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352-001 · Question #444
352-001 Question #444: Real Exam Question with Answer & Explanation
The correct answer is A: Convert area 100 into an NSSA.. An OSPF NSSA allows redistribution of external routes into a stub-like area using Type 7 LSAs, enabling injection of the static route to the partner WAN link without flooding the LSDB with Type 5 external LSAs.
Question
You are designing an OSPF network with multiple areas of for a large client. Due to the size of the routing domain, all areas except the backbone area are configured as stub areas. A new requirement is to connect a WAN link to a partner organization with a static route to one of the stub areas, area 100. What should you do to redesign area 100, if anything, in order to support this WAN link while minimizing the size of the link state database?
Options
- AConvert area 100 into an NSSA.
- BRedistribute the static route as OSPF type E1.
- CConvert area 100 into a normal area.
- DNo configuration changes to area 100 are needed.
Explanation
An OSPF NSSA allows redistribution of external routes into a stub-like area using Type 7 LSAs, enabling injection of the static route to the partner WAN link without flooding the LSDB with Type 5 external LSAs.
Common mistakes.
- B. Stub areas block all Type 5 external LSAs by design, so redistributing as OSPF E1 is not permitted without first changing the area type.
- C. Converting to a normal area allows all Type 5 external LSAs from the entire OSPF domain to flood into area 100, unnecessarily increasing the LSDB size.
- D. Stub areas cannot accept redistributed external routes by definition, so no static route can be injected into area 100 without a configuration change.
Concept tested. OSPF NSSA for external route redistribution in stub areas
Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/6208-nssa.html
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