The previous default configured systemd-resolved with `resolvectl dns
fips0 [<fips0_addr>]:5354`, intended to bypass an Ubuntu 22 systemd 249
interface-scoping bug. That target collides with the daemon's
mesh-interface filter on Linux: when an IPv6 packet's destination
belongs to a non-loopback interface, the kernel attributes the packet
to that interface in IPV6_PKTINFO (ipi6_ifindex == fips0) even though
loopback delivery is used (tcpdump shows lo). The mesh-interface filter
sees arrival_ifindex == mesh_ifindex and silently drops every query at
trace level — invisible to operators at the default debug level.
Net effect on stock deployments: every .fips query on systemd-resolved
hosts was silently dropped.
Daemon side
-----------
- Default `dns.bind_addr` changes from "::" to "::1" (IPv6 loopback
only). The mesh-interface filter is then defanged on the default
path because loopback isn't reachable from mesh peers. The filter
remains in place defensively for operators who explicitly bind "::"
to expose a mesh-reachable responder.
fips-dns-setup backend unification
----------------------------------
- New `try_global_drop_in` backend writes
/etc/systemd/resolved.conf.d/fips.conf with DNS=[::1]:5354 and
Domains=~fips. Inserted ahead of `try_resolvectl` in the dispatch
chain. The standard loopback path has no interface scoping, so
ipi6_ifindex reports lo and the filter passes.
- All other backends now target [::1]:5354 to match the daemon's
default IPv6-loopback bind:
- try_dns_delegate writes DNS=[::1]:5354
- try_dnsmasq writes server=/fips/::1#5354
- try_nm_dnsmasq writes server=/fips/::1#5354
- Fixed dns-delegate file path: was /etc/systemd/dns-delegate/, must
be /etc/systemd/dns-delegate.d/ (with .d suffix). systemd-resolved
silently ignored the previous path.
- fips-dns-teardown handles the new global-drop-in backend in cleanup.
- The legacy resolvectl per-link backend stays as a fallback,
documented to require careful daemon bind_addr coordination.
fips-gateway upstream pairing
-----------------------------
- gateway.dns.upstream default changes from 127.0.0.1:5354 to
[::1]:5354 to match the daemon's default bind. Linux IPv6 sockets
bound to explicit ::1 do not accept v4-mapped traffic, so the old
default would have caused the gateway's startup DNS reachability
probe to time out and systemd to restart-loop the service.
- Operators who set a non-default daemon `dns.bind_addr` must also
set `gateway.dns.upstream` to match — documented inline.
Documentation
-------------
- packaging/common/fips.yaml and packaging/openwrt-ipk fips.yaml
examples updated; rationale for the bind_addr choice and the
daemon/gateway pairing recorded inline.
Test coverage
-------------
- testing/dns-resolver/test.sh: real-fipsd end-to-end scenario added.
Builds fipsd in a Debian 12 builder image (cached), runs the daemon
with a real TUN in a privileged container, configures DNS via the
setup script, and asserts `dig @127.0.0.53 AAAA <npub>.fips` returns
AAAA. Refactored as a parameterized helper running across Debian
12/13 and Ubuntu 22/24/26 (5 e2e scenarios). Backend-aware
assertions: on systemd >= 258 the expected backend is dns-delegate;
on older systemd it's global-drop-in. Strict content checks fail CI
on any [::1]:5354 drift. fips-gateway also exercised in the
debian12 scenario to lock the gateway-upstream pairing. Renamed all
"fipsd" references to "fips" (project convention).
- testing/deb-install/ (new harness): builds the actual .deb via
cargo-deb in a Debian 12 builder image (cached), installs via apt
across each target distro, verifies maintainer scripts, conffile
placement, binary placement, and end-to-end .fips resolution after
start. Also exercises fips-gateway against the installed daemon to
verify the gateway/daemon default pairing on a real .deb path.
- This is the test layer that was missing — the previous harness only
verified config files were written, never that queries reached the
daemon.
Verified: dns-resolver 78/78 assertions, deb-install 55/55 assertions
across all 5 distros (debian:12, debian:trixie, ubuntu:22.04,
ubuntu:24.04, ubuntu:26.04).
Replace the resolvectl-only fips-dns.service with a detection script
that configures whichever DNS resolver is available:
1. systemd dns-delegate (systemd >= 258, declarative drop-in)
2. systemd-resolved via resolvectl (most systemd distros)
3. dnsmasq (standalone)
4. NetworkManager with dnsmasq plugin
5. Warning with manual instructions if none found
Service reloads are non-fatal — config is written and the backend
is recorded even if the reload fails, preventing state file cleanup
issues under set -e.
Teardown reads the recorded backend from /run/fips/dns-backend and
reverses the configuration, or cleans up all possible backends if
the state file is missing.
Includes a Docker-based test harness (testing/dns-resolver/test.sh)
covering all five backends across Debian 12, Debian 13, Fedora,
and bare systems.
Fixes#52.
Johnathan Corgan
