This chapter covers the following topics:
The Purpose of Multi-area OSPF—Explains OSPF multiple-area networks and the single area network issues they solve.
The Features of Multi-area OSPF—Describes router types, link-state advertisements, and the different types of areas.
The Operation of Multi-area OSPF—Explains LSA propagation, OSPF path selection between areas, and how OSPF calculates the costs of paths to other areas.
Design Considerations in Multi-area OSPF—Describes capacity planning, summarization, and the use of virtual links in multi-area OSPF.
Required Configuration Commands for a Multi-area OSPF Network—Describes configuring OSPF as the routing protocol and explains the network command in the context of OSPF.
Optional Configuration Commands for a Multi-area OSPF Network—Describes commands that ensure the multi-area OSPF network runs efficiently.
Working Configuration of Multi-area OSPF—Combines the concepts and commands described in the chapter to show an entire working configuration.
Verifying the Configuration of OSPF in a Multi-area Network—Covers the commands used to verify the configuration and monitor the network.
Troubleshooting a Multi-area OSPF Network—Covers the log-adjacency-changes command, the most useful debug commands, and common problems that occur in forming adjacencies.
This chapter discusses using OSPF in large networks—networks large enough to be broken up into multiple smaller areas for routing purposes. In order to design a multi-area OSPF network, you need a comprehensive grasp of the features of multi-area OSPF, the operation of OSPF across multiple areas, and, of course, the design considerations of such a network. This chapter discusses each of these topics.
The purpose of the "Do I Know This Already?" quiz is to help you decide what parts of this chapter to use. If you already intend to read the entire chapter, you do not necessarily need to answer these questions now.
The 23-question quiz, derived from the major sections in the "Foundation Topics" portion of the chapter, helps you determine how to spend your limited study time.
Table 7-1 outlines the major topics discussed in this chapter and the "Do I Know This Already?" quiz questions that correspond to those topics.
|Foundation Topics Section||Questions Covered in This Section||Score|
|The Purpose of Multi-area OSPF||1|
|The Features of Multi-area OSPF||2–6|
|The Operation of Multi-area OSPF||7|
|Design Considerations in Multi-area OSPF||8–11|
|Required Configuration Commands for a Multi-area OSPF Network||12–14|
|Optional Configuration Commands for a Multi-area OSPF Network||15–18|
|Working Configuration of OSPF in a Multi-area Network||19|
|Verifying the Configuration of OSPF in a Multi-area Network||20–22|
|Troubleshooting a Multi-area OSPF Network||23|
The goal of self-assessment is to gauge your mastery of the topics in this chapter. If you do not know the answer to a question or are only partially sure of the answer, you should mark this question wrong for purposes of the self-assessment. Giving yourself credit for an answer you correctly guess skews your self-assessment results and might provide you with a false sense of security.
|1.||What is the command to view CPU utilization?
|2.||What is an internal router?
|3.||What is the purpose of an ABR?
|4.||What do the initials ASBR represent?
|5.||How is routing information generated within an area propagated throughout the area?
|6.||Which of the following OSPF characteristics affect how the routing table is created?
|7.||Which two LSA types are propagated within an area?
|8.||Why does the frequency of the SPF algorithm increase with the size of the area?
|9.||Multiple areas are one of the main features of OSPF. Which of the following statements explains why this feature is such an important enhancement to earlier routing protocols?
|10.||Which is the best design for OSPF?
|11.||Which of the following must be observed when creating a virtual link?
|12.||What command is used to start an OSPF process?
|13.||Which of the following commands are the correct commands, in conjunction, for placing an interface with IP address 172.16.20.128 in area 1 and the interfaces associated with the 172.16.0.0 class B network in Area 0?
|14.||Which of the following statements about placing subnets into different areas are true?
|15.||Which of the following statements are true of the command summary-address 172.16.20.0 255.255.255.0?
|16.||Which command would be used on an ABR to configure the cost of a default route propagated into a stub or NSSA area?
|17.||What is the purpose of the command area 3 stub no-summary?
|18.||Which of the following commands shows the correct syntax for defining a virtual link?
|19.||In the following configuration, which areas will have default routes automatically propagated to the routers in the respective areas?
RouterA(config)# router ospf 100 RouterA(config-router)# network 18.104.22.168 0.0.0.15 area 3 RouterA(config-router)# network 22.214.171.124 0.0.0.15 area 2 RouterA(config-router)# network 126.96.36.199 0.0.0.255 area 0 RouterA(config-router)# area 2 stub RouterA(config-router)# area 3 stub no-summary RouterA(config-router)# area 3 default-cost 15
|20.||Which command is used to show the OSPF ABRs and ASBRs for which the internal router has entries in its routing table?
|21.||Which of the following is the correct command to show virtual links?
|22.||Which of the following are shown in the show ip ospf database command?
|23.||Which of the following events are shown in the debug ip ospf events command?
The answers to this quiz are found in Appendix A, "Answers to Chapter 'Do I Know This Already?' Quizzes and Q&A Sections." The suggested choices for your next step are as follows: