Bridging and Routing Concepts A-7Optimum Use of ResourceBridged networks use Spanning Tree Protocol (STP) to providenetwork resilience, by retaining redundant links on stand-by, in casethe primary link fails. This means that you are not making maximumuse of available resources.Routing protocols make each node aware of the primary and alternateroutes available, ensuring that resources are not wasted.Routers have been designed to provide the optimum route throughthe network from the workstation through to the destination resourcewith which the user wishes to communicate. In a very large networkthere could be multiple paths available, and these could change asdedicated links go in or out of service. These changes in networktopology are handled by routing protocols. However, when using theISDN the source network can dial direct to the destination network,and establish a point-to-point bridged or routed connection. Generally,when using this type of ISDN dial-up link, routing does not providemuch extra benefit.Network Organization, Structure and Physical LayoutSome organizations are structured into departments determined by thephysical layout of their work environment, so it is natural to divide thecorporate network into separate logical networks. Routing becomesthe obvious candidate for handling these individual LANs.The InternetThe protocol adopted by the Defense Data Network (DDN) for theInternet, is based on obtaining and abiding by, a registered Internetaddress range. This makes a router the ideal choice for accessing theInternet. Unfortunately, new applicants are likely to only get a Class Cregistered Internet address, preventing more than 254 connections onone bridged IP LAN.
