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Sunday, February 17, 2008

Synchronizing the Software Clock to the Hardware Clock on a Cisco Router

The router is a 2811 Cisco ISR, it has the following configuration regarding its clock settings:

!
clock timezone eastern -5
clock summer-time eastern recurring
!

Here is the current time on the router:

Certchaser#show clock
*10:10:41.235 eastern Sun Feb 17 2008

The actual time is 10:04

Setting the clock on the router can correct the time setting, currently this router is fast by about six minutes

Certchaser#show clock
*10:14:35.055 eastern Sun Feb 17 2008

Certchaser#clock set 10:09:00 february 17 2008

*Feb 17 15:09:00.000: %SYS-6-CLOCKUPDATE: System clock has been updated from 10:15:23 eastern Sun Feb 17 2008 to 10:09:00 eastern Sun Feb 17 2008, configured from console by console.

Certchaser#show clock
10:09:08.659 eastern Sun Feb 17 2008

After a reload the router returns to its incorrect time settings, this was verified by writing the config and reloading the router, then comparing to the current time on a PC. This router has a hardware clock, changing the software clock on the router does not update the hardware clock. The command to update the hardware clock is clock update-calendar The hardware clock can be displayed with the command show calendar

Certchaser#show clock
10:27:10.159 eastern Sun Feb 17 2008

Certchaser#show calendar
10:27:14 eastern Sun Feb 17 2008

Certchaser#clock set 10:21:00 february 17 2008

Feb 17 15:21:00.000: %SYS-6-CLOCKUPDATE: System clock has been updated from 10:27:36 eastern Sun Feb 17 2008 to 10:21:00 eastern Sun Feb 17 2008, configured from console by console.

Certchaser#clock update-calendar

Certchaser#show clock
10:21:19.083 eastern Sun Feb 17 2008

Certchaser#show calendar
10:21:27 eastern Sun Feb 17 2008

2 comments:

dawid2011ed said...

Cosme is right! It saved us in our rear end.

This was useful in submitting bundles of Ip's

CCNA

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