CCNA 3 v6 Chapter 9: Check Your Understanding Questions Answers

CCNA 3 v6.0 (Scaling Networks v6) Chapter 9: Multiarea OSPF: Check Your Understanding Questions Answers

1. Which statement describes a multiarea OSPF network?

  • It consists of multiple network areas that are daisy-chained together.
  • It has a core backbone area, with other areas connected to the backbone area.
  • It has multiple routers that run multiple routing protocols simultaneously, and each protocol consists of an area.
  • It requires a three-layer hierarchical network design approach.

Explanation: A multiarea OSPF network requires hierarchical network design (two levels). The main area is called the backbone area, and all other areas must connect to the main area.

2. What is one advantage of using multiarea OSPF?

  • It allows OSPFv2 and OSPFv3 to be running together.
  • It enables multiple routing protocols to be running in a large network.
  • It improves routing efficiency by reducing the routing table and link-state update overhead.
  • It increases routing performance by dividing the neighbor table into separate smaller tables.

Explanation: A multiarea OSPF network improves routing performance and efficiency in a large network. As the network is divided into smaller areas, each router maintains a smaller routing table because routes between areas can be summarized. Also, fewer updated routes means fewer LSAs are exchanged, thus reducing the need for CPU resources. Running multiple routing protocols simultaneously and implementing both IPv4 and IPv6 are not primary considerations for a multiarea OSPF network.

3. Which characteristic describes both ABRs and ASBRs that are implemented in a multiarea OSPF network?

  • They are required to perform any summarization or redistribution tasks.
  • They are required to reload frequently and quickly in order to update the LSDB.
  • They both run multiple routing protocols simultaneously.
  • They usually have many local networks attached.

Explanation: ABRs and ASBRs need to perform any summarization or redistribution among multiple areas and thus demand more router resources than a regular router in an OSPF area.

4. Which of the following is used to facilitate hierarchical scaling in OSPF?

  • Autosummarization
  • Frequent SPF calculations
  • The election of designated routers
  • The use of multiple areas

Explanation: OSPF supports the concept of using areas to prevent larger routing tables, excessive SPF calculations, and large LSDBs. Only routers within an area share link-state information. This allows OSPF to scale in a hierarchical fashion with all areas that connect to a backbone area.

5. Which two statements correctly describe OSPF type 3 LSAs? (Choose two.)

  • Type 3 LSAs are generated without requiring a full SPF calculation.
  • Type 3 LSAs are known as autonomous system external LSA entries.
  • Type 3 LSAs are known as router link entries .
  • Type 3 LSAs are used for routes to networks outside the OSPF autonomous system.
  • Type 3 LSAs are used to update routes between OSPF areas.

Explanation: Type 4 LSAs are known as autonomous system external LSA entries and are generated by an ABR to inform other areas of next-hop information for the ASBR. Type 1 LSAs are known as router link entries. Type 3 LSAs can be generated without requiring a full SPF calculation. Type 3 LSAs are used to carry routes between OSPF areas.

6. What OSPF LSA type is used to inform routers of the router ID of the DR in each multiaccess network in an OSPF area?

  • Type 1
  • Type 2
  • Type 3
  • Type 4

Explanation: OSPF has many different LSA types, including type 1, which contains a list of directly connected interfaces; type 2, which exists only for multiaccess networks and includes DR router ID; type 3, which is used by ABRs to advertise networks from other areas; type 4, which is generated by ABRs to identify an ASBR and provide a route to it; and type 5, which is originated by ASBRs to advertise external routes.

7. What type of OSPF LSA is originated by ASBRs to advertise external routes?

  • Type 1
  • Type 2
  • Type 3
  • Type 5

Explanation: OSPF has many different LSA types, including type 1, which contains a list of directly connected interfaces; type 2, which exists only for multiaccess networks and includes DR router ID; type 3, which is used by ABRs to advertise networks from other areas; type 4, which is generated by ABRs to identify an ASBR and provide a route to it; and type 5, which is originated by ASBRs to advertise external routes.

8. What routing table descriptor is used to identify OSPF summary networks that originate from an ABR?

  • O
  • O IA
  • O E1
  • O E2

Explanation: OSPF routes have several descriptors in IPv4 routing tables, including O, which indicates intraarea routes learned from a DR; O IA, which indicates summary interarea routes that are learned from a ABR; and O E1 or O E2, which indicate external routes that are learned from an ASBR.

9. Which command can be used to verify the contents of the LSDB in an OSPF area?

  • show ip ospf database
  • show ip ospf interface
  • show ip ospf neighbor
  • show ip route ospf

Explanation: The show ip ospf database command is used to verify the contents of the LSDB. The show ip ospf interface command is used to verify the configuration information of OSPF-enabled interfaces. The show ip ospf neighbor command is used to gather information regarding OSPF neighbor routers. The show ip route ospf command displays OSPF-related information in the routing table.

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