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

systemd-resolved additional config files

• Quickstart
• Files explained
• General commentary

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 that should be used everywhere. Enables DNSSEC (regardless of systemd-resolved not handling it properly), enables opportunistic DoT, caching and local DNS servers.
• dot-*.conf - configuration to use the DNS provider with DNS-over-TLS. If captive portals are a concern, DNSOverTLS=opportunistic. At least one of these should be used in addition to 00-defaults.conf
• nordvpn.conf - includes NordVPN’s resolver addresses for hosts using it
• README.md - you are reading it right now.

General commentary

• DNSOverTLS became supported in systemd v239, strict mode (true) 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 true or false or their own special option, for DNSSEC the allow-downgrade, for DNSOverTLS opportunistic.
  • Then again when was any system that outdated to not have working DNSSEC?
    • TODO: return to this configuration should that actually happen?
    • I am actually running Unbound simultaneously with resolv.conf pointing to both with options rotate edns0 trust-ad which might workaround that potential issue.

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

• https://wiki.archlinux.org/index.php/Systemd-resolved
  • Also provides the serious issues systemd-resolved+DNSSEC issues, https://github.com/systemd/systemd/issues/10579 & https://github.com/systemd/systemd/issues/9867
• request for strict DoT: https://github.com/systemd/systemd/issues/10755
• vulnerable to MITM: https://github.com/systemd/systemd/issues/9397