基础|Linux 虚拟网络设备之 bridge

admin 2022年3月31日08:23:33评论38 views字数 23860阅读79分32秒阅读模式

本文将通过实际的例子来一步一步解释bridge是如何工作的。

什么是bridge?

首先,bridge是一个虚拟网络设备,所以具有网络设备的特征,可以配置IP、MAC地址等;其次,bridge是一个虚拟交换机,和物理交换机有类似的功能。

对于普通的网络设备来说,只有两端,从一端进来的数据会从另一端出去,如物理网卡从外面网络中收到的数据会转发给内核协议栈,而从协议栈过来的数据会转发到外面的物理网络中。

而bridge不同,bridge有多个端口,数据可以从任何端口进来,进来之后从哪个口出去和物理交换机的原理差不多,要看mac地址。

创建bridge

我们先用iproute2创建一个bridge:

dev@debian:~$ sudo ip link add name br0 type bridge
dev@debian:~$ sudo ip link set br0 up

当刚创建一个bridge时,它是一个独立的网络设备,只有一个端口连着协议栈,其它的端口啥都没连,这样的bridge没有任何实际功能,如下图所示:

+----------------------------------------------------------------+
|                                                                |
|       +------------------------------------------------+       |
|       |             Newwork Protocol Stack             |       |
|       +------------------------------------------------+       |
|              ↑                                ↑                |
|..............|................................|................|
|              ↓                                ↓                |
|        +----------+                     +------------+         |
|        |   eth0   |                     |     br0    |         |
|        +----------+                     +------------+         |
| 192.168.3.21 ↑                                                 |
|              |                                                 |
|
              |                                                 |
+--------------|-------------------------------------------------+
               ↓
         Physical Network

这里假设eth0是我们的物理网卡,IP地址是192.168.3.21,网关是192.168.3.1

将bridge和veth设备相连

创建一对veth设备,并配置上IP

dev@debian:~$ sudo ip link add veth0 type veth peer name veth1
dev@debian:~$ sudo ip addr add 192.168.3.101/24 dev veth0
dev@debian:~$ sudo ip addr add 192.168.3.102/24 dev veth1
dev@debian:~$ sudo ip link set veth0 up
dev@debian:~$ sudo ip link set veth1 up

将veth0连上br0

dev@debian:~$ sudo ip link set dev veth0 master br0
#通过bridge link命令可以看到br0上连接了哪些设备
dev@debian:~$ sudo bridge link
6: veth0 state UP : <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 2

这时候,网络就变成了这个样子:

+----------------------------------------------------------------+
|                                                                |
|       +------------------------------------------------+       |
|       |             Newwork Protocol Stack             |       |
|       +------------------------------------------------+       |
|            ↑            ↑              |            ↑          |
|
............|............|..............|............|..........|
|
            ↓            ↓              ↓            ↓          |
|
        +------+     +--------+     +-------+    +-------+      |
|
        | .3.21|     |        |     | .3.101|    | .3.102|      |
|
        +------+     +--------+     +-------+    +-------+      |
|
        | eth0 |     |   br0  |<--->| veth0 |    | veth1 |      |
|
        +------+     +--------+     +-------+    +-------+      |
|
            ↑                           ↑            ↑          |
|
            |                           |            |          |
|            |                           +------------+          |
|
            |                                                   |
+------------|---------------------------------------------------+
             ↓
     Physical Network

这里为了画图方便,省略了IP地址前面的192.168,比如.3.21就表示192.168.3.21

br0和veth0相连之后,发生了几个变化:

  • br0和veth0之间连接起来了,并且是双向的通道

  • 协议栈和veth0之间变成了单通道,协议栈能发数据给veth0,但veth0从外面收到的数据不会转发给协议栈

  • br0的mac地址变成了veth0的mac地址

相当于bridge在veth0和协议栈之间插了一脚,在veth0上面做了点小动作,将veth0本来要转发给协议栈的数据给拦截了,全部转发给bridge了,同时bridge也可以向veth0发数据。

