I've configured my Vigor 2762 router (firmware 3.9.6.5_BT) as follows -

• LAN -> General Setup -> LAN1 Details Page -> DNS Server IP Address -> set to my desired dns servers

• LAN -> General Setup -> LAN1 IPv6 -> DNS Server IPv6 Address -> "Enable" and desired dns servers

• LAN -> General Setup -> checked "Force router to use "DNS server IP address" settings specified in LAN1"

The DNS servers provided by the router to the clients is correctly including the desired dns servers for both IPv4 and IPv6, but is also including my ISPs IPv6 dns server address as well (but not my ISPs IPv4 dns servers).

I want to enforce that DNS requests are only served by my desired dns servers - how can I remove the ISP IPv6 dns server?

I'm not sure if this is intended behaviour, but I'm also seeing this on the 2962.
We've disabled DNS Server IPv6 Address in order for this not to happen.

The obvious downside is that we don't have any IPv6 DNS servers.
We don't notice any issues as we're dual stack, but not ideal.

I suggest creating a ticket, as we should be able to disable this.
Could be something we are missing on the command line perhaps.

Thanks, I've sent a message to support.

I've done the same too, can't hurt.

Not sure how far you got with support, however this is a confirmed issue and will be fixed in the next firmware.

You obviously had better luck than me, support kept insisting that my ISP was "forcing" these nameserver onto the router which I don't even believe is possible.

In the mean time I have worked around the issue by adding a firewall rule on the router to block outgoing port 53 to the nameserver that is being incorrectly added. Bit of a kludge but it seems to work.