Before starting a VMware Cloud Foundation upgrade, read the documents mentioned here.
Before beginning the upgrade, check the release notes. Known upgrade issues and workarounds are documented in the VMware Cloud Foundation Release Notes. Reading the upgrade issues before you begin the upgrade process can save you time and effort. See https://docs.vmware.com/en/VMware-Cloud-Foundation/index.html.
Ports and Protocols
Review the information on VMware Ports and Protocols to ensure that the required ports are open before you begin an upgrade.