Refer to the exhibit. Traffic flow from router R1 to router R6 is delay-sensitive. It must consider potential link-failure and node-failure conditions. Which configuration must an engineer apply to ro

Question

Exhibits

Options

• AR1(config)# router ospf 1 R1(config-router)# area 1 range 192.168.20.0 255.255.248.0 R1(config-router)# area 2 range 192.168.32.0 255.255.240.0
• BR1(config)# router ospf 1 R1(config-router)# area 1 range 192.168.20.0 255.255.252.0 R1(config-router)# area 2 range 192.168.32.0 255.255.240.0
• CR1(config)# router ospf 1 R1(config-router)# area 1 range 192.168.20.0 255.255.252.0 R1(config-router)# area 2 range 192.168.32.0 255.255.253.0
• DR1(config)# router ospf 1 R1(config-router)# area 1 range 192.168.20.0 255.255.252.0 R1(config-router)# area 2 range 192.168.32.0 255.255.252.0

• A
  3% (1)
• B
  5% (2)
• C
  10% (4)
• D
  83% (33)

Explanation

Option D correctly applies /22 (255.255.252.0) masks to both area summarizations: 192.168.20.0/22 precisely covers the subnets in Area 1, and 192.168.32.0/22 precisely covers those in Area 2, giving R1 (as an ABR) accurate summary routes to re-advertise when R2 fails and traffic must take an alternate path to R6.

Why the distractors fail:

• A uses 255.255.248.0 (/21) for Area 1 - this is misaligned (192.168.20.0 is not on a /21 boundary; the correct boundary is 192.168.16.0) and also applies an overly broad /20 to Area 2, both causing incorrect or inconsistent routing.
• B gets Area 1 right but applies 255.255.240.0 (/20) to Area 2, which is far too broad - it would advertise a summary covering 192.168.32.0–192.168.47.255, pulling traffic toward subnets that don't exist and causing black holes.
• C gets Area 1 right but uses 255.255.253.0 for Area 2, which is an invalid subnet mask - valid masks must be a contiguous block of 1s followed by 0s in binary, and 253 (11111101) breaks that rule entirely.

Memory tip: Think of the two checks as "Real or Fake? Tight or Loose?" - first confirm the mask is a valid contiguous mask (eliminates C), then confirm it's the tightest mask that still covers all required subnets without overshooting (eliminates A and B). Only D passes both checks for both areas.

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