How to reject when a user logs in without realm?

[Navin]

Hi,
   I am new to radius . hence kindly excuse if my terminologies
are different from what is expected.

I am using Freeradius Version 1.1.7.
Is it possible to reject when a request comes from the NAS server
with a user logging in without a realm as suffix?

For example, if the FreeRadius server receives an authentication
request for the user navin , it has to reject. but if it receives
the request as navin at freescale.com it has to authenticate him.

I tried the below options:

I am not using the proxy request support.
Hence commenting proxy.conf file and setting proxy_requests  = no
in the radiusd.conf file.

Added the below in the radiusd.conf file with the intention that
users of realm freescale.com has to be authenticated and other users
should be rejected.

realm freescale.com {
         type            = radius
         authhost        = LOCAL
         accthost        = LOCAL
}

realm NULL {
         type            =  radius
         authhost        =  LOCAL
         accthost        =  LOCAL
         secret          =  test
}

In the radiusd.conf  under the section realm module config  options
ignore_null = yes
ignore_default = yes

for user at realm.

In the users file, added
navin at freescale.com Cleartext-Password := "navin123"

meaning authenticate navin having a password navin123.

But what i observed is, i get authenticated when i login as
navin and also as navin at freescale.com .

This has been verified with the radtest client program which
came along with the freeradius server.

Kindly do let me know if the user can be rejected access if he logs 
in without realm.

have a nice day,
navin