Synchronizing Software Clock and Hardware Clock

 

Synchronizing Software Clock and Hardware Clock

 

 

Here we'll see how in fact the software and hardware clocks on a Cisco router can have different times and how we can synchronise them between each other.

 

The following two commands show the difference in time between the two clocks on our Cisco router:

 

• R1# show clock
• 01:51:31.532 Athens Sun Apr 19 2009

 

• R1# show calendar
• 01:51:42 Athens Sun Apr 19 2009

 

While the difference is minor, we want to keep everything in our network synchronised as precisely as possible.

 

Keep in mind that 'show clock' refers to the software clock and 'show calendar' refers to the hardware clock of your router.

 

To synchronise the two clocks all we need to do is issue the following command:

 

• R1# configure terminal
• R1(config)# ntp update-calendar

 

The 'ntp update-calendar' forces the hardware clock to synchronise with the system's software clock. After a couple of minutes, we check to see if the two clocks have synchronised:

 

• R1# show clock
• 02:07:05.011 Athens Sun Apr 19 2009

 

• R1# show calendar
• 02:07:05 Athens Sun Apr 19 2009

 

We can see now that both clocks are accurately synchronised.