ping 的奇怪结果

Question

当我在 Ubuntu 机器上运行它时：

sudo ping google.com -c 25  -l 25

尽管事实上它应该（如果我没看错的话）一开始就发送所有 25 个数据包，但我每 2 秒收到大约 1 条线路。奇怪的是，它声称我正在获得以下 ping 时间：

--- google.com ping statistics ---
25 packets transmitted, 24 received, 4% packet loss, time 0ms
rtt min/avg/max/mdev = 23.370/28.067/32.902/2.895 ms, pipe 24

另外，如果我想提前保释，我需要为每个数据包敲一次 ctrl-C 。有没有人有任何线索可能导致这种情况？

Answer 1

如果您通过 IP ping，而不是通过主机名，您将收到预期的行为。

我仍在调查以找出这种情况的根源。

# find IP address of host
$ host -t a google.com
google.com has address 74.125.225.17
google.com has address 74.125.225.19
google.com has address 74.125.225.20
google.com has address 74.125.225.18
google.com has address 74.125.225.16

# pick an IP and ping it, all output is displayed at once
$ sudo ping 74.125.225.17 -c 25 -l 25
PING 74.125.225.17 (74.125.225.17) 56(84) bytes of data.
64 bytes from 74.125.225.17: icmp_seq=1 ttl=55 time=29.7 ms
64 bytes from 74.125.225.17: icmp_seq=2 ttl=55 time=30.4 ms
64 bytes from 74.125.225.17: icmp_seq=3 ttl=55 time=40.0 ms
64 bytes from 74.125.225.17: icmp_seq=4 ttl=55 time=40.4 ms
64 bytes from 74.125.225.17: icmp_seq=7 ttl=55 time=50.1 ms
64 bytes from 74.125.225.17: icmp_seq=5 ttl=55 time=50.4 ms
64 bytes from 74.125.225.17: icmp_seq=6 ttl=55 time=51.4 ms
64 bytes from 74.125.225.17: icmp_seq=8 ttl=55 time=52.4 ms
64 bytes from 74.125.225.17: icmp_seq=9 ttl=55 time=55.4 ms
64 bytes from 74.125.225.17: icmp_seq=10 ttl=55 time=56.4 ms
64 bytes from 74.125.225.17: icmp_seq=11 ttl=55 time=57.3 ms
64 bytes from 74.125.225.17: icmp_seq=13 ttl=55 time=58.3 ms
64 bytes from 74.125.225.17: icmp_seq=12 ttl=55 time=59.3 ms
64 bytes from 74.125.225.17: icmp_seq=14 ttl=55 time=60.3 ms
64 bytes from 74.125.225.17: icmp_seq=15 ttl=55 time=61.9 ms
64 bytes from 74.125.225.17: icmp_seq=16 ttl=55 time=62.3 ms
64 bytes from 74.125.225.17: icmp_seq=17 ttl=55 time=63.2 ms
64 bytes from 74.125.225.17: icmp_seq=18 ttl=55 time=64.2 ms
64 bytes from 74.125.225.17: icmp_seq=19 ttl=55 time=68.9 ms
64 bytes from 74.125.225.17: icmp_seq=20 ttl=55 time=69.2 ms
64 bytes from 74.125.225.17: icmp_seq=21 ttl=55 time=70.2 ms
64 bytes from 74.125.225.17: icmp_seq=22 ttl=55 time=75.9 ms
64 bytes from 74.125.225.17: icmp_seq=23 ttl=55 time=76.2 ms
64 bytes from 74.125.225.17: icmp_seq=24 ttl=55 time=77.2 ms
64 bytes from 74.125.225.17: icmp_seq=25 ttl=55 time=78.1 ms

更新

在通过 strace 运行 ping 之后，我发现它在名称解析上被挂断了（不足为奇）。然而，吸引我眼球的是avahi-daemon。该服务实现了 Apple 的 Zeroconf 架构（也称为“Rendezvous”或“Bonjour”）。换句话说，我不需要的功能。

停止 avahi-daemon 后，ping 行为恢复正常。

# sudo /etc/init.d/avahi-daemon stop

在启动期间禁用它可以通过以下方式完成：

# sudo update-rc.d -f avahi-daemon

另一种解决方法是简单地使用-n带有 ping的标志。挂断是在处理回复时执行的反向 DNS 查找。