This is an instrument for accessibility checks, which helps to get information about current state of selected network resource.
There are three types of resource checking: ping check, route check ("traceroute") and port check.
You can add or remove elements to the main checklist (in case of "Ping" check). Then you should press 'Knock' button and wait some time. Otherwise (which means other check types), you should deal with configured single-host checks.