* * If device do not use public (like 1.1.1.1) or custom DNS
I log all attempts by devices on my network to port 53. Android apps, roku, google home devices, and various others are quite aggressive about going directly to various DNS servers if they don't get what they want from the local DNS server.
Using wireshark to track what's going on it's not unusual to see 7,000 DNS requests for a domain I'm blocking in just a few seconds. The android client for youtube seems to be particularly persistent.
You should not
Or you completely compromise DNS chain and as result you can not trust results of dns resolve
Quite a few apps and devices ignore the DNS recommendations provided by radvd (for ipv6) and dhcp (for IPv4).
That way I can block youtube, instagram, netflix, imgur, reddit, and similar services that my kids are addicted to if they are avoiding homework and the like.
How exactly does that "compromise DNS chain"? Unbound is DNSSEC aware, and talks to the same root servers that the ISP, google, opendns, or similar services would talk to.
Sadly DoH will make this much more difficult.