NTP configuration

Answered Question
May 24th, 2010

Hi all,

I need to configure my router to act as NTP server but I need to understand the commands exactly when I issue the command

ntp master x

where x is the stratum number and in Cisco routers it is between 1 and 15.

I need to know how I can detrmine the stratum number?? and what is the deffierence? I know the meaninig of stratm 0,1,2 and 3 but for example what is the meaning of 5 or 10 what is the advantage and disadvantage of that?

I knew that the stratum level defines its distance from the reference clock. isit added to cisco routers if I need to build NTP networks?? and what is the best practice for that?

and if I just add the command: ntp master ( without the stratum number, what is the value?)

I have this problem too.
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Correct Answer by ganeshh.iyer about 3 years 10 months ago

Thank you for your reply,

I already know the meaning of stratum and level 1,2 and 3.

but as I mensioned eralier in Cisco router you can define stratum number between 1 and 15.

and this my question?

when I should use 1 and when I should use 2 or 10 or 15?

is it for configuring NTP networks??

Hi,

Let me try to explain what is startum is hope that will answer your question to configure starum number in ntp server acting switches,

The stratum is a measure for synchronization distance. Opposed to jitter or delay the stratum is a more static measure. Basically (and from the perspective from a client) it is the number of servers to a reference clock. So a reference clock itself appears at stratum 0, while the closest servers are at stratum 1. On the network there is no valid NTP message with stratum 0.

A server synchronized to a stratum n server will be running at stratum n + 1. The upper limit for stratum is 15. The purpose of stratum is to avoid synchronization loops by preferring servers with a lower stratum.

So it's upto you how you configure your ntp server with startum vlaue.

Hope to Help !!

Ganesh.H

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Average Rating: 5 (3 ratings)
trippi Mon, 05/24/2010 - 14:58

You woudl only use the ntp master command when not syncing with an external time source.

You should be syncing your router with an external time source.

ntp server x.x.x.x

Once it syncs, you can set other ntp clients to get their time from it.

Leo Laohoo Mon, 05/24/2010 - 15:13

Cisco's not really very enthusiastic about the "ntp master" command.

JustForVoice_2 Mon, 05/24/2010 - 15:55

Thank you for your answers.

but my problem does not solve.

I need to know the difference between

ntp master 5

and

ntp master 7

Is there any advantages or disadvantages??

Is there any reason to choose the stratum number??


I think if I choose stratum 1 the router will not reply for the request.

Leo Laohoo Mon, 05/24/2010 - 15:59

The lower the stratum number the higher the "trust level".  If you do need to configure the stratum number, go between 3-5.

JustForVoice_2 Mon, 05/24/2010 - 16:48

can I know why you choose 3 - 5

and could you please give me more details about:

The lower the stratum number the higher the "trust level"

what is the lower and what is the higher and where to configure?

Leo Laohoo Mon, 05/24/2010 - 20:43

If you have a low stratum number, you are trustworthy.  Meaning if a device has to choose between one with a stratum number of 3 and, say, a 6 the device will choose "3".

Why do I choose 3 to 5?  Because stratum 1 is used by devices that, in my personal opinion, have a good track of time.  Same with 2.

Normally when I set my SNTP/NTP, I never specify the stratum number.  I let the routers/switches sort themselves out.  PC/Laptops and printers use the default gateway to synchronize their time (which is the routers).  The APs also synchronize their time to the local router.

ganeshh.iyer Mon, 05/24/2010 - 22:19

can I know why you choose 3 - 5

and could you please give me more details about:

The lower the stratum number the higher the "trust level"

what is the lower and what is the higher and where to configure?

What is the use of startum and defination  vlaue 1, 2 and 3 so on is basically 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.

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.

As you progress through different stratum there are network delays involved that reduce the accuracy of the NTP server in relation to UTC.  Timestamps generated by an EndRun Stratum 1 Time Server will typically have 10 microseconds accuracy to UTC.  A stratum-2 server will have anywhere from 1/2 to 100 ms accuracy to UTC and each subsequent stratum layer (stratum-3, etc.) will add an additional 1/2-100 ms of inaccuracy.

For your question

what is the lower and what is the higher and where to configure?

Once you configure ntp master "startum vlaue (it can be 3 or 5) 3 is lower"

Hope to Help !!

Ganesh.H

Remember to rate the helpful post

JustForVoice_2 Tue, 05/25/2010 - 00:31

Thank you for your reply,

I already know the meaning of stratum and level 1,2 and 3.

but as I mensioned eralier in Cisco router you can define stratum number between 1 and 15.

and this my question?

when I should use 1 and when I should use 2 or 10 or 15?

is it for configuring NTP networks??

Correct Answer
ganeshh.iyer Tue, 05/25/2010 - 00:57

Thank you for your reply,

I already know the meaning of stratum and level 1,2 and 3.

but as I mensioned eralier in Cisco router you can define stratum number between 1 and 15.

and this my question?

when I should use 1 and when I should use 2 or 10 or 15?

is it for configuring NTP networks??

Hi,

Let me try to explain what is startum is hope that will answer your question to configure starum number in ntp server acting switches,

The stratum is a measure for synchronization distance. Opposed to jitter or delay the stratum is a more static measure. Basically (and from the perspective from a client) it is the number of servers to a reference clock. So a reference clock itself appears at stratum 0, while the closest servers are at stratum 1. On the network there is no valid NTP message with stratum 0.

A server synchronized to a stratum n server will be running at stratum n + 1. The upper limit for stratum is 15. The purpose of stratum is to avoid synchronization loops by preferring servers with a lower stratum.

So it's upto you how you configure your ntp server with startum vlaue.

Hope to Help !!

Ganesh.H

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