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352-001 · Question #534
352-001 Question #534: Real Exam Question with Answer & Explanation
The correct answer is B: Make the hub routers ABR. Placing spoke routers in totally stubby areas and making hub routers ABRs limits LSA flooding to spokes while providing reachability through a default route injected by the ABR.
Question
A large enterprise network has two data centers and a WLAN edge with a large hub-and spoke network. The complete network is configured as a single OSPF area, and spoke routers are connected to unreliable WAN links. Which two changes should you make to deploy LSA on the spoke routers? (Choose two)
Options
- APlace spoke routers in stub areas
- BMake the hub routers ABR
- CMake the hub routers ASBR
- DPlace spoke routers in totally stubby areas
- EKeep the spoke routers in normal areas
Explanation
Placing spoke routers in totally stubby areas and making hub routers ABRs limits LSA flooding to spokes while providing reachability through a default route injected by the ABR.
Common mistakes.
- A. Regular stub areas still permit Type 3 inter-area summary LSAs, so spoke routers on unreliable links would still receive significant LSA flooding compared to totally stubby areas.
- C. ASBRs redistribute external routing information into OSPF and do not control LSA flooding toward spoke routers on unreliable links.
- E. Leaving spoke routers in a normal OSPF area means they receive all LSA types, maximizing overhead and instability on unreliable WAN links.
Concept tested. OSPF totally stubby areas and ABR placement in hub-and-spoke
Reference. https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13703-8.html
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