When you configure a cluster, each node will have it's own physical hostname. These hostnames must be unique to allow the nodes in the cluster to be able to internally communicate with one another. But, you will also have a cluster alias, D, which is common to all nodes of the cluster. This cluster alias is what is used to access the cluster, and what users will see as in the URL.
The property changes needed to achieve this are shown in the "Installing and Configuring a Cluster Windchill Environment" section of the Advanced Deployment Guide. You can use the below link to find the version of the guide for your Windchill version: