LDAP service fails after Portal is upgraded to 3.6.0.
This issue is because the (Update.ISO) for 3.6.0 does not contain the "pam_ldap_rvbd-186-0.rvbd.x86_64.rpm" file; hence the update.iso file does not install that LDAP rpm when upgrading from 3.5.2 to 3.6.0 due to which LDAP authentication stops working.
This behavior is only valid when the customer upgrades from 3.5.2 to 3.6.0; however, LDAP rpm will automatically get installed if you perform a fresh install to 3.6.0.