1. Server chaining feature in OID is introduced in version 10.1.4.0.1
2. You use server chaining feature to map user/group/entries sitting in third party LDAP directory (AD, iPlanet) and access them through OID. This way you can avoid synchronization of entry (identity data) between OID and third party LDAP Server.
3. Currently (as of version 10.1.4.0.1) only Microsoft Active Directory & Sun iPlanet are supported for OID server chaining (as shown in figure above)
4. Currently only bind, compare(only for userpasswd attribute), modify and search ldap operation are supported
5. You can configure server chaining either from command line (ldap commands) or using OIDADMIN (gui tool to administer OID)
6. If attribute name in OID is same as attribute name in third party ldap server (iPlanet, AD) then mapping is not required (some attributes are mapped by default – orclguid, krbprincipalname)
7. Operation attributes, objects classes and OID specific attributes (starting with orcl) cannot be mapped using server chaining framework
OID Server Chaining guide from Oracle