If the box isn't passing prefixes to your router you can assign them statically, but then you have to count on the ISP not changing them.
The alternative is to use relay mode so your LAN endpoints get GUAs within the same single /64 that you do have.
I think that (ISP)box does pass prefix but only to the OpenWRT router.
Unless u mean by that to pass Delegated Prefix?
Anyway, following ur advice I added "relay mode" on LAN and WAN6 interface and now it seems to be working.
I will take a closer look to this later tomorrow.
Thanks for help.
config dhcp 'lan'
option interface 'lan'
option start '100'
option limit '150'
option leasetime '12h'
option dhcpv4 'server'
option ra 'relay'
option dhcpv6 'relay'
option ndp 'relay'
config dhcp 'wan6'
option interface 'wan6'
option ignore '1'
option master '1'
option ra 'relay'
option dhcpv6 'relay'
option ndp 'relay'
If i get it right, by using DHCPv6 rely agent (RA), my LAN hosts ask my ISP for IPv6.
Also, I cannot see any DHCPv6 settings on ISP box so I assume, DHCPv6 server is standing somewhere further upstream from ISP box?
In other scenario, if Delegated Prefix would be assigned/passed to the OpenWRT router (NOT my case), I would set DHCPv6 server on my OpenWRT
and define one or more of 16 available subnets (given that my DP = /60).
Is this correct?