I have some kind of strange behaviour of a NTP001, which communicates with a few Siemens PLC S7-300 and S7-400. At first I have to say, that the time synchronisation with a Windows 10 is working. The messages from Windows are sometimes wrong (time synchronisation did not work but was successful), but the NTP telegrams are ok.
I made a wireshark capture an there I can see a pattern:
request from Siemens PLC - time stamp from PLC included
reply from NTP001 - time stamp from NTP001 included
however time synchronisation did not work
request from Siemens PLC - time stamp from PLC included
reply from NTP001 - time stamp from PLC(!!!) included
Why the first correct telegram is ignored is also a question. But my question here is: why the NTP001 replies the time stamp from the PLC with the request time stamp? And had anyone the same issue with Siemens PLC?
To investigate this further, we would appreciate if you could provide the following information:
Does the issue occur with all PLCs or only specific devices?
Is the PLC configured to use standard NTP or SNTP?
Does the issue persist after rebooting the NTP001?
Can you reproduce the issue after rebooting the NTP001?
As an additional test, if another NTP server is available, please verify whether the Siemens PLC synchronizes successfully with it. This will help determine whether the behavior is specific to the NTP001 implementation or related to the PLC configuration.
Once we receive the requested information, we will continue investigating the issue in greater detail.
after a review of the wireshark captures we found the RATE signal in the answer of NTP001. This means that two requests from the same client are too close.
This behaviour can not be solved by rebooting the NTP001. And there is no option to switch off the blocking of fast requests. The PLC uses SNTP and there are no options to configure the ntp client.
So the NTP001 is not suitable for Siemens PLC S7-400. I don’t know if the NTP001 ist working with the new Siemens PLC S7-1500 series, but the S7-400 series is still active.
Our solution is to connect the NTP001 to a raspberry. There is Chrony installed which is working fine with Siemens PLC.
Thank you for sharing your insights and the workaround you implemented.
I have submitted a feature request to allow configuration of the request frequency. Our R&D team will review your suggestion, and I will get back to you with an update as soon as I receive their feedback.
At this time, the NTP001 does not support changing or disabling the NTP request rate.
To help us better understand your requirements, could you please provide more details about your use case? I will forward this information to our R&D team so they can evaluate the scope and intended use of this functionality. Your feedback may be taken into consideration for future firmware releases.
If this functionality is essential for your deployment, please note that we also offer the possibility of a custom development project tailored to your requirements.
I am only a user of Siemens S7-400. I can only switch on NTP client and set an IP-address. There is no documentation about the NTP client on S7-400. I have heard there is implemented a SNTP client but an AI-analysis of wireshark capture identifies the traffic as NTP protocol.
I don’t know why, but the wireshark capture shows after the first request of NTP client and correct reply from NTP001 there is a second request immediately after NTP001 reply. Maybe the time difference was too big and the second request was for verification of the NTP001 reply but this is only a guess and I have no background information.
