4 Configuring the Network Environment

Understanding Network Configuration

A client is any application that connects to Oracle Database to send or retrieve data. An Oracle Database client application can reside on any computer that has Oracle Database client software installed.

Oracle Net is a software layer that resides on the client computer and on the Oracle Database host computer. It establishes and maintains the connection between the client application and the database over a network, and exchanges messages between them using industry standard protocols.

For a client application and a database to communicate, the client application must be able to identify the database it wants to connect to, and the database must provide an identification. You can use a service name to connect to a database. A service name is a logical representation of a database, which is the way a database is presented to clients. A single database can be presented as multiple services.

Service names can provide location transparency so that the client application does not have to know the server's location. If the database is moved to another location, then you must reconfigure only Oracle Net. No changes are necessary to client applications.

This section contains these topics:

• Oracle Net Listener Configuration

• Client Connections

• Tools for Network Configuration

(DESCRIPTION=
   (ADDRESS=(PROTOCOL=tcp)(HOST=dbhost.example.com) (PORT=1521)))

(ADDRESS=(PROTOCOL=tcp)(HOST=host_name)(PORT=1521))

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

Viewing Listener Configuration

The Oracle Net listener (the listener) runs on your database host and handles incoming client requests. With Oracle Enterprise Manager Database Control (Database Control), you can view the status of the listener, which is set to start automatically whenever your host is restarted. You can also view the listener status at the command line.

To view information about the listener with Database Control:

• On the Database Home page, under the heading General, click the Listener link.

  The Listener page appears, displaying the following information about the listener:

  • Current status

  • Availability over the last 24 hours

  • Alias

  • Version

  • Oracle home for the listener

  • Net address

  • Configuration file (listener.ora) location

  • Start time

  • Host

  • (Optional) Status of Oracle Restart

To view information about the listener at the command line:

1. Open a command window.

2. Follow the steps listed in "Configuring the Operating System Environment Variables".

3. Enter the following command:

   lsnrctl status
   

Starting and Stopping the Listener

The Oracle listener is set to start automatically whenever the host is restarted. However, when your system encounters unforeseen circumstances, or when you have manually stopped the listener, you can restart it with Database Control or at the command line.

To stop the listener with Database Control:

1. On the Database Home page, under General, click the Listener link.

   The Listener page appears.

2. Click Stop.

3. Enter the host credentials, if you did not configure Preferred Credentials, then click Login.

4. On the Start/Stop Listener page, click OK to perform the specified action or Cancel to quit.

To start the listener with Database Control:

1. On the Database Home page, under the heading General, click the Listener link.

   The Listener page appears.

2. Click Start.

3. On the Start/Stop Listener page, click OK.

   After a couple of minutes, a confirmation message appears, indicating that the listener has been started.

To start or stop the listener at the command line:

1. Open a command window.

2. Follow the steps listed in "Configuring the Operating System Environment Variables".

3. Enter either of the following commands, depending on whether you want to start or stop the listener:

   lsnrctl start
   lsnrctl stop
   

Connecting to an Oracle Database from a Client Computer

This section describes how to use SQL*Plus and the easy connect naming method to connect to an Oracle database from a client computer. SQL*Plus is typically installed when you install Oracle Database client software. The easy connect naming method provides TCP/IP connectivity to databases without requiring you to configure Oracle Net Services.

You can use the instructions in this section to test your network configuration.

To connect to an Oracle database from a client computer using easy connect naming:

1. Complete the steps in "Configuring the Operating System Environment Variables".

2. Do one of the following to start SQL*Plus:

   • (UNIX, Linux, or Windows systems) Open a command window and enter the following command:

     sqlplus
     

   • (Windows systems only) Click Start, select Programs (or All Programs), then Oracle - HOME_NAME, then Application Development, and then SQL*Plus.

3. When prompted, enter the user name followed by an at sign (@) and a connect identifier, where the connect identifier has the following format:

   "host[:port][/service_name][:server][/instance_name]"
   

   The place holders used in the connect identifier format represent:

   • host — the name or IP address of the Oracle database host computer.

     Both IPv4 and IPv6 addresses are supported. IPv6 addresses must be enclosed in square brackets. See Oracle Database Net Services Administrator's Guide for information about IPv6 addressing.

   • port (optional) — the TCP port number on which the Oracle Net listener listens for connections.

     If port is excluded, then the standard port number 1521 is assumed.

   • service_name — a database service name.

     If no database service names are defined, then you can use the name of the default service that is created for the database. This service name consists of the global database name, which is made up of the DB_NAME and DB_DOMAIN initialization parameters as follows:

     DB_NAME.DB_DOMAIN
     

     If DB_DOMAIN is null, then the standard service name is just DB_NAME.

   • server — the type of service handler. Acceptable values are dedicated, shared, and pooled. If omitted, then the default type of server is chosen by the listener: shared server if configured, otherwise dedicated server.

   • instance_name — the instance to which to connect. When you specify only instance name, you connect to the default database service. If there is no default service configured in the listener.ora file, then an error is generated.You can obtain the instance name from the INSTANCE_NAME initialization parameter.

   For example, to connect as user NICK to the database service orcl.example.com on the host dbhost.example.com, enter the following at the user name prompt:

   nick@"dbhost.example.com/orcl.example.com"
   

   The following examples substitute IPv4 and IPv6 addresses for the host name:

   nick@"192.0.2.1/orcl.example.com"
   nick@"[2001:0DB8:0:0::200C:417A]/orcl.example.com"
   

4. When prompted, enter the user password.

Networking: Oracle By Example Series

Oracle By Example (OBE) has a series on the Oracle Database 2 Day DBA guide. This OBE steps you through the tasks in this chapter and includes annotated screenshots.

To view the Networking OBE, in your browser, enter the following URL:

http://www.oracle.com/technology/obe/11gr2_2day_dba/network/network.htm