OSPF Configuration and Troubleshooting: 20 Key Questions

Posted on Feb 9, 2025 in Telecommunication and Multimedia Engineering

  1. Which OSPF network type requires the election of a DR/BDR?

    Broadcast

  2. In an OSPF hub-and-spoke topology, what needs to be done to ensure that the spoke routers are never selected as DR and BDR?

    All spoke routers need to be configured with an OSPF interface priority of 0 (ip ospf priority) so that they will not become the DR/BDR.

  3. How to configure OSPF to advertise specific routes?

    A network administrator is implementing OSPF in a portion of the network and must ensure that only specific routes are advertised via OSPF. The following network statement would configure the OSPF process for networks 192.168.4.0, 192.168.5.0, 192.168.6.0, and 192.168.7.0, now located in the backbone area, and inject them into the OSPF domain:

    r1(config-router)# network 192.168.4.0 0.0.3.255 area 0

  4. What are two advantages of OSPF authentication?

    Two advantages that authentication provides that should be considered when planning an OSPF implementation are:

    • It prevents routing information from being falsified in transit.
    • It ensures that routing information comes from a valid source router.

  5. When will a router in an OSPF non-backbone area receive a default route from the ABR or ASBR?

    A router in an OSPF non-backbone area will receive a default route from the ABR or ASBR when:

    • The area is a totally stubby area.
    • The area is a NSSA totally stubby area.
    • The area is a normal area and the ASBR has been configured with the default-information originate always command.

  6. What are two reasons for creating an OSPF network with multiple areas?

    Two reasons for creating an OSPF network with multiple areas are:

    • To reduce SPF calculations.
    • To reduce use of memory and processor resources.

  7. What does OSPF use to calculate the cost to a destination network?

    Bandwidth

  8. Which three items must match between OSPF neighbors in order to form an adjacency?

    The following three items must match between OSPF neighbors in order to form an adjacency:

    • Hello/Dead Interval
    • Area ID
    • Authentication Type

  9. What neighbor relationship is developed between Router1 and Router2 when OSPF is operational and converged?

    A FULL adjacency is formed.

  10. What information will be in a router’s routing table after a reboot but before OSPF has converged?

    A fully converged five router OSPF network has been running successfully for several weeks. All configurations have been saved and no static routes are used. If one router loses power and reboots, the information in its routing table after the configuration file is loaded but before OSPF has converged will be: Directly connected networks that are operational.

  11. What are two effects of using multiple OSPF areas that reduce bandwidth and router overhead?

    Two effects of using multiple OSPF areas that reduce bandwidth and router overhead are:

    • Reduction in the size of the LSDB.
    • Limits on the propagation of type 1 and 2 LSAs.

  12. What is the function of the OSPF LSU packet?

    To announce new OSPF information.

  13. How does the router treat the authentication of OSPF packets that enter and leave FastEthernet interface 0/0?

    Two copies of every OSPF packet are sent, one with key 10 and one with key 20.

  14. Which type of OSPF packets are represented by the debug command output?

    Hello packets sent with a MD5 hashed authentication key id of 100.

  15. What destination address will RTB use to advertise LSAs?

    224.0.0.6

  16. Which two statements are correct about OSPF route summarization?

    The following two statements are correct about OSPF route summarization:

    • The metric of the summary route is equal to the lowest cost network within the summary address range.
    • The area 51 range 172.0.0.0 255.0.0.0 command identifies area 51 as the area that contains the range.

  17. Which two statements are correct about OSPF NSSA areas?

    The following two statements are correct about OSPF NSSA areas:

    • Type 7 LSAs are translated to type 5 LSAs by the ABR.
    • Type 7 LSAs are originated by the ASBR that is connected to the NSSA.

  18. How can correct OSPF topology change-behavior be verified as part of an implementation plan?

    Test link failure and router failure events.

  19. What is the correct method to configure route summarization on an OSPF router?

    Configure OSPF and instruct the ABR to summarize specific area routes.

  20. Which command can be used to determine the stability of an OSPF area?

    show ip ospf