FlexVPN and DMVPN are both Cisco technologies that use point-to-point GRE tunnels to create dynamic VPN networks. However, they differ in some aspects, such as:
* FlexVPN is a newer solution that requires newer hardware and IOS versions, while DMVPN is more widely supported on older devices1.
* FlexVPN is based on IKEv2, which is a more robust and efficient protocol than IKEv1, which is used by DMVPN (although DMVPN can also use IKEv2)2.
* FlexVPN uses static or virtual access interfaces for GRE tunnels, while DMVPN uses a single multipoint GRE interface. This allows more flexibility and visibility for FlexVPN tunnels2.
* FlexVPN does not require NHRP registration for spokes to communicate with the hub, while DMVPN does. This simplifies the configuration and reduces the overhead of NHRP3.
* FlexVPN has only one standard mode of operation, while DMVPN has three phases with different characteristics and configurations2.
References := 1: what is the difference between dmvpn and flexvpn 2: Cisco FlexVPN DMVPN, Part 1 - Overview and Design 3: DMVPN to FlexVPN Soft Migration Configuration Example