Tried to configure a OpenDNS filtering service on my Fritzbox modem with an ISP which offers IPv6. Don't even bother.
OpenDNS won't let you register a IPv6 subnet. The modem prefers IPv6 DNS servers (because there's often no CGNAT). So the Fritzbox selects the ISP's IPv6 DNS server over the IPv4 OpenDNS server, meaning no filtering occurs.
OpenDNS does allow access to the resolver via IPv6, but this does not work if you have an account with filtering preferences.
To be clear, this issue is with OpenDNS. Not Fritzbox. Not the IPv6 protocol.
#ipv6
The IPv4 prefix registration approach has some drawbacks. With IPv6 there is a better way to achieve the desired filtering. I thought OpenDNS had implemented this, but apparently not.
The better approach is that rather than attaching a filtering profile to a client IP range, the filtering profile is attached to a specific set of server IP addresses. Each time a user creates a filtering profile the service provider will have to allocate two IP addresses for that profile.
With IPv4 that approach would be prohibitive. There is no way OpenDNS have enough IPv4 address to allocate two to each user. But with IPv6 they surely have enough.
Doing it that way OpenDNS could tell you which two IPv6 addresses you should send your DNS queries to in order to get your customized filtering.
Glen T, heated, not stirred