What are the values we have provide as Primary URL and Secondry URL for manual Installation

Hi All, In my evnironment we are planning to install UD agent manually for agent based discovery. And we grouped 3 probes as a single cluster for high availability and better performance of probes. As per document we need to provide the probe IPs in Primary URL and Secondry URL while configuring the agent installation. So what is value we need to provide for Primary URL and Secondry URL fileds (Please check the screen shot for installatio page). Can we give our IP of server where cluster is configured or direct IPs of probe. What is best option to proceed. Your answers will be helpful for me. Thanks Swamy.