All network designers and administrators want their campus LAN (local area net-work) to run efficiently. Think of the campus as an airline hub. The flights coming into and going out of the hub impact the performance of the hub. Air traffic control must know and control the traffic patterns and schedules of the arriving and de-parting planes to prevent chaos and accidents. In the real world, however, networks don't operate this way. While Cisco routers dominate networks, they have to interoperate with many other network protocols and this can be a problem. The network support group ends up spending all of its time troubleshooting problems.