available, which are the most popular and how they diffirentiate from each other. Neat diagrams and examples are included to ensure no questions are left unanswered!

Section 5: Analysing Popular Tagging Protocols. 

Section 5.1: InterSwitch Link Analysis (ISL): Analysis of Cisco's proprietry ISL protocol. We take a look at how it is implemented and all available fields it contains.

Section 5.2: IEEE 802.1q Analysis: IEEE's 802.1q protocol is the most widely spead trunking protocol. Again, we take a look at its implementation with an analysis of all its fields.

Section 6: InterVLAN Routing. A very popular topic, routing between VLANs is very important as it allows VLANs to communicate. We'll examine all possible InterVLAN routing methods and analyse each one's advantages and disadvantages. Needless to say, our cool diagrams also make their appearance here!

Section 7: Virtual Trunk Protocol (VTP) (Subcategory)

Section 7.1: Introduction To The VTP Protocol. The introductory page deals with understanding the VTP concept. Why it's required and what are its advantages.

Section 7.2: In-Depth Analysis Of VTP. Diving deeper, this page will analyse the VTP protocol structure. It includes 3d diagrams explaining each VTP message usage and much more.

Section 7.3: Virtual Trunk Protocol Prunning (VTP Pruning). VTP Prunning is an essential service in any large network to avoid broadcast flooding over trunk links. This page will explain what VTP Prunning does and how it works by reading through our excellent examples. The diagrams used here have been given extra special attention!

Section 8: VLAN Security: This article covers VLAN Security best practices. Originally written for the U.S FedTech Magazine, it tackles a lot of important issues regarding VLAN Security.