By default NTP port 123 listen on any ip address.
NTP should listen on configured addresses only.
If there is no configuration, by default only need to listen to 127.0.0.1 and :: 1
[email protected]:~$ sudo netstat -tulpn | grep 123 udp 0 0 192.168.255.100:123 0.0.0.0:* 1435/ntpd udp 0 0 192.168.122.14:123 0.0.0.0:* 1435/ntpd udp 0 0 127.0.0.1:123 0.0.0.0:* 1435/ntpd udp 0 0 0.0.0.0:123 0.0.0.0:* 1435/ntpd udp6 0 0 2001:db8::dead:123 :::* 1435/ntpd udp6 0 0 fe80::5054:ff:febd::123 :::* 1435/ntpd udp6 0 0 fe80::2cf1:c0ff:fea:123 :::* 1435/ntpd udp6 0 0 fe80::5054:ff:fe52::123 :::* 1435/ntpd udp6 0 0 fe80::5054:ff:fea0::123 :::* 1435/ntpd udp6 0 0 ::1:123 :::* 1435/ntpd udp6 0 0 :::123 :::* 1435/ntpd [email protected]:~$