Company XYZ is designing the IS-IS deployment strategy for their multiarea IS-IS domain.

D (L1/L2 for ABRs and L1 for internal routers):This hierarchical approach minimizes LSDB size inside areas (L1 routers only maintain intra-area routes) while L1/L2 routers handle inter-area route propagation, reducing neighbor adjacencies and improving scalability.

Other options explained:

A: Level 2 everywhere results in larger LSDBs across all routers.

B: Only L2 routers at ABRs would isolate L1 domains improperly.

C: Pure L1 design prevents inter-area reachability.

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