During recent CU4 upgrades we wanted to validate connectivity to the systems during the agent installation process. This is really useful especially when looking for potential reboots (as discussed here) which may occur during CU4 deployments. I ran across the following tool (NirSoft PingInfoView) which was quick to download and worked well for this purpose! Just cut and paste the list of systems you are working with into OpsMgr into the tool prior to application of CU4 to identify any potential connectivity loss.