ion characters Character Description Synchronized to this peer Almost synchronized to this peer Peer selected for possible synchronization Peer is a candidate for selection Peer is statically configured The next column indicates the reference clock used for the listed server. This can be useful, but is usually only informative. For example, the first entry shows a reference clock of ACTS (Automated Computer Time Service). ACTS is a dial-up service from the National Institute of Standards and Technology (NIST). The second server shows a reference of GPS, indicating that it is receiving time from Global Positioning System satellites, which contain atomic clocks. The third column shows the stratum of the server listed. Servers that show stratum 16 are unavailable and are not providing time. To see whether your clock is synchronized, use the show ntp status command in IOS. This command will show you the status of NTP, including the stratum within which it is operating: R1-PBX#sho ntp stat Clock is synchronized, stratum 2, reference is 64.236.96.53 nominal freq is 250.0000 Hz, actual freq is 249.9924 Hz, precision is 2**24 reference time is D117CE2C.7FAFBB96 (14:57:32.498 EST Tue Mar 1 2011) clock offset is -4.8047 msec, root delay is 18.70 msec root dispersion is 444.19 msec, peer dispersion is 438.60 msec Chapter 38: Network Time Protocol loopfilter state is 'CTRL' (Normal Controlled Loop), drift is 0.000030117 s/s system poll interval is 64, last update was 3 sec ago. If your clock is not synchronized, the show ntp status command will explain the reasons why. In this example, I've removed all the NTP servers SO that there is no reference clock. Notice that the stratum is now 16: R1-PBX#sho ntp status Clock is unsynchronized, stratum 16, no reference clock nominal freq is 250.0000 Hz, actual freq is 249.9924 Hz, precision is 2**24 reference time is D117CB70. 76B05259 (14:45:52.463 EST Tue Mar 1 2011) clock offset is 0.0000 msec, root delay is 0.00 msec root dispersion is 0.42 msec, peer dispersion is 0.00 msec loopf