当我尝试查看 StackExchange 网站上一篇文章中的图片时，我很惊讶地在 Ubuntu 18.04 上的 Chromium 中看到了这个错误消息：
无法访问此网站
i.stack.imgur.com找不到 的服务器 IP 地址。
DNS_PROBE_FINISHED_NXDOMAIN
为了弄清楚发生了什么，我尝试tcpdump查看 DNS 请求和响应。我尝试重新加载出现错误的图像，这是我看到的 DNS 流量：
# tcpdump -pni any 'port 53'
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
20:10:17.618041 IP 127.0.0.1.42714 > 127.0.0.53.53: 3068+ A? i.stack.imgur.com. (35)
20:10:17.618080 IP 127.0.0.1.42714 > 127.0.0.53.53: 23569+ AAAA? i.stack.imgur.com. (35)
20:10:17.618861 IP 127.0.0.53.53 > 127.0.0.1.42714: 3068 13/0/0 CNAME i.stack.imgur.com.cdn.cloudflare.net., A 104.16.0.35, A 104.16.26.34, A 104.16.2.35, A 104.16.30.34, A 104.16.28.34, A 104.16.24.34, A 104.16.25.34, A 104.16.29.34, A 104.16.27.34, A 104.16.3.35, A 104.16.1.35, A 104.16.31.34 (277)
20:10:17.619395 IP 127.0.0.53.53 > 127.0.0.1.42714: 23569| 16/0/0 CNAME i.stack.imgur.com.cdn.cloudflare.net., AAAA 2001:67c:2b0:db32:0:1:6810:1f22, AAAA 2001:67c:2b0:db32:0:1:6810:1b22, AAAA 64:ff9b::6810:23, AAAA 2001:67c:2b0:db32:0:1:6810:223, AAAA 2001:67c:27e4:64::6810:123, AAAA 64:ff9b::6810:1f22, AAAA 2001:67c:27e4:64::6810:1f22, AAAA 2001:67c:27e4:64::6810:223, AAAA 2001:67c:27e4:64::6810:1b22, AAAA 2001:67c:27e4:64::6810:1922, AAAA 2001:67c:2b0:db32:0:1:6810:1d22, AAAA 64:ff9b::6810:123, AAAA 2001:67c:2b0:db32:0:1:6810:1e22, AAAA 64:ff9b::6810:1822, AAAA 2001:67c:2b0:db32:0:1:6810:1822 (505)
如您所见，DNS解析成功。但Chromium仍然向我显示相同的NXDOMAIN错误消息。当查找确实成功时，是什么原因导致Chromium报告NXDOMAIN？