ARP Flooding : By default, ACI will convert ARP broadcast traffic into unicast traffic and send it to the correct leaf node. This option can be disabled if traditional ARP flooding is needed. For the Unicast ARP to work you need to enable IP routing because the mapping database must be populated with the IP addresses of the endpoints. Hardware proxy must be enabled too. The capability to disable ARP flooding depends on the configuration of hardware proxy and IP routing as follows:
* If hardware proxy is turned off, then ARP flooding is on and cannot be turned off.
* If hardware proxy is turned on but IP routing is turned off, ARP flooding is on and cannot be turned off.
* If hardware proxy is turned on and IP routing is turned on, then you can disable ARP flooding. You may consider ARP flooding to be necessary because of silent hosts, but this is not completely true. It is true that disabling ARP flooding requires the mapping database to know the endpoint IP address, and for this IP routing must be turned on.
But even if the endpoint had been silent, Cisco ACI can resolve the endpoint IP address by sending ARP messages from the subnet IP address of the bridge domain. This feature is called ARP gleaning, and it requires the bridge domain to be configured with a subnet IP address.
