What advantage of placing the IS-IS Layer 2 flooding domain boundary at the core layer...

In an IS-IS design, placing the Level-1/Level-2 (L1/L2) boundary at the core limits the extent of the flooding domain, improving scalability and stability.

By limiting Level-2 flooding to the core, instability or frequent changes in the access/distribution layers (typically Level-1) do not impact the core.

The core remains stable, while routing changes are isolated within the Level-1 domains.

Other options explained:

A: Overlapping domains are not a design objective.

B: This has no direct impact on Layer 1 complexity.

C: IS-IS design must match topology hierarchy; this is not universally applicable.

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