Ubuntu 19.04のDNSの問題
最近、ラップトップを19.04（以前は18.04）にアップグレードしましたが、それ以来、DNS解決に問題があります。
アドレスを解決するのにちょうど15秒かかります。たとえば、次の例は、 "ping www.google.ch"コマンドのWiresharkトレースです。これは、DNS解決の不規則な動作を示しています（ログBLOBを貼り付けてすみません）。
1 0.000000000 127.0.0.1 127.0.0.53 DNS 82 Standard query 0x9885 A google.ch OPT 2 0.000040848 127.0.0.1 127.0.0.53 DNS 82 Standard query 0xf398 AAAA google.ch OPT 3 0.000472315 192.168.1.61 192.168.1.1 DNS 71 Standard query 0xbc08 A google.ch 4 0.000751989 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 5 0.003821221 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 6 0.004064023 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 7 0.005267971 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 8 0.005497112 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 9 0.006644819 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 10 0.006863866 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 11 0.007920878 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 12 0.008130719 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 13 0.009242334 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 14 0.009637573 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 15 0.010792517 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 16 0.011031800 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 17 0.012258637 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 18 0.012489432 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 19 0.013713170 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 20 0.013915614 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 21 0.014032986 192.168.1.1 192.168.1.61 DNS 87 Standard query response 0xbc08 A google.ch A 172.217.168.35 22 0.014322592 127.0.0.53 127.0.0.1 DNS 98 Standard query response 0x9885 A google.ch A 172.217.168.35 OPT 23 0.015102484 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 24 0.015277122 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 25 0.016431079 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 26 0.016609622 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 27 0.017757978 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 28 0.017919223 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 29 0.018984296 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 30 0.019164206 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 31 0.020291847 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 32 0.020465090 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 33 0.021606042 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 34 0.021834229 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 35 0.022902638 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 36 0.023076859 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 37 0.024185348 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 38 0.024369468 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 39 0.025402235 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 40 0.025557918 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 41 0.026557335 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 42 0.026681040 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 43 0.027705800 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 44 0.027808876 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 45 0.028793187 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 46 0.028893739 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 47 0.029878670 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 48 0.029986119 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 49 0.031010405 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 50 0.031127410 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 51 0.032151807 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 52 0.032261394 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x335e AAAA google.ch 53 0.033290733 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x335e Refused AAAA google.ch 54 5.001947117 127.0.0.1 127.0.0.53 DNS 82 Standard query 0x9885 A google.ch OPT 55 5.002322889 127.0.0.53 127.0.0.1 DNS 98 Standard query response 0x9885 A google.ch A 172.217.168.35 OPT 56 5.002450775 127.0.0.1 127.0.0.53 DNS 82 Standard query 0xf398 AAAA google.ch OPT 57 5.002829396 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 58 5.005749595 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 59 5.006000720 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 60 5.007085084 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 61 5.007278137 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 62 5.008493792 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 63 5.008726953 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 64 5.009760440 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 65 5.009962097 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 66 5.011064276 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 67 5.011294755 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 68 5.012464702 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 69 5.012696487 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 70 5.013803847 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 71 5.013991838 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 72 5.015081146 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 73 5.015311695 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 74 5.016397601 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 75 5.016572805 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 76 5.018326688 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 77 5.018522763 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 78 5.019673004 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 79 5.019905288 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 80 5.020942721 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 81 5.021117750 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 82 5.022175880 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 83 5.022368879 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 84 5.023497195 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 85 5.023727693 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 86 5.024716756 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 87 5.024917772 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 88 5.025940891 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 89 5.026242405 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 90 5.027396468 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 91 5.027627309 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 92 5.028669617 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 93 5.028844156 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 94 5.029909396 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 95 5.030099489 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 96 5.031241631 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 97 5.031470878 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 98 5.032507283 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 99 5.032684260 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 100 5.033712152 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 101 5.033923324 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 