只有当tcpdump正在监听时，wget才有效

我在XENpipe理程序上运行了两台使用Ubuntu trusty（Linaro-Developer版本）的虚拟机，使用以下简单的桥接networking设置：

在这里输入图像说明

后端域（dom0）：

br0 Link encap:Ethernet HWaddr 02:4d:04:41:96:a9 inet addr:141.79.67.109 Bcast:141.79.71.255 Mask:255.255.248.0 inet6 addr: fe80::4d:4ff:fe41:96a9/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4896629 errors:0 dropped:814 overruns:0 frame:0 TX packets:1134 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:356819584 (356.8 MB) TX bytes:277236 (277.2 KB) eth0 Link encap:Ethernet HWaddr 02:4d:04:41:96:a9 UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4906298 errors:0 dropped:0 overruns:0 frame:0 TX packets:2249 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:430584499 (430.5 MB) TX bytes:362740 (362.7 KB) Interrupt:44 lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:16 errors:0 dropped:0 overruns:0 frame:0 TX packets:16 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:1248 (1.2 KB) TX bytes:1248 (1.2 KB) vif1.0 Link encap:Ethernet HWaddr fe:ff:ff:ff:ff:ff inet6 addr: fe80::fcff:ffff:feff:ffff/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1049 errors:0 dropped:0 overruns:0 frame:0 TX packets:4767521 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:32 RX bytes:66258 (66.2 KB) TX bytes:416912687 (416.9 MB)

来宾域（domU）

 eth0 Link encap:Ethernet HWaddr 00:16:3e:54:95:f5 inet addr:141.79.66.105 Bcast:141.79.71.255 Mask:255.255.248.0 inet6 addr: fe80::216:3eff:fe54:95f5/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:4879495 errors:0 dropped:815 overruns:0 frame:0 TX packets:1049 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:358293232 (358.2 MB) TX bytes:80944 (80.9 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:8 errors:0 dropped:0 overruns:0 frame:0 TX packets:8 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:672 (672.0 B) TX bytes:672 (672.0 B)

在dom0中的Netwoking工作正常（apt-get，wget）。 Buti n domU我遇到一个非常奇怪的问题：ping运行良好，但apt-get和wget不起作用。

 root@MyUbuntu:~# wget -p http://google.com --1970-01-01 00:52:49-- http://google.com/ Resolving google.com (google.com)... 129.143.66.27, 129.143.66.29, 129.143.66.30, ... Connecting to google.com (google.com)|129.143.66.27|:80... connected. HTTP request sent, awaiting response... No data received.

我在dom0上安装tcpdump来debugging问题，运行一个简单的命令：

 tcpdump -i br0 -n "tcp and src 141.79.66.105"

但是，每当tcpdump正在监听wget和apt-get都能正常工作：

 root@MyUbuntu:~# wget -p http://google.com --1970-01-01 00:42:27-- http://google.com/ Resolving google.com (google.com)... 129.143.66.45, 129.143.66.49, 129.143.66.53, ... Connecting to google.com (google.com)|129.143.66.45|:80... connected. HTTP request sent, awaiting response... 302 Found Location: http://www.google.de/?gfe_rd=cr&ei=qJIzVs3qJqSh8wfLma_QCw [following] --1970-01-01 00:42:27-- http://www.google.de/?gfe_rd=cr&ei=qJIzVs3qJqSh8wfLma_QCw Resolving www.google.de (www.google.de)... 129.143.66.38, 129.143.66.42, 129.143.66.44, ... Reusing existing connection to google.com:80. HTTP request sent, awaiting response... 200 OK Length: unspecified [text/html] Saving to: 'google.com/index.html' [ <=> ] 19,468 --.-K/s in 0.003s 1970-01-01 00:42:27 (5.84 MB/s) - 'google.com/index.html' saved [19468] FINISHED --1970-01-01 00:42:27-- Total wall clock time: 0.09s Downloaded: 1 files, 19K in 0.003s (5.84 MB/s)

tcpdump是否打开允许stream量通过的任何端口？任何帮助非常感谢。谢谢。

当你启动tcpdump时，它将把接口置于混杂模式。这可能是tcpdump处于活动状态时允许数据到达domU的原因。

你可以通过在tcpdump命令中join--no-promiscuous-mode来testing这个理论。或通过手动将界面设置为混杂模式。

不知道如何帮助解决实际问题。

桥接时，物理接口必须处于混杂模式。这样可以看到并转发发往网桥和虚拟接口的数据包。

解决scheme是确保您的eth0configuration了“promisc”启用。