Interconnectivity between network hosts encompasses the physical layer or hardware layer, the protocols such as TCP and IP, the IP security services, and the applications that use the services of TCP and IP. To understand interconnectivity, you should first understand internetworking. For detailed information about internetworking, see Overview of internetworking.

Isolating network problems is an essential step in successful implementation of a network application. This topic introduces commands and techniques you can use to diagnose network connectivity problems.

Netstat reports are also available from the console environment by invoking the DISPLAY TCPIP,,NETSTAT command. For complete descriptions of these commands and examples of their output, see z/OS Communications Server: IP System Administrator's Commands.

When referring to these commands and their options throughout this section, both the TSO and z/OS® UNIX shell command options are listed, separated by a slash. For example, the recommendation to use Netstat to view the stack's HOME list of IP addresses appears as "use Netstat HOME/-h."

MVS-style data sets are written in capital letters (for example, hlq.TCPIP.DATA). Files names in the z/OS UNIX file system are written in lowercase (for example, /etc/hosts).