The correct answer is Software-defined networking because it allows networks to be configured dynamically through software controls, enabling rapid changes and segmentation without requiring physical changes to the network. This agility is preferable in a security context, as it allows an organization to swiftly adapt to new threats or security demands. VLANs, while offering segmentation, do not provide the same level of agility in reconfiguring network traffic flows. Traditional layered security and physical network segmentation are static and do not offer the flexibility to rapidly change configurations as SDN does.