DMVPN (Dynamic Multipoint VPN) is a kind of dynamic establishes VPN Tunnel technology. DMVPN uses the NHRP (Next Hop Resolution Protocol) technology to analyze the end address of VPN Tunnel in the Hub-And- Spoke under the network environment; and uses the Multipoint GRE Tunnel port to establish Multipoint GRE over IPSec VPN Tunnel. DMVPN is based on IPSec VPN and GRE VPN.