Spine-and-leaf networks scale access capacity by adding another leaf switch and connecting that leaf to every spine switch. That preserves the fabric's predictable any-leaf-to-any-leaf pathing and keeps oversubscription under control. A leaf switch is where servers, endpoints, or access-facing devices attach; spine switches provide the high-speed interconnection layer between leaves. Leaves do not connect to other leaves, and spines do not connect to other spines in the classic two-tier Clos design. Adding only a spine switch does not create additional access ports. Adding a leaf with a single uplink to one spine would create a bottleneck and break the equal-cost multipath design principle. CCNA 200-301 v1.1 Network Access and Network Fundamentals include spine-leaf as a modern data-center architecture pattern. The verified answer is D: add a leaf switch with connections to every spine switch. Reference: Cisco spine-leaf/Clos architecture design guidance.