A VLAN is a logical grouping of devices or users that can be grouped by function, department, or application regardless of their physical location.

VLANs are configured at the switch through software. The number of competing VLAN implementations can require the use of proprietary software from the switch vendor. Grouping ports and users into communities of interest, referred to as VLAN organizations, may be accomplished by the use of a single switch or more powerfully among connected switches within the enterprise. By grouping the ports and users together across multiple switches, VLANs can span single building infrastructures or interconnected buildings. VLANs assist in the effective use of bandwidth as they share the same broadcast domain or Layer 3 network. VLANs optimize the collection and use of bandwidth. VLANs contend for the same bandwidth although the bandwidth requirements may vary greatly by workgroup or department. The following are some VLAN configuration issues:

• A switch creates a broadcast domain
• VLANs help manage broadcast domains
• VLANs can be defined on port groups, users or protocols
• LAN switches and network management software provide a mechanism to create VLANs

VLANs help control the size of broadcast domains and localize traffic. VLANs are associated with individual networks. Therefore, network devices in different VLANs cannot directly communicate without the intervention of a Layer 3 routing device.

When a node in one VLAN needs to communicate with a node in another VLAN, a router is necessary to route the traffic between VLANs. Without the routing device, inter-VLAN traffic would not be possible.