Merge pull request 'Issue 198: the home network's DNS server ran outside the mesh, and its filter closed it' (#283) from jschoubben/the-lans-dns-is-the-mesh into main

2026-10-02 10:22:51 +00:00
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+---
+status: resolved
+opened: 2026-10-02
+located-in: [mesh-catalog modules/dnsmasq (listens on loopback and the machine's mesh address only), the home-server's DNS (a predecessor's dnsmasq configuration the mesh did not own), the home network's DHCP (hands out the home-server as every device's DNS)]
+fixed-by: mesh-catalog PR 214 (dnsmasq listens on addresses from a setting; docker's file takes no settings), mesh-controller PR 210 (the settings verb), mesh-catalog PR 215 (unifi network DNS tools), live 2026-10-02
+amended-design: []
+---
+
+# 198 — The home network's DNS server ran outside the mesh, and the mesh's filter closed it
+
+## What was observed
+
+Every phone on the home Wi-Fi had no internet, while a laptop on the same Wi-Fi did. The router's
+DHCP hands every device the home-server's LAN address as its DNS server. The home-server's DNS daemon
+was listening on that address, and every query to it timed out. The router itself answered the same
+query at once. The laptop worked because it resolves through its own local resolver, not through the
+server DHCP names.
+
+## Why it happened
+
+The DNS daemon on the home-server was not the mesh's. It ran under a configuration file a predecessor
+generated, listening on loopback, the mesh address and the LAN address. The mesh's `dnsmasq` module was
+assigned to the other three machines and not to this one, so no module on the home-server declared
+port 53. Its filter opens only what a module declares, so DNS from the LAN was dropped. It started when
+the home-server applied the filter this morning, after nine hours of applying nothing
+([issue 194](../194-the-hosts-own-former-archive-stops-every-apply/00-report.md)).
+
+Nothing said so. The daemon reported running, the filter applied cleanly, and the mesh had no record
+that the home network depended on a service it did not know.
+
+## Why it matters
+
+**A service the mesh does not know is closed by the mesh's filter, by design, and nothing asks whether
+something depends on it.** That is the right default for an unknown port. It is the wrong outcome for
+the one service a whole network was told to use. The gap is that a machine can run something
+important outside the mesh with nothing to show it.
+
+**The mesh's `dnsmasq` could not have served the LAN either.** It listened on loopback and the mesh
+address only. The reach of its DNS endpoints opens the filter, but the daemon would not have been
+listening on the LAN address anyway.
+
+## Open questions
+
+- Should a machine report the listening services the mesh does not own, the way it reports the links
+  that face outside? This one would have been visible before the filter closed it.
+- The LAN address the home-server answers on is now a setting, beside the reach that opens the filter.
+  Two statements that must agree. Should reach `public` on a DNS endpoint imply listening beyond the
+  mesh?
+
+## Resolved (2026-10-02)
+
+The home network was pointed at the gateway for DNS while the fix was built, which got the phones back
+within minutes. Then:
+
+- the mesh's `dnsmasq` takes the addresses it listens on beside the machine's from a setting, with
+  loopback as the mesh-wide default, so no other machine changed;
+- the home-server's layer adds its LAN address, and its DNS endpoints' reach is `public`. The router
+  forwards no DNS, so that means the LAN;
+- the module and its sibling `resolv-conf` were assigned to the home-server, replacing the
+  predecessor's daemon and configuration, which were kept aside;
+- the home network was pointed back at the home-server, through a new `unifi` tool.
+
+Checked live: from another machine on the LAN, public names and mesh names both resolve through the
+home-server's LAN address, and the mesh and the machine itself resolve as before.
+
+**One fault found on the way, and caught before it reached any machine.** A module's settings are
+merged into every mergeable file the module owns. The first attempt therefore put the new setting into
+docker's `daemon.json` as well as into dnsmasq's config, and dockerd refuses keys it does not know. The
+plan showed it before any push. The change was reverted and redone with docker's file declared to take
+no settings. The general fault, a module's settings reaching files they were not meant for, is still
+there for any module with more than one file.