DMVPN

DMVPN (Dynamic Multipoint VPN) is a solution to build scalable IPsec VPNs. DMVPN uses a hub and spoke topology where spoke-to-spoke VPNs are possible, without having to manually configure tunnels between all sites. It uses multipoint GRE for tunneling,  NHRP (Next Hop Resolution Protocol) to figure out the next hop IP addresses and IPsec for encryption and authentication. DMVPN supports routing protocols like RIP, OSPF, EIGRP and BGP.