9 Configuring and Administering Oracle Net Listener

Configuring Listening Protocol Addresses

Oracle Enterprise Manager and Oracle Net Manager can be used to configure protocol support for the listener.

The Oracle Net Listener endpoint address configuration accepts both IPv6 addresses and host names that resolve to IPv6 addresses, as explained in "IPv6 Interface and Address Configurations". This technique can create listening endpoints that service IPv6 clients.

Handling Large Volumes of Concurrent Connection Requests

If you expect the listener to handle large volumes of concurrent connection requests, then you can specify a listener queue size for its TCP/IP or IPC listening endpoints.

To specify the listener queue size, do the following:

• Specify the QUEUESIZE parameter at the end of the protocol address with its value set to the expected number of concurrent requests.

  The following example sets the queue size to 20:

  
  LISTENER=
   (DESCRIPTION=
    (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)(QUEUESIZE=20)))
  

  Note:

  The default number of concurrent connection requests is operating system-specific. The defaults for TCP/IP on the Linux operating system and Microsoft Windows follow:

  • Linux operating system: 128

  • Microsoft Windows XP Professional SP2: 10

  • Microsoft Windows 2003 Server Enterprise Edition: 200

Configuring Static Service Information

The listener uses the dynamic service information about the database and instance before using statically configured information in the listener.ora file. Configuration of static service information is necessary if you require remote database startup from a tool other than Oracle Enterprise Manager, or you have Oracle Database releases earlier than Oracle8i.

Table 9-1 describes static service settings in the listener.ora file.

To statically configure the listener, do the following:

1. Access the Net Services Administration page in Oracle Enterprise Manager.

   See Also:

   "Using Oracle Enterprise Manager to Configure Oracle Net Services"

2. Select Listeners from the Administer list, and then select the Oracle home that contains the configuration files.

3. Click Go. You may be prompted to log in to the database server.

   The Listeners page appears.

4. Select a listener, and then click Edit.

   The Edit Listener page appears.

5. Click the Static Database Registration tab, and then click Add.

   The Add Database Service page appears. Enter the required information in the fields.

6. Click OK.

   Note:

   You can also configure static service information with Oracle Net Manager. See Statically Configure Database Service Information in the online Help for additional information.

   The following example shows an excerpt of a listener.ora file statically configured for a database service called sales.us.example.com:

   SID_LIST_listener=
   (SID_LIST=
    (SID_DESC=
     (GLOBAL_DBNAME=sales.us.example.com)
     (SID_NAME=sales)
     (ORACLE_HOME=/u01/app/oracle/11g)))
   

Managing Oracle Net Listener Security

By default, Oracle Net Listener permits only local administration for security reasons. As a policy, the listener can be administered only by the user who started it. This is enforced through local operating system authentication. For example, if user1 starts the listener, then only user1 can administer it. Any other user trying to administer the listener gets an error. The super user is the only exception.

Oracle recommends that you perform listener administration in the default mode (secure by means of local operating system authentication), and access the system remotely using a remote login. Oracle Enterprise Manager can also be used for remote administration.

Setting Initialization Parameters for Service Registration

To ensure service registration works properly, the initialization parameter file should contain the following parameters:

• SERVICE_NAMES for the database service name

• INSTANCE_NAME for the instance name

• LOCAL_LISTENER for the local listener

• REMOTE_LISTENER for the remote listener, if any

For example:

SERVICE_NAMES=sales.us.example.com
INSTANCE_NAME=sales

The value for the SERVICE_NAMES parameter defaults to the global database name, a name comprising the DB_NAME and DB_DOMAIN parameters in the initialization parameter file. The value for the INSTANCE_NAME parameter defaults to the SID.

Registering Information with a Local Listener

By default, the PMON process registers service information with its local listener on the default local address of TCP/IP, port 1521. If the listener configuration is synchronized with the database configuration, then PMON can register service information with a nondefault local listener or a remote listener on another node. Synchronization occurs when the protocol address of the listener is specified in the listener.ora file and the location of the listener is specified in the initialization parameter file.

To have PMON register with a local listener that does not use TCP/IP, port 1521, configure the LOCAL_LISTENER parameter in the initialization parameter file to locate the local listener.

