They can simplify cabling, for example, but reducing the cabling from the access switches on the server racks to the core. Leaf-spine architectures have many other advantages in addition to creating a more robust switching fabric with fewer tiers of switches. This has become known also a “scale-out” architecture because new leaf-and spine combination can be added incrementally with new servers. Google is widely credited with popularizing the leaf-spine design with its Clos architecture, which enabled the company to quickly add the new leaf and spine switches to accommodate data center growth, without re-architecting the network. This approach uses as few switches as possible to create a large, non-blocking fabric. This system is equipped to handle east-west traffic from server to server, but it can also accommodate the north-south type, including emails and web content. Latency is improved and bottlenecks are minimized. There is no need to jump up and down the “tree” design.

The leaf-spine design has the advantage of placing each leaf switch just one hop away from another. A tree network might have multiple tiers of switches, stacked upon each other, each getting larger in capacity. The terms “leaf” and “tree” relate to the description of a network. This is especially the case in hyperscale data centers, where hundreds or thousands of servers might be connected to a network.

The leaf switch evolved in modern data centers as servers multiplied and network designs with more switching tiers – including perhaps an additional aggregation layer between the server access switches and the core – became less efficient as more racks of servers were added. This popular data center design architecture is known as “leaf-spine” and was popularized as data centers grew in scale. In this model, there are only two tiers of switches between the servers and the core network. Leaf switches are popular devices used in data centers to aggregate traffic from server nodes and then connect to the core of the network, consisting of spine switches.

Tor switch vs core switch