NTP configuration on Router

Unanswered Question
Mar 15th, 2010


I am trying to configure our main Router 7204 ( to pull 'Date and Time" from one of our servers on the network configured as an NTP (

Then I want to configured all other routers and switches to pull NTP data from our main router (

The current config I have is the following:

NOTICE: I don't think is workinng right beause the time isnot sync between devices.


scheduler allocate 3997 1000
ntp master

ntp update-calendar

ntp server

All other routers and switches

scheduler allocate 20000 1000
ntp clock-period 17178271
ntp server

Please let me know if I need to change the config.



I have this problem too.
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Richard Burts Mon, 03/15/2010 - 10:58


What kind of device is your router attempting to learn time from. You say that it is one of the servers on your network. Can you supply some detail about what kind of server? If it is a Windows server you may have a problem. Windows server usually run a simplified implementation of the time service and not a full implementation of NTP. So an IOS router will have problems in attempting to learn NTP time if the server is not running the full implementation of NTP. If it is a *nix type server it is more likely that it is running a full implementation of NTP.

It might help us understand the problem if you would post the output of show ntp association detail from your router.

I do not see any obvious problem with the config as you have given it.



Zeek Ferraros Mon, 03/15/2010 - 11:04

Yes, it is a Windows server 2003 R2.

Just wondering what's recommended.

Should I rather configure the master router with external NTP (public ip's) servers ?

Richard Burts Mon, 03/15/2010 - 11:24


I believe that there are 3 alternatives that you can consider:

- configure your router to learn time from an external/Internet NTP server. Advantages include that you will learn accurate NTP time. Disadvantages include that you are dependent on an external resource.

- configure your router to use SNTP rather than NTP. (sntp server x.x.x.x rather than ntp server x.x.x.x) Advantages include that you learn time from an internal resource and are not dependent on an external resource. Disadvantages include that SNTP is not as accurate as NTP - though for your purposes I believe that it is probably adequate).

- add some software or a hardware device on your Windows server that will run NTP and allow your router to learn NTP this way. Advantages include that you learn accurate NTP time from your internal resource. Disadvantages include potential expense to obtain the software or device, and the effort expended to install and run it.



Zeek Ferraros Mon, 03/15/2010 - 11:26

Thank you so much for your advice.

Here is how I will configure it for now.

ntp master
ntp update-calendar
ntp server 1.us.pool.ntp.org
ntp server prefer
ntp server 3.us.pool.ntp.org
ntp server 2.us.pool.ntp.org
ntp server 0.us.pool.ntp.org

Richard Burts Mon, 03/15/2010 - 11:51


I would suggest that you not use the configuration command: ntp master. If you do this your router will believe that it is authoritative and will use its own internal clock for sending time to other devices which use it as an NTP server. The internal clock of a router is generally not designed to be accurate enough to base an entire network to learn time from.

Depending on the router type the ntp update-calendar may or may not be a supported command.

Learning time from us.pool.ntp.org is a good idea and should work (assuming that you have IP connectivity to those devices and assuming that your network edge devices are not filtering traffic in a way that would deny NTP traffic. Keeping ntp server prefer in the config does no harm. But it seems that we have already identified that it is not working.



Zeek Ferraros Mon, 03/15/2010 - 12:47

great thanks.

The problem was because I had the wrong IP for the NTP server.

All routers are now sync.

Thanks a lot for your help.


Richard Burts Mon, 03/15/2010 - 13:05


I am glad that you got it resolved and that my suggestions were helpful. Thank you for posting back to the forum indicating that you had resolved the problem and what was the resolution. It makes the forum more helpful when people can read about a problem and can read what the problem turned out to be and what was done to resolve the problem.

The forum is an excellent place to learn about Cisco networking. I encourage you to continue your participation in the forum.




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