DNS Over TLS

Summary

Fedora will attempt to use DNS over TLS (DoT) if supported by configured DNS servers.

Owner

Name: Michael Catanzaro
Email: <mcatanzaro@redhat.com>
Name: Zbigniew Jędrzejewski-Szmek
Email: <zbyszek@in.waw.pl>

Current status

Targeted release: Fedora 34
Last updated: 2020-09-29
FESCo issue: <will be assigned by the Wrangler>
Tracker bug: <will be assigned by the Wrangler>
Release notes tracker: <will be assigned by the Wrangler>

Detailed Description

We will build systemd with -Ddefault-dns-over-tls=opportunistic to protect DNS queries against passive network attackers. An active network attacker can trivially subvert this protection, but we cannot make DoT mandatory because other operating systems do not do so and most DNS servers do not support it. DoT will only be used if the configured DNS server supports it and if it is not blocked by an active network attacker.

Note that DoT is different from DNS over HTTPS (DoH). In particular, DoT is not an anti-censorship tool like DoH. It does not look like regular HTTPS traffic, and it can be blocked by network administrators if desired, so it should not be a problem for corporate networks.

Feedback

Benefit to Fedora

DNS queries are encrypted and private by default, if the user's ISP supports DNS over TLS. Most probably don't, but users who manually configure a custom DNS server (e.g. Cloudflare or Google) will automatically benefit from DNS over TLS.

Scope

Proposal owners: change meson flags in systemd.spec
Other developers: N/A (nothing should be required)
Release engineering: #9772 (a check of an impact with Release Engineering is needed)
Policies and guidelines: N/A (nothing should be required)
Trademark approval: N/A (not needed for this Change)
Alignment with Objectives: Nope

Upgrade/compatibility impact

DoT will be enabled automatically on upgrade to F34. If DoT is unsupported, systemd-resolved will fall back to unencrypted DNS, so there should be no compatibility impact.

How To Test

TODO

User Experience

Users should not notice any difference in behavior, unless checking how DNS is sent in Wireshark.

Dependencies

No dependencies.

Contingency Plan

Contingency mechanism: revert the change
Contingency deadline: can be done at any time, before F34 beta freeze would be best
Blocks release? No
Blocks product? No

Documentation

See the section DNSOverTLS= in the manpage resolved.conf(5)

Release Notes