300-410 Question 68
Single answerAn enterprise network is configured with OSPF, and one of the branch offices has limited connectivity requirements. The network administrator wants to minimize the OSPF routing table size for the branch office while still allowing it to reach external networks through the main office router. Which OSPF configuration should be applied to the branch office router?
- A
Configure the branch office router as an OSPF stub area.
- B
Configure the branch office router as an OSPF totally stubby area.
- C
Configure the branch office router as a not-so-stubby area (NSSA).
- D
Disable OSPF on the branch office router and use static routes instead.
Show answer and explanation
Correct answer: B
Explanation
The most appropriate way to minimize the OSPF routing table size for the branch office while maintaining necessary connectivity is to configure the branch office router as an OSPF totally stubby area. This configuration ensures that only a default route is advertised to the branch office, significantly reducing the size of its routing table and optimizing resource utilization. Other options either fail to minimize the routing table enough or remove the benefits of OSPF altogether.
- A. Incorrect.
Configuring the branch office router as an OSPF stub area reduces the routing table size by blocking external Type 5 LSAs but still allows Type 3 summary LSAs. However, this does not completely minimize the routing table, as summary routes will still be present.
- B. Correct.
Configuring the branch office router as an OSPF totally stubby area eliminates both external Type 5 LSAs and Type 3 summary LSAs, minimizing the routing table to only include a default route to the area border router (ABR). This is the most efficient configuration for limited connectivity needs.
- C. Incorrect.
Configuring the branch office router as a not-so-stubby area (NSSA) is useful for injecting external routes into OSPF, but it does not minimize the routing table size for the branch office.
- D. Incorrect.
Disabling OSPF and using static routes might reduce complexity, but it eliminates the dynamic routing benefits of OSPF and is not the recommended solution in this scenario.