I have been searching for what I want to do for some time without success. I believe what I want to do is not very common, but a network guru could hopefully point me in the right direction. Sorry if I am not too good at explaining what I want.
I have a Raspberry Pi connected to the internet using ethernet via my WAN router.
I have a USB 4G/LTE modem with a SIM card that connects to the cellular network connected to the Raspberry Pi.
I also have some 4G/LTE sensors that connect to the cellular network.
I pay additional money to my cellular provider and they give my SIM cards a private static IP address that is not accessible via the internet or anyone else. They call this their IPX network.
Each of my SIM cards on this private network can communicate with each other via their individual static IP addresses (and my desired port).
First problem I need to solve... I don't know how to configure the network on the raspberry Pi to do the following.
Prevent the raspberry Pi from trying to access the internet using the USB 4G/LTE modem, i.e. Only use the ethernet port for internet access.
I will run an MQTT client that will subscribe to a topic on my server (located elsewhere) that is connected to the internet.
I plan to use python as the MQTT client.
When a message is published to the subscribed topic, my Python code will get the destination IP (one of the 4G/LTE sensors) from the published message and send other parts of the same message directly to the 4G/LTE sensor. The code in my sensor will handle the received message.
I think I can also have python create a TCP socket server that listens for any messages from my sensors on it's static IP address. If a message comes in on that TCP socket, I can then use python to forward that over MQTT back to my server over the internet using the ethernet port.
Can anyone help me configure the network setting for the ethernet port and the USB 4G/LTE modem so the Raspberry Pi only uses the ethernet for internet access and the USB 4G/LTE modem is only used for it's private IPX addresses?
Thanks in advance, and again I am sorry if I don't explain myself very well.