A. Enable the Export Route Control Subnet for the External Endpoint Group flag.
B. Enable an L30ut with Shared Route Control Subnet.
C. Configure subnets with the External Subnets for External EPG flag enabled.
D. Configure subnets with the Import Route Control Subnet flag enabled.
Explanation:
https://www.cisco.com/c/en/us/td/docs/switches/datacenter/aci/apic/sw/1-x/ACI_Best_Practices/b_ACI_Best_Practices/b_ACI_Best_Practices_chapter_01001.html
