What is Limit IP Learning To Subnet in ACI?

 Limit IP Learning To Subnet

--> Limit IP Learning To Subnet was originally known as "Enforce Subnet Check for IP Learning" in 1.1 APIC Release.

--> This option is enabled by default under "Bridge Domain" Configuration.

If this option is disabled on a bridge domain that had the option enabled, the following happens:

i) Cisco ACI doesn’t flush endpoint IP addresses learned on the bridge domain.

ii) MAC or IP address learning is not paused for 120 seconds.

If you enable the "Limit IP Learning To Subnet" from the disabled state then the following things happen:

i) Cisco ACI doesn’t flush endpoint IP addresses learned on the bridge domain.

ii) Endpoint IP addresses that do not belong to the bridge domain subnet are flushed.

iii) MAC or IP address learning are not paused for 120 seconds.

Reference:

https://www.cisco.com/c/en/us/solutions/collateral/data-center-virtualization/application-centric-infrastructure/white-paper-c11-739989.html#EndpointDataplaneLearning