Hello everyone. Before I start I'm pretty much a novice on this in comparison to others, I usually learn as I go along. I'll try to explain the best I can, but to cut to the chase I help manage a small radio station. Our main I.T. guy passed away a couple of years ago so most of the tech stuff has fallen onto my shoulders.

All of our network has been setup a while, we have a Flexnetwork 5130 switch as the main router. Assigning DHCP, subnets set up on it etc. This is managed not by myself but the council who set this up, and provide us with free internet along with it (which is great). Last few months however we were having internet outages frequently, which have now been resolved by them. But this got me thinking that I want to set up our own 4G/5G backup for our essential 'on air' machines (playout remote access, webstream, DAB relay), if there are any more planned or unplanned outages from our main ISP.

So I bought a TP-Link ER605, with a USB port to take a myfi plugin. I have that working through it fine, and I think I have my head around the failover method with it. However my issue is setting up the LAN side of things for our network.

The main Flexnetwork switch has been setup with separate subnets for different groups of machines. The main two in focus are the 'Office Network' (web browsing machines, printers etc), and the 'Myriad Network' (our music playout system). There's two machines on the 'Office' network I would like to have failsafe for, and three on the 'Myriad' one. I do have a few spare gigabit switches about to extend the network.

Basically I want the ER605 to mirror the DCHP settings & these 2 subnets that the flexnetwork switch has assigned to the machines, just simply passing through the ER605 which can switch to failsafe and feed these essential machines some 4G Internet if the main ISP goes out. Not have the ER605 start assigning it's own IP addresses to them from it's base '192.168.0.1' IP address, which I can't seem to stop it doing. Especially for our myriad system which needs to see the SQL Server that feeds it the music, and those are all static IP's. The 'Office Network' has a gateway address of 10.156.18.1, 'Myriad' 10.156.18.65.

I've done some browsing about online to see if I can find an answer, and just had a play around on site with Virtual Lan and different settings on the ER605 to no avail. Factory resetting it and then trying different methods over again. I hope that's fairly clear what I'm trying to do, if it is even possible at all. Just wondering if someone could give me some advice, or possibly point me to a guide if something of the same thing has been setup before. I fully admit there's probably a big chunk of info I'm missing here. Thanks all.