下面来检验一下是不是这样的:

通过veth0 ping veth1失败:

dev@debian:~$ ping -c 1 -I veth0 192.168.3.102
PING 192.168.2.1 (192.168.2.1from 192.168.2.11 veth0: 56(84) bytes of data.
From 192.168.2.11 icmp_seq=1 Destination Host Unreachable

--- 192.168.2.1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

为什么veth0加入了bridge之后,就ping不通veth2了呢?先抓包看看:

#由于veth0的arp缓存里面没有veth1的mac地址,所以ping之前先发arp请求
#从veth1上抓包来看,veth1收到了arp请求,并且返回了应答
dev@debian:~$ sudo tcpdump -n -i veth1
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on veth1, link-type EN10MB (Ethernet), capture size 262144 bytes
21:43:48.353509 ARP, Request who-has 192.168.3.102 tell 192.168.3.101length 28
21:43:48.353518 ARP, Reply 192.168.3.102 is-at 26:58:a2:57:37:e9, length 28

#从veth0上抓包来看,数据包也发出去了,并且也收到了返回
dev@debian:~$ sudo tcpdump -n -i veth0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on veth0, link-type EN10MB (Ethernet), capture size 262144 bytes
21:44:09.775392 ARP, Request who-has 192.168.3.102 tell 192.168.3.101length 28
21:44:09.775400 ARP, Reply 192.168.3.102 is-at 26:58:a2:57:37:e9, length 28

#再看br0上的数据包,发现只有应答
dev@debian:~$ sudo tcpdump -n -i br0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on br0, link-type EN10MB (Ethernet), capture size 262144 bytes
21:45:48.225459 ARP, Reply 192.168.3.102 is-at 26:58:a2:57:37:e9, length 28

从上面的抓包可以看出,去和回来的流程都没有问题,问题就出在veth0收到应答包后没有给协议栈,而是给了br0,于是协议栈得不到veth1的mac地址,从而通信失败。

给bridge配上IP

通过上面的分析可以看出,给veth0配置IP没有意义,因为就算协议栈传数据包给veth0,应答包也回不来。这里我们就将veth0的IP让给bridge。

dev@debian:~$ sudo ip addr del 192.168.3.101/24 dev veth0
dev@debian:~$ sudo ip addr add 192.168.3.101/24 dev br0

于是网络变成了这样子:

+----------------------------------------------------------------+
|                                                                |
|       +------------------------------------------------+       |
|       |             Newwork Protocol Stack             |       |
|       +------------------------------------------------+       |
|            ↑            ↑                           ↑          |
|............|............|...........................|..........|
|
            ↓            ↓                           ↓          |
|
        +------+     +--------+     +-------+    +-------+      |
|
        | .3.21|     | .3.101 |     |       |    | .3.102|      |
|
        +------+     +--------+     +-------+    +-------+      |
|
        | eth0 |     |   br0  |<--->| veth0 |    | veth1 |      |
|
        +------+     +--------+     +-------+    +-------+      |
|
            ↑                           ↑            ↑          |
|
            |                           |            |          |
|            |                           +------------+          |
|
            |                                                   |
+------------|---------------------------------------------------+
             ↓
     Physical Network

其实veth0和协议栈之间还是有联系的,但由于veth0没有配置IP,所以协议栈在路由的时候不会将数据包发给veth0,就算强制要求数据包通过veth0发送出去,但由于veth0从另一端收到的数据包只会给br0,所以协议栈还是没法收到相应的arp应答包,导致通信失败。这里为了表达更直观,将协议栈和veth0之间的联系去掉了,veth0相当于一根网线。

再通过br0 ping一下veth1,结果成功

dev@debian:~$ ping -c 1 -I br0 192.168.3.102
PING 192.168.3.102 (192.168.3.102) from 192.168.3.101 br0: 56(84) bytes of data.
64 bytes from 192.168.3.102: icmp_seq=1 ttl=64 time=0.121 ms

--- 192.168.3.102 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.121/0.121/0.121/0.000 ms

