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Spine-leaf / Clos

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Walkthrough

East-west across the Clos

Host A reaches Host B by leaf → spine → leaf. Spines are transit only; equal-cost paths exist across the spine tier.

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Spine 1Spine 2Leaf 1Leaf 2Leaf 3Leaf 4Host AHost BBorder leaf

Leaves attach servers. Spines interconnect leaves in a full bipartite mesh — no leaf–leaf fabric links are required.

Walkthrough

North-south via a border leaf

Egress uses a border/edge leaf role. Exact border placement is design-dependent; this walkthrough is illustrative of the underlay hop pattern.

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Spine 1Spine 2Leaf 1Leaf 2Leaf 3Leaf 4Host AHost BBorder leafillustrative egress

A border leaf attaches WAN or DC interconnect. It is still a leaf in the Clos — not a third STP-blocked tier.

Border topology varies by design; treat this node as illustrative.

Walkthrough

Single spine failure

With k equal spines, losing one spine removes about 1/k of fabric bandwidth under ECMP. Remaining spines continue to interconnect every leaf.

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Spine 1ECMP memberSpine 2ECMP memberLeaf 1Leaf 2Leaf 3Leaf 4Host AHost BBorder leaf

Healthy fabric: Leaf 1 has equal-cost uplinks to Spine 1 and Spine 2. East-west load shares across both.