How does an OSPF ABR prevent summary route information from being readvertised from an area into the network core (Area 0)?

Question

Options

• AIt uses poison reverse and split horizon.
• BIt compares the area number on the summary LSA to the local area.
• CIt only sends locally originated summaries to the backbone.
• DIt advertises only inter-area summaries to the backbone.

• A
  3% (2)
• B
  16% (10)
• C
  73% (45)
• D
  8% (5)

Explanation

An OSPF ABR prevents looping summary information back into Area 0 by a simple rule: it only originates (advertises) Type 3 Summary LSAs to the backbone for routes it has learned from its own non-backbone area(s). It does not re-flood Type 3 LSAs it receives from Area 0 back into Area 0. Because the ABR only generates summaries from routes it locally computed from attached non-backbone areas, backbone-originated summaries are never reflected back. Option A (poison reverse/split horizon) applies to distance-vector protocols like RIP, not link-state OSPF. Option B is incorrect because the mechanism is about LSA origination ownership, not area number comparison. Option D mischaracterizes the distinction - it is about locally originated vs. received summaries, not intra-area vs. inter-area.

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