Which protocol is used to communicate endpoint mapping information to the spine proxy?

COOP (Council of Oracles Protocol) is a custom, internally developed protocol within Cisco ACI that runs on the spine switches. Its primary function is to maintain a consistent, distributed database of endpoint (MAC and IP address) locations across the fabric, ensuring all leaf switches have accurate forwarding information.

LLDP (Link Layer Discovery Protocol) is used for discovering adjacent network devices at Layer 2, not for communicating endpoint mapping information within the ACI fabric.

OpFlex is a southbound protocol used for communication between the APIC and the leaf switches (or network devices), but it's not directly responsible for propagating endpoint mapping between leaf and spine switches for forwarding.

IS-IS (Intermediate System to Intermediate System) is a routing protocol used for path determination in IP networks, not for endpoint location database synchronization in ACI.