A search under
cn=monitor should do the trick, at least on iPlanet LDAP.
Don't know about the others, but I think it works the same, as long as they are truly LDAP compliant... so Active Directory is probably out of the question!!
$ ldapsearch -h 130.119.32.17 -p 391 -D "cn=directory manager" -w password -x -b cn=monitor objectclass=*
# extended LDIF
#
# LDAPv3
# base <cn=monitor> with scope sub
# filter: objectclass=*
# requesting: ALL
#
# monitor
dn: cn=monitor
objectClass: top
objectClass: extensibleObject
cn: monitor
version: iPlanet-Directory/5.1 Service Pack 2 B2003.028.2334
threads: 30
[...]
Hope it helps.
Andrea