And with newer decides that use DoH, you can no longer prevent devices from contacting their own DNS provider without totally firewalling them (or perhaps using some IP blacklist or whitelist, if available?)
Everything that I don't have complete visibility into the network stack of goes on a VLAN that does not forward traffic to the internet, it advertises a proxy via WPAD and DHCP option 252. I have a whitelist of hostnames that each device is allowed to make CONNECT requests to, so far there is only one.
If it's not a plain unencrypted HTTP request to my proxy, or a CONNECT request involving a server/device pair I've decided to trust, it's not going anywhere.
This breaks a lot of things that I would just as soon rather do without. I can't change my universal remote hub settings from the vendor portal, boo-hoo. I can't view my cameras from the hardened VLAN or from the internet (unless I VPN in first since the only copy of the recordings is on my local NAS)... good.
Looking at you, Chromecast that tries 8.8.8.8 40 times an hour even though you know perfectly damn well that 10.10.10.1 is working