Explanation/Reference:
Explanation:
The configuration of mGRE allows a tunnel to have multiple destinations. The configuration of mGRE on one side of a tunnel does not have any relation to the tunnel properties that might exist at the exit points.
This means that an mGRE tunnel on the hub may connect to a p2p tunnel on the branch. Conversely, a p2p GRE tunnel may connect to an mGRE tunnel. The distinguishing feature between an mGRE interface and a p2p GRE interface is the tunnel destination. An mGRE interface does not have a configured destination. Instead the GRE tunnel is configured with the command tunnel mode gre multipoint. This command is used instead of the tunnel destination x.x.x.x found with p2p GRE tunnels. Besides allowing for multiple destinations, an mGRE tunnel requires NHRP to resolve the tunnel endpoints. Note, tunnel interfaces by default are point-to-point (p-p) using GRE encapsulation, effectively they have the tunnel mode gre command, which is not seen in the configuration because it is the default.
The mGRE configuration is as follows:
!
interface Tunnel0
bandwidth 1536
ip address 10.62.1.10 255.255.255.0
tunnel source Serial0/0
tunnel mode gre multipoint
Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/DMVPDG/ DMVPN_2_Phase2.html