Thanks for the help.
Unfortunately its not a fix. I've tried all three options, none function correctly.
However it points towards the root of the issue I believe.
I have dnsmasq version 2.79, standard distribution of raspbian. It works, as in can co-exist with other name servers on other interfaces on the same box.
I've spent all day building a dnsmasq version 2.80, with the same compile time options as the raspbian stock. It works as well. This is the root of the pihole-FTL fork.
pihole-FTL fails with all the options on that radio button.
So there is diverging code in the pihole-FTL implementation, to make those selection options available from the gui. Presumably that selection overrides the settings in dnsmasq.conf that
set the bind-interfaces directive, which is what is needed to allow co-existance with other name servers.
Can anyone point me to where those options are handled in the pihole-FTL code please?
Not that I'm a great coder, but I'm motivated to look.
In passing, stock dnsmasq very helpfully lists the compile time options set in the binary from the command dnsmasq -v . On pihole-FTL that only lists the version. Unless there is another switch to list the compile time options, that is probably not an improvement.
Harry