HA with prefix delegation: Wrong gateway announced

[ajr]

In this HA setup, there are some VLANS, which are associated to WLANS by
unifi accesspoints. Each of them has a different subnet (by prefix id).
Prefix delegation works correctly and assigns addresses from the right prefix
to the mobile clients (using Track interface).
The setup is the same as described here https://forum.opnsense.org/index.php?topic=50602.msg259211#msg259211
The IP6 gateway announced in the past was that from system->gateways
(WAN_DHCP6), which is the LLA of the DSL-Router (fe80::cece:1eff:feb3:757f) and worked perfectly on failover.
This changed recently to LLAs like fe80::20d:b9ff:fe48:5c1e, which are unusable.

How can I force radvd to announce WAN_DHCP6 ?

Version:  26.7.8_2

[ajr]

After doing the setup (interfaces, DHCP6 and radvd) again from scratch,
tcp connections now work correctly.
In case of ping6 things get screwed up:

Incoming from WLAN shows global addresses:

Code Select Expand

oot@opn1:~ # tcpdump -nvi vlan03 icmp6
tcpdump: listening on vlan03, link-type EN10MB (Ethernet), snapshot length 262144 bytes
16:21:57.367066 IP6 (hlim 255, next-header ICMPv6 (58), payload length 32) fe80::184b:3cc0:64c8:616b > fe80::20d:b9ff:fe48:5c1e: [icmp6 sum ok] ICMP6, neighbor solicitation, length 32, who has fe80::20d:b9ff:fe48:5c1e
  source link-address option (1), length 8 (1): 2a:1d:b8:a7:3c:71
16:21:57.367311 IP6 (hlim 255, next-header ICMPv6 (58), payload length 24) fe80::20d:b9ff:fe48:5c1e > fe80::184b:3cc0:64c8:616b: [icmp6 sum ok] ICMP6, neighbor advertisement, length 24, tgt is fe80::20d:b9ff:fe48:5c1e, Flags [router, solicited]

16:22:30.765033 IP6 (hlim 255, next-header ICMPv6 (58), payload length 24) fe80::20d:b9ff:fe48:5c1e > fe80::c72:8634:5d07:76c5: [icmp6 sum ok] ICMP6, neighbor advertisement, length 24, tgt is fe80::20d:b9ff:fe48:5c1e, Flags [router, solicited]
16:22:34.992643 IP6 (flowlabel 0xc0c00, hlim 64, next-header ICMPv6 (58), payload length 16) 2003:cb:170f:6f3:48cc:5883:5412:514f > 2a02:2e0:3fe:1001:302::: [icmp6 sum ok] ICMP6, echo request, id 19531, seq 0

Outgoing at WAN shows only local addresses:

Code Select Expand

root@opn1:~ # tcpdump -nvi igb1 icmp6
tcpdump: listening on igb1, link-type EN10MB (Ethernet), snapshot length 262144 bytes
16:11:59.122356 IP6 (hlim 64, next-header ICMPv6 (58), payload length 9) fe80::20d:b9ff:fe48:5c1d > fe80::cece:1eff:feb3:757f: [icmp6 sum ok] ICMP6, echo request, id 44961, seq 15220
16:11:59.122714 IP6 (hlim 64, next-header ICMPv6 (58), payload length 9) fe80::cece:1eff:feb3:757f > fe80::20d:b9ff:fe48:5c1d: [icmp6 sum ok] ICMP6, echo reply, id 44961, seq 15220

A group rule exists to allow icmp v6 for all nets.