Which three layers make up the traditional three-tier enterprise network design?

The traditional three-tier enterprise network design consists of the Access, Distribution, and Core layers. The Access layer connects end devices like PCs and IP phones. The Distribution layer aggregates access layer switches, provides policy-based connectivity, and acts as a boundary for broadcast domains. The Core layer provides high-speed, fault-tolerant backbone connectivity between distribution layers and to external networks. Leaf and Spine are components of a two-tier (Spine-and-Leaf) architecture, which is a more modern design often used in data centers, not the traditional three-tier enterprise model.