Traditional data center network fabrics are often designed with three tiers of switches: core, aggregation, and access. Access switches connect to aggregation switches, which in turn connect to the core switches. The design topology of the physical layer can impact efficiency and latencies.

Figure 1. Physical Network Design
Physical Network Design

A two-tier leaf-and-spine network architecture is the preferred approach for building a new data center infrastructure. The two-tier architecture uses an access switch, or leaf, which is connected to an aggregation switch, or spine. The leaf switch provides connectivity between endpoints in the data center, while the spine switch provides high-speed interconnectivity between leaf switches. The leaf-and-spine network is connected in a full mesh, providing predictable communication and latency between endpoints. Ethernet connectivity is used from the host to the leaf switch, and the broadcast domain terminates at the leaf. External Border Gateway Protocol (eBGP) is often used for routing within the leaf-and-spine architecture.