+This mechanism allows for hierarchical directory services to be
+constructed.
+
+A referral object has a structural object class of
+{{EX:referral}} and has the same {{TERM[expand]DN}} as the
+delegated subtree. Generally, the referral object will also
+provide the auxiliary object class {{EX:extensibleObject}}.
+This allows the entry to contain appropriate {{TERM[expand]RDN}}
+values. This is best demonstrated by example.
+
+If the server {{EX:a.example.net}} holds {{EX:dc=example,dc=net}}
+and wished to delegate the subtree {{EX:ou=subtree,dc=example,dc=net}}
+to another server {{EX:b.example.net}}, the following named referral
+object would be added to {{EX:a.example.net}}:
+
+> dn: dc=subtree,dc=example,dc=net
+> objectClass: referral
+> objectClass: extensibleObject
+> dc: subtree
+> ref: ldap://b.example.net/dc=subtree,dc=example,dc=net
+
+The server uses this information to generate referrals and
+search continuations to subordinate servers.
+
+For those familiar with {{TERM:X.500}}, a {{named referral}} object is
+similar to an X.500 knowledge reference held in a {{subr}}
+{{TERM:DSE}}.
+
+
+!if 0
+H2: Immediate Superior Knowledge Information
+
+Immediate superior knowledge information may be provided in the
+entry at the root of a delegated subtree. The knowledge information
+is contained with {{EX:ref}} operational attribute.
+
+Extending the example above, a {{ref}} attribute can be added
+to the entry {{EX:dc=subtree,dc=example,dc=net}} in server B indicating
+that A holds the immediate superior naming context.
+
+> dn: dc=subtree,dc=example,dc=net
+> changetype: modify
+> add: ref
+> ref: ldap://a.example.net/
+
+The server uses this information to generate referrals to
+management operations.
+
+For those familiar with {{TERM:X.500}}, this use of the {{EX:ref}}
+attribute is similar to an X.500 knowledge reference held in a
+{{immSupr}} {{TERM:DSE}}.
+!endif
+
+
+H2: Superior Knowledge Information
+
+Superior knowledge information may be specified using the {{EX:referral}}
+directive. The value is a list of {{TERM:URI}}s referring to
+superior directory services. For servers without immediate superiors,
+such as for {{EX:a.example.net}} in the example above, the server
+can be configured to use a directory service with {{global knowledge}},
+such as the {{OpenLDAP Root Service}}
+({{URL:http://www.openldap.org/faq/index.cgi?file=393}}).
+
+> referral ldap://root.openldap.org/
+
+However, as {{EX:a.example.net}} is the {{immediate superior}}
+to {{EX:b.example.net}}, {{b.example.net}} would be configured
+as follows:
+
+> referral ldap://a.example.net/
+
+The server uses this information to generate referrals for operations
+acting upon entries not within or subordinate to any of the naming
+contexts held by the server.
+
+For those familiar with {{TERM:X.500}}, this use of the {{EX:ref}}
+attribute is similar to an X.500 knowledge reference held in a
+{{Supr}} {{TERM:DSE}}.
+
+
+H2: The ManageDsaIT Control
+
+Adding, modifying, and deleting referral objects is generally done
+using {{ldapmodify}}(1) or similar tools which support the ManageDsaIT
+control. The ManageDsaIT control informs the server that you intend
+to manage the referral object as a regular entry. This keeps the
+server from sending a referral result for requests which interrogate
+or update referral objects.
+
+The ManageDsaIT control should not be specified when managing regular
+entries.