mikaela.github.io/n/dns.md

---
title: Philosophical pondering on DNS and its features and usage
excerpt:
  What DNS server is used, does it support ECS, is that threat or possibility,
  and everything that doesn't have a better place?
layout: mini
permalink: /n/dns.html
redirect_from:
  - /n/ffupdater.html
  - /n/rethink.html
  - /n/esni.html
  - /n/ech.html
sitemap: true
lang: en
robots: noai
---

# DNS notes

_{{ page.excerpt }} For DNS resolvers, refer to [r/resolv.tsv](/r/resolv.tsv)_

<!-- editorconfig-checker-disable -->
<!-- prettier-ignore-start -->

<!-- START doctoc generated TOC please keep comment here to allow auto update -->
<!-- DON'T EDIT THIS SECTION, INSTEAD RE-RUN doctoc TO UPDATE -->
<em lang="fi">Automaattinen sisällysluettelo</em> / <em lang="en">Automatically generated Table of Contents</em>

- [Identifying DNS resolver](#identifying-dns-resolver)
  - [Identifying ECH support](#identifying-ech-support)
- [What is ECS?](#what-is-ecs)
  - [Why to use ECS?](#why-to-use-ecs)
  - [Why to not use ECS?](#why-to-not-use-ecs)
  - [Why to use private ECS?](#why-to-use-private-ecs)
  - [Is this a relevant question?](#is-this-a-relevant-question)
  - [Identifying support for ECS](#identifying-support-for-ecs)
- [[DNS0.eu] or [Quad9]?](#dns0eu-or-quad9)
- [CLI applications](#cli-applications)
- [Mobile applications](#mobile-applications)
  - [Android](#android)
  - [Rethink](#rethink)
  - [FFUpdater](#ffupdater)

<!-- END doctoc generated TOC please keep comment here to allow auto update -->

<!-- prettier-ignore-end -->
<!-- editorconfig-checker-enable -->

---

## Identifying DNS resolver

- [DNS-OARC's Check My DNS](https://cmdns.dev.dns-oarc.net) - popup under
  "Network".
- [dnsleaktest](https://dnsleaktest.com)
- [whatsmydnsserver](https://www.whatsmydnsserver.com)
- [ipleak.net](https://ipleak.net)
- [dnsadblock](https://dnsadblock.com/dns-leak-test/)
- [browserleaks.net/dns](https://browserleaks.net/dns)
- [dnscheck.tools](https://www.dnscheck.tools)

The above list is based on
[redirect2me/which-dns README alternatives section](https://github.com/redirect2me/which-dns/blob/main/README.md)

---

### 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.

- [Cloudflare Browser Check](https://www.cloudflare.com/ssl/encrypted-sni/)
  which still speaks of ESNI, while ECH replaced Encrypted Server Name
  Indication ages ago.
  - [crypto.cloudflare.com/cdn-cgi/trace](https://crypto.cloudflare.com/cdn-cgi/trace),
    look for `sni=encrypted`.
- [tls-ech.dev](https://tls-ech.dev/)
- BONUS: [OCSP stapling test](https://www.vpnhosting.cz/ocsp/)

---

## What is ECS?

[EDNS](https://en.m.wikipedia.org/wiki/Extension_Mechanisms_for_DNS)
[Client-Subnet](https://en.wikipedia.org/wiki/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](https://www.privacyguides.org/en/advanced/dns-overview/#what-is-edns-client-subnet-ecs)._

- /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 `/64`s and if your ISP (Internet Service Provider) follows
  [RFC 6177](https://datatracker.ietf.org/doc/html/rfc6177), it's assigned
  solely to you meaning the authoritative nameserver will know the request
  originated from your network.
  - However many ISPs, especially wireless ones, will just assign you a `64`
    which is required for
    [stateless address autoconfiguration](<https://en.m.wikipedia.org/wiki/SLAAC#Stateless_address_autoconfiguration_(SLAAC)>)
    which is the most common way of getting IPv6 address in your local area
    network as opposed to IPv4 where you would have
    [Dynamic Host Configuration Protocol (DHCP)](https://en.m.wikipedia.org/wiki/Dynamic_Host_Configuration_Protocol).
    - Your router does get the IPv6 subnet assignment for LAN distribution by
      means of
      [DHCPv6 Prefix Delegation](https://en.m.wikipedia.org/wiki/Prefix_delegation)
      which is also common on mobile networks.

