In high-density data center deployments, switches are placed in every rack, and in most cases, connected to a computing device such as a bare-metal server used by only one tenant or blade server chassis. To better enable access to the horizontal fiber optic cabling that connects in-rack switches to aggregation switches, they are usually positioned near the top of the rack, however. Top-of-rack (ToR) switches are most often placed at the top of the rack but can be placed anywhere in the rack. The in-rack network switch, in turn, is connected to aggregation switches, most often via fiber optic cable.

Top of rack architecture generally places a network fiber switch in every rack to connect easily with every other device in the rack. Top-of-rack switching is a data center architecture design in which computing equipment like servers, appliances and other switches located within the same or adjacent rack are connected to an in-rack network switch. Eamon McCarthy Earls, Global North Institute.

Tor switch vs leaf switch