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

[MarcH]

> systemd behaviour could be better for domains without '.'

One thing that would help with these confusing NXDOMAIN errors in
general (not just from NetworkManager) is for systemd to provide a more
verbose and possibly less "private"[*] mode that shows the requested
domains somewhere without having to use tcpdump on the side and try to
match timestamps, process IDs and what not. In fact this mode could be
considered "more secure" because of the added admin transparency. It
could be off by default for privacy reasons - depending on where the
information goes.

Maybe this more verbose mode exists and I missed it? Or a feature
request already filed? In either case please share, thanks.


[*] just guessing the current rationale

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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:
  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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