I, take a look at this step by step how to use LDAP authentication. It was my guide. For RedHat 7.0 http://www.redhat.com/support/manuals/RHL-7-Manual/ref-guide/s1-ldap-redhattips.html or this for ReadHat 6.1 http://people.redhat.com/alikins/ldap/ldap.html