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Commonly confused · Systems & Data Center

Spine-Leaf vs Three-Tier Architecture: What's the Difference?

The three-tier model uses access, distribution, and core layers and was optimized for north-south traffic between clients and servers. Spine-leaf is a two-layer Clos fabric where every leaf connects to every spine, giving predictable low latency for the east-west traffic between servers that dominates modern data centers.

Spine-Leaf Architecture

Full definition
vs

Three-Tier Architecture

Full definition
Spine-Leaf ArchitectureThree-Tier Architecture
LayersLeaf and spine (two)Access, distribution, core (three)
Optimized forEast-west (server to server)North-south (client to server)
Hop count between serversConsistent: leaf-spine-leafVariable, up to the core and back
Loop preventionLayer 3 ECMP routing, often VXLAN EVPN overlayOften STP at Layer 2, blocking redundant links
Link utilizationAll links activeRedundant links may be blocked
ScalingAdd leaves for ports, spines for bandwidthScale up larger chassis
Typical environmentData centers, private cloudCampus networks, legacy data centers
Remember it

Spine-leaf means every rack is two hops from every other rack.

Exam tip

Questions ask which design suits virtualized data centers with heavy east-west traffic (spine-leaf), and that leaves never connect to other leaves and spines never connect to other spines.

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