DMVPN spoke-to-spoke networks beyond two hubs with Open Shortest Path First (OSPF) as the routing protocol, the spokes use routes with the IP next-hop set to the hub router (not the remote spoke router as before), you can configure OSPF to use point-to-multipoint network mode rather than broadcast network mode. Configuring OSPF to use point-to-multipoint network mode removes the Designated Router (DR) and Backup Designated Router (BDR) requirements that restricted the DMVPN network to just two hubs . When using OSPF, each spoke still has all the individual spoke routes, because the DMVPN network must be in a single OSPF area and you cannot summarize routes within an OSPF area.

http://cisco.com/en/US/products/ps6635/products_white_paper0900aecd8055c34e.shtml

http://www.cisco.com/en/US/tech/tk583/tk372/technologies_white_paper09186a008018983e.shtml