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When configuring a DMVPN solution, which of the following technologies makes it possible for the spoke
routers to use dynamic IP addressing?

A. IPsec

B. mGRE

C. NHRP

D. Dynamic routing protocols

Explanation:
Next Hop Resolution Protocol (NHRP) allows the spoke routers to register their IP addresses with the
NHRP server, which is the hub router. It also allows the spoke routers to then learn the physical IP
addresses of the other spoke routers from the hub router, allowing for GRE links to be built dynamically as
needed between the spokes. This eliminates the need for the traffic to go through the hub router.
Dynamic Multipoint VPN (DMVPN) technology leverages the following associated technologies:
IPsec
mGRE
Dynamic routing protocols
NHRP
Cisco Express Forwarding
It makes it possible to build the hub router once, and add spokes later, making no additional changes to the
hub. The spokes are able to register with the hub and dynamically build their own connections to other
spokes using the IP addresses learned from the hub using NHRP. DMVPN also allows IPsec point-to-point
GRE tunnels to be built to new spokes with no IPsec peering configuration. The multipoint GRE technology
(mGRE) allows a single physical interface on the hub to be used for all spoke connections.
Finally, the routing protocols used by DMVPN allow the routers to share routing information, while Cisco
Express Forwarding (CEF) is a switching technology that improves performance while reducing the load on
the CPUs of the routers.
Objective:
VPN Technologies
Sub-Objective:
Describe DMVPN (single hub)
References:
Cisco > Dynamic Multipoint VPN (DMVPN) Design Guide (Version 1.1) > DMVPN Design Overview

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