In many cases, these broadcasts help users to find and use services.

However, from the network administrator's perspective, broadcasts use up bandwidth and affect every user's desktop in the switched network.

Some mechanism is needed to reign in the propagation of broadcasts.

When switches were first developed, they were essentially bridges with many ports.

All ports were in the same broadcast domain, just like a bridge. VLANs are created by logically segmenting a network into separate broadcast domains.

The advantage of this approach is that it can be done using switches that cost less than traditional routers.

However, each broadcast domain is typically considered to be a separate subnet.

To go between subnets, a Layer 3 component, such as a router, is still required.

VLANs can be based on the port identifier of a switch, on an end station's MAC address or Layer 3 address, or on directory or application information.

All three of these areas play an integral part in the setup of VLANs in your network.