Realm extraction

Hi all, I am new in free radius , so I have one question: How can I exctract Realm attribute in radiusd.conf name? So, I need to use it in LDAP filter to make search like : ldap { server = "localhost" identity = "uid=pr,ou=Staff,dc=domain,dc=com" password = secret basedn = "ou=People,dc=ivoho,dc=com" filter = "(uid=%{User-Name},ou=%{Realm-Name})" # base_filter = "(objectclass=radiusprofile)" ... how can I get Realm-Name variable ?