In OSPF, which LSA type is responsible for pointing to the ASBR router?

Question

Options

• Atype 1
• Btype 2
• Ctype 3
• Dtype 4

• A
  2% (1)
• B
  2% (1)
• C
  4% (2)
• D
  93% (52)

Explanation

OSPF LSA Type 4 – ASBR Summary LSA

Type 4 (ASBR Summary LSA) is generated by an ABR (Area Border Router) to advertise the location of an ASBR (Autonomous System Boundary Router) to other areas, allowing routers outside the ASBR's area to know how to reach it. Without Type 4, routers in remote areas would see the external routes (Type 5 LSAs) but have no path to the ASBR that originated them.

• Type 1 (Router LSA) is wrong - it describes a router's own links within a single area and has no inter-area function.
• Type 2 (Network LSA) is wrong - it is generated by the Designated Router (DR) on a multi-access segment to describe that segment's routers.
• Type 3 (Summary LSA) is wrong - it advertises inter-area network prefixes between areas, not the location of an ASBR.

Memory Tip: Think of it as a "4-ward to find the ASBR" - Type 4 points you toward the ASBR, while Type 5 carries the actual external routes it generates. They always work as a pair: Type 4 = who, Type 5 = what.

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