[Bug 1880258] Re: Add trailing dot to make connectivity-check.ubuntu.com. absolute and reduce NXDOMAIN warning noise

[Dan Streetman]

root at lp1880258-b:~# dpkg -l systemd|grep systemd
ii  systemd        237-3ubuntu10.44 amd64        system and service manager
root at lp1880258-b:~# host jifaslrjfiudrlj.com
Host jifaslrjfiudrlj.com not found: 3(NXDOMAIN)
root at lp1880258-b:~# journalctl -b -u systemd-resolved | grep NXDOMAIN
Mar 09 18:15:29 lp1880258-b systemd-resolved[786]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.
Mar 09 18:25:51 lp1880258-b systemd-resolved[786]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.


(upgrade/reboot)

root at lp1880258-b:~# dpkg -l systemd|grep systemd
ii  systemd        237-3ubuntu10.45 amd64        system and service manager
root at lp1880258-b:~# host jifaslrjfiudrlj.com
Host jifaslrjfiudrlj.com not found: 3(NXDOMAIN)
root at lp1880258-b:~# journalctl -b -u systemd-resolved | grep NXDOMAIN
root at lp1880258-b:~# 


** Tags removed: verification-needed verification-needed-bionic verification-needed-focal
** Tags added: verification-done verification-done-bionic verification-done-focal

** Changed in: systemd (Ubuntu Hirsute)
       Status: Fix Committed => Fix Released

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https://bugs.launchpad.net/bugs/1880258

Title:
  Add trailing dot to make connectivity-check.ubuntu.com. absolute and
  reduce NXDOMAIN warning noise

Status in network-manager package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Bionic:
  Fix Committed
Status in systemd source package in Focal:
  Fix Committed
Status in systemd source package in Groovy:
  Fix Committed
Status in network-manager source package in Hirsute:
  Fix Released
Status in systemd source package in Hirsute:
  Fix Released

Bug description:
  [impact]

  systemd-resolved emits a disturbingly large amount of NXDOMAIN log
  messages that do not actually indicate any real problem

  [test case]

  see original description, or look at any log from any recent Ubuntu
  system, or search google for endless complaints about NXDOMAIN
  messages logged by Ubuntu

  [regression potential]

  any regression would likely be isolated to systemd-resolved handling
  of a NXDOMAIN response from its upstream nameserver, including
  possibly failing to resolve a hostname or delays in resolving
  hostnames

  [scope]

  this is needed for all releases; the patch is not upstream, but
  carried by Ubuntu

  [original description]

  I normally don't like this, but it's a one-character change so it's
  easier to start with the solution:

  diff -u -r1.1 /usr/lib/NetworkManager/conf.d/20-connectivity-ubuntu.conf
  --- /usr/lib/NetworkManager/conf.d/20-connectivity-ubuntu.conf
  +++ /usr/lib/NetworkManager/conf.d/20-connectivity-ubuntu.conf
  @@ -1,2 +1,2 @@
   [connectivity]
  -uri=http://connectivity-check.ubuntu.com/
  +uri=http://connectivity-check.ubuntu.com./

  Making this name absolute instead of relative avoids spurious
  resolutions of "connectivity-check.ubuntu.com.your_domain." This
  removes a fair amount of NXDOMAIN error noise in journalctl.

  Observing the issue and the fix requires 3 terminals:

  1. tcpdump -i any 'port domain'
  2. journalctl --boot -u systemd-resolved -f

  3. nmcli c down "Wired connection 1"; nmcli c up "Wired connection 1"
   => observe the NXDOMAIN noise over a couple few minutes

  Now make the hostname absolute with the trailing dot above and run:
     systemctl reload NetworkManager
  Wait 1 min for things to stabilize. Test again:

  nmcli c down "Wired connection 1"; nmcli c up "Wired connection 1"
   => observe non-zero but significantly reduced NXDOMAIN noise over a couple few minutes

  Originally reported at https://askubuntu.com/a/1242611/117217

  Plenty of people annoyed by NXDOMAIN warnings, just Google it.

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