Timestamps are useful for viewing when certain events happen on a router. Timestanps are also helpful for troubleshooting, because they allow the network administrator to compare simultaneous events on network routers and analyze whether one occurrence caused, or was a result of, another.
If a router is configured to get the time from a Network Time Protocol (NTP) server, the times in the router's log entries may be different from the time on the system clock if the [localtime] option is not in the service timestamps log command. In the example below, the router gets its time from an NTP server and theservice timestamps log datetime command is issued. The show clock command displays a time of 14:12:26, yet when a configuration change is made immediately after the show clock command, the log message shows a time of 21:12:28, as shown in this example:
clock timezone PST -8
clock summer-time PDT recurring
service timestamps debug datetime
service timestamps log datetime
logging buffered 16000 debugging
ntp clock-period 17179272
ntp server 184.108.40.206
router#show clock14:12:26.312 PDT Thu Apr 27 2000
Enter configuration commands, one per line. End with CNTL/Z.
Apr 27 21:12:28: %SYS-5-CONFIG_I: Configured from console by vty0
Add the [localtime] option to the service timestamps log command. For example, if the current configuration is service timestamps log datetime, issue this global configuration command:
router(config)#service timestamps log datetime localtime
router(config)#^Z (ctrl z to exit)
The times should now be synchronized between the system clock and the log message timestamps.