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shell-things/etc/systemd/resolved.conf.d/README.md

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systemd-resolved additional config files

Quickstart

sudo systemctl enable --now systemd-resolved.service
sudo ln -rsf /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
# After changing configuration
sudo systemctl restart systemd-resolved

Files explained

  • 00-defaults.conf - configuration not touching resolvers. Disables DNSSEC (as systemd-resolved doesn’t handle it properly), enables opportunistic DoT and caching.
  • dot-*.conf - configuration to use the DNS provider with DNS-over-TLS. If captive portals are a concern, DNSOverTLS=no.
  • README.md - you are reading it right now.

General commentary

  • Based on my test DNSOverTLS is not supported in Ubuntu 18.04.x LTS (however at the time of writing this README.md, the current version is Ubuntu 20.04.0) (systemd v237). DNSOverTLS became supported in v239, strict mode (yes) in v243 (big improvements in v244).
    • TODO: find out when SNI became supported, I have just spotted it in the fine manual in 2020-06-??.
  • Domains has to be .~ for them to override DHCP. See https://www.internetsociety.org/blog/2018/12/dns-privacy-in-linux-systemd without which I wouldn’t have got this right.
  • DNSSEC may not work if the system is down for a long time and not updated. Thus allow-downgrade may be better for non-tech people, even with the potential downgrade attack. There are also captive portals, affecting DNSOverTLS. Both take yes or no or their own special option, for DNNSEC the allow-downgrade, for DNSOverTLS opportunistic.

Other links I have found important and my files are based on: