Setup 4G USB modem on RpiB+ connect to router

Hi Nigel, With what you are trying to achieve, I think you need to have a basic understanding of networking - IP ranges and sub-nets at least, to help with the issues you are having.

Maybe this will help -

With IP ranges, my own approach is to limit addresses to the expected maximum user count and if possible use static/fixed ip’s (usually tied to device MAC addresses). Not such an issue with wired connection but with WiFi and especially remote devices, you are providing doors into your network for a determined hacked to find. It depends if what you are working on has any privacy implications I guess, but as I said earlier, I’m old school.

Reading between the lines, I can’t help but think that you seem to be ‘re-inventing the wheel’ and are overlooking off the shelf solutions that have had years of development (i.e. quality routers) that are capable of fixing the problem. Just need some lateral thinking to work out what is best to do what you want with the minimum device count. Trust me, I have developed enough solutions over the last 45 years to understand just how easy it is to get tunnel vision and concentrate on resolving a problem that actually isn’t really there or is easily solved by buying the right bit of kit. I don’t want to discourage you at all, far from it but seem to be having basic issues. One project I am working on currently seems similar to yours - a central comm’s (Wifi, LTE, BTLE, SigFox & LoRA) ‘server’ with many remote, scattered devices providing data. The server uses multiple SD cards, which has taken a bit of effort to resolve, but is now working - the core products are not Rpi though. There are also OTA updates and management, local manual upgrades and data collection, Web Server and FTP components to cover all the client requirements.

I am happy to continue helping you as best I can but would prefer to do that outside this forum because the discussion will get quite technical and possibly move away from the ‘maker’ environment.

Steve W