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Systems & Data Center · Advanced

IP Fabric Underlay

The routed Layer 3 spine-leaf network, often using eBGP, that provides IP reachability and ECMP for an overlay such as VXLAN EVPN.

Definition

Juniper's reference design assigns each leaf a unique ASN and peers with spines over point-to-point eBGP, advertising loopbacks. BFD speeds failure detection. The underlay carries VTEP traffic, while the overlay (iBGP or eBGP EVPN) carries tenant reachability.

Example

Each QFX leaf peers eBGP with four spines and advertises its loopback for VTEP reachability.

Exam tip

Separate underlay (IP reachability) from overlay (tenant EVPN routes) in your answers.

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