安装了kvm之后，会多了一个virbr0，如下所示，我看着不顺眼就想把这个取消掉。
[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 ##显然有两个网桥
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 ##设置为开机不启动
Network default unmarked as autostarted
virsh # net-list
Name State Autostart
-----------------------------------------
default active no ###开始Autostart 对应的值为yes
virsh # quit
[root@nfs ~]# /etc/init.d/libvirtd restart
Stopping libvirtd daemon: [ OK ]
Starting libvirtd daemon: [ OK ]
但重启libvirtd服务后， virbr0依然存在！只好重启机器！
[root@nfs ~]# sync
[root@nfs ~]# reboot ##重启机器
[root@nfs ~]# Last login: Fri Feb 4 22:55:10 2011 from 192.168.1.155
[root@nfs ~]# ifconfig
......
####显示内容省略，已经没有看到virbr0 网桥了
[root@nfs ~]# virsh net-list
Name State Autostart
-----------------------------------------
[root@nfs ~]# virsh net-list --all ##显示了default网桥，但Autostart对应的列为no
Name State Autostart
-----------------------------------------
default inactive no
还有一种方法：先要在上面的基础上
[root@nfs ~]# virsh net-autostart default ##将default网桥恢复为随系统自动启动
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
显然virbr0已经没有了！
[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
显然virbr0 已经不存在了！
##官方文档！
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 显示不出来了，如何恢复它！
[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]#
机器网络不通的处理过程：留为备份
能ping 通外网8.8.8.8 ，显然已经正常！