Minha configuração do openntp é assim:
servers pool.ntp.org
sensor *
constraints from "https://www.google.com"
Estou vendo as seguintes mensagens:
constraint request to 2607:f8b0:4007:80b::2004
tls connect failed: 2607:f8b0:4007:80b::2004 (www.google.com): connect: Network is unreachable
no constraint reply from 2607:f8b0:4007:80b::2004 received in time, next query 900s
reply from 198.98.57.16: constraint check failed
reply from 35.171.237.77: constraint check failed
reply from 209.141.60.238: constraint check failed
reply from 104.238.179.228: constraint check failed