We have touched on referrals throughout the book. Referrals are defined in the Internet Draft "draft-ietf-ldapext-namedref-00.txt" or a successor to it. An LDAP server may return one or more referrals in the form of LDAP URLs to a client in two cases: (1) one or more of the entries that would be referenced by an operation have the referral object class and a ref attribute that contains one or more LDAP URLs, or (2) the base DN of the operation falls outside of any naming context managed by the server. The former type of referral is called a named reference; the latter is a superior reference. The Java LDAP SDK generally treats the two types the same.