Is my Aqara Hub M3 just… broken? Matter absolutely refuses to work (UniFi setup)

[JohnD]

In addition to your post:

@JohnD

Here are the three IPv6 address types that play a role:

• Link-Local (fe80::): Every device generates this address itself immediately after powering on. It is strictly limited to the physical network segment and is not forwarded by routers. Purpose: Initialization & emergency communication within the same room.
• GUA (2xxx::): The Global Unicast Address is usually assigned dynamically by the provider. It is globally unique, publicly routable, and enables communication across the entire Internet. Purpose: Communication with the Internet.
• ULA (fdxx::): The Unique Local Address is the stable, internal counterpart. The router specifies the network prefix, and the devices generate their own addresses (SLAAC). It is routable throughout the entire home network but not accessible from the Internet. Purpose: Stable communication within the home network, independent of the Internet provider.

What does this have to do with Matter-over-Thread and Matter-over-Wi-Fi? A router that sees a packet with a Link-Local address (fe80::) must discard it if it wants to leave the network. A Thread network is physically a separate subnet, distinct from the WLAN. Therefore, only ULA or GUA addresses work for communication between LAN/WAN and the sensor (Thread), as these are routable. Matter-over-Wi-Fi also works with Link-Local, since both devices are located in the same WLAN segment.