Disabling Default Gateway on Bridge Domain

C.

When a default gateway for endpoints is on an external device instead of a Cisco ACI bridge domain SVI, the feature that should be disabled on the bridge domain is proxy ARP.

Proxy ARP is a feature that enables a device to respond to ARP requests on behalf of another device that is not on the same physical network segment. When proxy ARP is enabled on a bridge domain, the Cisco ACI fabric will respond to ARP requests on behalf of the endpoints in the bridge domain, even if the default gateway is located outside the fabric. This can lead to suboptimal routing, as the external device may not have the same routing information as the Cisco ACI fabric.

Therefore, to avoid any potential routing issues and ensure that the correct default gateway is used for the endpoints, proxy ARP should be disabled on the bridge domain. This will allow the external device to respond to ARP requests for the default gateway IP address, ensuring that the endpoints use the correct default gateway for routing.

Unicast routing, ARP flooding, and unknown unicast flooding are not directly related to the issue of the default gateway being located on an external device, so these features do not need to be disabled in this scenario.