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Chatper 1: IntroductionThis chapter focuses on (1) the rationale for obtaining router performance measurements, (2) the use of various router performance measurements achieved through various components that can be monitored, and (3) a preview of the subsequent chapters. The chapter preview can be used by itself or in conjunction with the index to locate specific information that may be of interest.
While the previous three items is the primary focus of this chapter, before we turn our attention to those topics, a few words are in order about the relationship of this book to the series of Cisco field guides published by McGraw-Hill. This book is the third in the series of Cisco field guides to be published. Each field guide focuses on a specific topic: router access lists, IOS IP commands, and now Cisco router performance.
Since Cisco routers have evolved into very complex hardware and software products, it is very difficult and probably not desirable from both the authors' and readers' perspective to attempt to provide a comprehensive book that covers all router features and functions. Not many authors would be willing or have the experience to write a book that covers every router topic and more than likely consist of thousands of pages. Similarly, very few readers need to have in-depth knowledge of all aspects of Cisco routers. as a result, the authors felt that development of the field guide series, with each book focused on a key series of related functions or features on Cisco routers, would be more useful. Thus, this book focuses upon router performance, a narrow but most important topic that LaN administrators and network managers must understand to make the bestpossible use of Cisco routers and attached networks.
Rationale for Performance Measurements
The preface to this book briefly noted several reasons for periodically extracting router performance measurements. While the verification of service level agreements (SLaB) and observation of network errors are important, they are not the only reasons for examining different router metrics. Other reasons include considering when to replace or upgrade a router or individual router components as well as how to decide if additional interfaces are required to support network segmentation. another reason for examining router performance metrics is to determine if the resources of one or more routers might be employed more efficiently in a different router or if the router is leased or returned to the leasing company. This is because not all routers in a network are used at the same level. Thus, if your organization purchased a number of routers for use in a network, there is a high probability that routers at the periphery of a network do not require the same amount of memory or processor capability as routers at the core of a network. Occasionally, router performance measurements can provide your organization with information on how to rearrange the use of routers, replace one type of router with a more cost-effective router, or purchase a more suitable router to satisfy organizational communications requirements. although a router is no substitute for diagnostic testing equipment, it is important to note a router acts as an interface to both local area networks (LaNs) and wide area networks (WaNs). as such, a router is a network's focal point, and you can use its display capability to examine the state of different interfaces. This, in turn, provides information on the performance level of both LaNs and WaNs connected to the router, which indirectly affects router performance. For example, a high level of collisions on an Ethernet LaN connected to a router interface directly affects the ability of the router to transmit frames onto the LaN or receive frames transmitted to the device over that network.
Components to Monitor
From a hardware perspective, a router is a sophisticated computer that operates specialized software. The router's hardware is similar to a computer in that a router has a central processing unit (CPU), supports several types of memory, and can support different types of interfaces that provide connectivity to peripherals. However, unlike a computer, where peripherals are commonly printers, scanners, and similar devices, router peripherals are local and wide area networks that are connected to the router via different types of router interfaces...