With a hub, some cables, and some network interface adapters (or network interface cards, or NICs), you can turn a group of computers into a network. As networks grow larger, other types of hardware devices are needed. When a network grows beyond a certain point, the computers generate too much traffic for the network medium to handle. This is particularly true on Ethernet networks, which decrease in efficiency as traffic increases. This chapter examines some of the more complex components you can use to connect local area networks (LANs) together at the data-link and network layers. By using these tools, you can increase the network's size without diminishing its efficiency, even though network traffic increases significantly.