Need for VLANs

If a traditional bridge receives a frame with a broadcast, multicast, or unknown destination address, it forwards the data to all bridge ports except the port on which it was received. This process is referred to as bridge flooding. As networks grow and the amount and types of traffic increase, bridge flooding may create unnecessary traffic problems that can clog the Local Area Networks (LAN).

To help control the flow of traffic through a switch and meet the demands of growing networks, vendors have responded by using:

• Customized packet filtering to control which packets are forwarded.
• More routers as broadcast firewalls to divide the network into broadcast domains.
• Spanning Tree Protocol to control the flow of traffic among LANs (for redundant links).

Advantages with VLANs:

• Segment traffic and usage patterns in a manner similar to creating subnets and segments in traditional networks.
• Reduce the cost of equipment moves, upgrades, and other changes.
• Simplify network administration.
• Create logical work groups for users who share the same system resources.
• Users not required to share the same physical location.
• Reduce the need for routing to achieve higher network performance and reduced costs.
• Control or filter communication among broadcast domains.