I am running Buster on a RP3B+. It is configured as a stand-alone wifi access point running dnsmasq. No bridging to the eth0 / Internet. It also has a wired eth0 interface. Everything is working correctly.
I want to allow a user to set a static IP on the eth0. I also want to have a default IP that they can use if the mess up setting their own IP.
Traditionally this has been done with a small switch that resets the device to factory defaults. I don't want to do that.
I want to have a fixed static default IP plus a user set static IP running on eth0.
I understand that I do have the option of allowing a user to connect through the Wifi to set the IP. I will probably do that as well.
There are answers to this question out there but it appears many are out of date. I specifically want a solution that is compatible with Raspbian Buster (released only a few days ago at the time of writing) configured as a simple Access Point with wired ethernet.
I have mentioned the wifi AP setup only because it is not standard and may affect the setup of the eth0 interface. That includes installing dnsmasq. I just want to have 2x static IP addresses assigned to the eth0 interface.