CentOS6.3 KVM下设置网卡为桥接模式

KVM的默认网络模式为NAT，就是说借助宿主机模式上网，现在我们想改成桥接模式，这样外界就可以直接和宿主机里的虚拟机通讯了。
 
1，首先看一下默认的网络设置
 # cat /etc/libvirt/qemu/networks/default.xml
<network>
  <name>default</name>
  <uuid>1f118032-0345-4725-adcf-6b94f6aca19c</uuid>
  <bridge name="virbr0" />
  <mac address='52:54:00:F1:6B:6E'/>
  <forward/>
  <ip address="192.168.122.1" netmask="255.255.255.0">
    <dhcp>
      <range start="192.168.122.2" end="192.168.122.254" />
    </dhcp>
  </ip>
 </network>
 
2，再看一下虚拟机配置文件里面的网络设置
 #cat /etc/libvirt/qemu/Ubuntu10.04.xml
 <!--
 WARNING: THIS IS AN AUTO-GENERATED FILE. CHANGES TO IT ARE LIKELY TO BE
OVERWRITTEN AND LOST. Changes to this xml configuration should be made using:
  virsh edit ubuntu10.04
 or other application using the libvirt API.
 -->
 
<domain type='kvm'>
  <name>ubuntu10.04</name>
  <uuid>2eeb1395-39a2-a169-4da3-f22b20a1d34f</uuid>
  <memory unit='KiB'>1048576</memory>
  <currentMemory unit='KiB'>1048576</currentMemory>
  <vcpu placement='static'>1</vcpu>
  <os>
    <type arch='x86_64' machine='rhel6.3.0'>hvm</type>
    <boot dev='hd'/>
  </os>
  <features>
    <acpi/>
    <apic/>
    <pae/>
  </features>
  <clock offset='utc'/>
  <on_poweroff>destroy</on_poweroff>
  <on_reboot>restart</on_reboot>
  <on_crash>restart</on_crash>
  <devices>
    <emulator>/usr/libexec/qemu-kvm</emulator>
    <disk type='file' device='disk'>
      <driver name='qemu' type='raw' cache='none'/>
      <source file='/var/lib/libvirt/images/ubuntu10.04.img'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x05' function='0x0'/>
    </disk>
    <disk type='block' device='cdrom'>
      <driver name='qemu' type='raw'/>
      <target dev='hdc' bus='ide'/>
      <readonly/>
      <address type='drive' controller='0' bus='1' target='0' unit='0'/>
    </disk>
    <controller type='usb' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x2'/>
    </controller>
    <controller type='ide' index='0'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x1'/>
    </controller>
    <interface type='bridge'>  原来是interface type='default'
      <mac address='52:54:00:50:58:7e'/>
      <source bridge='br1'/>    原来是source network='default',这里的br1要根据你的物理网卡下面有讲
      <model type='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03' function='0x0'/>
    </interface>
    <serial type='pty'>
      <target port='0'/>
    </serial>
    <console type='pty'>
      <target type='serial' port='0'/>
    </console>
    <input type='mouse' bus='ps2'/>
    <graphics type='vnc' port='-1' autoport='yes'/>
    <sound model='ich6'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
    </sound>
    <video>
      <model type='cirrus' vram='9216' heads='1'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </video>
    <memballoon model='virtio'>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x06' function='0x0'/>
    </memballoon>
  </devices>
 </domain>
 
3，改完之后要更新一下配置文件
 
# virsh define ubuntu10.04.xml
 定义域 ubuntu10.04（从 ubuntu10.04.xml）
 #然后就可以virsh start ubuntu10.04了，不过现在物理网卡这块还没有改好