Local area network to local area network layouts

     Because the local area network is a standard in business and academic environments, it should come as no surprise that many organizations need the services of multiple local area networks and that it may be necessary for these LANs to communicate with each other. For example, a company may want the local
area network that supports its research department to share an expensive colorlaser printer with its marketing department’s local area network. Fortunately, it is possible to connect two local area networks so that they can share peripherals as well as software. The devices that usually connect two or more LANs are the switch and router.

     In some cases, it may be more important to prevent data from flowing between local area networks than to allow data to flow from one network to another. For instance, some businesses have political reasons for supporting multiple networks—each division may want its own network to run as it wishes. Additionally, there may be security reasons for limiting traffic flow between networks; or allowing data destined for a particular network to traverse other networks simply may generate too much network traffic. Devices that connect local area networks can help manage these types of services as well. For example, the switch can filter out traffic not intended for the neighboring network, thus minimizing the overall amount of traffic flow. Figure 1-4 provides an example of two LANs connected by a switch.

Two local area

networks connected by a switch