The device defaults route-advertise command to advertise the default route into the OSPF domain. Which of the following types of LSA does the default route belong to?

Question

Options

• AType 1 LSAs
• BType 2 LSAs
• CType 3 LSAs
• DType 4 LSAs
• EType 5 LSAs

• A
  18% (11)
• B
  3% (2)
• C
  2% (1)
• D
  7% (4)
• E
  70% (43)

Explanation

Option E is correct because the default-route-advertise command causes the router to act as an Autonomous System Boundary Router (ASBR) and inject a default route (0.0.0.0/0) into the OSPF domain as a Type 5 AS External LSA. Type 5 LSAs are specifically used to advertise routes that originate outside the OSPF autonomous system, which is exactly what a redistributed or generated default route is. Type 1 (Router LSA) and Type 2 (Network LSA) are wrong because they only describe topology within a single area, not external routes. Type 3 (Summary LSA) is generated by Area Border Routers to advertise inter-area routes, not external ones, and Type 4 (ASBR Summary LSA) just tells other areas how to reach the ASBR itself, not the actual external routes it carries.

Memory tip: Think "5 = External" -- Type 5 LSAs are flooded across the entire OSPF domain (except stub areas) and always come from outside, making them the only LSA type that can carry a default route injected from an external source.

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