但ping网关还是失败,因为这个bridge上只有两个网络设备,分别是192.168.3.101和192.168.3.102,br0不知道192.168.3.1在哪。

dev@debian:~$ ping -c 1 -I br0 192.168.3.1
PING 192.168.3.1 (192.168.3.1from 192.168.3.101 br0: 56(84) bytes of data.
From 192.168.3.101 icmp_seq=1 Destination Host Unreachable

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

将物理网卡添加到bridge

将eth0添加到br0上:

dev@debian:~$ sudo ip link set dev eth0 master br0
dev@debian:~$ sudo bridge link
2: eth0 state UP : <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 4
6: veth0 state UP : <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 master br0 state forwarding priority 32 cost 2

br0根本不区分接入进来的是物理设备还是虚拟设备,对它来说都一样的,都是网络设备,所以当eth0加入br0之后,落得和上面veth0一样的下场,从外面网络收到的数据包将无条件的转发给br0,自己变成了一根网线。

这时通过eth0来ping网关失败,但由于br0通过eth0这根网线连上了外面的物理交换机,所以连在br0上的设备都能ping通网关,这里连上的设备就是veth1和br0自己,veth1是通过veth0这根网线连上去的,而br0可以理解为自己有一块自带的网卡。

#通过eth0来ping网关失败
dev@debian:~$ ping -c 1 -I eth0 192.168.3.1
PING 192.168.3.1 (192.168.3.1from 192.168.3.21 eth0: 56(84) bytes of data.
From 192.168.3.21 icmp_seq=1 Destination Host Unreachable

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms

#通过br0来ping网关成功
dev@debian:~$ ping -c 1 -I br0 192.168.3.1
PING 192.168.3.1 (192.168.3.1from 192.168.3.101 br0: 56(84) bytes of data.
64 bytes from 192.168.3.1: icmp_seq=1 ttl=64 time=27.5 ms

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 27.518/27.518/27.518/0.000 ms

#通过veth1来ping网关成功
dev@debian:~$ ping -c 1 -I veth1 192.168.3.1
PING 192.168.3.1 (192.168.3.1from 192.168.3.102 veth1: 56(84) bytes of data.
64 bytes from 192.168.3.1: icmp_seq=1 ttl=64 time=68.8 ms

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 68.806/68.806/68.806/0.000 ms

由于eth0已经变成了和网线差不多的功能,所以在eth0上配置IP已经没有什么意义了,并且还会影响协议栈的路由选择,比如如果上面ping的时候不指定网卡的话,协议栈有可能优先选择eth0,导致ping不通,所以这里需要将eth0上的IP去掉。

#在本人的测试机器上,由于eth0上有IP,
#访问192.168.3.0/24网段时,会优先选择eth0
dev@debian:~$ sudo route -v
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
default         192.168.3.1     0.0.0.0         UG    0      0        0 eth0
link-local      *               255.255.0.0     U     1000   0        0 eth0
192.168.3.0     *               255.255.255.0   U     0      0        0 eth0
192.168.3.0     *               255.255.255.0   U     0      0        0 veth1
192.168.3.0     *               255.255.255.0   U     0      0        0 br0

#由于eth0已结接入了br0,所有它收到的数据包都会转发给br0,
#于是协议栈收不到arp应答包,导致ping失败
dev@debian:~$ ping -c 1 192.168.3.1
PING 192.168.3.1 (192.168.3.156(84bytes of data.
From 192.168.3.21 icmp_seq=1 Destination Host Unreachable

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 0 received, +1 errors100% packet loss, time 0ms

#将eth0上的IP删除掉
dev@debian:~$ sudo ip addr del 192.168.3.21/24 dev eth0

#再ping一次,成功
dev@debian:~$ ping -c 1 192.168.3.1
PING 192.168.3.1 (192.168.3.156(84bytes of data.
64 bytes from 192.168.3.1: icmp_seq=1 ttl=64 time=3.91 ms

