Chapter 9. Virtual LANs

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

Virtual LANs and Network Topologies 138

Switching Based on Network Frames 139

Implicit and Explicit Tagging 141

IEEE Standards for Virtual LANs 144

What Kind of Switch Should You Buy? 146

Chapter 8, "Network Switches," discussed switches that can be used to reduce the broadcast domain limit imposed by earlier networking technologies, such as hubs and bridges. LAN switches can be used to solve more problems than just reducing network traffic, however. This chapter discusses how switches can be used to create virtual LANs, or VLANs. Besides reducing the broadcast domain, switches configured for use in a VLAN can be used to solve many other problems:

• The changing physical topology of the LAN

• Security on the LAN

• Performance issues

• Centralized management of multiple LANs

• Limiting multicast traffic

Although a router can also be used to reduce a broadcast domain and create separate subnets in a network, switching technology works at a much faster pace. Thus, using VLANs in your network probably can enable you to get rid of a few slow routers that currently are being used to segment a LAN.