Which of the following WAN virtualization technology is used to create networks which span multiple base networks?

Cloud overlay networks use encapsulation protocols such as VXLAN or GRE to build virtual network topologies that span multiple different base networks, including on-premises, colocation, and cloud environments. This is the defining characteristic of WAN virtualization - abstracting the logical network from the physical underlay so traffic can traverse diverse base networks transparently. SD-WAN solutions rely on this overlay principle to connect distributed sites across multiple carriers or cloud backbones.

Virtual private networks create encrypted point-to-point or point-to-site tunnels for secure remote access but are not specifically classified as WAN virtualization technology designed to span multiple heterogeneous base networks at scale.

Virtual private cloud is a cloud provider construct that isolates a tenant's resources within a single cloud environment and does not span or virtualize multiple underlying base networks in the WAN sense.

Network peering connects two distinct networks directly to exchange traffic but does not create a virtualized overlay network or span multiple base networks under a unified virtual topology.