For a shared server environment, you can use the LISTENER attribute of the DISPATCHERS parameter in the initialization parameter file to register the dispatchers with a nondefault local listener. Because the LOCAL_LISTENER parameter and the LISTENER attribute enable PMON to register dispatcher information with the listener, it is not necessary to specify both the parameter and the attribute if the listener values are the same.

LOCAL_LISTENER is a comma-delimited list parameter. If a comma appears in the string, then the entire string must be enclosed in double quotation marks. Set the LOCAL_LISTENER parameter as follows:

ALTER SYSTEM SET LOCAL LISTENER=["]listener_address["][,...];

For example, if the listener address "ab,cd" is entered, then it resolves to one listener address. If the address is entered as ab,cd, then it resolves to two listener addresses, ab and cd.

For shared server connections, set the LISTENER attribute as follows:

ALTER SYSTEM SET DISPATCHERS="(PROTOCOL=tcp)(LISTENER=listener_address)";

In the preceding command, listener_address is resolved to the listener protocol addresses through a naming method, such as a tnsnames.ora file on the database server.

In Example 9-2, a database resides on host sales1-server. The listener on this host is named listener_sales1 and is configured to listen on port 1421 instead of port 1521.

Registering Information with a Remote Listener

A remote listener is a listener residing on one computer that redirects connections to a database instance on another computer. Remote listeners are typically used in an Oracle Real Application Clusters (Oracle RAC) environment. You can configure registration to remote listeners, such as with Oracle RAC, for dedicated or shared server environments.

In a dedicated server environment, you must enable the PMON background process to register with a remote listener. You do this by configuring the REMOTE_LISTENER parameter, which is a comma-delimited list parameter, in the initialization parameter file. The syntax of REMOTE_LISTENER is as follows:

ALTER SYSTEM SET REMOTE_LISTENER=["]listener_address["][,...];

In the preceding command, listener_address is resolved to the listener protocol addresses through a naming method such as a tnsnames.ora file on the database host. If a comma appears in the listener address, then the entire string must be enclosed in quotation marks.

In a shared server environment, you can use the same registration technique as for a dedicated server environment. Alternatively, you can set the LISTENER attribute of the DISPATCHERS parameter in the initialization parameter file to register the dispatchers with any listener. The syntax of the LISTENER attribute is as follows:

ALTER SYSTEM SET DISPATCHERS="(PROTOCOL=tcp)(LISTENER=listener_address)";

For example, assume that a remote listener named listener-sales2 listens on port 1521 on host sales2-server, and a database resides on host sales1-server. You want the listener on sales2-server to redirect connection requests to this database. Figure 9-1 illustrates this scenario.

Figure 9-1 Remote Listener

Description of "Figure 9-1 Remote Listener"

Example 9-3 shows how to register a remote listener in a dedicated server environment. In the example, the remote listener is sales2-server.

Registering Information with All Listeners in a Network

A network may contain multiple local and remote listeners. By default, all listeners are cross-registered with each other. By specifying a set of listeners in the LISTENER_NETWORKS initialization parameter, you can designate a subset of local listeners with a subset of remote listeners. Listeners specified by the LISTENER_NETWORKS parameter should not be specified by the LOCAL_LISTENER and REMOTE_LISTENER parameters.

The syntax of LISTENER_NETWORKS is as follows:

LISTENER_NETWORKS = '((NAME=network_name)
                      (LOCAL_LISTENER=["]listener_address[,...]["])
                      [(REMOTE_LISTENER=["]listener_address[,...]["])])'

In the preceding syntax, listener_address is resolved according to the rules of LOCAL_LISTENER and REMOTE_LISTENER.

LISTENER_NETWORKS = 
           '((NAME=network1) (LOCAL_LISTENER=local1) (REMOTE_LISTENER=remote1))',
           '((NAME=network2) (LOCAL_LISTENER=local2) (REMOTE_LISTENER=remote2))'

Configuring a Naming Method

The listener name alias specified for the LOCAL_LISTENER initialization parameter, REMOTE_LISTENER initialization parameter, or LISTENER attribute can be resolved through a tnsnames.ora file. A net service name entry can be created for the protocol address without the CONNECT_DATA section of the connect descriptor. Oracle Enterprise Manager and Oracle Net Manager cannot configure a tnsnames.ora file without the CONNECT_DATA information. To use listener name aliases, Oracle recommends you modify the tnsnames.ora file using a text editor.

