1、创建网桥的目的是为了让KVM虚拟机连接到这个网桥，从而使虚拟机可以和物理网络通信
2、当然，安装完kvm后，会自动建立一个网桥virbr0，这个网桥应该是nat模式

一、DHCP网桥创建
vim /etc/network/interfaces

这是interfaces配置文件的内容：

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
 
# The loopback network interface
auto lo
iface lo inet loopback
 
# The primary network interface
auto eth0
iface eth0 inet dhcp 物理网卡也为DHCP
 
auto br100
iface br100 inet dhcp 配置br100网桥为DHCP
bridge_ports eth0    配置br100建立在物理网卡eth0上
bridge_stp off
bridge_fd

创建完成后，重启网络

静态网桥
vim /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
 
# The loopback network interface
auto lo
iface lo inet loopback
 
# The primary network interface
auto eth0
iface eth0 inet static
address 192.168.89.3
gateway 192.168.89.2
netmask 255.255.255.0
network 192.168.89.0
broadcast 192.168.89.255
 
auto br100
iface br100 inet static
bridge_ports eth0
bridge_stp off
bridge_fd 0
bridge_maxwait 0
address 192.168.89.3
network 192.168.89.0
netmask 255.255.255.0
broadcast 192.168.89.255
gateway 192.168.89.2

创建完成后，重启网络