deref overlay

[Chris Card <ctcard@hotmail.com>]

Hi,
I'm trying to use the deref overlay with openldap 2.4.26.
I have added this to my slapd.d config:
dn: olcOverlay={2}deref,olcDatabase={1}bdb,cn=configobjectClass: olcOverlayConfigobjectClass: olcConfigobjectClass: topolcOverlay: {2}deref
which is my guess at what the config for the deref overlay should look like, but when I try and use it with ldap search I get this:
/opt/ods/openldap/bin/ldapsearch -h localhost -x -w ***** -D "cn=admin,dc=********,dc=com" -b "dc=**********,dc=com" -E\!deref=member:mail '(objectclass=groupOfNames)'# extended LDIF## LDAPv3# base <dc=blackspider,dc=com> with scope subtree# filter: (objectclass=groupOfNames)# requesting: ALL# with dereference critical control#
# search resultsearch: 2result: 12 Critical extension is unavailabletext: critical control unavailable in context
# numResponses: 1
slapd was built with these options:
./configure --with-threads=posix \	--with-tls \	--with-cyrus-sasl \	--enable-ldap \	--enable-debug \	--prefix=%{ldapserverdir} \	--libdir=%{ldapserverdir}/%{_lib} \	--enable-spasswd \	--enable-overlays \	--enable-modules \	--enable-slapi
so I assume that slapd has the deref overlay built into it ok.
I guess my config for the deref overlay is wrong or incomplete. I looked for a slapo-deref man page, but couldn't find one.
Is there documentation of the deref overlay config anywhere?
Chris