filter anonymous identity

Hello, on radius 1.1.x I have some users autenticating using an outer identity. This is annoying to me because in the radius.log file I cannot identify easily who is the real user autenticating, since outer identity can be anything. How can I forbid in freeradius configuration to use an outer identity or anonymous ? I wish to forbid autentications which uses an outer identity. howto have control over it ? thank you Rick