352-011 · Question #83
Refer to the exhibit company xyz has 150 branch location across the U.S. Each branch is connected to two aggregation router one router in each data center The network is configured with Multiple…
The correct answer is C. OSPF summarization. OSPF summarization at ABRs directly addresses both requirements simultaneously: by aggregating multiple specific routes into a single summary LSA, changes within one area (like a branch link flapping) don't trigger LSA flooding or SPF recomputation in other areas, as long as…
Question
Refer to the exhibit company xyz has 150 branch location across the U.S. Each branch is connected to two aggregation router one router in each data center The network is configured with Multiple OSPF with multiple OSPF areas and the aggregation router are ABRs A requirement is to keep an optimal path to the data centers and at the same time reduce the LSA propagation and SPF recomputation during a change in any part of the network Which design elements should be included on the aggregation router?
Exhibit
Options
- AOSPF NSSA
- Bdistribute lists
- COSPF summarization
- DOSPF totally stubby area
How the community answered
(28 responses)- A7% (2)
- B14% (4)
- C75% (21)
- D4% (1)
Explanation
OSPF summarization at ABRs directly addresses both requirements simultaneously: by aggregating multiple specific routes into a single summary LSA, changes within one area (like a branch link flapping) don't trigger LSA flooding or SPF recomputation in other areas, as long as the summary prefix remains stable - preserving optimal routing while containing instability.
Why the distractors are wrong:
- A (NSSA): NSSA is for areas that need to import external (Type 5) LSAs redistributed from other protocols - it solves an external redistribution problem, not inter-area propagation reduction.
- B (Distribute lists): These filter what ends up in the routing table, but the underlying LSAs still flood throughout the area and still trigger SPF runs - the problem isn't solved at the LSA level.
- D (Totally stubby area): This blocks all inter-area and external LSAs and injects only a default route - it would eliminate optimal path selection entirely, directly violating the requirement.
Memory tip: Think "ABR = Summarize at the Border." The ABR's job is to be a translator between areas - summarization is its native tool for keeping area changes local. If the question mentions ABRs + reducing propagation + keeping optimal paths, summarization is always the answer; stubby/totally-stubby trade path optimality for simplicity, which fails whenever "optimal" is a stated requirement.
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