DNS Names or IP Addresses? Consider the purpose of the cluster when When Internal and External DNS Names Vary If the internal and external DNS Localhost Considerations If you identify a server instances listen address as

Setting up WebLogic Clusters 10-3 at http:support.microsoft.comdefault.aspx?scid=kb;en-us;239924 .

10.1.5 Identify Names and Addresses

During the cluster configuration process, you supply addressing information—IP addresses or DNS names, and port numbers—for the server instances in the cluster. For information on intra-cluster communication, and how it enables load balancing and failover, see Section 3.1, WebLogic Server Communication In a Cluster. When you set up your cluster, you must provide location information for: ■ Administration Server ■ Managed Servers ■ Multicast location Read the sections that follow for an explanation of the information you must provide, and factors that influence the method you use to identify resources.

10.1.5.1 Avoiding Listen Address Problems

As you configure a cluster, you can specify address information using either IP addresses or DNS names. 10.1.5.1.1 DNS Names or IP Addresses? Consider the purpose of the cluster when deciding whether to use DNS names or IP addresses. For production environments, the use of DNS names is generally recommended. The use of IP addresses can result in translation errors if: ■ Clients will connect to the cluster through a firewall, or ■ You have a firewall between the presentation and object tiers, for example, you have a servlet cluster and EJB cluster with a firewall in between, as described in the recommended multi-tier cluster. You can avoid translation errors by binding the address of an individual server instance to a DNS name. Make sure that a server instances DNS name is identical on each side of firewalls in your environment, and do not use a DNS name that is also the name of an NT system on your network. For more information about using DNS names instead of IP addresses, see Section 11.7.3, Firewall Considerations.

10.1.5.1.2 When Internal and External DNS Names Vary If the internal and external DNS

names of a WebLogic Server instance are not identical, use the ExternalDNSName attribute for the server instance to define the servers external DNS name. Outside the firewall the ExternalDNSName should translate to external IP address of the server. If clients are accessing WebLogic Server over the default channel and T3, do not set the ExternalDNSName attribute, even if the internal and external DNS names of a WebLogic Server instance are not identical.

10.1.5.1.3 Localhost Considerations If you identify a server instances listen address as

localhost, non-local processes will not be able to connect to the server instance. Only processes on the machine that hosts the server instance will be able to connect to the server instance. If the server instance must be accessible as localhost for instance, if you have administrative scripts that connect to localhost, and must also be accessible by remote processes, leave the listen address blank. The server instance will determine the address of the machine and listen on it. 10-4 Using Clusters for Oracle WebLogic Server

10.1.5.2 Assigning Names to WebLogic Server Resources