If you are reading my personal notes (that being useful for you would bring me a
bit of happiness), please note that **_I am somewhat indecisive and change the
DNS resolver a lot (at least daily judging by my feelings), but do check the git
log._**

- [History of this page at GitHub](https://github.com/Mikaela/mikaela.github.io/commits/master/n/dns.md)

### 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.

- [Green Code](https://www.exove.com/green-code/)
  ([pdf](https://www.exove.com/app/uploads/2023/09/Green-Code-v2.pdf)
  [txt](https://www.exove.com/app/uploads/2023/09/greencode-v2.txt))

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](https://en.m.wikipedia.org/wiki/Edge_computing)
and may help with decreasing your _digital carbon footprint_.

I was also surprised to find speedy Google Play Store download in the middle of
sea (Helsinki-Tallinn) when switching from non-ECS to ECS nameserver. I wonder
if they had an [edge node](https://peering.google.com/#/) somewhere in clsoe
proximity or if it was juat happenstance.

_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](https://blog.apnic.net/2019/11/12/stop-using-ridiculously-low-dns-ttls/).

### 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. [...]

- [Cloudflare co-founder](https://news.ycombinator.com/item?id=19828702),
  emphasis mine.

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._

This isn't even mentioning that the internet isn't a nice place or foreign
advanced persistent threats or threat actors, who may not need a reason to
attack you.
[_CISA: Mitigating Cyber Threats with Limited Resources: Guidance for Civil Society_](https://www.cisa.gov/resources-tools/resources/mitigating-cyber-threats-limited-resources-guidance-civil-society)

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?

It's important to remember that authoritative nameserver is the one that knows
where the domain is hosted that you can see through e.g. `whois aminda.eu` which
will reply `lakas.ns.cloudflare.com` and `coco.ns.cloudflare.com`. Thus when you
perform a DNS query with ECS enabled, the USA will know your IP with the
accuracy of 256 users (poor example since
[this site is currently hosted on GitHub pages](https://github.com/Mikaela/mikaela.github.io/issues/153)).
Same as when you visit a domain ending
[`.af`, Afganistan will know](https://en.wikipedia.org/wiki/.af#Restrictions).

See also:

- [_Understanding the Privacy Implications of ECS_](https://yacin.nadji.us/docs/pubs/dimva16_ecs.pdf)

### Why to use private ECS?

_Android DoH3 option:_
[?](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/DnsResolver/PrivateDnsConfiguration.h)

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 a bit 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](https://adguard-dns.io/en/blog/dns-google-domains-fixed.html).
What if no one else uses the same DNS server as you, especially from your ISP? I
guess you can always advocate your DNS provider so it could be someone else too
(I couldn't)? If it works most of time, does that outweight the times it won't
work? Is perfect the enemy of good enough?

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

I am often observing Cloudflare and other public DNS providers connecting me to
Swedish servers when no ECS is used and so far the only place where I spent
significant amount of time with wrong private ECS was a school and considering
the drawbacks of ECS in the current world situation, I think private ECS is
easily the least bad option.

See the next section for testing "where you are." Consider also what is
important for you if you had to pick one or two from privacy, performance and
climate.

See also:

- [NextDNS (Medium.com): How we made DNS both fast and private with ECS](https://medium.com/nextdns/how-we-made-dns-both-fast-and-private-with-ecs-4970d70401e5)
- [AdGuard DNS: Privacy-friendly EDNS Client Subnet](https://adguard-dns.io/en/blog/privacy-friendly-edns-client-subnet.html)
- [DNS0 Privacy Policy](https://www.dns0.eu/privacy)

### 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.

Are you someone whom someone might want bad things to just for existing?

### Identifying support for ECS

Or what is being sent to the authoritative servers.

```bash
# 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.
```

- Note:
  [Cloudflare sends ECS only for `whoami.ds.akahelp.net`, nowhere else](https://developers.cloudflare.com/1.1.1.1/faq/#does-1.1.1.1-send-edns-client-subnet-header).

