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

[Ed Greshko]

On 20/02/2021 00:30, Lennart Poettering wrote:
> 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?

OK.  I have found that, using wireshark, there is a

Type: Router Solicitation (133)

followed by
Type: Router Advertisement (134)

which contains
ICMPv6 Option (Recursive DNS Server fe80::5054:ff:fe9a:e849)

>> 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...

Scratching my head on that one as well.

>> 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.
>

Well, I determined that in both the systemd-246.6-3 and systemd-246.10-1 cases (the only changes made)
the same Router Solicitation and Router Advertisement occur.

So, the only conclusion that I can come to is that something changed between the two versions of
systemd which results in the Recursive DNS Server option being ignored.

Would you consider this a candidate for a bug report against systemd?


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