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[Steve Langasek <steve.langasek@xxxxxxxxxxxxx>]

The resolvconf SRU also introduces regressions (LP: #1819625) and is in
the process of being reverted.

** Changed in: resolvconf (Ubuntu Bionic)
       Status: Fix Released => Triaged

** Changed in: resolvconf (Ubuntu Cosmic)
       Status: Fix Released => Triaged

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https://bugs.launchpad.net/bugs/1817903

Title:
  systemd-resolve appends "options edns0" to resolv.conf

Status in resolvconf package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Invalid
Status in resolvconf source package in Trusty:
  Invalid
Status in systemd source package in Trusty:
  Invalid
Status in resolvconf source package in Xenial:
  Invalid
Status in systemd source package in Xenial:
  Invalid
Status in resolvconf source package in Bionic:
  Triaged
Status in systemd source package in Bionic:
  Invalid
Status in resolvconf source package in Cosmic:
  Triaged
Status in systemd source package in Cosmic:
  Invalid
Status in resolvconf source package in Disco:
  Fix Released
Status in systemd source package in Disco:
  Invalid

Bug description:
  [impact]

  systems upgraded from pre-Bionic releases to Bionic or later will
  continue to use ifupdown/resolvconf for network conf and management,
  but resolvconf has a new systemd service in Bionic and later that
  pulls systemd-resolved stub-resolv.conf into its local configuration.
  With the recent addition of edns0 option to the stub resolver conf in
  systemd to fix bug 1811471, this means resolvconf now sets up the
  /etc/resolv.conf file to include upstream servers but also use edns.
  For any systems where the upstream resolver(s) don't support edns, dns
  lookups will break.

  [test case]

  == upgrade from pre-bionic (e.g. xenial) to bionic or later ==

  1) create a xenial system with ifupdown/resolvconf.  The ifupdown
  config needs to include an upstream name server (must be static).  At
  this point, once the network is configured and up, the resolvconf
  should have put the upstream name server(s) and search domain into the
  /etc/resolv.conf.  As is usual for pre-systemd releases, there should
  be no local dns resolver in /etc/resolv.conf (i.e. 127.0.0.53 should
  not be included) at this point.

  2) upgrade the system to bionic (alternately it should be possible to install bionic, then remove netplan and install/configure ifupdown and resolvconf, but I have not specifically tested this).  The upgrade will retain the ifupdown/resolvconf configuration, and will not change to netplan/systemd-networkd.  After upgrade is finished, the /etc/resolv.conf will contain:
    a) the upstream name server(s)
    b) options edns0
    c) the local stub resolver (127.0.0.53)
    d) search domain

  the fixed resolvconf will remove (b) and (c), and restore
  /etc/resolv.conf to what it contained in Xenial release, before the
  upgrade to Bionic.

  As mentioned, this case also should cover the situation of a native
  Bionic install, where netplan is removed and ifupdown/resolvconf is
  manually installed.

  == bionic or later install ==

  with a bionic install, ifupdown is not installed, instead netplan
  /systemd-networkd handle networking.  In this case, systemd-networkd
  manages the /etc/resolv.conf, and symlinks it to networkd's stub-
  resolv.conf which always contains only the local stub resolver
  (127.0.0.53) and (recently) options edns0, and local search domain.

  If resolvconf is installed while systemd-networkd is managing the
  network, then currently the resolv.conf contents will remain
  completely unchanged, still pointing to the local stub resolver.

  This resolvconf change will alter that, to revert the /etc/resolv.conf
  to Xenial's contents; specifically, the upstream name server(s) and
  search domain.  It will no longer include the local stub resolver nor
  edns0.

  [regression potential]

  Regressions due to this change would likely be seen in dns query
  failures with other system configurations.

  Additionally, for the case where systemd-networkd is actually managing
  the network, this change will stop sending dns traffic to the local
  stub resolver, and instead send it to the upstream name server(s).
  This will increase outgoing dns traffic (since it's no longer cached
  locally), but will matches the behavior from Xenial.  Additionally,
  resolvconf should not be needed when systemd-networkd is managing the
  network (and thus systemd-resolved is managing dns), and resolvconf
  can simply be uninstalled from the system to move back to normal use
  of the local stub resolver.

  [other info]

  This affects only Bionic and later; in Xenial and earlier, resolvconf
  does not include the 'resolvconf-pull-resolved' service to pull in the
  systemd-resolved stub config, which is what causes this problem.

  This also does not affect Debian, as it does not include the
  'resolvconf-pull-resolved' service either.

  original description:

  --

  Mint 19 (Ubuntu 18.04)

  Following latest mint update done on 24/02/2019, DNS is broken....

  nslookup and dig of certain domain names work as expected, ping does
  not (ip works but not domain name)

  After a day of trial and error, testing I found that the problem lies
  with the presence of

  "options edns0"

  in /run/resolvconf/resolv.conf (link to by /etc/resolv.conf)

  With option present many dns lookups fail with both FF and chrome browswers and thunderbird...
  This is on a home network, with router set as dns proxy for external wan, not using NetworkManager

  Deleting the option on live system results in the issue immediately
  disappearing, but on reboot it is added back in (by systemd-resolve ?)

  I cannot find any option to prevent this being added, so presumably it
  is hard-coded in systemd following the update?

  systemd:
    Installed: 237-3ubuntu10.13

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