A three-stage IP fabric is a scaled leaf-spine design that adds an additional layer above the spine layer to increase port scale and bandwidth. In common data center terminology, the stages are leaf, spine, and an upper spine layer often referred to as superspine. Traffic sourced from an endpoint attached to a leaf switch first enters the fabric at that leaf. If the destination is attached to a different leaf and the fabric is truly three-stage, the packet typically traverses from the source leaf up to a spine, then continues upward to the upper layer spine, then down to a destination spine, and finally down to the destination leaf. The option that best represents this stage progression is leaf to spine to spine to leaf, where the second spine in the sequence corresponds to the upper layer spine tier in a three-stage design.

By contrast, leaf to spine to leaf describes a two-tier leaf-spine fabric where a single spine hop connects any two leaves. The other options do not represent the standard end-to-end progression for traffic between leaves in a three-stage fabric. In practice, the underlay uses routed links with equal-cost multipath, so there can be multiple equal paths that still follow the same stage order. This preserves predictable forwarding behavior while allowing the fabric to scale beyond what a two-tier topology can support.