What is a commonality between DMVPN and FlexVPN technologies?

What is a commonality between DMVPN and FlexVPN technologies?
A . FlexVPN and DMVPN use IS-IS routing protocol to communicate with spokes
B . FlexVPN and DMVPN use the new key management protocol
C . FlexVPN and DMVPN use the same hashing algorithms
D . IOS routers run the same NHRP code for DMVPN and FlexVPN

Answer: D

Explanation:

In its essence, FlexVPN is the same as DMVPN. Connections between devices are still point-to-point GRE tunnels, spoke-to-spoke connectivity is still achieved with NHRP redirect message, IOS routers even run the same NHRP code for both DMVPN and FlexVPN, which also means that both are Cisco’s proprietary technologies.

Reference: https://packetpushers.net/cisco-flexvpn-dmvpn-high-level-design/