An enterprise needs to migrate its WAN core from EIGRP to IS-IS, and in the future it wants to enable IS-IS across all other regional networks connected to the WAN core. Which approach do you…

Question

Options

• AStart with L1 across the WAN core and then add the regional networks as L2 each.
• BStart with L1/L2 across the WAN core and then add the regional networks as L2.
• CStart with L2 across the WAN core and then add the regional networks as L1.
• DStart with L1/L2 across the WAN core and then add the regional network as L1/L2 as well.

• A
  13% (5)
• B
  18% (7)
• C
  64% (25)
• D
  5% (2)

Explanation

C is the correct recommended approach. In IS-IS, Level 2 is the backbone (analogous to OSPF Area 0), and Level 1 represents stub/regional areas. The WAN core serves as the transit backbone, so it should be built as an L2-only domain. Regional networks that attach to this backbone are then added as L1 areas, with L1/L2 routers at the boundary connecting each regional network to the L2 core. This creates a proper two-level hierarchy: a scalable L2 backbone with L1 regional areas. A is wrong because making the core L1 inverts the hierarchy - L1 is for stub areas, not backbones. B is wrong because regional networks should be L1, not L2. D is wrong because making all routers L1/L2 eliminates the benefits of hierarchical routing (summarization, contained flooding), defeating the purpose of a multi-level design.

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