Dual-stack is the correct IPv6 migration strategy for this corporation. The requirements state that users need access to both IPv4 and IPv6 resources, content providers will migrate over the next two years, and users will move in phases. Dual-stack supports exactly that model because hosts, routers, and services can run IPv4 and IPv6 simultaneously. Applications can select IPv6 or IPv4 based on DNS responses and protocol availability, while the organization gradually enables IPv6 without breaking existing IPv4 connectivity. NAT64 is useful for IPv6-only clients reaching IPv4-only services, but it introduces translation state and does not provide native dual protocol operation. NAT46 is a specialized translation direction and not the broad migration strategy here. Tunneling can connect IPv6 islands across IPv4 infrastructure, but the customer already has IPv4 peering and needs a phased endpoint and application migration, not only island interconnection. Dual-stack is straightforward operationally and gives the longest coexistence window while providers and applications transition. Reference topics: IPv6 migration, dual-stack deployment, DNS-based protocol selection, IPv4 and IPv6 coexistence, phased migration.