1-11 VLAN ConfigurationOverviewIntroduction to VLANEthernet is a network technology based on the Carrier Sense Multiple Access/Collision Detect(CSMA/CD) mechanism. As the medium is shared, collisions and excessive broadcasts are commonon an Ethernet. To address the issue, virtual LAN (VLAN) was introduced. The idea is to break a LANdown into separate VLANs, that is, Layer 2 broadcast domains whereby frames are switched betweenports assigned to the same VLAN. VLANs are isolated from each other at Layer 2. A VLAN is a bridgingdomain, and all broadcast traffic is contained within it, as shown in Figure 1-1.Figure 1-1 A VLAN diagramVLANs are logically divided on an organizational basis rather than on a physical basis. For example, allworkstations and servers used by a particular workgroup can be connected to the same LAN,regardless of their physical locations.VLAN technology delivers the following benefits:z Confining broadcast traffic within individual VLANs. This reduces bandwidth waste and improvesnetwork performance.z Improving LAN security. By assigning user groups to different VLANs, you can isolate them atLayer 2. For hosts in different VLANs to communicate, routers or Layer 3 switches are required.z Flexible virtual workgroup creation. As users from the same workgroup can be assigned to thesame VLAN regardless of their physical locations, network construction and maintenance is mucheasier and more flexible.How VLAN WorksTo enable a network device to identify frames of different VLANs, a VLAN tag field is inserted into thedata link layer encapsulation.
