Leaf-Spine Capacity Calculator
Size a leaf-spine fabric: total fabric bandwidth, per-leaf uplink capacity and the resulting oversubscription.
Inputs
Total Fabric Bandwidth
12,800Gbps
Uplink Capacity per Leaf
800Gbps
Oversubscription Ratio
1.5:1
Total Access Capacity
19,200Gbps
Ports Used on Each Spine
32
Step by step
Values used
Leaf switches = 16 switches; Spine switches = 4 switches; Uplinks from each leaf to each spine = 2 links; Uplink speed = 100 Gbps; Access ports per leaf = 48 ports; Access port speed = 25 Gbps
Leaf-Spine Capacity
fabric bandwidth = leaves × uplinks per leaf × uplink speed; oversubscription = access capacity per leaf ÷ uplink capacity per leaf.
Total Fabric Bandwidth
= 12,800 Gbps
Uplink Capacity per Leaf
= 800 Gbps
Oversubscription Ratio
= 1.5:1
Total Access Capacity
= 19,200 Gbps
Ports Used on Each Spine
= 32
How it works
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.
Formula
Leaf-Spine Capacity
fabric bandwidth = leaves × uplinks per leaf × uplink speed; oversubscription = access capacity per leaf ÷ uplink capacity per leaf.
- uplinks per leaf
- Spines × links to each spine
- oversubscription
- Access bandwidth divided by uplink bandwidth, quoted as x:1
Frequently Asked Questions
How is Leaf-Spine Capacity calculated?
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.
Why does Leaf-Spine Capacity matter?
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.
What values do I need to enter?
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.
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