NTP não está sincronizando com um servidor de horário externo

Question

Estou tentando sincronizar com um NTP externo ( pool.ntp.org ), mas o servidor está respondendo com esta mensagem:

Esta é a captura do Wireshark.

Network Time Protocol (NTP Version 3, client)
Flags: 0xdb, Leap Indicator: unknown (clock unsynchronized), Version number: NTP Version 3, Mode: client
Peer Clock Stratum: unspecified or invalid (0)
Peer Polling Interval: 17 (131072 sec)
Peer Clock Precision: 0.000000 sec
Root Delay: 0 seconds
Root Dispersion: 1 second
Reference ID: NULL
Reference Timestamp: Jul 30, 2018 11:59:46.359342699 UTC
Origin Timestamp: Jan  1, 1970 00:00:00.000000000 UTC
Receive Timestamp: Jan  1, 1970 00:00:00.000000000 UTC
Transmit Timestamp: Jul 30, 2018 12:09:19.234343299 UTC