確認したところ：
# $OpenBSD: ntpd.conf,v 1.16 2019/11/06 19:04:12 deraadt Exp $
#
# See ntpd.conf(5) and /etc/examples/ntpd.conf

servers pool.ntp.org
server time.cloudflare.com
sensor *

constraint from "9.9.9.9" # quad9 v4 without DNS
constraint from "2620:fe::fe" # quad9 v6 without DNS
constraints from "www.google.com" # intentionally not 8.8.8.8

悪ばかりだ