When you are configuring a DMVPN network, which tunnel mode should you use for the hub router configuration?

A.
GRE multipoint

B.
Nonbroadcast multiaccess

C.
Classic point-to-point GRE

D.
IPsec multipoint

Explanation:
http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/DMVPN_2_Phase2.html
The hub-and-spoke deployment model is the most common deployment model. This model is the
most scalable, and predominately mimics traditional Layer 2 leased line, Frame Relay, or ATM
hub-and-spoke networks. The headend is configured with a multipoint GRE (mGRE) interface, and
the branch with a point-to-point
(p2p) GRE interface.