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CCNP BSCI Exam: Using OSPF Across Multiple Areas

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Apr 25, 2003.

Chapter Description

OSPF is the industry-standard interior routing protocol designed for use in large networks and makes up approximately nine percent of the BSCI exam. Learn how OSPF works within a large multiarea network and about the operation of the protocol across OSPF areas.


The following scenarios and questions are designed to draw together the content of the chapter and to exercise your understanding of the concepts. There is not necessarily a right answer. The thought process and practice in manipulating the concepts is the goal of this section. The answers to the scenario questions are found at the end of this chapter.

Scenario 6-1

Refer to Figure 6-14, and design the addressing scheme for the network. After this is designed, write the configuration for the central router.

Figure 6-14Figure 6-14 The Diagram for Configuration Scenario 6-1

Ensure that you include the following:

  1. Address the network using the private network Design the addressing scheme so that it allows for the summarization of addresses between areas. Show the summarization that you allocate, and explain your reasons for your choices.

    Area 0 is using a prefix of 28 bits within the area.

    Area 2 is using a prefix of 22 bits within the area.

    Area 3 is using a prefix of 24 bits within the area.

    Area 4 is using a prefix of 30 bits for the serial connections. It is using a 28-bit prefix for the connections to the Ethernet routers. Do not include the subnets attached to the LANs in Area 4.

  2. Issue the commands for the main router Figure 6-14 to configure the following:

    • The router ID

    • The network commands to place the appropriate interfaces into the correct areas

    • The configuration of the totally stubby area (Area 3)

    • The configuration of the stub (Area 4)

    • Summarization between areas

    • The election of the central router as designated router, where appropriate

Scenario 6-2

Using Figure 6-15, answer the questions that follow.

Figure 6-15Figure 6-15 The Diagram for Configuration Scenario 6-2

The users in the network are complaining about the slowness of the network, particularly when trying to access the Internet. Examine the configuration in Example 6-11 in conjunction with Figure 6-15, and give reasons for any slowness or lack of connectivity that you can see on the network. Provide current configuration commands to correct any errors that you find.

Example 6-11 Configuring OSPF Example for Scenario 6-2

Router(config)#router ospf 100
Router(config-router)#network area 3
Router(config-router)#network area 2
Router(config-router)#network area 0
Router(config-router)#area 2 stub
Router(config-router)#area 3 stub no-summary
Router(config-router)#area 3 default-cost 15
Router(config-router)#interface FastEthernet0
Router(config-if)#ip address
Router(config-if)#no ip directed-broadcast
Router(config-if)#interface FastEthernet1
Router(config-if)#ip address
Router(config-if)#no ip directed-broadcast
Router(config-if)#interface Fddi0
Router(config-if)#ip address
Router(config-if)#no ip directed-broadcast
Router(config-if)#no keepalive

Router(config)#router ospf 100
Router(config-router)# network area 2
Router(config-router)#interface FastEthernet0
Router(config-if)#ip address
Router(config-if)#no ip directed-broadcast
Router(config-if)#ip ospf priority 100
Router(config-if)#interface FastEthernet1
Router(config-if)#ip address
Router(config-if)#no ip directed-broadcast
  1. There are problems with router B. There is inconsistency in the routing table, and the system is extremely slow. What commands would be used to identify the problem? In examining the diagram and configuration, what problems can you see?

  2. Router A is having problems connecting to Area 0, which is causing problems in other areas because this router is used to connect to Area 0. What commands would be used to identify the problem? In examining the diagram and configuration, what problems can you see?

  3. Issue the commands that would be used to correct the configuration problems that you see in the example configuration for routers A and B.

  4. When you issue the show ip ospf interface command, you notice that there is a discrepancy in the timers on the link between routers A and B. The transmit timer on Router A is set to 5, and the retransmit timer is set to 1. What problems would this cause? What command would be used to change the timers, and what are the default settings?

  5. There is an ISDN link into the Internet from Router B. The network manager has suggested that this link is the cause of some performance problems on the router. You have noticed that the interface is included in the OSPF network command. What might be the cause of the problem, and how could it be fixed?

Scenario 6-3

  1. Explain the purpose of the virtual link in Figure 6-16.

    Figure 6-16Figure 6-16 Network Diagram #1 for Scenario 6-3

  2. Is the configuration of the OSPF network shown in Figure 6-17 a valid configuration?

    Figure 6-17Figure 6-17 Network Diagram #2 for Scenario 6-17

  3. Why would a company implement this design?

5. Scenario Answers | Next Section Previous Section

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