350-401 Question #218: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. Which command when applied to the Atlanta router reduces type 3 LSA flooding into the backbone area and summarizes the inter-area routes on the Dallas router?

Options

• AAtlanta(config-route)#area 0 range 192.168.0.0 255.255.248.0
• BAtlanta(config-route)#area 0 range 192.168.0.0 255.255.252.0
• CAtlanta(config-route)#area 1 range 192.168.0.0 255.255.252.0
• DAtlanta(config-route)#area 1 range 192.168.0.0 255.255.248.0

Explanation

To reduce Type 3 LSA flooding into the OSPF backbone area and summarize inter-area routes from Area 1, the area 1 range command with an appropriate summary address must be applied on the Atlanta ABR.

Common mistakes.

• A. The area 0 range command is incorrect because summarization for routes originating in a non-backbone area (like Area 1) is configured using the non-backbone area ID (e.g., area 1) on the ABR.
• B. The area 0 range command is incorrect for summarizing routes originating from Area 1 into Area 0; the command should specify area 1 as the source area for summarization.
• D. While area 1 range is correct for the area ID, a 255.255.248.0 mask (indicating a /21 network) would summarize a larger block than a 255.255.252.0 mask (/22), and without specific details of the Area 1 subnets, 255.255.252.0 is a common summary for four /24 networks.

Concept tested. OSPF Inter-area Route Summarization

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-s/iro-15-s-book/ospf-cfg-area-sum.html

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