Oct 132013

The Oracle WebLogic Server 12c can use either Multicast or Unicast for cluster communications. Since WebLogic version 10, the default cluster communication is the Unicast.

Configuring Unicast for cluster communications

To improve Unicast reliability it’s recommended to enable two extra configurations.

The first thing is to add a JVM argument to every WebLogic Managed Server instance of the cluster. The Administration Server must be running to make the changes. After adding the JVM argument, the config.xml configuration file must be manually edited to make the second change. Therefore you will need to make sure every WebLogic Server instance is down, including the Administration Server.

Add the JVM argument:

1. Access the Administration Console with your web browser at http://myapp01.domain.local:7001/console.

2. Click on the Lock & Edit button to start a new edit session.

3. Navigate to Configuration | Server Start by clicking on the WebLogic Server name, then on the Server Start tab.

4. Add the argument-Dweblogic.unicast.HttpPing=true to the Arguments field. The argument must be added to all Managed Server instances of MYAPPS_Cluster: MYAPPSServer01, MYAPPSServer02, MYAPPSServer03, and MYAPPSServer04. Click on the Save button for every change.

5. Click on the Activate Changes button.

6. Navigate to Domain | Control by clicking on the MYAPPS_DOMAIN link to the left and then on the Control tab.

7. Select and shut down all servers from the list.

Edit the config.xml file:

1. Log in as a wls user to the first machine prod01 and navigate to the folder:

[[email protected]]$ cd $DOMAIN_HOME/config

2. Make a backup of the config.xml file:

[[email protected]]$ cp config.xml config.xml_backup

3. Open config.xml to be edited:

[[email protected]]$ vi config.xml

4. Find the <cluster> definition tag of MYAPPS_Cluster:





5. Add the <message-ordering-enabled tag:






6. Type :wq! to save the file and exit.

7. Copy the file to all machines in the domain:

[[email protected]]$ scp config.xml [email protected]:$DOMAIN_HOME/config

8. Start the Administration Server.

The-Dweblogic.unicast.HttpPing=true argument enables an internal health check on Unicast communications that improves its reliability and The <message-ordering-enabled> tag forces Unicast communications to be processed in order, avoiding some issues with JNDI updates and JMS Topics.

Using Multicast for cluster communications


When configured for using Multicast, the Managed Servers of the cluster subscribe to a Multicast address and port and listen for heartbeats and cluster messages. Unlike Unicast, Multicast communication uses UDP and broadcasts the message through the network and therefore does not guarantee that the message is received.

To configure the Multicast communication for the cluster:

1. Access the Administration Console with your web browser at http://myapp01.domain.local:7001/console.

2. Click on the Lock & Edit button to start a new edit session.

3. Expand the Environment tree on the left and click on Clusters.

4. Click on the MYAPPS_Cluster cluster to navigate to Configuration | General and click on the Messaging tab to navigate to Configuration | Messaging.

5. Change the Messaging Mode drop-down menu to Multicast. Configure the Multicast Address value to and the Multicast Port to 7001 (as shown in the following screenshot):

Configuring Messaging Mode Weblogic

6. Click on the Save button and then on the Activate Changes button.

7. Restart all Managed Servers of the MYAPPS_Cluster cluster.

Multicast Address and Multicast Port 7001 are the default values. The range from to can be used.

Configuring Multicast using WLST

1. Log in as a wls user to shell and start WLST:

[[email protected]]$ $WL_HOME/common/bin/wlst.sh

2. Connect to the Administration Server using wlsadmin as the user, <pwd> as the password, and t3://myapp01.domain.local:7001 as the server URL:

wls:/offline> connect(“wlsadmin”,”<pwd>”,”t3://myapp01.domain.local:7001″)

3. Run the following WLST commands to create the cluster and the server instances:









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