300-420 Question #211: Real Exam Question with Answer & Explanation

Question

Refer to the exhibit. A customer experienced an unexpected network outage when the link between R1 and R2 went down. An architect must design a solution to ensure network continuity in the event the link tails again. Which solution should the design include?

Options

• AMake R3 an L1L2 router.
• BMake R31 an L1 router.
• CMake Area 0 L2-only.
• DMake R11 an L2 router.

Explanation

To provide redundancy and restore connectivity when the R1-R2 link fails, making R3 an L1L2 router allows it to serve as a backup path between Area 0 (L2) and Area 1 (L1).

Common mistakes.

• B. Making R31 an L1 router would restrict its routing capabilities to within Area 1 only, preventing it from routing traffic to Area 0 and thus not providing a backup path across areas.
• C. Making Area 0 L2-only is not a standard or beneficial IS-IS configuration for redundancy, and Area 0 is typically the backbone area, often containing L2 routers.
• D. Making R11 an L2 router would not solve the problem of a failed R1-R2 link, as R11 is already in Area 0 and would still need a path to Area 1.

Concept tested. IS-IS L1L2 router for redundancy

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_isis/configuration/xe-3s/irs-xe-3s-book.html

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