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脚本1
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tunctl -t tap0 -u user_a
chmod 0666 /dev/net/tun
ifconfig eth0 0.0.0.0 promisc
ifconfig tap0 0.0.0.0 promisc
brctl addbr br0
brctl addif br0 eth0
brctl addif br0 tap0
ifconfig br0 192.168.1.6 netmask 255.255.255.0 up
ifconfig eth0 192.168.1.1 netmask 255.255.255.0 up
ifconfig tap0 192.168.1.2 netmask 255.255.255.0 up
route add default gw 192.168.1.1
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执行完“脚本1”后，ifconfig,结果如下（只列出部分信息）：
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eth0 Link encap:以太网 硬件地址 mac_eth0
inet 地址:192.168.1.1 广播:192.168.1.255 掩码:255.255.255.0
inet6 地址: fe80::ba88:e3ff:fe55:4c7a/64 Scope:Link
UP BROADCAST RUNNING PROMISC MULTICAST MTU:1500 跃点数:1
接收数据包:123168 错误:0 丢弃:0 过载:0 帧数:0
发送数据包:122567 错误:0 丢弃:0 过载:0 载波:1
碰撞:0 发送队列长度:1000
接收字节:138710498 (138.7 MB) 发送字节:13651772 (13.6 MB)
中断:49
tap0 Link encap:以太网 硬件地址 mac_tap0
inet 地址:192.168.1.2 掩码:255.255.255.0
UP BROADCAST PROMISC MULTICAST MTU:1500 跃点数:1
接收数据包:0 错误:0 丢弃:0 过载:0 帧数:0
发送数据包:0 错误:0 丢弃:0 过载:0 载波:0
碰撞:0 发送队列长度:500
接收字节:0 (0.0 B) 发送字节:0 (0.0 B)
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如果使用 brctl showstp br0 指令查看，则输出如下：
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br0
bridge id 8000.4e77c421c064
designated root 8000.4e77c421c064
root port 0 path cost 0
max age 20.00 bridge max age 20.00
hello time 2.00 bridge hello time 2.00
forward delay 15.00 bridge forward delay 15.00
ageing time 300.01
hello timer 0.48 tcn timer 0.00
topology change timer 0.00 gc timer 177.72
flags
eth0 (1)
port id 8001 state forwarding
designated root 8000.4e77c421c064 path cost 19
designated bridge 8000.4e77c421c064 message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
tap0 (2)
port id 8002 state disabled
designated root 8000.4e77c421c064 path cost 100
designated bridge 8000.4e77c421c064 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
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为何 tap0 不是 RUNNING 的呢？