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  • Nicholas O'Neill thinks this is interesting:

The NHRP reply is for the entire subnet rather than the specified host address.

From

Cover of Cisco Intelligent WAN (IWAN)

Note

This is signalled in the NHRP packet (NHRP Mandatory Part -> Client Information Entry) as "Prefix Length" as apposed to sending the address/mask. As we already know the destination address this is more optimal.