KVM三种网络类型：
[root@node124 opt]# virt-install --help| grep network
--pxe Boot from the network using thePXE protocol
-w NETWORK,--network=NETWORK
Configure a guest network interface. Ex:
--networkbridge=mybr0
--network network=my_libvirt_virtual_net
--network network=mynet,model=virtio,mac=00:11...
--nonetworks Don't createnetwork interfaces for the guest.
虚拟机默认通过NAT方式桥接到virbr0
[root@node124 opt]# brctl show
bridge name bridgeid STP enabled interfaces
virbr0 8000.525400a30536 yes virbr0-nic
vnet0
[root@node124 opt]# ifconfig
virbr0 Linkencap:Ethernet HWaddr52:54:00:A3:05:36 #宿主机桥接的网卡
inetaddr:192.168.122.1Bcast:192.168.122.255Mask:255.255.255.0
UPBROADCAST RUNNING MULTICASTMTU:1500 Metric:1
RX packets:44errors:0 dropped:0 overruns:0 frame:0
TXpackets:14 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RXbytes:3432 (3.3 KiB) TX bytes:1435 (1.4KiB)
vnet0 Linkencap:Ethernet HWaddr FE:54:00:37:E2:FA#虚拟机主机的网卡// vnet0桥接到virbr0网桥的端口上
inet6addr: fe80::fc54:ff:fe37:e2fa/64 Scope:Link
UPBROADCAST RUNNING MULTICASTMTU:1500 Metric:1
RXpackets:38 errors:0 dropped:0 overruns:0 frame:0
TXpackets:1571 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RXbytes:3532 (3.4 KiB) TX bytes:82555(80.6 KiB)
创建一个网桥并将物理网卡绑定到网桥上，在网桥上配置IP地址
创建一个新网桥：
[root@node124 opt]# brctl addbr br0
[root@node124 opt]# brctl show
bridge name bridgeid STP enabled interfaces
br0 8000.000000000000 no
virbr0 8000.525400a30536 yes virbr0-nic
vnet0
将网桥桥接到宿主机的真实网卡上(关联真实物理网卡)：
[root@node124 opt]# brctl addif br0 eth1
这时与eth1相连接的数据会断开，
将eth1的IP地址清除
#ip addr del dev eth1 192.168.2.124/16
将新创建的网桥配置一个跟eth1一样的IP地址：
#ifconfig br0 192.168.2.124/16 up
[root@node124 ~]# ifconfig
br0 Linkencap:Ethernet HWaddr00:0C:29:C2:AD:BA
inetaddr:192.168.2.124Bcast:192.168.255.255 Mask:255.255.0.0
inet6addr: fe80::20c:29ff:fec2:adba/64 Scope:Link
UPBROADCAST RUNNING MULTICASTMTU:1500 Metric:1
RXpackets:77272 errors:0 dropped:0 overruns:0 frame:0
TXpackets:46 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RXbytes:3686961 (3.5 MiB) TX bytes:7213(7.0 KiB)
eth1 Linkencap:Ethernet HWaddr00:0C:29:C2:AD:BA
inet6addr: fe80::20c:29ff:fec2:adba/64 Scope:Link
UPBROADCAST RUNNING MULTICASTMTU:1500 Metric:1
RXpackets:9078175 errors:0 dropped:0 overruns:0 frame:0
TXpackets:14618 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RXbytes:706370069 (673.6 MiB) TXbytes:4984824 (4.7 MiB)
[root@node124 ~]# brctl show
bridge name bridgeid STP enabled interfaces
br0 8000.000c29c2adba no eth1
virbr0 8000.525400a30536 yes virbr0-nic
vnet0
将虚拟机的网络桥接到br0上面，直接通过eth1网卡上网(直接桥接上网)
先停止虚拟机：
[root@node124 ~]# virsh shutdown CentOS-6.7-x86_64
1.通过virsh 编辑xml文件
[root@node124 ~]#virsh edit CentOS-6.7-x86_64
Domain CentOS-6.7-x86_64 XML configuration edited.
修改前:
52
53
54
55
56
57
修改后：
52
53
54
55
56
57
修改完成后，重新启动虚拟机;
[root@node124 ~]# virsh start CentOS-6.7-x86_64
Domain CentOS-6.7-x86_64 started
查看桥接的网卡：
[root@node124 ~]# brctl show
bridge name bridgeid STP enabled interfaces
br0 8000.000c29c2adba no eth1
vnet0
virbr0 8000.525400a30536 yes virbr0-nic
通过以上操作，现在虚拟机就相当于vmware的桥接网络，可以配置192.168.2.0/16网段的IP地址，并且可以上网
桥接相当于直接接到交换机的端口上,直接级连交换机
