Fresh installation of ntp v4 on redhat 8.
Ntpd and ntpdate will not communicate with any ntp server, giving a "no server suitable for synchronization found" message.
However, doing ntpdate -d 184.108.40.206 (for instance) works fine.
It turns out I need to use an unprivileged port with the -u option. The -d option automatically does this. So this will work:
ntpdate -u 220.127.116.11
Somewhere in my setup here port 123 is a problem. But no matter, just run ntpdate from crontab once a day (rather than ntpd) and all will be well.