By default, Catalyst switches add a simple uptime timestamp to logging messages. This is a cumulative counter that shows the hours, minutes, and seconds since the switch has been booted up. For example:
20w2d: %LINK-3-UPDOWN: Interface FastEthernet1/0/27, changed state to
down
21w3d: %SYS-5-CONFIG_I: Configured from console by vty0 (172.25.15.246) At exactly what date and time did that occur? Who knows!
Instead, you can configure the switch to add accurate clock-like timestamps that are easily interpreted. you can use the following command to begin using the switch clock as an accurate timestamp for syslog messages:
Switch(config)# service timestamps log datetime [localtime] [show-
timezone] [msec] [year]
Below is the output if we entered the command "service timestamps log datetime localtime show- timezone" (without"msec" keyword the output would not show time in milisecond)
*Mar 1 00:02:24 UTC: %LINEPROTO-5-UPDOWN: Line protocol on Interface
Loopback4, changed state to up