centos – “no server suitable for synchronization found” error when trying to run `ntpdate`

I am trying to get ntp to sychronise the time with the default server pool that is set on CentOS 6.

NTP has been stopped and started but it does not help. I have tried to force the update with the following command:

ntpdate -u pool.ntp.org

I get the follow error messages when I run the command:

17 Nov 13:40:46 ntpdate[30540]: no server suitable for synchronization found

NTP servers are reachable:

[root@GMA-DMS02-PMDS autoit]# ping pool.ntp.org
PING pool.ntp.org (162.159.200.123) 56(84) bytes of data.
64 bytes from time.cloudflare.com (162.159.200.123): icmp_seq=1 ttl=57 time=1.46 ms
64 bytes from time.cloudflare.com (162.159.200.123): icmp_seq=2 ttl=57 time=1.31 ms
64 bytes from time.cloudflare.com (162.159.200.123): icmp_seq=3 ttl=57 time=1.35 ms
64 bytes from time.cloudflare.com (162.159.200.123): icmp_seq=4 ttl=57 time=1.31 ms

NTP request does not receive a response

[root@GMA-DMS02-PMDS autoit]# ntpdate -d pool.ntp.org
17 Nov 15:05:39 ntpdate[7347]: ntpdate 4.2.6p5@1.2349-o Mon Feb  6 07:22:46 UTC 2017 (1)
Looking for host pool.ntp.org and service ntp
host found : dns.seby.io
transmit(45.76.113.31)
transmit(220.158.215.21)
transmit(203.57.115.181)
transmit(162.159.200.123)

Is it possible the ISP is blocking the response?

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