TheGreatWall VS doh-cf-workers

Here's lists: https://github.com/Sekhan/TheGreatWall

I run Pfsense and am able to block most common DoH services. I’m sure you will be able to configure similar options on opnsense. The best way to do this is a DNS block through AGH and an IP block with opnsense. Firefox provides what domains to block to disable their DoH, https://support.mozilla.org/en-US/kb/configuring-networks-disable-dns-over-https. You can also add these two lists to block most other common DoH services, https://github.com/oneoffdallas/dohservers, https://github.com/Sekhan/TheGreatWall. These lists will work with AGH for DNS blocking and for IP blocking aliases. If you have any Apple devices on your network you can use these domains to block private relay, https://raw.githubusercontent.com/Rogacz/private-relay/main/pr2.txt. I recommend you add these private relay domains as a custom entry in AGH to return NXDOMAIN so that the device shows that private relay is unavailable versus using a NULL response where it will say it’s available when it really isn’t. With these lists added to DNS blocklists as well as IP blocklists I have seen almost no DoH services getting through. The only service that I’ve experienced getting through the rules so far is Next DNS since it uses different IPs depending on what is fastest for your location, making it harder to block. I found a way to discover the IPs for their servers near you and will edit the post if I find the instructions again. Also make sure to completely block port 853 to block DoT. Lastly using these instructions from Pfsense, you can redirect or block all DNS queries that aren’t destined for your AGH instance. The instructions should be transferable to opnsense.

You can also have the pihole block these DoH servers, using this: https://github.com/Sekhan/TheGreatWall/blob/master/TheGreatWall.txt but for applications that have a list DoH IP's hardwired into them, then pihole blocking won't catch those because they connect without DNS lookups. You have to block them at your firewall.

Original: https://github.com/Sekhan/TheGreatWall

Another test is android also offers Private DNS under advanced settings if set to automatic it will send requests to google DoH, turn this off and see if that changes anything. You could also add the The Great Wall DoH pihole blocklist to see if that helps too: https://github.com/Sekhan/TheGreatWall/blob/master/TheGreatWall.txt

Hopefully this helps: https://github.com/Sekhan/TheGreatWall

For desktop browser, just change the Secure DNS/DNS over HTTPS settings to one of the servers in https://github.com/curl/curl/wiki/DNS-over-HTTPS, if they're all blocked, create your own with https://github.com/tina-hello/doh-cf-workers. On Android use Intra to load custom DoH, and on iOS use https://dns.notjakob.com/ to create the DoH profile.

If Cloudflare Workers aren't blocked, you can use https://github.com/tina-hello/doh-cf-workers to forward to it, though it only work with DNS over HTTPS client (most desktop browsers, Windows 11, iOS, macOS, Intra on Android and YogaDNS on older Windows)

DoH is another game entirely, even if you import the known DoH domains manually, anyone including dedicated kids, can create their own DoH proxy in minutes.

Even those who weren't interested in self-hosting might spend a couple of minutes hosting their own DNS proxy since it's much more flexible and don't require root or dedicated port (at least with DoH).

While you can in turn block those DoH servers (and probably block port 853 too to stop the default DoT & DoQ traffic), there are ridiculous amount of public DoH servers available, partly because of how easy it is to self-host AGH and expose the DoH endpoint to the public. Anyone can even create their own in minutes.

Check if your router support DNS over TLS (DoT) or DNS over HTTPS (DoH), that would ignore the ISP filtering, assuming the ISP doesn't just block port 853 for DoT, or filtering well-known DoH server, in which case just setup your own.

If you don't want to set up AGH at home or at a VPS, accept that the phones need to use the NextDNS/Nebulo/Intra/AdGuard app set to your NextDNS DoH endpoint while you block other providers, though this doesn't actually stop others from using their own/generic NextDNS, or even any provider if their DoH client support bootstrapping. Also, unless it's a seriously fancy router that analyzes traffic statistics, blocking DoH is merely using public list of DoH domains, anyone can create their DoH proxy which won't be blocked. Some routers have SNI filtering which can block websites regardless of the DNS used, but then you need to provide your own blocklist.

That's probably SNI filtering, but try other servers from https://adguard-dns.io/kb/general/dns-providers/ and https://github.com/curl/curl/wiki/DNS-over-HTTPS/ just in case, or make your own proxy on https://github.com/tina-hello/doh-cf-workers

If you want to go that route, keep in mind the entire Cloudflare Workers and Cloudflare Pages subdomains (workers.dev and pages.dev) can be used as free DoH proxy. Sure you can put the nuclear option, but it would break sites that do use them.

A purely DNS-based solution is bound to be easily bypassed, it's really simple to bootstrap the IP so there's no need to even use the network/OS DNS to resolve the custom DoH domain, with hundreds of publicly known DoH and trivial deployment of DoH forwarder you're fighting a losing game.