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DNS notes

For DNS resolvers, refer to r/resolv.tsv

Identifying DNS resolver

The above list is based on redirect2me/which-dns README alternatives section

Identifying ECH support

At it’s current state of implementation, Encrypted Client-Hello requires DNS-over-HTTPS in the browser level or it won’t be used. If downgrade from application level DoH to OS resolver is allowed, ECH will get disabled at least temporary. Thus I think this list belongs here close enough.

What is ECS?

EDNS Client-Subnet is a DNS extension letting the authoritative nameserver know your subnet, generally a /24 (IPv4) or a /56 (IPv6), but the revealed subnet size is up to your DNS resolver configuration.

See also simpler explanation at PrivacyGuides.org DNS Overview.

  • /24 is the first three parts of your IPv4 address e.g. 192.0.2.xxx. The last part of your IP address (the xxx) again is a number between 1 to 254 (since 0 is reserved for the network itself and 255 is the broadcast address).
  • /56 includes 256 /64s and if your ISP (Internet Service Provider) follows RFC 6177, it’s assigned solely to you meaning the authoritative nameserver will know the request originated from your network.

Why to use ECS?

Android DoH3 option: dns.google

[…] The longer the distance the data must travel from the data centre to the end-user device, the more energy the transmission consumes – regardless of the transmission path used. Intercontinental transmission networks are fundamentally very efficient. Transferring data from the United States to Europe may consume a fraction of the energy compared to the last kilometre from the base station to the mobile phone.

If you utilize services of internet giants or content delivery networks, ECS will likely give you the shortest distance, the lowest latency, the highest speed and may help with decreasing your digital carbon footprint.

The above means GAFAM, if you don’t use them in any form, there may not be a need for ECS.

If those matter to you, you may also like to consider increasing your minimum TTL to around an hour in a local server.

Criticizers will ask whether changing your DNS server will save the world? No, fighting climate change takes much more, while some of it is small effortless tasks which effect cumulates. Anyway, keep reading.

Why to not use ECS?

Android DoH3 option: cloudflare-dns.com

[…] we [Cloudflare] don’t pass along the EDNS subnet information. This information leaks information about a requester’s IP and, in turn, sacrifices the privacy of users. This is especially problematic as we work to encrypt more DNS traffic since the request from Resolver to Authoritative DNS is typically unencrypted. We’re aware of real world examples where nationstate actors have monitored EDNS subnet information to track individuals, which was part of the motivation for the privacy and security policies of 1.1.1.1.

[…]

We are working with the small number of networks with a higher network/ISP density than Cloudflare (e.g., Netflix, Facebook, Google/YouTube) to come up with an EDNS IP Subnet alternative that gets them the information they need for geolocation targeting without risking user privacy and security. Those conversations have been productive and are ongoing. […]

ECS will decrease the cost of mass surveillance as instead of having to surveill everything happening on the network, anyone between your DNS server and the authoritative nameserver can see which IP addresses access the site with a reasonable accuracy.

Then there are those with commercial interests, particularly outside of Europe, advertisers may be interested in making money out of the additional metadata. There may also be adblockers which don’t block the DNS request, causing the advertising company to receive your IP address (or close enough to it) even if you didn’t see the advertisement itself.

Some say the less metadata is produced, the smaller incentive there is for starting collecting and monetizing it.

Additionally researchers (below) have used it to perform cache poisoning against an individual target directing them to a wrong location and with low TTL making it near impossible to audit later.

What domains do you use? What if someone far above you knew regardless of Encrypted Client-Hello?

Are the domains you use DNSSEC-signed? Do you verify DNSSEC locally? Do you use HTTPS everywhere? Do you know to not accept warnings about certificate issues? Do the other (less technical) users of your network? Would you or them be a delicious target? Do you even use GAFAM services?

See also:

Why to use private ECS?

Android DoH3 option: ?

Do you want the benefits of ECS with the privacy and security of not having ECS? Private ECS is a compromise solution in the middle, although not without its own issues.

Your private DNS provider will lie for you and say that your IP address is somewhere else where it will also place many others from your ISP. However what if it says you are a customer of another ISP, possibly even located in another country? It tends to have greater accuracy with IPv4 than IPv6, see AdGuard Google Domains issue.

In that case you may get even worse performance than without ECS. Then again if everything works properly, you will get the benefit of ECS without the privacy impact and lessened security impact.

See the next section for testing “where you are.” Consider also what is important for you if you had to pick one or two.

See also:

Is this a relevant question?

It’s likely greener to just use adblocking DNS no matter where it is located, preferably on router level. I don’t trust router/DHCP provided DNS and encrypt it on the end device anyway. And if something needs unfiltered access (AdNauseam?), give it DNS over HTTPS like all browsers and curl have the ability nowadays.

Identifying support for ECS

Or what is being sent to the authoritative servers.

# https://support.google.com/interconnect/answer/7658602
dig +short TXT o-o.myaddr.l.google.com.
# https://www.akamai.com/blog/developers/introducing-new-whoami-tool-dns-resolver-information
dig +short TXT whoami.ds.akahelp.net.
dig +short TXT whoami.ipv6.akahelp.net.
dig +short TXT whoami.ipv4.akahelp.net.
# https://powerdns.org/useful-names/
dig +short TXT whoami-ecs.lua.powerdns.org.
dig +short TXT whoami-ecs.v6.powerdns.org.
dig +short TXT whoami-ecs.v4.powerdns.org.

DNS0.eu or Quad9?

