Which of the following is an LSA that floods the entire autonomous system in OSPFv3?

Question

Options

• AInter-Area-Prefix-LSA
• BAS-external-LSA
• CLink-LSA
• DIntra-Area-Prefix-LSA

• A
  16% (5)
• B
  75% (24)
• C
  3% (1)
• D
  6% (2)

Explanation

AS-external-LSA (Type 5) floods across the entire OSPFv3 autonomous system because it carries routing information learned from outside OSPF (via redistribution), and all routers in all areas need to know about external destinations. It originates from ASBRs and crosses area boundaries.

Why the distractors are wrong:

• A. Inter-Area-Prefix-LSA (Type 3): Flooded only within a single area by ABRs - it summarizes prefixes between areas but does not cross the AS boundary.
• C. Link-LSA (Type 8): Has the most limited scope - it floods only on a single link and is never forwarded beyond that link.
• D. Intra-Area-Prefix-LSA (Type 9): Floods only within its originating area, carrying prefix information for that area's routers and links.

Memory tip: Think of scope as a hierarchy - Link-LSA stays on the link, Intra-Area stays in the area, Inter-Area crosses areas (but not the AS edge), and AS-external crosses everything - it has "AS" right in the name, signaling autonomous-system-wide flooding.

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