[systemd-devel] systemd-resolved auto configure DNS server changed?

[Lennart Poettering]

On Fr, 19.02.21 16:29, Ed Greshko (ed.greshko at greshko.com) wrote:

> Link 2 (enp1s0)
>       Current Scopes: DNS LLMNR/IPv4 LLMNR/IPv6
> DefaultRoute setting: yes
>        LLMNR setting: yes
> MulticastDNS setting: no
>   DNSOverTLS setting: no
>       DNSSEC setting: no
>     DNSSEC supported: no
>   Current DNS Server: fe80::5054:ff:fe9a:e849%32767
>          DNS Servers: fe80::5054:ff:fe9a:e849%22096
>           DNS Domain: ~.
>
> The IPv6 address of fe80::5054:ff:fe9a:e849 is that of the Virtual Bridge and wireshark does confirm
> DNS requests are being sent to that address' port 53 where dnsmasq is running.
>
> I have no idea how systemd-resolved discovered this server?  Why wasn't a Fallback Server
> selected used?

The fallback servers are only used as last resort, if there's nothing
else known. They are *fallback* as the name says.

Most likely the DNS servers were acquire by your network management
solution (NetworkManager or networkd) and set on the device. Maybe
theym come from IPv6 RA?

> Then, continuing my research I upgraded systemd to systemd-246.10-1.fc33.  In that version
> there are no FallbackDNS servers defined by default.

Yeah, i think that's a bad change. I am not sure where the benefit of
having a non-working system is...

> Link 2 (enp1s0)
> Current Scopes: LLMNR/IPv4 LLMNR/IPv6
>      Protocols: -DefaultRoute +LLMNR -mDNS -DNSOverTLS DNSSEC=no/unsupported
>
> So, now my question, why wasn't the dnsmasq server found/configured as had been the case?
> An intentional change or unintentional change?

I am not sure which software manages that interface, but it would be
worth figuring that out, and then checking whether it propagated that
DNS info to resolved.

Lennart

--
Lennart Poettering, Berlin