Likely not the most common deployment scenario for a node running OpenWrt but nonetheless a viable one:
- upstream router providing DHCPv4 and stateful DHCPv6
- downstream OpenWrt node connecting through LAN port to upstream router as DHCP client
Configuring the upstream facing interface on the downstream node through UCI | LuCI it is possible to set proto either as DHCP client (v4) or DHCPv6 client but not both.
It would appear that logical interfaces
wan_6 are provided to cater for dual-stack DHCP scenarios, though not clear why it requires two separate logical interfaces and not just one.
That said what would be solution for a LAN port on the downstream node being served both, DHCPv4 and stateful DHCPv6, from the upstream router?