Posted by arlene

A VLAN can be thought of as the equivalent to a broadcast domain.

VLANs are a way to segment a network, as discussed above. When thinking of a VLAN, think of taking a switch and physically cutting it into two or more pieces with an axe. Special software features found in newer, more expensive switches, allow administrators to physically split one physical switch into multiple logical switches, thus creating multiple network segments that are completely separate from one another.

The VLAN is thus a logical local area network that uses a basis other than a physical location to map the computers that belong to each separate VLAN (e.g., each department within a company could comprise a separate VLAN, regardless of whether or not the department’s users are located in physical proximity). This allows administrators to manage these virtual networks individually for security and ease of configuration.

Let’s look at an example of using VLANs. There is an Engineering section consisting of 14 computers and a Research section consisting of 8 computers, all on the same physical subnet. Users typically communicate only with other systems within their respective sections. Both sections share the

Use of one Cisco Catalyst 2924 XL switch. To diminish the size of the necessary broadcast domain for each section, the administrator can create two VLANs, one for the Engineering section and one for

The Research section. After creating the two VLANs, all broadcast traffic for each section will be isolated to its respective VLAN. But what happens when a node in the Engineering section needs to ommunicate with a node in the Research section? Do the two systems connect from within the

Catalyst 2924 XL switch? No; this cannot occur since the two sections have been set up on two dif- rent VLANs. For traffic to be passed between VLANs (even when they are on the same switch) a uter must be used.

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