ldapcompare on rootDSE attribute types

Hello, what would be the correct DN for a compare on rootDSE? Although the examples of the manual page seem to be quite specific, none of the following seem to be correct:

:~> ldapcompare -x -Z -H ldap://localhost:9004 "" supportedControl:1.3.6.1.4.1.42.2.27.8.5.1 Compare Result: Inappropriate matching (18) Additional info: inappropriate matching request UNDEFINED

:~> ldapcompare -x -Z -H ldap://localhost:9004 dn: supportedControl:1.3.6.1.4.1.42.2.27.8.5.1 Compare Result: Invalid DN syntax (34) Additional info: invalid DN UNDEFINED

-Dieter