configuring NTP

Unanswered Question
May 10th, 2008

I would like to configure my 3750 switch as NTP server and synchronise for few windows servers

what all commands should i use

Any help on this


I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 3.8 (4 ratings)
Richard Burts Sat, 05/10/2008 - 07:48


If the switch is not learning time from some NTP server then Sam is correct that configuring the switch with ntp master will set the switch as an NTP server. This means that the network will be dependent on the accuracy of the clock in the switch. If the switch can learn NTP time from some server it would be more accurate. And if the switch is learning NTP time from some server then it is automatically set up to serve time to other devices and you do not need ntp master.

One other aspect of this involves the switch providing time to Windows servers. Windows uses a slightly different protocol than NTP by default. And unless you are running some application on them to utilize NTP they will not send NTP requests to the switch. You might try configuring ntp broadcast on the switch layer 3 interface for the PCs which will cause the switch to send NTP broadcasts which the PCs may process.



shiva_ial Sat, 05/10/2008 - 19:37

thanks richard,sam

rick,I am frequent user of cisco forum and

i found several posts by you with clarity. I am very happy to see reply from u

I am stuck in urgent situation to configure

3750 switch as NTP server and some windows servers has to synchronise with switch to get proper time,i havent used NTP configuration before,i need basic commands in simple way i should put,since the documents sam provided i have come across before from which i couldn't understand properly

"I need only commands to make this work"

any one can you help on this


shiva_ial Sat, 05/10/2008 - 23:44

any expert,

solution for this ?

is it best to synchcronise time from internet atomic time servers for NTP or what is the normal way of doing it

or setting it up manually on the switch the



Richard Burts Sun, 05/11/2008 - 03:42


I would say that the more common way is for devices to leaern NTP time from an external NTP server. If you want to find an external NTP server that you can use then this link will point you to a list of them:

Sam was correct in his suggestion that the most simple and direct solution is to configure the switch as an NTP server using the command ntp master 7. If you do this the switch will use its own clock, which you should make sure is set to the correct time. You could also configure ntp broadcast on the VLAN interface for the subnet(s) where the Windows servers are connected. Give that a try and let us know how it works.



shiva_ial Mon, 05/12/2008 - 20:27

thanks rick

but if i put the command ntp master 7 -it will use the timing from the local switch

then how will it synchronise with external NTP servers on the internet

will it synchronise or not


cisco_lad2004 Mon, 05/12/2008 - 22:29

it won't sunch with internet.

Switch becomes the master Clock, and relies on its own clock ( as started by Rick in previous replies).

If u servers are dependant on a reliable and guenuine NTP master, u need external clock.



shiva_ial Tue, 05/13/2008 - 22:54

so what is the command to syncronise with

internet ntp servers (external ntp)

from the list of servers available which i should use ,is there any command i should use for daylight changes.


cisco_lad2004 Wed, 05/14/2008 - 02:40

ntp server x.x.x.x where x.x.x.x is the address on a server u can reach.

for clock settings, see below exmaple:

this changes clock between summet time and winter time.

clock summer-time CEST recurring last Sun Mar 2:00 last Sun Oct 3:00



shiva_ial Thu, 05/15/2008 - 22:26


so to configure my switch to fetch time from internet ntp server should i use

switch#ntp server x.x.x.x (x.x.x.x is the ip address of internet ntp server.


shiva_ial Thu, 05/15/2008 - 23:03

thanks sam,

so my configuration would be if synchronise nasa ntp server od stratum 1

switch#ntp master stratum 2

switch#ntp server ntp server)

is it right


shiva_ial Sun, 05/18/2008 - 20:46

is the configuration mentioned above i should use to synchronise with internet NTP server.


k.cherian Sun, 05/18/2008 - 21:32


If you synchronizing the switch with an external server, you need not configure the switch as an ntp master.

That command is very much used if you using the switch as a stand alone server and nothing else.

-/ KC

shiva_ial Mon, 05/19/2008 - 02:19

hai cherian,

so if i put

switch#ntp server x.x.x.x (x.x.x.x-ip address of the internet server)

is it ok.will it get syncronised with the sever for atomic clock.


k.cherian Mon, 05/19/2008 - 03:38

Yes, it will, as long the server is reachable via that switch and that those NTP packets on port 123 are not blocked.

-/ KC


This Discussion