OSPF does not flood Type 5 LSA and Type 4 LSA into the Stub area. It advertises a default LSA to the Stub area and guides the data packet on how to reach the destination outside the AS.

Question

Options

• ATRUE
• BFALSE

• A
  71% (22)
• B
  29% (9)

Explanation

A is correct because OSPF Stub areas are specifically designed to reduce LSA flooding overhead by blocking Type 5 LSAs (External AS routes) and Type 4 LSAs (ASBR Summary routes) from entering the area. Instead, the Area Border Router (ABR) injects a single Type 3 LSA default route (0.0.0.0/0) into the stub area, giving routers inside a simple "send unknown traffic here" instruction to reach any external destination.

B is wrong because it contradicts OSPF's defined stub area behavior - stub areas do filter these LSA types by design, and the default route injection is a core part of how OSPF stub areas function.

Memory tip: Think of a "stub" like a dead-end road with a sign pointing back to the highway. Routers inside don't need a map of the whole internet (Type 5 external routes) - they just follow the default sign (Type 3 default LSA) to get out. If they needed the full map, it wouldn't be a stub.

No community discussion yet for this question.