[systemd-devel] About DNS servers and search domains in Router Advertisements

[Patrik Flykt]

	Hi,

Now that we have Router Advertisements and are able to also send
statically configured DNS servers and DNS search domains, I wonder
which set of DNS servers makes most sense to automatically add in
Router Advertisements.

The current status quo is DHCPv4, where one can configure the use of
the uplink DNS servers by setting EmitDNS=true and leaving DNS= server
list empty in the DHCPServer section. The easy way out is to define the
same variable and behavior for Router Advertisements, but what about
the other DNS servers that may be specified in other interfaces'
.network files or received via DHCP over these interfaces?

For example, there might be an interface that is neither the default
uplink, nor the current interface that is sending Router
Advertisements, but it nevertheless has DNS servers configured. Such
DNS servers are not considered by the DHCPv4 server at the moment,
might there have been a sinister plan behind this behavior?

One thing that cannot be added automatically to networkd are of course
the DNS servers configured directly to resolved.conf or any fallback
DNS servers. In addition, since search domains can also be sent, the
same policy is applicable to them - or is it? If we figure out what the
policy for DNS search domains is, the search domains should of course
also be sent out in DHCPv4 server messages.


Cheers,

	Patrik