What is a virtual local area network (VLAN) and why would I use one?
A virtual local area network (VLAN) is an abstracted or “virtual” LAN. A local area network or LAN is a hardware setup establishing a physical network. With VLANs, even hardware systems in different geographic locations can be part of the same VLAN. The IEEE.802.1Q specifications define the use of a VLAN.
VLANs allow for network partitioning: in a VLAN environment, different sets of hardware within the same space can be grouped into different VLANs that do not communicate with each other. Alternately, administrators can provide a “tunnel” between these VLANs at OSI layer 3.
One possible use of a VLAN would be to reduce traffic. By segmenting network traffic into different non-connected VLANs, administrators can cut down on network traffic. For example, messages meant for only one group of workstation users can go to only the computer group in a single VLAN. By the same token, VLANs can also simplify administration: where a physical LAN requires a lot of user provisioning, a VLAN can decrease the necessary labor around user changes. In fact, a major argument for VLANs is the much easier scalability and reconfiguration of a VLAN environment.
Another use of VLANs relates to standards and protocols. A business might have several operations or departments operating in the same physical building. With a simple LAN, all network traffic would travel across the entire network. To wall off operations, administrators can create different VLANs for two different departments that are not supposed to communicate with each other. One prominent example is in finance, where different arms of a financial institution are said to be independent of one another for the purposes of Sarbanes-Oxley or other rules or standards.