When you change something in your network configuration, rather than its the gateway or the IP addressing, you may come under serious troubleshooting on your Proxmox Cluster, so this document will guide you into the necessary steps needed to update your network settings on Proxmox.
Note : You must follow these steps on every single node of your cluster to let it able to handle the synchronization between each node once.
So firstly, you will need to change the network interface configuration of the system; it is preferable for you to set a static IP:
/etc/network/interfaces