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

[Sebastien Bacher]

We discussed it in our meeting, it probably makes sense to include it in
the next SRU we do but we don't believe it deserves rls tracking,
updating the tag according to that decision

** Tags removed: rls-ff-incoming
** Tags added: rls-ff-notfixing

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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:
  Triaged
Status in network-manager source package in Focal:
  Confirmed

Bug 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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