daf*_*fan 5 networking dns 19.04
我最近将我的笔记本电脑升级到 19.04（以前是 18.04），从那时起我在 DNS 解析方面遇到了问题。
解析任何地址只需要 15 秒。例如，这里是命令“ping www.google.ch”的wireshark跟踪，它显示了DNS解析中的不稳定行为（抱歉粘贴了日志blob）：
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
从评论中...
的符号链接/etc/resolv.conf设置为/run/systemd/resolve/stub-resolv.conf包含options edns0. 某些网络不响应此 DNS 扩展，并且 DNS 解析会中断。
我们使用以下命令重置符号链接：
sudo ln -s /run/systemd/resolve/resolv.conf /etc/resolv.conf
这可能也有效：
sudo ln -s /run/resolvconf/resolv.conf /etc/resolv.conf
后记：
您可能还遇到的一个问题是 DSL 连接的 MTU 设置。
Ubuntu 的网络配置中有一个 MTU 设置，路由器中有一个 WAN MTU 设置。
对于 DSL，常见的 MTU 设置是 1492。首先尝试该值，看看您的网站现在是否可以访问。
要确定正确的设置，请从所有 MTU 设置 = 1500 和 VPN = 关闭开始。（VPN 需要不同的测试）。
在终端中：
ping [-c count] [-M do] [-s packet_size] [host]
使用的选项是：
c count: ping 的次数M hint：选择路径MTU发现策略。可以是do（禁止分段，甚至是本地分段）、want（进行 PMTU 发现，当数据包大小较大时在本地分段）或dont（不设置 DF 标志）。s packet_size：指定要发送的数据字节数。您应该始终从 1472 开始，每次递减 10。一旦收到回复，就加 1，直到收到碎片数据包。取该值（最后一个有效值）并将该值加上 28 以考虑各种 TCP/IP 标头。例如。假设 1452 是正确的数据包大小（您首先收到对 ping 的 ICMP 回复）。实际 MTU 大小为 1480，这是我们正在使用的网络的最佳值。
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?
参考：如何使用 ICMP ping 确定正确的 MTU 大小
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