Information about DNS and network

Two years! https://en.wikipedia.org/wiki/2016_Dyn_cyberattack

Investigating Constellix https://constellix.com/ as a possible DNS replacement. Has anyone used it?

I keep reading about the combination of the reversed IP ie 1.16.172-IN-ADDR.ARPA in combination with the PTR record, in which the host bits are listed to complete the 4 octets of the address for which the reverse lookup will be possible.

I was wondering what would be the case if the particular hostname being referenced in the PTR record was not on the same subnet, ie the two addresses which I need to be able to reverse lookup are 172.16.10.1 and 172.16.20.1 ?

On a computer if I do a lookup of “A.com” I get 1.1.1.1 and if I do a lookup of “B.com” I get 1.1.1.1. When I do a lookup of “1.1.1.1” I get “B.com”. I can’t change the DNS servers on the PC, how do I tell my PC to use “A.com” over “B.com” when I do a lookup of 1.1.1.1?