A WebLogic cluster is a collection of WebLogic Server instances that work together to provide a reliable, scalable environment for your applications. WebLogic Server clusters increase reliability by supporting failover; WebLogic automatically switchs requests and processing to a redundant server upon the failure or abnormal termination of the currently-active server. A WebLogic cluster always contains one Administration Server that handles all the administrative duties like, for example, deploying applications and configuring your cluster. You do not deploy applications on the Administration Server, you deploy applications to the Managed Servers that make up the cluster.
Troubleshooting:
Your cluster should not share its multicast port with other applications on your network. If it does, conflicts can result, and you will have problems starting Managed Servers in the cluster, binding objects to the cluster wide JNDI tree, and deploying applications to the cluster. An error like the following in your managed server log is due to a conflicting multicast port/address.
