Save yourself a whole bunch of effort and money, just use dnsmasq, it is already probably installed, you need to verify two line of configuration, in /etc/dnsmasq.conf to set your internet dns server (use server=8.8.8.8 unless you don’t trust Google), and /etc/resolv.conf to use 127.0.0.1 as your sole name server, that means connection on 53 will go to dnsmasq on your local machine, and it will respond with it’s cached host, even if you can’t get to it, then asterisk will be content and everything moves on seamlessly , it can’t be easier than that, no? No muss no fuss and it WILL work for you, it is also free, unlike M$soft anything, FreePBX/Asterisk is rooted in Linux, why buy into anything else? even M$ uses it for anything really important 