Exam 300-620 topic 1 question 264 discussion

The difference of enabling and disabling the ARP flooding option appears once ACI learns a silent host IP. One of the benefits of enabling ARP flooding is to be able to detect a silent IP that moved from one location to another without notifying an ACI leaf. Because the ARP request is flooded within the BD, even if the ACI leaf still thinks the IP is at the old location, the host with the silent IP would respond appropriately so that the ACI leaf can update its entry accordingly. If ARP flooding is disabled, the ACI leaf would keep forwarding the ARP request only to the old location until the IP endpoint ages out. On the other hand, the benefit of disabling ARP flooding is to be able to optimize traffic flow by sending the ARP request directly to the location of the target IP, assuming no endpoint moves without notifying its movement via GARP and such. https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739989.html#Silenthostsconsiderations

For (L3) routed traffic to an unknown IP, the ACI leaf will generate an ARP request from its BD SVI (pervasive gateway) IP toward the unknown IP in order to detect and learn the unknown IP. Only the leaf with BD SVI IP for the unknown IP subnet will generate an ARP request. This behavior is originally triggered by the spine when the spine couldn’t find the unknown IP, even in the COOP database. This behavior is called silent host detection, or ARP gleaning. This behavior for (L3) routed traffic happens regardless of configuration, such as L2 Unknown Unicast or ARP flooding (mentioned below), as long as the traffic is routed to an unknown IP. https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739989.html#Silenthostsconsiderations