For example, if LOCAL_LISTENER is set to listener_sales1 and listener_sales1 uses TCP/IP on port 1421, then the entry in the tnsnames.ora file would be:

listener_sales1= 
  (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1421))

Starting and Stopping a Listener

To stop or start a listener, use one of the following methods:

• Using the Listener Control Utility to Start or Stop a Listener

• Using Oracle Enterprise Manager to Start or Stop a Listener

lsnrctl START [listener_name]

lsnrctl STOP [listener_name]

Managing a Listener in an Oracle Restart Configuration

The Oracle Restart feature enhances availability for the processes and applications in a single-instance database environment. You can add selected components to the Oracle Restart configuration. The Oracle Restart agents monitor the health of added components by periodically running check operations and restarting the components when necessary.

You can add the listener as a component to the Oracle Restart configuration. The listener is automatically started by Oracle Restart when it fails or is not running. For example, if you restart the database instance after a planned restart of the computer, then Oracle Restart restarts the listener. Server Control (SRVCTL) is a command-line interface that you can use to manage listeners in an Oracle Restart configuration.

To view all configured listeners, use the following command:

srvctl config listener

Determining the Current Status of a Listener

To show the current status of a listener, use either the STATUS command of the Listener Control utility or Oracle Enterprise Manager. The status output provides basic status information about a listener, a summary of listener configuration settings, the listening protocol addresses, and a summary of services registered with the listener.

lsnrctl STATUS [listener_name]

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=net)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 11.2.0.0.2
Start Date                15-NOV-2009 20:22:00
Uptime                    0 days 0 hr. 5 min. 22 sec
Trace Level               support
Security                  OFF
SNMP                      OFF
Listener Parameter File   /oracle/admin/listener.ora
Listener Log File         /oracle/network/log/listener.log
Listener Trace File       /oracle/network/trace/listener.trc
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=net)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=1521)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcps)(HOST=sales-server)(PORT=2484)))
 
Services Summary...
Service "sales.us.example.com" has 1 instance(s).
  Instance "sales", status READY, has 3 handler(s) for this service...
Service "hr.us.example.com" has 1 instance(s).
  Instance "hr", status READY, has 2 handler(s) for this service...
The command completed successfully

Monitoring Services of a Listener

The SERVICES command of the Listener Control utility provides detailed information about the services and instances registered with a listener and the service handlers allocated to each instance. To show information about the services and instances from the command line, enter:

lsnrctl SERVICES [listener_name]

Example 9-7 shows example output of the SERVICES command.

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=net)))
Services Summary...
Service "sales.us.example.com" has 1 instance(s).
  Instance "sales", status READY, has 3 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:0 refused:0 state:ready
         LOCAL SERVER
      "D000" established:0 refused:0 current:0 max:10000 state:ready
         DISPATCHER <machine: sales-server, pid: 1689>
         (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=52414))
      "D001" established:0 refused:0 current:0 max:10000 state:ready
         DISPATCHER <machine: sales-server, pid: 1691>
         (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=52415))
Service "hr.us.example.com" has 1 instance(s).
  Instance "hr", status READY, has 2 handler(s) for this service...
    Handler(s):
      "DEDICATED" established:0 refused:0 state:ready
         LOCAL SERVER
      "D000" established:0 refused:0 current:0 max:10000 state:ready
         DISPATCHER <machine: sales-server, pid: 11326>
         (ADDRESS=(PROTOCOL=tcp)(HOST=sales-server)(PORT=58361))
The command completed successfully

This output shows that two database services, sales.us.example.com and hr.us.example.com, are registered with the listener.

Client connection requests to sales.us.example.com are handled by two dispatchers named D000 and D001 and one dedicated server. All handlers have a status of ready, indicating that they are ready to receive connections.

Client connection requests to hr.us.example.com are handled by one dispatcher named D001 and one dedicated server.

The SERVICES command generates output with the following information as described in Table 9-3.

Monitoring Listener Log Files

When you notice any of the following conditions, review the listener log file for error information:

• Long connection establishment times

• Connectivity problems and refusals

• Unexpected shutdown of the listener that could indicate a denial-of-service attack