removes the distribution layer in favor of a spine-leaf design used in modern data center deployments

adds a distribution layer to free up resources from the Core for improved performance and routing throughput

a more scalable design over by leveraging a distribution layer to handle Layer 3 routing and access control in large deployments

uses only Layer 2 access on the Access and the Core with Layer 3 routing and access control provided at the distribution layer

is considered legacy by requiring a large flat layer-two broadcast domain from Core to Access and should be avoided