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NSE 6 - Network Security 7.6 Support Engineer Materials-Question 49 Discussion

What are two reasons that an OSPF router does not have any type 5 link-state advertisements (LSAs) in its link-state database (LSDB)? (Choose two answers)

  • A. The peer of the local router is using a prefix-list-out configuration to prevent all type 5 LSAs to be advertised.
  • B. The local router is located in a stub area.
  • C. IP protocol 89 is blocked between the local router and its peer.
  • D. There is no autonomous system border router (ASBR) in the network.
Correct Answer: B,D

Brave-Dump Clients Votes

BD 100%

Comments



Fatma Salih 2026-01-15 00:08:28

Selected Answers: B, D


most logical

Anonymous User 2026-04-06 04:57:06

Selected Answers: B, D


The router is part of a Stub area.

The router is part of a Totally Stubby area.

Why these are the correct reasons:
In OSPF, Type 5 LSAs are External LSAs. These are generated by an ASBR (Autonomous System Boundary Router) to advertise routes that originate from outside the OSPF domain (like static routes or redistributed BGP/RIP routes).

1. Stub Areas
A Stub Area is designed to reduce the size of the Link-State Database (LSDB) by blocking external routing information.

The Rule: Type 5 LSAs are strictly prohibited from entering a Stub area.

The Result: Instead of individual external routes, the ABR (Area Border Router) typically injects a default route (Type 3 LSA) so internal routers can still reach the outside world without needing the full external table.

2. Totally Stubby Areas
A Totally Stubby Area is even more restrictive than a standard Stub area.

The Rule: It blocks both Type 5 (External) and Type 3/4 (Inter-area) LSAs.

The Result: Like the Stub area, if a router is inside a Totally Stubby area, it will never see a Type 5 LSA in its database.

Why other area types do see Type 5 LSAs:
Backbone Area (Area 0): This area must have a full view of the network, including all Type 5 LSAs, so it can pass them to other standard areas.

Standard/Normal Areas: These areas receive all LSA types (1 through 5) by default.

Not-So-Stubby Areas (NSSA): While NSSAs also block Type 5 LSAs coming from the backbone, they allow external routes to be imported locally as Type 7 LSAs. Therefore, if the question asked why there are no Type 5s but there are external routes, NSSA would be a relevant factor. However, for a complete lack of external database entries, Stub/Totally Stubby are the primary answers.