300-410 Question 107
Single answerA network engineer is configuring OSPF in an enterprise environment. The engineer needs to design an OSPF area that minimizes routing table size by blocking external routes (Type 5 LSAs) while still allowing intra-area and inter-area routes, as well as a limited number of external routes redistributed from an ASBR. Which OSPF area type should be used?
- A
Backbone area
- B
Stub area
- C
Not-So-Stubby Area (NSSA)
- D
Totally stubby area
Show answer and explanation
Correct answer: C
Explanation
An NSSA (Not-So-Stubby Area) is the correct choice because it allows the OSPF area to block external Type 5 LSAs while still permitting the redistribution of external routes as Type 7 LSAs. This configuration meets the requirement of minimizing routing table size while enabling a limited number of external routes to be redistributed by an ASBR.
- A. Incorrect.
Backbone area (Area 0) is the core of an OSPF network and does not have any restrictions on external routes. It is not used for the purpose of limiting routing table size through blocking specific LSAs.
- B. Incorrect.
A stub area can block external routes (Type 5 LSAs) but cannot handle redistributed external routes. This does not meet the requirement for allowing a limited number of external routes.
- C. Correct.
An NSSA (Not-So-Stubby Area) allows blocking Type 5 LSAs while permitting the redistribution of external routes as Type 7 LSAs, which meets the requirement of allowing a limited number of external routes.
- D. Incorrect.
A totally stubby area would block all external routes (Type 5 LSAs) and inter-area routes (Type 3 LSAs), which does not meet the requirement of allowing a limited number of external routes.