New HA user here, been testing a couple of Ikea Matter over thread.
Using a Pi4, HAOS with a Sonoff dongle max connected directly via USB. My Ikea Kajplats bulb and Bilresa button work as expected, until the ethernet connection on the Pi is diconnected or the ethernet switch is powered off. Internet can be down and it works OK.
I had expected Thread / Matter to work totally standalone or am I mistaken?
Thanks in advance.
I experience that with SmartThings too, local automations with Zigbee devices work normally, local automations with Thread devices will not work if the Ethernet link is down even if Ethernet is not needed because the hub has Thread radio, it’s the only Thread border router and devices are connected to it directly.
It would be expected to fail if the Thread border router was external, after al the Matter controller would not be able to communicate with Thread devices if the local network link was down. Maybe that’s what’s happening: even if the TBR is integrated, it behaves as if it was a external TBR.
I found my ethernet crossover cable after much hunting.
Once HA had booted I swapped the ethernet (with internet connected) with the crossover cable to my laptop, things (that don’t need internet) worked as expected. My two Matter over thread devices worked without issue.
I disconnected the crossover cable and the devices stopped working. Reconnecting the crossover cable I noticed that the Ikea BILRESA dual button didn’t work, but I could use the HA interface to turn the bulb on & off.
Maybe this is what is really happening, the BILRESA dual button is loosing functionality when I remove the ethernet cable and not really Matter/Thread devices not working. I’ll try and find a way to test this, maybe a KB to turn bulb on/off or a timed event.
The BILRESA dual button started working after a few minutes connected to the internet.
Snap. A timed lights on / off automation does not work with Matter over Thread bulb, without an ethernet connection ; -(
Sometimes a disconnected (or connected to an unpowered or faulty) device will cause the internet interface in the HA hardware to actually disappear and that cause a ripple effect on Ethernet services, also the ones that are not directly using the public ethernet interface.
If you are using a hyperrvisor, then there might be an option to keep the ethernet interface alive even when the other end of the interface connection is down.
Thanks WallyR
Nothing in the logs suggest end0 is disappearing, I do see:
[NOTE]-AGENT---: Thread version: 1.4.0
[NOTE]-AGENT---: Thread interface: wpan0
[NOTE]-AGENT---: Radio URL: spinel+hdlc+uart:///dev/serial/by-id/usb-SONOFF_SONOFF_Dongle_Max_MG24_106fae8f8dfaef118b3391256d9880ab-if00-port0?uart-baudrate=115200&uart-init-deassert
[NOTE]-AGENT---: Radio URL: trel://end0
[NOTE]-ILS-----: Infra link selected: end0
snip (cable removed)
00:27:49.425 [W] P-InfraNetif--: failed to send ICMPv6 message: Cannot assign requested address, suggests infra link might be down, checking status.
00:27:49.426 [C] BorderRouting-: RsSender: Failed to send RS 1/3: Failed
Suggesting in needs to end0 infra link alive…maybe as designed.
I’m using a Pi4. I tried my RJ45 loopback adapter but that didn’t work.
Did end0 link come up?
No 
Maybe Pi hardware is too smart for loopback adapters. I tried in a Pi 4 & Pi 5, no joy. Work fine (100mb) on a couple of laptops I tested.
I use to know Gigabit PHYs in detail, but its been a while. I went back and looked at some notes, and I believe 802.3 1000BASE-T uses each pair in full-duplex (and uses all 8 pairs) and does echo cancellation on any reflections it gets back from what it Transmits out…so I would be surprised that loopbacks work for Ethernet running at 1Gbps.
I worked around this with a £10 USB powered TP-Link EH210 switch.
The Pi4 NIC link stays online, even when I power off the upstream switch.
Everything works so far (timed events from HA to lamp & Thread / Matter button to lamp).
thanks