Hello to the OPNsense community,
I´m new here, but I think I have found a bug in OPNsense 26.1.5.
The new IPv6 address assignment option "Identity Association" assigns a /63 instead of a /64 to the interface.
And also when I choose the 0x1 prefix, it also assigns a /63 which is not correct because the first /63 goes from `0000 - 0001`. So this wont work with multiple /63.
I´m looking forward to get informations if the bug is known already (I don´t found a forum topic about that) or not. :)
It does not do that per default. Identity association is the new version of the former "Track Interface". Thus, it depends on how many bits you have in your parent interface's prefix delegation size. AFAIK, you need a shorter than /64 prefix in order to be able to supply a full /64 prefix to any interface.
Maybe your ISP does not give you a /56 (which is pretty much the default) or you did not request as much on your WAN. How many bits is your IA_PD prefix?
Perhaps you should take a look at the official docs: https://docs.opnsense.org/manual/ipv6.html
Or my IPv6 guide (which is still based on track interface): https://forum.opnsense.org/index.php?topic=45822.0