A few years ago, most DPC networks were based on the traditional three-tier architecture. This architecture came from campus area networks. The traditional three-tier architecture is effective for most traffic models, including Southbound and Northbound DPC networks. It is widely used in practice and is mature and stable. However, as technology advances, this architecture no longer satisfies the needs of DPC networks. With the development of cloud computing, horizontal, or East-West traffic, begins to dominate in data centers. This applies to almost all cloud computing, virtualization, and big data services. The horizontal traffic model becomes the bottleneck for data transmission in vertical networks. This is due to many "extra" nodes for data trafficking, including routers and switches. Host-to-host access traffic has to pass through many upstream ports, which significantly reduces performance. Thus, the three-tier principle used to build networks adversely affects their performance. In other words, the three-tier architecture that is currently the mainstream can no longer meet the requirements of DPC networks.
In the Leaf-Spine architecture, traffic can be distributed across all available channels without congestion. As the number of connections to the Leaf switches increases, the link bandwidth oversubscription ratio increases and can be reduced by increasing the link bandwidth between the Leaf and Spine switches.
The Leaf-Spine architecture includes multiple, high-bandwidth direct connections to avoid slowdowns because of bottlenecks and provide high-performance forwarding with low latency.