Cluster without Virtual IP setup

Hi,

I have looked into my work VCS environment. Some VCS cluster nodes got VIP setup so I know when one of the node failed or exit, the virtual IP will failover to another node so that the client connection will still be connected to the service. However, I do see some two node clusters which do not have the VIP setup and the service group are both showing online each node. How does this failover happends in this situation?

Thanks