Some months ago I installed Z2MQTT and the MQTT app, with no special configuration (defaults all the way). And it works fine with a whole load of zigbee devices.
I’m now looking into how to get a couple of Fully Kiosk tablets onto MQTT so I can use their cameras as motion detectors, and it turns out I haven’t the faintest idea how to do that - but that’s a different topic. While poking around, I looked at the MQTT logs and found the following error message coming up every 5 seconds.
2026-08-29 17:30:56: New connection from fd0c:ac1e:2100::1:43288 on port 1883. error: received null username or password for unpwd check 2026-08-29 17:30:56: Client c6ed1456 [fd0c:ac1e:2100::1:43288] disconnected: not authorised.
How do I find out what device is being referred to?
That looks like it’s an IPv6 address.
Some Googln reveals that it is the internal IPv6 address assigned to the Docker bridge network (hassio) inside Home Assistant OS (HAOS
Are you entirely sure that’s a different topic? From the error, it looks like you have a device trying to connect via MQTT without a username/password. Have a read through this & this & check which integrations are using MQTT without a user/password.
So I’ve now created an mqtt_user user in HA and given it a password, but I can’t find anywhere I can use it. I’ve looked in the settings for every integration and app, and can’t see MQTT mentioned anywhere. All my Z2MQTT devices continue to be just fine. I can’t see anything in the Home Assistant Yellow integration that seems relevant. I must be missing something, but what?
It might just find it if you change that username to ‘mqtt’ .
I do it different, add a login in the mosquitto app configuration and in the MQTT integration screen use that login and password to connect.
I am not a HA Yellow user - I run each component separately (Dockerized).
However for most people there are only three components that require the password:
The MQTT broker - likely mosquitto.
Home assistant itself.
The Zigbee2MQTT container/process.
I am guessing that if you run a packaged version of HA, whenever you update the password it updates all three locations where the password is used concurrently **.
** - As noted above, I have to update all three manually due to my setup.
The only time you would need the password is if you want to connect directly to the MQTT broker, I have only done this for two reasons:
To debug/monitor whats going on.
To create my own devices/integrations.
With respect to registering your own devices you can start with the docs on mqtt-discovery:
However you will probably also need to browse the forums for working examples and/or watch the messages Z2M generates.
Thanks to everyone for their suggestions. I added a user in the MQTT app, and then used that user in the Z2MQTT integration, but am still getting the error messages. There must be something somewhere in the HA yellow that’s trying to connect, but I have no idea what it can be.