102 5.035076891 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 103 5.035307433 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x897a AAAA google.ch 104 5.036458185 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x897a Refused AAAA google.ch 105 10.005946641 127.0.0.1 127.0.0.53 DNS 82 Standard query 0x9885 A google.ch OPT 106 10.006376461 127.0.0.53 127.0.0.1 DNS 98 Standard query response 0x9885 A google.ch A 172.217.168.35 OPT 107 10.006552675 127.0.0.1 127.0.0.53 DNS 82 Standard query 0xf398 AAAA google.ch OPT 108 10.006923636 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 109 10.009568741 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 110 10.009795245 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 111 10.010954209 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 112 10.011184364 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 113 10.012458263 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 114 10.012691547 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 115 10.013805929 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 116 10.014036944 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 117 10.015165110 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 118 10.015403914 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 119 10.016501372 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 120 10.016710396 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 121 10.017809472 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 122 10.017988063 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 123 10.019114116 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 124 10.019353925 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 125 10.020505187 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 126 10.020741642 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 127 10.021814158 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 128 10.022045574 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 129 10.023153608 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 130 10.023336649 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 131 10.024412807 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 132 10.024632391 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 133 10.025813396 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 134 10.026244008 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 135 10.027357668 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 136 10.027535923 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 137 10.028599634 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 138 10.028776517 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 139 10.029782946 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 140 10.029961443 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 141 10.031008052 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 142 10.031186821 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 143 10.032214660 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 144 10.032393053 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 145 10.033518425 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 146 10.033744680 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 147 10.034887325 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 148 10.035116833 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 149 10.036226120 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 150 10.036458904 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 151 10.037515996 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 152 10.037775347 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 153 10.038839704 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 154 10.039017849 192.168.1.61 192.168.1.1 DNS 71 Standard query 0x2b09 AAAA google.ch 155 10.040061077 192.168.1.1 192.168.1.61 DNS 71 Standard query response 0x2b09 Refused AAAA google.ch 156 15.024825964 127.0.0.1 127.0.0.53 DNS 100 Standard query 0xb4e4 PTR 35.168.217.172.in-addr.arpa OPT 157 15.025320672 192.168.1.61 192.168.1.1 DNS 89 Standard query 0x0774 PTR 35.168.217.172.in-addr.arpa 158 15.038823507 192.168.1.1 192.168.1.61 DNS 127 Standard query response 0x0774 PTR 35.168.217.172.in-addr.arpa PTR zrh04s14-in-f3.1e100.net 159 15.039215285 127.0.0.53 127.0.0.1 DNS 138 Standard query response 0xb4e4 PTR 35.168.217.172.in-addr.arpa PTR zrh04s14-in-f3.1e100.net OPT
PTRクエリが完了すると（パケットnr 156あたり）、pingは15秒間ブロックされます。Aレコードがパケット21、55、106で3回受信されたとしてもです。
これは、ipv6をまったくサポートしないwifiで作業しているときにのみ発生します。自宅にはipv6があり、まったく問題ありません。問題のあるネットワークのwifi設定でipv6（gnome設定）を無効にしましたが、この動作には影響しません。
Systemdで解決された構成がデフォルトです。
$ cat /etc/systemd/resolved.conf
...
[Resolve]
#DNS=
#FallbackDNS=
#Domains=
#LLMNR=no
#MulticastDNS=no
#DNSSEC=no
#DNSOverTLS=no
#Cache=yes
#DNSStubListener=yes
#ReadEtcHosts=yes
@heynnemaのリクエストに応じて編集
$ ls -al /etc/resolv.conf
lrwxrwxrwx 1 root root 39 Aug 17 2018 /etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf
$ cat /etc/resolv.conf
# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients to the
# internal DNS stub resolver of systemd-resolved. This file lists all
# configured search domains.
#
# Run "resolvectl status" to see details about the uplink DNS servers
# currently in use.
#
# Third party programs must not access this file directly, but only through the
# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
# replace this symlink by a static file or a different symlink.
#
# See man:systemd-resolved.service(8) for details about the supported modes of
# operation for /etc/resolv.conf.
nameserver 127.0.0.53
options edns0
search media.int Home
$ dpkg -l *dnsmasq*
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name Version Architecture Description
+++-================-=============-============-============================================
un dnsmasq <none> <none> (no description available)
ii dnsmasq-base 2.80-1ubuntu1 AMD64 Small caching DNS proxy and DHCP/TFTP server
un dnsmasq-base-lua <none> <none> (no description available)
$ cat /etc/NetworkManager/NetworkManager.conf
[main]
plugins=ifupdown,keyfile
[ifupdown]
managed=false
[device]
wifi.scan-Rand-mac-address=no
$ systemd-resolve --status
Global
LLMNR setting: no
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
DNSSEC NTA: 10.in-addr.arpa
16.172.in-addr.arpa
168.192.in-addr.arpa
17.172.in-addr.arpa
18.172.in-addr.arpa
19.172.in-addr.arpa
20.172.in-addr.arpa
21.172.in-addr.arpa
22.172.in-addr.arpa
23.172.in-addr.arpa
24.172.in-addr.arpa
25.172.in-addr.arpa
26.172.in-addr.arpa
27.172.in-addr.arpa
28.172.in-addr.arpa
29.172.in-addr.arpa
30.172.in-addr.arpa
31.172.in-addr.arpa
corp
d.f.ip6.arpa
home
internal
intranet
lan
local
private
test
Link 10 (docker0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 9 (vethKHVDZJ)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 7 (lxdbr0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 6 (virbr0-nic)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 5 (virbr0)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 4 (enx4865ee119deb)
Current Scopes: none
DefaultRoute setting: no
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Link 3 (wlp2s0)
Current Scopes: DNS
DefaultRoute setting: yes
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 192.168.1.1
DNS Servers: 192.168.1.1
DNS Domain: ~.
