openwrt 网络的默认配置如下：
root@OpenWrt:/etc/init.d# ifconfig br-lan Link encap:Ethernet HWaddr D0:39:72:18:7C:FF inet addr:192.168.1.1 Bcast:192.168.1.255 Mask:255.255.255.0 inet6 addr: fdea:e40b:d8de::1/60 Scope:Global inet6 addr: fe80::d239:72ff:fe18:7cff/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:2482 errors:0 dropped:0 overruns:0 frame:0 TX packets:1591 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:235069 (229.5 KiB) TX bytes:134302 (131.1 KiB)
eth0 Link encap:Ethernet HWaddr D0:39:72:18:7C:FF UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:0 errors:0 dropped:0 overruns:0 frame:0 TX packets:0 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:0 (0.0 B) TX bytes:0 (0.0 B) Interrupt:45
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:864 errors:0 dropped:0 overruns:0 frame:0 TX packets:864 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:58752 (57.3 KiB) TX bytes:58752 (57.3 KiB)
dhcp是通过br-lan结点分配的，这个结点是个桥接的虚拟节点：
root@OpenWrt:/# brctl show bridge name bridge id STP enabled interfaces br-lan 7fff.d03972187cff no eth0
把usb0加入桥接：
root@OpenWrt:~# brctl addif br-lan usb0
root@OpenWrt:~# brctl show bridge name bridge id STP enabled interfaces br-lan 7fff.d03972187cff no eth0
启动usb0：
root@OpenWrt:~# ifconfig usb0 up [ 6523.200137] br-lan: port 2(usb0) entered blocking state [ 6523.205863] br-lan: port 2(usb0) entered forwarding state
addbr bridge的名称 #添加bridge；
delbr bridge的名称 #删除bridge；
addif bridge的名称 device的名称 #添加接口到bridge；
delif bridge的名称 device的名称#从bridge中删除接口
使用brctl命令创建网桥br1
brctl addbr br1
删除网桥br1
brctl delbr br1
将eth0端口加入网桥br1
brctl addif br1 eth0
删除eth0端口加入网桥br1
brctl delif br1 eth0
查询网桥信息