The concept of and benefits to utilizing VLANs A VLAN is logically dividing a switch into multiple, independent switches at layer 2. Each VLAN is its own broadcast domain that segment the broadcast domain among the different VLAN. The difference is that with VLANs, you still connect all the PCs to a single switch but you make the switch behave as if it were multiple, independent switches. The advantages of using VLANs are as follows: •VLANs increase the number of broadcast domains while reducing their size; this is the same effect that routers have, but without the need to buy a lot of routers or a big router with a lot of ports, so it's less expensive and easier to administer. •VLANs provide an additional layer of security: No device in any VLAN can communicate with a device in any other VLAN until you deliberately configure a way for it to do so. An example might be a server in VLAN 10 that holds sensitive employee files for HR; no PCs from other VLANs can access VLAN 10 (or the server in it), unless you specifically configure it to do so. •VLANs are flexible in terms of how they are used in network equipment: Imagine a building that has LAN cabling and a single switch installed, but four different tenants. You can create four different VLANs, one for each tenant, and no tenant will see or hear from the other tenants on the other VLANs. •VLANs can span across multiple switches using trunk links. This allows you to create a logical grouping of network users by function instead of location. If you want all the marketing people to be in their own broadcast domain and IP subnet, you can create a VLAN for them on the first switch; then, you can connect another switch using a trunk link, define the same VLAN on that switch, and the marketing users on the second switch are in the same VLAN and can communicate with the marketing users on the first switch, and are isolated from other VLANs on both switches. This capability can be extended across an enterprise network campus, so that marketing users in the Whitaker Pavilion could in theory be in a VLAN with other marketing users in the Valentine Pavilion. •The ability to trunk VLANs across multiple switches makes adding users, moving users, and changing users' VLAN memberships much easier.
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