Why More Data Center Teams Are Choosing NX-OS VXLAN EVPN Over Cisco ACI in 2026

I spent four hours last Tuesday troubleshooting why a new GPU node couldn't reach the MLflow registry during a training run. The ACI fabric was reporting the endpoint learned. The policy contract showed permit. But packets died silently somewhere between leaf switches. The root cause? A stale endpoint entry in the COOP database that the APIC controller hadn't reconciled. I fixed it by clearing the endpoint from the CLI, bypassing the abstraction layer entirely. That incident crystalized something I'd been seeing across three data center builds: when the controller's model of the network diverges from the actual forwarding state, you end up working around the abstraction, not through it. You SSH to the leaf switch and run show commands that reveal what's really happening in hardware. At that point, the controller is adding latency, not value. The Real Tradeoff Nobody Talks About ACI's pitch is clean: declare your intent through a GUI or API, and the fabric converges to that state. The A