Can't update OS on PiHole - cannot resolve any hostnames

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Expected Behaviour:

Raspberry Pi 3B+
Buster

Running sudo apt update to update the OS. I expect the update to run!

Actual Behaviour:

pi@Pi-hole:~ $ sudo apt update
Err:1 http://raspbian.raspberrypi.org/raspbian bullseye InRelease              
  **Temporary failure resolving 'raspbian.raspberrypi.org'**
Err:2 http://archive.raspberrypi.org/debian bullseye InRelease                 
  Temporary failure resolving 'archive.raspberrypi.org'
Reading package lists... Done             
Building dependency tree... Done
Reading state information... Done
44 packages can be upgraded. Run 'apt list --upgradable' to see them.
**W: Failed to fetch http://raspbian.raspberrypi.org/raspbian/dists/bullseye/InRelease  Temporary failure resolving 'raspbian.raspberrypi.org'**
**W: Failed to fetch http://archive.raspberrypi.org/debian/dists/bullseye/InRelease  Temporary failure resolving 'archive.raspberrypi.org'**
W: Some index files failed to download. They have been ignored, or old ones used instead.

Tried to see if its a bigger problem than just unable to resolve the raspberrypi.org domain. It is a bigger problem!

pi@Pi-hole:~ $ ping google.com
ping: google.com: Temporary failure in name resolution

Tried to update the Pi-Hole:

pi@Pi-hole:~ $ pihole -up
  [✓] Update local cache of available packages
  [i] Existing PHP installation detected : PHP version 7.4.25
  [✓] Checking for git
  [✓] Checking for iproute2
  [✓] Checking for whiptail
  [✓] Checking for ca-certificates

  [i] Checking for updates...
**fatal: unable to access 'https://github.com/pi-hole/pi-hole.git/': Could not resolve host: github.com**
  [i] Pi-hole Core:	up to date
fatal: unable to access 'https://github.com/pi-hole/AdminLTE.git/': Could not resolve host: github.com
  [i] Web Interface:	up to date
  [i] FTL:		update available

  [i] FTL out of date, it will be updated by the installer.

  [✓] Root user check

        .;;,.
        .ccccc:,.
         :cccclll:.      ..,,
          :ccccclll.   ;ooodc
           'ccll:;ll .oooodc
             .;cll.;;looo:.
                 .. ','.
                .',,,,,,'.
              .',,,,,,,,,,.
            .',,,,,,,,,,,,....
          ....''',,,,,,,'.......
        .........  ....  .........
        ..........      ..........
        ..........      ..........
        .........  ....  .........
          ........,,,,,,,'......
            ....',,,,,,,,,,,,.
               .',,,,,,,,,'.
                .',,,,,,'.
                  ..'''.

  [✓] Update local cache of available packages
  [i] Existing PHP installation detected : PHP version 7.4.25

  [✓] Checking apt-get for upgraded packages... 44 updates available
  [i] It is recommended to update your OS after installing the Pi-hole!

  [i] Checking for / installing Required dependencies for OS Check...
  [✓] Checking for grep
  [✓] Checking for dnsutils

  [✗] Retrieval of supported OS list failed. dig failed with return code 10. 
      Unable to determine if the detected OS (Raspbian 11) is supported
      Possible causes for this include:
        - Firewall blocking certain DNS lookups from Pi-hole device
        - ns1.pi-hole.net being blocked (required to obtain TXT record from versions.pi-hole.net containing supported operating systems)
        - Other internet connectivity issues

      https://docs.pi-hole.net/main/prerequesites/#supported-operating-systems

      If you wish to attempt to continue anyway, you can try one of the following commands to skip this check:

      e.g: If you are seeing this message on a fresh install, you can run:
             curl -sSL https://install.pi-hole.net | PIHOLE_SKIP_OS_CHECK=true sudo -E bash

           If you are seeing this message after having run pihole -up:
             PIHOLE_SKIP_OS_CHECK=true sudo -E pihole -r
           (In this case, your previous run of pihole -up will have already updated the local repository)

      It is possible that the installation will still fail at this stage due to an unsupported configuration.
      If that is the case, you can feel free to ask the community on Discourse with the Community Help category:
      https://discourse.pi-hole.net/c/bugs-problems-issues/community-help/

  Unable to complete update, please contact Pi-hole Support

So the Pi-Hole "simply" cannot resolve any domains.
I've found out that this only occurs when the Pi-Hole is set as the DNS server in my router. But if I change the router's DNS to its default (eg. 192.168.1.1), the Pi-hole can resolve the hostnames.

Debug Token:

Can't upload this, as my Pi-hole can resolve the hostname!

Shouldn't I still be able to access sites on the Pi-hole without having to change the DNS setting on the router?

Thanks.

Pi-hole doesn't change the DNS configuration of its host machine.

Do you run unbound as Pi-hole's upstream?

Thanks for your reply.

After installing and configuring Pi-Hole, I changed the DNS on my router to point to the Pi-Hole (192.168.1.XXX). After doing that I got all the errors that you see above when trying to update. If I changed the Router's DNS back to 192.168.1.1, the updates proceeded without error.

Ultimately, I decided to try a fresh install, this time using the earlier Buster release as the base OS, instead of the later Bullseye. I had no problems with running updates, even after changing the router's DNS to the Pi-Hole (192.168.1.XXX). After everything seemed to be working, I installed "unbound" and got that configured per this video: https://youtu.be/FnFtWsZ8IP0

When I'm on the dashboard, I see 30% of my queries are IPv6. During the initial Pi-Hole installation on Buster, I was not asked if I wanted to configure IPv6, only IPv4. I assume that 30% of my internet traffic will not go through Pi-Hole because it's using IPv6?

Thanks again.

If you had been using Pi-hole with unbound before, and your initial observation would have been for a first upgrade to or under Bullseye, you may have been affected by a DNS loop created between your upstream unbound and Pi-hole. For a complete background, see WARNING: Raspbian October 2021 release bullseye + unbound .

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