When you set up a VLAN on your network, you are segmenting computers with frequent traffic patterns into a virtual network of their own. This keeps traffic segmented and does not tie up resources that do not need to see the traffic. This is a means of decreasing the broadcast domain to only those users who need to see the broadcast and therefore decreasing network traffic for those who don't need to see the broadcast information.
For instance, if you have a server on port 1 of a switch in one building and computers on ports 3,4,5 use that server in another, you could set up a VLAN for ports 1,3,4,5 on the two switches. When the server advertises its services it will only got to ports 3,4 and 5. Their traffic is then routed directly between those ports and access is faster due to the decrease in broadcast traffic. It is less expensive to implement than a routed network and throughput is greater. Bandwidth allocation becomes easier with VLAN's as well.
VLAN's also allow you more options for security. Some VLAN implementations are proprietary, so you will want to contact your electronic vendor to determine how to implement it.
This was first published in October 2003