Upon creation of a cluster there is an option to enter
network ping test ip...
This IP is used by the server to determine if the network is still available. Cluster nodes will ping this address constantly, if none of the IPs is available. The node will know that it is offline and will give its services to the online node
It is recommended to put more than just one IP.
This can be any device on your network that is constantly on, router, gateway, printer, mail server etc.. ..