Homeassistant is assigning IPV6 adresses to devices in my network, or so it appears

Configuration Matter/Thread
1

I am having a weird issue.

In my network I started to notice that devices receive an IPV6 address from an unknown prefix.

Eg my mac has the following IPs:

en7: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	options=6464<VLAN_MTU,TSO4,TSO6,CHANNEL_IO,PARTIAL_CSUM,ZEROINVERT_CSUM>
	ether 98:fd:b4:9e:a0:d9
	inet6 fe80::8e5:9bd9:ef17:4a1d%en7 prefixlen 64 secured scopeid 0x1b
	inet6 fde5:b546:eb5b:3:405:7cda:bbdb:8d89 prefixlen 64 autoconf secured
	inet6 fdae:2e37:49b2:bf11:cc6:8ba1:b4be:69f1 prefixlen 64 autoconf secured
	inet 192.168.3.134 netmask 0xffffff00 broadcast 192.168.3.255

I get where the fde5:… address comes form. That is my own ULA prefix. But the fdae:2e37:49b2:bf11 is not one I have set anywhere in my network. So I wondered where this comes from.

A collegue suggested that the thread border router might be the culprit. And it might well be. The extended PAN for my network is ae2e3749b260bf11 and that matches the ipv6 prefix above.

So something, I susspes the openthread router, is broadcasting RA announcements for that prefix. And devices on my network are using that…

Questions:
why? What purpose does this have?

2

Matter & Thread Deep Dive

3

Yes the Thread Border Router on the LAN side is suppose to listen for RAs from other routers and if it doesn’t see the RA (or see the RA but it doesn’t have PIO), it will assign its own ULA and then send out RA/PIOs for it. Just as a check, is the ULA you yourself set up being advertised via RA?

4

Devices will normally also create an EUI-64 address by themself.and maybe others also.

1 Like
5

I would assume it is, but I might have to check that.

My router is a Ubiquity UCG. I would assume it would do the right thing out of the box.

EDIT: Checked it. RA is enabled, and prio is high.

6

Do you have IPv6 enabled on your HA box? Not sure how the OTBR behaves exaclty, but it could be that if IPv6 is disabled (which would make HA then not have an address of your networks ULA), the OTBR simply sends out a RA.