 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. This command will show you the status of NTP, including the stratum within which you're operating: 2950# sho ntp status Clock is synchronized, stratum 2, reference is 129.6.15.29 nominal freq is 249.5901 Hz, actual freq is 249.5791 Hz, precision is 2**18 reference time is C90B6253.35C5562A (18:08:03.210 EST Sun Nov 19 2006) clock offset is 4.3896 msec, root delay is 22.31 msec root dispersion is 13.55 msec, peer dispersion is 9.19 msec 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: 2950# sho ntp stat Clock is unsynchronized, stratum 16, no reference clock nominal freq is 249.5901 Hz, actual freq is 249.5790 Hz, precision is 2**18 reference time is C90DA30A.C8104777 (11:08:42.781 EST Tue Nov 21 2006) clock offset is 4.8738 msec, root delay is 20.45 msec root dispersion is 4.82 msec, peer dispersion is 1.25 msec Another way to show that NTP is driving the system clock is with the show clock detail command: 2950# sho clock detail .11:33:43.755 EST Tue Nov 21 2006 Time source is NTP Summer time starts 02:00:00 EST Sun Apr 1 2007 Summer time ends 02:00:00 EDT Sun Oct 28 2007 Configuring NTP NTP Server To configure an IOS device to be an NTP server, enter the command ntp master: 09(config)# ntp master When configuring an IOS device as an NTP server, it can take five minutes or more for