300-440 Question 109
Single answerAn enterprise network is implementing OSPF in a multi-area design. The network administrator wants to ensure that Area 1 does not receive external routes from other areas and only receives a default route from the backbone. However, Area 1 should still allow intra-area and inter-area routing. Which OSPF area type should be configured for Area 1?
- A
Backbone area
- B
Stub area
- C
Totally stubby area
- D
Not-so-stubby area (NSSA)
Show answer and explanation
Correct answer: C
Explanation
A totally stubby area is the correct choice when you want to block both external and inter-area routes while allowing only intra-area routes and a single default route from the backbone. This configuration ensures simplified routing and minimizes the size of the OSPF routing table in the stub area. The other area types do not meet these specific requirements.
- A. Incorrect.
Backbone area (Area 0) is the central area in an OSPF topology and cannot be configured to filter external routes in this manner. It serves as the transit area for inter-area traffic.
- B. Incorrect.
A stub area blocks external routes but still allows inter-area routes. This does not match the requirement to block both external and inter-area routes, while only allowing a default route from the backbone.
- C. Correct.
A totally stubby area blocks both external and inter-area routes, while only allowing a default route from the backbone. This matches the requirement for Area 1.
- D. Incorrect.
An NSSA is used to allow limited external routes into the area while also connecting to the backbone. This does not meet the requirement to block all external routes while allowing only a default route.