VLAN stands for Virtual local area network. A local area network that maps workstations on some other basis than geographic location (for example, by department, type of user, or primary application).
However, to understand VLANS, you first need to have an understanding of the LAN concept. A LAN can usually be defined as a broadcast domain. Hubs, bridges and switches located in the same network segment connecting all terminal devices. These devices can communicate with each other without the help of a router; therefore they’re in the same broadcast domain. Routers are used to separate these domains.
As a network grows, more and more routers are needed to separate the users into multiple broadcast and collision domains, while still being able to provide connectivity between all the network segments. These routers add latency which is quite essential to the networking related matters. The latency is caused by the time taken to route the packages from one network to another.
The VLANS can be looked at as a group of devices physically located on different LAN segments, but which can communicate with each other as if they were all part of the same LAN segment.
As every network concept, VLANS have certain benefits, but some disadvantages or limitations as well.
Advantages:
* Increased network performance – by definition, switched networks have increased performance over shared media devices, because they reduce the size of the collision domains. By grouping the users into the same vlan, you can also increase network performance by limiting the broadcast traffic. Therefore, less traffic will require routing outside the network, and the latency/router load will decrease.
* Higher manageability – Managing vlans is flexible, easier and cheaper. This makes the large networks more manageable, by allowing centralized configuration for devices physically located in different areas.
* Less configurations – This is easier for network administrators since software configurations can be made uniform across the devices located in the same vlan. This includes the network settings, IP addresses, subnet masks and local network protocols.
* Independent from the network topology – VLANS basically allow multiple different workgroups to be connected logically inside a single broadcast domain. Having the physical structure in place, it’s quite easy to add/configure ports in new locations for existing VLANS (for example if a department expands or relocates).
* Higher security – VLANS can provide additional security that’s not available in a shared media network. By default, a switched network delivers the packet only to their intended recipients and broadcasts frames only to other members of the same VLAN. This allows the network administrator to segment users requiring a dedicated communication channel and separate them from the rest of the network, regardless of the physical location.
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Disadvantages:
* From the performance point of view, an average local area network typically operates at 100mbps and <5ms latency.On the other hand, wide area networks (unless talking about national ISPs) typically operate at a lower speed and higher latency. Therefore, a VLAN will always perform as well as the worst network segment it contains. So from this point of view, a VLAN is less efficient than a LAN.
* Virus risk – Because in a VLAN basically all the users are in the same network, if one user gets infected with a network virus, there’s a high risk that the rest of the users will get infected as well
* Equipment limitations – Routing between vlans is accomplished with the help of a router. If our whole network is not very large, our router can take the workload. Otherwise, it’s not a good idea to load everything on a single router.
For more information on VLAN read What is VLAN
http://www.tech-faq.com/vlan.shtml
