The ipa-server-install and ipa-replica-install commands replace the list of NTP servers in the /etc/ntp.conf file with Red Hat Enterprise Linux default servers. As a consequence, NTP servers configured before installing IPA are not contacted, and servers from rhel.pool.ntp.org are contacted instead. If those default servers are unreachable, the IPA server does not synchronize its time via NTP. To work around this problem, add any custom NTP servers to /etc/ntp.conf, and remove the default Red Hat Enterprise Linux servers if required. The configured servers are now used for time synchronization after restarting the NTP service by running the systemctl restart ntpd.service command.