Hello  @ImtiazAli 

1) Actually IPv4 DNS works fine for IPv6 resolutions. Both query types AAAA & A are supported by most DNS v4 servers

2) "sync ipv4 account" option is only available for PPPoE. On my side, I use a Tunnel 6to4 (only option available with my ISP)

3) My concern is not about Google DNS here. My concern is that when I manually enter DNS IPs for IPv6, it has to be a v6 address. Actually I would like to not mention any DNS IPv6 address and rely only on the IPv4 DNS which can also resolve my v6 addresses.

  @ImtiazAli that's right. But it's still a common practice to leverage a v4 transport DNS to resolve v6 addresses.

Anyway, I am just asking for simple feature request: enabling entering a v4 address for v6 resolution as part of the DHCPv6 or even better, allowing no specific DNS config for IPv6. In this case, clients would simply use their v4 DNS...

  @ImtiazAli these's a difference between transport level and service level:

-DNS is a service resolving various types: MX for mail, A for v4, AAAA for v6. Entire list is available here: https://en.wikipedia.org/wiki/List_of_DNS_record_types. There no such a thing telling that is DNS transport (v4 or v6) should restrict the the ability to resolve anything

-Likewise, BGP is a service running over v4 transport or v6 transport. Whatever transport it uses it can still exchange v4 prefixes or v6 prefixes.

Actually this is quite important to ease transition toward v6.

So again, letting the ability for TPlink deco customers to uncheck a box would ease that (this is feasible with most other competing products).