Internetworking refers to the science of connecting individual local-area networks (LANs) to create wide-area networks (WANs), and connecting WANs to form even larger WANs. An internetwork is therefore a collection of separate networks connected by intermediate networking devices (such as routers, bridges, and gateways) such that it functions as a single large network. Internetworking is complex because it has to take into consideration the fact that diverse networks use diverse network protocols. Communication needs to be supported across disparate technologies. Different networks could use different types of media or operate at varying speeds. Internetworks need to be able to offer seamless connectivity. Despite the challenges involved, internetworks are becoming increasingly used as they operate at very high speeds and offer broadband support of bandwidth-intensive applications such as voice and video-conferencing.

Internetworking evolved in response to several network problems, including that of isolated LANs, which secluded branch office communications...