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

[Benjamin DeCamp]

I'm having similar problems with DNS resolution in Bionic Ubuntu-Server.

After configuring the netplan file, with the "local" search suffix, name
resolution works, but I see a 5 second delay for any DNS name ending in
.local.

When watching wireshark during the DIG request, the local system makes
about 25 successful DNS queries to the correct dns server, and the
correct response is returned for all 25 queries. This happens in seconds
0 to 1. Then there is a pause of 4 seconds, then an identical query and
response occurs at second 5, then the DIG result is returned, and the
response is cached by systemd-resolvd.

For some reason the DNS resolver is ignoring all 25 of its first
attempts to resolve the name in the first 0-1 seconds. Then it waits for
4 seconds, makes a single query, and this result is accepted and used.

This netplan file is the only configuration change after installation of
Bionic 18.04.2 Server:

$ cat /etc/netplan/01-netcfg.yaml
# This file describes the network interfaces available on your system
# For more information, see netplan(5).
network:
 ethernets:
  eth0:
   addresses: [192.168.9.2/24]
   gateway4: 192.168.9.254
   nameservers:
    search: [local]
    addresses: [192.168.9.1]
 version: 2


** Attachment added: "lots of ignored correct query-responses, then at time=5, a single accepted query-response is made"
   https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1765477/+attachment/5242115/+files/wireshark-ignored-responses.PNG

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https://bugs.launchpad.net/bugs/1765477

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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