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

[MarcH]

Public bug reported:

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.

** Affects: systemd (Ubuntu)
     Importance: Undecided
         Status: New

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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 systemd package in Ubuntu:
  New

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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