350-401 Question 434
Select 3You are configuring OSPF in a large enterprise network. The network includes an area with devices that have limited resources and need to reduce the size of their OSPF routing table. You also have an area that requires inter-area route summarization, and another area designated for external route redistribution. Which combination of OSPF area types should you implement to meet these requirements?
- A
Stub area for devices with limited resources
- B
Totally stubby area for inter-area route summarization
- C
Not-so-stubby area (NSSA) for external route redistribution
- D
Backbone area (Area 0) for external route redistribution
- E
Totally stubby area for devices with limited resources
- F
NSSA for inter-area route summarization
Show answer and explanation
Correct answers: A, C, E
Explanation
To optimize OSPF for the given requirements, the appropriate solution involves using a stub area or totally stubby area for devices with limited resources to reduce routing table size. An NSSA is suitable for external route redistribution, as it allows external routes in a controlled manner without flooding the entire OSPF domain. Inter-area route summarization is not explicitly handled by stub or totally stubby areas but is a function of area border routers (ABRs) and is configured separately.
- A. Correct.
Stub areas are designed to reduce the size of OSPF routing tables by blocking external routes (Type 5 LSAs) and allowing only intra-area and default routes. This is well-suited for devices with limited resources.
- B. Incorrect.
Totally stubby areas are not designed for inter-area route summarization; they block both external routes (Type 5 LSAs) and inter-area routes (Type 3 LSAs), allowing only a default route.
- C. Correct.
Not-so-stubby areas (NSSAs) are used to redistribute external routes (e.g., from RIP or BGP) into OSPF without flooding the entire OSPF domain with those external routes.
- D. Incorrect.
The backbone area (Area 0) is required for OSPF inter-area communication, but it is not specifically designed for external route redistribution.
- E. Correct.
Totally stubby areas are ideal for devices with limited resources because they block both external and inter-area routes, significantly reducing the routing table size.
- F. Incorrect.
NSSAs are not designed for inter-area route summarization; their purpose is to handle external route redistribution while minimizing the impact on OSPF areas.