A virtual LAN (VLAN) is a group of networking devices in the same broadcast domain. The top part of Figure 8-1 shows an example of a simple VLAN, where every device is in both the same collision and broadcast domains. In this example, a hub is providing the connectivity, which represents, to the devices connected to it, that the segment is a logical segment. | CISCO CERTIFIED NETWORK ASSOCIATE CCNA Virtual LANs 1900 and 2950 VLAN Configuration Two Minute Drill Q A Self Test 8 Virtual LAN Overview VLAN Connections VLAN Trunk Protocol 2 Chapter 8 Virtual LANs As was mentioned in Chapters 2 and 7 layer-2 devices including bridges and switches always propagate certain kinds of traffic in the broadcast domain broadcasts multicasts and unknown destination traffic. This process impacts every machine in the broadcast domain layer-2 network . It impacts the bandwidth of these devices connections as well as their local processing. If you were using bridges the only solution available to solve this problem would be to break up the broadcast domain into multiple broadcast domains and interconnect these domains with a router. With this approach each new broadcast domain would be a new logical segment and would need a unique network number to differentiate it from the other layer-3 logical segments. Unfortunately this is a costly solution since each broadcast domain each logical segment needs its own port on a router. The more domains that you have the bigger the router that you have to purchase. As you will see in this chapter switches also have the same problem with traffic that must be flooded. You will see however that switches have a unique solution to reduce the number of router ports required and thus the cost of the layer-3 device that you need to obtain virtual LANs and trunking. CERTIFICATION OBJECTIVE Virtual LAN Overview A virtual LAN VLAN is a group of networking devices in the same broadcast domain. The top part of Figure 8-1 shows an example of a simple VLAN where every device is in both the same collision and broadcast domains. In this example a hub is providing the connectivity which represents to the devices connected to it that the segment is a logical segment. The bottom part of Figure 8-1 shows an example of a switch with four PCs connected to it. One major difference between the switch and the hub is that .
