"I want to use a USB-tethered phone as an automatic backup internet connection for my home network. Here's what I'm working with — help me design and build it.
Interview me first on these points:
Router — Make, model, firmware. Does it support multi-WAN / WAN failover / "Link Backup"? If not, are you willing to flash OpenWrt or replace it? Primary ISP — What technology (fiber, cable, DSL)? How often does it go down, and for how long? Phone — iPhone or Android? Carrier? Unlimited data or capped? Does the plan include tethering/hotspot? Intermediate host — Do you have a Linux box, Raspberry Pi, or server that's always on and physically near both the router and where the phone can sit plugged in? What OS/distro? Does it have at least 2 spare ethernet ports (or one port + a USB ethernet adapter)? Network layout — What's your LAN subnet? Where does the router sit relative to the candidate host? Reliability needs — Is this for working from home (need sub-10s failover)? Just keeping smart devices alive? How much i