OpenLDAP 2.0.x
root DSE (DSA-Specific Entry)

DSAのroot (basedn が '')には特殊なエントリがある → rootDSE
  % ldapsearch -x -b '' -s base '(objectclass=*)' '+' '*'
   dn:
   objectClass: top
   objectClass: OpenLDAProotDSE
   namingContexts: dc=example,dc=com
   supportedControl: 2.16.840.1.113730.3.4.2
   supportedExtension: 1.3.6.1.4.1.4203.1.11.1
   supportedExtension: 1.3.6.1.4.1.1466.20037
   supportedLDAPVersion: 2
   supportedLDAPVersion: 3
   supportedSASLMechanisms: DIGEST-MD5
   supportedSASLMechanisms: CRAM-MD5
   ref: ldap://root.openldap.org/
   subschemaSubentry: cn=Subschema

  Note: 
    '*' → all user attributes
    '+' → all operational attributes