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300-420 · Question #352

Refer to the exhibit. An architect is designing an ISIS solution with these requirements: - The backbone area will grow to 50 routers in the next 12 months. - Routers A1 and A2 must avoid suboptimal…

The correct answer is C. area 49.000 L1, area 49.001 L1, area 49.002 L2, and area 49.003 L2. To meet the ISIS design requirements for scalability, optimal routing, summarization, and route-leaking, the architect must configure areas 49.000 and 49.001 as L1, and areas 49.002 and 49.003 as L2.

Advanced Addressing and Routing Solutions

Question

Refer to the exhibit. An architect is designing an ISIS solution with these requirements:

  • The backbone area will grow to 50 routers in the next 12 months.
  • Routers A1 and A2 must avoid suboptimal routing.
  • Summarization and route-leaking should be allowed in areas 49.002 and

49.003. Which solution must the architect select?

Exhibit

300-420 question #352 exhibit

Options

  • Aarea 49.000 L2, area 49.001 L1, area 49.002 L1, and area 49.003 L1
  • Barea 49.000 L1, area 49.001 L2, area 49.002 L2, and area 49.003 L2
  • Carea 49.000 L1, area 49.001 L1, area 49.002 L2, and area 49.003 L2
  • Darea 49.000 L2, area 49.001 L2, area 49.002 L1, and area 49.003 L1

How the community answered

(32 responses)
  • A
    9% (3)
  • B
    19% (6)
  • C
    69% (22)
  • D
    3% (1)

Why each option

To meet the ISIS design requirements for scalability, optimal routing, summarization, and route-leaking, the architect must configure areas 49.000 and 49.001 as L1, and areas 49.002 and 49.003 as L2.

Aarea 49.000 L2, area 49.001 L1, area 49.002 L1, and area 49.003 L1

Configuring 49.000 as L2 and others as L1 would not create a scalable or optimally routed L2 backbone that spans across the central points (A1, A2) and allows summarization in the other specified areas.

Barea 49.000 L1, area 49.001 L2, area 49.002 L2, and area 49.003 L2

Configuring 49.000 as L1 and 49.001, 49.002, 49.003 as L2 would make 49.001 a backbone area, which might not align with the logical diagram or the need for A1 to handle both L1 for 49.000 and L2 for 49.002.

Carea 49.000 L1, area 49.001 L1, area 49.002 L2, and area 49.003 L2Correct

This design establishes a contiguous Level 2 (L2) backbone comprising areas 49.002, 49.003, and the interconnecting link between routers A1 and A2, allowing it to scale to 50 routers. Routers A1 and A2 function as L1/L2 routers, connecting the Level 1 (L1) areas (49.000 and 49.001) to the L2 backbone and ensuring they have L2 adjacency to avoid suboptimal routing. Summarization from L1 into L2 and route-leaking from L2 into L1 are also supported at A1 and A2.

Darea 49.000 L2, area 49.001 L2, area 49.002 L1, and area 49.003 L1

Configuring 49.000 and 49.001 as L2 makes them part of the backbone, while 49.002 and 49.003 are L1; this structure might lead to less flexible summarization options in the specified areas compared to making 49.002/49.003 part of the L2 backbone.

Concept tested: ISIS area design and level configuration

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

Topics

#ISIS routing#Area design#L1/L2 routing#Route leaking

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