Check the NTP Peers

Purpose

Ensure that the clock time on the router is synchronized with the time on the NTP server.

Action

To check NTP peers, enter the following JUNOS CLI operational mode command:

user@host> show ntp associations

Sample Output 1

user@host> show ntp associations 

     remote           refid      st t when poll reach   delay   offset  jitter

==============================================================================

*coetanian.junip .GPS.            1 u   22   64  377    6.861   -1.297   0.811

Sample Output 2

user@jhost> show ntp associations

>      remote           refid      st t when poll reach   delay   offset  jitter

> ==============================================================================

>  ntp1.usno.navy. PSC.            1 -   44   64   77   86.829  -1830.3 915.177

>  Tick.UH.EDU     USNO.           1 -   36   64   77   42.560  -1835.3 917.667

What It Means

Sample output 1 is synchronized with the NTP server because there is an asterisk (*) at the beginning of the output. Also, the router with the asterisk (*) is the master router and the system is synchronizing with this NTP server.

Sample output 2 shows that the time on the server and router is so far apart that NTP will not attempt to synchronize. The offset value of 1830 is too large a difference and the jitter value of 917.667 is also too large to provide reliability to the offset value.

As a general rule, if the time difference between the server and the router is less than 100 seconds, NTP adjusts the router's clock speed so that it drifts towards the server's time. For instance, if the router clock is running fast, NTP slows the clock down so that the time of day only advances 900 milliseconds every time the server's clock advances a full second. The time on the two clocks gradually becomes identical. When the clock time is the same, NTP adjusts the clock on the router to keep in step with the server's time.

For more detailed information on configuring the NTP server, see the JUNOS System Basics Configuration Guide.