146Appendix E: Understanding IP and IP addressing
application that the user needed to access. Otherwise, the user required a separate line and terminal device for each application.
As the number of communications duties grew (such as addressing, route selection, and error detection and correction), there came a point where the applications had to be uncoupled from the communications “network.” Specialized computers were created to take over the communications duties. Termed
The majority of an enterprise’s networks are now interconnected into one internetwork. The internetwork typically consists of a physical topology of multiprotocol routers connected together using a wide assortment of LAN and
What made Internetworking possible was the widespread acceptance of connectionless network layer protocols. A connectionless datagram or packet is a
What is routing?
Routing is the process of directing packet traffic between networks according to predetermined criteria. The goal of routing is to make the most efficient use of network resources. It does this by eliminating unnecessary packet copies and forwarding packet data using the optimum path. The device that carries out this process is called a router. The most common forwarding criterion is the packet destination address. A router either discards or passes a packet, based on whether the destination is on a known network (that is, a network that is connected to, or reachable by, another port on the router).
In general, a router discards a packet if the packet protocol is not supported by the router. For example, if a
Routing and routed protocols
Each internetworking architecture (for example, TCP/IP) includes at least one routed protocol and one routing protocol.
