NTP Master Command

Answered Question
Dec 3rd, 2009

Currently i am deploying a network wide NTP set up. All works fine but we have some confusion over the use of " NTP master "

If we do not include the NTP master command on the catalyst cores the NTP set-up does exactly what we expect.

When we add NTP master on the core catalyst switches with a high startum ( ntp master 5 for example ) we see that the cores seems to flick between the internal clock on 127.x.x.x and the actual main NTP source server on the network - even though the stratum value of this server is lower ( ie stratum 3 )

than the actual core NTP master 5 .....

Is this normal behaviour ? does the catalst core look at all the clocks and decide its the best time source regardless of stratum value ?? does it occasionally look at clocks and then decide that the server is sometimes the best source ( when we do sh ntp associations the NTP master seems to change from the core switch to the true NTP master server and then back again ) ?

Or should  we simply not bother with the  NTP master command - I understand ( maybe mistakenly ) that the master command just means that the cat will use itself as master when it loses connection to the main NTP server ?

Confused !

any help gladly appreciated.

I have this problem too.
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Correct Answer by Edison Ortiz about 4 years 4 months ago

It could be a timing issue.

The NTP server with stratum of 3 does not respond on time the switch automatically looks to itself as a time provider.

You should remove the 'NTP Master' command to avoid this issue. By default, if this switch is the only one configured with the external NTP server, it will act as NTP Master for the rest of devices in your network pointing to this switch as the NTP server.

Regards

Edison

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Correct Answer
Edison Ortiz Thu, 12/03/2009 - 10:09

It could be a timing issue.

The NTP server with stratum of 3 does not respond on time the switch automatically looks to itself as a time provider.

You should remove the 'NTP Master' command to avoid this issue. By default, if this switch is the only one configured with the external NTP server, it will act as NTP Master for the rest of devices in your network pointing to this switch as the NTP server.

Regards

Edison

ganeshh.iyer Thu, 12/03/2009 - 22:26

Hi,

Hope the following brief about NTP stratum can solve your problem.

In the world of NTP, stratum levels define the distance from the reference clock.  A reference clock is a stratum-0 device that is assumed to be accurate and has lttle or no delay associated with it.

A server that is directly connected to a stratum-0 device is called a stratum-1 server.  This includes all time servers with built-in stratum-0 devices, such as the EndRun Time Servers, and also those with direct links to stratum-0 devices such as over an RS-232 connection or via an IRIG-B time code.

The basic definition of a stratum-1 time server is that it be directly linked (not over a network path) to a reliable source of UTC time such as GPS, WWV, or CDMA transmissions.   A stratum-1 time server acts as a primary network time standard.

A stratum-2 server is connected to the stratum-1 server OVER A NETWORK PATH.  Thus, a stratum-2 server gets its time via NTP packet requests from a stratum-1 server.  A stratum-3 server gets its time via NTP packet requests from a stratum-2 server, and so on.

Regards

Ganesh.H

Inderjeet Singh Sun, 10/28/2012 - 23:42

"ntp master" command is used to make the router act as an ntp server with it's own hardware clock as a source.

i.e. not to be used when you have a real ntp server in your network, or when you can sync to a reliable internet source.

The "ntp server x.x.x.x" command (x.x.x.x being your ntp server address) should be enough to make the router act as an ntp server.


Higher stratum means less reliable.

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Posted December 3, 2009 at 8:49 AM
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