Note: Many topics at this site are reduced versions of the text in "The Encyclopedia of Networking and Telecommunications." Search results will not be as extensive as a search of the book's CD-ROM.

An internetwork is a set of interconnected networks that form a single communication system, allowing any node on any network to connect with any other node. The Internet Protocol suite (TCP/IP) and Novell's IPX/SPX protocol suite are the most common internetworking protocols. An internetwork has the following characteristics and features:

• End-to-end transparency    Information may flow from source to destination essentially unaltered.


• Addressing    Each interconnected network has its own unique network address, and each node has a unique address on the network to which it is attached.


• Packets    Information is delivered in packets, which contain parts of a complete transmission. If a packet is lost or corrupted, only that packet needs to be resent, not the entire transmission. Packets have a destination address, but not a defined path and, therefore, can be routed around failed links on the internetwork.


• Routers and routing    Routers are devices that interconnect the networks and forward packets to their destinations.

An internetwork protocol like IP provides an addressing scheme that overlays the connected networks. The postal ZIP code system provides an analogy. It is an overlay addressing scheme that uniquely identifies regions, cities, and individual post offices so that mail may be routed on a national scale. At the same time, each city retains its traditional addressing scheme (street addresses) for local mail delivery. Likewise, individual networks use their own MAC-based addressing schemes to forward frames of information to other nodes on the same LAN.

An internetwork may have a mesh topology, meaning that many routers are interconnected in a way that provides multiple paths through the network. Routers forward packets along the best path based on information that has been discovered about the topology of the network. Routing protocols provide the mechanism for finding these paths. Routers gather information about the networks they are connected to and then forward this information to other routers. Each router then builds forwarding tables based on this information. See "Routing."

The Internet is the biggest internetwork. It consists of thousands of interconnected public and private networks. Each network is called an autonomous system because it is managed by a distinct authority.

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