A referral is a redirection mechanism that tells client applications that a requested entry or set of entries is not present on the Directory Server but can be accessed on another server. Referrals can be used when entries are located on another server. The Directory Server implements two types of referrals depending on the requirement.
- Referral on Update plugin. The Directory Server provides a Referral on Update plugin to create any referrals for update requests (add, delete, modify, or modDN operations) on read-only servers. For example, given two replicated directory servers where one server is a master (read-write) and the other, a read-only server, you can configure a referral for any client update requests on the second directory server to point to the master server. If a client application sends an add request, for example, on the second directory server, the directory server responds with a referral that indicates any updates should be made on the master server. All read requests on the read-only server will be processed as normal.
- Smart Referrals. The Directory Server supports smart referrals that map an entry or a specific branch of a DIT to an LDAP URL. Any client requests (reads or writes) targeting at or below the branch of the DIT will send a referral to the server designated in the LDAP URL.