How should multiple OSPF areas be designed when deployed on a classic three-layer (core/distribution/access) network hierarchy?

Placing the flooding domain boundary at the edge of the core layer does not align with route summarization opportunities, which typically exist where access networks terminate at distribution layer ABRs.

Simply placing the boundary within the distribution layer ignores the primary design principle of enabling route aggregation at those boundaries, which is the actual reason the distribution layer is commonly chosen.

OSPF area hierarchy does not need to mirror the physical three-layer topology; area design should be driven by scalability and aggregation goals, not physical layer alignment.

Placing OSPF flooding domain boundaries with route aggregation in mind allows ABRs to summarize inter-area routes, preventing individual link-state changes from flooding throughout the entire OSPF domain. This reduces the LSDB size in each area, limits LSA propagation, and decreases SPF computation overhead across area boundaries.