# avahi

The local network's name and service discovery (mDNS/DNS-SD) as a module (novox/hq to-be 42 Phase 1,
research 027).

## What it owns

- The `avahi` package.
- `avahi-daemon.service`, running and enabled.

## What it improves

It was on all four machines and owned by none. It is now declared, and its tools show why discovery
does not work today:

- **The packet filter drops mDNS.** The mesh's filter has no rule for inbound UDP 5353 on any of the
  four machines, so avahi announces this machine but hears no other machine's answers. A browse
  finds nothing, and resolving even the machine's own `.local` name times out. A module's `listens`
  can reach the private network, this machine or anywhere, but not the local link. Opening the port
  to anywhere would answer the internet on a public machine, so the module opens nothing. This needs
  a decision in novox/hq: a local-link source scope for `listens`. Until then, `avahi_status` reports
  `inbound_mdns_accepted: false`, and browse and resolve say so whenever they hear nothing.

## What it leaves found

- **`nss-mdns` and `/etc/nsswitch.conf`.** An ordinary lookup reaches avahi only through the
  `hosts:` line. That line is one ordered list shared by every name source: containers, files, DNS,
  mDNS and the resolver daemon. The host can write a marked block into a file, but it cannot add a
  member to a line. Owning the whole file would make this module the owner of every machine's name
  resolution. On 2026-10-04 all four machines had the same file, with `mdns4_minimal` wired by hand
  and nss-mdns installed. Both are left as found, and `avahi_status` reports the wiring.
- `/etc/avahi/avahi-daemon.conf`, including each workstation's hand-set `allow-interfaces`, which
  names that machine's own network interface.

## Tools

| tool | | answers |
|---|---|---|
| `avahi_status` | r | the daemon, its version and configuration, the `hosts:` line and whether mdns is on it, nss-mdns, whether the filter accepts inbound 5353, systemd-resolved beside it, and notes |
| `avahi_browse` | r | every service announced in a few seconds (`avahi-browse -prt`), resolved where possible, narrowed to a type |
| `avahi_resolve` | r | a `.local` name through avahi and through the name service side by side, or an address to its name |
| `avahi_services` | r | what this machine publishes from `/etc/avahi/services` |