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Expected Behaviour:
I am using ubuntu server latest on my raspberry pi 400, running latest version of pi-hole. On my iphone i can see that the dns servers provided to me by the dhcp server running on my pi-hole is 192.168.1.249 (the private ip address of the pi-hole) and the raspberry pi's ipv6 address. Everything works fine on my iphone. On my desktop computer running windows 11, I expect that both dns servers are pointing to my pihole, but this isnt the case. my ipv4 dns server is 192.168.1.249 (the correct address) but the ipv6 address given by the piholes dhcp server is pointing to my router, not the pi.
Actual Behaviour:
my ipv6 dns server from pihole's dhcp server is the pi's ipv6 address, not my routers.
new update, for some reason this issue has spread to my iphone too. this could be because my router doesnt support disabling the ipv6 dhcp server? i dont really know what is wrong
It is your router's job to advertise an IPv6 DNS server address via NDP/RA/RDNSS to be used by your IPv6 clients.
Currently, your router is advertising its own IPv6 address as DNS server, allowing your clients to by-pass Pi-hole.
You'd have to find a way to configure your router to stop advertising its own IPv6 as DNS server, or to advertise one of your Pi-hole host machine's local IPv6 addresses instead.
You'd have to consult your router's documentation sources on further details for its IPv6 configuration options.
If your router doesn't support configuring IPv6 DNS, you could consider disabling IPv6 altogether, provided you'd not depend on IPv6 for reasons.
If your router doesn't support that either, your IPv6-capable clients will always be able to bypass Pi-hole via IPv6.
For ipv4 I have CGNAT which works well but i cant port forward so for that reason i use ipv6, which means i cant really disable ipv6. i can't change my ipv6 dns server on my router, but i think my router actually uses the pi-hole as its dns, so any device using the router's dns server will just use pi-hole but with 1 extra hop i guess. this is fine for me as long as no devices are bypassing the pi-hole whenever something is blocked.
If your router allows configuring its upstream IPv6 DNS servers, using Pi-hole as your router's upstream should work.
You may want to consider disabling Pi-hole's DHCP server's IPv6 support, which would stop Pi-hole from advertising its own IPv6 in addition to your router's RAs, to avoid the potential confusion of one client request appearing under its own IPv6 address while the next is originating from your router.
When using Pi-hole as your router's upstream, you should also make sure that you do not close a (partial) DNS loop by having Pi-hole send DNS queries to your router, either by using it as one of Pi-hole's upstreams or by enabling Conditional Forwarding.