Which Cisco VPN technology can use multipoint tunnel, resulting in a single GRE tunnel interface on the hub, to support multiple connections from multiple spoke devices?

DMVPN (Dynamic Multipoint VPN) leverages mGRE on the hub, which enables one tunnel interface to support dynamic, on-demand tunnels to any number of spoke routers without requiring a separate point-to-point tunnel per spoke. This is the defining architectural feature that distinguishes DMVPN from traditional GRE VPN designs. NHRP (Next Hop Resolution Protocol) works alongside mGRE to allow spokes to discover each other's real addresses.

GETVPN is a tunnel-less, group-based encryption solution designed for MPLS networks and does not use GRE tunnel interfaces at all.

Cisco Easy VPN uses a client-server model with point-to-point IPsec tunnels and does not employ mGRE multipoint interfaces on the hub.

FlexVPN is a standards-based IKEv2 framework that can support various topologies but is a separate technology from DMVPN and is not defined by the mGRE multipoint hub interface architecture.