Home
Link 2 (enp0s31f6)
Current Scopes: DNS
DefaultRoute setting: yes
LLMNR setting: yes
MulticastDNS setting: no
DNSOverTLS setting: no
DNSSEC setting: no
DNSSEC supported: no
Current DNS Server: 10.136.8.10
DNS Servers: 10.136.8.10
10.137.24.10
DNS Domain: media.int
ボーナスとして、ここに私のルートがあります：
$ ip r
default via 192.168.1.1 dev wlp2s0 proto dhcp metric 600
10.0.0.0/8 via 10.168.38.1 dev enp0s31f6 proto static metric 10
10.168.38.0/24 dev enp0s31f6 proto kernel scope link src 10.168.38.154 metric 100
169.254.0.0/16 dev virbr0 scope link metric 1000 linkdown
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 linkdown
192.168.1.0/24 dev wlp2s0 proto kernel scope link src 192.168.1.61 metric 600
192.168.122.0/24 dev virbr0 proto kernel scope link src 192.168.122.1 linkdown
192.168.224.0/24 dev lxdbr0 proto kernel scope link src 192.168.224.1
新しい編集：
/etc/resolv.confを手動で編集し、resolvectl statusから返されたDNSサーバーを使用すると、問題が解決します。
この問題は、systemd-resolvedがリゾルバーとして使用されている場合にのみ存在します。可能な限りの値でオプションDNSSECを変更してみました。まだ同じ問題。
だから私は最終的に回避策としてスクリプトを作りました：
$ cat bin/fix-dns.sh
#!/bin/bash
Sudo sed -i '/^nameserver/ s/127.0.0.53/10.136.8.10/' /etc/resolv.conf
これを変更するにはどうすればよいですか？なぜリゾルバーはipv6にそれほど多くを要求し、なぜクライアントに回答を与える前にPTRレコードを待つのですか？
よろしくお願いします。
コメントから...
/etc/resolv.confのシンボリックリンクは、/run/systemd/resolve/stub-resolv.confを含むoptions edns0に設定されました。一部のネットワークはこのDNS拡張に応答せず、DNS解決が機能しません。
シンボリックリンクをリセットします：
Sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
これもおそらくうまくいったでしょう：
Sudo ln -s /run/resolvconf/resolv.conf /etc/resolv.conf
ポストノート：
また、DSL接続のMTU設定に問題がある場合もあります。
Ubuntuのネットワーク構成にはMTU設定があり、ルーターにはWAN MTU設定があります。
DSLの場合、一般的なMTU設定は1492です。先に進んでこの値を最初に試し、Webサイトにアクセスできるかどうかを確認してください。
正しい設定を判別するには、すべてのMTU設定= 1500およびVPN =オフから始めます。 （VPNには別のテストが必要です）。
ターミナルで：
ping [-c count] [-M do] [-s packet_size] [Host]
使用されるオプションは次のとおりです。
c count：pingする回数M hint：パスMTU検出戦略を選択します。do（断片化を禁止し、ローカルの断片化も禁止）、want（PMTU検出を実行、パケットサイズが大きい場合はローカルで断片化）、またはdont（設定しない= DFフラグ）。s packet_size：送信するデータのバイト数を指定します。
常に1472から始めて、毎回10ずつ作業を進める必要があります。応答を受け取ったら、断片化されたパケットを取得するまで1ずつ増やします。その値（最後の適切な値）を取り、値に28を追加して、さまざまなTCP/IPヘッダーを考慮します。例えば。 1452が適切なパケットサイズであるとしましょう（最初にpingへのICMP応答を取得した場所）。実際のMTUサイズは1480です。これは、使用しているネットワークに最適です。
ping -c 4 -M do -s 1472 8.8.8.8 # this will probably show fragmentation
ping -c 4 -M do -s 1462 8.8.8.8 # may show fragmentation
ping -c 4 -M do -s 1452 8.8.8.8 # no fragmentation?
ping -c 4 -M do -s 1453 8.8.8.8 # still no fragmentation?