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 3.916/3.916/3.916/0.000 ms

#这是因为eth0没有IP之后,路由表里面就没有它了,于是数据包会从veth1出去
dev@debian:~$ sudo route -v
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.3.0     *               255.255.255.0   U     0      0        0 veth1
192.168.3.0     *               255.255.255.0   U     0      0        0 br0
#从这里也可以看出,由于原来的默认路由走的是eth0,所以当eth0的IP被删除之后,
#默认路由不见了,想要连接192.168.3.0/24以外的网段的话,需要手动将默认网关加回来

#添加默认网关,然后再ping外网成功
dev@debian:~$ sudo ip route add default via 192.168.3.1
dev@debian:~$ ping -c 1 baidu.com
PING baidu.com (111.13.101.20856(84bytes of data.
64 bytes from 111.13.101.208: icmp_seq=1 ttl=51 time=30.6 ms

--- baidu.com ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 30.690/30.690/30.690/0.000 ms

经过上面一系列的操作后,网络变成了这个样子:

+----------------------------------------------------------------+
|                                                                |
|       +------------------------------------------------+       |
|       |             Newwork Protocol Stack             |       |
|       +------------------------------------------------+       |
|                         ↑                           ↑          |
|.........................|...........................|..........|
|                         ↓                           ↓          |
|        +------+     +--------+     +-------+    +-------+      |
|        |      |     | .3.101 |     |       |    | .3.102|      |
|        +------+     +--------+     +-------+    +-------+      |
|        | eth0 |<--->|   br0  |<--->| veth0 |    | veth1 |      |
|        +------+     +--------+     +-------+    +-------+      |
|            ↑                           ↑            ↑          |
|            |                           |            |          |
|
            |                           +------------+          |
|            |                                                   |
+------------|
---------------------------------------------------+
             ↓
     Physical Network

上面的操作中有几点需要注意:

如果是在虚拟机上做上述操作,记得打开网卡的混杂模式(不是在Linux里面,而是在虚拟机的配置上面,如VirtualBox上相应虚拟机的网卡配置项里面),不然veth1的网络会不通,因为eth0不在混杂模式的话,会丢掉目的mac地址是veth1的数据包

上面虽然通了,但由于Linux下arp的特性,当协议栈收到外面的arp请求时,不管是问101还是102,都会回复两个arp应答,分别包含br0和veth1的mac地址,也即Linux觉得外面发给101和102的数据包从br0和veth1进协议栈都一样,没有区别。由于回复了两个arp应答,而外面的设备只会用其中的一个,并且具体用哪个会随着时间发生变化,于是导致一个问题,就是外面回复给102的数据包可能从101的br0上进来,即通过102 ping外面时,可能在veth1抓不到回复包,而在br0上能抓到回复包。说明数据流在交换机那层没有完全的隔离开,br0和veth1会收到对方的IP应答包。为了解决上述问题,可以配置rp_filter, arp_filter, arp_ignore, arp_announce等参数,但不建议这么做,容易出错,调试比较麻烦。

在无线网络环境中,情况会变得比较复杂,因为无线网络需要登录,登陆后无线路由器只认一个mac地址,所有从这台机器出去的mac地址都必须是那一个,于是通过无线网卡上网的机器上的所有虚拟机想要上网的话,都必须依赖虚拟机管理软件(如VirtualBox)将每个虚拟机的网卡mac地址转成出口的mac地址(即无线网卡的mac地址),数据包回来的时候还要转回来,所以如果一个IP有两个ARP应答包的话,有可能导致mac地址的转换有问题,导致网络不通,或者有时通有时不通。解决办法就是将连接进br0的所有设备的mac地址都改成和eth0一样的mac地址,因为eth0的mac地址会被虚拟机正常的做转换。在上面的例子中,执行下面的命令即可:

dev@debian:~$ sudo ip link set dev veth1 down
#08:00:27:3b:0d:b9是eth0的mac地址
dev@debian:~$ sudo ip link set dev veth1 address 08:00:27:3b:0d:b9
dev@debian:~$ sudo ip link set dev veth1 up

bridge必须要配置IP吗?

