[Bug 1779438] Re: Cannot resolve names using systemd-resolved stub resolver

[Dimitri John Ledkov]

To revert to using upstream dns servers directly instead of stub, change
/etc/resolv.conf to point at /run/systemd/resolve/resolv.conf instead of
../run/systemd/resolve/stub-resolv.conf

However, it would be nice to figure out what domain you are trying to
resolve, and what is the result of it.

Can you e.g. reproduce both queries against resolved dns server and
upstream dns server, and capture systemd-resolved logs and/or network
traffic with wireshark?

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https://bugs.launchpad.net/bugs/1779438

Title:
  Cannot resolve names using systemd-resolved stub resolver

Status in systemd package in Ubuntu:
  Incomplete

Bug description:
  Description:	Ubuntu 18.04 LTS
  Release:	18.04

  I am running a clean install of Ubuntu 18.04.
  This bug was also present for me on a clean install of Ubuntu 17.10 and I had a solution, but it appears to no longer work.

  What I expect to happen: Ping other hosts on network by name

  What happened instead:
  I can't ping other machines on network via name.
  From my Ubuntu 18.04 machine, I `ping ubuntu-test-1` and `ping ubuntu-test-1.localdomain` but neither work. I can ping by IP address though.

  The other machines on the network are Ubuntu Server 16.04.3 machines
  and can ping each other by name also.

  All machines on network including problem one receive DHCP leases from
  same server (192.168.20.1)

  I believe the problem is systemd-resolved stub resolver.

  `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 to the
  # internal DNS stub resolver of systemd-resolved. This file lists all
  # configured search domains.
  #
  # Run "systemd-resolve --status" to see details about the uplink DNS servers
  # currently in use.
  #
  # 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.

  nameserver 127.0.0.53
  search localdomain

  
  If I change the nameserver line to the IP of my nameserver, not the stub, resolution works.

  nameserver 192.168.20.1
  search localdomain

  Now I can ping hosts by name.

  I used to solve this problem like this...

  `sudo systemctl disable systemd-resolved.service`
  `echo "nameserver 192.168.20.1" | sudo tee -a /etc/resolvconf/resolv.conf.d/tail`
  `sudo reboot`

  But /etc/resolvconf/resolv.conf.d no longer exists, and it's about
  time this problem was fixed :)

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