mDNS hostname not resolvable on fresh single-NIC install — per-interface mdns "default" does not announce

[PfisterFactor]

Describe the issue you are experiencing

On a fresh Home Assistant OS 17.1 installation with a single wired NIC (end0) and no VLANs, homeassistant.local is not resolvable via mDNS from other devices on the same subnet. Direct IP access works fine (http://192.168.0.217:8123).

The root cause is that the end0 network interface's mDNS mode defaults to "default", which in practice does not result in mDNS announcement — despite broadcast_mdns: true being set at the host level.

Key findings:

1. Host-level mDNS is enabled but ineffective:

   {"hostname": "homeassistant", "broadcast_mdns": true}

2. Per-interface mDNS is "default" (not "announce"):

   {"interface": "end0", "primary": true, "mdns": "default"}

3. The hassio_multicast container only binds to the internal hassio bridge, not the physical end0 interface:

   mdns-repeater (6): dev hassio addr 172.30.32.1 mask 255.255.254.0 net 172.30.32.0
   

   Container stats showed network_rx: 0, network_tx: 0. Restarting the container did not help.

4. The Supervisor's generate.py maps DEFAULT → DEFAULT (NM value -1) without promoting it to ANNOUNCE on the primary interface, even when broadcast_mdns: true. The NM → systemd-resolved chain for value -1 does not result in mDNS announcement in practice.

Workaround: Explicitly setting mdns: "announce" on end0 via the Supervisor API resolves the issue immediately:

curl -X POST -H "Authorization: Bearer $SUPERVISOR_TOKEN" -H "Content-Type: application/json" \
  -d '{"ipv4":{"method":"auto"},"mdns":"announce"}' \
  http://supervisor/network/interface/end0/update

Suggested fix: When the Supervisor generates connection settings for the primary interface and broadcast_mdns is true, "default" should be promoted to "announce". This could be done in get_connection_from_interface(). Related: home-assistant/supervisor#5520 (PR that added per-interface mDNS controls) states "if status is not set: it will fallback to current behaviour - set it to announce" but the code maps DEFAULT → DEFAULT without promotion.

What operating system image do you use?

rpi4-64 (Raspberry Pi 4/400 64-bit OS)

What version of Home Assistant Operating System is installed?

17.1

Did the problem occur after upgrading the Operating System?

No

Hardware details

• Raspberry Pi 4 Model B (64-bit)
• Wired ethernet via end0 (single NIC, no VLANs)
• Network: 192.168.0.0/24, UniFi-managed, mDNS enabled on network, no mDNS reflector needed (single LAN)
• Supervisor: 2026.02.2
• Core: 2026.2.2
• Multicast add-on: 2026.02.0

Steps to reproduce the issue

1. Fresh install HAOS 17.1 on Raspberry Pi 4 with single wired NIC
2. Confirm broadcast_mdns: true via GET /host/info
3. Check end0 interface via GET /network/interface/end0/info — observe "mdns": "default"
4. From another device on the same subnet, try ping homeassistant.local — fails with "Unknown host"
5. Confirm direct IP works: ping 192.168.0.217 — succeeds
6. Run POST /network/interface/end0/update with {"mdns":"announce"} — homeassistant.local resolves immediately

Anything in the Supervisor logs that might be useful for us?

2026-02-22 16:12:52.618 INFO (MainThread) [supervisor.api.middleware.security] /network/interface/end0/update access from a0d7b954_ssh
2026-02-22 16:12:53.112 INFO (MainThread) [supervisor.host.network] Updating local network information

No errors related to mDNS or multicast in supervisor logs. The multicast plugin restart showed:

2026-02-22 16:12:00.457 INFO (MainThread) [supervisor.plugins.multicast] Restarting Multicast plugin
2026-02-22 16:12:00.468 INFO (MainThread) [supervisor.docker.manager] Restarting hassio_multicast

Anything in the Host logs that might be useful for us?

2026-02-22 22:12:52.646 homeassistant NetworkManager[536]: <info>  [1771798372.6460] audit: op="connection-update" uuid="2992ef21-e629-3cbb-8fab-04e817ca06f7" name="Supervisor end0" args="connection.timestamp,connection.mdns" pid=174031 uid=0 result="success"
2026-02-22 22:12:52.765 homeassistant systemd-resolved[522]: end0: Bus client reset search domain list.
2026-02-22 22:12:52.767 homeassistant systemd-resolved[522]: end0: Bus client set default route setting: no
2026-02-22 22:12:52.773 homeassistant systemd-resolved[522]: end0: Bus client reset DNS server list.
2026-02-22 22:12:53.035 homeassistant systemd-resolved[522]: end0: Bus client set search domain list to: localdomain
2026-02-22 22:12:53.038 homeassistant systemd-resolved[522]: end0: Bus client set default route setting: yes
2026-02-22 22:12:53.042 homeassistant systemd-resolved[522]: end0: Bus client set DNS server list to: 192.168.0.1

Multicast container logs (before and after restart) only ever showed the internal bridge:

mdns-repeater (6): dev hassio addr 172.30.32.1 mask 255.255.254.0 net 172.30.32.0

Additional information

Related issues:

• Default mDNS settings results in network flooding in networks with reflectors enabled supervisor#5435 — mDNS flooding with reflectors on multi-NIC setups (different scenario: multi-homed + reflectors)
• Add network interface settings for mDNS/LLMNR supervisor#5520 — PR that added per-interface mDNS/LLMNR controls (merged). PR description says "if status is not set: fallback to announce" but code maps DEFAULT → DEFAULT.
• HAOS reverse DNS takes 7.5s before it fails, making lots of things painfully slow #3768 — Reverse DNS slow due to mDNS on hassio bridge (related but about performance)
• Hostname homeassistant.local not resolved + errors in avahi browser #2918 — homeassistant.local not resolved (closed/stale, older version, x86-64)
• HASSOS 5.6 - mDNS (.local) broken #1047 — mDNS broken in HAOS 5.6 (closed, old version)

This issue is distinct from the above: it affects a simple single-NIC, single-LAN fresh install with no mDNS reflectors or VLANs involved. The core problem is that mdns: "default" on the primary interface does not result in mDNS announcement despite broadcast_mdns: true.

[agners]

This seems a very AI generated analysis, and is really not helpful as it covers up what the exact observation is you are seeing.

The default configuration of NetworkManager is to announce on a new network interface (see NetworkManager.conf). In a quick test, a new installation using 17.1 on my network announced itself perfectly fine. There must be something else wrong on your end.

Please provide the unprocessed information on what you are observing exactly, how you test, as well as the output of the host logs.

[magicus]

I noticed my HA instance has stopped responding to my-ha-hostname.local, and I think this was after upgrading HA OS. I can help with providing logs etc, if I know what to provide.

[PfisterFactor]

1. I imaged Home Assistant OS 17.1 via the Raspberry Pi Imager to my Raspberry Pi 4 Model B
2. Plugged in my PI, attached via Ethernet directly to my router
3. Observed that it did not announce via mDNS on my network http://homeassistant.local:8123 - but the home assistant setup was accessible via direct IP on my local network

I then gave Claude code SSH access to my instance and told it to resolve the issue and write up a report on its findings (which it did). I will provide host logs later today when I get home

[magicus]

I found a solution to my problem. I went into Settings / System / Network in my HA installation, and noticed that the hostname field was set to "homeassistant", not my previously chosen computer name. So I changed it back, and then everything worked. This has worked for years and years, so something must have changed recently, either resetting my previous configuration, or overriding it somehow.