在我们常见的物理交换机中,有可以配置IP和不能配置IP两种,不能配置IP的交换机一般通过com口连上去做配置(更简单的交换机连com口的没有,不支持任何配置),而能配置IP的交换机可以在配置好IP之后,通过该IP远程连接上去做配置,从而更方便。

bridge就属于后一种交换机,自带虚拟网卡,可以配置IP,该虚拟网卡一端连在bridge上,另一端跟协议栈相连。和物理交换机一样,bridge的工作不依赖于该虚拟网卡,但bridge工作不代表机器能连上网,要看组网方式。

删除br0上的IP:

dev@debian:~$ sudo ip addr del 192.168.3.101/24 dev br0

于是网络变成了这样子,相当于br0的一个端口通过eth0连着交换机,另一个端口通过veth0连着veth1:

+----------------------------------------------------------------+
|                                                                |
|       +------------------------------------------------+       |
|       |             Newwork Protocol Stack             |       |
|       +------------------------------------------------+       |
|                                                     ↑          |
|.....................................................|..........|
|
                                                     ↓          |
|
        +------+     +--------+     +-------+    +-------+      |
|
        |      |     |        |     |       |    | .3.102|      |
|
        +------+     +--------+     +-------+    +-------+      |
|
        | eth0 |<--->|   br0  |<--->| veth0 |    | veth1 |      |
|
        +------+     +--------+     +-------+    +-------+      |
|
            ↑                           ↑            ↑          |
|
            |                           |            |          |
|            |                           +------------+          |
|
            |                                                   |
+------------|---------------------------------------------------+
             ↓
     Physical Network

ping网关成功,说明这种情况下br0不配置IP对通信没有影响,数据包还能从veth1出去:

dev@debian:~$ ping -c 1 192.168.3.1
PING 192.168.3.1 (192.168.3.156(84) bytes of data.
64 bytes from 192.168.3.1: icmp_seq=1 ttl=64 time=1.24 ms

--- 192.168.3.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 1.242/1.242/1.242/0.000 ms

上面如果没有veth0和veth1的话,删除br0上的IP后,网络将会不通,因为没有设备和协议栈完全相连

bridge常用场景

上面通过例子展示了bridge的功能,但例子中的那种部署方式没有什么实际用途,还不如在一个网卡上配置多个IP地址来的直接。这里来介绍两种常见的部署方式。

虚拟机

虚拟机通过tun/tap或者其它类似的虚拟网络设备,将虚拟机内的网卡同br0连接起来,这样就达到和真实交换机一样的效果,虚拟机发出去的数据包先到达br0,然后由br0交给eth0发送出去,数据包都不需要经过host机器的协议栈,效率高。

+----------------------------------------------------------------+-----------------------------------------+-----------------------------------------+
|                          Host                                  |              VirtualMachine1            |              VirtualMachine2            |
|                                                                |                                         |                                         |
|       +------------------------------------------------+       |       +-------------------------+       |       +-------------------------+       |
|       |             Newwork Protocol Stack             |       |       |  Newwork Protocol Stack |       |       |  Newwork Protocol Stack |       |
|       +------------------------------------------------+       |       +-------------------------+       |       +-------------------------+       |
|                          ↑                                     |                   ↑                     |                    ↑                    |
|..........................|.....................................|...................|.....................|....................|....................|
|
                          ↓                                     |                   ↓                     |                    ↓                    |
|
                     +--------+                                 |               +-------+                 |                +-------+                |
|
                     | .3.101 |                                 |               | .3.102|                 |                | .3.103|                |
|
        +------+     +--------+     +-------+                   |               +-------+                 |                +-------+                |
|
        | eth0 |<--->|   br0  |<--->|tun/tap|                   |               | eth0  |                 |                | eth0  |                |
|
        +------+     +--------+     +-------+                   |               +-------+                 |                +-------+                |
|
            ↑             ↑             ↑                       |                   ↑                     |                    ↑                    |
|
            |             |             +-------------------------------------------+                     |                    |                    |
|
            |             ↓                                     |                                         |                    |                    |
|
            |         +-------+                                 |                                         |                    |                    |
|
            |         |tun/tap|                                 |                                         |                    |                    |
|
            |         +-------+                                 |                                         |                    |                    |
|
            |             ↑                                     |                                         |                    |                    |
|
            |             +-------------------------------------------------------------------------------|--------------------+                    |
|
            |                                                   |                                         |                                         |
|            |                                                   |                                         |                                         |
|
            |                                                   |                                         |                                         |
+------------|---------------------------------------------------+-----------------------------------------+-----------------------------------------+
             ↓
     Physical Network  (192.168.3.0/24)

