RT-AX86U Pro running 3006.102.4 dropping IPv6 ULA address

[hartacus]

I use native IPv6, my ISP provides a static /64. I also use a ULA assigned to the router via 'dhcpc-event' script, together with a corresponding range of ULAs provided to LAN devices via 'dnsmasq-postconf' script, to help Pi-hole resolve local hostnames of IPv6 clients sensibly.
After updating to asuswrt-merlin 3006.102.4, I have noticed that the IPv6 ULA assigned to the router is being periodically removed.
The 'dhcpc-event' script checks whether the ULA exists in the output of ip addr show dev

ip addr show dev br0

and if not it adds the ULA via

ip -6 addr add [ULA]/64 dev br0

The system log shows that it's being silently removed (not sure by what), and then re-added again next time the script runs - the script logs a different message when the ULA is found vs when the ULA is added, and it's intermittent.
Prior to the update, the script would log the message when the ULA was added at boot, and then subsequent messages would just be saying that the ULA was found over and over again.
Has anything changed, like flushing all IPv6 addresses when receiving DHCPv6 assignment from the ISP, or anything else that would cause the address to drop?
IPv6 connectivity is fine through all this, it's just messing with the ULA addressing and consequently breaking Pi-hole IPv6 client name resolution.

 

[dave14305]

There are a few places in the firmware where it will run ip -6 addr flush scope global dev br0. Search these files for flush in quotation marks. That would do it.

asuswrt-merlin.ng/release/src/router/rc/udhcpc.c at main · RMerl/asuswrt-merlin.ng

Third party firmware for Asus routers (newer codebase) - RMerl/asuswrt-merlin.ng

github.com

asuswrt-merlin.ng/release/src/router/rc/services.c at main · RMerl/asuswrt-merlin.ng

Third party firmware for Asus routers (newer codebase) - RMerl/asuswrt-merlin.ng

github.com

 

[dave14305]

Wondering out loud if the Pi-Hole could be configured to advertise just the ULA instead of the router? You’d have to be very careful and know what to do if it breaks everything.

Edit:

https://www.reddit.com/r/ipv6/comments/1af0r2v/using_rpi_to_advertise_ula_how_to_make_it_work