Chapter 6. Managing virtual LANs (VLANs)
Recall from chapter 2 that you need to keep broadcast domains small to avoid network performance problems like flooding and interrupts. On a large network, this brings with it the nasty side effect of having to split devices into separate broadcast domains.
But separating broadcast domains isn’t just about necessity, nor is it a concern for only large networks. Many organizations—even small ones—want to maintain separate broadcast domains for security. For example, a company may want to keep computers in the Human Resources department in a separate broadcast domain from computers in the Marketing department.
In chapter 2, I illustrated one way to achieve such a configuration using two separate, disconnected switches. Although this is certainly a valid approach, it’s not very efficient. Having at a minimum one switch per broadcast domain costs more money, takes up more space, and requires more management overhead than putting all devices into one big broadcast domain.
So what do you do? At first it may seem you’re stuck choosing between two bad options. Do you ensure a reliable network, or do you try to keep costs down? Fortunately, there’s a third option that gives you both: use virtual LANs (VLANs).