Spent some time figuring this out so thought I would share for the next person with a similar issue.
Here is the config for the following scenario:
- New Zealand Fibre Broadband (Chorus)
- Provider: Contact Energy
- Nanopi R5S
- OpenWrt 21.02.3 (FriendlyWRT fork)
... config interface 'wan' option device 'eth0.10' option proto 'dhcp' config interface 'wan6' option device 'eth0.10' option proto 'dhcpv6' ...