mikaela.github.io/n/dns.md

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# DNS notes

_For DNS resolvers, refer to [r/resolv.tsv](/r/resolv.tsv)_

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- [Identifying DNS resolver](#identifying-dns-resolver)
  - [Identifying ECH support](#identifying-ech-support)
- [To ECS or not to ECS?](#to-ecs-or-not-to-ecs)
  - [Identifying support for client-subnet](#identifying-support-for-client-subnet)
- [Mobile applications](#mobile-applications)
  - [Android](#android)
  - [Rethink](#rethink)
  - [FFUpdater](#ffupdater)

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## Identifying DNS resolver

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

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/)

## To ECS or not to ECS?

[_Understanding the Privacy Implications of ECS_](https://yacin.nadji.us/docs/pubs/dimva16_ecs.pdf)
brings up two bigger issues EDNS client-subnet:

- Authoritative nameserver is given part of the subnet, which can be
  personally identifiable and as the connection between recursor and
  authoritative is unencrypted, anyone between them can observe all the
  queries.
  - Think of VPNs where traffic within the VPN is encrypted, but it won't
    magically encrypt plain traffic leaving it.
- Anyone between the recursive and authoritative nameservers can perform cache
  poisoning attack and give it a narrow target. With short TTL, it may be
  impossible to audit afterwards. Only DNSSEC can protect from this, but
  DNSSEC signing isn't used that widely.

These issues bring additional questions:

- Do you care?
  - If you run open wireless network and offer everyone ECS nameserver such as
    Google DNS through DHCP while using manually configured encrypted DNS by
    yourself, is there any cause for concern? You can always say it was
    someone using your open network? Or if this is a multi-user system like
    VPS running titlefetcher bot or Matrix homeserver, who knows who triggered
    the original queries and where? SteamOS? Speed over all as it's only used
    for gayming. Virtual machine lab? Who cares. Larger organization? That may
    be a big target?
  - How much does getting local content matter to you? More or less than
    increased resource use of contacting a server further away? Is private ECS
    an option? ([r/resolv.tsv](/r/resolv.tsv))
- What is the impact of domains you visit being surveilled?
  - This page mentions cases like FFUpdater where the surveillance would
    reveal that I interact with github.com and other sites it downloads apk
    files from, which hardly matters, but how about you?
- What is the impact of cache poisoning tailored to you?
  - Everything is encrypted and TLS certificates wouldn't match so would you
    continue to the wrong site regardless of the prompt, or decide something
    is wrong and try again later. How about your users?

### Identifying support for client-subnet

Or what is being sent to the authoritative servers.

```bash
dig +short TXT o-o.myaddr.l.google.com.
dig +short TXT whoami.ds.akahelp.net.
dig +short TXT whoami.ipv6.akahelp.net.
dig +short TXT whoami.ipv4.akahelp.net.
```

- Note: Cloudflare sends ECS only for whoami.ds.akahelp.net.

## 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 ove
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`).

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.

### [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.

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.

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`
- `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`