Internet partially available : DNS issues ?

Hello,

Since a few days I have been having weird internet connections issues, where some apps/service do not seem to be able to connect to the internet. The problem seems to be related to DNS (could be wrong though).

The symptoms

I have tried to address each of these issues individually but without success:

• Cannot authenticate remotely with my plex server with a new device (but streaming remotely with other devices works fine)
• Plex is not able to find matches for new movies / find metadata anymore (but for instance Radarr/Sonarr are able to find new movies)
• Trying to pull images from docker result in the following error Get "https://registry-1.docker.io/v2/": dial tcp: lookup registry-1.docker.io on [::1]:53: read udp [::1]:xxxxx>[::1]:53: read: connection refused
• apt-get install commands results in the following (for instance trying to install snap: Err:1 http://deb.debian.org/debian buster/main amd64 snap amd64 2013-11-29-9 Could not resolve 'deb.debian.org' E: Failed to fetch http://deb.debian.org/debian/pool/main/s/snap/snap_2013-11-29-9_amd64.deb Could not resolve 'deb.debian.org'

What I have tried

I have tried to add nameserver 8.8.8.8 nameserver 8.8.4.4 to /etc/resolv.conf, followed by systemctl daemon-reload and systemctl restart docker but not luck there.

I of course tried to reboot, no luck either (my /etc/resolv.conf got restored to an empty file, apart from comments)

Possible lead

A few months ago I remember trying to find out why I could not use the port 53 for a docker container and I could not not identify which process was already using it. I did try a few things involving dnsmasq if I remember correctly. This could be related (but it was working fine for a while, so not directly related).

I am running OMV 5.5.

Any inputs appreciated, thanks.

Thank you for taking the time to answer, I appreciate it.

The output of the commands is shown below:

$ ping -c 4 8.8.8.8
PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
64 bytes from 8.8.8.8: icmp_seq=1 ttl=117 time=11.9 ms
64 bytes from 8.8.8.8: icmp_seq=2 ttl=117 time=12.1 ms
64 bytes from 8.8.8.8: icmp_seq=3 ttl=117 time=12.7 ms
64 bytes from 8.8.8.8: icmp_seq=4 ttl=117 time=14.3 ms

--- 8.8.8.8 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 5ms
rtt min/avg/max/mdev = 11.917/12.743/14.257/0.921 ms
$ ping -c 4 google.com
ping: google.com: Name or service not known
$ cat /etc/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients directly to
# all known uplink DNS servers. This file lists all configured search domains.
#
# Third party programs must not access this file directly, but only through the
# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
# replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.

# No DNS servers known.
$ ls -al /etc/resolv.conf
lrwxrwxrwx 1 root root 32 Jun 29 10:30 /etc/resolv.conf -> /run/systemd/resolve/resolv.conf
$ systemctl status systemd-resolved.service
● systemd-resolved.service - Network Name Resolution
   Loaded: loaded (/lib/systemd/system/systemd-resolved.service; enabled; vendor preset: enab
  Drop-In: /usr/lib/systemd/system/systemd-resolved.service.d
           └─resolvconf.conf
   Active: active (running) since Sat 2023-07-29 10:32:45 CEST; 7h ago
     Docs: man:systemd-resolved.service(8)
           https://www.freedesktop.org/wiki/Software/systemd/resolved
           https://www.freedesktop.org/wiki/Software/systemd/writing-network-configuration-ma
           https://www.freedesktop.org/wiki/Software/systemd/writing-resolver-clients
 Main PID: 772 (systemd-resolve)
   Status: "Processing requests..."
    Tasks: 1 (limit: 4915)
   Memory: 8.9M
   CGroup: /system.slice/systemd-resolved.service
           └─772 /lib/systemd/systemd-resolved

$

I am planning on upgrading to OMV 6 as soon as time allows.

Thanks

That did the trick ! I had indeed configured a static IP. I am bit ashamed not to have thought about this fix, though I am puzzled as to why the DNS servers somehow disappeared from my network configuration.

Many thanks for your help !