Testing commands with loopback

In order to test your local machine, an address is reserved that always refers to your local host rather than any other hosts on a network. For IPv4, this class A network address is 127.0.0.1. For IPv6, the reserved loopback address is ::1. You can also specify loopback as the host name. Not all commands and clients shipped with z/OS® Communications Server V2R1 support IPv6 addresses or hostnames that resolve to IPv6 addresses.

You can use the loopback address with any TCP⁄IP command that accepts IP addresses. When you issue a command with the loopback address, the command is sent out from your local host’s client and continues until it reaches the IP layer on your local host. The command is then sent on to your local host’s server.

Note: Any command or data that you send using the loopback address never actually goes out on any network.

You can also use a nonloopback local IP address for testing. It can be any local IP address assigned to a device, even though the device may not be active, but cannot be a multicast or broadcast address. The nonloopback address provides a faster response but may not reach the IP layer on your host.

The loopback address is commonly used as the first step in diagnosing network problems. The information you receive indicates the state of your system and checks to ensure that the client and server code for the function you are testing is operating properly. You should see the same response as for a normal, successful command. If the client or server code is not operating properly, the same message that would be returned for an unsuccessful command is returned.