Your system TCP/IP configuration may be a single or multiple stack configuration. You might want to run multiple TCP/IP stacks on the same system to provide network isolation for one or more of your applications. For instance, you may have multiple OSA Features, each one connecting your system to a different network. You can assign a TCP/IP stack to each one. Common INET (CINET) is used in a multiple IP stack configuration. See IBM z/OS Communications Server: IP Configuration Guide and IBM z/OS Communications Server: IP Configuration Reference for more information on how to configure your system for multiple IP stacks.
If your system is configured with multiple IP stacks, you must decide whether WebSphere Application Server will listen on sockets served by all the stacks or by only one. You can force WebSphere Application Server to listen on only a single IP stack by using the _BPXK_SETIBMOPT_TRANSPORT environment variable. The setting for this variable is described in the IBM z/OS Communications Server: IP Configuration Guide. In your configuration, this variable is set through a WebSphere Managed Variable. You can set this variable through the administrative console by clicking Environment > WebSphere Managed Variables and following the steps for adding a new variable. Since WebSphere Managed Variables can be specified at cell, node, and server scope, take care in choosing the scope at which you want this variable set. In general, you will set this variable at node scope.
Depending on your configuration objectives, when you restrict WebSphere Application Server to using only a single IP stack, you may also want to direct WebSphere Application Server to use a resolver configuration tailored for use with the specified stack. This might involve setting the RESOLVER_CONFIG environment variable. This variable can also be set as a WebSphere Managed Variable. There are many options for configuring your TCP/IP resolver, and using this environment variable is just one of them. The Understanding Resolvers section in IBM z/OS Communications Server: IP Configuration Guide can help you decide which resolver configuration is right for you.