Refer to the exhibit.

Options C and D represent the two ACI policy approaches that decouple security membership from a simple one-subnet-one-group design. Multiple EPGs can be associated with the same bridge domain. Because the bridge domain owns the Layer 2 forwarding space and gateway subnet, endpoints using the same IP subnet can be classified into different EPGs through interface, VLAN, virtual-domain, or microsegmentation criteria. Contracts between those EPGs then enforce separate security policy without creating different IP networks, which is the design expressed by Option D. Endpoint Security Groups provide a more flexible model. ESGs separate security classification from the EPG and bridge-domain forwarding structure and can group endpoints or EPGs within a VRF according to security intent. This enables policy groups to be constructed across existing network-centric EPGs without redesigning their subnets, supporting the approach in Option C. Cisco explains that traditional EPGs combine forwarding and security and are tied to one bridge domain, whereas ESGs move security enforcement to an independent grouping layer. Options B and E create different bridge domains and subnets, so they do not satisfy the requirement that endpoints share the same IP subnet. Security Group Tags alone do not define the required ACI endpoint classification and contract model described in Option A. Using EPGs within a shared bridge domain and using ESG-based security grouping are therefore the two valid segmentation mechanisms. Cisco ACI Endpoint Security Group design guide

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