Although the nodePolling configuration will make the hub poll the node often, the unregisterIfStillDownAfter configuration will let the hub unregister the node if the poll doesn't produce an expected result. Let's say a node is down, and the hub tries to poll the node and is unable to connect to it. At this point, how long the hub is going to poll for the availability of the node is determined by the unregisterIfStillDownAfter parameter. Beyond this time, the hub will unregister the node.

The command to do that is as follows:

java -jar selenium-server-standalone-3.12.0.jar -role node -hub http://192.168.0.1:1111/grid/register -nodePolling 5 -unregistIfStillDownAfter 20000

Here, the hub will poll the node every five seconds; if the node is down, the polling will continue for 20 seconds, that is, the hub will poll four times and then unregister the node from the grid.