You want to log significant NTP events.
Use the ntp logging command to enable the logging of NTP events:
Router2#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router2(config)#ntp logging Router2(config)#end Router2#
Starting in IOS Version 12.3(7)T, Cisco added the NTP logging feature. By implementing this feature, the router will log significant NTP events such as peer loss, peer reachability, and clock synchronization events.
To view the NTP logging events on the router, use the following command:
Router2#show logging | include NTP 000019: Jan 29 10:57:52.633 EST: %NTP-5-PEERSYNC: NTP synced to peer 172.25.1.5 000020: Jan 29 10:57:52.637 EST: %NTP-6-PEERREACH: Peer 172.25.1.5 is reachable 000023: Jan 29 10:57:53.635 EST: %NTP-6-PEERREACH: Peer 172.25.1.3 is reachable 000024: Jan 29 11:01:20.653 EST: %NTP-4-PEERUNREACH: Peer 172.25.1.5 is unreachable 000026: Jan 29 11:15:11.985 EST: %NTP-4-UNSYNC: NTP sync is lost Router2#
In this example, we can see that the router initially synchronized its time to server 172.25.1.5 before the server became unreachable, causing the router to lose synchronization. This kind of forensic information can assist you in investigating NTP issues.