docker

由于容器运行在自己单独的network namespace里面,所以都有自己单独的协议栈,情况和上面的虚拟机差不多,但它采用了另一种方式来和外界通信:

+----------------------------------------------------------------+-----------------------------------------+-----------------------------------------+
|                          Host                                  |              Container 1                |              Container 2                |
|                                                                |                                         |                                         |
|       +------------------------------------------------+       |       +-------------------------+       |       +-------------------------+       |
|       |             Newwork Protocol Stack             |       |       |  Newwork Protocol Stack |       |       |  Newwork Protocol Stack |       |
|       +------------------------------------------------+       |       +-------------------------+       |       +-------------------------+       |
|            ↑             ↑                                     |                   ↑                     |                    ↑                    |
|............|.............|.....................................|...................|.....................|....................|....................|
|            ↓             ↓                                     |                   ↓                     |                    ↓                    |
|        +------+     +--------+                                 |               +-------+                 |                +-------+                |
|        |.3.101|     |  .9.1  |                                 |               |  .9.2 |                 |                |  .9.3 |                |
|        +------+     +--------+     +-------+                   |               +-------+                 |                +-------+                |
|        | eth0 |     |   br0  |<--->|  veth |                   |               | eth0  |                 |                | eth0  |                |
|        +------+     +--------+     +-------+                   |               +-------+                 |                +-------+                |
|            ↑             ↑             ↑                       |                   ↑                     |                    ↑                    |
|            |             |             +-------------------------------------------+                     |                    |                    |
|            |             ↓                                     |                                         |                    |                    |
|            |         +-------+                                 |                                         |                    |                    |
|            |         |  veth |                                 |                                         |                    |                    |
|            |         +-------+                                 |                                         |                    |                    |
|            |             ↑                                     |                                         |                    |                    |
|            |             +-------------------------------------------------------------------------------|--------------------+                    |
|            |                                                   |                                         |                                         |
|
            |                                                   |                                         |                                         |
|            |                                                   |                                         |                                         |
+------------|
---------------------------------------------------+-----------------------------------------+-----------------------------------------+
             ↓
     Physical Network  (192.168.3.0/24)

容器中配置网关为.9.1,发出去的数据包先到达br0,然后交给host机器的协议栈,由于目的IP是外网IP,且host机器开启了IP forward功能,于是数据包会通过eth0发送出去,由于.9.1是内网IP,所以一般发出去之前会先做NAT转换(NAT转换和IP forward功能都需要自己配置)。由于要经过host机器的协议栈,并且还要做NAT转换,所以性能没有上面虚拟机那种方案好,优点是容器处于内网中,安全性相对要高点。(由于数据包统一由IP层从eth0转发出去,所以不存在mac地址的问题,在无线网络环境下也工作良好)

上面两种部署方案中,同一网段的每个网卡都有自己单独的协议栈,所以不存在上面说的多个ARP的问题

链接:https://segmentfault.com/a/1190000009491002

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  • 本文由 发表于 2022年3月31日08:23:33
  • 转载请保留本文链接(CN-SEC中文网:感谢原作者辛苦付出):
                   基础|Linux 虚拟网络设备之 bridgehttp://cn-sec.com/archives/565887.html

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