Reply To: Multiple network gateways?
Several questions here. Firstly multiple gateways are fine, as you say it’s the default gateway address that determines what goes where. Businesses often do this to separate say VOIP and data.
External access via 4G is a movable feast but you don’t need to spend £260 on a Draytek that will do 4G load balancing / failover. Here’s a screenshot from my basic 2760.
4G through a USB dongle will stymie DDNS as they basically act as routers. They present their own private IP to the router and do not pass through the ISP allocated IP address. It’s how their protocol works and no way around it.
Therefore the router needs a SIM card slot and yes a Draytek with one does cost a lot more. But as far as IP addresses are concerned, most carriers will give you one of their internal IP addresses so DDNS is again stymied. I am with Three and the default APN of three.co.uk does this, however if I change the APN to 3Internet I get a public IP and DDNS is back on. So even with your router sorted out you are in the hands of the 4G carrier.
The question you need to ask is do you really need to remotely administer your router via 4G? This is what is causing you all the grief.
What I do at some customers sites is install a Pi and let VNC deal with the negotiation through whatever network between me and it. I can then run tools or a browser on the Pi.