No matter what I do, my server can't synchronize with NTP

08 Sep 2015

So I have a RHEL 6 server configured with the correct NTP server. Correct? At least that is I what thought. But it will not sync with the NTP server. I can ping the NTP server, I can connect to it using nc to UDP port 123. I have restarted ntpd a couple of times and it still won’t work. What the hell is wrong?

Ping ntp server? Yes. nc -vzu ntp.example.com 123? yes

nc -vzu ntp.example.com 123
Connection to ntp.example.com 123 port [udp/ntp] succeeded!

Tried force sync using ntpdate? Checked

ntpdate -d  ntp.example.com
20 Aug 20:56:14 ntpdate[11025]: ntpdate 4.2.6p5@1.2349-o Mon Mar  9 14:24:09 UTC 2015 (1)
Looking for host ntp.example.com and service ntp
host found : ns1.cat.com
 transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
192.168.1.50: Server dropped: no data
server 192.168.1.50, port 123
stratum 0, precision 0, leap 00, trust 000
refid [192.168.1.50], delay 0.00000, dispersion 64.00000
transmitted 4, in filter 4
reference time:    00000000.00000000  Mon, Jan  1 1900  6:55:25.000
originate timestamp: 00000000.00000000  Mon, Jan  1 1900  6:55:25.000
transmit timestamp:  d9804cf2.19367c4f  Thu, Aug 20 2015 20:56:18.098
filter delay:  0.00000  0.00000  0.00000  0.00000
     0.00000  0.00000  0.00000  0.00000
filter offset: 0.000000 0.000000 0.000000 0.000000
     0.000000 0.000000 0.000000 0.000000
delay 0.00000, dispersion 64.00000
offset 0.000000

20 Aug 20:56:19 ntpdate[11025]: no server suitable for synchronization found

The answer to the problem lies in this part of the output

transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
transmit(192.168.1.50)
192.168.1.50: Server dropped: no data

I found a Red Hat KB article which says “Server dropped: no data” indicates a problem. Besides, my server is transmitting- “transmit(192.168.1.50” but it is not receiving. On a working server, running the same command, this is what I get. Note that it is sending and receiving.

ntpdate -d ntp1.corp.cat.com
4 Sep 01:08:52 ntpdate[23977]: ntpdate 4.2.6p5@1.2349-o Mon Mar  9 14:24:09 UTC 2015 (1)
Looking for host ntp1.corp.cat.com and service ntp
host found : ntp.corp.cat.com
transmit(192.168.1.50)
receive(192.168.1.50)
transmit(192.168.1.50)
receive(192.168.1.50)
transmit(192.168.1.50)
receive(192.168.1.50)
transmit(192.168.1.50)
receive(192.168.1.50)
server 192.168.1.50, port 123
stratum 4, precision -24, leap 00, trust 000
refid [192.168.1.50], delay 0.02588, dispersion 0.00000
transmitted 4, in filter 4
reference time:    d993b3c7.b3909a66  Fri, Sep  4 2015  1:08:07.701
originate timestamp: d993b3f5.0af26a1f  Fri, Sep  4 2015  1:08:53.042
transmit timestamp:  d993b3f5.0ac72c86  Fri, Sep  4 2015  1:08:53.042
filter delay:  0.02592  0.02600  0.02591  0.02588
     0.00000  0.00000  0.00000  0.00000
filter offset: 0.000535 0.000465 0.000516 0.000521
     0.000000 0.000000 0.000000 0.000000
delay 0.02588, dispersion 0.00000
offset 0.000521

4 Sep 01:08:53 ntpdate[23977]: adjust time server 192.168.1.50 offset 0.000521 sec

After talking to team managing NTP, the server is configured with the wrong NTP server. After replacing it with the right NTP server, I am back in business.