NTP as Server and Client


I would like to have 1 unit, can be a PC or PLC, which act as a NTP server.

Then I would like 1 PLC to receive the time from the first mentioned NTP server, so he will be configured as a NTP Client.

This second PLC should then also act as a NTP server to a network of PLC:s.

The last line of units will then act as NTP Clients to the second mentioned server.

I have tried using library AsARCfg and also only configured the settings on the CPU properties.
But as soon as both servers are active the clients wont receive the time from selected/second NTP Server.
I have tried to also Enable the DNS Service and configured default gateway with no success.

Is it possible to handle the NTP in this way or am I configuring something wrong?

I can post more pictures on my setup if the answer is that is it possible to handle the NTP in this way.


When using a hierarchy like this you need to set the servers to have hierarchical settings for the “Stratum of local clock” in the Time Synchronization settings.

The top level should have the lowest value and the value should increase as you go deeper in the hierarchy.

As an example using the numbering in your picture.

Server 1 → Stratum 5
Server 2 → Stratum 6


in general this setup should be possible but I think that the “Stratum” of the settings you have done is too low

PLCs do not accept the time from a server where the stratum is too high.
Please try to set a stratum of 3 for the initial NTP Server



in addition to what the colleguages already mentioned:
what version of Automation Runtime you’re using? In general it should work but I can remember, that some time ago in AR there was an issue having server and client both activated. Unfortunately I can’t remember the exact version, but if you’re not using the latest AR, please update an check again.

And please keep in mind that a NTP server doesn’t inform activly the clients about time changes. Depending on the time a NTP client is running and on the former NTP sync state of the client, it can last some time (up to about 17 minutes) until the client asks the server for a time update.
Please have a look here for details:

Best regards!

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Hello Alexander,
Thanks for quick response!
We are using AS 4.12, and AR G4.93.

My issue seems to be solved by changing the parameter “Stratum of local clock”.

Thanks for the explanation regarding the update behavior of the clients!

Best regards,

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Thanks for quick support and for providing the solution to my problem!
Have a good day!

Regards Simon

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