IPv6 DHCP Relay

[symon]

Hello everyone,
I am fairly new to IPv6 so please bear with me as I might just have gotten something wrong. Also this are my first steps with Opnsense as I just got a HW instance (TERRA, Opnsense 20.1.7) and am fiddling around.

My setup is the following: I use the Opnsense appliance behind a consumer grade router (router, switch, wifi... as provided by my ISP) to split the network up into several virtual networks (using VLAN-Tags and some more switches). So basicly it just creates some VLANs, adds a DHCP4 to each one and then NATs to the outside. This is working very nicely for IPv4.

Now I would like to add IPv6 to my networks (this time no NAT, off course). Sadly the ISP machine does not support prefix delegation. So the WAN-Interface will receive one IPv6 /64 prefix. This is not enough for multiple subnets.
So my first question is: The correct way to solve this problem without changing the ISP box should be to relay all DHCP6 requests from the subnets to the WAN-net so that the clients will be assigned /64-Prefixes from the upstream router and the Opnsense-Box can track those to provide appropriate firewalling. Is that correct?

If that is the case: how is this accomplished? The WAN-Prefix should be changing every now and then as well as the ISP-Boxes IPv6. So what is the correct IP to put in Services->DHCPv6->relay->Destination Server?Also what are the correct settings for Interfaces->VLANXX->IPv6 Configuration Type?

Or did I miss the whole concept?
Thanks for helping me out.