[Bug 1765477] Re: 5s delay in AAAA dns resolving; artful and earlier is quick

[Alberto Donato]

I'm seeing this in eoan, too.

Whenever I try to access a host in my lan, host resolution takes 15s
(tried timing "ping -c 1" and "nslookup"

a "dig <host>" query is immediate, but a "dig AAAA <host>" also takes
15s.

It seems it's trying 3 times, each with a 5s timeout before failing.

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Title:
  5s delay in AAAA dns resolving; artful and earlier is quick

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  Basic steps:
  lxc launch ubuntu-daily:bionic bionic-daily
  lxc exec bionic-daily bash
  sleep 10s (because of #1765173)
  time host -d bionic-daily.lxd # or whatever domain your containers use by default

  In bionic, there is a 5s delay when requesting the AAAA record:

  
  root at wondrous-grackle:~# time host -d wondrous-grackle.lxd
  Trying "wondrous-grackle.lxd"
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50934
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;wondrous-grackle.lxd.		IN	A

  ;; ANSWER SECTION:
  wondrous-grackle.lxd.	0	IN	A	10.0.100.125

  Received 54 bytes from 127.0.0.53#53 in 0 ms
  Trying "wondrous-grackle.lxd"

  (5s delay here)

  
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 17153
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;wondrous-grackle.lxd.		IN	AAAA

  Received 38 bytes from 127.0.0.53#53 in 1 ms
  Trying "wondrous-grackle.lxd"
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 12145
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;wondrous-grackle.lxd.		IN	MX

  Received 38 bytes from 127.0.0.53#53 in 0 ms

  real    0m5.023s

  
  In artful and xenial, there is no such delay and the (correct) empty reply is almost instantaneous.

  See https://pastebin.ubuntu.com/p/KP5DBcKyJr/

  
  In both cases, /etc/resolv.conf points at 127.0.0.53

  
  systemd version:
   *** 237-3ubuntu8 500
          500 http://br.archive.ubuntu.com/ubuntu bionic/main amd64 Packages

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