Any type of LDAP service, whether it is an actual server or a gateway to other LDAP services, is called an LDAP server.
You can specify multiple directory services for high-availability failover protection in libtcl*.cfg. Not every directory service in the list must be an LDAP server.
In the following example, if the connection to test:389 fails, the connection fails over to the DCE driver with the specified directory information tree (DIT) base. If this also fails, a connection to the LDAP server on huey:11389 is attempted. Different vendors employ different DIT base formats.
[DIRECTORY] ldap=libdldap.so ldap://test:389/dc=sap,dc=com dce=libddce.so ditbase=/.:/subsys/sap/dataservers ldap=libdldap.so ldap://huey:11389/dc=sap,dc=com
See the Open Client Client-Library/C Programmer’s Guide and the Open Client Client-Library/C Reference Manual.