A library data-center leaf-spine fabric load-balances VXLAN traffic across multiple underlay uplinks. What does underlay ECMP primarily hash on for those encapsulated flows?
Select an answer to reveal the explanation.
Short Explanation
The underlay trucks only read the outer shipping label—source/dest VTEP, UDP ports, and friends. That’s the entropy ECMP uses to spray flows across spines. Inner tenant headers stay sealed in the box unless something is doing deep inspection you didn’t ask for.
Full Explanation
Underlay routers and switches treat VXLAN packets as IP/UDP traffic. ECMP hashing therefore uses outer header fields (and typically UDP source-port entropy set by the ingress VTEP) to distribute flows across equal-cost paths. Relying solely on inner tenant headers would require underlay devices to parse past encapsulation, which standard fabric forwarding does not do. Proper entropy helps municipal fabrics avoid polarization when many overlay flows share the same VTEP pair.