Server ID with Modbus TCP - why and how to find out?

Hi Teltonika-Team and community,

I want to connect a power meter with an RUT241 via Modbus TCP, read out the values and send them via the “Data to Server” feature to a MQTT broker. I have done so with various meters and it works perfectly.

However, what always gives me headache (and now with a new meter acutally blocks me) is the required Server ID field.

The Server ID is often the same for the same meter models / manufacturers, however, we connect sometimes to already existing setups, where the ID could have been changed. I assume this is now the case. I do not get a connection, already tried some obvious IDs which ususally work (e.g., 1-10 and 248-255).

In the wiki (e.g., here Modbus TCP Master MQTT Gateway - Teltonika Networks Wiki), it states that one can set the Slave ID to 0 in order to repond to all adresses. However, the field only allows values from 1-255.

My questions:

  1. Is there a way to respond to all adresses?
  2. Is there a way to find out the ID remotely via the RUT?
  3. Why is this field even required, since with Modbus TCP, I address the Device via IP, not Device ID like in Modbus RTU? I understand that it would be required, when using the RUT as Modbus TCP <> Modbus RTU Gateway, however, this is not my use-case here.

Thanks and let me know, if I have not descibed my problem clear enough.


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