As part of setting up an ntp client it is a good idea to confirm what peers the system is synchronizing time with. To list peers you use the following command:
ntpq -pn
remote refid st t when poll reach delay offset jitter
==============================================================================
*10.1.1.1 108.61.73.243 2 u 911 1024 377 2.021 -1.184 1.537
Some times, however, the command is not able find the peers. This happens when IPv6 is enabled on the client. The error you will get will look like this:
$ ntpq -np
::1: timed out, nothing received
***Request timed out
In my case, since I'm not using IPv6, the issue was fixed by disabling IPv6 using the instructions here: Disable IPv6 in CentOS 6.6