Fix .local resolve on Ubuntu

 


# `.local` (mDNS) resolution on Ubuntu 24.04 — troubleshooting aide


Setup assumed: LAN interface (e.g. `enpXsY`), a Docker bridge (`docker0` — ignore it).

Goal: resolve `myserver.local` etc. via mDNS, falling back to a local/unix DNS server for the LAN.


## Symptoms


```

resolvectl query myserver.local

myserver.local: resolve call failed: No appropriate name servers or networks for name found

```


## Diagnose


```bash

resolvectl status

```


Read two levels:


1. **Global** — `Protocols: +mDNS` means mDNS is enabled globally.

2. **Per-link** — the LAN interface must show `mDNS/DNS-SD` in `Current Scopes`.

   ⚠️ Per-link settings **override** the global section. Typical failure:

   global `+mDNS` but the LAN link shows `-mDNS` (another link, e.g. a bridge,

   may correctly show `+mDNS`).


## Fix


### 1. Enable mDNS globally (persistent)


`/etc/systemd/resolved.conf` (or a drop-in so the main file stays clean):


```bash

sudo mkdir -p /etc/systemd/resolved.conf.d

sudo tee /etc/systemd/resolved.conf.d/mdns.conf <<'EOF'

[Resolve]

MulticastDNS=yes

LLMNR=yes

EOF

sudo systemctl restart systemd-resolved

```


### 2. Enable mDNS on the LAN link (if still `-mDNS` after step 1)


```bash

sudo resolvectl mdns <LINK> yes   # <LINK> = link number from `resolvectl status` (e.g. 2)

```


This is **ephemeral** (survives daemon restart, may not survive reboot).

If it reverts after reboot, find the persistent per-link source:


```bash

grep -ri "mdns" /run/systemd/network/ /etc/systemd/network/ /etc/netplan/ 2>/dev/null

```


- `/etc/systemd/network/*.network` → set `MulticastDNS=yes` in the `[Link]` section of the matching file, `sudo systemctl restart systemd-networkd`

- netplan (`/etc/netplan/*.yaml`) → fix YAML, `sudo netplan apply`


### 3. Verify


```bash

resolvectl status               # LAN link → Current Scopes: ... mDNS/DNS-SD

resolvectl query myserver.local

```


## If mDNS scope is up but queries still fail


mDNS is multicast and **peer-to-peer**: it only works if the target host is

actively *publishing* its name.


- Publishes by default: macOS, Raspberry Pi, Synology, many NASes, phones.

- Does NOT publish by default: plain Ubuntu/Debian servers (needs avahi-daemon),

  most Linux servers, often Windows servers.


Check what's publishing:


```bash

sudo apt install avahi-utils

avahi-browse -a

```


If the target isn't listed, mDNS will never resolve it — use unicast DNS:


```bash

sudo resolvectl dns <LINK> <your-dns-server-ip>   # ephemeral

```


Persistent: `DNS=<ip>` in the matching `.network` file, or `nameservers:`

in the netplan YAML.


## Pitfalls (learned the hard way)


- **Do NOT edit `/etc/resolv.conf`** — it's a symlink to

  `/run/systemd/resolve/stub-resolv.conf`, auto-regenerated on every

  systemd-resolved restart, and it doesn't parse INI sections at all.

  Config lives in `/etc/systemd/resolved.conf` + `/etc/systemd/resolved.conf.d/*.conf`.

- `resolvectl` (query/control) ≠ `resolvconf` (legacy tool, not used here).

- If `resolved.conf` says "Managed by NetworkManager" but NM isn't running,

  the header is stale — edit it directly. If NM *is* running, use

  `/etc/NetworkManager/NetworkManager.conf.d/` with `mdns=both` in `[main]`.

- mDNS doesn't cross subnets/VLANs or Wi-Fi client-isolation.

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