1. About Network Bridge
A network bridge is a Link Layer device which forwards traffic between networks based on MAC addresses and is therefore also referred to as a Layer 2 device.
It makes forwarding decisions based on tables of MAC addresses which it builds by learning what hosts are connected to each network.
A software bridge can be used within a Linux host in order to emulate a hardware
bridge, for example in virtualization applications for sharing a NIC with one or more virtual NICs.
Example： Sample ifcfg-br0 interface configuration file
DEVICE=br0
TYPE=Bridge
IPADDR=192.168.1.100
NETMASK=255.255.255.0
ONBOOT=yes
BOOTPROTO=none
NM_CONTROLLED=no
DELAY=0
Example：Sample ifcfg-eth0 interface configuration file
DEVICE=eth0
TYPE=Ethernet
HWADDR=08:00:27:72:C0:A0
BOOTPROTO=none
ONBOOT=yes
NM_CONTROLLED=no
BRIDGE=br0
原文：http://jerrydai.blog.51cto.com/12141841/1871537