Directory Server - RFC 2891 Server Side Sorting

[halll7]

I'm performing searches on Directory Server using java and JNDI. I'm trying to use server-side sorting as described in RFC 2891. JNDI supports this through the SortControls class, eg:

final SortControl reqControls = new SortControl("cn", Control.CRITICAL);        
final LdapContext initCtx = new InitialLdapContext(env, new Control[]{reqControls});

I'm finding that the second line here causes an exception:

javax.naming.OperationNotSupportedException: [LDAP: error code 12 - Unavailable Critical Extension]

And in the server's access log I get this:

[26/Jan/2009:11:31:51 +0000] conn=44 op=0 BIND dn="cn=Directory Manager" method=128 version=3, failed to parse LDAP controls
[26/Jan/2009:11:31:51 +0000] conn=44 op=0 RESULT err=12 tag=97 nentries=0 etime=0

My question is, do I need to configure a particular extension, or does Directory Server simply not support RFC 2891?

[halll7]

After further investigation, I have found that the SortControl only works when used in conjunction with the VirtualListViewControl (part of Sun's JNDI booster pack, not in core JDK). I can find nothing in the FedoraDS documentation that says they have to be used together, but I thought this might be useful info to someone hitting the same problem as me.