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84 lines
4.2 KiB
Markdown
84 lines
4.2 KiB
Markdown
# systemd-resolved additional config files
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- [Quickstart](#quickstart)
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- [Files explained](#files-explained)
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- [General commentary](#general-commentary)
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## Quickstart
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```bash
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sudo systemctl enable --now systemd-resolved.service
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sudo ln -rsf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
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# After changing configuration
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sudo systemctl restart systemd-resolved
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```
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## Files explained
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- `00-defaults.conf` - configuration that should be used everywhere.
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Enables DNSSEC (regardless of systemd-resolved not handling it properly),
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enables opportunistic DoT, caching and local DNS servers (because they
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should exist anyway as I don't trust systemd-resolved entirely. Anyway if
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there truly is no local resolver, systemd-resolved will detect that and act accordingly.)
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- To rephrase, this is to be used together with other files, especially
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some of those beginning with `10-dot-`.
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- `05-do53-dna-moi.conf` - DNS servers used by DNA and Moi (who is on DNA's
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network and owned by them)
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- `05-do53-elisa.conf` - DNS servers used by Elisa and apparently their
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Saunalahti still exists here as well.
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- `10-dot-*.conf` - configuration to use the DNS provider with DNS-over-TLS.
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At least one of these should be used in addition to `00-defaults.conf`
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- `98-local-resolver.conf` attempts to configure localhost resolver and
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disables unnecessary features for that scenario. The number 10 takes
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priority over 00 and 05 so if a DNSOverTLS=true is uncommented, it will
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also apply to the former ones that are unlikely to support it. When
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numbering the files, I didn't think I would be adding the plaintext DNS
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servers that I am unlikely to use whenever Unbound is available (and I
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currently have only one system that has systemd-resolved while not having
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Unbound and it seems to prefer DoT over my router anyway).
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- `99-lan-resolver.conf.sample` when renamed would allow enabling resolvers on
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LAN assuming they are trusted. Note that if used together with
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`98-local-resolver.conf`, DNSSEC would be disabled.
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- `README.md` - you are reading it right now.
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## General commentary
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- DNSOverTLS became supported in systemd v239, strict mode (true) in
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v243 (big improvements in v244).
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- TODO: find out when SNI became supported, I have just spotted it in the
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fine manual in 2020-06-??.
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- Domains has to be `.~` for them to override DHCP. See https://www.internetsociety.org/blog/2018/12/dns-privacy-in-linux-systemd
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without which I wouldn't have got this right.
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- DNSSEC may not work if the system is down for a long time and not updated.
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Thus `allow-downgrade` may be better for non-tech people, even with the
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potential downgrade attack. There are also captive portals, affecting
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`DNSOverTLS`. Both take `true` or `false` or their own special option,
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for DNSSEC the `allow-downgrade`, for DNSOverTLS `opportunistic`.
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- Then again when was any system that outdated to not have working DNSSEC?
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- TODO: return to this configuration should that actually happen?
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- I am actually running Unbound simultaneously with `resolv.conf` pointing
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to both with `options rotate edns0 trust-ad` which might workaround that
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potential issue.
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- DNS server priority is the one they are specified in. The first working one
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will be used when it won't work anymore and then the next is used as long
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as it works and then it's back to the beginning.
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- https://github.com/systemd/systemd/issues/16322#issuecomment-724143641
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Other links I have found important and my files are based on:
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- https://wiki.archlinux.org/index.php/Systemd-resolved
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- Also provides the serious issues systemd-resolved+DNSSEC issues, https://github.com/systemd/systemd/issues/10579 & https://github.com/systemd/systemd/issues/9867
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- request for strict DoT: https://github.com/systemd/systemd/issues/10755
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- vulnerable to MITM: https://github.com/systemd/systemd/issues/9397
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