DMVPN
Dynamic Multi-point Virtual Private Network (DMVPN) is an older tunneling technology for WAN utilization that allows for simplified configuration of a hub-and-spoke topology while offering support for dynamic spoke-to-spoke tunnels. The technology also includes support for IPsec encryption across the tunnels, allowing for secure communications between all of the enterprise locations.
Similar to SD-WAN, DMVPN is capable of carrying the SGT information across the encrypted tunnel architecture. While there are numerous advantages and benefits when using SD-WAN as compared to DMVPN, numerous DMVPN deployments exist in production today.
The details of how DMVPN itself works are discussed in various Cisco Press texts. For questions on configuring DMVPN, please review those works.