350-401 Question #918: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. An engineer must reduce the number of Type 1 and Type 2 LSAs that are advertised to R4 within OSPF area 0. Which configuration must be applied?

Options

• AR1# conf t
• BR4# conf t
• CR2# conf t
• DR2# conf t

Explanation

Configuring an OSPF area as Not-So-Stubby Area (NSSA) allows external routes to be injected into it as Type 7 LSAs while restricting other external LSA types from entering, thus contributing to overall LSA reduction.

Common mistakes.

• B. Configuring R4 as an NSSA area border router would not achieve the stated goal, and Area 0 itself cannot be configured as an NSSA area as it is the backbone.
• C. Configuring a stub area on R2 would prevent Type 5 and Type 4 LSAs from entering that area, but it does not directly address the reduction of Type 1 and Type 2 LSAs within Area 0 and does not fit the NSSA context implied by the correct answer.
• D. Configuring an NSSA Totally Stubby Area (no-summary) on R2 would prevent Type 3, 4, and 5 LSAs from entering that area; while reducing LSA types, it doesn't align with the specific choice A and Type 1/2 LSAs.

Concept tested. OSPF area types and LSA reduction

Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13689-18.html

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