Bug#969903: /usr/bin/resolvectl: systemd-resolved resolves name differently than dig

[Nicolas Évrard]

Package: systemd
Version: 246.4-1
Severity: normal
File: /usr/bin/resolvectl

Dear Maintainer,

Today we migrated a forum from one server to another hence its IP
address changed. Trying to access the new home of this service I
noticed that I continuously stumbling upon the old one (I know the DNS
propagation takes some time but it seemed long).

Anyway here's the output of my musings with resolvectl:

    nicoe at mirabelle:~% resolvectl flush-caches
    nicoe at mirabelle:~% resolvectl status
    Global
           LLMNR setting: yes
    MulticastDNS setting: yes
      DNSOverTLS setting: no
          DNSSEC setting: no
        DNSSEC supported: no
    Fallback DNS Servers: 80.67.169.12
                          2001:910:800::12
                          1.1.1.1
                          2606:4700:4700::1111
                          8.8.8.8
                          2001:4860:4860::8888

    Link 3 (wlan0)
          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: fd00::e228:6dff:fe97:ceb
             DNS Servers: 192.168.1.1
                          fd00::e228:6dff:fe97:ceb

    Link 4 (docker0)
          Current Scopes: none
    DefaultRoute setting: no
           LLMNR setting: yes
    MulticastDNS setting: no
      DNSOverTLS setting: no
          DNSSEC setting: no
        DNSSEC supported: no
    nicoe at mirabelle:~% resolvectl query forum.rscl.be
    forum.rscl.be: 91.121.64.208                   -- link: wlan0
                   2001:41d0:1:73d0::1             -- link: wlan0

    -- Information acquired via protocol DNS in 7.3ms.
    -- Data is authenticated: no
    nicoe at mirabelle:~% dig @fd00::e228:6dff:fe97:ceb +short forum.rscl.be
    91.121.132.126
    nicoe at mirabelle:~% dig @192.168.1.1 +short forum.rscl.be
    91.121.132.126

As you can see the DNS result obtained with dig differs from the one
of resolvectl although AFAIU systemd-resolved is using the wlan0 link
and thus the same DNS servers.

This is quite puzzling and I'd like to understand what's going on.
I tried restarting the service instead of flushing the caches and it
results in the same behaviour.

Regards,

-- Package-specific info:

-- System Information:
Debian Release: bullseye/sid
  APT prefers unstable
  APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.7.0-3-amd64 (SMP w/8 CPU threads)
Locale: LANG=fr_BE.UTF-8, LC_CTYPE=fr_BE.UTF-8 (charmap=UTF-8), LANGUAGE=en_US:en
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)

Versions of packages systemd depends on:
ii  adduser                 3.118
ii  libacl1                 2.2.53-8
ii  libapparmor1            2.13.4-3
ii  libaudit1               1:2.8.5-3+b1
ii  libblkid1               2.36-3
ii  libc6                   2.31-3
ii  libcap2                 1:2.43-1
ii  libcrypt1               1:4.4.17-1
ii  libcryptsetup12         2:2.3.4-1
ii  libgcrypt20             1.8.6-2
ii  libgnutls30             3.6.14-2+b1
ii  libgpg-error0           1.38-2
ii  libidn2-0               2.3.0-1
ii  libip4tc2               1.8.5-3
ii  libkmod2                27+20200310-2
ii  liblz4-1                1.9.2-2
ii  liblzma5                5.2.4-1+b1
ii  libmount1               2.36-3
ii  libpam0g                1.3.1-5
ii  libpcre2-8-0            10.34-7
ii  libseccomp2             2.4.3-1+b1
ii  libselinux1             3.1-2
ii  libsystemd0             246.4-1
ii  libzstd1                1.4.5+dfsg-4
ii  mount                   2.36-3
ii  openntpd [time-daemon]  1:6.2p3-4+b1
ii  util-linux              2.36-3

Versions of packages systemd recommends:
ii  dbus  1.12.20-1

Versions of packages systemd suggests:
ii  policykit-1        0.105-29
pn  systemd-container  <none>

Versions of packages systemd is related to:
pn  dracut           <none>
ii  initramfs-tools  0.137
pn  libnss-systemd   <none>
ii  libpam-systemd   246.4-1
ii  udev             246.4-1

-- Configuration Files:
/etc/systemd/resolved.conf changed:
[Resolve]
FallbackDNS=80.67.169.12 2001:910:800::12 1.1.1.1 2606:4700:4700::1111 8.8.8.8 2001:4860:4860::8888
DNSSEC=no


-- no debconf information