Understanding Network Configuration

Oracle Net Listener Configuration

On the database server, the Oracle Net listener, commonly known as the listener, is a process that listens for client connection requests. The default listener configuration file is called listener.ora, and it is located in the ORACLE_HOME/network/admin directory. The file contains a protocol address that identifies the database. This address defines the protocol the listener is listen on and any other protocol specific information. For example, the listener could be configured to listen at the following protocol address:

(DESCRIPTION=
   (ADDRESS=(PROTOCOL=tcp)(HOST=my-server) (PORT=1521)))

This example shows a TCP/IP protocol address that specifies the host machine of the listener and a port number.

The listener.ora file is automatically configured during installation, but can be configured with Enterprise Manager. For more information, see "Viewing Listener Configuration" and "Starting and Shutting Down the Listener" .

Client Configuration

When a client requests a connection, the listener on the server brokers the request and forwards it to the Oracle database.

The client uses a connect descriptor to specify the database it wants to connect to. This connect descriptor contains a protocol and a database service name. A database can have multiple services defined, so a specific service must be specified for the connection. In a preconfigured database, there is only one service, the name of which defaults to the global database name.

The following example shows a connect descriptor that enables clients to connect to a database service called mydb.us.acme.com:

(DESCRIPTION=
   (ADDRESS=(PROTOCOL=tcp)(HOST=my-server) PORT=1521))
   (CONNECT_DATA=
      (SERVICE_NAME=mydb.us.acme.com)))

You can define your connect descriptors in your tnsnames.ora file on the client machine, located in the ORACLE_HOME/network/admin directory. You can use Oracle Net Manager to configure this file as described in "Configuring Oracle Networking on Client Machines" .

Connection Requests

Users initiate a connection request by providing a connect string. A connect string includes a username and password, and a connect identifier. This connect identifier can be the connect descriptor itself, or a name that resolves to the connect descriptor. One of the most common connect identifiers is a net service name, a simple name for a service. The following example shows a connect string that uses the net service name mydb as the connect identifier.

CONNECT hr/hr@mydb

While the connect identifier shown here is relatively simple, others can be long and inconvenient to use if your environment configuration is more complex. With long connect identifiers, you can map the net service name to the connect descriptor. This mapping information is stored in one or more repositories of information that are accessed with naming methods.

Naming Methods

Oracle Net provides support for the following naming methods:

• Local Naming

• Directory Naming

• Easy Connect Naming

• External Naming

The preconfigured database uses local naming. Only this form of naming is used in this book.

CONNECT username/password@host[:port][/service_name]

CONNECT hr/hr@my-server:1521/mydb