Exam 300-620 topic 1 question 172 discussion

Export Route Control Subnet—The control advertises specific transit routes out of the fabric. This is for transit routes only Import Route Control Subnet—This control allows routes to be advertised into the fabric with Border Gateway Protocol (BGP) and Open Shortest Path First (OSPF) External Subnets for the External EPG (also called Security Import Subnet)—This option does not control the movement of routing information into or out of the fabric. Shared Route Control Subnet—Subnets that are learned from shared L3Outs in inter-VRF leaking must be marked with this control before being advertised to other VRFs Shared Security Import Subnet—This control is the same as External Subnets for the External EPG for Shared L3Out learned routes. https://www.cisco.com/c/en/us/td/docs/dcn/aci/apic/5x/l3-configuration/cisco-apic-layer-3-networking-configuration-guide-52x/route-and-subnet-scope-layer3-config-52x.html

A is the right choice

A is correct. Aggregate Export This option can be used only for 0.0.0.0/0 with “Export Route Control Subnet”. When both “Export Route Control Subnet” and “Aggregate Export” are enabled for 0.0.0.0/0, ACI creates an IP prefix-list with “0.0.0.0/0 le 32”, which matches any subnets. Thus, this option can be used when an L3Out needs to advertise (export) any routes to the outside. D advertises all routes, but questions states only default route.