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(DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST =)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = finance.world) ) ) salesprod = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST =)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = salesprod.world) ) ) custprod = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = custprod)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME = custprod.world) ) ) Three databases are listed in the tnsnames.ora file in Listing 10-6, and all three have different features that distinguish them. The first entry is for the finance database, which is on the desktop computer, NTL-ALAPATISAM. The salesprod database is located on the UNIX server, whose IP address is 172.11.150.1, and Oracle Net can connect to it using port 1521 and the TCP protocol. The last database uses a symbolic name, custprod, instead of the IP address, to denote the host server. If you were to add a fourth database, orderprod, located on the host with IP address 172.16.11.151, to this tnsnames.ora file, you would need to add the appropriate connect identifier to the tnsnames.ora file, as shown here: orderprod = (DESCRIPTION = (ADDRESS_LIST = (ADDRESS = (PROTOCOL = TCP)(HOST = 172.16.11.151)(PORT = 1521)) ) (CONNECT_DATA = (SERVICE_NAME =orderprod.world) ) Once you configure a net service name and modify the tnsnames.ora file, here s how you connect to the database: 1. Distribute the new service name configuration to your clients. You may do so by copying the tnsnames.ora and sqlnet.ora files to your clients, who must have the Oracle Client software installed. Alternatively, you can use the Oracle Net8 Assistant or Net8 Configuration Assistant to configure the net service names on the client itself. 2. Make sure the listener on the server where the database is running is started. Check that the listener is using the same protocol and address as that you configured for the net service name in the tnsnames.ora file. Also make sure that the listener is using the TCP/IP protocol and is listening on the default port 1521.

3. Make sure that the target database you re trying to connect to is running. 4. Test the new connection by using the following syntax: CONNECT username/password@net_service_name Although local naming is quite easy to implement, it is a cumbersome method to use if you have a large number of client installations that need to access the database server directly because you need to maintain a local copy of the tnsnames.ora file on all your local clients. Furthermore, when you change hosts or add databases to your system, you need to ensure that you make the changes in all your client tnsnames.ora files. Of course, if you have a small client base, the maintenance of the tnsnames.ora files shouldn t be a problem.

I prefer using the Oracle Net Configuration Assistant (NCA) to add a new service to my tnsnames.ora file, rather than manually adding it to the file. Like the listener.ora file, the tnsnames.ora file is somewhat tricky, with all its parentheses, and it s easy to make a mistake when you re manually editing it. Creating new services using the GUI is very easy, with the NCA prompting you for the server name, database name, network address, and protocol type. Once you re done configuring the connection, there will be a new or updated tnsnames.ora file in the default location that includes the database services you just added. To use the NCA, you must first install the Oracle Client software on the client machine by using the Oracle Client CD. The NCA comes bundled with both the server and the client versions of the software. You can create a connection and test it, all in under a minute. Here are the steps involved in using the NCA to configure a new service name in your tnsnames.ora file: 1. Start the Oracle Net Configuration Assistant on a UNIX/Linux server with the netca command, as shown here: $ export DISPLAY=172.16.14.15:0.0 $ netca