Router advertisement and dns configuration

[bma]

Hi,

i'll try to understand an option in router advertisement, if it does what the text tells me.

Target
I just want to deliver IPv4 DNS servers to my subnet, but dont want to disable IPv6 completely.


If "Do not send any DNS configuration to clients" (DontDns) work as told, the clients should not get any DNSv6 server... so thats what i want


In "dns_option_off" i see my IPv4 DNS servers and the same IPv6 DNS two times
In "dns_option_on" we have again the IPv4 DNS servers and the IPv6 DNS only one time

So when "DontDns" is checked, it seems that no information is send, but why is the default gateway used as DNS?

Is this something from the ISC DHCPv6 that has to be changed or is this a Windows 11 thing?


Regards

[meyergru]

You probably have DHVPc6 enabled on top of RA (i.e. "Stateless" configuration) which then always distributes (probably only) DNS info. The option you mentioned should only influence RDNSS.

[bma]

Indeed ISC DHCPv6 is enabled.

So the only chance is, disable DHCPv6 on this interface? I dont see any option to not deliver the DNS servers (which are blank atm). Setting ::1 as delivered DNS server could work, but feels dirty

[meyergru]

Actually, if you use RA, then you only need DHCPv6 for clients that are unable to use RDNSS. If there are none, you might as well disable DHCPv6 if you do not need it to distributed DNS servers at all (i.e. "Unmanaged" mode) - it does nothing else, anyway.