350-401 Question 436
Select 3You are configuring an OSPF network for a large enterprise. Certain areas need to minimize routing table sizes by summarizing routes, while other areas need to restrict external route propagation to reduce resource usage. Additionally, a router must handle both inter-area and external routes. Which combination of area types and router types should you configure to meet these requirements?
- A
Configure a stub area to restrict external route propagation.
- B
Configure an NSSA (Not-So-Stubby Area) to allow limited external routes while minimizing routing table size.
- C
Use an area border router (ABR) to summarize routes between different OSPF areas.
- D
Use an autonomous system boundary router (ASBR) to handle both inter-area and external routes.
- E
Use a totally stubby area for inter-area summarization and external route propagation.
Show answer and explanation
Correct answers: A, B, C
Explanation
To meet the requirements of minimizing routing table sizes and restricting external route propagation, you must use stub areas and NSSAs appropriately. Stub areas block external routes, while NSSAs allow limited external routes and maintain reduced table sizes. Additionally, ABRs are essential for summarizing routes between areas. The combination of these configurations ensures optimal OSPF behavior for the enterprise network.
- A. Correct.
Stub areas are used to restrict external route propagation, which is beneficial in reducing unnecessary routing information within the area.
- B. Correct.
NSSA is designed to allow external routes but in a limited fashion, while also providing the ability to minimize routing table sizes. This is useful for areas that need external connectivity but cannot afford an unrestricted flow of external routes.
- C. Correct.
ABRs are responsible for summarizing routes between OSPF areas. This helps reduce the size of the routing table in different areas and simplifies network management.
- D. Incorrect.
ASBRs inject external routes into the OSPF domain but are not specifically required in the given scenario. The focus here is on summarization and restricted external route propagation.
- E. Incorrect.
Totally stubby areas restrict both inter-area routes and external routes. However, this is not suitable for the scenario since inter-area summarization and selective external route allowance are required.