To understand the principles of DMVPN Phase I, remember these facts:

• Spokes use point-to-point GRE tunnels;
• Hub site has multipoint GRE tunnel;
• All the traffic flows through the hub site;
• The next-hop for routes received over DMVPN must be the hub site;
• NHRP is used by the hub site to get spokes’ tunnel endpoint addresses.
• Spoke sites use NHRP just to register with the hub site.