Self-assigned IPv6 address vs DHCP

[NOYB]

Been running IPv4 only with reserved DHCP provided address.
Recently have enabled IPv6 on the WAN & LAN.
Noticed today that the HDHR4-2US has assigned itself an IPv6 address based on the LAN prefix (not link-local) and it's MAC address.

How can I make it obtain it's IPv6 address from the DHCPv6 server?

HDHomeRun CONNECT
Model: HDHR4-2US
Firmware: 20250506

[rikd]

make sure you set up your router to advertise the DHCPv6 server and NOT prefix information within the Router Advertisement.

[NOYB]

DHCPv6 server is configured to handout addresses for the LAN and works with other DHCPv6 clients for reserved and non-reserved addresses.

LAN Prefix: xxxx:xxxx:xxxx:xxx1
Reserved Host: HDHR4-2US ::200

HDHR4-2US should get xxxx:xxxx:xxxx:xxx1::200
Instead is has xxxx:xxxx:xxxx:xxx1: + IPv6 converted MAC address. Presumably via SSDP.

"...NOT prefix information within the Router Advertisement."
Not sure what is meant by that.

Router is OPNsense using ISC DHCPv6.

[rikd]

on OPNSense you need to modify the Router Advertisement mode to 'managed' if you want to use ONLY the DHCPv6 on the network, which is what you'll need for address reservation
All other modes (other than 'router only') will provide prefix info for SLAAC configuration which is how the HDHomeRun is creating its IPv6 address.

EDIT: checking if we actually support DHCPv6

[rikd]

confirmed
we do not support DHCPv6 client at this time.
On our list of things to do.

So.. in this scenario the HDHomerun cannot support a reserved IPv6 address and will make use of the prefix information in the Router Advertisement to use SLAAC to generate a valid IPv6 address for the network. This means you will need to ensure the OPNSense has the Router Advertisement mode set to one of unmanaged, or stateless for the HDHomerun to generate an IPv6 using the address prefix (will always generate the link local).

[NOYB]

Router Advertisement "Assisted" mode will also support autoconfiguration. Sort of a DHCPv6 and SLACC mix.

Did notice though that with autoconfiguration it didn't seem to get the local dns server. Maybe there is some additional config needed for that. I force all dns to use local resolver. All other dns is blocked.

[rikd]

from opnsense docs, assisted is:
Stateful configuration, address configuration provided by DHCPv6, although advertised routes can also be used on Stateless Address Autoconfiguration setups (SLAAC).
pfsense is similar.
wasn't clear if the prefix info would still be in the RA, or just the routing info.

I'll investigate the DNS server info from the RA options issue. I suspect not supported at this time, just the IPv6 allocation from the prefix info. If so then will enable the DNS along with the DHCPv6 client enablement.

[NOYB]

I was running assisted mode when it self-assigned the MAC based address with the LAN prefix. So the prefix info must have been available.