You can specify a connect identifier in the connect string when you start the Data Pump Export utility. This identifier can specify a database instance that is different from the current instance identified by the current Oracle System ID (SID). The connect identifier can be an Oracle*Net connect descriptor or a net service name (usually defined in the tnsnames.ora file) that maps to a connect descriptor. Use of a connect identifier requires that you have Oracle Net Listener running (to start the default listener, enter lsnrctl start). The following is an example of this type of connection, in which inst1 is the connect identifier:
expdp hr@inst1 DIRECTORY=dpump_dir1 DUMPFILE=hr.dmp TABLES=employees
Export then prompts you for a password:
Password: password
The local Export client connects to the database instance defined by the connect identifier inst1 (a net service name), retrieves data from inst1, and writes it to the dump file hr.dmp on inst1.
Specifying a connect identifier when you start the Export utility is different from performing an export operation using the NETWORK_LINK parameter. When you start an export operation and specify a connect identifier, the local Export client connects to the database instance identified by the connect identifier, retrieves data from that database instance, and writes it to a dump file set on that database instance. Whereas, when you perform an export using the NETWORK_LINK parameter, the export is performed using a database link. (A database link is a connection between two physical database servers that allows a client to access them as one logical database.)
Oracle Database Administrator's Guide for more information about database links
Oracle Database Net Services Administrator's Guide for more information about connect identifiers and Oracle Net Listener