In my experience DNS0.eu tends to have better filtering and reporting options than Quad9, while servers being located only in the European Union is mildly problematic when your users start traveling outside it either for work or leisure, which across continents tends to bring round-trips overseas. Additionally private ECS (see above) tends to be bad poor for IPv6 and for very small AS like a school, it directs to another side of the country, but that is a very minor issue.

Meanwhile Quad9 blocking seems almost as good in tests like this and they give me impression of more transparency (as opposed to DNS0.eu only having a Twitter X account). Quad9 also has more options on whether to ECS or not (see above).

The end-users traveling outside of the EU is also solved as they have servers all around the world.

Back to DNS0.eu, while disabling private ECS is not an option, they do have other options; default filters, no filters, heavier filtering (zero) and kids.

Conclusion

As the size and confusion this page induces to anyone else than me shows, I have spent too much time thinking about DNS and related matters.

  • Android: while the system only gives the option between cloudflare-dns.com and dns.google (HTTP/3, see below), web browsers are free to choose the DoH server. If the device is not expected to travel far outside the EU, DNS0.eu may be a safe choice, otherwise Quad9.
    • As I have to support devices going outside of the EU, I lean towards Quad9.
  • iOS (or Apple in general): same question, do the devices travel outside of the EU? Both provide configuration profiles.
  • Personal computers: I have reached the cursed conclusion of using Unbound upstreams DNS0 for IPv4, Quad9 ECS for IPv6 and using the hosts file to point web browsers away from DNS0.eu IPv6 using IPv4 mapped IPv6 addresses.
    • Especially the last part is cursed.
    • Yes, ECS has privacy concerns, however theoretically it’s only a fallback if IPv4 goes down (very rare, has happened for short periods of time in my experience), but the environment also weights my decision. See above on whether to ECS or not.
  • Personal servers: Personal preference, you could even use all of the DNS servers or be your own recursor. I again have small preference towards Quad9 ECS as titlefetching for unencrypted IRC connection is already open for mass surveillance and there is no telling who triggered a DNS query there anyway.
  • Business/association/enterprise/whatever device: there may be free political/regulational/bureaucratic/whatever brownie points for using DNS0.eu with the queries not being transmitted outside of the EU.

This may also be a wrong approach entirely and it should just be an adblocking DNS as noted before.

Additionally DNS filtering for web browsers may be irrelevant if browser policy enforces extensions that block malicious domains (such as µBlock Origin or AdNauseam) or even Google Safe Browsing.

Mobile applications

With the exception of those apps that config I remember otherwise or share it with desktop versions etc.

Android

Use either cloudflare-dns.com (which doesn’t have ECS) or dns.google (which has ECS) as the (Settings → Network & Internet → Advanced →) Private DNS server as they have special handling and are thus DNS over HTTPS3 instead of the usual DNS over TLS. This can be confirmed with https://1.1.1.1/help (when using cloudflare-dns.com).

Then setup your web browser (including Firefox (other than stable which disables about:config) and Chrome) to use DNS over HTTPS with your preferred server and while at it enabling HTTPS only mode.

At least https://security.cloudflare-dns.com/dns-query won’t downgrade to system DNS resolver so malware.testcategory.com is blocked and that will hopefully affect other filtering DNS servers and actual malicious domains as well. Meanwhile nudity.testcategory.com loads as expected outside of https://family.cloudflare-dns.com/dns-query.

If testing Cloudflare, see also:

Do other Android based OSes contain the special handling of specific Private DNS domains turning into DNS-over-HTTP/3?

Rethink

NOTE! This pretends to be a VPN and thus breaks things depending on seeing the IP directly such as wireless debugging LAN IP, Briar LAN connections, cause warnings in Ooni Probe and disable automatic testing, Syncthing Fork will not autostart due to detecting the network as metered, unless it’s given permission to run in metered networks.

  1. Use either GitHub or F-Droid release as Google Play doesn’t have blocklists.
  2. Enable it.
  3. In Android Settings, Internet, Advanced, VPN, select Rethink, make it always-on and block connections not using it.
  4. Disable private DNS in Android settings too, as it conflicts.
  5. In Rethink itself open Configure.
  • DNS: enable whatever DNS you prefer.
  • DNS: Visit on-device blocklists.
  • DNS: Consider enabling Use in-app downloader, DNS booster
  • DNS: Disable Prevent DNS leaks to avoid breakage.
  • Network: enable Use all available networks (experimental)
  • Network: Loopback (experimental)
    • This also implies the previous option.
  • Network: Choose IP version: Auto
  • Network: Perform connectivity checks
  1. Remember to also visit Android app details for Rethink, in battery menu select unrestricted and in network allow unlimited data even with data saver.

Hopefully there is no situation where Rethink stops working and thinks it’s still working. As can be deduced from this section, sometimes Rethink and I disagree with each other. I don’t guarantee I know what I am doing.

FFUpdater

  • https://dns0.eu;2a0f:fc80::;2a0f:fc81::;193.110.81.0;185.253.5.0
  • https://open.dns0.eu;2a0f:fc80::ffff;2a0f:fc81::ffff;193.110.81.254;185.253.5.254
  • https://doh.opendns.com/dns-query;2620:119:35::35;2620:119:53::53;208.67.222.222;208.67.220.220
  • https://dns11.quad9.net/dns-query;2620:fe::11;2620:fe::fe:11;9.9.9.11;149.112.112.11
  • https://dns12.quad9.net/dns-query;2620:fe::12;2620:fe::fe:12;9.9.9.12;149.112.112.12