The United States Postal Service routes a huge number of letters and packages each day. To do so, the postal sorting machines run fast, sorting lots of letters. Then the letters are placed in the correct container and onto the correct truck or plane to reach the final destination. However, if no one programs the letter-sorting machines to know where letters to each ZIP code should be sent, the sorter can't do its job. Similarly, Cisco routers can route many packets, but if the router doesn't know any routes, it can't do its job.
This chapter introduces the basic concepts behind IP routing protocols and lists some of the key features of each of the IP routing protocols covered on the INTRO exam. Cisco expects CCNAs to demonstrate a comfortable understanding of the logic behind the routing of packets and the different but related logic behind routing protocols—the protocols used to discover routes. To fully appreciate the nuances of routing protocols, you need a thorough understanding of routing—the process of forwarding packets. You might even want to review the section "IP Routing and Routing Protocols," in Chapter 5, "Fundamentals of IP," for a review of routing, before proceeding with this chapter.
For those of you studying for the CCNA exam, if you are following the reading plan outlined in the introduction, you will move to the CCNA ICND Exam Certification Guide after this chapter. For those of you studying just for the INTRO exam, this chapter completes the coverage of topics related to IP and IP routing.
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