When configuring OSPF for a multi-area design in an HPE network, which feature optimizes routing by reducing the number of routes advertised between areas?

Question

Options

• AStub area configuration
• BRoute summarization
• CDefault route propagation
• DLSA filtering

• B
  90% (26)
• C
  3% (1)
• D
  7% (2)

Explanation

Route summarization (B) directly reduces the number of routes advertised between OSPF areas by aggregating multiple specific prefixes into a single summary route at Area Border Routers (ABRs), shrinking routing tables and optimizing inter-area routing - which is precisely what the question asks about.

Why the distractors are wrong:

• A (Stub area) reduces routes by blocking external LSAs (Type 5) from entering an area and replacing them with a default route, but this is a topology restriction, not a mechanism that actively summarizes or reduces advertised routes between areas.
• C (Default route propagation) injects a 0.0.0.0/0 route to give areas a path out, which simplifies routing but doesn't reduce the number of specific routes being advertised - it adds a route.
• D (LSA filtering) can suppress specific LSAs between areas but is a filtering/blocking tool, not an optimization technique designed to consolidate routes; it can also cause routing black holes if misapplied.

Memory tip: Think of summarization as "zip compression for routes" - you take many files (specific prefixes) and compress them into one archive (summary route) before sending it across the area boundary. If a question mentions reducing the number of routes advertised, that's always summarization.

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