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Appendix E. Introduction to Virtual LANs (VLANs)
Virtual LANs
A VLAN is defined as a group of location and topology independent devices that
communicate as if they are on the same physical LAN. This means that the LAN
segments are not restricted by the hardware that physically connects them; the
segments are defined by flexible user groups that you create using various network
management tools.
With VLANs, you can define your network according to:
v
Departmental groups: For example, you can have one VLAN for the Marketing
department, another for the Finance department, and another for the
Development department.
v
Hierarchical groups: For example, you can have one VLAN for directors,
another for managers, and another for general staff.
v
Usage groups: For example, you can have one VLAN for users of e-mail and
another VLAN for users of multimedia application services.
Benefits of VLANs
Implementing VLANs has three main advantages:
v
It eases the change and movement of devices on IP networks.
v
It helps to control broadcast traffic.
v
It provides extra security.
How VLANs ease change and movement
With traditional IP networks, network administrators spend much of their time
dealing with moves and changes. If users move to a different IP subnet, the IP
addresses of each device must be updated manually.
With a VLAN setup, if a device in VLAN 1 is moved to a port in another part of the
network, you only need to specify that the new port is in VLAN 1.
How VLANs control broadcast traffic
With traditional networks, congestion can be caused by broadcast traffic that is
directed to all network devices whether they require it or not. VLANs increase the
efficiency of your network because each VLAN can be set up to contain only those
devices that need to communicate with each other; therefore, limiting broadcast
traffic to only those segments within the VLAN.
How VLANs provide extra security
Devices within each VLAN can communicate only with devices in the same VLAN.
Figure 75 on page 118 shows a network configured with three VLANs—one for each
of the departments that access the network.
© Copyright IBM Corp. 1999
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