Apologies that I’m going to sound a bit vague here - I am new to IPv6 - only learning now for this problem.
I’m running HAOS in a headless KVM on Ubuntu. Everything works well except - I am running Home Assistant Matter Hub to expose my Home Assistant devices to Google Home via Matter. This works amazingly well for software labelled as alpha release, but I’m finding that after some time (about a week) it stops working - Google Assistant says the devices are offline.
I’ve been doing some troubleshooting and think that it is stopping due to an underlying IPv6 connectivity issue. I don’t use IPv6 for anything else so each interface only has a link local address. My network is flat/bridged. I’ve found that when the Matter Hub appears to stop working I can’t ping my Google Home with IPv6 from HAOS. I can ping the IPv4 address. This got me curious and I found that I can’t ping any IPv6 addresses from HAOS at this time. But, strangely, I can ping the “main” (enp0s2 in my case) IPv6 address of the VM from outside the HAOS host.
I have found that rebooting either the wireless access point that my Google Home is connected to or rebooting HAOS restores connectivity. Rebooting the Google Home does not restore connectivity.
Just a double-check, when pinging IPv6 link-local addresses, one often has to specify the interface that they want to ping from. I have a setup similar to yours with HAOS only having one interface; from the HAOS shell, using ping -6 fe80::59f6:a5f4:503c:99b5 does not work, whereas ping -6 fe80::59f6:a5f4:503c:99b5%enp0s2 does work.
One other possibility that comes to mind, is if there are any Ethernet L2 switches with IGMP snooping enabled, this may every so often drop multicast which is used a lot in IPv6. Rebooting systems will have them re-register their multicast addresses with the switches which gets traffic flowing again. But if it ran fine for a week, then this is likely not the issue.
Thank you - I did not know about that way to specify the interface. Only “ping6 -I …”, which the ping provided by HAOS does not seem to understand.
# ping -6 fe80::22df:b9ff:fe30:8b0e
No response from fe80::22df:b9ff:fe30:8b0e
# ping -6 fe80::22df:b9ff:fe30:8b0e%enp0s2
fe80::22df:b9ff:fe30:8b0e%enp0s2 is alive!
I was really confused - because I was actively working on this now and found that although the Home Assistant Matter Hub is working fine, I could not ping my Google Home.
Now I just need to wait until the devices go offline to Google Home again and re-check.