NTP (Network Time Protocol) is a protocol used for clock synchronization among different devices. Enabling NTP in your network devices will cause that they all have the same time so operations flow smoothly and log analysis can be actually useful. I can’t stress enough how important it is.

So, let’s configure the NTP on a standard Cisco Catalyst Switch so the switch can synchronize to a NTP Server. The procedure below is a BASIC NTP configuration for a Cisco Catalyst switch but it can be used also in older routers (No ASR or Nexus, where the config is slightly different). We’ll discuss advanced NTP topics in further posts.

Before starting the configuration, you need a Time Server already up and running, which it can be your own server or a free public one. You can find a list of public ntp servers in this link:

• http://support.ntp.org/bin/view/Servers/NTPPoolServers

Configuring the NTP association

switch#config terminal
switch(config)# ntp server ip_address_of_ntp_server

and optionally if you want logs about the NTP operation (e.g.,failed to reach the time server)

switch(config)# ntp logging
switch(config)#end

Save your changes

switch#copy running-config startup-config

Now, when you see your configuration you will notice something like this

switch#show running-config | incl ntp
ntp logging
ntp server x.x.x.x
ntp clock-period some_numeric_value    

The value is automatically calculated by the switch to compensate the time differences between the ntp client and the ntp server. Do not remove or modify this line.

Note: For redundancy, it’s best to specify more than one ntp server. In the scenario that the first NTP server fails our can’t be reached, your devices would get clock sync from the next server. To accomplish this, simply add another line like this.

switch(config)# ntp server ip_address_of_ntp_server1
switch(config)# ntp server ip_address_of_ntp_server2

And that’s it.

Verifying the NTP association is working

To verify your device it’s connected properly to the time server, use the following command:

switch#show ntp status

You should see an output like this:

Clock is synchronized, stratum number, reference is ip_address_of_ntp_server
and more information about the clock offset and the precision of the sync.

You’re all set! Good luck.