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A few days ago I had ntp setup on my network, and everything was running fine. One node was set to sync with upstream servers, and the rest of the nodes from the one set to sync upstream.

Yesterday I updated from CentOS 6.4 -> 6.5 and now all of the ntp functionality has ceased to operate as expected.

In efforts of trying to debug the situation, I ran the following on the upstream server:

$ -> ntpq -pnd
::1: timed out, nothing received
***Request timed out

$ -> ntpq -4 -pnd
1 packets reassembled into response
remote           refid      st t when poll reach   delay   offset  jitter
2 packets reassembled into response
*    2 u   42   64   37   77.742  189.392  14.812
2 packets reassembled into response   .GPS.            1 u   44   64   37   73.786  216.082  18.406
2 packets reassembled into response   .GPS.            1 u   48   64   37   22.617  189.405  15.996
2 packets reassembled into response     .LOCL.          10 l  306   64   20    0.000    0.000   0.000

I get the same results (save for diff ip) on the nodes. It seems, somehow the ntp service is defaulting to ipv6, which I do not have configured. I've read some sites saying to pass -4 to the ntpd service, but how would I do that using chkconfig? Some other readings indicated that I should disable ipv6 via the kernel, but this seems like overkill.

Any suggestions?

For the sake of completeness, adding config file:

driftfile /var/lib/ntp/drift

# Permit time synchronization with our time source, but do not
# permit the source to query or modify the service on this system.
restrict default kod nomodify notrap nopeer noquery
restrict -6 default kod nomodify notrap nopeer noquery

# Permit all access over the loopback interface.  This could
# be tightened as well, but to do so would effect some of
# the administrative functions.

restrict mask nomodify notrap

server iburst



# In case net access is temporarily down
fudge stratum 10
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restrict -6 ::1? – SaveTheRbtz Jan 11 '14 at 21:18
Damn, your right that was it. Must have removed it by accident for some reason. – Mike Purcell Jan 12 '14 at 0:56
Ugh on another note. You fell victim to the worst ntp practical joke. Somewhere someone decided that it would be funny to recommend kod without limited, kod is useless without limited. wherever you see kod change it to kod limited. This has nothing to do with your problem but it is the right way to configure the default rate limiting. – dfc Jan 13 '14 at 5:52
@dfc: Duly noted, thanks for the input. – Mike Purcell Jan 13 '14 at 5:52
@dfc: Weird... I ran ntpq -pn on all the local nodes and they are all favoring the local server (, whereas they used to favor the local ntp server ( Wonder if the kod (without limited) caused the issue? Before the update I used to see chatter between the local ntp server and nodes, but now, nothing, just log entries on the nodes. – Mike Purcell Jan 13 '14 at 6:03
up vote 0 down vote accepted

Since it's trying to use IPv6 you probably want to allow it in your config file:

restrict -6 ::1
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