From ESXi ssh or shell -> nc -uz <VC FQDN/IP> port -> to test the udp 902 connectivity test to vcenter
From vCenter -> you can check using telnet
for VCSA shell or ssh -> curl -v telnet <ESXi host IP/FQDN>:port - This can only be valid for TCP 902 and for udp, you need to do packet capture.
Another quick help is if the ESXi host disconnects from vCenter every 60 seconds- high chances of 902 udp blocked
Thanks,
MS