Size a leaf-spine fabric: total fabric bandwidth, per-leaf uplink capacity and the resulting oversubscription.
In a two-tier Clos every leaf connects to every spine, so leaf uplink capacity is spines multiplied by link speed multiplied by links per spine, and the fabric total is that figure across all leaves. Comparing it with the access ports on a leaf gives the oversubscription the design accepts. Fabric bandwidth and oversubscription decide whether east-west traffic congests under load, and spine port count is the hard limit on how many leaves the fabric can ever hold.
Leaf-Spine Capacity
fabric bandwidth = leaves × uplinks per leaf × uplink speed; oversubscription = access capacity per leaf ÷ uplink capacity per leaf.
fabric bandwidth = leaves × uplinks per leaf × uplink speed; oversubscription = access capacity per leaf ÷ uplink capacity per leaf. In a two-tier Clos every leaf connects to every spine, so leaf uplink capacity is spines multiplied by link speed multiplied by links per spine, and the fabric total is that figure across all leaves. Comparing it with the access ports on a leaf gives the oversubscription the design accepts.
Fabric bandwidth and oversubscription decide whether east-west traffic congests under load, and spine port count is the hard limit on how many leaves the fabric can ever hold.
This calculator takes 6 inputs: Leaf switches, Spine switches, Uplinks from each leaf to each spine, Uplink speed, Access ports per leaf, Access port speed. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.