This feature is essential to support new features of Windows such as Microsoft Direct Access.
When a DirectAccess client is on the Internet, each name query request is compared against the namespace rules stored in the NRPT. If a match is found, the request is processed according to the settings in the NRPT rule. The settings determine the DNS servers to which each request will be sent.
For more information about NRPT, please view the following TechNet website: