安裝了kvm之後，會多了一個virbr0，如下所示，我看着不順眼就想把這個取消掉。
[root@nfs ~]# ifconfig
br0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet addr:192.168.1.62 Bcast:192.168.1.255 Mask:255.255.255.0
eth0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet6 addr: fe80::2e0:6fff:fe12:ac8a/64 Scope:Link
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
virbr0 Link encap:Ethernet HWaddr 52:54:00:11:B2:F3
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
[root@nfs ~]# brctl show ##顯然有兩個網橋
bridge name bridge id STP enabled interfaces
br0 8000.00e06f12ac8a no eth0
virbr0 8000.52540011b2f3 yes virbr0-nic
[root@nfs ~]# virsh net-list
Name State Autostart
-----------------------------------------
default active yes
[root@nfs ~]# virsh
virsh # net-autostart --disable default ##設置爲開機不啓動
Network default unmarked as autostarted
virsh # net-list
Name State Autostart
-----------------------------------------
default active no ###開始Autostart 對應的值爲yes
virsh # quit
[root@nfs ~]# /etc/init.d/libvirtd restart
Stopping libvirtd daemon: [ OK ]
Starting libvirtd daemon: [ OK ]
但重啓libvirtd服務後， virbr0依然存在！只好重啓機器！
[root@nfs ~]# sync
[root@nfs ~]# reboot ##重啓機器
[root@nfs ~]# Last login: Fri Feb 4 22:55:10 2011 from 192.168.1.155
[root@nfs ~]# ifconfig
......
####顯示內容省略，已經沒有看到virbr0 網橋了
[root@nfs ~]# virsh net-list
Name State Autostart
-----------------------------------------
[root@nfs ~]# virsh net-list --all ##顯示了default網橋，但Autostart對應的列爲no
Name State Autostart
-----------------------------------------
default inactive no
還有一種方法：先要在上面的基礎上
[root@nfs ~]# virsh net-autostart default ##將default網橋恢復爲隨系統自動啓動
Network default marked as autostarted
[root@nfs ~]# /etc/init.d/libvirtd restart
Stopping libvirtd daemon: [ OK ]
Starting libvirtd daemon: [ OK ]
[root@nfs ~]# ifconfig
br0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet addr:192.168.1.62 Bcast:192.168.1.255 Mask:255.255.255.0
eth0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet6 addr: fe80::2e0:6fff:fe12:ac8a/64 Scope:Link
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
virbr0 Link encap:Ethernet HWaddr 52:54:00:11:B2:F3
inet addr:192.168.122.1 Bcast:192.168.122.255 Mask:255.255.255.0
[root@nfs ~]# virsh net-list
Name State Autostart
-----------------------------------------
default active yes
[root@nfs ~]# virsh net-destroy default
Network default destroyed
[root@nfs ~]# virsh net-list
Name State Autostart
-----------------------------------------
[root@nfs ~]# virsh net-undefine default
Network default has been undefined
[root@nfs ~]# ifconfig
br0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet addr:192.168.1.62 Bcast:192.168.1.255 Mask:255.255.255.0
eth0 Link encap:Ethernet HWaddr 00:E0:6F:12:AC:8A
inet6 addr: fe80::2e0:6fff:fe12:ac8a/64 Scope:Link
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
顯然virbr0已經沒有了！
[root@nfs ~]# virsh net-list --all
Name State Autostart
-----------------------------------------
[root@nfs ~]# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.00e06f12ac8a no eth0
顯然virbr0 已經不存在了！
##官方文檔！
You can remove all libvirt virtual networks on the machine:
Use 'virsh net-list --all' to see a list of all virtual networks
Use 'virsh net-destroy $net-name' to shutdown each running network
Use 'virsh net-undefine $net-name' to permanently remove the network
下面是virbr0 顯示不出來了，如何恢復它！
[root@nfs networks]# cd /usr/share/libvirt/networks/
[root@nfs networks]# ls
default.xml
[root@nfs networks]# clear
[root@nfs networks]# ls
default.xml
[root@nfs networks]# virsh net-list --all
Name State Autostart
-----------------------------------------
[root@nfs networks]# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.00e06f12ac8a no eth0
vnet0
[root@nfs networks]# virsh net-define /usr/share/libvirt/networks/default.xml
Network default defined from /usr/share/libvirt/networks/default.xml
[root@nfs networks]# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.00e06f12ac8a no eth0
vnet0
[root@nfs networks]# virsh net-list --all
Name State Autostart
-----------------------------------------
default inactive no
[root@nfs networks]# virsh net-start default
Network default started
[root@nfs networks]# virsh net-autostart default
Network default marked as autostarted
[root@nfs networks]# virsh net-list --all
Name State Autostart
-----------------------------------------
default active yes
[root@nfs networks]# brc
brcm_iscsiuio brctl
[root@nfs networks]# brctl show
bridge name bridge id STP enabled interfaces
br0 8000.00e06f12ac8a no eth0
vnet0
virbr0 8000.5254001e3f67 yes virbr0-nic
[root@nfs networks]#
機器網絡不通的處理過程：留爲備份
能ping 通外網8.8.8.8 ，顯然已經正常！