Updating NTP Servers on Cisco Switches

Wanted to briefly write a note for updating the NTP server on a Cisco switch. This is generally good if moving to on premise NTP servers is something I’d like to do someday.

Currently this is the configuration for the NTP server in the configuration.

!
ntp server 192.168.0.200
!

Login to the switch and go into the configuration prompt.

configure terminal

Remove the NTP server configuration from the switch. In this case it’s pointing to the IP address 192.168.0.200. This will need to be removed so the switch doesn’t have any old configuration.

no ntp server 192.168.0.200

Then configure the NTP server to point to the new one.

ntp server 192.168.1.200

One good way to know that this works is by checking the NTP associations using the appropriate show command.

show ntp associations

Below we should see the available configuration and the delay of the time server. If there is a ref clock available and the time is correct. There is a good chance the time is synced.

  address           ref clock        st   when   poll reach  delay offset  disp
*~192.168.1.200     10.50.38.170     2    973   1024   377  0.846   0.624 0.050
 * sys.peer, # selected, + candidate, - outlyer, x falseticker, ~configured

Another method to test is using the show ntp status command. This will for sure tell you if the clock is synced.

show ntp status