Top-of-Rack Switch Calculator
Count top-of-rack switches for a row from server NIC ports, uplink reservations and dual-ToR redundancy.
Inputs
Switches Required
40switches
Switches per Rack
2switches
Server Ports to Terminate
800ports
Spare Access Ports per Rack
44ports
Access Port Utilisation
47.62%
Step by step
Values used
Racks = 20 racks; Servers per rack = 20 servers; Data NIC ports per server = 2 ports; Ports per switch = 48 ports; Ports reserved for uplinks = 6 ports; Dual-ToR (split NICs across two planes) = Yes
Top-of-Rack Switch
usable ports = ports per switch − uplink reservations; switches per rack = ceil(server ports ÷ planes ÷ usable ports) × planes.
Switches Required
= 40 switches
Switches per Rack
= 2 switches
Server Ports to Terminate
= 800 ports
Spare Access Ports per Rack
= 44 ports
Access Port Utilisation
= 47.62
How it works
Server ports are the product of servers and NIC ports per server, and only the ports not reserved for fabric uplinks can terminate them. Dual-ToR halves the load on each plane but doubles the switch count, because each plane must be able to carry the rack alone. Switch count drives licence, optics and power budgets, and forgetting the uplink reservation is how a 48-port switch turns out to hold only 42 servers.
Formula
Top-of-Rack Switch
usable ports = ports per switch − uplink reservations; switches per rack = ceil(server ports ÷ planes ÷ usable ports) × planes.
- planes
- 1 for single ToR, 2 when each server NIC pair splits across redundant switches
- usable ports
- Access ports left after uplinks are set aside
Frequently Asked Questions
How is Top-of-Rack Switch calculated?
usable ports = ports per switch − uplink reservations; switches per rack = ceil(server ports ÷ planes ÷ usable ports) × planes. Server ports are the product of servers and NIC ports per server, and only the ports not reserved for fabric uplinks can terminate them. Dual-ToR halves the load on each plane but doubles the switch count, because each plane must be able to carry the rack alone.
Why does Top-of-Rack Switch matter?
Switch count drives licence, optics and power budgets, and forgetting the uplink reservation is how a 48-port switch turns out to hold only 42 servers.
What values do I need to enter?
This calculator takes 6 inputs: Racks, Servers per rack, Data NIC ports per server, Ports per switch, Ports reserved for uplinks, Dual-ToR (split NICs across two planes). The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.