Count fabric and access cables for a leaf-spine build, including a spares allowance.
A full-mesh leaf-spine needs one cable from every leaf to every spine for each parallel link, which grows as the product of the two tiers. Access cabling is per NIC port, and a 10% spares allowance covers breakage and moves. Cabling is often the largest single line item and the longest lead time in a fabric build, and a recount after installation starts is expensive.
Cable Count
fabric cables = leaves × spines × links per pair; access cables = leaves × servers per leaf × NIC ports; add the spares percentage.
fabric cables = leaves × spines × links per pair; access cables = leaves × servers per leaf × NIC ports; add the spares percentage. A full-mesh leaf-spine needs one cable from every leaf to every spine for each parallel link, which grows as the product of the two tiers. Access cabling is per NIC port, and a 10% spares allowance covers breakage and moves.
Cabling is often the largest single line item and the longest lead time in a fabric build, and a recount after installation starts is expensive.
This calculator takes 6 inputs: Leaf switches, Spine switches, Links between each leaf and spine, Servers per leaf, NIC ports per server, Spares allowance. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.