what is dmvpn

Dynamic Multiple VPN (or DMVPN) is a complex topic, but it’s a security configuration that could allow businesses that use a wide range of remote endpoints (or flexible endpoints that move location often) to make sure they can keep the security of their network in place, which making sure it’s flexible and not prohibitive in costs.
DMVPN Components 
Multiple GRE tunnel interfaces: a single GRE interface that can secure several IPsec tunnels, reducing the overall scope of the DMVPN configuration
IPsec tunnel endpoint discovery: meaning that static crypto maps between individual IPsec tunnel endpoints do not have to be configured
Routing Protocols: which can allow the DMVPN to find routes between different endpoints much more effectively
NHRP: which can deploy spokes with assigned IP addresses that can then be connected to from the central DMVPN hub.
DMVPN Phases
There are three distinct types, or phrases, of DMVPN design, all of which can be found on the Cisco DMVPN design guide. To summarize them briefly, however, they are as follows:
Understanding DMVPN 
DMVPN allows data exchanges on a secure network without the use of a headquarter’s VPN server or router. While a VPN acts as a connector between remote sites and HQ, or between different branches, the DMVPN creates a mesh VPN protocol that can be applied selectively to connections being utilized in the business already. Each different site (or spoke) can connect to one another securely. This is done using VPN firewall concentrators and routers, with DMVPN configuration on the routers in place at remote sites to allow the DMVPN mesh to be applied to the connection that it’s making at the time.

what is dmvpn