350-401 · Question #218
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?
The correct answer is C. Atlanta(config-route)#area 1 range 192.168.0.0 255.255.252.0. 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.
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?
Exhibits
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
How the community answered
(27 responses)- A4% (1)
- B4% (1)
- C81% (22)
- D11% (3)
Why each option
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.
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.
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.
The `area <area-id> range <ip-address> <mask>` command is used on an ABR (Area Border Router) to summarize Type 3 LSAs originating from the specified `area-id` (Area 1 in this case) before they are advertised into the backbone (Area 0), thus reducing LSA flooding. A 192.168.0.0/22 (255.255.252.0) mask is a common summary for /24 networks.
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
Source: 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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