capitulo 5 cisco ccna 2

capitulo 5 cisco ccna 2.This chapter focuses on issues related to these two logical branches: on which interface a router should enable the routing protocol and which neighbor relationships each router should establish. This chapter builds on what has been discussed in the first three chapters of this section (Chapters 8, 9, and 10) regarding configuration, but will focus on finding out incorrect configuration issues through the show and debug commands alone.This chapter begins with a brief introduction to several broadcast concepts for troubleshooting routing protocol errors. The next section focuses on which interface the router is routing protocol enabled on, and the final section talks about routing protocol neighbor relationships. Note that Enhanced Interior Gateway Routing Protocol (EIGRP) and Open Shortest Path First (OSPF) are discussed repeatedly throughout the chapter.11.1 "Do I Know That Already?" The mini-testThe chapters in this book that deal with troubleshooting bring together concepts and principles from many other chapters, including some from the Cisco CCENT/ CCNA ICND1 Certification Exam Guide book. These chapters also show how to tackle some of the more difficult questions on the CCNA exam. So, reading these chapters is helpful for the candidates regardless of the knowledge level of the existing readers. Because of this, all of the troubleshooting chapters do not have "Do I already know this?" subtests. Of course, if the reader is already particularly confident in troubleshooting OSPF and EIGRP, they can skip most of this chapter by referring directly to the "Test Prep" section at the end of the chapter.11.2 Fundamentals11.2.1 Perspectives on Troubleshooting Routing ProtocolsSince the job of the routing protocol is to populate the routing table in the router with the current best routes, you need to troubleshoot potential problems with the routing protocol, starting with the IP routing table. Based on the basic information known about the interconnected network, including the IP address, subnet mask, and routing protocol of the router, you can calculate the number of subnets that should be in the routing table of the router and list the possible next-hop routers for each path. For example, the interconnected network shown in Figure 11-1 has six subnets, and the routing table of router R1 lists all six subnets, including three directly connected routes, two routes known from R2 (172.16.4.0/24 and 172.16.5.0/24), and another route known from R3 (172.16.6.0/24).A reasonable troubleshooting step should then be to analyze this interconnect, look at the routing table and find the missing routes. If one or more of the expected routes are missing, then the next step is to determine if the router is getting routes from the expected next-hop router (neighbor router). The next step is then the isolation problem, which can face considerable discrepancies and requires determining whether one router is having problems forming a neighbor relationship with another router, or whether it has established a functioning neighbor relationship but cannot obtain all of the routes.224 Chapter 11 Troubleshooting IPv4 Routing ProtocolsFor example, imagine that Rl, shown in Figure ll-l, has been informed of a route from subnet 172.16.4.0/24 and has not received a route from subnet 172.16.5.0/24. In this example, R1 and R2 have clearly formed a functioning neighbor relationship. Based on the above,the root cause of the problem may still be related to the routing protocol or perhaps unrelated to the routing protocol. For example, the cause of the problem might be due to the LAN interface in the lower part of R2 being closed. However, if Rl does not have a route to 172.16.4.0/24 or 172.16.5.0/24, it is possible that there is a problem with Rl's neighbor relationship with R2.