| Each chapter in the technologies section of this book discusses not only what you need to know but also why you need to know it. For IP addressing and routing, consider the following items: The importance of IP IP is used throughout the public Internet and on most organizations'networks, and is therefore the most important routed protocol to the majority of businesses today. IP is not limited to sending traditional data such as files and e-mailsit forms the basis for many other technologies and solutions, as described in later chapters in this book. For example, IP telephony uses an IP network for voice traffic, eliminating many of the costs associated with long-distance calls and at the same time introducing other capabilities to your telephone network. (IP telephony is described in Chapter 7, "Voice Transport Design.") Toronto's Pearson International Airport's new terminal is a further example of how IP is being used as the foundation for an intelligent system. At this terminal, a variety of communications systems and applications were put onto a single, secure, IP-based network. For example, when a gate at the airport is used by one airline, the system provides access to that airline's applications for check-in, baggage tracking, and so forth, and the IP phones provide that airline's telephone service. When another airline uses the same gate later in the day, the configuration changes so that the new airline's applications and telephone service can be accessed instead.[1] Cisco calls this a common-use network a single communications infrastructure shared by all tenants of the terminal.[2] The importance of proper IP addressing Correct IP addressing is crucial to making an IP network work, and if done properly, addresses can be summarized. Summarization ensures that the routing tables are smaller and therefore use less router memory, that the routing updates are smaller and use less network bandwidth, and that network problems can be localized (changes are sent to fewer routers). All of these benefits can result in a more stable network that adjusts faster to changes. The importance of proper routing protocol selection Routers learn about paths to destinations from other routers by using a routing protocol. Many IP routing protocols are available to choose from, each with its own advantages and disadvantages. The key is to understand the requirements for your network, understand how the routing protocols work, and match the network requirements to the routing protocol specifications. In some cases, it might be appropriate to run multiple routing protocols. Understanding how they will interact and how to avoid problems in a mixed routing protocol environment is important to the successful operation of your network.
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