---

## [DNS0.eu] or [Quad9]?

In my experience [DNS0.eu] tends to have better filtering and
[reporting options](https://www.dns0.eu/report) than [Quad9], while
[servers being located only in](https://www.dns0.eu/network) the
[European Union](https://european-union.europa.eu) 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](https://techblog.nexxwave.eu/public-dns-malware-filters-tested-in-september-2024/)
and they give me impression
[of more transparency](https://quad9.net/about/transparency-report) (as opposed
to
[DNS0.eu only having a <del>Twitter</del> X account](https://twitter.com/dns0eu)).
[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](https://quad9.net/service/locations/).

Back to [DNS0.eu], while disabling private ECS is not an option, they do have
other options; [default filters](https://www.dns0.eu),
[no filters](https://www.dns0.eu/open),
[heavier filtering (zero)](https://www.dns0.eu/zero) and
[kids](https://www.dns0.eu/kids).

[DNS0.eu]: https://www.dns0.eu
[Quad9]: https://quad9.net

---

## CLI applications

- `drill` gets often mentioned, Fedora has it in `ldns-utils`, so others
  probably have it in similarly named packages.

## 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](https://cs.android.com/android/platform/superproject/main/+/main:packages/modules/DnsResolver/PrivateDnsConfiguration.h)
and are thus DNS over HTTPS3 instead of the usual DNS over TLS. This can be
confirmed with [`https://1.1.1.1/help`](https://one.one.one.one/help) (when
using `cloudflare-dns.com`). **_However is connectivity in limited networks and
maybe a bit faster speed in bad network more important than a level of security
reached by a filtering resolver?_**

Then setup your web browser (including Firefox Nightly (other channels disable
`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`](https://malware.testcategory.com) is blocked and
that will hopefully affect other filtering DNS servers and actual malicious
domains as well. Meanwhile
[`nudity.testcategory.com`](https://nudity.testcategory.com) loads as expected
outside of `https://family.cloudflare-dns.com/dns-query`.

If testing Cloudflare, see also:

- [1.1.1.1/help](https://one.one.one.one/help) for general troubleshooting
- [help.teams.cloudflare.com](https://help.teams.cloudflare.com) for filtering
  although it just sends you to
  - [radar.cloudflare.com](https://radar.cloudflare.com) where
    [IP](https://radar.cloudflare.com/ip) is worth checking too.
- [speed.cloudflare.com](https://speed.cloudflare.com) for speed testing

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

- GrapheneOS:
  [yes](https://github.com/GrapheneOS/platform_packages_modules_DnsResolver/blob/13/PrivateDnsConfiguration.h)
- LineageOS:
  [yes](https://github.com/LineageOS/android_packages_modules_DnsResolver/blob/lineage-20.0/PrivateDnsConfiguration.h)
  - /e/OS:
    [yes](https://gitlab.e.foundation/e/os/android_packages_modules_DnsResolver/-/blob/v1-t/PrivateDnsConfiguration.h)

### [Rethink](https://github.com/celzero/rethink-app)

**_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.

**_NOTE ESPECIALLY!_** _Android Auto_ cannot be used when there is a "VPN"
connected (why? ask Google, not me). Additionally you may encounter
[questionable battery drain](/n/androidbattery.html).

1. Use either GitHub or F-Droid release as Google Play doesn't have blocklists.
1. Enable it.
1. In Android Settings, Internet, Advanced, VPN, select Rethink, make it
   always-on and block connections not using it.
1. Disable private DNS in Android settings too, as it conflicts.
1. 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.
1. I also have a suspicion that Android _Developer_ Setting
   `Always keep mobile data active` is interfering with Rethink as always-on VPN
   causing connectivity issues or it not being sure whether "metered" or
   unmetered network is being used.
   1. The setting is enabled by default nowadays, to access it, go to about
      phone and rapidly tap `Software build number` (backtranslated to English
      from Finnish (like everything else (TODO: check in English)).
   1. Once you are a developer, `System Settings` (within `Settings`) should
      have a new `Developer Settings` menu `Mobile data always active` is under
      `Connection properties` section (which is above `Input`)

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://github.com/Tobi823/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`

---