Ethan Banks of The Peering Introvert comments:
One of the most interesting elements of SDN architectures is traffic forwarding. How does traffic get from one point to another in an SDN world? Cisco ACI’s traffic forwarding approach is intriguing in that it neither relies on the controller for forwarding instructions, nor does it rely on a group of network engineers to configure it. Rather, Cisco ACI fabric is a self-configuring cloud of leaf and spine switches that forward traffic between endpoints without forwarding tables being programmed by the Application Policy Infrastructure Controller (APIC). APIC assumes forwarding will happen, worrying instead about policy.
The notion of a self-configuring fabric that delivers traffic with no outside instruction sounds mystical. How, exactly, does Cisco ACI forward traffic? Wanting to understand the basics myself, I spent time reviewing presentations by engineers from the Cisco ACI team, and have distilled the information down as best as I could.
This is *the* definitive guide to how traffic is forwarded through ACI. Read it. Know it. You will see this material again.
Read more: Cisco ACI Fabric Forwarding In A Nutshell