Replication Agent for Oracle uses JDBC™ for communications with all replication system components.
The Oracle JDBC driver must be installed on the Replication Agent host machine, and the directory this driver is installed in must be in the CLASSPATH environment variable.
The TNS Listener Service must be installed and running on the primary database so the Replication Agent instance can connect to it. See the Oracle Database Net Services Administrator's Guide. See the Replication Agent Installation Guide for the specific JDBC driver and version to install.