Explanation/Reference:
Explanation:
NPS trace logging files
You can use log files on servers running Network Policy Server (NPS) and NAP client computers to help troubleshoot NAP problems. Log files can provide the detailed information required for troubleshooting complex problems.
You can capture detailed information in log files on servers running NPS by enabling remote access tracing. The Remote Access service does not need to be installed or running to use remote access tracing.
When you enable tracing on a server running NPS, several log files are created in %windir %\tracing.
The following log files contain helpful information about NAP:
IASNAP. LOG: Contains detailed information about NAP processes, NPS authentication, and NPS

authorization.
IASSAM. LOG: Contains detailed information about user authentication and authorization.

Membership in the local Administrators group, or equivalent, is the minimum required to enable tracing.
Review details about using the appropriate accounts and group memberships at Local and Domain Default Groups (http://go.microsoft.com/fwlink/?LinkId=83477).
To create tracing log files on a server running NPS
Open a command line as an administrator.

Type netshras set tr * en.

Reproduce the scenario that you are troubleshooting.

Type netshras set tr * dis.

Close the command prompt window.

Reference: http://technet.microsoft.com/en-us/library/dd348461%28v=ws.10%29.aspx