The IAS server is the basic component of IAS. It receives authentication requests from NAS servers and compares the requests to the contents of a Windows NT user database, and returns authentication information to the NAS using the RADIUS protocol. The RADIUS server processes authentication requests by directing the authentication request to the Windows NT Domain Controller.
The RADIUS server selects the appropriate authentication provider based on the prefix or suffix of the user-attribute field in the RADIUS packet. For example, in the user ID someone@microsoft.com, @microsoft.com is the suffix, which designates the user’s realm. The relationship between prefix or suffix and the authentication provider can be specified in Internet Authentication Service Properties.