Public NTP Servers by IP

Some network device vendors (think “Cisco”) recommend configuration without DNS lookup abilities. This improves the performance of the device and removes any reliance on DNS services by your router, firewall, switch, etc.

The absence of DNS lookup abilities can add new difficulty when trying to reference servers that are normally reached by name. In the case of NTP servers, the US NIST organization maintains a good list of publicly accessible time servers referenced by both name and IP. You can find the list at

NTP is an important service to have working for many reasons. The ones that immediately come to mind include: accurate date/time stamps for log entries (very useful for troubleshooting), and synchronization for time-sensitive services like IPSec or Kerberos.

Cisco IOS NTP Commands

Here are some basic Cisco IOS commands for changing and viewing your NTP configuration. It is probably best to use either NTP or SNTP, but not both.

  • ntp server IP.ADD.RE.SS
  • ntp update-calendar
  • show ntp status
  • show ntp associations
  • sntp server IP.ADD.RE.SS
  • show sntp
  • show clock
  • show run | include ntp

About notesbytom

Keeping technology notes on to free up my mind to solve new problems rather than figuring out the same ones repeatedly :-).
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