Explanation/Reference:
Explanation:
To configure NPS as a RADIUS proxy, you must create a connection request policy that contains all of the information required for NPS to evaluate which messages to forward and where to send the messages.
When you configure Network Policy Server (NPS) as a Remote Authentication Dial-In User Service (RADIUS) proxy, you use NPS to forward connection requests to RADIUS servers that are capable of processing the connection requests because they can perform authentication and authorization in the domain where the user or computer account is located. For example, if you want to forward connection requests to one or more RADIUS servers in untrusted domains, you can configure NPS as a RADIUS proxy to forward the requests to the remote RADIUS servers in the untrusted domain. To configure NPS as a RADIUS proxy, you must create a connection request policy that contains all of the information required for NPS to evaluate which messages to forward and where to send the messages.
When you configure a remote RADIUS server group in NPS and you configure a connection request policy with the group, you are designating the location where NPS is to forward connection requests.

References:
http://technet.microsoft.com/en-us/library/cc754518.aspx