Selecting a stack when running multiple instances of TCP/IP

Socket application programs in a multi-stack (CINET) environment must contend with the following questions:

• How the socket program selects which TCP/IP stack to use for its socket communication
• How the TCP/IP resolver code executing in the socket application address space decides which TCP/IP resolver configuration data sets to allocate
  Note: If a resolver GLOBALTCPIPDATA setup file is used, a local TCPIP.DATA cannot override any explicit statements in the global file and cannot override any resolver statements. Therefore, in a CINET environment, the TCPIPJOBNAME statement should not be specified in the GLOBALTCPIPDATA file. Also, using the GLOBALTCPIPDATA file with CINET requires that the resolver TCPIP.DATA statements are able to be used by all stacks. For example, the IP addresses specified by the NameServer statement must be accessible from all stacks. If they are not, then the GLOBALTCPIPDATA file should not be used and you should continue with multiple TCPIP.DATA data sets. For details, see The resolver.

To answer these questions, a distinction must be made between standard servers and clients (those that come with the z/OS® Communications Server product), and other socket application programs, including those you might have written yourself.